Treatment and recovery of arsenic-containing fumes

　　In nature, arsenic is usually enriched in copper, lead, zinc, nickel, cobalt, gold and silver in the form of toxic sand (FeAsS), toxic sand (FeAsS2), toxic sand (FeAs2), Cu3AsS3, andrographite (As2S3) and dioecious (As2S3) minerals. During non-ferrous metallurgy, many high arsenic solid materials are produced, such as roasting and smelting dust. These materials contain up to 5 - 50% arsenic and also contain significant amounts of valuable metals that are returned directly to the smelting process, causing arsenic to circulate and accumulate in the system and therefore should usually be treated separately for arsenic removal. Arsenic is a highly toxic carcinogen and its application is gradually being reduced. In the face of increasingly stringent environmental standards, how to treat various materials with high arsenic has become a major issue threatening the survival of the non-ferrous metallurgical industry.

　　At present, there are two main methods to deal with arsenic-containing soot, one is pyro separation and the other is wet separation. In pyroproduction, the separation of arsenic from other elements is achieved by the boiling point difference between arsenic oxides and other elements.CN103602835A published the alternative reduction method to obtain crude arsenic and antimony, CN103602834A published the selective redox method to obtain As2O3 and crude antimony with low purity, and CN104294053A published the arsenic-containing soot with reduced volatile arsenic method with a purity of 97.0% or more. However, if the dust contains arsenic-like metals (e.g., antimony), the purity obtained is not high. The three main processes for wet production are water leaching, acid leaching and alkali leaching. However, only products such as sodium with low purity can be obtained, and there has been no further research on the recovery of valuable metal powder. CN105567983A published a water and alkali leaching process of copper refining dust, so that arsenic is separated from the metal, and the arsenic products prepared are not marketable, and the arsenic content in the leaching residue is still high. CN104357668A published a method of leaching and electrodeposition of arsenic with foul acid, and acid leaching and electro CN105648226A and CN105648227A published a method to achieve arsenic-antimony separation by oxygen-pressure alkaline leaching. The arsenic-antimony separation was more thorough, but the resulting sodium arsenic was not treated and precious metals such as tellurium and antimony were not recovered.

　　There are more research papers and related patent reports on arsenic removal and extraction of valuable metals from arsenic-containing soot, but the comprehensive recovery of valuable elements is low, the market for arsenic products is limited, and there are safety hazards. Therefore, the existing technology still needs to be improved and developed.

　　During any roasting operation containing arsenic soot, a certain amount of soot is generated depending on the fineness of the charge and the roasting conditions. Cyclone separators are used to treat the medium dust. However, due to the fineness of the dust generally with the cyclone can not. The dust must comply with dust emission regulations. The formula used to determine allowable dust emissions in Nevada, USA.

　　(I) E = 0.0193W0.67 when the dry material feed rate is less than 3000kg /h

　　(2) For dry material feed rates above 30,000 kg/h E = 11.78W.011-18.14

　　Where E - allowable dust emission, kg/h.

　　W - process feed rate, kg/h.

　　If lime is used to control SO2, this method of arsenic-containing soot can remove dust sufficiently to comply with air emission regulations; if dust removal is not sufficient, dust removal must be performed with an electric or bag filter.

　　In addition, as mentioned earlier, the gold content of the very fine dust generated during roasting is usually higher than the average gold content of the coarse ore or concentrate, and there may be large gold losses from the fine dust that cannot be recovered by the cyclone. Therefore the installation of electrostatic precipitator or baghouse can achieve a dual purpose; reduce dust emission to air and improve the gold recovery rate.