Research On Recovery Of Valuable Metals From Electroplating Sludge By Smelting

Electroplating sludge is the sludge formed after the treatment of electroplating wastewater,which contains valuable metals,but also a dangerous solid waste.At present,there are mainly wet process and fire process.At present,the main electroplating sludge treatment process is still the fire process.This study focuses on the key scientific and technical problems in the fire process,and draws the following main conclusions and innovations:（1）By roasting electroplating sludge at high temperature,phase transformation law and element migration law of electroplating sludge at high temperature are analyzed.Temperature is the most important factor affecting phase change of electroplating sludge.It is concluded that the formation process of metal sulfide in electroplating sludge is as follows:the reduction and decomposition products of calcium sulfate above 1000℃are mainly calcium sulfide and calcium oxide,among which calcium sulfide will be iron sulfide,copper oxide and nickel oxide as corresponding metal sulfides.（2）Thermodynamic calculation results of melting point and viscosity of slag in electroplating sludge smelting process show that when the ratio of FeO to SiO₂ is between 0.4 and 1.8,the melting point of slag decreases first and then increases with the increase of the ratio of FeO to SiO₂.When the ratio of CaO to SiO₂ is between 0.3 and 1.1,the minimum melting point of slag is also different.At a lower melting point,the ratio of FeO to SiO₂ is between 0.8 and 1.4,and the increase of the ratio of CaO to SiO₂ will significantly increase the melting point of slag.In the above ratio range,the slag viscosity decreases with the increase of the ratio of FeO to SiO₂ and CaO to SiO₂,and the higher the temperature,the lower the slag viscosity.（3）When FeO:SiO₂:CaO:Al₂O₃=1:1:0.5:0.057,the addition of carbon powder is 1.5%（relative to electroplating sludge）,melting temperature is 1200℃,melting time is 120min,98.29%copper and 98.12%nickel in electroplating sludge can be recovered.Smelting products for matte,mainly for porphyry（Cu₅FeS₄）,chalcocite（Cu₂S）,a small amount of metal copper,nickel sulfide,pyrite formed at high temperature eumelt.The grade of copper and nickel is 46.56%and 3.11%,which can be sold as matte products.The grade of copper and nickel in smelting slag is only 0.27%and 0.083%,realizing efficient recovery of valuable metals of copper and nickel.