Study On The Recovery Process Of Alumina From Aluminium Concentrate Through Bayer Method

In recent years,more than 200 million tons of aluminum associated with pyrite has been discovered in Fengshan Conunty Guangxi,beneficiate pyrite and aluminium concentrate after effective of aluminium concentrate 40 million tons can be acquired,the alumina grade of the aluminium concentrate reaches amount 67%,meanwhile with titanium and scandium,niobium and another rare earth elements.This concentrate has extremely high comprehensive utilization value.However,the research on alumina recovery rarely can be rarely reported-there isn't technology has been used for the vast sums of aluminium concentrate.However,the research for alumina recovery rarely can be seen-there isn't technology has been used for the vast sums of aluminium concentrate.This thesis,selecting aluminium concentrate as the research object,adopts Bayer process to recover alumina,at the same time get enrichment of titanium in leaching residue.It is of great significance to promote the development of non-bauxite resources and alleviate the shortage of aluminum resources in China.In the paper,we adopted Bayer process under special conditions to recovery alumina from aluminium concentrate.It mainly includes the leaching of aluminium concentrate and the decomposition of sodium aluminate solution.(1)Chemical composition analysis indicated that the aluminium concentrate about the characteristics of high aluminum,high silicon,low iron(iron oxide is as low as 1.14%).The A/S is 5.59,titanium,scandium and another rare earth element much higher than general bauxite.It has extremely high comprehensive utilization value.XRD pattern of aluminium concentrate indicates,nearly 100%of aluminum is in diaspore.form.It has dense structure and refractory ore digestion.Particle size distribution indicates that the ore average size is 56.49 ?m,so it can be leached directly without crush.The thermodynamic analysis indicated that in Bayer process main reactions of the main mineral phases in aluminium concentrate with NaOH are sequenced:kaolinite>anatase>diaspore.At normal temperature,alumina can react with NaOH,resultant is soluble sodium aluminate,at the same time titanium exists in stable form in Na2O·3TiO2.(2)Through orthogonal test and single factor experiment of leaching aluminium oxide,systematic study on influence of digestion temperature,digestion time,liquid to solid rate,Na2O/Al2O3 ratio and stirring speed on leaching ratio of aluminium oxide.aluminium concentrate is hard to be leached at lower temperature,when temperature is up to 264?,the leaching ratio has shown increasing trend.Orthogonal test experiment shows,the optimum leaching conditions are:temperature280?,Na2O/Al2O3 ratio 2.05,leaching time 75mins,liquid to solid of ingredient 4:1,relative leaching ratio up to 99.89%,meanwhile in residue contain of TiO2 more than 9%,almost twice than before.It order to be advantageous for recycling titanium in the leaching process without adding calcium oxide.The kinetics of leaching process of ore indicates that in lower temperature phase-boundary reaction is the controlling step.Leaching reaction be controlled by solid-film diffusion is in higher temperature,further more Ea=70.64kJ/mol.The SEM-XRD analysis shows that the residue is floccule after leaching,and the particles become smaller as the leaching temperature increases.The main phase is sodalite,Sodium aluminosilicate hydrate and diaspore.And the intensity of the fingerprint peak bauxite varies with the increase of leaching temperature and the extension of leaching time.(3)Through orthogonal test and single factor experiment of decomposition of sodium aluminate solution,systematic study on influence of Na2O/Al2O3 ratio of sodium aluminate solution,decomposition time,decomposition temperature,conditions of seed,and stirring speed on decomposition rate of sodium aluminate.When the coefficient of the seed more than 0.5,the decomposition rate of sodium aluminate has showed increasing trend.Orthogonal test experiment showed,the optimum decompose conditions are:Na2O/Al2O3 ratio of sodium aluminate solution 1.6,decomposition temperature 62?,seed ratio 1.5,decomposition time 60h,Activation of the seed,the decomposition ratio is 55.65%.XRD-XRF pattern of decomposition product shows that main pattern is Gibbsite,the purity of 97.67%.