Research On New Technology Of Green Recovery Of Secondary Precious Metals And Rare Earth Metals

Rare and precious metals has become an irreplaceable strategic resource to ensure national security.It is widely used in metallurgy,aerospace,military and national defense and other fields.Precious metals are scarce in nature.Although rare earth metals are abundant in reserves,their abundance is low.Therefore,extracting rare earth and precious metal from secondary resources can save natural resources and realize the sustainable development strategy of China's land resources.The waste circuit board is not only a kind of solid waste,but also a valuable resource rich in valuable metals.Rare earth molten salt electrolytic slag is an important secondary resource of rare earth and it contains rich rare earth resources.In the present work,the waste memory modules(WMMs)and the rare earth fluoride molten salt electrolytic slag(REFMSES)are taken as as the research object.The effects of temperature,time,and material ratio on the dissociation of non-metals and metals in WMMs are investigated,and the degradation mechanism of the non-metallic(brominated epoxy resin,fiberglass,etc.)during molten alkali treatment is discussed from the thermodynamic viewpoint.The results show that the degradation rate of non-metallic materials in the memory moudles can reach 95.45%if the reaction is continuously kept for 50 min in the reaction kettle,when the temperature is 400? and Mmixture of hydroxides/MWMM is 5/1.The brominated epoxy resin is degraded to small molecules by breaking bonds step by step.The toxic element Br is absorbed by the molten base to form bromine salt.The heavy metal Pb was recovered into the mixed metal,and the recovery process was green and efficient.The obtained metal mixture contains the elements Cu,Fe,Ni,and also precious metals Au and Ag.Subsequently,the metal mixture is separated into Fe-rich and Cu-rich substances by using magnetic separation.The precious metals Au and Ag are almost enriched in Cu-rich substance and high-value group mainly containing gold,silver and copper is obtained.The rare earth in the rare earth fluoride molten salt electrolytic slag is recovered by acid leaching and roasting.The leaching effects of hydrochloric acid and hydrochloric/nitric mixed acid on rare earth are investigated in the acid leaching method.K2CO3?Na2CO3?KOH?NaOH?K2SiO3 are selected as the conversion agents in the roasting process to study their effects on the mineral phase reconstruction of REFMSES.Based on the Analysis the experiment process and product,KOH and K2SiO3 are finally selected as conversion agents.Through mineral phase reconstruction,fluorines are converted to fluoride salt and rare earths are converted to water-insoluble substances.The rare earth is separated from fluorine by water leaching.The purity of rare earth oxide is 99.1%after acid leaching,precipitation and burning.The recovery rates of rare earths for the two different conversion agents are 98.1%and 97.6%,respectively.F-ion of the fluorinated wastewater is removed by coagulation deposition method.The concentration of F-ion is 3.982-4.964 ppm,which is in conformity with the discharge standard of national industrial wastewater?10mg/L.