Sodium tungstate dihydrate may be prepared by different methods such as alkaline hydrolysis, crystallization, extraction, soda solution pressure cooking, and so on.
Alkaline Hydrolysis to Prepare Sodium Tungstate Dihydrate
Step 1: Wolframite ore is crushed to 320 mesh, and alkaline hydrolysis is carried out in reactor with 30% caustic soda. The reaction equation is as follows:
MnWO4?FeWO4+4NaOH→2Na2WO4+Fe(OH)2?Mn(OH)2
Step 2: The reaction product obtained in step 1 is reacted with calcium chloride to obtain calcium tungstate. The reaction equation is as follows:
Na2WO4+CaCl2→CaWO4+2NaCl
Step 3: Hydrochloric acid is added into the calcium tungstate obtained in step 2 to generate tungstic acid. The reaction equation is as follows:
CaWO4+2HCl→CaCl2+H2WO4
Step 4: The tungstic acid obtained in step 3 is reacted with caustic soda to form sodium tungstate. The reaction equation is as follows:
H2WO4+2NaOH→Na2WO4?2H2O
After evaporation, crystallization, centrifugation, dehydration and drying, the sodium tungstate product is obtained.
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