Role of Pyrolysis Temperature on Arsenic and Lead Leaching Potential in a Biochar-Amended Sediment

The leaching of contaminants is a complex, pivotal process for understanding how biochar can immobilize them effectively. In this study, we investigated the impact of biochar, produced at different temperatures, on the behavior of arsenic (As) and lead (Pb) in leached sediments. Before leaching, we combined biochar with sediment, allowing it to naturally age for 365 days. The biochar derived from sugarcane straw was pyrolyzed at 350 °C (BC350), 550 °C (BC550), and 750 °C (BC750). Using UV–Vis spectroscopy, we assessed changes in dissolved organic carbon quality and examined geochemical alterations employing high-performance liquid chromatography–inductively coupled plasma mass spectrometry (HPLC–ICP-MS). The addition of biochar decreased Pb mobility while increasing As mobility. The extent of immobilization varied depending on the pyrolysis temperature: BC750 notably reduced Pb leaching by 54%, whereas BC350 enhanced As mobility by 2.5 times. Although no leaching of monomethylarsonic or dimethylarsinic acids occurred, both BC350 and BC750 amplified As³⁺ leaching by 2.5 times. In summary, biochar addition at different temperatures altered the environmental fate of As and Pb. Higher pyrolysis temperatures, as seen with BC750, were more effective in mitigating Pb mobility, reducing sediment leaching by 54%. Interestingly, exogenous dissolved organic carbon and phosphorus promoted As leaching.