Study On Process And Mechanism Of Recovery Of Iron And Zinc From Copper Slag By Rotary Hearth Furnace Direct Reduction

Copper slag,a byproduct of copper smelting by pyrometallurgy,occupies a large amount of land and pollutes the environment.The iron in copper slag mainly exists in the form of ferric silicate,which is very difficult to be recovered.At present,the treatment of copper slag is only aimed at recovering copper,cobalt ·and other metals.However,there are few studies on the recovery of iron and zinc in the slag.And all of the studies stay in the stage of small-laboratory,there are no reports of large-scale pilot test equipment or industrial production on the recovery of iron and zinc.In this paper,the copper slag obtained by a slow cooling and flotation method was studied.Firstly the distribution characteristics of iron,zinc and other elements in copper slag were identified by studying the characteristics of the copper slag.After careful relevant data referring and comparition of different treatment processes,the rotary hearth furnace direct reduction-magnetic separation technology for comprehensive recovery of iron and zinc as the valuable metals in the copper slag was adopted finally.A small scale experimental simulation device of rotary hearth furnace was designed and made,which well simulates the reduction characteristic of the industrial production rotary hearth furnace,including heating mode,the heating system of the pellets from low to high temperatures,reduction container,the number of pellet layers(material thickness)and recovery of zinc oxide dust by the flue gas dust collecting system.With this device,in a good roasting condition of the copper slag pellets containing-carbon,the effects of the types and dosages of reducing coal,dosages of additives,roasting temperature simulated in high temperature zone of rotary hearth furnace,roasting time,pellet layers(material thickness)and magnetic separation conditions were investigated for recovery of iron and zinc.On this basis,a rotary hearth furnace line with a capacity of 30000 t/a was used for pilot test verification.The results have showed that direct reduction iron powder with 90.38%Fe can be obtained with a recovery of 88.12%,and the zinc oxide powder with zinc content of 58.89%and zinc volatilization rate of 98.42%can be collected.It is proved that process of recovery of iron and zinc from the copper slag by rotary hearth furnace direct reduction is feasible.X-ray diffraction(XRD),scanning electron microscopy with energy dispersive spectroscopy(SEM-EDS)and polarizing microscope were employed to investigate the mechanism of direct reduction-magnetic separation of copper slag for recovery of iron and zinc.It showed that the addition of limestone and industrial sodium carbonate can not only effectively reduce the starting temperature of direct reduction,destroy the Fe2SiO4 structure of the copper slag,but also promote the reduction of iron oxide and the growth of metallic iron grains.The reduction effects of pellets in different material layers were analyzed,the results showed that the pellets from the bottom to the top,with the increase of radiation heat received by the pellets,the metallization rate of the pellets increased gradually and the iron in the metalized pellets changed from the diffusion state to the iron-joined crystal,and the recovery rate of the reduced iron powder gradually increased.Zinc oxide powder was mainly produced in the form of zinc oxide(ZnO)accounting for 97.44%,and lead was mostly produced in the form of lead sulfate(PbSO4),accounting for 74.13%.