不同生物质来源生物炭对Pb(Ⅱ)的吸附特性

以水稻秸秆、小麦秸秆、荔枝树枝为原料,在300、400、500、600℃下制备生物炭,并表征其理化性质,考察热解温度、初始p H、矿物组分等因素对生物炭吸附Pb(Ⅱ)的影响。结果表明,不同热解温度对水稻和小麦秸秆炭吸附Pb(Ⅱ)的影响很小,而荔枝树枝生物炭对Pb(Ⅱ)的吸附量随热解温度升高而显著增大。在p H3.0~6.0的范围内,三种生物炭对溶液中Pb(Ⅱ)的吸附量呈上升趋势;在25℃时,三种生物炭的等温吸附曲线符合Freundlich吸附模型,荔枝树枝生物炭对Pb(Ⅱ)的吸附效果最佳。三种生物炭吸附Pb(Ⅱ)的主导机制可能是其与矿物组分的共沉淀作用,而荔枝树枝生物炭还可能存在Pb(Ⅱ)与-OH、-COOH之间的离子交换作用,C=C键中的π电子在吸附过程中也有一定的贡献。

Adsorption of Pb(Ⅱ)by biochars derived from three types of biomass

Three different raw materials, including rice straw, wheat straw, and lychee branches, were used to produce biochars by pyrolysis at 300, 400, 500, and 600℃. The characteristics of the biochars obtained were analyzed. The effects of biochar pyrolysis temperature and mineral composition and initial solution pH on Pb(Ⅱ)adsorption by biochars were examined. Results showed that pyrolysis temperature exhibited no obvious influence on Pb(Ⅱ)adsorption by rice and wheat straw derived biochars, while the adsorption of Pb(Ⅱ)by lychee derived biochar increased with increasing pyrolysis temperature. As solution pH increased from 3.0 to 6.0, the amount of Pb(Ⅱ)adsorbed on all biochars gradually increased. Adsorption isotherms of Pb(Ⅱ)by these biochars fit the Freundlich model well. In addition, lychee-derived biochar showed greater Pb(Ⅱ)adsorption than the biochars derived from rice and wheat straws. Chemical precipitation of Pb(Ⅱ) with mineral components might be the main mechanism of Pb(Ⅱ)adsorption by these biochars. Lychee-derived biochar contained a variety of functional groups, such as-OH,-COOH, and C=C, thus providing different adsorption sites, including aromatic-πstructures(for cation-πinteraction)and oxygen-containing groups(for ion exchange adsorption)for Pb(Ⅱ)adsorption.