Phosphorus removal by a synthetic iron oxide-gypsum compound

Phosphorus pollution is a major concern for soil and water management. This study assesses the phosphate and organic phosphorus removal capacity of an iron oxide-gypsum compound (named OX) in batch trials. Phosphate solutions ranging from 0.001 to 10 mg P l(-1) were tested and OX proved to be an effective fixing agent. Solutions with different ionic strengths did not affect this reactivity. Phosphate removal was not altered by pH values between 4 and 8, but increased significantly with higher values. Near-completion of this reaction was observed after some minutes. The combined effects of precipitation with calcium (gypsum) and sorption onto the oxide explain these interesting properties. The phosphate removal capacity was demonstrated on field samples. The compound also promoted the hydrolysis of a model organic phosphorus molecule. Contact of OX with solutions with pH values between 4 and 10 did not alter its stability but caused pH levelling to neutral values. Other secondary effects involve sulfate and calcium release. OX reactivity with different phosphorus species under various conditions is interesting for application to water and soil remediation processes aiming to control phosphorus pollution. (C) 1999 Elsevier Science B.V. All rights reserved.