Coprecipitation of phosphate with calcite

Abstract

The mechanism of phosphate coprecipitation with calcite is proposed on the basis of homogeneous distribution of phosphate in the crystal at 20°C and pH 7.9-9.5. At a constant pH, phosphate content of calcite is proportional to total phosphate concentration in aqueous solution. PO^3-₄ ions are uptaken into the calcite lattice, where 3 CO^2-₃ ions are replaced by 2 PO^3-₄ ions in aqueous solution, as described by the ion exchange equilibrium: 3(CO^2-₃)_S + 2(PO^3-₄)_L ↔ 3(CO^2-₃)_L + 2(PO^3-₄)_S where S and L represent calcite and aqueous solution, respectively.