Biochar as a green amendment has been used to immobilize heavy metals in contaminated soil. Apart from the importance of the amendment itself, the interaction with soil components like clay minerals might also influence the immobilization behavior of biochar. Here, we examined the impact of a typical soil mineral, bentonite, on the immobilization of Pb by barley grass-derived biochar, and elucidated the underlying mechanisms by dividing biochar into dissolvable and undissolvable fractions. Results showed that biochar and bentonite could immobilize Pb through mechanism of electrostatic sorption, complexation, and precipitation. Compared to sole undissolvable biochar, coexistence of bentonite rapidly raised pH of the mixture over 7.0, leading the free Pb²⁺ transformed into more stable Pb₂CO₃(OH)₂ (K_sp = 1.3 × 10⁻¹⁸) instead of PbCO₃ (K_sp = 1.5 × 10⁻¹³), finally increased Pb²⁺ removal rate by 1.47 times. As for the dissolvable biochar, the generation of dissolvable biochar-bentonite-Pb²⁺ ternary complex raised the Pb²⁺ removal rate by 59.6% with the presence of bentonite. Small angel XRD analysis showed that the free Pb²⁺ and dissolvable biochar-associated Pb²⁺ could enter the interlayer space of bentonite and thus expanded the d-spacing from 1.28 nm to 1.36–1.50 nm, which might favor the formation of ternary complex. Findings of this study not only provided a new insight into the immobilization of heavy metals by biochar in soil, but also emphasized the importance of interaction between biochar and soil minerals.

生物炭作为绿色改良剂已被用于将重金属固定在受污染的土壤中。除了修正案本身的重要性外，与土壤成分（如粘土矿物）的相互作用也可能影响生物炭的固定行为。在这里，我们检查了一种典型的土壤矿物膨润土对大麦草衍生生物炭固定化Pb的影响，并阐明了将生物炭分为可溶和不可溶级分的潜在机制。结果表明，生物炭和膨润土可以通过静电吸附，络合和沉淀机制固定铅。与唯一的不可溶解的生物炭相比，膨润土的共存使混合物的pH值迅速提高到7.0以上，从而导致游离Pb ²⁺转化为更稳定的Pb ₂用CO ₃（OH）₂（K _sp  = 1.3×10 ^-18）代替PbCO ₃（K _sp  = 1.5×10 ^-13），最终将Pb ^2+的去除率提高了1.47倍。对于可溶解的生物炭，在存在膨润土的情况下，可溶解的生物炭-膨润土-Pb ²⁺三元络合物的产生将Pb ^2+的去除率提高了59.6％。小天使XRD分析表明，游离Pb ²⁺和可溶解的生物炭相关Pb ²⁺可能会进入膨润土的层间空间，从而将d间距从1.28 nm扩大到1.36–1.50 nm，这可能有利于三元络合物的形成。这项研究的发现不仅为生物炭在土壤中固定重金属提供了新的见解，而且还强调了生物炭与土壤矿物之间相互作用的重要性。