Study on the defluorination process of lithium hexafluorophosphate by-product ammonium chloride based on chemical-flocculation precipitation method
The fluorine-containing absorption solution produced by the ammonium chloride pretreatment device of lithium hexafluorophosphate was used as the treatment object,and the calcium source and flocculant polyacrylamide(PAM)were added to defluorinate the solution by the chemical-flocculation-precipitation method.The influences of calcium source,pH,reaction temperature,stirring time and other factors on the defluorination effect of the absorption solution were investigated.The interaction and significance of the influencing factors were analyzed by response surface tests,and the defluorination process parameters were optimized.The results show that under the same flocculation conditions,the influences on the defluorination effect were in the following order:pH>CaCl2 input>reaction tempera-ture>stirring time.The optimal defluoridation conditions were 113%CaCl2 input(compared with the theoretical amount of CaCl2 required for defluoridation),pH=7.1,reaction temperature 50℃,stirring for 55 min,and the residual fluoride concentration in the absorbent under the optimal conditions was 3.73 mg/L.
chemical precipitation methodflocculation precipitation methodammonium chloridedefluorinationresponse surface testabsorbing liquidpolyacrylamide
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