Sodium tungstate crystal may be prepared by the crystallization of sodium tungstate solution.
Removal of Arsenic and Silicon from Sodium Tungstate Solution by Crystallization
The removal of arsenic and silicon from impure Na2WO4 solution was investigated by crystallization using the liquors (m(As)/m(WO3)=0.32×10-3~2.94×10-3, m(Si)/m(WO3)=1.26×10-3~5.84×10-3) from middle-grade mixed wolframite and scheelite concentrate decomposed with NaOH by mechanical activation and tungsten residue leached by traditional digestion. The influences of the crystallization ratio and the addition of Al2O3 on removing impurities of As and Si were investigated.
It was concluded that the results of removing impurities are related with the crystallization ratio of sodium tungstate and higher than 90% of removal ratio of arsenic and silicon can be obtained under the conditions of 80%~90% of Na2WO4 crystallizing ratio. High quality Na2WO4solution can be reached and the values less than 3.50×10-5 for m(As)/m(WO3) and 3.56×10-4 for m(Si)/m(WO3) in the pure Na2WO4 solution can be obtained for the impure Na2WO4 solution containing 3.21×10-4 of m(As)/m(WO3) and 2.41×10-3 of m(Si)/m(WO3).
It was also found that the addition of aluminum oxide can improve the process and better results can be obtained when Al2O3 was activated by chemical method. Under the same conditions the removal ratio of arsenic and silicon can be increased from 88.48% to 94.65% and from 89.77% to 97.74% respectively compared with no Al2O3 addition.
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