Flotation separation of strontium via phosphate precipitation

摘要

Flotation separation of strontium (Sr) from wastewater via phosphate precipitation was investigated. While 37.33% of Sr precipitated at highly alkaline pH in the absence of PO43-, it completely precipitated as Sr-3(PO4)(2) at a molar ratio ([ PO43-]:[Sr2+]) of 0.62 at a lower pH value. The presence of Ca2+ hindered Sr precipitation, yet it could be overcome by increasing the PO43- dose. Sodium dodecyl sulfate (SDS) was a better collector for dispersed air flotation of Sr-3(PO4)(2) than cetyl trimethyl ammonium bromide, or mixed collector systems of SDS and saponin. The highest separation efficiency of 97.5% was achieved at an SDS dose of 40 mg/L. The main mechanism in the precipitate flotation is adsorption of anionic SDS on the positively charged surface of colloidal Sr-3(PO4)(2) via electrostatic interaction. SDS enhanced the aggregation of Sr-3(PO4)(2) precipitates as the size increased from 1.65 to 28.0 mu m, which was beneficial to separation as well.