Abstract

The removal of Zn²⁺ from dilute aqueous solution using maize (Zea mays) wrapper as the biosorbent is reported in this paper. Batch experiments were carried out to assess biosorption kinetic and equilibrium behaviour of Zn²⁺ by varying parameters such as pH, contact time and initial metal ion concentration at 27ºC. The analysis of residual metal ions was determined using atomic absorption spectrophotometer. The pH study shows that the initial pH would play a vital role in the biosorption of the Zn²⁺ from solution. The optimum pH obtained was in the range pH 5 - 7, therefore pH 6 was used for other studies. The kinetic study shows that uptake of Zn²⁺ increased with time and that maximum biosorption was obtained within 60 min of the process. The result obtained showed that the pseudo-first order model correlated with the experimental data better than the pseudo-second order model examined in this study. Freundlich and Langmuir isotherm models were used to analyse the experimental data of the biosorption process. The Freundlich and Langmuir equations obtained are   log Г = 0.643 log C_e + 1.1177 and 1/Г = 0.0411/C_e + 0.009, respectively. The correlation factors are 0.9971 and 0.9889, respectively. The free energy change for the biosorption of Zn²⁺ at 27ºC, initial concentration of 100 mg L^-1 and pH 6 is –7.663 kJ mol^-1 within 60 min. These results indicate that maize wrapper has potential for the removal of Zn²⁺ from industrial wastewater.

Key words: Biosorption, Zn(II), isotherm, maize wrapper, kinetic studies.