Study On The Method And Mechanism Of Selective Separation And Recovery Of Tellurium And Bismuth From Dashuigou Tellurium Deposit

Tellurium is an indispensable important material in strategic emerging industries,and bismuth is a safe and non-toxic"green metal".Both are widely used in new energy,information technology,high-end equipment manufacturing,aerospace and other fields.The Panxi region in China has the only independent tellurium deposit in the world-Dashuigou tellurium deposit.This ore is a polymetallic symbiotic ore with high tellurium and bismuth content,which will be an excellent raw material for the production of tellurium and bismuth products in the future.However,due to the complex phase and low grade of Te and Bi in the Dashuigou tellurium ore,no substantial breakthrough of the Dashuigou tellurium ore can be obtained,further restricting the comprehensive utilization of the ore,which leads to fail to translate resource advantages into industrial advantages.Aiming at the problem of enrichment and metallurgical separation of Dashuigou tellurium ore,this work conducts scientific research about the separation method and mechanism of Te and Bi.Based on the process mineralogical characteristics of Dashuigou tellurium ore,an acidic oxidative leaching followed by selective reduction was proposed to recover the Te and Bi in Dashuigou tellurium ore.The spontaneity of the relevant reactions related to this process was studied,theφ-p H diagrams of Te-H₂O,Bi-H₂O and other systems and the ion complex composition diagram in the livixium were established,the hydrolysis characteristics of metal ions in the livixium was clarified,and selective reduction conditions of Te and Bi in lixivium were obtained.Thus,the possibility of separation of Te and Bi from Dashuigou tellurium ore was analyzed from the thermodynamic perspective.Then,a series of experiments were carried out to systematically investigate the relevant physical and chemical evolutions based on this process.The main results are as follows:（1）The grades of Te and Bi in Dashuigou tellurium ore are low,and the content of Fe and S is high.The main minerals include dolomite（Ca CO₃·（Mg,Fe,Mn）CO₃）,muscovite(KAl₂(Al Si₃O₁₀)（OH）₂),pyrite（Fe S₂）,pyrrhotite（Fe S）,and so on.Te and Bi are present in the ore in the form of Bi Te and Bi₂Te₂S.Bi Te,Bi₂Te₂S and sulfide are closely embedded in the intergranular or fissures of the gangue.（2）Te and Bi can be effectively extracted from Dashuigou tellurium ore in H₂SO₄-Fe Cl₃ media.Te and Bi in Dashuigou tellurium ore can be leached in the form of Te⁴⁺or HTe O₂⁺and Bi³⁺respectively,and Bi³⁺will be complexed with Cl^-.It is necessary to control the p H of livixium to prevent the hydrolysis of metal ions.The leaching experiments were performed with Dashuigou tellurium ore,where the grades of Te and Bi are 1.52%and 2.99%,respectively.The leaching ratios of Te and Bi can reach 95.61%and 95.77%,respectively.The appropriate leaching conditions are:particle size of 104-150μm,leaching temperature of 90^oC,leaching time of 40 min,H₂SO₄ concentration of150 g/L,Fe³⁺concentration of 60 g/L,and liquid-solid ratio of 6:1 m L/g.The leaching process of Dashuigou tellurium ore meets the shrinkage unreacted nucleus model.The apparent leaching activation energies of Te and Bi are 12.91 k J·mol^-1 and 9.53 k J·mol^-1,respectively,which means that the restrictive link is the diffusion of solid layer.Within20 minutes of the initial leaching,dolomite is dissolved rapidly,forming rod-shaped Ca SO₄,which gradually coarsens and grows up;（Mg,Fe,Al）（Si,Al）O_x（OH）_y is dissolved mainly within 40 min;Si O₂ and Fe-S minerals are difficult to be dissolved.（3）Te and Bi can be effectively separated from livixium by using Na₂SO₃ to reduce Te followed by using Fe powder to replace Bi.When Na₂SO₃ is used to selectively reduce Te in the livixium,the recovery ratio of Te can reach 99.83%,the loss rate of Bi can be less than 2%,and the grade of crude tellurium can reach 93.78%.The appropriate process conditions for the selective reduction of Te is as follows:the excess coefficient of the reductant Na₂SO₃ dosage is 16,the reduction time is 10 min,and the reduction temperature is 80^oC.Stirring can accelerate the dissolution of the reductant to promote the reaction.Then,iron powder is used to replace the Bi in the solution after selective reduction.The recovery ratio of Bi can reach 99.39%,and the grade of crude bismuth can reach 92.35%under appropriate conditions:the excess coefficient of the reductant Fe powder dosage of 7.5,replacement time of 40 min,and replacement temperature of 60^oC.The recycle leaching of Dashuigou tellurium ore can reduce the Fe³⁺content in the livixium and increase the concentrate of Te and Bi in the livixium to further reduce the reductant dosage.