Application of coconut coir pith for the removal of sulfate and other anions from water

Activated carbon was developed from coconut coir pith using ZnCl2 and investigated to assess the possible use of this adsorbent for the removal of sulfate from water. The influence of various parameters such as agitation time, sulfate concentration, adsorbent dose, pH and temperature has been studied. Equilibrium adsorption data followed both Langmuir and Freundlich isotherms. The Langmuir adsorption capacity (Qo) was found to be 4.9 mg/g. Adsorption followed second-order rate kinetics. The per cent adsorption was maximum in the pH range 3.0–9.0 (90–54%) and desorption was higher at pH 2.0 (58–74%) and pH 11.0 (83–97%) for different concentrations of sulfate used in this study. pH effect and desorption studies showed that ion exchange and chemisorption mechanisms were involved in the adsorption process. ΔG0 was found to be –25.8, –26.2, –27.5 and –28.8 kJ/mol at 35, 40, 50 and 60EC, respectively. ΔS0 and ΔH0 of adsorption were found to be 132.7 J/K/mol and 15.4 kJ/mol, respectively. Effects of foreign ions on the adsorption of sulfate have been investigated. Removal of sulfate from synthetic ground water was tested. The Langmuir adsorption capacity of other anions such as nitrate, phosphate, vanadate, molybdate, thiocyanate and chromate was also investigated. Results showed that ZnCl2 activated coir pith carbon was effective for the removal of sulfate and other anions from water.