Arsenic immobilization as crystalline scorodite by gas-diffusion electrocrystallization

The safe immobilization of arsenic present in liquids is a key environmental challenge due to the inherent toxicity of arsenic. This immobilization is mostly restricted by the application of chemicals and several stages of oxidation and precipitation. Although the formation of bioscorodite is a greener alternative, it is intensive in the use of energy for aeration, and it is costly due to nutrient addition. The electrochemically-driven crystallization of arsenic into scorodite is proposed here to overcome these limitations. We disclose gas-diffusion electrocrystallization (GDEx) for the immobilization of arsenic into highly crystalline scorodite (FeAsO4·2H2O) by the in situ production of oxidizing substances (i.e., H2O2) on gas-diffusion electrodes. GDEx yielded an exceptional arsenic immobilization efficiency of up to 70% without the use of any primary minerals or seed crystals. At 70 °C and using As3+ as the precursor, polydisperse micrometric scorodite particles were obtained (from fine particles of