Electroflotation of precipitated phosphate from synthetic solution

Abstract

-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.

Impact of pH and Ionic Molar Ratios on Phosphorous Forms Precipitation and Recovery from Different Wastewater Sludges

“…However, it led to the recovery of alternative precipitates, rich in ACP. Results showed great potential for ACP precipitation using Ca(OH) 2 :P, where recovery reached 99% at pH = 9.5, which, considering an initial Ca:P ratio of 1.95, was a result fully consistent with previous literature [59,60]. At pH below 9, recovery of 89.5% was achieved.…”

“…Although studies showed that calcium phosphate minerals could be utilized as fertilizers as well, these turned out not to be as efficient as pure struvite [64], as their P-available content in soils was lower than the latter but was still acceptable [65]. Calcium phosphate compounds are also difficult to settle [60,66]. ACP, in time, will be transformed to more stable forms, such as hydroxyapatite (HAP).…”