Research On New Technology Of Acidic Decomposition Of Scheelite Using H₂O₂as Synergic Agent

Abstract:Tungsten proves a significant strategic metal. Among tungsten resources, high quality wolframite is depleting gradually while the dominating scheelite(CaWO4) becomes crucially important in China. Therefore, the methods for processing scheelite have been highlighted in tungsten industry. Though appearing advantages, the conventional processes generally have problems of high energy consumption and environmental pollution. In order to overcome these drawbacks, a new process was proposed in this thesis. Hydrogen peroxide (H2O2) as chelating agent was introduced into HCl solution for decomposing scheelite. The main contents and conclusions are as follows:(1) The leaching kinetics of scheelite in the HCl-H2O2system was performed. It indicated that the leaching of scheelite accords with the Avrami-Erofeev kinetic model equation in the range of experimental conditions. Accordingly, the reaction order was equal to0.29and the apperant activation energy was38.93kJ·mol-1demonstrating that the controlling factor is phase-boundary reaction.(2) The technological test of the leaching of scheelite concentrate and synthetic scheelite in the HC1-H2O2system was explored. The results showed that both tungsten materials could be decomposed at ambient temperature and pressure conditions. The leaching of WO3was only about50%at optimum conditions for scheelite concentrate and its residue had similar leaching results. The reason needs further investigation. While the latter could be totally decomposed at optimum conditions(CHCl=1.5mol·L-1, CH2O2=2.4mol·L-1, T=30℃, L/S=10mL·g-1). In addition, the consumption of HCl reduces substantially and the volatility loss of HCl could be controlled effectively when processing synthetic scheelite.(3) Furthermore, study on the thermal decomposition of peroxytungstic acid was conducted. It was found that peroxytungstic acid is inclined to decompose at great rate for its poor thermal stability. And the rate increases with the increasing of temperature and the concentration of free hydrogen ion in solution. This process could be applied for separating W and Mo because the thermal stability of their peroxide is different. The seperation factor of W and Mo is more than110at60℃with free [H+] of2.5mol·L-1when mMo/mWO3is about2.5%.Hereby, a flowsheet for producing H2WO4as the intermediate production was designed via the combination of the two parts above.