Kinetics and morphology analysis of struvite precipitated from aqueous solution under the influence of heavy metals: Cu2+, Pb2+, Zn2+

The present study examined the influence of metal ions (Cu2+, Pb2+, and Zn2+) on kinetics and morphology of struvite precipitated from aqueous solutions containing equimolar ratios of struvite components: Mg2+, NH4+, PO4-3. Kinetics of the struvite precipitation in the presence of metal ions [0,1, 10, 50 and 100 ppm] was evaluated through the change of pH of the precipitating solution. The kinetic evaluation demonstrated that the precipitation satisfactorily followed the first-order kinetic with respect to Mg2+. It was found that for the three metal ions tested, the higher the concentrations of the metal ions: 0, 1, 10, 50, 100 ppm, the less the crystals obtained and the lower the rate constants. Depending on the concentrations of the metal ions added into the solution, the rate constants varied from 4.344 to 1.056 h(-1) which agree with most published values. It was postulated that the metal ions were adsorbed onto the surface of the crystals and hence retarded the growth. The crystals obtained were characterized using SEM-EDX and XRPD Rietveld. The characterization revealed that the precipitates were mainly struvite of various sizes (between 10 and 60 pm) with sylvite as impurities. It is envisaged that the present study would add to the understanding of the removal of metal ions from industrial wastewater through struvite precipitation.