Low-temperature calcination of “C”-grade phosphate from christmas island

Abstract

Christmas Island in the Indian Ocean possesses large reserves of a “C”-grade phosphate ore which is unsuitable for normal fertiliser production on account of its extremely high iron and aluminium content. The phosphate of this material occurs in the form of crandallite and millisite, rather than apatite. Although this ore is of little agronomic value in its raw state, low-temperature calcination at approximately 450°c results in degradation of the mineral lattice with enhanced solubility of the phosphate content. Chemical extraction tests and pasture growth trials on Papatoetoe silt loam have shown that the calcined product compares favourably to superphosphate as a source of fertiliser phosphorus.