The removal of arsenic and silicon from impure Na 2WO 4 solution was investigated by crystallization using the liquors
( m (As)/ m (WO 3)=0.32×10 -3 ～2.94×10 -3 , m (Si)/ m (WO 3)=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 Al 2O 3 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 Na 2WO 4 crystallizing ratio. High quality Na 2WO 4 solution can be reached and the values less than 3.50×10 -5 for m (As)/ m (WO 3) and 3.56×10 -4 for m (Si)/ m (WO 3) in the pure Na 2WO 4 solution can be obtained for the impure Na 2WO 4 solution containing 3.21×10 -4 of m (As)/ m (WO 3) and 2.41×10 -3 of m (Si)/ m (WO 3). It was also found that the addition of aluminum oxide can improve the process and better results can be obtained when Al 2O 3 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 Al 2O 3 addition.