CN100430159C - Media and methods for treating residual ore after mining activities - Google Patents

Abstract

This invention provides a medium and method for treating tailing bodies of mining activities including the steps of vermicomposting a mixture of wood particles and sewage; applying the mixture to the tailing bodies; and planting vegetation on the tailing bodies.

Description

Media and methods for treating residual ore after mining activities

technical field

The present invention relates to media and methods for treating tailings from mining activities.

Background technique

Human activities such as mining generate large amounts of waste that cause economic and environmental problems. This is due to the fact that disposing of these wastes not only requires expensive large areas of land, but also the wastes pollute the soil, groundwater and air. In particular, the mining of platinum, gold and other minerals has considerable environmental impact due to the creation of large tailing dams. Residual ore is generated as a slime waste stream during mineral processing and is an essentially non-biologically viable medium with limited water holding capacity and a high percent alkali saturation. In addition, residual ore also contains high concentrations of potentially environmentally toxic heavy metals that can leach into groundwater.

Walmsley's (1987) study showed that although residual ores are not saline, they contain high concentrations of manganese, iron and sulfur, which are toxic to plants at high concentrations. For example, platinum residue consists mainly of sand (75%) and silt (20%), with the remaining 5% of the particulate being clay and negligible organic components. The above factors therefore complicate the proper revegetation of the remnants to achieve their pre-mining land use potential and contribute to the environmental degradation of the area. In addition to inorganic residues, platinum mining further produces large amounts of organic waste, namely Saligna eucalyptus sawdust and sewage sludge. Residue dams pose a range of environmental hazards due to their physical and chemical properties, including air, dust and groundwater pollution, while dumped wood chips add to the fire hazard during the hot, dry summer months.

The sawdust generated during the extraction of platinum originates from the explosion of intact wooden pillars in the ground. The result is that wood chips are processed together with ore during the initial milling and extraction stages of mineral processing. Sawdust components are separated by screening as a by-product prior to platinum extraction. Due to the explosion, wood chips contain high concentrations of nitrates, high enough to cause health problems such as methaemoglobinaemia (DWAF 1996) when they leach into groundwater. Currently, wood chips are burned at high cost.

Slime, wood chips and sewage therefore present ecological and environmental responsibilities to the mining industry.

The main purpose of a residual mine remediation program is to restore the site to its pre-contamination condition, which often includes revegetation to stabilize the treated soil. This is difficult and expensive due to the difficulty in obtaining topsoil as well as the lack of organic matter, elemental imbalance and lack of essential nutrients in residual ore dams. In one attempt to deal with these problems, topsoil has been implanted from other areas (which then need to be rehabilitated) or regularly treated with inorganic fertilizers, which is costly and ecologically unsustainable. Most residual ore dumps are currently rehabilitated by planting grass over the dump. However, promoting viable and sustainable vegetation is a problem due to the infertility and phytotoxicity of the growing medium.

U.S. Patent No. 6,004,069 discloses a method for providing a subaerial inorganic composite protective cover on sulfide-containing residual ore and mineral waste with sulfide, the method comprising the following steps:

i) providing a deposit of sulfide particulate material comprising at least one of remnant ore comprising sulfide minerals, waste rock having sulfide, and mineral waste having sulfide, the sulfide particulate material having low hydraulic conductivity, the deposit has an apex and a slope enclosing an angle greater than 0.5 degrees with the horizontal;

ii) depositing a first particulate layer on the sulfide particulate material deposit, the first particulate layer comprising an average particle size between 10Em and 200.mu.m and a hydraulic conductivity greater than 10.sup.-7cm/sec, Inert fine matter having a matric suction value greater than 4 cm of water, depositing the first particulate layer such that the first particulate layer extends over the sulfide material deposit to a depth of more than 4 cm;

iii) depositing a second particulate layer on the sulfide particulate material deposit, the second particulate layer comprising inert fine particulate matter having an average particle size, a hydraulic conductivity between 10.sup.-3 and 1 cm/sec, the hydraulic conductivity of the second particle layer is at least an order of magnitude higher than that of the first particle layer, and the following matrix suction values , the ratio of the matrix suction value of the second particle layer to the fundamental suction value of the first particle layer is less than 1:2, and the second particle layer is deposited to provide the second particle layer on the first particle layer extending at a depth that is at least 1.5 times the value of the matric suction measured in cm of water for the second particle layer; and,

iv) depositing a third particulate layer on the sulfide particulate material deposit, the third particulate layer comprising inert coarse particulate matter having an average particle size greater than 3 mm and a hydraulic conductivity greater than 1 cm/sec, subjecting the third particulate layer to Depositing to provide the third particle layer extends over the second particle layer at a depth greater than 6 cm.

The inert fine material contained in the first particulate layer is selected from the group consisting of oxidized mill residues, low sulfide-containing mill residues, desulfurized mill residues, neutralized mill residues, loess, fine sand, Sandy clay, sandy loam, fly ash, silt, till, fine material of alluvial origin and mixtures thereof.

The inert fine particulate material contained in the second particulate layer is selected from the group consisting of granulated slag, granulated desulfurized slag, desulfurized rock, fine gravel, finely crushed rock, winter sand, and mixtures thereof.

The inert coarse particulate material contained in the third particulate layer is selected from the group consisting of crushed rock, crushed stone, crushed limestone, pebbles and naturally occurring coarse material, crushed crushed material and mixtures thereof.

Some disadvantages of the methods described above are that no organic substances are added to the top layer and are relatively complex and expensive as many different substances and steps are involved. Therefore it is not commercially viable.

Contents of the invention

It is therefore an object of the present invention to provide a medium and method for treating residual ore with which the aforementioned problems and disadvantages are overcome or at least alleviated.

According to a first aspect of the present invention there is provided a method of treating a body of residual ore from mining activities, the method comprising the step of applying wood particles to the body of residual ore.

The wood particles may be wood chips recovered from waste wood, and may be a by-product of mining activities, more particularly in the form of wood ore pillars that disintegrate in blasting operations.

The sawdust can be pretreated with acid.

The acid may be, for example, nitric acid (HNO ₃ ).

The sawdust can be applied to the top layer of the residual ore body, such as in the form of an overburden.

In a preferred form of the method, the wood chips are processed into the residual ore body, such as by mechanically and/or manually excavating the wood chips into the residual ore body.

The wood chips are preferably processed into the ore body at a level of about 30 cm below the outer surface of the ore body.

The sawdust can be applied to a residual ore body in the form of a dam to restore the dam.

However, in a preferred form of the method, the wood chips are applied intermittently to the residual ore dam as it develops.

Wood chips are preferably applied at a rate of 60-90 tonnes per hectare of residual dam surface.

In further accordance with the invention, the method comprises the further step of composting the wood chips prior to the step of applying the wood chips to the body of residual ore.

Yet further according to the invention, the step of composting the wood chips comprises the step of verm composting the wood chips.

The step of composting the wood chips may include the further step of mixing the wood chips with another source of organic material.

Other sources of organic material may include sewage.

The wood chips and sewage can be mixed to enable the formation of compost, which can thereafter be inoculated with worms to enable the formation of a worm composting medium.

The worm may be from the species earthworm (Eisenia fetida).

If the availability of sewage is not a limiting factor, wood chips and sewage can be mixed in a ratio of 3:1 or 3:2.

According to another aspect of the present invention, a residual ore dam treated according to the above method of the present invention is provided.

According to another aspect of the present invention, there is provided composted media for treating residual ore bodies from mining activities, the media comprising a mixture of wood particles and another source of organic material.

The wood particles may be wood chips recovered from waste wood that is a by-product of mining activities.

The sawdust may be in the form of timber ore pillars that disintegrate during blasting operations.

Other sources of organic material may be in the form of sewage.

This mixture can be further made into worm compost.

The medium may further include selection of microorganisms.

Description of drawings

Figure 1.1 is a flow chart of the method according to the invention.

Figure 1.2 is a final view of the dam showing grass growing on its sides to restore the residual ore dam.

Figure 2.1 is a schematic design of treatments and repetitions on platinum mucus according to the method of the present invention.

Figure 2.2 depicts an RDA biplot showing the relationship of wood chip application (0, 5, 15 and 30 tons ha ⁻¹ ) to the nutrient availability of the growth medium.

Figure 3.1 depicts the temperature (°C) profile of the composting and vermicomposting systems over the first 28 days.

Figure 3.2 depicts the _CO2 (%) graphs for the composting and vermicomposting systems over the first 28 days.

Figure 3.3 depicts the _O2 (%) graphs for the composting and vermicomposting systems over the first 28 days.

Figure 4 depicts a graph of mean body weight (g) ± SD of earthworms (E. fetida) (n=150) over 84 days.

Figure 5 is a perspective view of a hay windrow for composting or vermicomposting media for treating mining activity residual ore bodies in accordance with the present invention.

Detailed ways

The invention will now be further described by means of a number of embodiments, with reference to the drawings and diagrams. For the sake of clarity, the descriptions of the figures are each presented in relation to the exemplary embodiments.

Example 1

This example refers to the attached figure below, in which:

Figure 1.1 is a flow chart of the method according to the invention; and

Figure 1.2 is a final view of the dam showing grass growing on its sides to restore the residual ore dam.

A mining method including a method of treating or rehabilitating a mineral residue dam in accordance with the present invention is generally illustrated by the parts and flow diagram in Figure 1.1.

The mineral may be, for example, platinum (Pt) ore 10 . Mining products and wastes including wood particles in the form of wood chips or wood chips are indicated as 12. The wood fragments originate from the well-known timber mine pillars that splinter during blast operations in mining. This mixture is fed to a flotation stage 14 where the lighter waste wood is separated from the heavier platinum and slurry in a known manner.

Platinum and slurry at outlet 16 are also separated at 20 in a well known manner. The platinum is recovered at 22 and the remaining slurry is pumped at 24 to a remote location to form a residual ore dam 26, also in known manner.

Waste wood at outlet 18 of flotation stage 14 is milled and rolled at 28 to form wood chips 30 .

It has been determined that known residual mine dams contain unacceptably high concentrations of water-refractory elements that can leach from stormwater and enter groundwater sources, thereby contaminating those water sources. The elemental composition in the wood chip sample and the residual ore dam sample, which are water soluble and mobile as described above and determined by known extraction procedures, are shown in Table 1.1, respectively.

Table 1.1

In Table 1.2 is shown the composition of the mixture corresponding to the elements in Table 1.1, where wood chips 30 are applied to the residual ore dam 26 as shown in step 32 in Figure 1.1.

Table 1.2

From the results of analyzes performed on wood chips and residual ore, respectively, it is clear that the macroelement concentration of residual ore contains high calcium (Ca), magnesium (Mg), sodium (Na), sulfate (SO ₄ ) and chlorine ( Cl) concentration. High _SO4 concentrations in residual ore indicate the ability to generate acid over time. This is evidenced by the low bicarbonate (HCO ₃ ) concentration remaining in the sample, showing that the buffering capacity in the remnant ore is almost exhausted. The need for increased adsorption capacity is also indicated by the high alkali saturation of 21.48% and high electrical conductivity (EC) of 2.09 mScm ^-1 , meaning that those elements that are currently unbound will be carried by any rainwater past the dam into the groundwater. As for trace elements, the concentrations of zinc (Zn) and manganese (Mn) and the potentially toxic heavy metals aluminum (Al), nickel (Ni), cobalt (Co) and arsenic (As) all exceeded the recommended standard values, and they were present in residual The ore showed a high concentration. In contrast, despite containing a high Al concentration, wood chips provide a means to adsorb some excess elemental concentration.

The negative surface charge of wood chips is known to attract and bind certain elements, and the results in Table 1.2 clearly show that increasing the rate of wood chip application has decreased Ca, Mg, K, Na, _SO4 , Cl, Mn, Cu, Zn, Ni and The trend of Co concentration. The decrease in the concentrations of the above elements in the extractable water fraction is also clearly reflected by the lower electrical conductivity (EC) after application of increased volumes of wood chips. Thus, the concentrations of elements potentially leachable into groundwater gradually decreased as the rate of wood chip application increased.

It has been found that pretreatment of wood chips with a 0.01% nitric acid ( _HNO3 ) solution will result in a lower wood chip application rate with the same efficiency in reducing the concentration of potentially toxic elements.

Likewise, as described in more detail below in Example 5, pre-vermcomposting wood chips (with or without sewage sludge) increases the bulk density of the material that must be applied to the residue and reduces composting time part.

It has further been found that an application rate of 60-90 tons of wood chips per hectare of residual ore dam surface produces good results.

Referring to FIG. 1.2 showing a dam 26 , acid pretreated wood chips are processed into the dam 26 at a level 34 approximately 30 cm below the dam outer surface 36 . The wood chips are preferably machined into the fixed sides of the dam intermittently over a period of time as the dam is formed.

It is believed that the negative surface charge of wood chips significantly increases the cation exchange capacity (CEC), thereby reducing the movement of potentially toxic elements into groundwater.

This residual ore can be further rehabilitated by sowing grass seeds on the above-mentioned sides. It is anticipated that due to the nitrate levels present in the dam sides 38 that include wood chips, little or no inorganic fertilizer is required to promote the growth of grass 40 .

Example 2

This example refers to the attached figure below, in which:

Figure 2.1 is a schematic design of the treatment and repetitions on platinum mucus according to the method of the present invention; and

Figure 2.2 depicts an RDA biplot showing the relationship of wood chip application (0, 5, 15 and 30 tons ha ⁻¹ ) to the nutrient availability of the growth medium. The species-environment correlation for the first axis is 0.749.

experimental design

The experimental site was built on a platinum residue dam and consisted of a 24×4m ² small piece of land that was monitored for one and a half years. The individual designs for the different treatment groups are summarized in Figure 2.1. The experiment consisted of 6 treatments on 3 replicate plots and 4 control plots.

Process 1-3

The first 3 treatments were combined with current revegetation and fertilizer application on minerals according to standard practice, but with increased wood chip application (Treatment 1: 5 tons ha ⁻¹ ; Treatment 2: 15 tons ha ⁻¹ ; Treatment 3: 30 tons t ha ^-1 ). Wood chips treated with Zantate and untreated wood chips were applied in a ratio of 1:1. The following fertilizers were applied to the first 3 treatments:

a) superphosphate 1200kgha ^-1

b)NH ₄ SO ₄ 350kgha ^-1

c)KCl 400kgha ^-1

The first three treatments were revegetated with a mixture of stolons and rhizomes of Cynodon dactylon and Cynodon nlemfuensis collected near the residual mine dam. Bermudagrass and stargrass were planted in equal proportions in 6 rows per plot.

Process 4

The 4th treatment was improved with 30 tons of ha ^-1 wood chips and the same fertilizer application as used for the first 3 treatments. Small plots were prepared with 10 kgha ^-1 of Cenchrus ciliaris (Molopo), 10 kgha ^-1 of Chloris gayana, 5 kgha ^-1 of Eragrostis curvula (PUK E436) and 5 kgha ^-1 seed mixture of Eragrostis lehmanniana was used for revegetation.

Process 5

Treatment 5 was improved with 30 tons of ha ^-1 wood chips and fertilizer application as used in the previous treatment. The seed mixture consisted of a mixture of 5 pioneer grass species, 5 perennial grass species and 3 potential creeping grass species (Table 2.1).

Table 2.1: Species mix sown in Treatment 6

Process 6

Treatment 6 was improved with 30 tons of ha ^-1 wood chips. Chemical analysis of the residual ore (Table 2.5) was used to determine fertilization rates for optimum growing conditions. A fertilizer of 800 kgha ^- 1 ammonium monosulfate (MAP) was applied to improve the nutrient status of the growing medium. Small plots were revegetated with a grass seed mixture similar to that used in Treatment 5 (Table 2.1).

Materials and Methods

botanical measurement

Planting on this site is regularly monitored with bridgepoint apparatus installed on 1 ^m2 frames. The frequency of the species and the basic coverage of the species were thus determined with 125 points m ⁻² . Standard grass biomass was subsequently determined. The standard biomass established in the 1 m ² signal area (quadrant) was trimmed with wool shears and sorted according to species. The biomass was dried at 60°C for 48 hours and weighed.

Soil Sampling and Analysis

Soil samples (about 500 g) were collected with a soil auger. A 50 gram subsample was quantified for particle size distribution according to the procedure advocated by the American Society for Testing and Materials (1961). Soil samples were chemically analyzed by the 1:2 (v/v) extraction procedure described by Black (1965) to determine water-soluble basic cation components (Ca, Mg, K, and Na) and trace elements (Fe, Mn, Cu and Zn) and heavy metals (As, Se, Al, Cr, Co, Ni, Pb and Cd).

Water-soluble basic cations (Ca, Mg, K and Na), trace elements (Fe, Mn, Cu, Zn) and heavy metals (As, Se, Al, Cr, Co, Ni, Pb and Cd) with Spectr.AA -250 (Varian, Australia) was quantified by atomic absorption spectroscopy. Anions (F, Cl, _NO3 , _PO4 and _SO4 ) were quantified using ion chromatography (Metrohm 761, Switzerland). 75ml of soil was used for a 1:2 extraction analysis. Ammonia ( _NH4 ) concentrations were quantified by the ammonia selective electrode method as described by Banwart et al. (1972). The content of bicarbonate ( _HCO3 ) in the soil was determined by potentiometric titration with standard 0.005M HCl solution at an endpoint pH 4.5 (Skougstd et al., 1979). Boron (B) concentrations were determined colorimetrically with absorption at 420 nm by the formimine-H-method described by Barrett (1978) with a VEGA 400 spectroquant.

Soil pH and electrical conductivity (EC) were determined in 1:2 extracts at 25°C with a WTW LF92 conductivity meter.

1997)。RDA是受限的线性分类排列(ordination)方法，因此也是将分类排列与回归整合的直接梯度分析技术(Ter Braak，1994)。应用分类排列和直接梯度分析作为分析工具的优点是它可提供变量和相关环境因素之间关系的图示结果。由美国能源部(USA Department of Energy)确立的筛选基准(Efroymson等人，1997)可用作毒理学指导方针。Plant, soil and water chemistry data were analyzed with STATISTICA ver.6 (StatSoft, Inc.2001). The effect of treatment and wood chip concentration was studied using Redundancy Analysis (RDA) (Ter Braak and

1997). RDA is a restricted linear ordination method and thus a direct gradient analysis technique that integrates categorical alignments with regression (Ter Braak, 1994). The advantage of applying taxonomic permutations and direct gradient analysis as analytical tools is that it provides graphical results of relationships between variables and relevant environmental factors. Screening criteria established by the USA Department of Energy (Efroymson et al., 1997) can be used as toxicological guidelines.

result

plant composition

Tables 2.2, 2.3 and 2.4 summarize the species frequency, base cover and biomass measured in the six treatment and control plots. Fourteen grass species were encountered during the survey. The treatments with the highest species richness were treatments 5 and 6, which were seeded with the species mixture shown in Table 2.2. The seed mix used in Treatment 4 produced the highest total base coverage (5.2%). All other treatments, including controls, had very similar base coverage (±3%). Total biomass between plots did not differ significantly due to high variability in standard biomass. The total biomass was highest in the plot treated with Treatment 6. This is mainly due to the vitality of Tribulus terrestris.

Table 2.5 Soil chemistry of platinum slime and wood chips produced in the Impala platinum mineral processing where wood chip experiments were tracked.

Tribulus ciliates var. Molopo was the most successful species established from seed based on frequency, base cover and biomass results. Other species that also performed satisfactorily were Tribulus terrestris var. Gayndah (treatment 6), Lyman's browgrass (Lyman's lovegrass) (treatments 4-5) and Teff curvae (treatment 4). Surprisingly, Digitaria eriantha (SmutsFinger Grass) (Mentis 2000), which usually does very well in rehabilitated areas, could not be established in the experimental plots. One possible reason for the unsuccessful establishment of crabgrass woolen hair was the dry conditions at the beginning of the experiment.

soil chemistry

Three samples were taken from the residual ore for stoichiometric quantification and to determine fertilizer application for treatment 6 (Table 2.5). Samples 2 and 3 are chemically very similar, but the nutrient concentration in sample 1 is considerably greater than the first two samples. This shows high variability in sample chemical composition. The 1:2 aqueous extracts (Table 2.5) further show that heavy metal toxicity to plants can be a serious problem in unmodified residues. Plant growth can be affected as a result of increased soil solution concentrations of Pb, Cr, Co, Se and especially As (Efrotmson 1997).

The results of the 1:2 water extraction procedure shown in Table 2.6 show the concentrations of elements in the soil solution that could be adsorbed by plants in February 2002. Typically, the concentrations of the macroelements (Ca, Mg and K) are slightly lower than those preferred for efficient growth. Phosphate and nitrate available in the soil solution have also been depleted by plant assimilation. The concentration of _NO3 and _PO4 will be the limiting factor for plant growth.

Table 2.6: Average chemical properties of growth medium samples collected on plots of the platinum slime experiment modified with 5, 15, 30 t HA ^-1 wood chips and 3 revegetation treatments. The mean (mean) and standard error (Std err) of all combined plots (All), treatments 1-6 and the control plot (C) are shown.

With the exception of Cu, no potential micronutrient toxicity occurs at the present pH level. Cu is present in elevated concentrations up to 0.827 μmol/dm ³ (the potential level of phytotoxicity according to Efroymson (1997) is 0.94 μmol/dm ³ ).

The pH of the growth medium was kept alkaline (average pH for all treatments: 7.8±0.025). The low EC also confirmed the low nutrient status of the growth medium and further showed that salinity was irrelevant. The sodium sorption ratio SAR was also lower than the recommended value of 1, thus indicating the absence of potential soil sodicity.

By comparing Tables 2.5 and 2.6, it is possible to determine changes in the chemical nature of the residue due to time, plant growth and application of wood chips. The concentration of all macroelements in the residual ore is considerably reduced. Sulphate concentrations remained relatively the same or decreased slightly in the control plots and the plots treated with low concentrations of wood chips. The sulphate concentration in the growth medium solution was also reduced considerably in Treatment 6, which is not typical compared to other treatments also treated with 30 t ha ^-1 wood chips. The concentrations of trace elements Fe, Mn and Cu were increased, thereby showing an increase in the solubility of these elements. However, zinc and boron concentrations were reduced. The pH of the soil solution remained relatively the same at about 7.8. Conductivity also dropped considerably from 2.267 mS/cm (unmodified remnant) to 0.296 mS/cm at the end of the study.

To elucidate the effect of increasing wood chip application on the chemical properties of residual ore, RDA was performed and the results are presented as RDA bidirectional plots of species (chemical variables) versus wood chip application as a factor (Fig. 2.2). Because only one variable is tested, both the canonical axis and the ordination axis are represented on the first ordination axis. The chemical variable as a substance type was 74.9% correlated with wood chip application as an environmental factor. According to Fig. 2.2, the chemical variables most associated with the applied gradient of wood chips were B, P and Cu (positive correlation) and pH (negative correlation). The pH of the medium will acidify with increasing wood chip application and the concentration of B and especially Cu will increase. Because macronutrient concentrations (Ca, Mg, K, Na, _SO4 ) and electrical conductivity (EC) were weakly correlated with the first taxonomic permutation axis, these variables were less affected by increased wood chip application.

Table 2.7 presents the correlation matrix among soil chemical variables. The salinity of the growing medium is overwhelmingly due to sulfates, and especially calcium, potassium and magnesium sulfates. Calcium, magnesium and potassium are also highly correlated. Sodium however correlates better with chloride. Iron, manganese and copper are all related to each other. The only significant negative correlation was between iron and ammonium.

Table 2.7: Significant correlations between nutrients in growth medium solutions sampled at the wood chip experimental plot site of the Impala platinum mine in March 2002.

Ca Mg K NaSO ₄ NH ₄ Cl Fe Mn Cu

Mg 0.896 ^＊＊＊

K 0.825 ^＊＊＊ 0.735 ^＊＊＊

Na 0.412 ^＊ 0.670 ^＊＊＊ 0.261

SO ₄ 0.958 ^＊＊＊ 0.949 ^＊＊＊ 0.783 ^＊＊＊ 0.578 ^＊＊

NH ₄ 0.166 0.167 0.089 0.137 0.190

Cl 0.220 0.504 ^＊＊ 0.248 0.840 ^＊＊＊ 0.364 -0.062

Fe -0.346 -0.157 -0.190 0.034 -0.310 -0.511 ^＊＊ 0.340

Mn -0.171 0.049 -0.225 0.316 -0.102 -0.217 0.443 ^＊ 0.622 ^＊＊＊

Cu 0.051 0.122 0.083 0.222 0.052 -0.410 ^＊ 0.3253 0.607 ^＊＊ 0.651 ^＊＊＊

EC 0.966 ^＊＊＊ 0.972 ^＊＊＊ 0.817 ^＊＊＊ 0.606 ^＊＊＊ 0.980 ^＊＊＊ 0.177 0.425 ^＊ -0.249 -0.052 0.106

0.05，0.01和0.001的显著性.

Significance at 0.05, 0.01 and 0.001.

conclusion and suggestion

Based on the vegetation reconstruction results, many species that were applied especially in high-diversity mixtures could not be established. The results show that seed mixtures of Tribulus ciliates, Lyman's brow, Panicum maximum and Teff curvaceae are sufficient. Dragon claw millet (Eleusine coracana) was the most successful pioneer species. A possible reason for the poor performance of the Feld prairie grass species was the low seeding rate of 1-2 kg/ha. Seeds (mass-sowing species) must be sown at a rate of not less than 5kg/ha to ensure successful establishment. Bermudagrass and stargrass tillers and runners can also be planted in intervals for erosion control. It is preferred to use bermudagrass instead of star grass because bermudagrass is native to the region, is more drought tolerant and forms a more effective cover. The results also showed that the treatment 4 seed mixture was more successful than the treatment 5 and 6 seed mixtures. In treatment 4, fewer species were applied, but the same results were obtained as for the seed mix used in treatments 5 and 6. Both seed mixes provided the same amount of coverage, with treatment 4 having substantially higher coverage than treatments 5 and 6. Based on the results, different seed mixtures should also not affect biomass production. Biomass was more affected by the establishment of a particular species (in this case Tribulus ciliates) than by the total composition of the seed mixture.

The chemical growth conditions of the residual ore were considerably improved during the course of the experiments. The greatest considerations regarding the soil nutrient status of modified slime materials are their low fertility and the potential for toxicity of trace elements and heavy metals, especially copper, chromium, selenium and arsenic. Despite the potential for phytotoxicity, grass vigor and life intensity appeared to be satisfactory. If the chemical composition before and after the residual ore is compared, it shows that the residual ore is easy to seepage. This may be a worthy consideration with regard to groundwater contamination.

The improved plots were expected to have elevated _NO3 concentrations due to initial high nitrate concentrations in residual ore and wood chips, however this was not the case. A possible explanation for this is the high mobility of NO ₃ , which leads to a large exudation of NO ₃ and a high rate of uptake by plants, which explains the vigor of plants (Mengel & Kirby, 1987). A further explanation is nitrogen fixation due to high C/N ratios, resulting in some inorganic N being fixed as organic N by soil microorganisms (Tainton 2000).

Example 3

This example refers to the attached figure below, in which:

Figure 3.1 depicts the temperature (°C) profile of the composting and vermicomposting systems over the first 28 days. SS, sewage sludge; WC, wood chips; EM, microbial inoculation; e/w, earthworms;

Figure 3.2 depicts the _CO2 (%) graphs for the composting and vermicomposting systems over the first 28 days. SS, sewage sludge; WC, wood chips; EM, microbial inoculation; e/w, earthworms; and

Figure 3.3 depicts the _O2 (%) graphs for the composting and vermicomposting systems over the first 28 days. SS, sewage sludge; WC, wood chips; EM, microbial inoculation; e/w, earthworms.

Materials and Methods

Inoculation of organic waste, earthworms and microorganisms

Air-dried wood chips (WC) and sewage sludge (SS) samples were obtained from platinum mines. The earthworm (e/w) species used was the earthworm (Eisenia fetida) ("tiger worm"), which is a terrestrial and potential waste composting worm (Edwards and Bohlen, 1996). The breeding stocks of earthworms (Eisenia fetida) used in this study were maintained on livestock manure at a temperature of ±25°C. Only mature genital annulus worms were used for the purpose of this study. A commercial microbial preparation (EM ^™ ) consisting mainly of Pseudomonas, Lactobacillus and Saccharomyces species was used for the inoculation experiments.

Composting and Worm Composting Experiments

A mixture of WC and SS was applied in a mixing ratio of 3:1 (kg ^-1 dry weight). The dry ingredients were mixed and humidified to a moisture content of 70% (by weight) with distilled water. Five treatment groups consisting of WC+SS, WC+SS+EM, WC+SS+e/w, WC+SS+EM+e/w and WC mixture were studied with 3 replicates. The substrates were placed in plastic bins (60x40x30 cm), placed in an environmental chamber (25°C) and composted for a period of 28 days. In the treatment with earthworms, 100 mature earthworms were introduced after a composting period of 28 days to avoid exposing the earthworms to possible high temperatures during the initial thermophilic phase of composting.

Physical and Chemical Parameters

From day 0 (referring to the time of initial mixing of waste prior to decomposition) to day 28, CO ₂ and O ₂ and temperature were measured with a portable CO ₂ and O ₂ analyzer (Gas Data PCO ₂ ). Whenever _CO2 increases or _O2 decreases exceed the levels in the air, ventilation is artificially increased to reverse the trend.

At the beginning and end of the experiment, the total solids (TS), volatile solids (VS), ash content, particle size distribution, NH ₄ ⁺ , NO ₃ ⁻ , NO ₂ ⁻ , pH, total and soil available P (P-Bray 1), Total Organic Carbon (TOC), % Lignin and % Cellulose.

TS was determined as a residue dried at 80°C for 23 hours and VS was determined by ashing the dried samples at 550°C for 8.5 hours (APHA et al., 1989). The particle size distribution was determined by sieving 100 g of material through sieves with mesh openings of 4.75, 4.00, 2.00 and 1.00 mm, respectively. Particle sizes are reported as geometric mean and geometric standard deviation as described by Ndegwa and Thompson (2001).

Anions _NO3- ^, _NO2- were determined by capillary electrophoresis (Waters Quanta 4000, Capillary Electrophoresis System, Waters, MA) as described by Heckenberg et al ^. (1989). _NH4 ⁺ concentrations were quantified by the ammonia selective electrode method as described by Banwart et al. (1972). The pH of the substrate was determined in the 1:2 extract at 25° C. with a calibrated pH meter (Radiometer PHM 80, Copenhagen) after an equilibration period of 12 hours with intermittent agitation.

P _[total] concentrations were determined colorimetrically using the vanadomolybdate method. This entails pipetting 200 mL of the digested sample solution into a 50-mL volumetric flask, adding 10 mL of vanadium molybdate reagent to the flask and diluting this volume with deionized water and mixing. After 10 minutes, the concentration was read on a colorimetric continuous flow analysis system (Continuous Flow Analysis System, Skalar, The Netherlands).

TOC was determined by an independent laboratory using the Walkley-Black method (Walkley and Black, 1934), while P-Bray 1 was determined using Bray extractant No. 1 (Bray and Kurtz, 1945).

% NDF, % Lignin and % Cellulose

% NDF (Neutral Detergent Fiber, the insoluble fraction of plant cells), % Lignin and % Cellulose were determined according to Rowland and Roberts (1999). For NDF determination, samples were air dried and ground (<1 mm). Percent dry material was determined by drying air-dried samples at 105°C for 3 hours, and a dry weight correction factor was determined; ie 100/% dry matter.

The reagent consisted of 18.61 g EDTA and 6.81 g Na ₂ B ₄ O ₇ ·10H ₂ O dissolved in 500 mL deionized water, then 30 g sodium lauryl sulfate (SLS) and 10 mL 2-ethoxyethanol (etoxyethanol) were added. 4.56 g _of anhydrous _Na2HPO4 were dissolved in water alone, mixed with other solutions and finally diluted to 1000 mL.

0.5 g of the air-dried material was placed in a 250-mL Erlenmeyer flask and 100 mL of neutral detergent reagent was added. Bring the solution to a boil and cook for 1 hour. While still hot, the solution was filtered through a pre-weighed frit (No. 2) while applying light suction. The residue was washed with 3 x 50 mL of boiling deionized water followed by acetone until no more color was removed while applying suction until the fibers appeared dry. The fibers were then dried at 105°C for 2 hours, cooled to room temperature in a desiccator and weighed.

Percentage NDF is calculated from the following equation:

%NDF=100×dry weight correction factor×[(weight of sinter + fiber)-(weight of sinter)]/sample weight

For the determination of lignin, the reagent used was 720 mL diluted to 72% (w/v) concentrated sulfuric acid with 540 mL deionized water. The frit was half-filled with cooled (15°C) _H2SO4 reagent and stirred into a smooth paste with _a glass rod, and _the liquid level was maintained by refilling with _H2SO4 as it dried. After 3 hours the acid was filtered off in vacuo and the contents washed with hot water and acetone until the residue was free of acid reagent. The sinter was then dried at 105° C. for 2 hours, cooled in a desiccator and weighed again. It was then ignited at 550°C, cooled in a desiccator and weighed again. The percent lignin is then calculated from the following equation:

% lignin = (100 x dry weight correction factor) x [(weight of sinter + lignin + ash) - (weight of sinter + ash)]/sample weight

% Cellulose was determined by subtracting % Lignin from % NDF.

Microbial analysis

The amount of viable aerobic colony forming units was quantified by plate count as the number of colony forming units (CFU) present per 1 g of sample developed over 48 hours. The samples were plated on Chromocult agar at 25°C. The presence of E. coli and Salmonella was determined by an independent laboratory using the method specified by the British Standards Institution (1998).

Statistical Analysis of Data

计算机软件包进行分析，且所有值均表示为平均数±SD(标准偏差)。用于统计学显著性的概率水平为P＜0.05，且将参数的或非参数的检验用于比较不同的处理组。The data in this study used

Analysis was performed by a computer software package and all values are expressed as mean ± SD (standard deviation). The probability level for statistical significance was P<0.05, and parametric or nonparametric tests were used to compare different treatment groups.

Results and discussion

The temperature profiles during the composting phase (first 28 days) of the different treatments are represented in Figure 3.1. In none of the treatments was the temperature raised above 33°C, which did not meet the requirements of the EPA (Environmental Protection Agency) PFRP (Process to Further Reduce Pathogens) contained in US-EPA 40 CFR Part 503 (Hay, 1996). Although temperature development is an indicator of microbial activity (Jimenez and Garcia, 1991), the observed reduced temperature may be a result of the high moisture content of the material (70%) rather than a lack of microorganisms. Therefore, it is possible that higher temperatures can be reached if the initial moisture content of the material is lower at the time of loading. On the other hand, low temperatures can help to preserve N in composted material, since high temperatures can lead to high losses of N in the form of _NH in the early stages of composting (Sanchéz-Mondero et al., 2001).

Based on low temperature and EPA requirements, it was decided to perform analysis for total coliforms, E. coli and Salmonella in the final product. The presence of coliform bacteria is often used as an indicator of the overall sanitary quality of soil and water environments and is easy to detect (Hassen et al., 2001). Escherichia coli is the most representative bacterium in the group of fecal coliforms (Le Minor, 1984) and can therefore be used as an indicator of the presence of fecal coliforms. The presence of Salmonella is considered to be a major concern for the hygienic quality of composts due to the disease that can result from contamination (Hay, 1996).

No E. coli or Salmonella was detected in any of the products, which means that the final product in this study should be safe for general distribution. The total number of coliforms was between 2430 and 2903 CFU g ^-1 .

The percent _CO2 and _O2 levels in the air are represented in Figures 3.2 and 3.3, with the maximum activity observed for the first 8 days. This corresponds to the observed temperature rise which is normal during the usual composting process (Tuomela et al., 2000). Nutrient parameters (TOC, P _[total] , P-Bray 1, NH ₄ , NO ₂ and NO ₃ ) of the different treatments at the time of loading are presented in Table 3.1, and at the time of loading, there was no difference between treatments containing SS. Significant differences (P > 0.05) were observed for the measured parameters. The mean percent changes in these parameters after composting and worm composting are presented in Table 3.2. There were no significant differences (P > 0.05) in the mean percent change in TOC among the different groups. This is due to the fact that the temperature in the process was not higher than 33 °C and the loss of C from the system was minimal in the form of _CO .

Table 3.1: Nutrient parameters (± SD) in the mixing ratio at the time of loading

(n=9).

Means with the same letter have no significant difference (P<0.05)

TOC, total organic carbon; P-Bray 1, soil extractable P; SS, sewage sludge;

WC, wood chips; EM, microbial inoculation; e/w, wormworms.

All SS-containing treatments showed a significant increase in total P from 78.60 -> 100%. Although all treatments showed an increase in P-Bray 1 values, this increase was statistically significant (P<0.05) only in the SS+WC and SS+WC+EM groups. Ghosh et al. (1999) found that organic waste composted by worms released relatively large amounts of P-Bray 1 . They attribute this to the fact that earthworms acquire P as a nutrient for their in vivo synthesis and release the remaining P in mineralized form, and postulate that worm composting may be an effective method to generate better P nutrition from organic waste. This is in contrast to other studies where soluble P decreases after composting (Vuorinen and Saharinen, 1997) and after worm composting (Ndegwa and Thompson, 2001).

The concentration of N in composted waste material is one of the most important factors in studies determining its agroeconomic value, and NH ₄ and NO ₃ are the most interesting because of their direct assimilation by the roots of plants (Sanchéz- Mondero et al., 2001). NH ₄ showed a significant (P<0.05) decrease of 92.57->100% in all SS-containing treatments, while WC treatment showed an increase of more than 100%, and the actual final value was 1.77±0.80 mmol L ⁻¹ . _NO2 levels showed significant (P<0.05) increases in all SS-containing treatments, while no significant (P>0.05) changes were observed in WC treatments. According to Sanchéz-Mondero et al. (2001), the presence of _NO2 in composted material is a clear indication of anaerobic conditions during composting. This is due to the high moisture content of the material, which leads to the development of an anaerobic microenvironment. All treatment groups showed a significant (P<0.05) increase in _NO3 over 100%. This can be explained by the fact that nitrogen compounds evolve as follows during composting:

2NH ₄ ⁺ +3O ₂ →NO ₂ ^- +4H ⁺ +2H ₂ O (Nitrosomonas)

2NO ₂ ^- +O ₂ →2NO ₃ ^- (Nitrobacter)

However, there were differences in the following significant (P<0.05) ranges between the different treatments; SS+WC+e/w and SS+WC+EM+e/w>SS+WC and SS+WC+EM>WC .

At the end of the study, the concentration of NO ₃ was higher than that of NH 4 , indicating that a correct composting process had taken place (Finstein and Miller, 1985). Furthermore, the ratio of NH ₄ :NO ₃ (Table 3.2), which is an indicator of compost maturity, was below 0.16 for all treatments ranging from 0.011-0.0016 except in the WC treatment (0.27) (Zucconi and de Bertoldi, 1987). There were no significant (P > 0.05) differences between the proportions in the SS-containing treatments, indicating no differences in the evolution of nitrogenous products between composting, microbial inoculation, and worm composting.

Table 3.2: _{112 -} day ^composting and

Mean percent change in nutrients after worm composting (n = 9).

Significantly different from the initial content (P<0.05)

^a a, b, c - Means with the same letter have no significant difference (P>0.05)

^bChange (%)=[(initial-final)/initial]×100

ND: not detected; TOC, total organic carbon; P-Bray 1, soil extractable P;

EM, microbial inoculation; e/w, earthworms; SS, sewage sludge; WC, wood chips.

The physical parameters (TS, VS, ash, % NDF, % lignin and % cellulose) and pH of the different treatments at the beginning of the experiment are presented in Table 3.3, where no significant differences were observed in the parameters between the different groups (P > 0.05) difference. The mean percent changes in these parameters after the end of composting and worm composting are presented in Table 3.4, where no significant (P > 0.05) differences were observed in the WC treatment. After 112 days of composting and worm composting, the pH of WC showed a 5.75% decrease (P>0.05), while those in the sewage sludge treatment showed an increase between 13.67 and 26.47%, both statistically significant ( P<0.05). This follows the alkaline trend of pH during composting, where an initial decrease is observed due to the formation of organic acids, followed by an increase as a result of ammonium release (Tuomela et al., 2000). TS and ash content showed an overall increase, while VS and lignin showed an overall decrease, but these changes were statistically significant (P<0.05) only in the worm composting treatment.

Table 3.3: Mixing Ratio Physical Parameters at Loading (±SD)

(n=9).

a, b- means with the same letter have no significant difference (P>0.05)

TS, total solids; VS, volatile solids, NDF, neutral detergent fibers; EM, microbial inoculum;

e/w, earthworms; SS, sewage sludge; WC, wood chips.

Table 3.4: Comparison of mean percent changes in physical parameters in different processing types ^a (n = 9)

Significantly different from the initial content (P<0.05)

^a ab, c - Means with the same letter have no significant difference (P>0.05)

^b change (%) = (initial - final) / initial] × 100

TS, total solids: VS, volatile solids; NOF, neutral detergent fibers;

EM, microbial inoculation; e/w, earthworms; SS, sewage sludge; WC, wood chips

According to Neuhauser et al. (1988), an increase in ash content and a decrease in VS are indicators of stabilization of composted materials. The increase in TS is due to the fact that the worm composted material is physically degraded and thus has increased density, and the moisture content of the material (as a function of TS) is significantly lower. It was also observed that the material exhibited a decrease in volume, although this was not quantitative. This reduction in volume and moisture content correlates with reduced handling and shipping costs.

%NDF and %cellulose were significantly (P<0.05) decreased in all SS-containing treatments, and there were no significant (P>0.05) differences among the different treatments. Cellulose degradation is associated with microbial biomass (Entry and Bachman, 1995), and can also be used by surface earthworms as a direct food source (Zhang et al., 2000), however, reducing soil biomass after passing through the earthworm gut (Zhang et al. et al., 2000), which could explain why cellulose breakdown was partly higher in the treatment without earthworms, although not statistically significant (P > 0.05). Significant (P<0.05) reductions in % lignin were observed in only two worm-composted treatments. This is due to the fact that lignin degradation is regulated by the thickness of the material (Tuomela et al., 2000) and the fact that earthworms eat, mill and digest organic waste, converting it into finer materials (Aranda et al., 1999).

Entry and Bachman (1995) also postulated that cellulose rather than lignin degradation was related to microbial biomass, while Faure and Deschamps (1991) found that inoculation of organic waste with cellulolytic and lignin-degrading bacteria had no effect on degradation. Further, earthworms can consume material with high lignin content, resulting in persistent population size (Senpati et al., 1999).

The results of the particle size analysis are given in Table 3.5 and expressed as geometric mean and standard deviation and percent change. The worm composting treatment inoculated with EM had the greatest reduction in particle size, followed by the worm composting treatment without inoculation. These two groups also showed lower heterogeneity observed, indicated by higher geometric standard deviations. This is due to the presence of biologically inactive materials such as plastics (a by-product of explosions used in mining) in wood chips.

Table 3.5: Particle size of products from each process at the beginning and end

(geometric mean ± geometric standard deviation) characteristics and percent change

EM, microbial inoculation; e/w, earthworms; SS, sewage sludge; WC, wood chips,

Day 0 refers to the time of initial mixing of waste before decomposition

Therefore, based on the reduction in TS and VS and the increase in ash content, it can be presumed that vermicomposting industrially generated wood chips and sewage sludge is better than composting them alone. It was also shown that only the worm composting treatment showed a significant reduction in lignin, and that the addition of microbial inoculum did not increase the rate of decomposition.

Example 4

This example refers to the attached figure below, in which:

Figure 4 depicts a graph of mean body weight (g) ± SD of earthworms (E. fetida) (n=150) over 84 days. ^* Significant difference (P<0.05). (SS-sewage sludge; WC-wood chips; EM-microbial inoculation).

Materials and Methods

Air-dried wood chips (WC) and sewage sludge (SS) samples were again obtained from the platinum mine.

Earthworm (e/w) species E. fetida ("tiger bug") was applied again. A commercial microbial preparation (EM ^™ ) consisting mainly of Pseudomonas, Lactobacillus and Saccharomyces species was used for inoculation experiments.

Applied substrate

A mixture of WC and SS was applied in a mixing ratio of 3:1 (kg ^-1 dry weight). The dry ingredients were mixed and humidified to a moisture content of 70% (by weight) with distilled water. Two treatment groups each consisting of WC+SS and WC+SS+EM mixtures were studied with 3 replicates. The substrates were placed in plastic worm bins (60 x 40 x 30 cm), placed in an environmental chamber (25°C) and composted for 28 days. One hundred mature worms were introduced after a 28-day composting period. This was done to avoid exposing the worms to possible high temperatures during the initial thermophilic phase of composting.

success rate of growth and reproduction

After the 28-day composting period, worm biomass was determined and substrate moisture content monitored every 14 days during the 94-day period. Biomass was determined by taking 50 worms from each container, washing them in distilled water and allowing them to dry on paper towels. It was then weighed with a Sartorius balance in a weighing boat filled with water. This is done to prevent the worms from drying out and thereby affecting the weight of the earthworms.

Egg bag viability was determined by randomly harvesting 72 egg bags from each container and placing them in multiple dishes filled with distilled water. The water in these dishes was changed every 3 days to prevent bacterial growth which could negatively affect the results. Egg bags hatched and the number of hatchlings per egg bag were recorded over a 4-week period.

Heavy Metal Analysis

Nine earthworms per group were taken from the substrate before and at the termination of the experiment. The worms were then placed on wet filter paper in Petri dishes for 24 hours to allow their intestinal contents to be decontaminated. This was done to prevent misleading results regarding the actual heavy metal content in body tissues due to the presence of heavy metals in intestinal contents. After this 24 hours, the worms were washed in distilled water, dried on paper towels and frozen to death. They were weighed individually and frozen (-74°C) in polytop vials for heavy metal analysis at a later stage. Substrate samples were also taken, placed in plastic bags and refrigerated until heavy metal analysis. Worm and compost samples were digested as described by Katz and Jennis (1983). The samples were dried and milled separately, followed by ash at 550°C. They were then placed individually in test tubes and 10 mL of 55% nitric acid (HNO ₃ ) was added. It was left overnight at room temperature to initiate the digestion process. The next day the samples were heated at 40-60°C for 2 hours, then at 120-130°C for 1 hour, after which they were allowed to cool. 1 mL of 70% perchloric acid (HClO) was added and the mixture was heated again at 120-130°C for 1 hour. Samples were allowed to cool before adding 5 mL of distilled water. The sample was then reheated at 120-130°C until white fumes were emitted. Allow the sample to finally cool before microfiltration.

The solution was filtered through Whatman No. 6 filter paper into a 20 ^cm3 volumetric flask using a Sartorius microfilter-holder and plastic syringe. Make up to 20 ^cm of filtrate with distilled water. The 20 cm ³ solution was filtered through 0.45 μm Sartorius nitrocellulose filter paper into polyethylene containers and analyzed for different metals by Inductively Coupled Plasma Spectroscopy (ICP-AES).

Statistical Analysis of Data

计算机软件包进行分析，且所有值均表示为平均数±SD(标准差)。用于统计学显著性的概率水平为P＜0.05，且将参数的或非参数的检验用于比较处理组。The data in this study used

Analysis was performed by a computer software package and all values are expressed as mean ± SD (standard deviation). The probability level for statistical significance was P<0.05, and parametric or nonparametric tests were used to compare treatment groups.

result

There was no stage where any mortality was observed during the course of the study, and the average biomass change of earthworms (E. fetida) is represented in FIG. 4 . The average biomass of earthworms in the SS+WC treatment was 0.44 ± 0.01 g compared to 0.43 ± 0.02 g in the SS+WC+EM treatment before introduction into the mixture treatment. There was no significant difference between these two values (P>0.05). On the 14th day, the average biomass of earthworms reached a maximum of 0.81±0.02g and 0.77±0.02g in the SS+WC and SS+WC+EM groups, respectively, which were significantly (P<0.05) higher than the initial biomass . From 14 to 84 days, the average biomass decreased to 0.49±0.03g in SS+WC and 0.51±0.01g in SS+WC+EM, and there was a significant difference between the two values (P< 0.05). These values were all significantly (P<0.05) higher than the initial biomass.

Egg bags produced in the SS+WC group had an average hatch success rate of 46.8±2.4% (n=216), which was significantly (P<0.05) lower than 68.0±2.8% in the SS+WC+EM group. The average hatch number per egg bag was 2.7±0.1 for SS+WC and 3.0±0.2 for SS+WC+EM group, with no significant difference between the two values (P>0.05).

The heavy metal contents of Al, As, Cu and Ni in the two substrate mixtures are summarized in Table 4.1 and no significant differences (P > 0.05) were found for these selected metals. The initial and final body heavy metal loads present in earthworm tissues are presented in Table 4.2. Initially, there was no statistical difference (P > 0.05) between the heavy metal contents of earthworm body tissues in the two groups. At the end of the experiment, the heavy metal content of earthworms in SS+WC was significantly (P<0.05) higher than all heavy metals measured at the beginning, except for As which was below the detection limit of 0.05 μg.g ⁻¹ . In earthworms exposed to SS+WC+EM, heavy metals showed no significant difference after 84 days (P>0.05). Bioconcentration factors (BCF) for different heavy metals in earthworm body tissues after the 84-day worm composting period are presented in Table 4.3. It is obvious that the BCF of earthworms for Al, Cu and Ni in the SS+WC group is almost twice that in the SS+WC+EM group.

Table 4.1: Heavy metal content after 112 days of composting and worm composting (n=9)

Significant difference (P>0.05)

SS-sewage sludge; WC-wood chips; EM-microbial inoculation

Table 4.2: Heavy metal content in earthworm body tissues before and after worm composting (n=9)

Significantly different from the initial content (P<0.05)

There is no significant difference in the means of ^{a, b} with the same letter (P>0.05)

SS-sewage sludge; WC-wood chips; EM-microbial inoculation

Table 4.3: BCF (bioconcentration factor) of earthworm body tissues after 84 days of worm composting

There is no significant difference in the means of ^{a, b} with the same letter (P>0.05)

BCF=[e/w]/[substrate]

Nd - not detected

SS-sewage sludge; WC-wood chips; EM-microbial inoculation

discuss

From the results (Fig. 4 and Tables 4.1-4.3), it is evident that earthworms in both treatment groups were exposed to a mixture of pollutants including Al, Cu and Ni. This makes the estimation of the effects of toxicants difficult, since the actual danger to the organism is determined by the availability of these toxicants. The role of Cu (Spurgeon and Hopkin, 1995; Van Gestel et al., 1991) and Ni (Lock and Janssen, 2002; Scott-Fordsmand et al., 1998) on growth and reproduction is well documented, but there is currently no or only one for Al. Very little information available. Furthermore, the literature on the effect of these metals as a mixture on earthworms (E. fetida) is lacking. Regarding the possible hazards of these metals in the application of restoration procedures, Al, Cu and Ni are all above the range suggested by DWAF (1996) for use in agriculture. These factors should be considered when selecting plant species for restoration and monitoring the infiltration of these metals into groundwater.

Growth data are comparable to previous studies in which earthworms (E. fetida) were found to achieve an average biomass of ± 0.45 g under optimal conditions (Reinecke et al., 1992). The fact that the average biomass of worms exposed to SS+WC was significantly (P<0.05) lower than those exposed to SS+WC+EM is a direct cause of the bioavailability of heavy metals in these substrates. However, both groups showed a reduction in biomass after 14 days (Figure 4), which may be attributed to the presence of elevated heavy metal concentrations. Therefore, growth can be considered as a sensitive parameter for estimating the effects of Al, Cu and Ni on earthworms (E. fetida). This is consistent with previous findings on the effect of Cu in the form of CuNO ₃ on growth (Reinecke and Reinecke et al., 1996), who found that the growth of earthworms (E. fetida) was negatively affected by substrate concentrations of 200 μg.g ^-1 Influence.

Considering growth as the end point, it can be assumed that worm composting of wood chips and sewage sludge using earthworms (E. fetida) is economically viable. Considering that earthworms performed better in mixtures containing microbial inoculum and with average biomass as an endpoint, better results could be expected in large-scale worm composting techniques.

The average hatching success, which can be considered the endpoint of reproductive success, was significantly (P<0.05) higher in the SS+WC+EM group than in the SS+WC group, although there was no difference in the average hatch numbers between the two (P >0.05).

Venter and Reinecke (1988) estimated that egg bags produced by earthworms (E. fetida) had an average hatch success rate of 73%, and that each egg bag produced an average of 2.7 hatchlings. The hatching success rate of 68% produced by worms in the SS+WC+EM mixture was slightly better than the 73% determined by Venter and Reinecke (1988), but the egg bag hatching success rate in the SS+WC mixture was very low at 45% . The data on incubation success in SS+WC substrate with high Ni (551 μg.g ⁻¹ ) and Cu (315 μg.g ⁻¹ ) concentrations are in agreement with the results of the previous authors. Lock and Janssen (2002) reported that the EC ₅₀ of Ni based on egg bag production was 362 μg.g ^-1 , while Spurgeon and Hopkin (1995) found that worm reproduction was significantly reduced in copper-contaminated soil. Reinecke and Reinecke (1996) found that earthworms (E. fetida) exposed to a copper concentration of 200 μg.g ^-1 did not produce egg bags. Hatch success is therefore a more sensitive parameter than growth when estimating the potential for application of earthworms (E. fetida) in worm composting wood chips and sewage sludge.

The fact that hatching success was higher in the group inoculated with the microbes may be attributed to the fact that Ni and Cu, which have deleterious effects on reproductive success, were less available to the worms. Microorganisms are able to concentrate metals both actively (bioaccumulation) and passively (biosorption) (Unz and Shuttleworth, 1996). It has been shown experimentally that Saccharomyces (Simmons et al., 1995) and Pseudomonas (Churchill et al., 1995) show large variations in the biosorption of metals, both of which are present in the inoculum. This may provide a possible explanation for the inconsistency in growth and reproductive success observed between the two groups. This fact is confirmed by the heavy metal body burden observed in the body tissues of earthworms, where the worms containing the inoculum in the substrate had significantly lower (P < 0.05) levels of Al, Cu and Ni, which was also reflected by the calculated BCF .

in conclusion

It can be assumed that the growth of earthworms (E. fetida) is not inhibited when used as a worm composting species of industrially produced wood chips and sewage sludge or as an addition to microbial inoculation. Earthworms in the SS+WC treatment group had reduced reproductive success and bioaccumulated Al, Cu, and Ni in their body tissues. In contrast, earthworms in the treatment with added microbial inoculum did not bioaccumulate any heavy metals in their body tissues and had significantly higher reproductive success than their equivalents in the treatment without microbial inoculum. This shows that the microorganisms present in the inoculum render the heavy metals present in the wood chips and sewage sludge mixture unavailable through their biosorption or bioaccumulation.

It thus appears that the most economically feasible route to bioconversion of wood chips and sewage sludge by earthworms (E. fetida) is the addition of microbial inoculum.

Example 5

This example refers to the attached figure below, in which:

Figure 5 is a perspective view of a hay windrow for composting or vermicomposting media for treating mining activity residual ore bodies in accordance with the present invention.

From the pilot studies it was concluded that for successful composting of wood chips (WC) and sewage sludge (SS) a 3:1 mixing ratio was required and the composting/worm composting process extended to 4-6 months.

In order to commercialize the method according to the present invention, the first step was to compost WC and SS for 30 days by building hay rows, an example of which is represented in FIG. 5 . The material was thereafter covered with netting (to prevent bird predation) and worm composted with earthworms (Eisenia fetida) for 4-5 months at a rate of 25 g worms per kg material.

As shown in Figure 5, the optimum size for constructing a row of hay is 2 tons of compost mixture per meter of length, which is 1 m high and 2 m wide. This means that 50kg of earthworms should be applied per hay row.

The medium of compost and vermicompost thus obtained was then mixed into the residual ore as described in Examples 1 and 2 above.

It has been found that composting and vermicomposting media according to the present invention can provide a favorable alternative and/or addition to soil improvement using topsoil, and subsequently waste wood chips and sewage sludge as a major source of organic carbon and nitrogen when carried out according to the present invention After bioconversion, it is a source of essential nutrients and organic matter for growing organisms. Wood chips are further beneficial organic amendments during revegetation and the main reason for using wood chips as an amendment is that they promote cation exchange capacity, thereby reducing base saturation and improving the ability of mucus to absorb excess salt. Wood chips can also improve the physical properties of growing media by increasing water retention. Organic materials can also stimulate biological activity, which is necessary for nutrient recycling.

A further advantage of the method is the use of waste from mining such as slime, wood chips and sewage for rehabilitating residual ore and for reducing soil, groundwater and air pollution.

It will be appreciated that variations are possible in the details of the medium and method of treating residues from mining operations in accordance with the present invention without departing from the scope of the appended claims.

Claims (21)

1. A method of treating a residual ore body from mining activities, the method comprising the step of applying wood particles to the residual ore body by processing wood particles into the residual ore body to a level up to 30 cm below the outer surface of the residual ore , wherein the wood particles are recovered from waste wood that is a by-product of mining activities. 2. A method according to claim 1, wherein the waste wood is in the form of wood ore pillars which have been disintegrated in the blasting operation. 3. A method according to claim 1 or 2, wherein the wood particles are pretreated with an acid. 4. The method according to claim 3, wherein the acid is nitric acid. 5. A method according to claim 1 or 2, wherein the microparticles are applied to a residual ore body in the form of a dam to rehabilitate the dam. 6. A method according to claim 5, wherein the wood particles are applied at a rate of 60-90 tons per hectare of residual ore dam surface. 7. A method according to claim 1 or 2, wherein the particles are applied to the residual ore body intermittently during its formation. 8. A method according to claim 1 or 2, comprising the step of composting the wood particles prior to the step of applying the particles to the body of residual ore. 9. The method of claim 8, wherein the step of composting the wood particles comprises the step of verm composting the particles. 10. The method of claim 9, wherein the step of composting the wood particles further comprises the step of mixing the particles with another source of organic material. 11. The method of claim 10, wherein the source of another organic material comprises sewage. 12. A method according to claim 11, wherein the wood particles and sewage are mixed to form compost, which compost can thereafter be inoculated with worms so that it forms a medium for worm composting. 13. A method according to claim 12, wherein the worms are from the species Earthworms. 14. A method according to claim 12 or claim 13, wherein the wood particles and sewage are mixed in a ratio of between 3:1 and 3:2. 15. A method according to claim 1 or 2, comprising the step of growing selected plants on the treated residual ore body. 16. The method according to claim 15, wherein the plant is selected from the group consisting of Tribulus ciliates var. terrestris; Tribulus ciliates var. Geinda; Lyman's brow and Teff curvae and mixtures thereof. 17. A residual ore body treated according to the method of any one of claims 1-16. 18. A composted medium for treating a body of residual ore from mining activities, the medium being added to the body of residual ore to a level up to 30 cm below the outer surface of the residual ore, the medium comprising wood particles and another organic material source, where the wood particles are in the form of wood chips recovered from waste wood that is a by-product of mining activities. 19. A medium according to claim 18, wherein the wood particles are in the form of wood ore pillars which disintegrate during the blasting operation. 20. A medium according to claim 18 or 19, wherein the source of another organic material is in the form of sewage. 21. A medium according to claim 18 or 19, wherein the mixture is further vermicompostable.

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