REMOVAL OF PHOSPHATE AND AMMONIUM ION FROM DOMESTIC WASTEWATER USING CLAY FELDSPAR IN WUPA SEWAGE TREATMENT PLANT ABUJA

Abstract

ABSTRACT The aim of this study is centered on the sustainability of feldspar as an adsorbent as opposed to other clay minerals such as plastic clay, red clay and barite. BET analysis of the clay minerals considered in this study revealed that raw feldspar had the highest surface area and pore volume of 332.8 m2/g and 0.218 cc/g respectively. Similarly, the clay minerals were used in adsorption study with feldspar producing the best removal efficiency of 90.00 % and 73.96 % for ammonium and phosphate ions respectively. The BET results and the adsorption test showed that feldspar was a better adsorbent than the other adsorbents. Thermal activation of feldspar was carried out at temperatures of 500700℃ using muffle furnace. The BET results of the thermal activation revealed that feldspar activated at 600℃ has the highest surface area and pore volume of 533.9 m2/g and 0.272 cc/g respectively. The FT-IR results indicated that several functional groups were involved in the adsorption process of the phosphate and ammonium ions some of which were O-H, N-H and C-O groups. The SEM results showed that irregular-layered structures of the raw feldspar became smooth and regular after thermal activation. The effects of pH, adsorbent dosage, temperature, contact time and initial PO43- and NH4+ concentrations on the adsorption of phosphate ions and ammonium ions were investigated using atomic adsorption spectrocopy (ASS). The adsorption studies of phosphate ion and ammonium ion onto feldspar increased with contact time, adsorbent dosage and temperatures until optimum values were reached. The maximum adsorption efficiency of the activated feldspar for 4 mg/L phosphate ion and 15 mg/L ammonium ion solution amounted to 80.25 % and 90.89 % respectively with pH of 6.2, temperature of 30 ℃, adsorbent dose of 0.5 g and contact time of 30 min. Isotherm studies indicated that the Temkin model can well describe the adsorption process due to the high correlation coefficient (R2) values of 0.836, 0.6931 and 0.8685 at 30, 40 and 50 ℃ for phosphate ion removal and similarly 0.9221, 0.8483 and 0.9222 for ammonium ion removal. Kinetic studies revealed that the adsorption process was best fitted to the pseudo-second order kinetics with high R2 values ranging from 0.9958-0.99875 and 0.985-0.9997 for phosphate ion and ammonium ion removal respectively. The thermodynamic studies showed that the reactions were spontaneous and exothermic in nature due to the increasing negative values of the free energy (ΔGo), the positive values of the entropy (ΔSo) and the negative values of the enthalpy (ΔHo).