Batch sorption studies

The batch sorption experiments were performed with NB and AAB in order to determine their potential towards CIP removal from water. Optimization studies were carried out by dispersing 0.2 g/L of the adsorbent using a known volume of CIP solution (30 mg/L) in a dark 100-mL capped glass bottle. The sorbent-sorbate solutions (in duplicate) were shaken (200 rpm) in an orbital shaker at ambient temperature. To get insights into the effect of solution pH on CIP sorption, the experiments were performed in the pH range of 3.0–9.0. To assess the optimum adsorbent dosage for sorption experiments, the effect of various adsorbent dosages (0.1–0.8 g/L) was studied. The sorption kinetic studies were carried out with different interaction times (0–240 min). To study the sorption isotherms, the effect of initial CIP concentrations (5–200 mg/L) was investigated. The effect of ionic strength (0.05–0.5 M) on the sorption process was also investigated. Before NB and AAB were added, the solution pH was adjusted using NaOH (0.1 M) and/or HCl (0.1 M). After equilibration time, the sorbent-sorbate solution was separated using syringe driven filter (0.45 μm). All the experiments were done in duplicate. The amount of CIP sorbed onto NB and AAB (q_e; mg/g) and percentage removal (R; %) were calculated using the following equations (Eqs. (1–2)):

Reusability study is helpful in illustrating the regenerating capability of the bentonite clay. The regeneration experiments in batch mode were performed with NB and AAB based on the aforementioned batch optimization studies. Two eluents (0.1 M NaOH and 0.1 M HCl) were selected to test the regeneration potential of bentonite. After equilibrium was achieved, the separated adsorbents were washed several times and dried. Thereafter, a known volume of the eluent was agitated with the adsorbent for 4 h. Then, the adsorbent was washed with milli-Q water, dried, and used for the next cycle again. The regenerating experiment was repeated for five consecutive cycles.