Pyrolytic Oil Based Drilling Cuttings/Orange Peel Biochar for Passivation and Remediation of Copper Lead Contaminated Soil

Abstract

An 83‑day passivation and remediation experiment was conducted by incorporating pyrolytic oil‑based drilling cuttings (OBDC)/orange peel (OB) biochar (OBDCs‑OB) into soil co‑contaminated with Cu(II) and Pb(II). The study systematically investigated the passivation efficiency of OBDCs‑OB on copper‑lead contaminated soil and its subsequent influence on soil microbial communities. Results demonstrated that OBDCs‑OB possessed abundant surface functional groups including hydroxyl (–OH) and carboxyl (–COOH), mineral constituents such as carbonate rocks and clay minerals, and a well‑developed porous architecture, all of which rendered it a highly effective adsorbent. Compared with untreated blank soil, the cation exchange capacity (CEC) of OBDCs‑OB‑amended soil increased substantially by 18.29 cmol/kg, while the pH was stably maintained at 6.80 throughout the experimental period. Furthermore, the acid‑soluble fractions of Cu(II) and Pb(II) in the soil decreased by 18.21% and 20.07%, respectively, and the potential leaching toxicity of copper and lead was reduced by 52.8% and 92.8%, unequivocally confirming the effective passivation of both heavy metals. Concurrently, the maximum soil microbial population reached 8.6×10¹⁰ cfu/g, and peak activities of dehydrogenase and urease were recorded at 127.10 μg·TPE/(g·6 h) and 167.10 mg·NH₃‑N/(kg·24 h), respectively, indicating a marked enhancement in microbial community diversity, richness, and overall growth promotion.