Hydrometallurgical Extraction And Recovery Of Valuable Metals From Dust In Bottom Blowing Copper Smelting Process

As copper smelting technology developed,the production capacity of refined copper has been rapidly increased with high-grade copper mines lacking,resulting in more and more copper ores containing impurities such as lead,arsenic,zinc and cadmium entering the smelting system.Bottom-blowing bath smelting has been gradually popularized for its adaptability to handle complex polymetallic ores,low-grade copper ores and precious metal associated ores with high content of gold and silver.During the smelting and converting of copper,dust is formed by volatile elements such as Pb,As and Zn with copper.On the one hand,the dust has a damaging effect on the environment because of its high content of arsenic.On the other hand,the dust contains a large number of valuable metals such as copper,lead and zinc,which has high recovery value.Guided by the concept of sustainable development,it is imperative to develop the process for recovery of valuable metals from dust and harmless treatment of arsenic elements.In the paper,recovery of valuable metal elements from the electrostatic precipitator dust produced in the"bottom-blowing smelting+PS converting"and"bottom-blowing smelting+bottom-converting"processes was regarded as the object of study,and laboratory and industrial experiments were carried out around acid leaching of dust,arsenic removal from leaching solution and extraction of valuable metal elements.The main research results are listed as follows:（1）Sulfuric acid was used for selective leaching of dust.Cu,Zn,As and Cd were effectively separated from Pb,Bi,Au and Ag under the conditions of leaching time of 1 h,leaching temperature of 90～95°C,initial concentration of sulfuric acid of 30 g/L,L:S=4:1,mechanical stirring,blasting air and leaching twice.The leaching rates of Cu,Zn,As and Cd reached 85～90%,>95%,60～65%,90～95%respectively.（2）The method of"As precipitation by Cu（OH）₂-separation of copper and arsenic by alkali leaching-As fixation by Ca（OH）₂"was used for As removal from dust leaching solution.The results showed that the As in leaching solution finally entered slag in the form of Ca₃（As O₄）₂·Ca（OH）₂·4H₂O.The slag was entrusted to enterprises with hazardous waste treatment qualification for treatment to reduce pollution.（3）The recovery of copper,cadmium and zinc from the solution after arsenic removal was studied by the process of"copper recovery by electrodeposition-cadmium removal by zinc replacement-crystallization by evaporation and concentration for the preparation of feed grade zinc sulfate monohydrate".The results showed that through two electrodepositions,copper was recovered as 95～98%cathode copper and75%black copper powder.Cadmium was removed from the solution after copper removal twice by zinc powder replacement and cadmium was enriched once at room temperature.The content of cadmium in the treated solution was less than 0.85 mg/L,copper ion concentration less than 0.5mg/L,As ion less than 0.1 mg/L,zinc ion concentration over 100 g/L.cadmium slag containing 80%cadmium was sent to the cadmium refinery for further treatment.The feed grade zinc sulfate monohydrate containing more than 35.0%zinc was obtained by evaporating the solution after cadmium removal in evaporation reactor.（4）Industrial tests were carried out on the hydrometallurgical part of copper dust.The results showed that the leaching rates of Cu,Zn,Pb and Cd could reach over 85%,80%,60%and 90%,respectively.On this basis,a hydrometallurgical system for copper dust was established with an annual treatment capacity of 30 kt,and the annual revenue could eventually reach more than 36 million.