改性稻壳生物炭对水中Cd^2+的吸附性能研究

Adsorption of Cd^2+from Aqueous Solution by Modified Rice Husk-derived Biochars

为提高生物炭对水中Cd^2+的吸附去除性能,以BC1和BC22种稻壳生物炭为基础材料,分别采用NaOH和FeCl 3溶液制备得到NBC1和NBC2以及FBC1和FBC2改性稻壳生物炭,并通过吸附动力学和等温吸附实验研究6种生物炭对水中Cd^2+的吸附性能。结果表明,对于50 mg·L^-1 Cd^2+溶液,当生物炭投加量为1 g·L^-1时,BC1、BC2对Cd^2+的吸附量分别为14.76和13.72 mg·g^-1,NBC1、NBC2对Cd^2+的吸附量分别为未改性稻壳生物炭的3.26和2.47倍,而FBC1、FBC2对Cd^2+的吸附量则仅为未改性稻壳生物炭的1.03和0.74倍,NaOH改性稻壳生物炭能显著提高稻壳生物炭对Cd^2+的吸附能力,而FeCl 3改性对稻壳生物炭吸附Cd^2+的能力影响不大。稻壳生物炭对Cd^2+的吸附符合准二级动力学和Langmuir模型,为单分子层吸附过程;NBC1和NBC2对Cd^2+的最大吸附量(131.58和98.04 mg·g^-1)明显高于FBC1和FBC2(30.30和23.26 mg·g^-1)。与FeCl 3改性相比,NaOH改性显著增强稻壳生物炭对Cd^2+的吸附能力,其主要原因为NaOH使生物炭表面碱性含氧官能团增多,从而增强了生物炭与Cd^2+之间的离子交换和沉淀作用。

To improve Cd^2+adsorption ability of biochar in aqueous solution,NaOH-and FeCl3-modified biochars(NBC1,NBC2 and FBC1,FBC2)were prepared based on two kinds of original rice husk-derived biochars(BC1,BC2).Moreover,Cd^2+adsorption performances of the six materials were explored by the kinetics and isothermal adsorption experiments.Results show that Cd^2+equilibrium adsorption capacities of BC1 and BC2 were 14.76 and 13.72 mg·g^-1 under the condition of Cd^2+concentration 50 mg·L^-1 and biochar dosage 1 g·L^-1,respectively.NaOH-modification enhanced the Cd^2+adsorption ability of rice husk-derived biochars consistently and significantly,and the equilibrium adsorption capacities of NBC1 and NBC2 were 3.26 and 2.47 times that of BC1 and BC2,respectively.However,FeCl3-modification had little effect on Cd^2+adsorption of the biochars,and the equilibrium adsorption capacities of FBC1 and FBC2 were only 1.03 and 0.74 times that of BC1 and BC2.The process of Cd^2+adsorption onto the original and modified rice husk-derived biochars was more consistent with the pseudo-second-order model and the Langmuir model,and it was assumed that the adsorption mainly occurs in monolayers.The maximum adsorption capacities of NBC1 and NBC2(131.58 and 98.04 mg·g^-1,respectively)were significantly higher than that of FBC1 and FBC2(30.30 and 23.26 mg·g^-1,respectively).The reason for Cd^2+adsorption capacity enhancement of NaOH-modified biochars is that NaOH-modification increased the amount of alkaline oxygen-containing functional groups on the surface of biochars,which enhances biochars′cation exchange and precipitation capacity with Cd^2+.