The capability of cow hoof (CH) to remove Zn(II) from aqueous solution under the influence of sorbent size, solution pH, contact time, and sorbent dosage was investigated through batch studies. Equilibrium studies were conducted at three different temperatures (298, 308, and 318？K) by contacting different concentrations of Zn(II) solution with a known weight of cow hoof. The biosorption of Zn onto cow hoof was found to increase with increase in the mass of sorbent used while the biosorption efficiency was found to decrease with increase in sorbent particle size. The optimum conditions of pH 4 and contact time of 60 minutes were required for maximum removal of Zn(II) by cow hoof (mesh size 212？μm). The equilibrium data were modelled using Langmuir, Freundlich, and Dubinin-Radushkevich (D-R) isotherm models. The data were best fitted by Langmuir model. The kinetic data were analysed using Lagergren kinetic equations and these were well fitted by the pseudo-second-order kinetic model. The thermodynamic parameters showed that the biosorption process was feasible, spontaneous, and endothermic. 1. Introduction Water is an essential life-sustaining natural resource and as such, its fitness for life sustenance should be constantly maintained and preserved. Unfortunately, heavy metals and other pollutants generated from different industrial and agricultural activities constantly put the purity and life-sustaining ability of this important natural resource under threat. The threat generated by the presence of heavy metals becomes particularly worrisome because of their nonbiodegradability, toxicity, persistency, and bioaccumulation tendency [1–3]. These metals have been implicated in causing health challenges such as accumulative poisoning, cancer, brain damage, lung damage, and hepatic and renal damage [4, 5]. Zinc is a trace element that is essential for human health. It is important for the physiological functions of living tissues and regulates many biochemical processes. But excessive ingestion of zinc, especially at levels of 100–500？mg/day, can bring about serious health problems, which include stomach cramps, skin irritations, vomiting, nausea, and anaemia [1, 6]. There are strict environmental regulations in most developed and developing countries with regard to contaminants discharged from industrial operations. This means that industries need to develop on-site or in-plant facilities to their own effluents and minimize the contaminant concentrations to acceptable limits prior to their discharge [7]. This necessity has seriously enhanced the demand for
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