Heavy metals are frequently present in the aquatic streams by different industrial wastewaters. The presence of these metals in the environment is of importance concern due to their toxicity and health effects on the human and living creatures. In the present investigation, different agricultural solid wastes namely: eggplant hull, almond green hull, and walnut shell were introduced as low cost adsorbents and used for the removal of heavy metals such as cobalt, strontium and mercury ions from aqueous solutions. Activation process and/or chemical treatments using H2O2 and NH3 were performed on these raw materials to increase their adsorption performances. The effectiveness of these adsorbents was studied in batch adsorption mode under a variety of experimental conditions such as: different chemical treatments, various amounts of adsorbents, initial metal-ion concentrations, pH of solutions, contact times, and solution temperatures. To the best of our knowledge, most of these adsorbents have not been previously used for the removal of mentioned ions from water. High metal adsorption efficiencies were achieved for all cases only in the first 2-3 minutes of adsorbents’ contact times. The optimum doses of almond green hull adsorbent for the maximum Sr(II) adsorption were found to be 0.2 and 0.3 g for 45 and 102 mg/L solutions, respectively. Optimum dose of this sorbent for maximum cobalt-ion adsorption were 0.25 g for 51.5 mg/L concentration and 0.4 g for 110 mg/L concentrated solutions. The maximum adsorption capacity of this sorbent for cobalt was found to be 45.5 mg/g. Maximum adsorption capacity of eggplant hull for mercury was 147.06 mg/g which is higher than most conventional adsorbents. The monolayer adsorption capacity of mercury for walnut shell was obtained as 151.5 and 100.9 mg/g for two different treated sorbents. The adsorption behaviors of metal ions on optimum adsorbents were also examined. It was observed that adsorption of all metal ions follows both Langmuir and Freundlich isotherms. The present study revealed that such low cost materials could be used as efficient adsorbents for the removal of heavy metal ions from wastewater streams.

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