Production of Liquid Alum from Aluminum-Anodizing Sludges

• Published in: Water science and technology Vol. 17; no. 4-5; pp. 541 - 550
• Main Authors: Saunders, F M, Harmon, C B
• Format: Journal Article
• Language: English
• Published: London IWA Publishing 01.01.1985
• Subjects: Alum; Aluminium; Aluminum; Aluminum oxide; Aluminum sulfate; Anodizing; High temperature; Reclamation; Sludge; Sludge solids; Sulfuric acid; Sulphuric acid
• ISSN: 0273-1223; 1996-9732
• DOI: 10.2166/wst.1985.0158

Wastewaters from the aluminium anodizing industry were usually treated by neutralization, conditioning with polymer, and gravity sedimentation, giving a clear effluent suitable for re-use or discharge, and a sludge that might be thickened and dewatered for land disposal. The feasibility of recovering liquid alum (aluminium sulphate) from these sludges, by batch extraction with sulphuric acid at high temperature (100C) was investigated. Sludges from 2 different plants were used in the experiments; the processes used in these plants, the treatment of the wastewaters, and the characteristics of the sludges produced, are summarized in tables. Acid extraction of the sludges was rapid and complete within about 45 minutes, and production of commercial-strength liquid alum could be achieved with dewatered sludges containing 15.5-16.8 per cent inert solids. To obtain this concentration of inert solids, a minimal dry solids content of 21-24 per cent would be required, and improved sludge dewatering would, therefore, be necessary for this process to be commercially viable.