Study On The Process Of Recovering Gallium From Brown Corundum Dust

Gallium is an indispensable rare metal in modern industry.With the development of semiconductor and solar cell industries,its market demand is gradually increasing.The recovery of gallium from secondary resources has attracted more and more attention.In this paper,using brown fused alumina dust as raw material,the gallium was extracted from this kind of solid resources and concentrated in solution by roasting,leaching followed by solvent extraction.ICP-MS,EPMA,XRF,SEM-EDS,particle size analysis and thermogravimetric analysis were used to analyze and characterize the raw material of the brown corundum dust.The results show that the main chemical components of the brown corundum dust are silicon,aluminum and potassium,totally accounting for 81.92 wt.%in the form of oxides.The main existing phases are amorphous silicate,corundum and potassium sulfate.The gallium occurs as sodium galliate and potassium galliate present in the potassium-rich phase,which is coated with amorphous silicates and the corundum.The overall particle size of the raw material is mainly distributed within-120+0.2μm,accounting for84.17%.The large particles distributed in-1200+200μm are mainly composed of alloy and carbide with high hardness.The thermodynamics of roasting reactions of the brown corundum dust was calculated by HSC Chemistry 6.0.The results show that the main phase of the raw material can transform into sodium silicate,sodium aluminum silicate and potassium aluminum silicate phases when sodium salt is applied as the roasting additive.While main phases including calcium silicate and calcium aluminum silicate are produced after roasting with calcium salt.The results show that the activation effect of sodium salt roasting is better than that of calcium salt roasting.The optimum roasting conditions for sodium salt are temperature of 850℃,holding time of 20 min,mass ratio m(additive)/m(dust)being 0.5,and while for calcium salt the temperature is 850℃,time is 2 h,and the mass ratio m(additive)/m(dust)is 0.8.The phases composition of the roasted material is in good agreement with the thermodynamics calculation.After activation by roasting with sodium carbonate,the phase composition of the dust material is reconstructed,and most of the components are converted into sodium salt with good acid solubility.The activated materials were leached by sulfuric acid and hydrochloric acid at atmospheric pressure to extract the gallium.The optimal leaching temperature is 80℃,the leaching time is 90 min,the sulfuric acid concentration is 4.6mol/L and the stirring rate is 800 rpm.Under this optimal leaching conditions,the gallium leaching rate is 93.11%.In case of the hydrochloric acid leaching,the optimal leaching temperature is 50℃,the leaching time is 40 min,the acid concentration is 6 mol/L,and the stirring rate is 480 rpm,and under these conditions,the leaching rate of gallium reaches 91.78%.These two kinds of inorganic acid both perform better in preventing silicon from transferring into the solution during leaching.After hydrochloric acid leaching,tailings are mainly composed of amorphous silicon dioxide,sodium chloride and potassium chloride.The tailings obtained after the sulfuric acid leaching mainly constitutes amorphous silicon dioxide,potassium aluminum sulfate,sodium aluminum silicate and sulfate.The gallium in sulfuric acid leaching solution was extracted by trioctylamine+sodium chloride+260#sulfonated kerosene system.In this system Cl~-plays a key role and the amount of sodium chloride has significant influence on the extraction efficiency.When the concentration of sodium chloride is 100 g/L,the extraction of gallium is 88.05%at O/A of 1 under the optimal extraction conditions.The main impurity elements such as silicon and iron are extracted together with gallium,and while most of aluminum and potassium is separated.When the concentration of the extractor(TBP/n-decanol volume ratio of 2:3)is 50 vol%,the extraction of gallium is up to 95.45%.The loaded organic phase can be stripped by mild deionizing.The optimum stripping temperature is 50℃and the optimum stripping time is 10 min.