Selective Conversion And Extraction Of Copper And Arsenic From Copper Electrolytic Sludge

Copper electrolytic sludge,a byproduct of copper electrolysis purification process,contains approximately 30-60%copper and 10-40%arsenic.The hazardous accumulation or traditional pyrometallurgical refining of copper electrolytic sludge poses significant risks to both the environment and human health.Harmless and resourceful disposal techniques that promote copper extraction and recycling from copper electrolytic sludge are necessary to mitigate environmental hazards and alleviate the strain caused by copper resource scarcity.During the anode copper electrolytic refining process using copper scraps,floating anode sludge is formed due to its low arsenic content which reduces current efficiency and cathode copper quality.However,when arsenic content is between 0.03%-0.3%in the anode copper,it can reduce the formation of floating anode sludge.Therefore,this study proposes a synergistic approach by co-disposing Copper electrolytic sludge with copper scraps to achieve controlled transfer of arsenic from copper electrolytic sludge to copper scraps and effective copper resource recovery.In this study,Ca（OH）₂ was added to Copper electrolytic sludge and oxidized through roasting to fixate arsenic in the roasted slag.Subsequently,roasted slag and copper scraps were co-refined through pyrometallurgical refining to transfer arsenic to anode copper and recover copper simultaneously.During the anode copper electrolytic refining,most of the arsenic would form anode sludge while a small portion would reform as copper electrolytic sludge during electrolyte purification.To dispose of this Copper electrolytic sludge,the study proposed the use of alkaline reduction smelting to recover copper in crude form and arsenic concentrated in slag,reducing diffuse pollution caused by arsenic.The primary research conclusions of this paper are as follows:（1）The main phases of copper and arsenic in the copper electrolytic sludge were CuSO₄·5H₂O,Cu₃（As O₄）₂,Cu₃As,Cu,As,As₂O₃,and As₂O₅.Direct oxidative roasting of copper electrolytic sludge leads to arsenic volatilization efficiency over 25%.However,neutral oxide CuO can promote the oxidation of As₂O₃ to form Cu₃（As O₄）₂.Ca（OH）₂ was chosen as a fixative for the roasting stage due to its stronger affinity with alkaline oxides than acidic oxides or neutral oxides.The study found that As₂O₃,Cu₃As,and As in copper electrolytic sludge could be oxidized by O₂during the roasting process to form As₂O₅,which then reacted with Ca（OH）₂ to form Ca₃（As O₄）₂,thereby reducing arsenic volatilization efficiency.However,excessive Ca（OH）₂ addition can result in the encapsulation of Cu₃As in copper electrolytic sludge,hindering oxygen transfer to Cu₃As,causing it to be oxidized to As₂O₃ but not further to Ca₃（As O₄）₂,and therefore increasing arsenic volatilization efficiency.Additionally,an increase in oxygen partial pressure promotes the oxidation of As₂O₃ to As₂O₅and further reduces arsenic volatilization efficiency.Under the optimal conditions of 84%Ca（OH）₂ addition,an oxygen partial pressure of 1.0,a roasting temperature of 500℃,and a roasting time of 60 min,the arsenic volatilization efficiency was reduced to 3.76%,and the As and Cucontents in the roasted slag were 24.43%and 18.55%,respectively.（2）The process involves mixing the roasted slag and copper scraps in a ratio of 1:125 by weight,adding 0.3%Si O₂,and subjecting the mixture to a pyrometallurgical refining process at 1250℃.The process involves an oxidation stage using O₂ at a flow rate of 40 m L/min for 30 minutes followed by a reduction stage using CO at a flow rate of 20 m L/min.During the oxidation stage,arsenic is trapped in the slag,while impurities such as Pb and Fe from the copper scraps enter the slag.During the reduction stage,the arsenic in the roasted slag is reduced to volatile As₂O₃ and then further reduced to elemental As.The molten copper forms a Cu-As alloy that restricts the volatilization of arsenic.The arsenic volatilization efficiency is only 6.1%,and the As,Pb,and Fe content of the resulting anode copper is 0.17%,0.1%,and 0.01%,respectively,meeting the standards for electrolytic refining.（3）The basic reduction smelting method can efficiently recover copper from copper electrolytic sludge and reduce the dispersion of arsenic.In this process,sodium carbonate is used to reduce the viscosity of the melting slag,improve the separation efficiency between the crude copper phase and the slag phase,and reduce the As₂O₃ and As₂O₅ in copper electrolytic sludge to Na As O₂ and Na₃As O₄,which reduces the reduction of arsenic oxides to elemental arsenic and thereby lowers the arsenic content in the crude copper.Increasing the amount of sodium carbonate,raising the melting temperature,and extending the holding time can increase the copper recovery rate from copper electrolytic sludge and help reduce the arsenic content in the crude copper.However,excessive coke addition can cause over-reduction of CuSO₄ to CuS,which may be carried into the slag and result in copper losses.Under the optimal reaction conditions of 3.5%coke addition,a melting temperature of 1400℃,57%sodium carbonate addition,and a holding time of 150 min,the copper recovery rate from copper electrolytic sludge can reach 94.15%,with a copper content of 96.51%and an arsenic content of 2.86%.Moreover,70.41%of the arsenic is enriched in the melting slag,achieving the goal of copper recovery from copper electrolytic sludge and reducing the dispersion of arsenic.