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| Isotherm studies on biosorption of As(III) and Hg(II) ions from aqueous solution using cellulosic biosorbent derived from Okra (Abelmoschus Esculentus) stem. |
Amadi, O.K., Odidiozor, C.J., Okoro, I.A.
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Abstract:
An effective biosobent was developed from cellulosic biosorbent produced from Okra stems and their various biosorption characteristics were studied for removal of toxic metal ions As(III) and Hg(II) from their aqueous solutions. A series of experiments were conducted in a batch system to assess the effects of the system variables such as pH, initial metal ion concentration and temperature. The biosorbent studied exhibits high efficiency for the metal ions adsorption. The equilibrium adsorption data were analyzed by the Langmuir, Freundlich, Temkin and Dubnin-Rudishkelvish isotherm models. The equilibrium data indicates the following order to fit the isotherms: Freundlich is greater than Temkin is greater than Dubin-Radushkelish is greater than Langmuir. The maximium adsorption capacity Hg(II) and As(III) ions were found to be 6.180 mg/g and 7.930 mg/g, 0.802 mg/g and 14.104 mg/g for UOS and MOS respectively. It is also found that unmodified okra stem showed maximum adsorption for Hg2+ at pH 6 ( 9.918 mg/g) and pH 8( 9.9938 mg/g). Also As(III) ions showed maximum adsorption at pH 4(9.6816) for unmodified and pH 8( 9.9954 mg/g) for modified okra stem. Different thermodynamic parameters, like Gibbs free energy (?G), enthalpy (?H) and entropy (?S) of the adsorption process have also been evaluated. The thermodynamic parameters of As(III) and Hg(II) ions biosorption indicated, the process was spontaneous and endothermic. The results showed in percent mean value of sorption for As(III) and Hg(II) ions as 99.37 % and 99.96 % for neat Okra cellulosic biosorbent, and 99.95 % and 99.96 % for modified Okra cellulosic biosorbent. These results showed that the neat material can be effective without introducing any new chemical substances to the environment through the modification exercise. The results indicated that the biosorbent studied was found to be a promising alternative for the adsorption of As(III) and Hg(II) ions from aqueous solution. The sorption affinity for the two metal ions studied showed As(III) > Hg(II).
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