Electroflotation of precipitated phosphate from synthetic solution

S G Da Cruz,A J B Dutra,M B De M Monte

doi:10.1590/0104-6632.20170343s20160040

S G Da Cruz, A J B Dutra + Show 1 more

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https://doi.org/10.1590/0104-6632.20170343s20160040

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Abstract

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 μm. 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.

Highlights

Industrial and agricultural expansion currently demands a growing exploitation of phosphorus sources in the environment to supply human needs
According to some authors (Abbona et al, 1986; Musvoto et al, 2000; Liu et al, 2009), hydroxyapatite precipitation starts at pH> 5; the precipitation reaction kinetics is not favored and other species, such as amorphous calcium phosphate, octacalcium phosphate and brushite, act as precursors of the hydroxyapatite precipitation
Gray and Schwab (1993) reported that calcium phosphate precipitation is almost complete at pH values higher than 9.8

Summary

Introduction

Industrial and agricultural expansion currently demands a growing exploitation of phosphorus sources in the environment to supply human needs. This wide utilization of phosphates leads to a considerable amount of phosphorus-containing wastes being discharged into water bodies, demanding previous treatment to avoid eutrophication. Aluminum and iron salts present the disadvantage of generating sludge, which cannot be reused or reclaimed (Urano and Tachikawa, 1991). This problem does not occur with calcium salts, as they react with phosphate to generate precipitates such as hydroxyapatite, monetite, brushite and amorphous calcium phosphate, among others, which are compounds normally

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