*2.9. Desorption and Regeneration of the Adsorbent*

Desorption studies help to recover the adsorbate and adsorbent. Thus, the regeneration of the adsorbent may be important to reduce cost processes and to recover the pollutant extracted from the solution [37]. The viability of desorption and reuse of eggshell was evaluated using 0.5 M NaOH solution. First, 0.5 g of eggshell was stirred with 40 mL of dye (100 mg/L, pH 5), at 25 ◦C, 100 min of contact time, and 500 rpm for the adsorption phase. The adsorbent was dried and added into 40 mL of NaOH solution for desorption at a constant speed of 500 rpm for 100 min at 25 ◦C. The dye concentration in the solution was measured at 100 min, after the centrifugation of the samples at 3000 rpm for 5 min to separate the solid phase.
