Phosphate microbial mineralization removes nickel ions from electroplating wastewater

Nickel ions in electroplating wastewater can be removed by the bio-mineralization method. Bacillus subtilis can produce alkaline phosphatase, which hydrolyzes organophosphate monoesters and produces phosphate ions. Fourier-transform infrared spectroscopy (FTIR) showed that the precipitated material contains phosphate ions. X-ray diffraction (XRD) showed that nickel ions in electroplating wastewater react with Bacillus subtilis and organophosphate monoesters to obtain nickel phosphate octahydrate (Ni3(PO4)2·8H2O). The removal efficiency of nickel ions could reach 76.41% with the optimum content of the organophosphate monoester (0.02 mol), Bacillus subtilis powder (2 g), pH (6), standing time (36 h), and reaction temperature (25 °C) in the medium solution (100 mL). The average particle size of Ni3(PO4)2·8H2O was 80.51 nm, which was calculated by the Scherrer formula. The Lorentz–Transmission Electron Microscope (L-TEM) further showed that Ni3(PO4)2·8H2O was composed of clusters of irregular nanoparticles, and the individual particle size was in the range of 40–90 nm. The TGA curve shows that the mass loss of crystal water was 25.45%, which was close to the theoretical total mass loss of 28.24% in bio-Ni3(PO4)2·8H2O.