Sodium tungstate solution containing high impurities should be purified.
Purification of Sodium Tungstate Solution with High Impurities
Sodium tungstate solution out of sodium phosphate decomposition of scheelite contains high impurities. To solve this problem, the purifying effects of fluoride (F), phosphorous (P), silicon (Si) and arsenic (As) by basic magnesium carbonate was studied. Effects of basic magnesium carbonate dosage, pH value, reaction temperature, reaction time on impurities purifying were researched. The removal mechanism of impurities was also researched.
The results showed that when the dosage of basic magnesium carbonate was controlled under the following conditions (Mg/F=0.56 with pH value, reaction temperature and reaction time respectively as 9 and 90°C and 180 min), the removal rates of fluoride and phosphorous can reached more than 95% and that of arsenic and silicon reached 36% and 72%. The impurities of sodium tungstate solution can be purified to: ρF≤0.3 g/L, ρp≤0.006 g/L, ρAs≤0.02 g/L, ρSi≤0.11 g/L. Analysis showed fluoride reacted with basic magnesium carbonate to form NaMgF3.
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