老化作用对水稻秸秆生物炭吸附Cd(Ⅱ)能力的影响

Effect of ageing on Cd adsorption ability by rice-straw derived biochar

环境变化使生物炭材料发生老化作用,老化后的生物炭是否仍具有较强的吸附能力是评价生物炭对Cd修复的长期稳定性的重要指标.本文采用自然老化(Spontaneous aging,SPON),冻融循环老化(Freeze-thaw cycles aging,FTC)和高温老化(High temperature aging,HT)的方法对水稻秸秆生物炭进行2个月的人工加速老化,运用扫描电镜(SEM-EDS)、元素分析仪、傅里叶红外光谱分析仪(FTIR)研究老化作用对秸秆生物炭材料的影响,再通过等温吸附实验研究生物炭老化前后对Cd吸附性能特征的变化.结果表明,老化作用使生物炭材料局部发生破碎,增加了生物炭表面O/C比.老化作用显著影响秸秆生物炭表面的官能团,降低了生物炭表面—OH的数量,增加了CO、—COOH和Si—O—Si的数量,出现了C≡C键,可为Cd提供更多的吸附位点.等温吸附试验进一步证明了老化后的生物炭提高了对Cd(Ⅱ)的吸附性能.与生物炭原样相比,冻融循环老化、高温老化、自然老化使生物炭的Cd最大吸附量分别达到了26.49、33.30、23.40 mg·g^(-1),增加了27.8%,60.7%,12.9%.本研究表明老化作用改变了生物炭材料的表观结构和官能团,增强了对Cd(Ⅱ)的吸附能力,因此生物炭对Cd的修复具有一定的长期稳定性.

The adsorption ability of aged biochar for Cd is a key factor of assessing the long-term stability of Cd immobilization. The aim of this study was to investgate the process of biochar aging with Spontaneous aging（SPON）,Freeze-Thaw Cycles aging（FTC） and High Temperature aging（HT）. The surface properties of biochar and aged biochar were characterized by scanning electron microscopy（SEM） coupled to energy dispersive spectrometry（EDS）,Fourier-transformed infrared spectroscopy（FTIR）,and elemental analysis. Then a batch sorption experiment was carried out to determine the Cd（Ⅱ） adsorption ability on biochar and aged biochar. The result of SEM-EDSindicated that there were no significant change in the porous structure of biochar,but some breakage was found in aged biochar. In the meanwhile,ageing process increased the O / C ratio of biochar. The FTIR analysis indicated that the hydroxyl groups were reduced,but the oxygen-containing function groups on biochar increased,such as CO,—COOH and Si—O—Si. The increased oxygencontaining function groups may provide more adsorption sites for Cd（Ⅱ）. The batch sorption experiment demonstrated that the adsorption capacity of Cd（Ⅱ） on the aged biochar were obviously improved in comparison with the original biochar. The maximum adsorption capacities were increased by 27.8%,60.7% and 12.9%,respectively after high temperature aging,freeze-thaw cycles aging and spontaneous aging. Our results indicated that the aging effect influenced the surface properties of biochar,and the aged biochar had higher Cd adsorption capacity compared with original biochar. As a result,the Cd immobilization by biochar has long-term stability.