Synchronous Separation And Recovery Of Zinc, Lead And Tin By Carbon-based Reduction Of Complex Polymetallic Zinc Oxide Fume

The complex polymetallic zinc oxide dust from the process of treating blast furnace slag from the rotary hearth furnace has a characteristics of high lead,tin,fluorine,chlorine and sulfur.When the dust is treated by traditional hydrometallurgical process,a lot zinc leaching residue produce and zinc leaching rate decreases.The zinc leaching residue needs to be treated by pyrometallurgical process.Meanwhile,the recovery of tin and synchronous reduction,separation and recovery of valuable metals cannot be achieved.Carbothermic reduction method is used to realize synchronous reduction,separation and recovery of zinc,lead and tin from the zinc oxide dust.Finally the zinc-based volatiles and crude lead-tin alloy were obtained.The main research contents and conclusions are as follows:(1)The reduction thermodynamic of the zinc,lead and tin compounds in the zinc oxide dust during carbothermic reduction process was analyzed.The results show that it is feasible in thermodynamics to reduce zinc,lead,tin compounds to metal in a strong reducing atmosphere when temperature exceeds 1192K.During the reduction of lead sulfate,part of the sulfur will combine with zinc to produce zinc sulfide.(2)The volatilization behavior of zinc,lead,tin,sulfur,and arsenic in zinc oxide dust during carbothermal reduction was studied.The results indicate that the volatilization rate of these elements increases with increasing temperature.The holding time have no significant effect on the zinc volatilization rate.Adding calcium oxide can inhibit the volatilization of lead and tin in the reduction stage,while adding bentonite can only inhibit the volatilization of lead.Under the conditions of temperature of 1300?,coke dosage of 14.04%,holding time of 120min and no addictive,the volatilization rates of zinc,lead,tin are 98.56%,58.49%and 89.28%respectively.The volatilization rates of zinc,lead,tin are 99.60%,32.16%,57.70%respectively with calcium oxide dosage of 5%,and the volatilization rates of zinc,lead,tin are 99.12%?37.44%?83.25%respectively with bentonite dosage of 5%.Under the above reduction conditions,the zinc,lead,tin contents of the zinc-based volatiles are 68.48%,22.18%,6.99%respectively.The zinc,lead,tin contents of the crude lead-tin alloy are 0.23%,72.44%,2.46%respectively.(3)The effect of pretreatments on the volatilization behavior of lead and tin was studied.After calcination at 900?,the removal rates of fluorine,chlorine,sulfur are97.38%,97.41%,30.02%respectively.Under the conditions of temperature of1300?,coke dosage of 14.04%,holding time of 120min and no addictive,the volatilization rates of lead and tin decreased to 30.46%and 57.83%,respectively,from 58.49%and 89.28%without calcination.(4)“Ball making-Drying and calcination-Carbothermic reduction”process kilogram grade experiment was carried out.The results demonstrate that the volatilization rates of zinc,lead,tin are 98.34%,54.31%,73.20%respectively and the slag rate is 5.88% under the conditions of raw material dosage of 2000g,temperature of 1300?,coke dosage of 14.04%,holding time of 120min and no additive.The zinc,lead,tin contents of the metal product are 2.86%,86.84%,6.72%respectively.Based on the theoretical calculation of the chemical composition of the slag obtained from the electric furnace smelting of the zinc oxide dust,the Si O₂-Ca O-Al₂O₃ ternary system was selected as the slag type.The efficient extraction and synchronous reduction,separation and recovery of zinc,lead,tin from the zinc oxide dust with high lead,tin,fluorine,chlorine,sulfur contents can be realized by carbothermal reduction method.The crude zinc and lead-tin alloy can be obtained as products.