Study On Extraction Of Rare Earth Element Scandium From Red Mud

Red mud is a solid powdery waste discharged from the process of extracting alumina from bauxite and has strong alkalinity.The annual red mud produced in China is tens of millions of tons,and the utilization rate is very low,causing a large accumulation of red mud and serious damage to the environment.Scandium is a typical rare lithophile element.It has a rare reserve in the earth's crust and is widely distributed in ilmenite,zirconium ore,bauxite,rare earth ore,etc.The content of Sc2O3 is 40-150?g·g^-1 in bauxite and more than 98%is enriched in red mud.The content of Sc can reach 0.02%,so red mud is a good raw material for industrial extraction.Sc has great economic value and is mainly used for doping of sodium lamps,solid oxide fuel cells,lasers and aluminum alloys,and also for aerospace industry and sports equipment manufacturing.Therefore,extracting scandium from red mud has certain development significance and economic value.Bayer's red mud is taken as the research object in this thesis,and the object composition and the amount of Sc in Bayer red mud were studied by means of instrumental analysis such as XRD and ICP.The research shows that the main phase composition of Bayer red mud is hematite Fe2O3,quartz Si O2 and aqueous sodium aluminosilicate(Na2O)1.31Al2O3(Si O2)2.01(H2O)1.65,and the content of Sc in red mud is46.6 mg/kg.The single-factor experiment and orthogonal experiment were carried out to study the process conditions of hydrochloric acid leaching in red mud.The primary and secondary order of influencing factors were determined.The optimal leaching conditions for hydrochloric acid leaching Sc in red mud were 10 mol/L HCl,while the leaching temperature is 50?,the liquid-solid ratio is 6:1,and the leaching time is 1 h.After immersing the red mud three times under the optimal conditions,the leaching rate of Sc reached 75.2%.The extraction system of P204+kerosene was used to extract Sc from hydrochloric acid leaching solution.The distribution ratio,separation coefficient and extraction rate of Sc,iron and aluminum were studied to determine the optimum extraction conditions of Sc.The addition of TBP to the extractant can effectively improve the emulsification during stripping and accelerate the stratification.The optimal extraction conditions for the final determination of Sc were 3%P204+1%TBP+kerosene,O/A=12.5:25,extraction for15 min,at this time the extraction rate of Sc reached more than 99%.The Sc is separated from most of the aluminum and iron in the leachate,while the aluminum is hardly extracted and a small portion of the iron is co-extracted.The iron,aluminum and titanium impurity ions in the extracted phase were removed by scrubbing,and the Al³⁺,Fe³⁺was removed by washing the extract phase with 6 mol/L HCl under an O/A ratio of 3:1.4 mol/L H2SO4+0.5 mol/L H2O2 was used to remove Fe²⁺and Ti⁴⁺impurities in the extraction phase and the washing ratio was O/A=1:1.The Sc in the extracted phase was stripped with 2.5 mol/L Na OH under an O/A ratio of 3:1.The stripping was carried out at 50?for 15 min and the stripping rate was 92.3%.The scandium hydroxide precipitate was washed with secondary water to remove soluble impurity ions.The prepared scandium oxalate product was washed with secondary water to remove impurities,and the product obtained can be qualitatively judged to contain Sc2(C2O4)3·6H2O by XRD.The ICP method can be used to quantitatively determine the content of scandium in the product and the result is 1.26%(12.6 g/kg).Compared with the content of scandium in the original dried red mud(46.6 mg/kg),the product was enriched by 270 times and the total recovery of scandium was 43%.