Removal of arsenic from arsenic tailings slurry in a concentrator by sulfide-sulfate method

In sorting arsenic-containing non-ferrous metals and precious metal ores process, it is discharged to the tailings slurry discarded tailings are contaminated arsenic. This is because in the process of sorting the ore, and leaching arsenic in the arsenic was further subjected to washing results in the tailings from the arsenic minerals (e.g., scorodite, arsenic, pyrite, etc.). In order to prevent arsenic-containing sewage and its infiltrating polluted water system, it is necessary to reduce the arsenic content in the slurry discharged into the tailings by using a stable sediment which converts arsenic into easy-to-preserve and a method of arsenic removal from the slurry. Emission standards.
The arsenic removal process for tailings slurry developed by the National Institute of Nonferrous Metals of the Soviet Union is based on the method of precipitating arsenic from solution using iron monosulfide. This process is characterized by the use of a mixture of iron monosulfide and ferrous sulfate. The amount of ferrous sulfate added must be such that the pH of the tailings slurry is reduced to 6.7 to 7.2. Far more than a metal processing company jointly scheelite mineral processing plant using this technology, and several other ore deposits were tested. In all cases, the concentration of arsenic is reduced by the purification to a specified discharge standard (ie less than 0.05 mg/l).
The sulphide-sulphate process from the tailings slurry of the concentrator is: preparing iron sulphate and sodium sulphide solution, using ferrous sulphate and iron monosulfide formed during the mixing of sodium sulphide and ferrous sulphate solution. The mixture is used to treat the slurry, allowing the slurry to settle in the tailings and returning the clarified water from the slurry (see figure).

Treatment with the above method still does not guarantee that the slurry is well clarified in the tailings field. Therefore, in the process flow, the use of aluminum sulfate as a coagulant to supplement the slurry is also specified.
In order to determine the quality of purification during the production of the concentrator, sampling and analysis of the tailings slurry and sewage purification points were carried out every ten days. It can be seen from Table 1 that the content of arsenic in the liquid phase of the tailings slurry reaches the sanitary standard.

In the absence of arsenic removal in the concentrator, the arsenic content in the tailings increased with depth, while in the tailings of the Far East Multimetals concentrator, the arsenic content decreased with increasing depth. The arsenic content of the water discharged from the drainage well is the lowest. This indicates that the tailings slurry after arsenic removal by the sulfide-sulfate method is gradually deoxidized by itself after being stored under natural conditions, and the pH value is stabilized at about 6.0. Under these conditions, the pulp is not harmful to the surrounding environment. This is because the concentration of arsenic in the aqueous phase does not exceed the maximum allowable concentration and does not cause arsenic to be washed out of the solid phase. The arsenic-free pulp can also be automatically deoxidized under natural conditions. But this will lead to the opposite result, because arsenic can be washed away from the slurry violently. This proves that it is reasonable, feasible and necessary to use sulphide-sulfate method to remove arsenic from arsenic-containing tailings slurry.
The slag removal method was used to test the slurry of the concentrator under laboratory conditions. After the pulp is processed, it is clarified for one month and the arsenic content does not exceed 0.05 mg/L.
Therefore, the arsenic removal of the tailings slurry by the sulfide-sulfate method can reduce the arsenic content in the sewage to the highest allowable concentration and obtain a stable waste that can be stored for two years. In the production practice of sorting tungsten ore, the purification of tailings slurry and the utilization of circulating water are first realized. The various process indicators have not been reduced.
When sulphide ore is selected, the consumption of iron monosulfide can be reduced due to the presence of natural sulphide in the solid phase of the tailings slurry, such as pyrrhotite. Because pyrrhotite can dephosphorize the solution. As a result, the consumption of sodium sulfide required to obtain iron monosulfide is reduced by 75% compared to the initial consumption of the concentrator. This did not reduce the effect of arsenic removal (see Table 3). Under the conditions of the re-introduction purification system, the arsenic content in the purified circulating water and tailings slurry did not exceed the maximum allowable concentration. If the purification system is destroyed and the consumption of ferrous sulfate is reduced, the pH of the purified tailings slurry is still alkaline and no purification will occur. Due to the reduced consumption of sodium sulfide, an economic benefit of approximately 70,000 rubles is expected.

When the National Institute of Nonferrous Metals of the Soviet Union conducted an industrial test on the ore processing process of a tungsten oxide ore and a primary tungsten ore of a certain deposit, the arsenic removal of the tailings slurry was tested by the sulfide-sulfate method. It should be noted that the tailings slurry can be treated with the sulfide-sulfate method under different conditions for the use of different processes in these ores (flotation-re-election process for the separation of oxidized ores and flotation process for the selection of sulfide ores). The arsenic content in the liquid phase was reduced to 0.05 mg/l. Under natural conditions, even if the pulp is kept for one and a half years, its concentration will not increase. Adding scheelite concentrate to the combined tailings slurry, the hydrochloric acid solution obtained at the time of selection is one of the characteristics of the process of sorting such ore. This will result in a sharp increase in the calcium content of the slurry aqueous phase. In order to avoid the complexity of the purification process by avoiding the calcium which is harmful to the flotation of scheelite, it is recommended to neutralize the hydrochloric acid solution with soda before mixing with the tailings slurry. According to the test results, the following methods of arsenic removal were adopted:
The hydrochloric acid solution was treated with a 10% soda solution (used in an amount of 7.2 to 7.5 kg/ton of ore) prior to mixing with all spent tailings.
The combined tailings slurry is treated with a mixture of iron monosulfide and ferrous sulfate. When preparing the mixture, the consumption of sodium sulfide and iron sulfate is 0.7 to 0.8 kg/ton and 24 to 26 kg/ton ore, respectively.
The water cycle after purification by the sulfide-sulfate method, the comparison of the fresh water and the cycle selection index shows that the use of circulating water does not reduce the quality of the concentrate and the WO ₃ recovery rate of the concentrate.
Based on the results of industrial tests for ore sorting, followed by sulfide-sulphate purification of tailings pulp and the use of recycled water processes, the design department is recommended to design.
From the comparison of drug consumption, in many cases, the consumption of these agents is very large, and effective measures are needed to reduce their consumption. If the sulfide-sulfate method is used, the circulating water will be contaminated by SO ₂ ^-4 and Na ⁺ ions, which will greatly enhance the mineralization of circulating water. In order to prevent river water from being contaminated by these ingredients that exceed health standards, it is necessary to dilute the waste water with river water. The use of this method is limited due to the high consumption of the medicament during purification. In order to reduce the consumption of chemicals and the mineralization of circulating water, some supplementary measures should be taken.

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