Theoretical And Applied Research On Acid Leaching Of Arsenic From Metallurgical Dust And Recovery Of Arsenic And Indium

Dust with high content of arsenic contains a certain amount of harmful element arsenic and a variety of valuable metal elements.Its resource utilization is of great significance for saving mineral resources and protecting ecological environment.In view of the problems of high energy consumption and solution resource failure in traditional processes.According to the types and occurrence states of recyclable elements in the dust,this paper adopts acid oxidation leaching system to achieve complete leaching of valuable metals such as arsenic and indium in arsenic-containing dust.A smelting slag system of Fe-Si-Ca-Na with lower temperature was constructed to recover lead from leaching residue,and zinc,cadmium,arsenic and indium were extracted from leaching solution by sulfide precipitation,arsenic sulfide reduction,cooling crystallization and extraction.In addition,metal arsenic was prepared by carbothermal reduction in the form of calcium arsenate to create a new way of consumption of arsenic.The main conclusions and innovations are as follows:（1）The investigation of elements behaviors in the acid oxidation system shows that the increasing of acidity and temperature can effectively reduce the potential required for oxidation of arsenic in low state to high state,and thus leaching arsenic and valuable elements into the solution in the form of H₃AsO₄ and sulfate,respectively while lead remains in the leaching residue in the form of lead sulfate.When the leaching temperature is 170℃,the acid concentration is 100g/L,the liquid-solid ratio is 10mL/g,the leaching time is 2.5h,the partial pressure of oxygen is 2.0MPa,and the stirring speed is 500r/min,The first-stage leaching efficiencies of As,Cd,In and Zn are 98.19%,98.98%,91.72%and 95.32%,respectively.After two stages of acid leaching,arsenic content of the residue is 0.11%and lead content is 46.52%.The leaching kinetics study shows that the leaching behavior of the dust conforms to Avrami model.When the leaching temperature is lower than 140℃,the n value is less than 0.5 and the leaching reaction is controlled by diffusion.When the leaching temperature is higher than 140℃,the n value is more than 0.5 and the leaching reaction is controlled by the mixture of diffusion and chemical reaction.（2）Thermodynamic results show that the addition of sodium can significantly reduce the smelting temperature of lead sulfate reduction.When the slag temperature was controlled at 1050℃,the lead recovery efficiency reached more than 98%when the molar ratio of Na₂CO₃/PbSO₄was 1.3,the molar ratio of C/PbSO₄ was 0.7 and the reduction time was 75min.The action mechanism of sodium carbonate mainly has two points:first,sodium carbonate participates in the reduction reaction of lead sulfate and converts lead sulfate into lead carbonate with lower reduction decomposition temperature,which greatly promotes the reduction of lead sulfate;Second,sodium carbonate reacts with iron,silicon and calcium to produce sodium-containing slag with low melting point,forming a smelting slag of Fe-Si-Ca-Na with lower temperature,thus significantly reducing the smelting temperature.（3）Sulfide precipitation method can achieve preferential separation of Zn and Cd in acid leaching solution.When the excess coefficient of As₂S₃ is 1.2,the reaction temperature is 65℃and the reaction time is 10min,the removal efficiencies of Cd and Zn are 96.12%and 94.78%,respectively.The experimental results show that the reduction of As（Ⅴ）by As₂S₃ reaches 98.4%and the precipitation efficiency of In is only 4.3%when the concentration of H₂SO₄ is 121.2g/L,the reduction temperature is 85℃,the dosage of As₂S₃ is 1.4 and the reduction time is 2.0h.The purity of cooling crystallized arsenic trioxide reaches 98.56%.Arsenic leaching and reduction in acid leaching solution can be realized synchronously by replacing arsenic sulfide with arsenic filter cake.The leaching efficiency of arsenic is 89.86%,and the reduction efficiency of As（Ⅴ）is 95.86%.When the ratio was 1/9,the extraction efficiencies of impurity ions As,Cd,Sb,Zn and Fe were only 1.22%,0.43%,1.30%,3.06%and 0.83%,respectively,while the extraction efficiency of target ion indium was 99.41%.The concentration of indium was 29.07g/L.Indium can be separated and enriched by extraction and reverse extraction of indium from the reduced solution.It has been proved that the combination of sulfide precipitation,reduction,cooling crystallization and extraction can realize the resource recovery of arsenic and valuable metals in the arsenic-containing solution.（4）Thermodynamic results of calcium arsenate reduction show that when the temperature is higher than 577.52℃,calcium arsenate will be reduced to elemental arsenic,and the product is mainly in the form of As₄（g）.In order to fully reduce the arsenic component in calcium arsenate as far as possible and get the ideal reduction product,avoid the generation of As₂O₃,the reduction temperature must be between 650℃and 952.88℃.The amount of reducing agent carbon should meet the requirement that the mole ratio of C/Ca₃（AsO₄）₂ is greater than 3.When the reduction temperature is 900℃,the amount of carbon powder is 14%,and the reduction time is 2.0h,the reduction efficiency of arsenic reaches 99.22%,and the content of elemental arsenic is 99.41%.The reduction mechanism is as follows:when the temperature is between 25℃and 100℃,the crystal water in calcium arsenate loses weight firstly;At 290～550℃,calcium arsenate is reduced to form calcium arsenite without gaseous arsenic products.At 550～1100℃,CO₂ reacts with carbon in the product to form CO,and the high reducibility further promotes the reduction of calcium arsenite to arsenic vapor.The condensation of arsenic vapor is As₄（g）directly condensed into solid metal arsenic.The results of industrial test show that it is feasible to prepare metallic arsenic by carbothermal reduction of calcium arsenic.The arsenic reduction efficiency is above 98%,the purity of elemental arsenic in the reduction product is about 95%,and the arsenic content in the reduction residue is about 0.53%.This paper includes 85 figures,42 tables and 207 references.