Oxidation dissolution of arsenopyrite (FeAsS) is oneof the importantsources of arsenic contamination in soil and groundwater. Biochar,a commonly used soil amendment and environmental remediation agent,is widespread in ecosystems, where it participates in and influencesthe redox-active geochemical processes of sulfide minerals associatedwith arsenic and iron. This study investigated the critical role ofbiochar on the oxidation process of arsenopyrite in simulated alkalinesoil solutions by a combination of electrochemical techniques, immersiontests, and solid characterizations. Polarization curves indicatedthat the elevated temperature (5-45 degrees C) and biochar concentration(0-1.2 g center dot L-1) accelerated arsenopyriteoxidation. This is further confirmed by electrochemical impedancespectroscopy, which showed that biochar substantially reduced thecharge transfer resistance in the double layer, resulting in smalleractivation energy (E (a) = 37.38-29.56kJ center dot mol(-1)) and activation enthalpy (Delta H* = 34.91-27.09 kJ center dot mol(-1)).These observations are likely attributed to the abundance of aromaticand quinoid groups in biochar, which could reduce Fe-(III) and As-(V)as well as adsorb or complex with Fe-(III). This hinders the formationof passivation films consisting of iron arsenate and iron (oxyhydr)-oxide.Further observation found that the presence of biochar exacerbatesacidic drainage and arsenic contamination in areas containing arsenopyrite.This study highlighted the possible negative impact of biochar onsoil and water, suggesting that the different physicochemical propertiesof biochar produced from different feedstock and under different pyrolysisconditions should be taken into account before large-scale applicationsto prevent potential risks to ecology and agriculture.
Biochar promotes the weathering of arsenopyrite and exacerbatesthe release of arsenic to soil and water by impeding the formationof passivated films of iron arsenate and iron (oxyhydr)-oxide.

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