Study On Phase Transformation And Leaching Behavior Of Copper And Cobalt By Reduction Roasting With Pyrite Cinder

Pyrite cinder is the waste residue produced after pyrite acid making.Its stacking will occupy a lot of land,pollute soil and water,and cause environmental problems,which will bring additional operating costs to enterprises.In addition,pyrite cinder also contains a large number of valuable metals such as iron,copper and cobalt,which leaded to a waste of resources.In order to realize the comprehensive utilization of resources in pyrite cinder,this paper takes the pyrite cinder containing copper and cobalt as the research object,recovers the valuable metals in it by using the technological processes of direct acid leaching,coal based reduction roasting leaching magnetic separation and gas-based reduction roasting leaching magnetic separation,characterizes the physicochemical properties of the product by combining XRD,XPS and chemical phase analysis,and preliminarily explores the phase transformation law of copper and cobalt.The main research contents and conclusions were as follows:Through multi-element analysis,the grades of iron,copper and cobalt in pyrite cinder are 54.87%,0.30%and 0.36%respectively.The phase analysis showed that iron mainly existed in the form of hematite,and copper mainly existed in the form of copper sulfate,free copper oxide,combined copper oxide and primary copper sulfide;Cobalt mainly existed in the form of CoSO₄,CoFe₂O₄and Co₃O₄.The direct acid leaching of pyrite cinder showed that the fineness D₅₀of raw material was 20.46μm.The leaching temperature was 70℃,the stirring speed was 400 r/min,the liquid-solid ratio was 4:1mL/g,the mass concentration of sulfuric acid was 160 g/L,and leached for 4h,the leaching rate of copper and cobalt was 64.35%,66.99%and 11.62%respectively;The iron grade of leaching residue was 55.98%.Direct magnetic separation was difficult to improve the grade of iron.The coal based roasting leaching magnetic separation process of pyrite cinder showed that when the coal ratio was 10%and the temperature was 800℃for 60min,the fineness of coal based roasting slag was D₅₀=60.04μm.Under the conditions of stirring speed of 400 r/min,liquid-solid ratio of 4:1 mL/g,mass concentration of sulfuric acid of160 g/L and leaching temperature of 70℃for 5h,the leaching rates of copper and cobalt were 78.36%and 41.13%respectively.Magnetic separation of leaching residue can obtain iron concentrate with iron grade of 62.81%and recovery of 90.57%.Although iron and copper are effectively recovered under coal based conditions,the cobalt leaching rate was low.Whether the cobalt leaching rate can be improved under gas based conditions will be explored later.The gas-based roasting leaching magnetic separation process of sulfuric acid residue showed that when the volume fraction of CO was 30%and the temperature was 550℃for 30min,the fineness D₅₀of gas-based roasting residue was 55.28μm.Stirring speed was 400 r/min,liquid-solid ratio was 4:1 mL/g,sulfuric acid mass concentration was 160g/mL,leaching temperature was 70℃for 4h,copper and cobalt leaching rates were86.15%and 72.22%respectively.Iron concentrate with iron concentrate grade and recovery of 62.35%and 98.53%could be obtained by leaching residue magnetic separation.Under the condition of gas base,the comprehensive recovery of valuable metals such as iron,copper and cobalt was better realized.XRD analysis showed that with the increase of reduction roasting temperature（coal based and gas based）,hematite gradually changes to magnetite.Under the condition of coal based roasting,hematite in pyrite cinder completely changed to magnetite at 850℃;Under the condition of gas-based roasting,hematite in pyrite cinder was completely transformed into magnetite,and the temperature was reduced to 700℃.XPS analysis showed that after reduction roasting of sulfuric acid residue,copper mainly existed in the form of divalent copper.The analysis of binder phase showed that it was mainly CuO and CuS,which was easy to leach with sulfuric acid;After coal based reduction roasting,Co₃O₄in pyrite cinder was gradually reduced to CoFe₂O₄,which reduced the leaching rate of cobalt.After gas-based low-temperature roasting at 550℃,Co₃O₄and CoFe₂O₄were reduced,which improved the leaching rate of cobalt.