Regeneration of alkali leaching solution through precipitation using calcium hydroxide

Sodium hydroxide (NaOH) is known to be capable of selectively leaching phosphorus from oolitic iron ores. The main limitation on implementing this leaching approach is the expense of NaOH. In order to make sodium hydroxide leaching practical, a method is needed for removing the dissolved phosphorus from solution and inexpensively regenerating the sodium hydroxide. In this work, removal of phosphorus from solution was achieved using calcium hydroxide (Ca(OH)2), which is significantly less expensive than NaOH. The addition of Francolite seed crystals greatly accelerates the precipitation rate. Up to 99.9% of phosphorus in solution was removed within thirty minutes. A leaching comparison between fresh and regenerated caustic solution was performed, with removal rates of 51.9% and 52.2% respectively, demonstrating that the regenerated leaching solution was still effective for removing phosphorus.