This work pertains to a novel continuous column process for As(III) oxidation using commercial activated carbon as a promising catalyst in acidic solutions on a minipilot scale. Notable efficiency of arsenic oxidation is validated in continuous column tests treating 5 g/L As(III) acidic solutions with activated carbon in the presence of oxygen. Residence time, pH, dissolved oxygen, and initial As(III) concentration are proved to be the significant impacting parameters on the arsenic oxidation process. Insights into the oxidation pathway by Fourier-transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) illustrate that the efficient oxidation of arsenic is attributed to the ample oxygen functionalities on the carbon surfaces, which play a role in the in situ formation of hydrogen peroxide. This study provides a promising process for the application of activated carbon in arsenic oxidation from highly concentrated arsenic waste solutions in the mining and metal industries.