CN102061177A - Heavy metal zinc polluted soil curing agent taking industrial waste carbide slag as raw material - Google Patents

Abstract

A solidification agent for heavy metal zinc-contaminated soil using industrial waste carbide slag as raw materials, comprising: ordinary Portland cement and industrial waste carbide slag, the mass percentage of which is: 70%-80%: 20%-30%. Cement is a commonly used curing agent for the treatment of heavy metal-contaminated soil. By adding cement powder or cement slurry to the contaminated soil and stirring it fully, the effect of improving the strength of the solidified soil can be achieved. Cement is used alone in the project, and the mixing ratio is relatively large, around 12%-18%. Even so, it is still difficult to guarantee the strength, durability and curing quality of the solidified soil. In response to this phenomenon, the present invention proposes a solidification formula for heavy metal zinc-contaminated soil using industrial waste carbide slag as raw material. The formula is composed of cement, carbide slag and bentonite. By promoting the hydration reaction of cement, the Zn ^{2 +} Ability to achieve the purpose of reducing the amount of cement and improving the curing effect.

Description

Heavy metal zinc-contaminated soil solidification agent using industrial waste carbide slag as raw material

Technical field:

The invention relates to the technical field of heavy metal-contaminated soil treatment, in particular to a curing agent formula for treating heavy metal zinc-contaminated soil. the

Background technique:

In recent years, with the development of cities in our country, many chemical and electronic companies have moved their sites from urban areas to the outer suburbs. Due to the imperfect technology of most companies to deal with the "three pollutants" discharges, the foundation soil of the original site was polluted by heavy metals and became industrial pollution. earth. The physical and mechanical properties of the polluted foundation soil will change, resulting in a reduction in the bearing capacity of the foundation, resulting in instability or destruction of buildings, and a series of engineering quality accidents; on the other hand, the pollution components in industrially polluted sites will migrate to the surrounding environment, Harm the health of local residents and the ecological environment. Therefore, what kind of technology to use to treat industrially polluted sites to meet the needs of secondary development and utilization is an important issue in the process of modern urban construction in my country. the

Chemical solidification is currently the most widely used method for treating heavy metal-contaminated soil. The so-called chemical curing treatment refers to the process of chemically blending and containing hazardous waste in a dense inert substrate to stabilize it. The inert material used for chemical curing is called a curing agent. the

Traditional solidification materials include cement, lime, and fly ash, among which cement plays a major role. Mechanism of cement solidification of heavy metals: The cement reacts with the moisture in the polluted soil to form a gel, which contains the harmful substance particles and gradually hardens to form a cement solidification body. The structure of this solidified body is mainly the hydration reaction product C-S-H of cement (a kind of amorphous colloidal multi-microporous material with a high surface area, which can absorb a large amount of cations by physical means), and the hydration crystal body contains pollution. The particles of matter make the harmful substances in the polluted soil be enclosed in the solidified body, so as to achieve the purpose of harmlessness and stabilization. Practice has proved that the use of cement to solidify soil contaminated by various heavy metal ions has a certain effect, and some heavy metal ions can also be wrapped in the lattice of the cement matrix, thereby effectively preventing the leaching of heavy metal ions. However, high cement content is required in the project, and the pure use of cement will undoubtedly increase the cost. Practice has proved that the durability of the contaminated soil solidified by pure cement is not ideal. In addition to cement, there are traditional curing agents such as fly ash and lime. Studies have shown that the unconfined compressive strength of contaminated soil after curing with these two materials is low, and the concentration of heavy metal ions is high, which cannot meet the requirements of engineering and environmental protection. To sum up, traditional curing agents have the disadvantages of high cost, poor durability of solidified soil, difficulty in effectively wrapping heavy metal ions in contaminated sites, and inability to effectively improve the strength of contaminated soil foundations. the

Calcium carbide slag is the waste residue produced when calcium carbide is _used to produce acetylene, an _important chemical raw material _. matter and a small amount of organic matter. According to the statistics of the National Development and Reform Commission, in 2003, the domestic production of calcium carbide was 5.3 million tons, and calculated as 1.2 tons of calcium carbide slag per ton of calcium carbide consumed, the national production of calcium carbide slag exceeded 6 million tons. Calcium carbide slag has high water content, high alkalinity, and large flow rate, which is a key pollution source of sewage pipe network; while the main component of dry carbide slag is calcium oxide, which is a highly alkaline substance with a pH value of more than 12. Discharging and storing calcium carbide slag often occupies a large amount of cultivated land, and the land stored for a long time is severely calcified, making it very difficult to recultivate. If not properly managed, it will have a serious impact on the local ecological environment. How to comprehensively reuse carbide slag and turn waste into treasure is an urgent issue for enterprises.

Invention content:

In order to solve the shortcomings of the existing heavy metal-contaminated soil curing agent, especially the heavy metal zinc-contaminated soil curing agent, that the cost is high, the durability of the solidified soil is poor, and the curing effect is not good, the present invention provides a heavy metal Zinc-contaminated soil curing agent, the invention can not only reduce the cost of curing agent, enhance the curing effect of contaminated soil, but also turn carbide slag into treasure, and play the role of comprehensive utilization and environmental protection. the

The present invention has the following technical solutions:

A heavy metal zinc-contaminated soil solidifying agent using industrial waste carbide slag as raw material, comprising: ordinary Portland cement and industrial waste carbide slag, the mass percentage of which is: 70%-80%: 20%-30%, wherein the carbide slag Mass in completely dry state. the

Beneficial effect:

For heavy metal zinc-contaminated soil, chemical solidification method is a suitable in-situ treatment scheme. Its advantage lies in the use of solidification agent to change soil physical and chemical properties, fix toxic Zn ²⁺ , and reduce the migration of toxic substances to deep layers and groundwater. The most important thing is the type and quality of the curing agent. In the soft soil foundation with low moisture content, the mixing ratio of cement is about 12%-18%, and a large amount of cement is needed in the construction process. At the same time, the price of cement materials is relatively high, accounting for most of the treatment cost; In the soft soil area with moisture content, the cement mixing ratio is larger, and it is difficult to guarantee the treatment effect. The curing agent proposed by this patent can effectively make up for the deficiency of traditional curing agents. According to the current test results, industrial waste calcium carbide slag (in a completely dry state) can replace 20%-30% of the cement consumption, thereby saving 20%-30% of the cost, and the solidified soil using the patented solidifying agent has higher strength and stronger Good durability and lower Zn ²⁺ leachability.

Description of drawings:

Figure 1 is a comparison chart of the unconfined compressive strength of zinc-contaminated soil cured by different formulations. the

Figure 2 is a comparison chart of the cumulative mass loss rate of different formulations of solidified zinc-contaminated soil in dry-wet cycles. the

Figure 3 is a comparison chart of Zn ²⁺ leachable concentration in zinc-contaminated soil immobilized by different formulations.

Detailed ways:

Example 1

A heavy metal zinc-contaminated soil solidifying agent using industrial waste carbide slag as raw material, comprising: ordinary Portland cement and industrial waste carbide slag, the mass percentage of which is: 70%-80%: 20%-30%, in this implementation In the example, the mass percent of ordinary Portland cement and industrial waste carbide slag is: 70%: 30%, 80%: 20% or 72%: 28%, and the ordinary Portland cement can be P.O.32.5 ordinary silicon Salt cement and carbide slag are completely dry. the

Example 2

A solidification agent for heavy metal zinc-contaminated soil using industrial waste carbide slag as raw material, the solidification agent is composed of ordinary Portland cement, industrial waste carbide slag and sodium-based bentonite, wherein ordinary Portland cement and industrial waste carbide slag The mass percentage is: 70%-80%: 20%-30%, the mixing amount of sodium bentonite is not more than 15% of the sum of ordinary portland cement and industrial waste calcium carbide slag mixing amount, in the present embodiment , the mass percentage of ordinary Portland cement and industrial waste carbide slag is: 70%: 30%, 80%: 20% or 75%: 25%; the mixing amount of sodium bentonite is ordinary Portland cement and industrial waste 15%, 12%, 0.1% or 7% of the sum of carbide slag additions. the

According to the above formula, the present invention mixes it evenly to obtain the finished curing agent. The dosage of curing agent is 15% or 18% (quality of curing agent/quality of heavy metal zinc polluted soil after complete drying). Table 1 and Table 2 respectively give the basic physical and chemical properties and chemical composition of carbide slag. the

Because one of the raw materials used in the solidifying agent of the present invention is an alkaline substance, calcium carbide slag provides a higher pH value environment for the solidification process of the polluted soil, so that the hydration and solidification reaction of the cement is accelerated, and the ^Zn in the polluted soil is in the alkali simultaneously. Under mild conditions, hydroxides and carbonates that are insoluble in water are formed, and Zn ²⁺ is fixed in the lattice of the cement matrix, thereby effectively preventing the leaching of Zn ²⁺ from harming the environment. A small amount of sodium-based bentonite mixed in can effectively improve the durability of the polluted solidified soil and enhance the solidification and stabilization effect on Zn ²⁺ .

Table 1 Basic physical and chemical properties of carbide slag

Table 2 Analysis of the chemical composition of carbide slag

The present invention will be further described below in conjunction with indoor test result:

A galvanizing workshop in Lianyungang City was relocated, and the soil from the original site was taken for inspection. The main physical and chemical indicators of the in-situ soil are shown in Table 3. The chemical analysis results show that the Zn ²⁺ content of the soil in the most seriously polluted area (the Zn ²⁺ mass accounted for 1% of the completely dry The percentage of the total mass of polluted soil) is 0.5%.

Detect the moisture content of the polluted soil, and use the NJ-160 cement slurry mixer to pour water while stirring for 5 minutes to configure the polluted soil into a polluted soil with a moisture content of 60% (the water quality in the polluted soil accounts for the percentage of the completely dried polluted soil mass) Put the sample into the sample barrel and seal it to make the moisture content uniform. Add 15% (the mass percentage of the curing agent to the completely dry contaminated soil) curing agent to the prepared contaminated soil sample, and stir for 5 minutes with the same type of agitator. In order to compare the effects of the curing agent of the present invention and the traditional pure cement curing agent, the curing agent adopts three formulas: formula A: pure cement; formula B: 70% cement+30% carbide slag; formula C: 70% cement+20% calcium carbide Slag + 10% sodium bentonite. After stirring evenly, take out the solidified soil and fill it into a mold of 5cm (diameter) × 10cm (height), vibrate it by hand, scrape it flat, make a sample, cover it with a film, let it stand for 24 hours, demould, and put it in 24°C and 100°C % humidity in the curing room for 7 days, 28 days, 56 days and 90 days respectively. In order to compare the effect of the new curing agent and the traditional pure cement formula on improving the strength and durability of the contaminated soil and controlling the dissolution performance of Zn ²⁺ , unconfined compressive strength tests and dry-wet cycle tests were carried out on each group of samples at different ages. And TCLP leaching experiment.

The experimental results show that: using the curing agent of formula B and C can improve the strength of the polluted site more obviously (refer to Figure 1 for the unconfined compressive strength test results); the durability of the solidified soil using formula B and C is also better than that of formula The solidified soil of A (refer to Figure 2 for the results of the dry-wet cycle test); the results of the TCLP leaching test show that the curing agents of formulas B and C are more effective in curing Zn ²⁺ than formula A (refer to Figure 3 for the results of the leaching rate test) .

Table 3 The main physical indicators of soil samples

Soil sample name Moisture content (%) specific gravity Plastic limit (%) Liquid limit (%) pH value soft soil 45 2.72 25.8 55.1 8.20

1. Unconfined compressive strength test

The unconfined compressive strength test is based on the "Highway Soil Test Regulations" (JTG E40-2007), using the YSH-2 lime soil unconfined pressure instrument, and the compression rate is 1mm/min. The curing ages of the samples were 28 days, 56 days and 90 days respectively. Three parallel samples were taken from each group for the unconfined compressive strength test, and the average value was used as the unconfined compressive strength. Draw it into Figure 1. From the analysis of the results in Figure 1, it can be seen that at each age specified in the test, the strength of the solidified zinc-contaminated soil of formula B and C is 20%-33% and 15%-27% higher than the strength of the solidified soil of formula A, respectively. The effect of C increasing the strength is more obvious. the

2. Wet and dry cycle test

The dry-wet cycle test is carried out according to the Japanese standard [Public Works Research Institute: Final Report of Cooperative Research, 1997, pp.77-82]. When the curing age reaches 28 days, 2 parallel samples are taken from each of the 3 groups of solidified soil (the test results are averaged), and the dry-wet cycle test is carried out (see Table 4 for the dry-wet cycle test method). the

Table 4 Dry-wet cycle test method

A total of ten levels of dry-wet cycles are carried out. At the end of each level of dry-wet cycle test, the mass m _n of solidified soil samples with different formulations is measured, and the mass loss rate is calculated by combining the initial mass m ₀ of the sample Analysis cumulative mass loss rate ∑w _n =w ₁ +w ₂ +... _wn . The mass loss rate data records of the samples are shown in Table 5, and the cumulative mass loss rate comparison is shown in Figure 2.

Table 5 Accumulative mass loss rate of various formulations of solidified zinc-contaminated soil in dry-wet cycle test

According to Fig. 2, it can be seen that the cumulative mass loss rate of the solidified soil adopting formula A after ten dry-wet cycles is 1.5 times and 2.5 times that of the solidified soil adopting formula B and formula C, respectively. It can be seen that the solidified soil adopting formula B and formula C Durability is better than the solidified soil using A formula. the

3. TCLP leaching test

The test of Zn ²⁺ leaching concentration in the solidified heavy metal zinc contaminated soil with different formulas is based on the TCLP (US Environmental Protection Agency. Technical Assistance Document for Complying with the TC Rule and Implementing the ToxicityCharacteristic Leaching Procedure (TCLP) recommended by the US Environmental Protection Agency [ R].USA, Washington DC, www.epa.gov, 1994) method is measured, and adopts atomic absorption method to detect the ^Zn concentration in the leachate. The curing ages of the solidified soil samples used in the TCLP leaching test were 7d and 28d, and two parallel samples were used, and the average value was taken as the results. The test results are shown in Figure 3.

The test results are shown in Figure 3, and the results show that the concentration of Zn ²⁺ detected in the leachate of the formula A sample is 1.2 times the value measured in the leachate of the B and C formula samples at the same age. It can be seen that formula B and formula C have better Zn ²⁺ curing effect on zinc-contaminated soil than formula A.

Claims (2)

1. A solidifying agent for heavy metal zinc-contaminated soil using industrial waste carbide slag as raw material, characterized in that it comprises: ordinary Portland cement and industrial waste carbide slag, and its mass percentage is: 70%-80%: 20%- 30%. 2. the heavy metal zinc-contaminated soil solidifying agent taking industrial waste carbide slag as raw material according to claim 1 is characterized in that, said solidifying agent is made up of ordinary Portland cement, industrial waste carbide slag and sodium bentonite, wherein , the mass percentage of ordinary Portland cement and industrial waste carbide slag is: 70%-80%: 20%-30%, the amount of sodium bentonite added is not greater than the amount of ordinary Portland cement and industrial waste carbide slag 15% of the sum.

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