DE10314416B4 - Process for the separation of toxic heavy metal ions from waste water - Google Patents

Abstract

method for the separation of toxic heavy metal ions from wastewater, at the heavy metal ions at 50 ° C up to 700 ° C Calcined aerated concrete granules whose main components are synthetic 1.13 nm tobermorite and quartz, adsorbed and as water-insoluble heavy metal silicates be attached.

Description

The The invention relates to a method for the separation of toxic heavy metal ions from wastewater.

The Cleaning of waste water is an extraordinary one important task in the field of environmental protection. In the prior art Numerous methods have been developed for wastewater treatment, including processes such as neutralization, precipitation, flocculation, Redox reactions, ion exchange, adsorption and the like. These methods can used individually or in combination to the desired effect to achieve. Ion exchangers are also effective at separation different metal ions from wastewater. Suitable adsorbents For example, metal hydroxides such as aluminum hydroxide and iron hydroxide, as well as activated carbon, cellulose, kaolin or titanium dioxide (see W. Knoch, wastewater supply, wastewater treatment and waste disposal, VCH, Weinheim 1991).

One Disadvantage of the prior art method is that suitable Adsorbents and ion exchangers for the respective purpose must be specifically synthesized and therefore often higher Cause costs. There is therefore a need for a very inexpensive Material that effectively removes toxic heavy metal ions from wastewater possible power.

From the publication WO 97/06222 are already known cost-effective filter media or Ab- / adsorbent for gases and liquids based on rubber mulch, but the main use is in use as oil filter mats. The rubber mulch may contain admixtures belonging to a large number of very different substance classes, eg. B. also aerated concrete particles. The WO 97/06222 However, no reliable information on the functionality of these admixtures, but only the indication that the absorbent mats or filter mats have a nonspecific mechanical filter effect or due to the porosity of the materials used nonspecific pumping speed. The in the WO 97/06222 described means, including aerated concrete alternatively z. B. belongs to cork or wood shavings as absorbent admixture, therefore act with respect to heavy metal solutions only as absorbent material. However, information on which components of the substances used in the oil filter mats have a specific effect on heavy metal ions is not included.

The publication DE 102 10 786 A1 is a "process for the preparation of highly reactive reagents for the purification of water, which is contaminated with organic, inorganic or biological pollutants or ingredients" removable. In the adsorber mixture used in this process, gas concrete dust is also mentioned without functional specification as one of almost 30 merely summarily enumerated materials which can be used as additives in the preparation of the adsorber mixtures. Although attention is drawn to the usability of the adsorbent mixtures prepared for the removal of heavy metals from water. However, the document contains no indications as to which constituents of the main components and additives used in the adsorber mixtures are specifically suitable for converting heavy metal ions into water-insoluble compounds.

Furthermore, from the document DE 697 04 169 T2 a "process for purifying a metal ion-containing fluid by contacting said fluid with a material which adsorbs said metal ions", wherein said sorbent material consists of feldspar of natural origin composed of albite, anorthite, orthoclase and quartz in variable proportions. In the absence of a functional specification of the constituents of the feldspar ore, the DE 697 04 169 T2 No data on a suitable pretreatment of porous concrete materials to remove heavy metal ions from wastewater adsorptively and to form water-insoluble compounds.

Around to overcome the mentioned disadvantages of the prior art, The inventors of the present invention have extensively studied carried out and found that suitably pretreated cellular concrete materials suitable for the separation of heavy metal ions from waste water.

aerated concrete materials consist mainly of tobermorite, quartz, calcite, dolomite, Albite, Caolinite, Biotite and Orthoclase, with the main constituents Tobermorite and quartz include. They fall in granular or powder form in big Quantities in the molding and machining of aerated concrete components and there is a big one Need for novel uses for this Material.

Some studies have been known in the prior art that synthetic tobermorites are both ion-exchangeable and capable of accepting metal ions in the lattice. According to the results of El-Korashy, the synthetic 11.3 A tobermorites showed the ability to inhibit Ca ²⁺ against Me exchanging and accepting tall (M ⁺ ) cations (M ⁺ = K ⁺ , Na ⁺ , Li ⁺ ) from their hydroxides (see SA El-Korashy, Monatshefte für Chemie, 1997, 128, 599-607). It was found that the reactivity depends strongly on the pH value and the cation field strength, but less on the ionic radius of the alkali metal used. Stade found that the uptake of metal hydroxides is thought to be due to a reaction of the hydroxide with the SiOH groups on the surface of the intermediate layer (see H. Stade, Chem. Concr. Res. 1989, 19, 802). Hydrolysis of the Si-O-Si bonds facilitated the cation exchange process. With higher concentrations of the alkali metal hydroxide, the M ⁺ ↔ Ca ²⁺ exchange process within the liner would take place to a lesser extent.

Of the Invention is based on the object, a method for adsorptive Separation of toxic heavy metal ions from wastewater the basis of cellular concrete materials.

DETAILED DESCRIPTION OF THE FIGURES

1 Figure 11 is a graph showing the dependence of the specific surface area of an aerated concrete sample on the calcination temperature.

2 Figure 11 is a graph showing the dependence of the specific surface area of an aerated concrete sample on the caicination time.

3 Figure 11 is a graph showing ion dissociation from cellular concrete in an aqueous suspension of aerated concrete granules.

4 Figure 3 is a graph showing X-ray powder diffraction patterns of an untreated and a water-treated aerated concrete sample.

5 shows an IR spectrum of a 24-hour water-treated aerated concrete sample.

6 shows X-ray powder diffractograms of aerated concrete granules after treatment with 0.1 M and 1 M potassium chromium (III) sulfate solution.

7 shows X-ray powder diffractograms of aerated concrete granules after treatment with 0.035 M and 0.35 M potassium chromium (III) sulfate solution.

DETAILED DESCRIPTION OF THE INVENTION

The The object underlying the invention is achieved by a method for Separation of toxic heavy metal ions from wastewater, at the heavy metal ions at 50 ° C up to 700 ° C Calcined aerated concrete granules whose main components are synthetic 1.13 nm tobermorite and quartz, adsorbed and as water-insoluble heavy metal silicates be attached.

The Grain size of the used Aerated concrete granules are in a range of 1 micron to 10 mm, preferably in a range of 45 μm to 2 mm, and more preferably in a range of 45 μm up to 800 μm. Porous concrete granules with a wide grain size range can be easily by sieving into individual fractions with the desired particle size ranges be split. It was found that aerated concrete particles with very small grain sizes (<45 μm) one stronger basic surface character have, as aerated concrete particles with average grain sizes in the range from about 0.500 to 0.710 mm. This may be appropriate in choosing Particle size fractions for the subsequent use as adsorbents play a role.

The calcination increases the specific surface area of the aerated concrete granules. In the context of the present invention, the effect of calcining on the specific surface area of aerated concrete granules was examined in more detail. As a physical characteristic of the aerated concrete granules, the specific surface area was determined by the BET method. The volume of nitrogen gas is measured, which corresponds to a monomolecular coverage of the surface, and the results are used to calculate the total surface area (outer and inner). In particular, it was investigated how the specific surface area changes as a function of the calcination temperature and the calcination time (see Example 1). The annealing of aerated concrete samples (for a grain size of 0.315-1.4 mm) led first to an increase of the surface up to 600 ° C and then from 196 ° C to a steep surface shrinkage. The results of the BET measurements for the specific surface at different temperatures are in 1 shown. The enlargement of the surface at temperatures below 600 ° C is explain with release of the coordinatively bound water in the crystal lattice. Above 600 ° C, structural changes are likely to occur.

Further measurements showed that the size of the aerated concrete surface is also dependent on the calcination time. 2 shows the experimental data for this dependence.

at Calcination over 10 hours at a temperature of 50 ° C is hardly a change the specific surface to observe; at 10 to 20 hours it rises steeply, and at over 20 to It takes off slowly for 50 hours. This surface reduction depending on from the calcination time is with a kinetic conversion of the material can be explained.

The Calcination temperature is not particularly limited and is usually in a range of 30 ° C to 1200 ° C, preferably in a range from 50 ° C up to 700 ° C. Particularly preferred is a calcination temperature range of 100 ° C to 600 ° C. Also the Calcination time is not particularly limited. It usually lies in a range of 10 minutes to 7 days, preferably in one range between 2 hours and 48 hours, and most preferably in a range between 1 h and 24 h.

It was also examined whether the aerated concrete granules its alkali and Release alkaline earth ions in aqueous solution and exchange with other metal cations or record them can. To this possibility to prove granules samples were shaken in water for 24 hours. After that the aqueous solution was decanted and by atomic absorption spectroscopic investigation the type and the concentration of dissociated ions determined (see embodiment 2). The aerated concrete was then dried and X-ray powder diffractometry and IR spectroscopy (see embodiments 3 and 4).

In the aqueous solution, Ca ²⁺ , Na ⁺ , K ⁺ and Al ^{3+ were} qualitatively detected after 24 hours. Table 1 shows the quantitative results of the AAS analysis for the dissociated cations. It has been found that essentially calcium ions and sodium ions are released. The release of potassium ions and aluminum ions is orders of magnitude lower. Thus, the prerequisite for a successful storage and adsorption of toxic heavy metal ions in the aerated concrete granules. TABLE 1 No Al mol / l 10 ^-6 K mol / l 10 ^-6 Na mol / l 10 ^-3 Ca mol / l 10 ^-3 1. 4.79 0.307 1.02 3,35 Second 1.05 0.422 3.85 2.90 Third 9.02 0,465 1.21 4.03 4th 9.32 0,376 1.03 3.6 5th 3.74 0,417 0.97 3.0 Concentration of the dissociated cations in a system of 2 g aerated concrete material in 100 ml H ₂ O after 24 h.

In 3 the average of the concentration of dissociated cations is shown. From this information it can be seen clearly that mainly Ca ^{2 +} - and Na ⁺ ions are released.

in the Result of these investigations on the behavior of aerated concrete granulates in water Suspension was thus found to be substantially non-toxic Sodium and calcium ions are released.

The powder diffractograms of the treated aerated concrete samples hardly differ from those of the untreated material ( 4 , see embodiment 3). Due to the cationic dissociation it was observed that only the size of the crystals decreases.

IR spectroscopic measurements were carried out on KBr pellets in the middle and near infrared range. 5 Figure 14 shows a typical IR spectrum of an aerated concrete sample exposed to water for 24 hours treated and then filtered off and dried. All characteristic bands are visible in the mid-infrared range (450, 670, 780, 870, 970, 1400-1500, 1630, 3400 cm ^-1 ) and in the near-infrared range (4500 and 5200 cm ^-1 ) as in untreated aerated concrete. Interesting is the fact that the intensities of the bands increase at 1430, 3500 and 4500 cm ^-1 compared to untreated aerated concrete. This can be explained by the water absorbed by the aerated concrete material. This additional water absorption is possible by coordination with the SiO ₄ tetrahedra. The splitting of the band between 1400-1500 cm ^-1 into two new ones at 1450 and 1480 cm ^-1 and the more intense band at 4500 cm ^-1 supports the assumption that the deformation oscillation δSiOH actually appears between 1400-1500 cm ^-1 .

In a preferred embodiment is the heavy metal-containing wastewater with a suitable amount Autoclaved aerated granules and stirred until the heavy metals concerned Completely are adsorbed on the aerated concrete granulate. The duration of this process generally ranges between 0.5 and 24 hours. The heavy metal-loaded aerated concrete granules can subsequently filtered off known processes, dried and a landfill supplied become.

The Heavy metal ions in aqueous Suspension of aerated concrete granules can be adsorbed include generally metals of groups 3 to 15 of the periodic table as well the actinide. In a preferred embodiment, the heavy metal ions, the in aqueous Suspension of aerated concrete granules can be adsorbed, in particular the metals chromium, molybdenum, Tungsten, manganese, cobalt, nickel, copper, cadmium, mercury, thallium, Lead, Eismut, Uranium and Thorium.

A typical example of the inventive separation of a toxic heavy metal ion from an aqueous solution (eg wastewater) by means of the calcined aerated concrete granules is the separation of Cr ³⁺ ions from solutions of potassium chromium (III) sulfate. To demonstrate the effect of the aerated concrete granules, aerated concrete granules were stirred with aqueous solutions of potassium chromium (III) sulfate for 24 hours and then filtered off. In the obtained filtrates, the residual Cr ³⁺ ions as well as the aluminum, sodium and calcium ions liberated by ion exchange were quantified. Table 2 shows the concentrations of chromium, aluminum, sodium, and calcium ions after reaction with aerated concrete. Table 3 shows the calculated values for Cr in the solid phase compared to the Ca ^{2 +} - (+ Ca in the form of CaSO ₄ ), Na ⁺ and Al ³⁺ ions. Table 2 Molecular weight of KCr (SO ₄ ) ₂ -Lsg, · 10 ^-3 [mol / l] Ausgangskonz. Cr, [mg equiv. / L] Metal concentration after reaction with aerated concrete, [mg equiv. / L], after 24 h Cr al N / A Ca 1 26 0.0097 0.0598 91 207 2 104 0.0129 0.0043 130 251.5 4 280 0.0167 0.0450 102 274.5 6 312 0.0333 0.0032 85 280 8th 416 0.0373 .0710 102 300 10 520 0.0219 0.0200 98.7 240 12 624 0.0400 0.0430 159 203 16 832 0.0482 0.0450 100 234.5 20 1040 0.1936 .0860 133 223 Concentration of the metal cations of the aerated concrete after a reaction with potassium chromium (III) sulfate Table 3 Molecular weight of KCr (SO ₄ ) ₂ -Lsg, · 10 ^-3 [mol / l] Ingested amount Cr in the solid phase, [mg-equiv. / G] Σ Ca + Na + Al +. Ca (in the form of CaSO ₄ ) 1 25.9904 300.8700 2 103.9871 358.3143 4 279.9833 381.6850 6 311.9667 371.4132 8th 415.9627 410.4910 10 519.9781 350.7500 12 623.9600 370.0630 16 831.9518 396.7050 20 1039.8064 430.2710 Calculated values for Cr in the solid phase

It can be clearly seen from the results that as the starting concentration of chromium is increased, the sum of the mg-equiv. / L of metal ions liberated and Ca ²⁺ in the form of calcium sulfate is substantially lower than the total amount of Cr-absorbed by the aerated concrete phase. ions. This does not correspond to an equivalent ion exchange of the chromium with the metal cations of the material, but at the same time an ion exchange and an integration of the chromium in the mineral lattice. Increasing the chromium concentration in the starting solution made ion exchange more difficult. In contrast, the uptake of chromium ions was preferred.

By means of the XRD analysis, the changes in the crystal structure of the aerated concrete pellets after the adsorption of chromium (III) ions were investigated. The XRD spectra showed that after the reaction of the aerated concrete granules with the potassium chromium (III) sulfate new reflexes are present. These structural changes are associated with the release of calcium, potassium, and sodium ions, and an exchange process of these metal ions with the chromium ions from the solution and with the incorporation of the chromium ions into the lattice. The new sharp reflections belong to the formed Cr-silicate units ( 6 and 7 ).

Thus, the realization of the present invention is based on the following essential aspects:
In the separation according to the invention of toxic heavy metal ions from wastewaters by means of calcined aerated concrete granules, exclusively non-toxic metal ions are liberated by ion exchange. These are essentially sodium and calcium ions, and to a lesser extent, potassium and aluminum ions. In the separation according to the invention of toxic heavy metal ions from wastewaters by means of cellular concrete granules, water-insoluble heavy metal silicates are formed which are firmly bound to the cellular concrete material. This allows for easy and complete separation and subsequent landfill of the heavy metal loaded cellular concrete materials.

at the method according to the invention At the same time an ion exchange and an integration of the toxic heavy metal ions into the crystal lattice of the cellular concrete material. As an industrial waste product, the aerated concrete granules are extremely inexpensive for the purpose of the invention usable.

The Invention will now be explained in more detail with reference to embodiments. It It is understood that these embodiments are illustrative only Have character and should not limit the invention in any way. For professionals In the field of adsorption and wastewater treatment it becomes obvious be that various modifications and additions are made can, without departing from the essence of the invention.

EMBODIMENTS

embodiment 1

Calcination of aerated concrete granules

The aerated concrete granules used were subjected to a calcination treatment (cf. 1 and 2 ). If desired, the calcined aerated concrete granules were sorted by sieving into grain size ranges. Further treatment is not required for use in wastewater treatment.

embodiment 2

AAS analysis of aerated concrete granules in water Suspension liberated ions

To detect the ions exchanged from aerated concrete granules in aqueous suspension, 5 different aerated concrete granulate samples (2 g each) in water (100 ml) were shaken for 24 hours. The aqueous solution was then decanted and the type and concentration of the ions dissociated were determined by atomic absorption spectroscopic analysis (AAS). In the aqueous solution after 24 hours Ca ²⁺ , Na ⁺ , K ⁺ and Al ^{3+ were} qualitatively detected (see Tables 1 and 3 ).

embodiment 3

X-ray powder diffraction- Examination of aerated concrete granules after treatment with water

The treatment of aerated concrete granules with water was carried out as described in Example 2. Subsequently, the aerated concrete granules were filtered off and dried. X-ray powder diffractometry has been shown to reduce the size of the crystals when treating the aerated concrete granules due to cationic dissociation but substantially preserve the overall structure ( 4 ).

embodiment 4

IR spectroscopic investigation of n Adsorbents based on aerated concrete granules

The Treatment of aerated concrete granules with water was as in the embodiment 2 described performed. Subsequently the aerated concrete granules were filtered off and dried. IR spectroscopic Measurements were taken in the middle and near infrared regions on KBr pellets carried out.

embodiment 5

Series of experiments on the adsorption of chromium (III) ions from aqueous solutions by means of aerated concrete granules

Porous concrete granules were suspended in an aqueous solution of potassium chromium (III) sulfate and stirred for 24 hours at room temperature. Subsequently, the aerated concrete granules loaded with Cr ^{3+ were} filtered off and dried. In the filtrate, the concentrations of chromium, aluminum, sodium, and calcium ions were quantified (see Tables 2 and 3).

embodiment 6

XRD analysis of aerated concrete granules according to Adsorption of chromium (III) ions from aqueous solutions

As described in Example 5, aerated concrete granules were suspended in an aqueous solution of potassium chromium (III) sulfate and stirred for 24 h at room temperature. Subsequently, the aerated concrete granules loaded with Cr ^{3+ were} filtered off and dried. By means of XRD analysis, the changes in the crystal structure were investigated (cf. 5 ).

Claims (4)

Process for the separation of toxic heavy metal ions from waste water containing heavy metals nen calcined at 50 ° C to 700 ° C calcined aerated concrete granules whose main constituents synthetic 1,13-nm tobermorite and quartz, adsorbed and annealed as water-insoluble heavy metal silicates. Method according to claim 1, characterized in that the used aerated concrete granulates have particle sizes in a range from 1 μm to 10 mm, preferably in a range of 45 μm to 2 mm, and most preferably in a range of 45 μm up to 800 μm exhibit. Method according to claim 1 or 2, characterized that the heavy metal ions are metals of groups 3 to 15 of the periodic table and the actinides include. Method according to claim 3, characterized that the heavy metal ions in particular the metals chromium, molybdenum, tungsten, Manganese, cobalt, nickel, copper, cadmium, mercury, thallium lead, bismuth, Include uranium and thorium.