RU2711766C1 - Method of decontaminating and recycling sulphide arsenic-containing wastes - Google Patents

Abstract

FIELD: chemistry; processing of wastes.

SUBSTANCE: invention relates to decontamination and disposal of solid arsenic-containing wastes and can be used in preparation of hardening stowing mixture of waste space in mines. Processing of sulphide arsenic-containing wastes involves mixing of wastes and fusion with elementary sulfur. Prior to melting, wastes are dried to moisture content of not more than 4 %, disintegrated to grain size of not more than 1.6 mm, after which obtained waste powder is heated to 120–155 °C and mixed with molten sulfur. Ratio of sulphide arsenic-containing wastes and fused elemental sulfur in mixture is 1:2.5–3.5. Obtained mixture is granulated, cooled and a granular glassy mixture with diameter of 2–5 mm is obtained.

EFFECT: method enables to obtain a mixture with maximum flowability and minimum viscosity, which leads to minimum water wash-out of arsenic.

1 cl, 1 dwg, 3 tbl

Description

The invention relates to the field of non-ferrous metallurgy and the chemical industry, in particular, to the disposal and disposal of arsenic-containing sulfide materials.

In the production of non-ferrous metals, arsenic trisulfide precipitates (cakes) are formed. The placement and storage of such compounds requires the organization of special landfills for highly hazardous waste, which causes large economic costs and negative environmental consequences. In the metallurgical, and often in chemical industries, there is the problem of neutralizing solid arsenic-containing sulfide cakes - waste of the third hazard class.

A known method of neutralizing arsenic-containing products, including melting the starting material to produce vitreous arsenic trisulfide (Naboychenko S.S., Mamyachenkov S.V., Karelov S.V., Arsenic in non-ferrous metallurgy / Ed. By S.S. Naboyuchenko - Yekaterinburg: UB RAS, 2004, p. 223). In the known method to increase the stability of sulfide arsenic-containing sublimates and cakes from oxidation, the precipitated arsenic sulfide is melted in the presence of 5-50% sulfur additive. The result is a water-insoluble form of sulfide, and the volume of the product is reduced by 19 times compared with the volume of the original sulfide.

The disadvantages of this method include low efficiency, low efficiency of the neutralization process and the lack of solutions for the disposal of the resulting product.

As shown by experiments carried out under the conditions of the known method, during melting due to the high volatility of arsenic trisulfide in the smelting furnace, the latter sublimates and enters the atmosphere in the form of vapors, which negatively affects the environmental friendliness of the method as a whole and requires the construction of expensive gas treatment plants.

In addition, the obtained arsenic vitreous trisulfide ingots during storage do not provide a sufficient degree of neutralization, since the surface of the ingot is oxidized by water and air oxygen with the formation of arsenic hydroxy and thio compounds well soluble in water

As2S3 + 2H2O↔HASO2 + H3AsS3

As2S3 + 3H2O↔H3AsO3 + H3AsS3

As2S3 + 6O2↔As2 (SO4) 3

The low efficiency of the known method is also caused by the following: - for the implementation of the process, it is necessary to use a melting unit (furnace), which requires significant capital and operating costs.

The closest analogue to the claimed invention is a Method for processing waste containing arsenic sulfide (Patent SU 1542046 class C22 B7, authors: Khalemsky AM, Gertman EM, Ivenko N.V., Ivakin A.A., Shtin A.P. , Maksimova L.G.). A method of processing waste containing arsenic sulfide, including heating it in the presence of elemental sulfur to obtain sparingly soluble alloys, characterized in that in order to increase the strength characteristics of the alloy, reduce toxicity and volume, the process is conducted in the presence of 0.5-3.0 mass% sulfide copper at an elemental sulfur flow rate of 4.0-4.5 mass% at 165-220 ° C and a pressure of 5-20 kgf / cm2.

The disadvantages of the closest analogue include:

1. The need for additives of 0.5-3.0 mass% of copper sulfide, which causes the loss of the initial copper-containing raw materials, reduces the total extraction of copper in the process and reduces its economic efficiency.

2. In the claimed temperature range of 165-220 ° C, the efficiency of obtaining water-insoluble alloys is very low due to the fact that, at temperatures above 160 ° C, molten sulfur turns into a very viscous, inactive dark brown mass that does not have good fluidity, wettability and mixing.

The lack of fluidity in the molten sulfur prevents the wetting, mixing, and uniform distribution of the components of copper and arsenic sulfides with molten elemental sulfur and obtaining a homogeneous mass, which, in turn, can lead to increased leaching of arsenic with water.

3. The need to create pressure during the preparation of the mixture in the range of 5-20 kgf / cm ² complicates the process, requires the use of special expensive press equipment and increases the economic costs of processing arsenic waste.

4. Lack of solutions for the disposal of the resulting product.

Given the noted disadvantages of the prototype, a more efficient technology was developed and proposed, characterized in that in it the molten elemental sulfur is used not as an additive to obtain sparingly soluble compounds, but as an insulating medium, in the mass of which the encapsulated substance is evenly distributed.

The properties of molten liquid sulfur allow the process of neutralizing arsenic-containing wastes by isolating arsenic trisulfide cake in a mass of sulfur

Elemental sulfur is not oxidized by atmospheric oxygen and does not dissolve in water and is a highly effective and stable encapsulating substance in the natural environment.

The objective of the invention is to develop solutions for the disposal and disposal of solid arsenic-containing sulfide waste. The technical result of the claimed invention is to increase the mobility of a mixture of arsenic trisulfide powder with a moisture content of not more than 4%, particle size up to 1.6 mm and molten elemental sulfur in the temperature range 120-155 ° C at a flow rate of 2.5-3 per one part by weight of arsenic-containing sulfide waste, 5 parts by weight of sulfur. Within the claimed parameters of the method provides the maximum fluidity of the resulting mixture and its minimum viscosity, as well as the minimum leachability of arsenic with water.

The problem is solved in that in the method of processing the disposal of arsenic-containing sulfide waste and its disposal, including heating the waste powder to 120-155 ° C, melting sulfur, mixing hot components, granulating the resulting mixture and adding sparingly soluble granules to the hardening filling mixture, the following are provided differences:

- liquid elemental sulfur is used not as an additive to obtain a sparingly soluble compound, but as a neutralizing substance, in the mass of which powdered arsenic compounds are evenly distributed;

- copper sulfide is not used - a valuable source of copper-containing raw materials;

- the temperature of the molten sulfur is maintained in the range of 120-155 ° C instead of the recommended in the prototype 165-220 ° C;

- the resulting mixture of sulfide precipitates and molten sulfur after mixing is granulated. Granules are used as one of the components in the preparation of a hardening filling mixture of the spent space in the mines.

The essence of the proposed method is as follows:

When neutralizing solid arsenic-containing sulfide wastes, molten elemental sulfur is used as an insulating medium, in the mass of which the encapsulated substance-powder compounds of arsenic are evenly distributed.

Arsenic trisulfide waste, if necessary, is dried to a moisture content of 4% or lower, disintegrated to a particle size of minus 1.6 mm, heated to a temperature of 120-155 ° C and mixed with molten sulfur in a predetermined ratio: one weight part of arsenic-containing sulfide waste by 2, 5-3.5 parts by weight of sulfur. Next, the easily moving mixture is granulated, cooled, and a granular glassy mixture with a diameter of 2-5 mm is obtained, which is disposed of in the preparation of a hardening filling mixture.

The filling mixture is used to fill the spent space in the mines.

To test the proposed method for the neutralization of arsenic trisulfide precipitates, as well as in a mixture with gypsum and cadmium and bismuth sulfides, we used reference data on the temperature dependence of the viscosity of molten liquid sulfur and laboratory studies of the influence of individual process parameters on the properties of the obtained granular samples.

The molten liquid sulfur allows the process of neutralizing arsenic-containing wastes by isolating the arsenic-containing powder in the mass of molten sulfur, since after cooling the resulting mixture is not oxidized by atmospheric oxygen and does not dissolve in water and is highly efficient and stable in the natural environment, reliably isolating hazardous arsenic wastes;

A measure of mobility (fluidity), wettability, ability to mix with other substances and their uniform distribution in the volume of molten sulfur is its viscosity. Depending on the temperature, viscosity varies over a wide range from easily mobile and fluid to a viscous, slow-moving bitumen-like mass (Melnik B.D., Melnik E.B. Brief engineering reference book for inorganic matter technology. Graphs and nomograms. Khimiya Publishing House, Moscow, 1968, p. 137; Handbook of sulfuric acid. Edited by K. Malina / - M., Chemistry, 1971, p. 42, 43, 45).

The graphical dependence of the viscosity of molten sulfur on temperature is shown in Figure 1, which clearly shows the minimum viscosity in the temperature range 150-155 ° C.

It was experimentally established that in the temperature range 120-155 ° C the viscosity of molten sulfur varies from 11.25 to 6.745 cps and sulfur retains mobility and fluidity (table 1), at a temperature of 160 ° C its viscosity increases 410 times to a value of 2668 cps, and at 220 ° C it reaches 45,000 cps. In the temperature range 160-220 ° C, molten sulfur turns into a sedentary, non-stirred mass.

Therefore, the working temperature range of the encapsulation of a mixture of precipitation of arsenic trisulfide, metal sulfides and gypsum in the mass of molten sulfur is 120-155 ° C.

In order to determine the parameters at which the best result of neutralizing the precipitate of arsenic trisulfide with obtaining water-stable mixtures is achieved, the necessary experimental studies were carried out.

Empirically determined the limiting indicators of humidity and particle size of the precipitate of arsenic trisulfide and the specific consumption of sulfur by weight for neutralized powders.

The initial arsenic-containing sulfide precipitate was presented in the form of a mono compound As ₂ S ₃ and in a mixture with sulfides of cadmium, bismuth and gypsum.

Approximate compositions of arsenic-containing sulfide sediments, (%):

1. The precipitate of the mono compound As ₂ S ₃ - 90-95, impurities 5%;

2. A mixture of precipitation: As ₂ S ₃ - 37-40; CdS - 2-4; Bi ₂ S ₃ - 1-3; CaSO _{4⋅H 2} O - 20-3; others - 15%.

Arsenic sulfide precipitates were dried to a moisture index of 0; 1.5; 3.0; 4.5%, disintegrated and dispersed on sieves to obtain fractions: from minus 1.6 to plus 0.6; from minus 0.6 to plus 0.1; "Minus" 0.1 mm. The minus fractions of the precipitate were used to prepare mixtures with various amounts of elemental sulfur, the mass ratio of which, [precipitate As ₂ S ₃ ]: [sulfur], varied from 1: 1 to 1: 3.5.

As ₂ S ₃ and sulfur powders were heated separately to various temperatures in the range of 120-160 ° С, after melting, the sulfur was mixed and stirred for 30-60 seconds, as a result, a thick, motionless or thick mobile, or fluid mass was obtained. The resulting hot mass was granulated to obtain granules with a diameter of 3-5 mm.

Part of the granules was placed in water with different pH values of 3.5; 7.0; 11.0 and controlled leachability of arsenic. The duration of continuous contact of the samples with water was 50 days. Periodically, after 5 days, water samples were taken and analyzed for arsenic content (table 2).

Another part of the granules was used as one of the components for the preparation of a hardening mixture for laying the waste space in the mines.

The results of studies of the influence of various parameters on the properties of the resulting encapsulated mixtures are presented in table 3.

Experimental studies on the influence of liquid sulfur temperature on the properties of the obtained granular mixture samples were carried out in experiments 2 and 8. In the temperature range 120-150 ° C, samples were obtained from which arsenic is not washed out by water, and the hot mass was sufficiently mobile and lends itself well to granulation . The experimental data on the effect of temperature on the properties of mechanical mixtures “elemental sulfur - arsenic trisulfide powder” are in good agreement with the reference data on the temperature dependence of the viscosity of molten sulfur (Fig. 1, Table 1). At 160 ° C, elemental sulfur becomes viscous and loses fluidity, which does not allow arsenic trisulfide powder to be wetted by molten sulfur and evenly distributed in its volume. The mass is not homogeneous.

In order to determine the maximum humidity at which water vapor is evolved, a series of experiments 4 and 6 was carried out. It is known that the moisture contained in the powders can interact with arsenic trisulfide to form soluble forms of arsenic. The experiments allowed us to establish that at a moisture content of more than 4.5%, water vapor is released, which causes an increase in the leachability of arsenic. Therefore, a humidity of not more than 4.0% is accepted as a limiting parameter.

The effect of the particle size distribution of arsenic-containing sulfide powders on the properties of the mixtures obtained was studied (experiments 5 and 7). It was found that when the minus size of the fractions is 1.6 mm, homogeneous in structure are formed with a uniform distribution of arsenic trisulfide powders, metal sulfides and gypsum in the volume of liquid sulfur. With a particle size greater than 1.6 mm, As ₂ S ₃ powders are not evenly distributed in the volume of liquid sulfur and a clot-like distribution is observed in the granules.

The reliability of the obtained granular mixtures and their stability in water without leaching of arsenic largely depends on the mass ratios of the mixed powders and elemental sulfur. Mixing powders of As ₂ S ₃ mono-compound with elemental sulfur within the mass ratios [As ₂ S ₃ : S] and a mixture of powders of As ₂ S ₃ , CdS, Bi ₂ S ₃ and CaSO ₄ .H ₂ O sulfides within 1: [ 1 ÷ 2.5] showed that up to a ratio of 1: 2.5 a dense, difficult to mix and poorly granulated mass is formed, which does not allow to carry out the process of obtaining mechanical mixtures (experiment No. 1, 3, 9). Satisfactory mobility and fluidity, hence the mixing and granularity of the mass, is observed at a ratio of [As ₂ S ₃ ] or [As ₂ S ₃ , CdS, Bi ₂ S ₃ , CaSO ₄ .H ₂ O] to liquid elemental sulfur by mass 1: [ 2.5 ÷ 3.5], respectively (experiments 2, 4, 5, 6, 7, 8). The washout of arsenic from the filling mixture in these experiments is less than the maximum permissible value of 0.05 mg / dm ^{3 by} about 10 times.

Claims (1)

A method of processing sulfide arsenic-containing waste, including mixing waste and fusion with elemental sulfur, characterized in that before melting the waste is dried to a moisture content of not more than 4%, disintegrated to a particle size of not more than 1.6 mm, after which the resulting waste powder is heated to 120-155 ° C and mixed with molten sulfur, the ratio of sulfide arsenic-containing waste and molten elemental sulfur in the mixture is 1: 2.5-3.5, after which the mixture is granulated, cooled and a granular glassy mixture with a diameter of rum 2-5 mm.

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