Heavy metals constitute a group ofinorganic chemical hazards for the ecosystems and human health because of theirhigh toxicity in the industrial aqueous waste water. Heavy metals are naturally occurring elements that have ahigh atomic weight and a density at least 5 times greater than that of water 1. Fordecades, water pollution has been studied because of the rapid industrialdevelopment which increased the production and use of heavy metals, resultingin high concentrations of heavy metals often being discharged into waterbodies.
Industries such as mining 2, 3, tanneries, metal plating, fertilizerindustries, battery and pesticide production, ore refineries and the paperindustry 4 are the major contributing sources of heavy metal. Heavy metals,such as zinc (Zn), lead (Pb), copper (Cu), iron (Fe), nickel (Ni), and cadmium(Cd) are toxic, carcinogenic, persistent in nature and tend to bioaccumulate 5. La source : Article 1 Severalmethods have been proposed for efficient heavy metal removal from water,including but not limited to chemical precipitation, ion exchange, membranefiltration and electrochemical technologies 6, 7, 8, 9, 10. Among thesetechniques, adsorption has proven the flexibility in design and operation and,in many cases it will generate high-quality treated effluent. In addition,owing to the reversible nature of most adsorption processes, the adsorbents canbe regenerated by suitable desorption processes for multiple use 11, and manydesorption processes are of low maintenance cost, high efficiency, and ease ofoperation 12.
Therefore, the adsorption process has come to the forefront asone of the major techniques for heavy metal removal from water/wastewater. This technology is cheap andenvironmentally friendly if low cost adsorbents are used. In the search for lowcost adsorption materials over the past years, many researchers shifted theirinterests into the use of animal wastes, such as chicken feathers, animalbones, Ensis siliqua Shell, snailshells, … 13, 14, 15 ,16 . Since the cost of anadsorbent depends on its abundance, availability and effectiveness, animal wasteshave been extensively studied. There are many parameters that affect the efficiency of an adsorptionprocess, such as pH, temperature, adsorbent dosage and initial metalconcentration.
For instance, pH may affect the metal availability, functionalgroups on the surface of the adsorbents and ionic strength17. In case ofadsorbent dosage and metal concentration, the efficiency mainly depends on theavailability of active sites and the competition for active sites 18. Article1 The purpose of the present review is tostudy the feasibility of valorization anddevelop a new cost low biosorbent to remove heavy metals from wastewaters byadsorption technique using Calcined Cow Leather as a new abundant material andan eco-friendly biosorbent for the removal of Cu, Znand Ni from metal contaminated wastewater and evaluate the effects of pH,contact time, adsorbent dosage and initial metals concentration on metal uptakeand removal efficiencies. The biosorption behavior wasanalyzed using the Langmuir, Freundlich, Temkin and Dubinin-Radushkevichadsorption isotherms. The experimental data of adsorption kinetics wereanalyzed using the pseudo-first and pseudo-second order kinetic models and thethermodynamics of this process were also studied.