Recovery of phosphate from surface waters using a calcium silicate composite material for potential application in environmental remediation

M.J. Cairns, C. Krauss, J.H. Johnston
Victoria University of Wellington, NZ

Keywords: phosphate, adsorption, recovery, calcium, silicate


In many locations, contamination of surface waters by phosphate due to agricultural run-off is becoming a major environmental concern. Currently, there are no effective means for its removal, due to the low phosphate concentration (< 1 mg P/ L) in the run-off waters and the requirement for a low-cost process due to the large volume of water which requires treatment. We propose the use of a novel nano-structured calcium silicate material as suitable for such remediation work. The nano-structured calcium silicate used is a proprietary material developed within our group. It is inexpensive to prepare and provides a desirably high surface area with chemically active calcium ions readily accessible on the particle surface. Phosphate is rapidly adsorbed by the material, forming brushite (CaHPO4.2H2O) within the pores of the silicate. Modification of the sorbent with magnetic centres facilitates the removal of the spent sorbent and allows for its recovery and re-use as a possible fertiliser. The material is able to rapidly remove 90% of the phosphate from 0.3 mg P /L solution, with the rate of uptake adjustable by altering the calcium content of the silicate during its preparation.