RU2747153C1 - Method for production of water-insoluble waste of arsenic sulfides - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to methods for producing water-insoluble arsenic sulfide waste that does not pollute the natural environment during storage or disposal. It can be used in the preparation of a hardening filling mixture of waste space in mines. The production of water-insoluble arsenic sulfide waste involves mixing and sintering wet arsenic sulfide waste with powdered elemental sulfur. The consumption of sulfur is 15-50 wt.% of the mass of wet arsenic sulfide waste. Sintering is carried out in a cellular matrix at a temperature of 170-180ºC and granules with a diameter of 4-6 mm are obtained. After that, two layers of kuzbass varnish are applied to the surface of the granules.

EFFECT: method provides the leachability of arsenic from waste in the range of 0-0.01 mg/dm³, depending on the pH of the water.

1 cl, 5 tbl, 2 ex

Description

The invention relates to methods for producing water-insoluble arsenic sulfide wastes that do not pollute the natural environment during storage or disposal. It can be used in the preparation of a hardening filling mixture of a worked-out space in mines.

The method can be used in the metallurgical industry in the production of non-ferrous metals and in the chemical industry.

Arsenic is a common impurity in ores and concentrates of non-ferrous, rare and noble metals and plays a specific role in their processing.

First, it complicates the flow of technological processes and degrades the quality of marketable products.

Second, arsenic is one of the few elements for which there is very limited demand.

The lack of widespread demand leads to the storage and accumulation of various types of arsenic-containing waste that pollute the environment in open areas of enterprises.

In the production of non-ferrous metals, sediments (cakes) of arsenic trisulide are formed. In connection with the above, in metallurgical, and often in chemical production, there is a problem of neutralizing solid arsenic-containing sulfide cakes.

The placement and storage of such compounds requires the organization of special landfills for highly hazardous waste, which causes high economic costs and negative environmental consequences.

A characteristic of the stability of arsenic sulfide compounds in the natural environment is their solubility in water and oxidizability in air.

Powdered sulfides are most susceptible to oxidation. Glassy arsenic sulfides, presented in the form of compact monolithic blocks, are the least toxic compounds, they are slightly soluble in water and do not dissolve even in concentrated hydrochloric acid. However, they are susceptible to oxidation by atmospheric oxygen, after which they dissolve well in water.

A known method of neutralizing arsenic-containing products, including the melting of the starting material to obtain glassy arsenic trisulfide (Naboychenko S.S., Mamyachenkov S.V., Karelov S.V., Arsenic in nonferrous metallurgy / Edited by S.S. Naboychenko - Yekaterinburg: UB RAS, 2004, p. 223).

In the known method to increase the stability of sulfide arsenic fumes and cakes from oxidation in connection with the developed surface, the precipitated arsenic sulfide is melted in the presence of 5-50% sulfur addition; as a result, a water-insoluble form of sulfide is obtained, and the volume of the product is reduced 19 times compared to the volume of the original sulfide.

The significant disadvantages of the known method include the low efficiency and low profitability of the neutralization process and the lack of solutions for the disposal of the resulting product.

During melting, due to the high volatility of arsenic trisulfide in the smelting furnace, the latter sublimes and enters the atmosphere in the form of vapors, which has an extremely negative effect on the environmental friendliness of the method as a whole and requires the construction of expensive gas treatment facilities.

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

As ₂ S ₃ + 2H ₂ O↔HAsO ₂ + H ₃ AsS ₃

As ₂ S ₃ + 3Н ₂ O↔H ₃ AsO ₃ + H ₃ AsS ₃

As₂S₃+ 6O₂↔As₂(SO_four)₃

The low efficiency of the known method is also caused by the following:

- to carry out 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: Halemsky AM, Gertman EM, Ivenko NV, Ivakin AA, Shtin AP , Maksimova L.G.) A method for processing waste containing arsenic sulfide, including heating them 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 carried out in the presence of 0.5 -3.0 wt.% Copper sulfide at an elemental sulfur consumption of 4.0-4.5 wt.% At 165-220 ° C and a pressure of 5-20 kgf / cm ² .

The significant disadvantages of this method include:

- the need to add 0.5-3.0 wt.% copper sulfide, which causes the loss of the original copper-containing raw materials, reduces the total extraction of copper in the technological process and reduces its economic efficiency;

- in the temperature range declared by the authors of 165-220 ° C, the efficiency of obtaining alloys sparingly soluble in water 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 of molten sulfur prevents 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 by water;

- the need to create a pressure in the preparation of a mixture in the range of 5-20 kgf / cm ² complicates the technological process, requires the use of special expensive pressing equipment and increases the economic costs of processing arsenic-containing waste;

- the disadvantage of the technology under consideration is the lack of proposals for the technology for placement, storage or disposal of the obtained sparingly soluble alloys, since the disposal of hazardous chemical waste at landfills will require significant financial costs, which will significantly worsen the technical and economic indicators of the production of non-ferrous metals.

A similar technological solution is the Method for the neutralization and disposal of sulfide arsenic-containing waste (Patent RU 2711766 class C22B 7/00, authors: Bulatov K.V., Zakirnichny V.N., Verkhorubova A.V., Perederiy O.G.), including mixing waste and fusion with elemental sulfur. The waste is dried to a moisture content of no more than 4%, disintegrated to a particle size of no more than 1.6 mm, the resulting powder is heated to 120-155 ° C and mixed with molten sulfur, while the ratio of sulphide arsenic-containing waste and molten 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 2-5 mm is obtained. A layer of elemental sulfur is applied to the surface of the granules.

The leachability of arsenic with water at pH 3.5-12.0 from granules does not exceed 0.05 mg / dm ³ .

This method has the following disadvantages.

The multistage technology, work with molten sulfur and its storage, the complexity of the granulation process and the use of expensive equipment, high specific consumption of elemental sulfur per ton of waste (2.5-3.5 t / t), an increase in the mass of waste several times.

Taking into account the noted disadvantages of the prototypes, a more effective technology was developed and proposed, characterized in that sulfur is used not as an additive to obtain poorly soluble compounds, but as a binder that combines particles of arsenic sulfides into granules. A distinctive feature of the technology is that sulfur is mixed with waste in solid form, not liquid. There are also no separate operations for melting sulfur and granulating the mixture. There is no special, separate, operation for drying arsenic sulfide waste. Sulfur consumption is reduced to 15-50% per ton of wet waste. The leachability of arsenic with water at pH 3.5-12.0 from granules does not exceed 0.01 mg / dm ³ .

The problem is solved by the fact that in the method for producing water-insoluble arsenic sulfide waste, including mixing and sintering a wet sulfide precipitate with powder sulfur, the powder sulfur consumption is 15-50 wt.% Of the mass of wet arsenic sulfide waste, sintering is performed at a temperature of 170- 180 ° C in a cellular matrix, in which the cake is granulated into granules of 4-6 mm, two layers of Kuzbasslak are applied to the granules.

The essence of the proposed method is as follows: Lumps of wet waste disintegrate to a powdery state while mixing with powdered elemental sulfur in a mixer.

The resulting mixture is loaded into a cellular matrix with a cell diameter of 5-6 mm.

The cellular matrix is placed in an oven and at a temperature of 170-180 ° C drying, sintering and granulation of the mixture take place in each cell of the matrix. Granulation allows you to utilize sinter granules in the composition of hardening filling mixtures for mines as a filler.

To prevent the leaching of arsenic from the granules, two layers of Kuzbasslak are applied to their surface.

Then the granules are dried and disposed of as a filler in the composition of the hardening filling mixture for mines.

An example of the implementation of the method

To implement the proposed method for producing water-insoluble arsenic sulfide waste, a real cake of a copper smelter was used with the following composition: total arsenic 39.4%, total sulfur 35%, and lead 8.9%, copper 1.3%, iron 1.1%.

Arsenic is in the form of the compound As ₂ S ₃ . In addition to metals, the waste contains about 20-30 kg of sulfuric acid in one ton of wet cake. Moisture content in cake 50-65 wt%

Example 1

In order to determine the parameters at which the best result of As ₂ S ₃ cake sintering with obtaining compounds poorly soluble in water was achieved:

The cake of arsenic sulfides, humidity 50%, with an admixture of up to 5% As ₂ O ₃ , was mixed with a given amount of elemental sulfur in a screw mixer, ground to a powdery state and uniform distribution of sulfur in the cake.

The resulting mixture was loaded into the cells of the silicone matrix and placed in a temperature controlled sintering oven. During sintering, sinter granules are formed in the cells. The granules were placed in water with a pH of 3.5 and 8.0 and the change in the concentration of arsenic in water over time was monitored.

In the process of sintering in the cells of the matrix, the mixture is dried, sintered and granulated. Granules with a diameter of 5-6 mm are formed in the cells.

Obtaining a sinter of elemental sulfur and arsenic trisulfide at a temperature of 180 ° C, depending on the thickness of the mixture layer, takes place within 40-90 minutes, taking into account the drying period of the cake.

The strength of the resulting sinter granules depends on the consumption of elemental sulfur (Table 1).

In the region of low sulfur consumption, up to 15%, arsenic is washed out from the sinter granules in significant quantities, since not all particles of arsenic trisulfide powder are covered with sulfur, which indicates a lack of a binder (sulfur). This conclusion is confirmed by the mechanical strength of the granules.

Within the flow rate of 15-50% of elemental sulfur, strong sinter granules are formed (Table 1), and the migration of arsenic from them is at a minimum level (0.07-0.08 mg / dm ³ ).

An increase in the flow rate from 50 to 100% causes an increase in the leachability of arsenic from the granules, which can be explained by the formation of a large number of pores in the sinter granules, through which water contacts with arsenic compounds.

The addition of elemental sulfur to the cake of arsenic trisulfide during sintering at temperatures above 180 ° C provides the formation of arsenic polysulfides. For example, for the formation of polysulfide As ₂ S _4, it is necessary to add 7 wt.% Of sulfur to the sulfur present in the original dry cake As ₂ S _3, and keep it at a temperature of more than 180 ° C.

The formation of arsenic polysulfides occurs during the melting of sulfur, accompanied by the destruction of linear-serrated crystal structures and the appearance of closed ring structures S _{8 of} liquid sulfur [4].

Heating molten sulfur from 155 ° C to 187 ° C causes rupture of the ring structures S ₈ and the appearance of long-chain compounds, the terminal atoms of which are bonded to each other. " The appearance of active atoms at the ends of linear chains explains the chemical activity of sulfur and the formation of arsenic polysulfides.

Below is the calculation of the degree of polysulfidicity of arsenic compounds depending on the amount of added powdered sulfur.

Arsenic monosulfide contains: arsenic 75 g, sulfur 32 g. The percentage of arsenic and sulfur is

S = (75 + 32) × 100: 107 = 29.9 wt%

As = 100-29.9 = 70.1 wt%

The molecular weight of As ₄ S ₃ is

As ₄ S ₃ = 75 × 4 + 32 × 3 = 396 g

The molecular weight of sulfur is 96 g

The content of arsenic and sulfur in% is equal to

S = 96 × 100: 396 = 24.2 wt%

As = 100-24.2 = 75.8%

The degree of polysulfidicity of a compound is calculated as the ratio of the difference between the total sulfur content and the monosulfur content to the monosulfur content.

n = (96-32) / 32 = 2

Compound As ₂ S ₃

The molecular weight of the compound is

As ₂ S ₃ = 75 × 2 + 32 × 3 = 246

The molecular weight of sulfur is 96 g

The content of arsenic and sulfur in wt% is equal to

S = 96 × 100: 246 = 39.02 wt%

As = 100-39.02 = 60.98 wt%

The polysulfide degree of arsenic trisulfide is

n = [(96: 2) - 32] / 32 = 16/32 = 0.5

The calculation results are summarized in Table 2.

Sulfur, added to the cake of arsenic trisulfide in an amount of 7-12.6 wt%, during sintering at a temperature of more than 180 ° C transforms arsenic trisulfide into semisulfides As ₂ S ₄ and As ₂ S ₅ .

Example 2

To check the effect of sulfur consumption and temperature on the formation of cakes, the following was done. The consumption of elemental sulfur varied from 10 to 200% of the mass of the initial wet (50%) arsenic trisulfide cake, the experimental results are shown in Table 3. The leachability of arsenic from the cake granules did not exceed the MPC = 0.05 mg / dm ³ at a sulfur consumption of 15-50 wt.% without encapsulating the granules of the cake with Kuzbasslak.

From table 3 it follows that the optimum sintering temperature is 170-180 ° C. The sinter granules obtained at this temperature have a leachability of arsenic of 0.01-0.05 mg / dm ³ .

At temperatures above 180 ° C, oxidation of arsenic trisulfide to its trioxide, which is readily soluble in water, and an increase in the concentration of arsenic in water are observed.

Experiments on the effect of the duration of the contact of the sinter granules with water showed that the leaching out of arsenic in time increases significantly (Table 4).

The application of a waterproof layer to the surface of the granules eliminates the leachability of arsenic.

In industry, the technology of bitumen encapsulation of waste is widely used. The disadvantage of bitumen coatings is the need to melt and maintain the bitumen in a molten state. Kuzbasslak, being a bituminous product of cold application, is devoid of this disadvantage.

The advantages of Kuzbasslak include the possibility of its rapid drying on the surface of granules.

The experimentally established consumption of bitumen varnish for encapsulating sinter granules in two layers reaches 30% of the granule mass.

According to the recommendation TU 2312-007-243586611-08 for Kuzbasslak, resistant, waterproof encapsulating coatings of Kuzbasslak are obtained by applying at least two layers. The application of several layers of Kuzbasslak on the sinter granules is associated with an increase in the duration of their drying.

Duration of drying of each layer of varnish at a temperature of 100 ° C according to GOST 5631-79 is 20 minutes, and two layers does not exceed one hour. After applying the first layer, pores not filled with varnish are observed on the surface of the granules, and after the second, the surface becomes smooth, shiny and without pores. The effect of the number of Kuzbasslak layers applied on the sinter granules on the leachability of arsenic is shown in Table 4.

The results presented in Table 4 indicate that reliable encapsulation is achieved when two layers of Kuzbasslak are applied.

After drying, the cake granules encapsulated with BT 577 varnish were added to the hardening filling mixture as an inert filler. Test samples were prepared from the filling mixture.

After setting, the samples were placed in water with a pH of 8.0 and the concentration of arsenic in the water was monitored over time.

The leachability of arsenic from samples of the hardening backfill mixture containing 4% of sinter granules coated with two layers of Kuzbasslak was classified as "traces" by chemical analysis (Table 5).

Long-term contact of samples of the filling mixture with water does not affect the leaching of arsenic (Table 5).

The presence of sinter granules in the composition of the hardening insert up to 4% does not affect the duration of hardening and mechanical compressive strength.

Claims (1)

A method for producing water-insoluble arsenic sulfide waste, including mixing and sintering wet waste of arsenic sulfides with powdered elemental sulfur, characterized in that the consumption of powder sulfur is 15-50 wt.% Of the mass of wet waste of arsenic sulfides, sintering is performed at a temperature of 170-180 ° C in a cellular matrix, in which the cake is granulated to obtain granules of 4-6 mm, after which two layers of Kuzbasslak are applied to the surface of the granules.