It is mainly aimed at the disposal of washing water and mother liquor in the production process of ternary precursor and ferric phosphate precursor, as well as the treatment of high salt wastewater such as fluoride waste gas absorption solution in electrolyte. This process has the advantages of low comprehensive treatment cost and high impurity removal rate, and the obtained by-products such as sodium sulfate, ammonium sulfate, monoammonium phosphate and ammonium chloride are of high quality and can produce a large profit.