The content of Fe, S and As in the chemical production waste residue is relatively high, and it also contains a certain amount of metal elements such as Zn, Pb, Ag, etc. It is an industrial waste residue with great comprehensive utilization value. For a long time, most of these waste residues have been buried or stored in place, which not only pollutes the surrounding environment, but also underutilizes a large number of valuable elements.

Arsenic has special uses in agriculture, electronics, medicine, metallurgy, chemical industry and other fields, and can be used to prepare pesticides, wood preservatives, glass decolorizers, etc. At present, the market demand for arsenic is increasing, and the annual output of arsenic in the world (calculated as As2O3) is about 50,000 tons. my country’s “Hygienic Standards for Industrial Enterprises” stipulates that the maximum allowable mass concentration of arsenic in ground water is 0.04 mg/L, and the daily average maximum allowable mass concentration of arsenic compounds (calculated as arsenic) in the atmosphere of residential areas is 0.003 mg/m3. The industrial “three wastes” discharge trial standard stipulates that the maximum allowable mass concentration of arsenic and its inorganic compounds is 0.5mg/L. Using modern wastewater treatment technology, arsenic-containing wastewater can be easily discharged up to the standard. However, the pollution and harm to the environment caused by the solid arsenic-containing waste residues produced in the smelting process and the arsenic-containing residues produced by the treatment of waste water and waste acid have not been completely eradicated, and a large number of valuable metals have not been fully utilized. It is still far from the requirements of the environmental protection department. The problem of arsenic damage has been studied since the early 1970s. Japan, the former Soviet Union, Sweden and my country have done a lot of research work on arsenic removal, and have formed many effective methods to control arsenic damage.

There are two methods for treating arsenic-containing solid waste:

One is to use fire methods such as oxidative roasting, reduction roasting and vacuum roasting, and the arsenic is directly recovered in the form of white arsenic; It is separated and then further treated by sulfidation or other harmless treatment. Wet arsenic removal includes physical removal of arsenic and chemical removal of arsenic. Arsenic extraction by fire method has low cost and large processing capacity, but if the production process is not well controlled, it is easy to cause secondary pollution of the environment; wet extraction of arsenic can meet the requirements of environmental protection and has the advantages of low energy consumption, less pollution and high efficiency, but the process It is more complicated and the processing cost is relatively high.

At present, the wet arsenic removal process of chemical precipitation method is widely used, and the effect of removing arsenic is also the best. In recent years, there have been many studies using this method to treat arsenic-containing solid waste.

(1) Traditional arsenic fixation method

The arsenic fixation method is a simple and effective method to prevent arsenic pollution, but the utilization rate of various arsenic slag is low, and the deep burial and stacking cause a great waste of resources, and the arsenic slag will be oxidized by bacteria and dissolved in certain conditions. water, leading to secondary pollution of arsenic. Some research results and TCLP leaching experiments in the 1980s showed that calcium arsenate slag had poor stability and high solubility, but after high temperature calcination, the solubility of calcium arsenate and calcium arsenite decreased, and the calcination temperature The higher it is, the less soluble it is. The lime precipitation method for arsenic-containing wastewater plus calcium arsenate calcination technology has been applied in several copper smelters in Chile, and achieved good results. Arsenic-iron co-precipitation forms arsenic-bearing ferrihydrite, which is a widely used arsenic fixation method in the world.

(2) Roasting method

Arsenic smelting is a traditional arsenic extraction process. In this method, crude white arsenic is prepared from high arsenic waste by oxidative roasting, or crude white arsenic is reduced and refined to prepare elemental arsenic. Oxidative roasting of arsenic-containing slag at 600℃~850℃ can volatilize 40%~70% of arsenic. Adding vulcanizing agent (pyrite) can volatilize 90%~95% of arsenic. After roasting the arsenic residue, the arsenic removal rate can reach 98%.

(3) Sulfuric acid leaching method

Wet extraction of arsenic is the fundamental way to eliminate the environmental pollution caused by arsenic in the production process. Chen Weiping of Hunan University extracts arsenic by traditional wet method

(4) Alkaline leaching method

Alkaline oxidation leaching of arsenic-containing waste using NaOH and passing air to convert arsenic into sodium arsenate, and then through causticization, acid decomposition, and reduction crystallization process, the crude product As2O3 is obtained. Sumitomo Corporation of Japan and the former Soviet Union nonferrous mine Metallurgical Research Institute has used this method to deal with arsenic waste. The arsenic-containing waste was leached with 225g/L NaOH solution. The leaching conditions were: t=180℃, P(O2)=2MPa, and the liquid-solid mass ratio was 10:1. One stage of leaching for 4 hours, the recovery rate of arsenic in the solution was 90%. In addition, ammonia leaching solution or the mixture of ammonia and ammonium sulfate can be used as arsenic residue leaching reagent. The leaching conditions are: t=80℃, P(O2)=400kPa.

(5) Salt leaching method

The copper sulfate replacement method is a relatively mature method for treating arsenic sulfide slag. Toyo Smelter of Sumitomo Corporation of Japan is a representative manufacturer of white arsenic using this method. The company adopts a non-oxidative leaching method. After the arsenic in the arsenic sulfide filter cake is replaced by Cu2+ in copper sulfate, it is reduced with more than 6% SO2 to obtain As2O3, which realizes the separation from other heavy metal ions and obtains high-purity As2O3.

(6) Other methods

In addition to the above main methods for the treatment of arsenic-containing solid waste, there are bacterial leaching method, nitric acid leaching method, organic solvent extraction method and arsenic trioxide saturation solubility method. The disadvantage of these methods is that the leaching rate is low, and the industrial production is not easy to achieve, so the promotion value is not high.