Equilibrium experiments: Equilibrium isotherms of Bentonite clay were determined by placing
a constant mass of 1 g of clay with 50 mL lead ions solution in glass bottles on an agitation shaker.
The concentration of lead ion solution ranged between 50 and 1300 ppm during each isotherm run.
While, the concentration of chromium ions ranged between 50 and 800 ppm. The particle size of
clay was 0.25 mm with temperature as 20°C for isotherm determination. Based on the preliminary
observations, the adsorption process attained the state of equilibrium after 30 min, thus the
equilibrium experiments were run for 3 h to ensure that the adsorption process is in equilibrium.
After this process, the samples were filtered, diluted and the absorbance was measured by atomic
absorption spectroscopy. The absorbance of samples was converted to concentrations using the
standard calibration curves of lead and chromium ions.