Study On Roasting-leaching Process And Mechanism Of Low Temperature Alkaline System For Pegmatite Lithium Concentrate

At present,the lithium extraction technology of pegmatite lithium concentrate is mainly treated with spodumene by sulphuric acid curing and lepidolite by sulphate roasting.The main problems of these two processes are high temperature of lithium concentrate treatment and high energy consumption.In this paper,the mineral composition and physicochemical properties of three different pegmatite lithium concentrates,spodumene,zinnwaldite and lepidolite were analyzed.Thermodynamic analysis and roasting additive experiment show that NaOH and CaO as roasting additives can react with aluminosilicate minerals more fully at a lower temperature and destroy the mineral structure,which lays a foundation for low temperature lithium extraction from pegmatite lithium concentrate.The process conditions of alkaline system roasting for pegmatite lithium concentrate were determined.The optimum roasting conditions for spodumene concentrate are as follows:mass ratio of NaOH/CaO/spodumene concentrate 2:0.4:1,roasting temperature 650?,roasting time 1.5 h.The optimum roasting conditions for lepidolite concentrate are as follows:mass ratio of NaOH/CaO/lepidolite concentrate 2:0.5:1,roasting temperature 650?,roasting time 1.5 h.The optimum roasting conditions for zinnwaldite concentrate are as follows:mass ratio of NaOH/CaO/zinnwaldite concentrate 2:0.5:1,roasting temperature 650?,roasting time 1.5 h.This process effectively reduces the roasting temperature of traditional lithium concentrate from 850?1050? to 650?.The leaching conditions of pegmatite lithium concentrate roasted products were determined.The optimum leaching conditions of spodumene concentrate roasted products are as follows:the ratio of liquid to solid 4,the leaching time 60 min,the leaching temperature 90?,and the leaching rate of Li is 91.2%.The optimum leaching conditions for lepidolite concentrate roasted products are as follows:the ratio of liquid to solid 4,the leaching time 60 min,the leaching temperature 90?,and the leaching rates of Li,Rb and Cs are 90.8%,98.6%and 96.2%,respectively.The optimum leaching conditions for zinnwaldite concentrate roasted products are as follows:the ratio of liquid to solid 2,the leaching time 60 min,the leaching temperature 90?,and the leaching rates of Li,Rb and Cs are 87.1%,98.6%and 30.7%,respectively.The leaching rate of Rb and Cs in lepidolite is increased from about 30%to more than 95%while the leaching rate of lithium is guaranteed.The mechanism of low temperature alkaline system roasting-water leaching reaction of pegmatite lithium concentrate shows that the[Si-O]structure and[Al-O]structure of pegmatite lithium concentrate are destroyed by NaOH and CaO at 300? and 500?,respectively.When the roasting temperature at 650?700?,the mineral structure of pegmatite lithium concentrate is destroyed,Si and Al in lepidolite and spodumene roasted products are separated from each other and formed corresponding silicate and aluminate,in addition,a large amount of Na4Ca(OH)6 is generated.However,Fe3+ in the roasting process inhibits the crystallization of silicate,resulting in the formation of dense glass phase.In addition,CaO exists in the roasted products.However,Fe3+ in the roasted products inhibited the crystallization of silicate and formed a dense amorphous glass phase,which was the main reason hindering the leaching of Li.At the same time,CaO in the roasted products will form a dense Ca(OH)2 layer during the leaching process and hinder the leaching of Li.In this paper,low temperature alkaline roasting-water lithium extraction process was used to achieve low temperature(650?)roasting pegmatite lithium concentrate recovery of lithium,rubidium,cesium,energy saving and emission reduction.This study provides a new idea for direct lithium extraction from pegmatite lithium concentrate in industry.