改性生物炭对镉离子吸附性能研究

以废弃松木屑为原料采用热分解法制备生物炭,并以氨气、硝酸、硫化钠和溴水4种化学试剂分别对其进行表面改性。采用BET、FTIR和Bohem滴定等技术对改性前后的生物炭进行表征,研究溶液pH值、初始溶液Cd2+浓度、吸附时间等因素对Cd2+吸附特性的影响,并探讨改性生物炭的吸附机理。结果表明,改性生物炭具有较大的比表面积、发达的孔结构和多种表面官能团;在一定范围内,随溶液pH值的增大、Cd2+浓度的升高、吸附时间的延长,改性生物炭对Cd2+的去除率逐渐提高,其中氨气改性生物炭对Cd2+的吸附效果最优,在溶液pH值为6、初始溶液Cd2+浓度为50mg/L、生物炭加入量为2g/L、吸附时间为6h时,氨气改性生物炭对Cd2+的吸附容量可达12.3mg/g;拟二级动力学方程和等温吸附模型均能较好地描述改性生物炭对Cd2+的吸附过程,其中氨气改性生物炭的Langmuir与Freundlich吸附常数最大。

Adsorption of cadmium ions by chemically modified biochar

With waste pine sawdust as the raw material, biochar was prepared by pyrolysis method. The surface of biochar was modified by four chemicals(ammonia gas, nitric acid, sodium sulfide and bromine water), respectively. The modified and unmodified biochar were characterized by BET method, FTIR and Bohem titration.The effects of pH value, initial concentration of Cd²⁺ solution and adsorption time on the Cd²⁺ adsorption performance of biochar were researched. The adsorption mechanism of modified biochar was also discussed. The results show that the surface-modified biochar has higher specific surface area, well-developed pore structure and more surface functional groups. Within a certain range, Cd²⁺ removal rate gradually increases with the increase of pH value, initial concentration of Cd²⁺ solution and adsorption time. Ammonia modified biochar shows the best adsorption performance, with Cd²⁺ adsorption capacity of 12.3 mg/g under the condition of pH value at 6, Cd²⁺ initial concentration at 50 mg/L, biochar dosage at 2 g/L and adsorption time at 6 h. Pseudo-second-order kinetics equation and isothermal adsorption model are both suitable to describe the adsorption process of Cd²⁺ by the modified biochar, and ammonia modified biochar exhibits the maximum Langmuir and Freundlich adsorptive coefficients.