TREATMENT OF CONCENTRATED WASTE LIQUID FROM BOROFLUORIDE BATH

PURPOSE:To eliminate pollutional problems and to perform efficient treatment of waste liquid by feeding back supernatant liquid or filtrate generated by the reaction between concentrated waste liquid of fluoride and solution of treating chemical for the dissolution of said treating chemical. CONSTITUTION:CaF and CaSO4 are settled and withdrawn from the bottom of a decantor 3, filtered with a filter press 6 and discharged in the form of solid product. On one hand, the filtrate contg. F from the filter press 6 is stored in a tank 5. The supernatant liquid contg. F in the decantor 3 is transferred through a valve 4 and is stored in the tank 5 together with the above described filtrate. The filtrate and the supernatant liquid stored in the tank 5 are fed back to a slaked lime tank 7 and an aluminum sulfate tank 8, and is used as a solvent for dissolving each chemical. Obtd. solution is transported to a reaction tank 2 where it is allowed to react with the concentrated liquid from a concentrated liquid tank 1.