Magnesium phosphate crystallization in a fluidized-bed reactor: Effects of pH, Mg:P molar ratio and seed

The effects of influent pH, the magnesium:phosphate (Mg:P) molar ratio, seed type and inorganic ions (F−, SO42- and NO3-) on phosphate removal were investigated in a fluidized-bed reactor (FBR). Environmental scanning electron microscopy (ESEM), X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDS) were used to characterize the products collected from the FBR. Experimental results show that pH and the Mg:P molar ratio played significant roles in phosphate removal. Increasing the influent solution pH from 10 to 12 increased the final phosphate removal from 55% to around 100%. At influent solution pH of 8, increasing the Mg:P molar ratio from 1 to 1.5, and 2 raised the phosphate removal as well to 17%, 28% and 34%, respectively. The seed used and its presence had an effect on the initial phosphate removal rate. Phosphate removal efficiencies were 86%, 88% and 93% for the unseeded FBR, the FBR seeded with calcium phosphate and the FBR seeded with magnesium phosphate, respectively. The inorganic ions in simulated thin film transistors-liquid crystal display (TFT-LCD) wastewater did not significantly impact the phosphate removal. The XRD analysis confirmed that several magnesium phosphate species formed in all FBR experiments.