Recovering sodium aluminate solution from an aluminium etchant bath - to use as phosphate precipitating agent in clarifying plant

摘要

An EO etchant bath is directly connected to an E6 etchant bath for decorative surface etching of aluminium surfaces, the EO bath being used to remove oxide layers from ancillary electrodes and frames. Either continuously or at intervals the EO bath soln. with comparatively high sodium hydroxide and low aluminium concentration is fed into the E6 bath. Additionally rinsing water from the rinser following the EO etchant bath is fed back into the EO bath and E6 solution is removed to ensure that the concentration of dissolved aluminium does not exceed a critical value. ADVANTAGE - The etching process is controlled whilst the removed solution of sodium aluminate is used to precipitate phosphate out of water in a purifying plant.