Electroflotation of precipitated phosphate from synthetic solution

The phosphate recovery from a 20 mg L-1 Na2HPO4 solution through precipitation with Ca(OH)2 followed by electroflotation was evaluated. X-ray diffraction and particle size measurements indicated that the precipitates were a mixture of hydroxyapatite and calcium-deficient hydroxyapatite, with size ranging from 3 to 10 mm. Electroflotation with Na-oleate as surfactant was used to recover the precipitates. The surfactant adsorption was evaluated through zeta potential measurements. The influence of Na-oleate concentration, pH and bubble size on phosphate recovery was investigated. In the absence of Na-oleate, a phosphate recovery of 50% was achieved, while in the presence of 20 mg L-1 of Na-oleate it was increased to 90%, at pH 11. The phosphate recovery also increased with Ca(OH)2 concentration increase and bubble size decrease, reaching 100% at 300 mg L-1 Ca(OH)2 and bubble size around 39 μm.