DE2407197B2 - Process for treating powdery or sludge-like materials containing harmful heavy metals - Google Patents

Description

The invention relates to a method for the treatment of harmful heavy metals containing, powdery or sludge-like materials, especially waste materials, in which these with water glass be mixed.

Environmental pollution from heavy metals such as cadmium or chromium is at risk human health and has become a serious problem. Heavy metals Sludge is discharged from various drainage devices in waste treatment. However, since no procedures for the treatment of sludge containing heavy metals have been introduced so far, under the current conditions, these are deposited untreated in fields and mountains or in the sea or stacked in factories where they are exposed to the elements. This justifies the concern that harmful Heavy metals are flushed out and lead to renewed environmental pollution. This also applies to I dust and slag containing heavy metals or sludge or powdery chemical waste products Procedure.

The method of the above-mentioned method known from German Offenlegungsschrift 2 100627 Art only sees a mixing of crushed waste materials with water glass and the immediate Landfilling of the solidified product obtained in this way, however, under the influence of the weather conditions does not bind the harmful heavy metals sufficiently permanently.

The object of the invention is now to create a method of the type mentioned at the outset, which is simple Way by converting the harmful heavy metals into poorly soluble substances in products that can be used safely for soil backfilling.

To solve this problem, the method of 197

initially mentioned type according to the invention characterized in that the za treated materials are mixed with finely divided iron oxide and / or clay and with water glass and the mixture obtained is heated ^{to temperatures between 700 and 1300 c C to form slag or clinker material.}

According to a preferred embodiment, 0.5 to 3, preferably 1.5 to 2.5 parts by weight of finely divided iron oxide and / or clay and 0.1 to U), preferably 0.6 to 0.9 parts by weight of water glass are added per part by weight of the heavy metal-containing material Mixes and the mixture is heated to temperatures between 800 and 1250.degree. C., preferably between 900 and 1200.degree. C., for 30 to 120, preferably 50 to 70 minutes. The mixture is expediently granulated and dried before heating. During the heating process, the heavy metals present together with the added iron oxide or clay form sparingly soluble heavy metal ferrites or silicates and, with the added water glass, glasses containing heavy metals.

The method according to the invention is used in particular for the treatment of solid-containing waste, which contain heavy metals and cannot be dumped or deposited as they arise. This includes sludge, ashes, from dust collectors arising from the treatment of runoffs Dust, heavy metal-containing waste from chemical processes, products obtained by comminution of heavy metal-containing masses such as slag and residues from the recovery of heavy metals and other active ingredients sludge-like products, such as residues from acid treatment and the Separation of heavy metals by chlorination.

While the advantages according to the invention are not achieved below a heating temperature of 700 ° C the upper limit temperature of 1300 ° C results in consideration of the fact that melting the substance to be heated and damage to the heating device is avoided. The heating time depends on the type of starting material, the amount of additives, the heating temperature and the firing device, taking into account the required minimum heating time of the sizes mentioned can be determined. The amount of additives depends on the composition the materials to be treated and the type and amount of heavy metals they contain and can, if necessary, be determined by a few preliminary experiments, whereby the advantages according to the invention can normally be achieved within the specified ranges.

The clays used according to the invention are silicates, which are common soil constituents and too those the kaolinite group, the montmorillonii group, the pyrophyllite group, chlorite and the general Materials called clay, for example Gairome clay, Kibushi clay (belonging to the kaolinites belonging), slate, pottery clay and other silicate-containing materials formed by the solidification of clay, loam or silt Materials belong.

The water glass used should preferably have a high silicate content. An increase in Additional amount reduces the water absorption of the sintered mass and leads to its use to backfill the soil to increase the strength and to reduce the contact area of the

Heavy metals with the surrounding water, for example Rainwater and groundwater.

The iron oxide used should advantageously have a small particle size. That in general Material called "rouge" (polished red) is suitable for this.

In the following preferred embodiments of the method on the basis of examples and under Further explained with reference to the drawings. It shows

1 shows a graphic representation of the extraction of a heated material of the MO-N A ₂ SI ₃ O ₇ -SeOe with ammonium acetate,

2 shows a graph of the water absorption as a function of the amount of water glass added and

3 shows a graphic representation of the time course of heavy metal extraction by ammonium acetate.

example 1

_{10 parts by weight of Fe 2} O ₃ and water were added to a mixture of one part by weight each of CdO, CuO, PbO and ZnO and, after mixing, the product obtained was granulated and heated in a muffle furnace at 900 ° C. for one hour. The coarse, molten conglomerate obtained in this way was crushed to a particle size of at most 0.15 mm and extracted with a 1 normal aqueous ammonium acetate solution, the pH of which had been adjusted to 4.5 with acetic acid, to extract the heavy metals contained therein. It was found that the aqueous ammonium acetate solution, based on the total content of the individual heavy details in the conglomerate, had extracted 21% Cd, 1.2% Co, 5.7% Pd and 1.1% Zn and converted about 80% or more into compounds which were insoluble in an aqueous ammonium acetate solution having a pH of 4.5.

Example 2

10 parts by weight of kaolin and water were added to a mixture of 1 part by weight each of CdO, CuO, PbO and ZnO and the product obtained after mixing was granulated and heated in a muffle furnace at 900 ° C. for one hour. The molten conglomerate obtained showed only a relatively low strength, so that it was to be assumed that it would break into fragments when used for soil backfilling. The molten conglomerate mm was crushed to a particle size of at most 0.15 and ₆ emäß extracted Example 1 with 1 N aqueous ammonium acetate solution. It was found that, based on the total content of the individual heavy metals in the conglomerate, 13% Cd, 0.2% Cu, 0.4% Pb and 1.6% Zn had been extracted and about 90% or more of the heavy details were converted into compounds insoluble in an aqueous ammonium acetate solution having a pH of 4.5.

B e i s ρ i e 1 3

For a mixture of one part by weight of CdO each. CuO, PbO and ZnO were added in experiment A, seven parts by weight of Fe ₂ O ₂ and three parts by weight of kaolin, and in experiment B three parts by weight of Fe ₂ O ₃ and seven parts by weight of kaolin. After adding water, the mixture was mixed and granulated and the product obtained was heated in a muffle furnace at 900 ° C. for one hour. The obtained, coarse, molten conglomerate showed in test A a water absorption in 48 hours of 18% and in test B a water absorption in 48 hours of 21%. The melted conglomerates were each comminuted to a particle size of at most 0.15 mm and extracted with an aqueous ammonium acetate solution according to Example 1. It was

ίο found that, based in each case on the total content of the individual heavy metals in the conglomerate, in test A 16% Cd, 0.4% Cu, 1.8% Pb and 1.9% Zn and in test B 14% Cd, 0, 2% Cu, 0.4% Pb and 1.8% Zn had been extracted and

5 about 85% or more of the heavy metals in both cases had been converted into compounds that in an aqueous ammonium acetate solution with a pH 4.5 were insoluble.

Example 4

In a series of experiments, a mixture of one part by weight of CdO, Cr ₂ O ₃ , CuO, Mn ₂ O ₃ , PbO and ZnO each with .94 parts by weight of water glass (sodium silicate No. 3; Na ₂ 0.3SiO ₂ ) was used.

as mixed and the mixture in each case for one hour heated in a muffle furnace at 600 ° C or 700 ° C or 800 ° C or 900 ° C. The respectively received molten conglomerates were glassy. The heavy metals contained therein were extracted each extracted with a 1 normal aqueous ammonium acetate solution, its pH value adjusted to 4.5 with acetic acid. The results are shown graphically in FIG. the Heavy metal oxides have been converted into compounds as a result of glass formation, which in an aqueous Ammonium acetate solution with a pH of 4.5 were insoluble. The one melted at 900 ° C The conglomerate was examined for its X-ray refraction, but no crystals were found could become. This shows that the heavy metal oxides had been vitrified.

Example 5
In a further series of tests, one part by weight of a sludge produced by treating the waste water of an existing chrome plating plant was each mixed with 2 parts by weight of kaolin and 0.0 or. 0.3 or 0, <> or 0.9 parts by weight of water glass (sodium silica: No. 3) mixed, the obtained

Mixture granulated: and dried and then heated in a muffle furnace at 900 ° C for one hour. Of the The sludge used contained 19.8 percent by weight Cr, S, 3 percent by weight Ni, 5.4 percent by weight Ca and 3.2 weight percent Cu. To the received

Conglomerates, the percentage of water absorption was determined in 48 hours. The results of this Experiments are shown graphically in FIG. Fig. 2 shows that the water absorption of the molten Conglomerate with increasing addition of water glass

takes. This is an important prerequisite for increasing the strength of the conglomerate.

Example 6

In further experiments, one part by weight was used of the sludge according to Example 5 with two parts by weight of kaolin and 0.6 parts by weight of water glass (Sodium silicate No. 3, as anhydride) mixed, the resulting mixture granulated and then a

Heated in a muffle furnace at 900 ° C for an hour. The resulting coarse, molten conglomerate became Crushed to a particle size of 0.15 mm or less and immersed in a 1 normal aqueous ammonium acetate solution introduced, the pH of which had been adjusted to 4.5 by acetic acid. In one Another attempt was the coarse conglomerate of spherical particles with a diameter of about 13 mm as it was incorporated into the ammonium acetate solution. In both cases, the Solution determined amount of heavy metal transferred as a function of time. The results of this Experiments are shown graphically in Fig. 3, the solid lines referring to a particle size conglomerate comminuted by a maximum of 0.15 mm and the dashed lines on the non-comminuted Refer to conglomerate. Fig. 3 shows that 98% or more of the heavy metals contained in the sludge had been converted into poorly soluble compounds.

Example 7

In a further experiment, one part by weight of the dried sludge according to Example 5 and 6 with two parts by weight of polishing red and 0.6 parts by weight of sodium silicate No. 3 mixed as anhydride, the mixture obtained is granulated and then heated in a muffle furnace at 900 ° C. for one hour. Of the The rough clinker obtained showed a water absorption of 25% in 48 hours. The heated mass was crushed to a particle size of 0.15 mm or less and immersed in a 1 normal aqueous solution for 10 days Ammonium acetate solution was introduced, which had been adjusted to a pH of 4.5 with acetic acid was. The dissolved amounts of heavy metals were 1.4 percent by weight Cu and 0.8 percent by weight Cr and 0.6 weight percent Ni.

Examples

The experiment of Example 7 was repeated, but now instead of two parts by weight of polishing red one part by weight of buffing red and one part by weight of kaolin was used. The clinker obtained showed a water absorption of 21% in 48 hours and after comminution to a particle size of a maximum of 0.15 mm after introduction into the aqueous ammonium acetate solution a dissolution of 1.1 weight percent Cu, 0.4 percent by weight Cr and 0.3 percent by weight Ni.

Example 9

In a further experiment, the sludge according to Example 5 with 1.5 parts by weight of kaolin and 0.75 parts by weight of commercial sodium silicate No. 3 (water content: 60%) mixed, the one contained Mixture granulated and then placed in a rotary kiln with an average residence time of one hour heated at a maximum temperature of 1200 ° C. The product obtained showed water absorption

in 48 hours of 4.7% and no leaching of the heavy metals Cu, Cr and Ni in water.

For this purpose 3 sheets of drawings

Claims (3)

24 S claims: 1. Process for the treatment of harmful heavy metals, powdery or containing sludge-like materials, especially waste materials, in which these mixed with water glass are, characterized in that the materials to be treated with finely divided Iron oxide and / or clay and with water glass »° are mixed and the mixture obtained for Formation of slag or clinker material heated to temperatures between 700 and 1300 ° C will. 2. The method according to claim 1, daduich ge ¹ S indicates that per part by weight of the heavy metal-containing material 0.5 to 3, preferably 1.5 to 2.5 parts by weight of finely divided iron oxide and / or clay and 0.1 to 1.0, preferably 0.6 to 0.9 parts by weight of water glass are added. 3. The method according to claim 1 or 2, characterized in that the mixture 30 to 120, preferably 50 to 70 minutes to temperatures between 800 and 1250, preferably between 900 and 1200 ° C is heated.