Particle size control of the biogenic scorodite during the GAC-catalysed As(III) oxidation for efficient arsenic removal in acid wastewaters

Abstract The synthesis of biogenic scorodite combined with the oxidation of As(III) catalysed by granular activated carbon (GAC) was previously demonstrated. However, the colloidal size of the formed scorodite particles is still a bottleneck, as it would hinder the easy separation of the precipitates in a full-scale application. Here, we studied the effect of GAC concentration on biological scorodite precipitation at thermoacidophilic conditions in batch experiments. Higher arsenic removal efficiency and precipitation of larger and more stable scorodite particles were found only in biotic tests and at low catalyst concentration of 4 g L−1. Furthermore, with 4 g L−1 GAC, the Fe and As predominantly precipitated in solution while with 20 g L−1 GAC the Fe and As predominantly precipitated on the GAC. For experiments with 4 and 20 g L−1 of GAC, the average particle size was 66 and 2.6 μm, respectively. This could be explained by the lower saturation level of the solution at the lower GAC level. This study shows for the first time that the oxidative catalytic capacity of GAC can be used to influence crystallization of scorodite.