Flotation separation of strontium via phosphate precipitation.

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 PO4 3- , it completely precipitated as Sr3 (PO4 )2 at a molar ratio ([PO4 3- ]:[Sr2+ ]) of 0.62 at a lower pH value. The presence of Ca2+ hindered Sr precipitation, yet it could be overcome by increasing the PO4 3- dose. Sodium dodecyl sulfate (SDS) was a better collector for dispersed air flotation of Sr3 (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 Sr3 (PO4 )2 via electrostatic interaction. SDS enhanced the aggregation of Sr3 (PO4 )2 precipitates as the size increased from 1.65 to 28.0 μm, which was beneficial to separation as well.