The influence of modification methods on physico-chemical and sorption properties of sepiolite

A Mechanism Assessment and Differences of Cadmium Adsorption on Raw and Alkali-Modified Agricultural Waste

“…This indicates that during the sorption of Cd 2+ ions onto functional groups of CS and MCS, hydrogen ions are released into solutions, lowering the pH PZC of both sorbents (Figure 1). Comparing these values with those obtained for the same solid/liquid ratio in the KNO 3 solution, it can be concluded that the decrease in pH PZC after Cd 2+ adsorption involved specific sorption as the binding mechanism [12]. Keeping in mind that the adsorption experiments were done at pH < 6.0, where the surfaces of CS and MCS are positively charged, the electrostatic forces are not responsible for Cd 2+ adsorption onto the investigated materials, but by the specific sorption through the complex in the forms (sorbent-O)-Cd + or (sorbent-O) 2 -Cd.…”

“…Keeping in mind that the adsorption experiments were done at pH < 6.0, where the surfaces of CS and MCS are positively charged, the electrostatic forces are not responsible for Cd 2+ adsorption onto the investigated materials, but by the specific sorption through the complex in the forms (sorbent-O)-Cd + or (sorbent-O) 2 -Cd. The fact that the sorption of Cd 2+ ions on both CS and MCS occurs in solutions with pH values much below the value of pH PZC, indicates the formation of bonds between the adsorbed species and the sorbents' surface oxygen groups, or the precipitation of hydroxides on the sorbents' surfaces [12]. The binding mechanism could be explained by the following equation:…”