Study On The Decomposition Mechanism Of Scheelite By Sodium Bisulfate Roasting And Impurity Transformation And Migration Behavior

The main alkali decomposition and ion exchange process in domestic tungsten smelting has prominent problems such as large water consumption,large waste water and high production cost.Therefore,based on the research of scheelite roasting transformation,our research group has carried out essential innovation on the traditional tungsten smelting system,and proposed a new idea of sodium bisulfate roasting and decomposition of scheelite.This method can realize the efficient roasting transformation of scheelite and at the same time,The use of roasting to remove flotation agents to prevent reaction tank overflowing,eliminate the ion exchange process caused by the large amount of water consumption,waste water and other problems,greatly save the production cost.In order to establish the theoretical basis of sodium bisulfate roasting process of scheelite decomposition and further guide the new roasting process,the mechanism of sodium bisulfate roasting process of scheelite decomposition and impurity transformation and migration behavior were studied in this paper.The main contents and results are as follows:（1）（1）The high temperature thermal reaction behavior of sodium bisulfate roasting and decomposition of scheelite was studied by TG-DSC.The results show that when T≥50℃,Na HSO₄·H₂O is dehydrated,and when the temperature continues to rise to 120℃≤T≤246℃,melt Na HSO₄ fully releases free H⁺,which combines with Ca WO₄ and converts into intermediate H₂WO₄,and H₂WO₄ is further decomposed into WO₃.（2）The phase transformation process of sodium bisulfate roasting and decomposition of scheelite was analyzed by XRD.The results show that WO₃,Ca SO₄ and Na₂SO₄ are the products of scheelite after roasting with sodium bisulfate.The increase of roasting temperature,time and dosage of sodium bisulfate can promote the conversion of Ca WO₄ to WO₃.（3）SEM-EDS was used to observe the surface morphology of scheelite and products with different roasting time.The results show that under roasting conditions,sodium bisulfate can effectively destroy scheelite particles,and the generated WO₃ is evenly dispersed in the matrix of Na₂SO₄ and Ca SO₄,while gangue in scheelite does not participate in the reaction.With the extension of roasting time is beneficial to the decomposition of scheelite,while gangue in scheelite does not participate in the reaction.（4）Kinetics of sodium bisulfate roasting scheelite decomposition was studied by model method.The results show that the reaction process of sodium bisulfate roasting and decomposition of scheelite complies with the first-order reaction equation.The process is controlled by chemical reaction,and the apparent activation energy E_a of the reaction is 3.4k J·mol^-1.（5）The transformation and migration behaviors of characteristic impurities P,As and Mo and the effect of related substances on tungsten in the process of roasting scheelite with sodium bisulfate were systematically studied through the roasting experiment of pure impurities and Na HSO₄·H₂O and the thermodynamics of arsenic impurities decomposition-oxidation.The results show that:The results showed that Ca₅（PO₄）F roasted with Na HSO₄·H₂O and transformed into gaseous H₃PO₄ and P₂O₅,as well as soluble Na₃PO₄.Ca Mo O₄ reacts with Na HSO₄·H₂O to form Mo O₃,part of Mo O₃ is converted to Na_2m[Mo O₂（SO₄）₂]_m,part of Mo O₃is volatilized into gas phase,and the rest of Mo O₃ coexisted with roasted products.As₂S₃,As₂S₂and Fe As S are oxidized to As₂O₅,while Fe As O₄ is not roasted with sodium bisulfate and coexist with roasted products.