Patent ID: 6955796

Claim:
A process for recovering phosphorus from an aqueous sludge that contains elemental phosphorus and rendering the residue non-hazardous comprising (A) separating said sludge into (1) a slurry of water containing suspended phosphorus and dirt particles; and (2) coarse solids; (B) adding a flocculating agent to said slurry to settle said suspended phosphorus and dirt particles; (C) recovering said settled phosphorus and dirt particles from said water; (D) heating said recovered phosphorus and dirt particles to melt elemental phosphorus therein; (E) adding a coalescing agent to said heated phosphorus and dirt particles to coalesce said melted phosphorus particles; (F) separating said melted elemental phosphorus from said dirt particles; (G) mixing said coarse solids from step (A) with hot water to melt phosphorus sludge therein; (H) separating melted phosphorus sludge from coarse inert solids; (I) reacting said melted phosphorus sludge with chromic acid, whereby elemental phosphorus therein separates from water and solids and forms a separate phase; (J) recovering said separated elemental phosphorus phase; (K) adding reducing agent to said water and solids from step (I) to reduce Cr +6 to Cr +3 ; and (L) adding alkali to said water and solids from step (K) to convert any residual elemental phosphorus into compounds of phosphorus.