Recovery of aluminum alum from waste anode-oxidizing solution

Recovery of aluminum alum (aluminum ammonium sulfate) by crystallization fr om waste anode-oxidizing solution in the aluminum surface finishing industr y was investigated in this study. Effects of various operating conditions i ncluding the mole ratio of ammonium hydroxide and aluminum ion, temperature and seed alum dosage on the aluminum alum formation, acid recovery and alu minum ion removal were examined. Both one- and two-step processes of crysta llization were employed in synthesizing the aluminum alum and in the meanti me in reducing the aluminum ion concentration in the waste anode-oxidizing solution. Based on the test results, optimum operating conditions were reco mmended for efficient operation of the crystallization process. The residua l acid solution after crystallization was found suitable for reuse in the a node-oxidizing process. (C) 1998 Elsevier Science Ltd. All rights reserved.