METHOD FOR RECOVERY OF AQUEOUS WASH IN PHOSPHATE CHEMICAL CONVERSION AND APPARATUS FOR METAL SURFACE TREATMENT

摘要

This invention is related to a method for recovery of aqueous wash in a phosphate chemical conversion of a shaped metal product involving carrying out chemical conversion and subsequent cleaning with water, wherein said cleaning with water is performed in one or more stages and comprises a step of withdrawing aqueous wash from a first cleaning stage and adjusting the pH of the wash with at least one acid selected from the group consisting of phosphoric acid, nitric acid, hydrofluoric acid, hydrosilicofluoric acid and fluoroboric acid, a step of treating said pH-adjusted aqueous wash with a first reverse osmosis membrane to separate it into a first filtrate and a first concentrate, and a step of neutralizing said first filtrate with an alkali and treating the alkali-neutralized filtrate with a second reverse osmosis membrane to separate it into a second filtrate and a second concentrate, said first concentrate being recycled for said phosphate chemical conversion, said second filtrate being recycled as aqueous wash for said aqueous cleaning, and said second concentrate being discarded from the system.