Removal of lead (II) and cadmium (II) from aqueous solutions by adsorption on date pits modified by DTPAD

The objective of this work is to study the adsorption of lead and cadmium on raw date pits. In a second phase we cross linked carboxylic functions from Diethylenetriaminepentaacetic dianhydride (DTPAD) on raw date pits in order to evaluate any improvement of the adsorption capacity of the adsorbent. We used mathematical models of Langmuir, Freundlich, Temkin and Dubin-Radushkevich to represent the adsorption isotherms and evaluate which model fits correctly the adsorption mechanism. It was observed that the adsorption capacity of raw date pits (RDP) was increased after the functionalization of RDP with DTPAD. According to Langmuir isotherm, the maximum uptake capacities (q(max)) were 15.625 mg and 59.17 mg of lead(II) per gram of RDP and modified-RDP respectively, while they were 8.55 mg and 89.3 mg of cadmium(II) per gram of RDP and modified-RDP respectively. The adsorption energy for RDP powder was 22 kJ/mol and 10 kJ/mol for Pb2+ and Cd2+ respectively, suggesting that the process of the adsorption of Pb2+ is a chemisorption while an ion exchange process is dominant in the adsorption of Cd2+. The adsorption energy was around 8.45 kJ/mol and 7.07 kJ/mol on modified-RDP powder for Pb2+ and Cd2+ respectively; inducing that an ion exchange reaction occurs for Pb2+ and a physisorption takes place for Cd2+. We performed FT-IR spectroscopy to characterize the raw and the modified powder. The analysis of the powder via scanning electronic microscopy indicates the formation of linking bridges.