Recovery of phosphate and ammonium as struvite from semiconductor wastewater

The recovery of phosphate (PO43−) and ammonium (NH4+) from fluoride-containing wastewater of semiconductor manufacturer was investigated in this study. Magnesium chloride (MgCl2·6H2O) was used as precipitation reagent. Effects of molar ratio and pH were examined. When at 1:1 stoichiometric ratio of [Mg2+]:[PO43−], 47.4% of PO43− was removed at pH 9. Removal efficiency of PO43− increased significantly with increased molar ratio, and it reached 92.1% as molar ratio increased to 3:1. Removal efficiency of ammonium increased as molar ratio of magnesium to phosphate increased from 1:1 to 2:1. However, removal efficiency of ammonium decreased when under higher molar ratio. The experimental results were in agreement with the model prediction using PHREEQC. Addition of excess ammonium to the wastewater is beneficial for struvite (MgNH4PO4) precipitation. The formations of struvite and bobierrite ((Mg)3(PO4)2·8H2O), as produced under different reaction conditions, were confirmed by SEM, EDS, XRD, and wet chemical analysis. The experimental results proved that removal and recovery of phosphate and ammonium from semiconductor wastewater is feasible.