Removal of Zinc (II) Ions by Wheat Bran and Waste Coffee as Low-Cost Biosorbents

In this research, wheat bran and waste coffee without any chemical treatment are used as low-cost biosorbents for the removal of zinc ions from an aqueous solution. Parameters such as contact time, adsorbent dose, initial concentration, and pH were studied. To describe adsorption equilibrium, Langmuir and Freundlich isotherms were used. Experimental results confirm that the adsorption of zinc ions on waste coffee fits well with the Langmuir isotherm while Freundlich isotherm is a better fit for wheat bran. The maximum capacity of zinc ions adsorbed, with the Langmuir model for wheat bran is a bit higher (qmax= 9.01 mg/g) than waste coffee (qmax= 6.41 mg/g). The thermodynamic parameters, enthalpy (ΔHo), entropy (ΔSo), and Gibbs free energy (ΔGo), provide that the adsorption process is exothermic, spontaneous, and favorable for both used biosorbents. The structure of both biosorbents was analyzed by the pH of the point zero charge (pHPZC) and FT-IR spectra.