Comparison of Impact of Carbonate Content, Cation Exchange Capacity and Specific Surface Area in the Retention of Heavy Metal Contaminant by Bentonite, Kaolinite, and Nano-Clay

Carbonate, Cation exchange capacity and Specific surface area are the three factors which  play a significant role in the retention of heavy metal contaminants by the soil. However, the amount and role of each of these three factors in heavy metal retention process is not clearly known. Accordingly, this experimental study attempts to examine the role of each of these factors on the heavy metal retention process. This study has been performed by the use of bentonite clay sample (which has 8% natural carbonate, significantly large specific surface area  and cation exchange capacity), kaolinite (which has 4% natural carbonate, small specific surface area and cation exchange capacity), industrial nano-clay called Cloisite®Na+ (free of carbonate, large specific surface area and considerable cation exchange capacity), industrial nano-clay called Cloisite®30B (free of carbonate, large specific surface area  and small cation exchange capacity), and laboratory sample of nano-clay called SLB (Surface Layer Bentonite) (free of carbonate, large specific surface area  and considerable cation exchange capacity).
In this regard, by conducting a series of geotechnical and geo-environmental experiments, the interaction process of kaolinite clay samples, bentonite, industrial Cloisite®Na+, industrial Cloisite®30B, and laboratory nano-clay SLB with heavy metal contaminants of lead and copper were experimentally explored and studied.
The analysis of experimental studies including soil buffering capacity, X-ray diffraction test and the measurement of heavy metal retention by soil samples indicate that in comparing of carbonate content, cation exchange capacity, and specific surface area of soil samples the significant role of each parameter in heavy metal retention is as follows, respectively:   
Carbonate > Cation exchange capacity (CEC) > Specific surface area (SSA).