Study On The Separation And Recovery Of Valuable Metals From Electroplating Sludge By Chlorinating Roasting And Its Resource Utilization

Electroplating sludge is a typical hazardous solid waste produced in the process of electroplating wastewater treatment by chemical precipitation method.The heavy metals（chromium,nickel,copper,zinc）in the electroplating sludge are not only harmful to the environment but also important metal resources.Therefore,the extraction of heavy metals from electroplating sludge is of great significance to environmental protection and resource recovery.The main phases of common electroplating sludge are calcium carbonate and calcium sulfate.It is difficult to achieve efficient and selective extraction of heavy metals by using traditional leaching methods.Meanwhile,the coexistence of multiple heavy metals in the leachate would greatly increase the difficulty of heavy metal reuse.In this paper,two chlorinating roasting-leaching methods were proposed to achieve selective extraction of heavy metals from electroplating sludge whose main phases were calcium carbonate and calcium sulfate,respectively.Furthermore,the high-value utilization of the recycled electroplating sludge leachate to prepare electrode materials for supercapacitors was studied.The research content includes the following three aspects:（1）For electroplating sludge containing Ca CO₃,chlorinating volatilization-dilute acid leaching method was adopted.Under oxidizing atmosphere,calcium chloride was used as chlorinating agent for chlorinating roasting.Zinc and copper were converted to volatile chlorides.Under the promotion of Ca CO₃,Cr（III）reacted with oxygen to transform into Cr（VI）,and then chromium was extracted by dilute acid leaching.Finally,the selective extraction of chromium,zinc,and copper was realized.Under the optimal conditions（1000℃,4 h,the mass ratio of calcium chloride to sludge was 0.7:1）,the extraction rates of Zn and Cu were more than100%,100%,and the extraction rate of Cr was 82.1%.（2）For the electroplating sludge containing Ca SO₄,chlorinating roasting-water leaching method was adopted.Under inert atmosphere（N₂）,HCl was used as chlorinating agent for low-temperature chlorinating roasting.Firstly,chromium,nickel,and copper were converted into corresponding chlorides,and then Cr Cl₃ is converted into water-insoluble Cr₂O₃ through temperature regulation,while nickel and copper still exist in water-soluble Ni Cl₂ and Cu Cl₂.Finally,selective extraction of nickel and copper was realized by water leaching.Under the optimal conditions（1000℃,4 h,the liquid-solid ratio of HCl to sludge was 1.2:1）,the extraction rates of Ni and Cu were 93.6%,90.7%,respectively.（3）Furthermore,the high-value utilization of electroplating sludge leaching solution was studied.Ni and Cu in the leachate were used as metal sources,Ni-Cu LDH materials were prepared by the template method and applied to supercapacitors.The abundant mesoporous and macroporous structures in the sheet-shaped Ni-Cu LDH provide channels for rapid ion transmission.The specific capacitance of the sheet-shaped Ni-Cu LDH is as high as 1694 F g^-1and is superior to that of the Ni-Cu LDH prepared by a pure chemical reagent.Additionally,Ni-Cu LDH has good cycling performance（capacitance retention of 73.3%,2000 cycles）.