RU2795034C1 - Method for removing arsenic from substandard tin concentrates - Google Patents

Abstract

FIELD: removing arsenic from tin concentrates.

SUBSTANCE: method for removing arsenic from tin concentrates containing 10-15% arsenic. Steam chamber oxidative leaching of the original concentrate in an acid medium is carried out, followed by separation of the solid and liquid phases, alkaline atmospheric leaching of the oxidized cake to obtain commercial tin concentrate. At the same time, autoclave oxidative leaching of the initial tin concentrate is carried out until the degree of oxidation of sulphides is at least 98%, and the pulp after autoclave oxidation is subjected to conditioning at a temperature of 70-100°C and with constant stirring for 1-6 hours.

EFFECT: arsenic is removed from concentrates.

1 cl, 2 dwg, 2 tbl

Description

The method is designed to remove arsenic from tin concentrates containing arsenic and sulfur in the form of sulfide minerals such as arsenopyrite and pyrite. Such concentrates are obtained, for example, during the processing of tailings accumulated in the tailings of mining and processing enterprises that processed tin-containing ores. According to the content of arsenic, these concentrates often do not meet the current standards (Methodological recommendations for the application of the Classification of reserves of deposits and predicted resources of solid minerals. Tin ores. M., 2007. 42 s).

A known method of removing arsenic by autoclave oxidative leaching of the concentrate in an acidic environment at a temperature of 180-210°C and a partial oxygen pressure of 0.3-0.7 MPa (Schneerson Ya. Metals, 1995, No. 5, pp. 20-23). Under these conditions, tin minerals (mainly cassiterite) do not undergo changes, while sulfides are intensively oxidized.

Arsenic, iron and sulfur partially go into solution, and partially remain in the solid residue, mainly in the form of basic iron sulfates, scorodite and gypsum. It is not possible to quantitatively remove arsenic from the initial concentrates at high arsenic contents by this method.

A known method of removing arsenic by autoclave oxidative leaching of the concentrate in an alkaline environment at a temperature of 140-150°C and a partial oxygen pressure of 0.3-1 MPa [Khryashchev S.V. et al. Autoclave processing of gold-bearing concentrates // Tsvetnye metally. 1969. No. 7, p. 15-18).

Under these conditions, the tin minerals do not change, while the sulfides are completely oxidized. Arsenic and sulfur go into solution, iron remains in the solid residue:

The advantage of this method is the ability to reduce the arsenic content to 0.3% or less, which satisfies the current standards for high-quality tin concentrates. The disadvantage of this method is the high consumption of alkali. A known method for the two-stage removal of arsenic from substandard tin concentrates (figure 1), taken as the closest analogue (Lapin A.Yu. Petersburg, May 28 - June 01, pp. 62-64). At the first stage, the substandard concentrate with a low arsenic content is subjected to autoclave oxidative leaching in an acidic medium at a temperature of 180-230°C and an oxygen partial pressure of 0.3-0.7 MPa. In the second stage, the dehydrated and washed solid autoclaved residue is subjected to alkaline leaching with hot (80-95°C) sodium hydroxide solution (NaOH) at atmospheric pressure. The scorodite contained in the solid autoclave residue decomposes with the transition of arsenic into solution:

At the same time, basic iron sulfate also decomposes:

which further increases the consumption of alkali. This method also makes it possible to obtain finished concentrates that are conditioned in terms of arsenic content, if its content in the original tin concentrate is less than 10%.

The disadvantages of the method are:

1. Not applicable to high arsenic concentrates. If the original tin concentrate contains more than 10-12% arsenic, then it is impossible to obtain a ready-made tin concentrate (with As≤0.3%) using this method.

2. High consumption of alkali. This is explained by the significant content of not only scorodite, but also basic iron sulfates in the autoclave residue.

The objective of the proposed method is to eliminate the noted disadvantages of the method, the closest analogue.

The claimed technical result is achieved by the fact that in the proposed method for removing arsenic from substandard tin concentrates, including autoclave oxidative leaching of the original concentrate in an acidic environment and alkaline atmospheric leaching of the oxidized solid residue, unlike the closest analogue, the autoclave leaching process is carried out until the degree of oxidation of sulfides is not less than 98%, and the acidic pulp after autoclave oxidation is subjected to conditioning, which consists in holding the pulp with stirring for 1-6 hours at a temperature of 70-100°C and atmospheric pressure.

The technological scheme of the proposed method for removing arsenic from substandard tin concentrates is shown in figure 2. Tin concentrates are received for processing, obtained, for example, during the processing of technogenic raw materials. In terms of tin content, they meet the current standards, but in terms of arsenic content (up to 15%) they are substandard.

The head stage of the proposed method is autoclave oxidative leaching (AOW), which is carried out in an acidic environment at a temperature of 180-230°C and an oxygen pressure of 0.3-0.7 MPa. The process temperature should not be less than 180°C to exclude the formation of elemental sulfur. Being molten, elemental sulfur selectively wets the initial sulfides (pyrite and arsenopyrite), forming a film that prevents access to oxygen and, in the end, stops the leaching process.

The process proceeds autogenously due to the heat released as a result of the oxidation of sulfides (reactions 5-7):

Part of the arsenic from arsenopyrite goes into solution in the form of arsenic acid (reaction 5), and part remains in the solid phase, but already in the form of iron arsenate, an analogue of the natural mineral scorodite (reaction 6). In addition, a certain amount of arsenic is present in the autoclave residue as an isomorphic impurity in the basic ferrous sulfate, which is formed as a result of Fe ³⁺ hydrolysis (reactions 8, 9). Usually, 30 to 40% of arsenic goes into solution. The duration of the head stage should be sufficient to oxidize almost all sulfides and all arsenopyrite, since the remaining unoxidized arsenopyrite passes into the finished concentrate, polluting it with arsenic and making it difficult to achieve the required conditions. Therefore, the degree of oxidation of sulfides and arsenopyrite should be at least 98-99%, especially for concentrates with an arsenic content of more than 10-12%.

The pulp leaving the autoclave is cooled in a self-evaporator to a temperature of = 100°C and enters the conditioning stage, which consists in stirring the hot autoclave pulp at a temperature of 70–100°C for 1–6 h. Under such conditions, the equilibrium of reaction (8) shifts to on the reverse side, there is a dissolution of the basic iron sulfate and the transition of sulfur from the solid autoclave residue into the solution:

At the same time, an additional amount of arsenic associated with basic iron sulfate passes into the solution;

which makes it possible to raise the total transition of arsenic into solution to ~ 55-60%. Acid pulp after conditioning enters the stage of separation of solid and liquid phases. The solid residue (solid phase) after conditioning separation is subjected to alkaline leaching, which is carried out under atmospheric conditions. However, due to the absence of basic iron sulfates in the conditioning residue, the alkali consumption is reduced compared to the closest analogue.

The pulp obtained after alkaline treatment is subjected to separation of solid and liquid phases. The solid residue (solid phase) is a ready-made standard tin concentrate with an arsenic content of <0.3%.

The acid conditioning solution (liquid phase after separation of the solid and liquid phases) is neutralized with limestone and lime and sent to the tailings. Arsenic in this case turns into non-toxic scorodite FeAsO ₄ ⋅ 2H ₂ O.

Alkaline solution after alkaline processing of the pulp and separation into solid and liquid phases is processed by known methods, while regenerating part of the alkali. Thus, the proposed method makes it possible to involve concentrates with a high content of arsenic in processing and reduces the consumption of alkali during subsequent alkaline processing. The conditioning process is reagentless and does not require heat.

Brief description of the drawings

The figure 1 shows the flow diagram for the removal of arsenic from substandard tin concentrate taken as the closest analogue.

The figure 2 shows the flow diagram for the removal of arsenic from substandard tin concentrates according to the proposed method. Examples of the implementation of the proposed method.

The foregoing is confirmed, but not limited, by examples of the implementation of the proposed method in comparison with the closest analogue method. Experimental verification of the proposed method and its comparison with the closest analogue was carried out on two types of initial tin concentrates. The composition of the concentrates is given in Table 1. In both concentrates, sulfides are represented mainly by arsenopyrite, pyrite is present in a subordinate amount. The particle size of concentrates - more than 95% of the class - 74 microns.

Experiments on autoclave oxidative leaching were carried out in an 8-liter autoclave. The process temperature was 210°C, the partial pressure of oxygen was 0.5 MPa. The process was terminated after the absorption of the main mass of oxygen ceased. In experiments on the proposed method, autoclave oxidation was stopped after the complete cessation of oxygen uptake, which guaranteed 98-99% oxidation of sulfides and arsenides. Conditioning was carried out in the same autoclave. To do this, the autoclave pulp was cooled to a temperature of 85–95°C, the gas phase was discarded, and stirring was continued at atmospheric pressure for 4 h. The resulting pulp was cooled to 50–60°C and filtered on a vacuum filter. The solid residue (cake) was washed with water, placed in a glass vessel and subjected to alkaline leaching (L:T=4:1, 100 g/l NaOH) at a temperature of 95°C for 2 h at atmospheric pressure. In some experiments, for comparison, conditioning was not performed. The results obtained are shown in Table 2.

It can be seen that for concentrate I (As content 2.5%, experiments 1 and 2), the finished concentrate (<0.3% As) conditioned for arsenic can be obtained both by the proposed method and by the closest analogue method (without conditioning ). The role of conditioning in this case is to reduce the consumption of caustic soda by 10 -15%.

For concentrate II (As content 13.9%), conditioning is mandatory (cf. runs 3 and 5). In the absence of conditioning, alkali treatment does not allow obtaining a finished concentrate with the desired arsenic content. It can also be seen that the incomplete oxidation of sulfides (experiment 4) makes it impossible to obtain a conditioned tin concentrate, even in the case of conditioning. Compared with the closest analogue, the proposed method makes it possible to obtain conditioned tin concentrates even from high arsenic (more than 10-12% As) initial concentrates.

Claims (1)

A method for removing arsenic from tin concentrates containing 10-15% arsenic, including autoclave oxidative leaching of the original concentrate in an acid medium, followed by separation of the solid and liquid phases, alkaline atmospheric leaching of the oxidized cake to obtain a commercial tin concentrate, characterized in that the autoclave oxidative leaching of the original tin concentrate is carried out until the degree of oxidation of sulfides is at least 98%, and the pulp after autoclave oxidation is subjected to conditioning at a temperature of 70-100 ° C and with constant stirring for 1-6 hours.

Images