Roasting and Leaching Process of Mixture of Rare Earth Silicates Slag and Ammonium Sulfate

The rare earth was extracted from low-grade rare earth tailings by the technological process of high temperature direct reduction magnetic separation roasting with( NH4)2SO4water bath leaching in this work. The main influence factors on the leaching rates of rare elements in roasted products were investigated including amount of ammonium sulfate,roasting temperature and roasting time. The existing state of rare earth after direct reduction at high temperatures,the phase of rare earth after roasting with( NH4)2SO4at different temperatures,and the chemical composition of leaching solution and residue were characterized by SEM-EDS,XRD and TG-DSC. The results showed that the high-grade rare earth slag and powdered iron were obtained by high-temperature roasting and magnetic separation. Rare elements existed mainly in the form of Ca2RE8( Si O4)6O2and CaRE2( Si O4)2. The leaching rate of La,Ce and Nd could reach 96. 13%,98. 88% and 97. 1% respectively,under the following optimized experimental conditions: 8∶ 1 of( NH4)2SO4to slag mass ratio,400 ℃ of roasting temperature for 45 min,80 ℃ of water bath leaching temperature for 1 h and 10∶ 1 of leaching liquid-solid ratio. By roasting with( NH4)2SO4,the rare earth were transformed into their corresponding sulfate( NH4) RE( SO4)2and RE2( SO4)3. Simultaneously,Ca F2 partially turned into Ca SO4.