The influence of competitive inorganic ions on phosphate removal from water by adsorption on iron (Fe+3) oxide/hydroxide nanoparticles-based agglomerates

Phosphate removal from water solution by using iron (Fe+3) oxide/hydroxide nanoparticles-based agglomerates (AggFe) suspension was investigated for efficiency and cost- effectiveness. The influence of inorganic ions (HCO−3, Cl−, and SO4−2) that are usually present in municipal and industrial wastewater on the adsorption process is reported here. The adsorption properties of the adsorbent were investigated in solutions containing different inorganic ions concentrations at different pH levels. A strong concentration effect of the used AggFe, HCO3 and pH level of the purified water solution on removal efficiency was shown. It was found that phosphate adsorption onto the AggFe suspension may be described by pseudo-second order reaction kinetics and the Langmuir isotherm model. The rate-limiting step of phosphate adsorption onto AggFe suspension may be described by intra-particle diffusion of ions onto and within the adsorbent. The unique adsorption properties of synthesized AggFe adsorbent are demonstrated. This technique achieved a residual phosphate concentration of less than 0.1 ppm as PO4 also at high concentration (500 ppm) of the competitive HCO3 ion, which is acceptable by water quality regulations. The phosphate adsorption capacity on the AggFe at pH level of solution at pH 7.5 and an equilibrium concentration of 0.1 ppm as P was compared with reported results and are about 1.5 times higher than these values for granulated ferric hydroxide (fraction < 63 μm) for pH level 5.5, and more than one order of magnitude higher than other values reported in the literature. It was shown that Cl− and SO4−2 ions had no significant effect on the phosphate adsorption kinetics.