The presence of heavy metals in the environment is of important concern due to their toxicity and health effects on human and other living creatures. Cobalt is one of the usual toxic heavy metal present in the waste water of nuclear power plants and many other industries. The standard level of cobalt in drinking water is 2 µgL-1 but values up to 107 µgL-1 have been also reported. Many different adsorbents have been used for the removal of cobalt. In the present investigation, almond green hull, an agriculture solid waste, was used for the adsorption of Co(II) from aqueous solutions. The efficiency of this adsorbent was studied using batch adsorption technique under different experimental conditions such as adsorbent dose, initial metal-ion concentration, contact time, adsorbent particle size, and chemical treatment. Optimum dose of adsorbent for maximum metal-ion adsorption were 0.25 g for 51.5 mgL-1 and 0.4 g for 110 mgL-1 concentrated solutions, respectively. Also, the adsorption of Co(II) on almond green hull followed pseudo second-order kinetics. Adsorption isotherms were expressed by Langmuir and Freundlich adsorption models. The Langmuir adsorption model fits the experimental data reasonably well compared to the Freundlich model. Maximum adsorption capacity of this new sorbent was found to be 45.5 mgg-1. The present study revealed that such a low cost material may be used as an efficient adsorbent for the removal of cobalt from wastewater streams.

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