4369168 Regeneration of carbon employed in the wet process production of alkali metal phosphates

Abstract

In a process for regenerating the activated carbon and in the purification of brown phosphoric acid or alkali phosphates obtained via the so-called wet process employing mineral acid digestion of crushed phosphate rock, the activated carbon used to filter brown H3 PO4 is removed from service, washed with water, the initial washings being recovered to reclaim phosphoric acid, and then steeped in a basic aqueous solution, e.g., aqueous alkali hydroxide, alkali carbonate, ammonium hydroxide, loweralkyl amines or loweralkanol amines. After again water washing the activated carbon, to remove residual base, the activated carbon is either returned to service or steeped in an aqueous solution of mineral acid, e.g., sulfuric, hydrochloric, or nitric acid, again washed with water to remove residual acid and returned to service. Usually, the acid steep need not be employed with every base cycle to maintain good decolorization, although if desired the acid steep can be used with each caustic cycle.