Reclamation of phosphate from bright dip drag-out

Abstract From the Canadian patent

Rinse acid collected from an aluminum bright dipping operation is reacted with soda alkalies at 80°C or higher to yield a solution of trisodium phosphate Na3PO4, sodium aluminate, NaAIO2, sodium nitrate NaNO3, and trace, insolubles. The hot solution is quickly filtered to remove all insoluble impurities and then cooled so that the trisodium phosphate crystallizes out which after filtering, leaves a mother liquor containing some remaining trisodium phosphate and soluble impurities, namely sodium aluminate, and sodium nitrate. The mother liquor is then recycled repeatedly with further batches of rinse acid to maximize the phosphate recovery. i.