Equilibrium biosorption isotherm for lead ion on chaff

A new adsorbent system for removing lead ion from aqueous solutions has been investigated. This new adsorbent is cereal chaff, an agriculture product in middle-west region in China. Variables of the system include biosorption time, chaff dose and solution temperature. The experimental results were fitted to the Langmuir, Freundlich, Koble-Corrigan and Temkin model isotherms to obtain the characteristic parameters of each model. Both the Langmuir and Koble-Corrigan isotherms were found to best represent the measured biosorption data. According to the evaluation using the Langmuir equation, the maximum biosorption capacities of lead ion onto chaff was 12.5 mg g−1 at 293 K. Using the thermodynamic equilibrium coefficients obtained at different temperatures, various thermodynamic parameters, such as ΔG0, ΔH0 and ΔS0, have been calculated. The thermodynamics of lead ion-chaff system indicates spontaneous and exothermic process. It was concluded that an increase in temperature result in a lower metal loading per unit weight of the chaff.