Mukhtar DH. Abbas - Department of Environmental Engineering, Civil Engineering Faculty, Babol Noshirvani University of Technology, Iran & Engineer in Directorate of Al-Qadissiyeah Environment – Ministry of Environment, Iraq.
Daryoush Yousefi Kebria - Department of Environmental Engineering, Civil Engineering Faculty, Babol Noshirvani University of Technology, Iran.

Introduction: The study objective is to remove heavy metals from an aqueous solution using recycled bentonite clay waste (RBCW) as a low-cost and green adsorbent in a continuous system. The produced RBCW results from thermal remediating of the hazardous industrial bentonite clay waste that is a by-product of used engine oil recycling plants. Materials and Methods: The doses of the RBCW adsorbent were (۱.۰, ۱.۵, and ۲.۰) g mixed with (۳۰, ۴۰, and ۵۰) g of the crystalline sand to produce bed depth columns of (۲۲, ۳۰, and ۳۸ cm), respectively. The influent concentrations of all adsorbates were (۲۰, ۵۰, and ۱۰۰) ppm, and the flow rates of the continuous system were (۰.۵, ۱.۰, and ۲.۰) mL/min. Results: The BET, XRF, and SEM tests and the experimental data approved that RBCW is active material for heavy metals adsorption. The adsorption capacity and breakthrough time of Pb, Cd, Cr, Zn, and Ni for dominant parameters (flow rate of ۱.۰ mL/min, adsorbent mass of ۱.۰ g, and influent concentration of heavy metals of ۲۰ ppm) were ۷۰.۳۶, ۳۶.۰۵, ۲۷.۵۵, ۲۱.۶۷, and ۱۸.۶۳ mg/g, and ۳۵, ۱۹.۷۳, ۱۱.۳۸, ۶.۲۵, and ۸.۱۳ hr, respectively. Conclusion: The RBCW adsorbent has more than one advantage in industrial and environmental issues. The (R۲) values for Thomas, Yoon-Nelson, and BDST models were higher than ۰.۹. Moreover, the breakthrough curves of experimental data were more fitted with the Yoon-Nelson model due to the high value of R۲ and low values of Chi-square, absolute average deviation, and standard deviation.

Adsorption, Sand, Metals, Heavy, Water, Permeability.