PRODUCTION OF ALUMINA GEL USING SURFACE-TREATMENT WASTE WATER OF ALUMINUM MATERIAL AND PRODUCTION OF CRYSTALLINE ALUMINUM HYDROXIDE

摘要

PROBLEM TO BE SOLVED: To obtain alumina gel scarcely containing harmful sulfate radical from a sludge formed by the neutralizing treatment of waste liquid by treating the sludge under high pH condition to get a gelatinous aluminum hydroxide. ;SOLUTION: An Al-containing alkaline and/or acidic waste water produced by the surface-treating process of an Al material composed of Al or an Al alloy is neutralized to pH5-9, the produced sludge of gelatinous aluminum hydroxide is coagulated and precipitated, the clear neutral supernatant is treated as drainage water and the concentrated liquid having high impurity content is subjected to a high pH treatment by adjusting the pH of the solution to ≥9.0, preferably 9.4-11.0 by the addition of sodium hydroxide. The content of the residual sulfate radical in the sludge produced by the solid-liquid separation is remarkably reduced and becomes almost zero at pH9.4. The content of Na remaining after the water-washing treatment increases at pH11.0 or over. The separated solution is disposed as the drainage and the recovered cake-formed or extremely viscous sludge is repeatedly subjected to the similar operation.;COPYRIGHT: (C)1997,JPO