ELUTION BEHAVIOR OF DEPHOSPHORAZATION SLAG TO VARIOUS ACIDS AND EFFECT OF ADDITION OF AQUEOUS ALKALI TO ACID ELUATE

We recently developed a method for efficiently recovering phosphoric acid from dephosphorization slag. The most important processes in this recovery technique involve elution of the dephosphorization slag into an acid solution (acid-elution process) and the addition of an alkali to the acid eluate to form a precipitate (alkali-precipitation process). Ultimately, we settled the use of an aqueous nitric acid solution for the acid-elution step, while an aqueous ammonia solution proved to be the optimal choice to accomplish alkali precipitation. Herein, we describe the procedures used to compare the utility of nitric acid with that of hydrochloric acid, sulfuric acid, and citric acid in the acid-elution process, and describe our comparison of an aqueous sodium hydroxide with that of an aqueous ammonia in the alkali-precipitation process. Finally, we summarize our findings on the acids and alkalis that proved to be suitable for this technology.