Novel Process For Scheelite Decomposition By Mechanochemical Milling

With the excellent behaviors in physical and chemical properties,tungsten has been widely applied to industrial manufacturing.Scheelite,as the major source of tungsten,is the important strategic resources in our country.Improving the utilization efficiency of tungsten is of great significance,as well as extracting tungsten from scheelite efficiently.The novel process of mechanochemical decomposition of scheelite was investigated in this paper and the main contents were summarized as follows:（1）A novel process of sodium hydroxide（NaOH）decomposition of scheelite by mechanochemical milling was developed.The results of the experiments showed that the strong collision and shearing force induced by milling operation provided essential dynamic condition for the caustic decomposition of scheelite.Compared to the traditional process,the dosage of NaOH was decreased obviously and the high temperature and pressure were avoided in the novel process.The effects of the dosage of aluminum hydroxide and sodium hydroxide,rotational speed,mass ratio of ball to material and milling time on the caustic process of scheelite were studied systematically.It could be concluded that scheelite concentrate could be effectively decomposed with a quite low alkali consumption,forming sodium tungstate（Na2WO4）and calcium hydroxide（Ca（OH）₂）powders.With the addition of aluminum hydroxide（Al（OH）₃）as calcium immobilization reagent,to transform calcium hydroxide into water-insoluble katoite(Ca₃Al₂（OH）₁₂)mechanochemically,sodium tungstate solution could be obtained after water washing and filtration.And the recovery of tungsten,on the condition of the dosage of Al（OH）₃ 1.0 time to stoichiometry,the dosage of NaOH 1.4 times to stoichiometry,the mass ratio of ball to materials 49:1,the rotational speed 600 rpm and the milling time of 120 min for NaOH and scheelite and another 60 min after Al（OH）₃ addition,reached up to 95.9%,while that was less than 60%using the considerable amount of NaOH in traditional process.（2）Based on the above study,the feasibility of aluminum-based ores replacing with Al（OH）₃ as calcium immobilization reagents was investigated.The results indicated that any of kaolinite(Al₄(Si₄O₁₀)（OH）₈),gibbsite（Al（OH）₃）and diaspore（α-AlOOH）could react with Ca（OH）₂ to form grossular(Ca₃Al₂（SiO₄）_3-x（OH）_4x).Among the three actual minerals,kaolin performed the best in immobilizing calcium,while diasporic bauxite performed the poorest.And it was observed that the dosage of the reacting ores in actual minerals was the key factor affecting the effects.Increasing the dosage of gibbsite to 1.5 times to stoichiometry,a 91.3%of tungsten recovery could be obtained.In addition to increasing the dosage,the addition of stoichiometric water（H₂O）could obviously improve the effect of diaspore according to its reaction mechanism,with a tungsten recovery more than 88%obtained.To sum up,compared with the traditional caustic process,scheelite concentrate can be effectively decomposed with much less NaOH,a simpler separation path of tungsten from calcium impurities,no thermal treatment and atmospheric pressure by this novel process.And this process also provides an alternative application to act as calcium immobilization reagents for available aluminous minerals,like kaolin and bauxite.