Research On Novel Acid Process Of Low-grade Wolframite-scheelite Mixed Ore

Tungsten is an important part of modern high-tech materials.The complex mineralogy along with depleting grades of ore reserves force us to re-examine today’s tungsten metallurgy process.Direct hydrometallurgical processing of low-grade concentrates（WO₃≤20%）may become an effective method as it breaks through the limitation of mineral grade and allows increasing the recovery rate.But the lower-grade concentrate means more impurities,which puts unprecedented pressure on the hydrometallurgy process.In this paper,the HCl-H₃PO₄ method is selected to achieve the efficiency and clean decomposition of low-grade wolframite-scheelite mixed ore.Based on the study of the properties and behavior of elements,a multi-element comprehensive recovery process of"preprecipitation-extraction separation"was proposed.Mainly achievements are shown below:（1）The theoretical basis of efficient mineral decomposition is established by calculating the great thermodynamic trend of leaching process.Under the optimized process conditions,the acid leaching rate reached 64.32%and the slag contained 12.6%WO₃;after Na OH leaching,the total W leaching rate is more than 99%,and the slag contained only0.12%WO₃.This method achieved efficiency decomposition with lower energy consumption and costs.（2）The behavior of W,Fe and Ca in H₃PW₁₂O₄₀-HCl-TBP-sulfonated kerosene system was investigated.The saturation capacity of W and the extraction stoichiometry of W were determined by saturated capacity method and the slope method.In addition,the study determined that the co-extraction of Ca（II）lead to the loss of W.Fe（III）reduces the thermal effect of extraction process from ln D-1/T plots and the increasing Fe（III）concentration promotes the partition ratio in the log D-log[TBP]_org plots.Under the different Fe（III）concentration,the extractive complex froms as H₃PW₁₂O₄₀·（0.72～0.89）TBP.Based on above study,"Ca-removal and solvent extraction methods"was proposed for the acidic leachate riched calcium and rion.（3）H₂SO₄ is used to remove Ca from the leachate,H₂SO₄concentration and inital temperature effect the Ca-removal process.Under the optimized conditions,85%Ca is removed and the precipitate is a mixture of Ca SO₄·2H₂O and Ca SO₄·0.5H₂O（total impurity content<0.7%,WO₃ content<0.5%）.The extraction experiments of the Ca-removal solution focus on th separation of W/Fe.Under the optimizate conditions,the extraction efficiency of W and Fe were 96.2%and 26.5%,respectively,andβ_W/Fe reached 3.62.In stripping process with Na OH,W was transferred into the aqueous phase as highly soluble sodium tungstate,whereas Fe was precipitated as ferric hydroxide（WO₃ content<1%）.In this process,W and valuable elements in acid leachate can be separated and extracted,then Ca and Fe can be reused as by-products respectively.Finally,the accumulation of impurities in the process of acid solution and reagent cycle were clarified,and the cycle stability of each process was verified.The basic process framework of overall cycle and zero discharge was preliminarily constructed.The novel process breaks through the limit of grade to realize the efficient decomposition of low-grade concentrate.Efficient recovery,purity by-products and full solution and reagent cycle are more in line with the current green and clean situation.There are 66 figures,29 tables and 95 references in this paper.