Investigation of sorption of Hg(II) ions onto coconut husk from aqueous solution using radiotracer technique

Abstract

Summary The sorption of Hg(II) ions onto coconut (Cocos nucifera) husk has been studied using radiotracer technique. Maximum sorption (96) of Hg(II) ions (7.39×10-6M) onto sorbent surface is achieved from 10-3M HNO3 solution in 30min agitation time using 100mg of coconut husk. The sorption data follow the Freundlich and Dubinin–Radushkevich (D–R) isotherms. Sorption capacity (6.84 ± 0.45 mmol g-1) and sorption energy (10.6 ± 0.13 kJ mol-1) have been evaluated using these isotherms. Among the ions tested to monitor their influence on the sorption, Ba(II), fluoride and tartarate increased the sorption, while thiosulfate, bromide and thiocyanate reduced (< 63 > 26) the sorption. The cations K(I), Ce(III), Cr(III), Fe(III) and Zr(IV) partially suppressed the sorption. The variation of sorption with temperature yields thermodynamic parameters ΔH = -37.42 kJ mol-1 ΔS = -1057J mol-1K-1 and ΔG = -2.58 ± 0.05 kJ mol-1 at 298 K. The negative values of enthalpy and free energy reflect the spontaneous and exothermic nature of sorption, respectively. The selectivity studies of sorbent show that the coconut husk column can be used to separate Hg(II) ions from Se(IV), Zn(II), I(I) and Tc (VII). The sorbent has a potential in radiochemistry to separate gamma energies of 203Hg (279 keV) from 75Se (265 and 280 keV).