Multi-cycle regeneration of arsenic-loaded iron-coated cork granulates for water treatment

Abstract

The chemical desorption of arsenic from saturated iron-coated cork granulates (ICG) and the regeneration capacity of this adsorbent for further reuse was investigated in batch and continuous modes. Different types of eluents were tested at different concentrations for evaluating their desorption capacity, and leaching of total organic carbon (TOC), iron content, and characterization by SEM/EDS were used to assess the eluents' attack on the adsorbent structure. The NaOH 0.1 M solution achieved the highest arsenic removal rate from saturated media; however, it was aggressive to the adsorbent structure, as reflected in high TOC values found in the eluate, higher iron leaching from the adsorbent, and degradation of cork cellular structure. The Elovich model fitted best (r2 > 0.98) the desorption kinetics when using NaOH as eluent. The less basic solution of NaOH 0.01 M proved to be less aggressive to ICG and allowed media regeneration for at least four adsorption-desorption cycles, while remaining an arsenic adsorption capacity of 1 mg g−1 in both batch and continuous modes. ICG's adsorption capacity was less affected after various cycles than other adsorbents, so this material proved to be potentially applicable as an alternative green solution for arsenic removal from water. The adsorbent was also successfully applied in continuous mode to remove arsenic from real groundwater and was able to maintain arsenic concentration under 10 and 50 μg L−1 for 140 and 341 bed volumes, respectively. This work provided good insights on arsenic desorption from ICG and its further application in similar real scenarios.