Recovery of phosphorus and aluminum from spent acid from the bright-dip aluminum finishing process

摘要

In the process of the invention spent phosphoric acid is concentrated and stripped with air to a greater than 50% P2O5 concentration to remove nitric acid. As a result of concentrating the spent acid a portion of the aluminum precipitates as monoaluminum phosphate, which is recovered by filtration. The filtrate is then ammoniated to produce a monoammonium phosphate solution. The solids precipitated during ammoniation and comprising aluminum ammonium phosphate which contains other metal phosphates are washed and reacted with aqueous ammonia to form diammonium phosphate.