Dissolution behavior of calcium tungstate in oxalic acid solutions

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• 作者：A.O. Kalpakli ; ^{aok13@istanbul.edu.tr} ; S. Ilhan ; C. Kahruman ; I. Yusufoglu
• 关键词：Calcium tungstate ; Scheelite ; Oxalic acid ; Chelate ; Dissolution mechanism
• 刊名：Hydrometallurgy
• 出版年：2012
• 期刊代码：38_0304386x
• 类别：ce
• 出版时间：June, 2012
• 卷：121-124
• 期：Complete
• 页码：7-15
• 文件大小：1178 K

摘要

Scheelite mineral (CaWO₄) is the main raw material used in tungsten production. In this study the dissolution of synthetically prepared CaWO₄ in oxalic acid (H₂C₂O₄) solutions was studied. The effect of following parameters on the dissolution of reaction was investigated: stirring speed, temperature, H₂C₂O₄ concentration and particle size. The amounts of tungsten leached were followed by using Inductively Coupled Plasma-Optical Emission Spectrometer (ICP-OES) instrument. X-ray Powder Diffraction (XRD), Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) analytical techniques were used to characterize the leach residues. The results obtained show that the dissolution reaction takes place in two steps: first, the intermediate calcium aqua oxalato tungstate (Ca[WO₃(C₂O₄)H₂O]) chelate compound was obtained. Second, this compound reacted with H₂C₂O₄ to form water soluble hydrogen aqua oxalato tungstate (H₂[WO₃(C₂O₄)H₂O]) and solid CaC₂O₄H₂O. CaC₂O₄H₂O formed covered the surfaces of unreacted CaWO₄ particles as a protective layer and the dissolution reaction was interrupted after a certain conversion at high temperatures and H₂C₂O₄ concentrations.