Regeneration of As(V) loaded granular activated carbon through desorption in FeCl3, CaCl2 and MgCl2 aqueous solutions.

As(V) adsorption on granular activated carbon (GAC) and subsequent desorption in dH2O was modeled using the pseudo-first and pseudo-second order kinetic models. Regeneration was achieved by immersing loaded GAC in NaCl, FeCl3, CaCl2 and MgCl2 aqueous solutions. As(V) detection after desorption was highest for NaCl but subsequent adsorption was lowest. Regeneration was highest in FeCl3 solution of pH 2 followed closely by pH 3, but As(V) precipitation appeared superior at pH 3. Molar ratios of Fe, Ca and Mg to As were tested in the range of 0.75:1 to 12:1 where a logarithmic relation was found between the molar ratio and As(V) desorption as diluted in HNO3 and H2O and subsequent adsorption. Precipitation was nearly complete in FeCl3, limited in MgCl2 at a ratio of 12:1 and not observed in CaCl2. While kinetic values were lower than in previous tests, the pseudo-first and pseudo-second order models could accurately describe desorption in CaCl2 and MgCl2 but not in FeCl3 due to precipitation. Desorption in FeCl3 was most effective in precipitating As(V), being highest at a molar ratio of 6:1, but regeneration was slightly higher at a molar ratio of 12:1.

Regeneration of As(V)-loaded granular activated carbon through electrocoagulation.

As(V)-loaded granular activated carbon was regenerated through electrocoagulation assisted by elution with NaCl. Adsorption of As(V) by activated carbon was highest at pH 6, and subsequent desorption in water was highest at pH 11, followed by pH 3. Lower initial pH improved arsenic removal during electrocoagulation, NaCl concentration was insignificant, but removal increased with current density. Adding Fe(II) before electrocoagulation led to an improved removal efficiency up to a concentration of 30 mg/L. Regeneration of As(V)-loaded activated carbon increased with current density and time up to a maximum of 85%. An increase in NaCl concentration to 6000 mg/L further improved regeneration to 92%. Regeneration at a lower current density only dropped slightly from 54% to 51% when doubling activated carbon concentration, demonstrating excellent scalability. Repeated adsorption-desorption tests were performed, where 81% and 69% regeneration were obtained after four regenerations with NaCl concentrations of 6000 and 750 mg/L, respectively. NaCl concentration in the tested range did not influence electrocoagulation but improved regeneration through elution. The combination of electrocoagulation and elution facilitated a higher regeneration efficiency, meanwhile removing As(V) from the solution through adsorption on iron hydroxide. PRACTITIONER POINTS: As(V)-loaded activated carbon was regenerated by electrocoagulation with elution. Regeneration increased with regeneration time and current density up to 85%. Addition of 6000 mg/L NaCl further increased regeneration to 93%. Regeneration of 82% was achieved after four regenerations. NaCl did not affect electrocoagulation but improved regeneration through elution.