Study On Cascade Separation Of Arsenic,antimony And Alkali From Arsenic-alkali Residue And Recovery Of Metallic Arsenic

China is a large country in antimony smelting.Pyro-smelting antimony produces a large amount of arsenic-alkali residue with high toxicity and high risk,with an annual output of 5000-6000 tons,causing a great burden to enterprise production and ecological environment.The comprehensive recovery of valuable components in arsenic-alkali residue is not only environmentally friendly,but also can‘turn waste into treasure’,with good environmental and economic benefits.At present,arsenic-alkali residue resource treatment technology has the problems of complex arsenic-alkali separation process,incomplete separation,large alkali consumption and waste of resources,and large amount of arsenic residue generation,which needs harmless treatment.In response to these problems,based on the characteristics of potential value and low toxicity of metal arsenic,a new process of‘wet leaching-hydrothermal arsenic precipitation-carbothermal reduction’of arsenic-alkali residue was studied and developed to realize cascade separation of arsenic,antimony and alkali and the recovery of metallic arsenic.The research results of the new process are as follows:（1）For the arsenic-alkali residue of an enterprise in Hunan,it is found that the contents of arsenic and antimony were low,2.74%and 1.22%,respectively.Arsenic was mainly assigned with sodium arsenate,while the main phase of alkali was sodium carbonate,and antimony was mainly sodium antimonate.Based on the solubility difference of arsenic,antimony and alkali fugitive phases,the research on water leaching of arsenic-alkali residue was carried out,and the effects of leaching process parameters on the leaching rate of arsenic,antimony and sodium were investigated.The optimal process parameters were obtained as follows:leaching time 30 min,liquid-solid ratio 3:1 and leaching temperature 45℃.Under the conditions,the leaching rate of arsenic was 95.3%,the leaching rate of antimony was only 1.6%,and the leaching rate of sodium was 86.7%.The results shows that the increase of temperature can improve the leaching rate of arsenic,but the leaching rate of antimony also increases,mainly because the residue of antimony is also leached,which is not conducive to the separation of arsenic and antimony.Therefore,the leaching temperature chosen for water leaching should not be too high.The antimony residue obtained by water leaching enters the antimony smelting system to recover antimony.The alkaline leachate is used for further recovery of alkali.（2）For the separation of arsenic and alkali in alkaline leaching solution,the study on hydrothermal arsenic precipitation of calcium oxide was carried out.The optimal process parameters of hydrothermal precipitation of arsenic were as follows:initial p H=11,hydrothermal temperature 180℃,reaction time 6 h,Ca/As molar ratio 24:1.Under the condition,the precipitation rate of arsenic in the alkaline leaching solution was 95.3%,and the main phases of arsenic precipitation residue are Ca₅（As O₄）₃（OH）,Ca CO₃ and Ca（OH）₂,the crystals of calcium hydroxide and calcium carbonate grow rapidly and their particles are larger,which weakens the wrapping effect on arsenate ions,promotes the contact possibility between the arsenate ions and calcium ions,and improves the arsenic precipitation rate.The arsenic precipitation lye is used as the raw material for alkali recovery and is crystallised by evaporation and concentration to obtain a mixed alkali composed of NaOH,NaOH·H₂O,Na₂CO₃ and other phases,which can be returned to antimony smelting for arsenic removal.The arsenic precipitation residue is used for further recovery of metallic arsenic.（3）For the arsenic precipitation residue containing calcium arsenate,the feasibility of recovering metallic arsenic from arsenic precipitation residue by carbothermal reduction was verified through thermodynamic calculation and thermogravimetric behavior analysis.The carbothermal reduction process of arsenic precipitation residue was studied based on the results of calculation and analysis.The results showed that the volatilization rate of arsenic reached 93.1%under the conditions of 10%carbon powder addition,1000℃reduction temperature and 3 h reduction time.The volatile product is mainly elemental arsenic,with an arsenic content of 92%,which can be further purified and stored as arsenic resources.The main phase of reduction residue is calcium oxide,which can be recycled for hydrothermal precipitation of arsenic.Compared with the traditional arsenic-alkali residue treatment process,the new arsenic antimony alkali cascade separation and metallic arsenic recovery process of“water leaching-hydrothermal arsenic precipitation-carbothermal reduction”of arsenic-alkali residue developed in this study has the advantages of realizing the step separation of arsenic antimony alkali,recovering arsenic as non-toxic elemental arsenic,arsenic precipitant calcium oxide can be recycled,and no refractory anions or anions are introduced into the whole process.32 figures,14 tables and 111 references...