POTENTIAL REMOVAL OF ARSENIC VIA OXIDATION AND ADSORPTION ON IRON PRECIPITATES USING AN ENVIRONMENT-FRIENDLY OXIDANT, FERRATE (VI)

Arsenic contamination of natural waters poses serious environmental concerns globally. New environment-friendly and inexpensive arsenic removal methodologies are needed to remediate arsenic containing water. The objective of this research was to test the technical feasibility of arsenic removal via oxidation and subsequent adsorption on iron precipitates generated during arsenic-contaminated water treatment with ferrate (VI). Bench-scale batch experiments with Taguchi array experimental design were conducted to determine the removal of As(III) and to identify the key operating factors influencing the removal efficiency of As(III). Four operating factors, namely reaction temperature, initial pH, molar ratio of concentration of Fe(VI) to initial As(III) concentration ([Fe(VI)]:[As(III)]₀), and initial ionic strength, were studied. Characteristics of iron precipitates generated and potential release/leaching of arsenic from the precipitates were also studied. Preliminary results show that 99% of the arsenic was removed after treatment with ferrate. The order of influence of the four factors in terms of As removal was [Fe(VI)]:[As(III)]₀ > initial pH > temperature > initial ionic strength. Removal efficiency dramatically increased with increase in the molar ratio of Fe(VI) to arsenic concentration (from 1:1 to 100:1), and decrease in the pH (from 9 to 5). The iron precipitates generated in the process had an average size of 152 nm and zeta potential of 38.5 mV, and adsorbed arsenic irreversibly with no leaching in presence of calcium chloride. From these preliminary results, it seems like ferrate (VI) can be a viable and environmentally friendly treatment option for removal of arsenic from contaminated waters.