The effectiveness of biochar as a sorptive material to remove contaminants, particularly heavy metals, from water is dependent on biomass type and pyrolysis condition. Biochars were produced from pulp mill sludge (PMS) and rice straw (RS) with nitrogen (N₂) or carbon dioxide (CO₂) as the purging gas. The sorptive capacity of the biochars for cadmium(II), copper(II), nickel(II) and lead(II) was studied. The heavy metal adsorption capacity was mainly affected by biomass type, with biochars adsorption capacities higher for lead(II) (109.9-256.4 mg g^-1) than for nickel(II) (40.2-64.1 mg g^-1), cadmium(II) (29.5-42.7 mg g^-1) and copper(II) (18.5-39.4 mg g^-1) based on the Langmuir adsorption model. The highest lead(II) adsorption capacities for PMS and RS biochars were 256.4 and 133.3 mg g^-1, respectively, when generated using N₂ as the purging gas. The corresponding lead(II) adsorption capacities were 250.0 and 109.9 mg g^-1, respectively, when generated using CO₂ as the purging gas. According to the intraparticle diffusion model, 30-62% of heavy metal adsorption was achieved in 1 h; film diffusion was the rate-dominating step, whereas pore diffusion was a rate-limiting step. Ion exchange and complexation between heavy metals and biochar surface functional groups such as carbonyl and hydroxyl groups were effective mechanisms for heavy metal sorption from the aqueous solution. We conclude that proper selection of both the feedstock type and the purging gas is important in designing biochars for the effective removal of potentially toxic metals from wastewater.

生物炭作为吸附材料从水中去除污染物（尤其是重金属）的有效性取决于生物质的类型和热解条件。由木浆厂的污泥（PMS）和稻草（RS）以氮气（N ₂）或二氧化碳（CO ₂）作为吹扫气体来生产生物炭。研究了生物炭对镉（II），铜（II），镍（II）和铅（II）的吸附能力。重金属的吸附能力主要受生物质类型的影响，铅（II）（109.9-256.4 mg g ^-1）的生物炭吸附能力高于镍（II）（40.2-64.1 mg g ^-1），镉（II）的生物炭吸附能力。）（29.5-42.7 mg g ^-1）和铜（II）（18.5-39.4 mg g ^-1）基于Langmuir吸附模型。当使用N ₂作为吹扫气体产生时，PMS和RS生物炭的最高铅（II）吸附能力分别为256.4和133.3 mg g ^-1。当使用CO ₂产生时，相应的铅（II）吸附容量分别为250.0和109.9 mg g ^-1作为净化气体。根据颗粒内扩散模型，在1 h内重金属吸附率达到30-62％。膜扩散是速率控制的步骤，而孔扩散是速率限制的步骤。重金属与生物炭表面官能团（例如羰基和羟基）之间的离子交换和络合是从水溶液中吸附重金属的有效机制。我们的结论原料类型和吹扫气体两者的，适当的选择是在设计生物炭从废水有效去除潜在的有毒金属的重要的。