Adsorption of arsenic by natural pozzolan in a fixed bed: Determination of operating conditions and modeling

The presence of arsenic at relatively high concentrations in water as a result of natural and human activity discharges requires proper treatment before use. Arsenic was analyzed using a spectrophotometric method. Experiments were carried out in a column packed with natural pozzolan (black, red) from Djoungo (Cameroon) at different pH (5, 7, 9), initial arsenic concentration (100 μg/L, 200 μg/L, 400 μg/L) and flow velocity (0.39 cm/min, 0.79 cm/min, 1.57 cm/min). Results showed that the bed saturation time (outlet concentration from the bed ≥ 10 μg/L) is longer for a lower pH, flow velocity and initial arsenic concentration. Two kinetics models; Adams-Bohart and Thomas were applied to the experimental data to predict the breakthrough curves using linear regression and to determine the characteristic parameters of the column. The Thomas model was found appropriate for the description of the whole breakthrough curves, whereas the Adams–Bohart model could only predict the initial part of the breakthrough curves. Using water with low arsenic concentration, pozzolan demonstrated its effectiveness in arsenic removal below the acceptable level (10 μg/L).