Key Laboratory of High-temperature and High-pressure Study of the Earth's Interior, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China.
University of Chinese Academy of Sciences, Beijing 100039, China.
Environ Sci Technol. 2023 Jun 6;57(22):8373-8384. doi: 10.1021/acs.est.2c09874. Epub 2023 May 24.
Oxidation dissolution of arsenopyrite (FeAsS) is one of the important sources 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 influences the redox-active geochemical processes of sulfide minerals associated with arsenic and iron. This study investigated the critical role of biochar on the oxidation process of arsenopyrite in simulated alkaline soil solutions by a combination of electrochemical techniques, immersion tests, and solid characterizations. Polarization curves indicated that the elevated temperature (5-45 °C) and biochar concentration (0-1.2 g·L) accelerated arsenopyrite oxidation. This is further confirmed by electrochemical impedance spectroscopy, which showed that biochar substantially reduced the charge transfer resistance in the double layer, resulting in smaller activation energy ( = 37.38-29.56 kJ·mol) and activation enthalpy (Δ* = 34.91-27.09 kJ·mol). These observations are likely attributed to the abundance of aromatic and quinoid groups in biochar, which could reduce Fe(III) and As(V) as well as adsorb or complex with Fe(III). This hinders the formation of passivation films consisting of iron arsenate and iron (oxyhydr)oxide. Further observation found that the presence of biochar exacerbates acidic drainage and arsenic contamination in areas containing arsenopyrite. This study highlighted the possible negative impact of biochar on soil and water, suggesting that the different physicochemical properties of biochar produced from different feedstock and under different pyrolysis conditions should be taken into account before large-scale applications to prevent potential risks to ecology and agriculture.
黄铁矿（FeAsS）的氧化溶解是土壤和地下水中砷污染的重要来源之一。生物炭作为一种常用的土壤改良剂和环境修复剂，广泛存在于生态系统中，它参与并影响与砷和铁相关的硫化物矿物的氧化还原活性地球化学过程。本研究通过电化学技术、浸泡实验和固体特性相结合，研究了生物炭在模拟碱性土壤溶液中对黄铁矿氧化过程的关键作用。极化曲线表明，升高温度（5-45°C）和生物炭浓度（0-1.2 g·L）加速了黄铁矿的氧化。这进一步得到电化学阻抗谱的证实，表明生物炭大大降低了双层中的电荷转移电阻，从而导致更小的活化能（ = 37.38-29.56 kJ·mol）和活化焓（Δ* = 34.91-27.09 kJ·mol）。这些观察结果可能归因于生物炭中丰富的芳族和醌型基团，这些基团可以还原 Fe(III)和 As(V)，并吸附或与 Fe(III)络合。这阻碍了由铁砷酸盐和铁（氧）氢氧化物组成的钝化膜的形成。进一步的观察发现，生物炭的存在加剧了含有黄铁矿地区的酸性排水和砷污染。本研究强调了生物炭对土壤和水可能产生的负面影响，建议在大规模应用之前，应考虑到不同原料和不同热解条件下生产的生物炭的不同物理化学性质，以防止对生态和农业造成潜在风险。
