Al改性柠条生物炭对P的吸附特性及其机制

为高效利用生物质能源，以常见农林废弃物柠条为原料，在650℃、3h条件下，采用限氧热裂解法制备生物炭，通过直接修饰法用Al改性柠条生物炭，进行批量吸附P实验.利用4种等温吸附模型（Langmuir、Freundlich模型、Temkim、D-R模型）和4种吸附动力学模型（准一级动力学、准二级动力学、Elovich模型、颗粒内扩散模型）以及pH值、添加量影响试验，探讨Al改性生物炭对P的吸附特性.同时，使用FTIR红外、元素分析、SEM和比表面积及孔径分析等技术表征了生物炭的理化性质，揭示了Al改性生物炭对P的吸附机理，并对比了多种改性生物炭对P的吸附效果.结果表明：柠条生物炭（NB）对P的吸附量很低，Al改性柠条生物炭（Al-NB）最佳改性比例为0.2：1，对P的吸附量是NB的8.35倍.Langmuir模型能够很好的描述Al-NB对P的等温吸附过程；Al-NB对P的吸附动力学符合准一级动力学模型，说明其吸附通过边界扩散完成的单层吸附.Al-NB对P的理论最大吸附量为19.97mg/g，平衡时间为24h.随着添加量的增大，Al-NB对P的吸附量不断减小，去除率逐渐增加，2.5g/L为最佳添加量；最适pH为4～10，当pH=7时，达到最大；吸附P后，溶液的pH值向中性范围倾靠，有一定缓冲作用.吸附机理包括：静电吸附作用，配体交换（羟基），P与阴离子（NO₃^-）交换，颗粒内表面络合作用等.以期为水体富营养化治理提供科学依据.

Adsorption characteristics and mechanism of phosphate from aqueous solutions on Al modification biochar produced from Caragana Korshinskii

In order to utilize the waste biomass resources efficiently, Caragana Korshinskii was selected as raw material to produce biochar at 650℃ for 3h by oxygen-limited pyrolysis, using Al modified caragana biochar by direct modification method, and the adsorptions of phosphate in aqueous solutions were evaluated. The effects of initial phosphate concentration and contact time in batch sorption experiments were investigated by the four kinds of isothermal adsorption model (Langmuir, Freundlich, Temkim, D-R model) and the four kinds of adsorption kinetics model (Pseudo first-order, Pseudo second-order, Elovich model, Intraparticle diffusion model), respectively. In addition, the adsorption properties of Al modified biochar on phosphate were investigated by the effects of isothermal adsorption, adsorption kinetics, pH and addition concentration, respectively. The influencing factors of adsorption characteristics about caragana biochar (NB) and Al modification caragana biochar (Al-NB) were discussed by characterized for their elemental composition, functional groups, surface area, surface morphology and scanning electron microscope. The results showed that the adsorption capacity of NB to phosphate was very low; however, when the optimum modification ratio of Al-NB was 0.2:1, the adsorption capacity reached the largest, which is 8.35 times higher than that of the unmodified NB. The adsorption kinetics was best fitted by the pseudo-first order model, while the isothermal adsorption was best described by Langmuir isotherms, indicating that the beneficial adsorption process was monolayer via the boundary diffusion. The adsorption equilibrium was reached in 24h, and the maximum adsorption capacity of reached 19.97mg/g. With the increase of Al-NB addition amount, the adsorption capacity of phosphate decreased and the removal rate gradually increasing. The best addition amount was 2.5g/L. The optimum pH was 4~10, and the adsorption capacity reached the largest when pH=7. After adsorption phosphate, the pH of the solution was leaned to the neutral range and had a certain buffer effect. The mechanism of phosphate adsorbed by Al-NB mainly includes:electrostatic attraction, ligand exchange (hydroxyl), anion exchange (NO₃^-), as well as the inner-sphere surface complex formation process. It was demonstrated that Al-NB could be considered as a promising material to immobilize phosphate in contaminated Eutrophication water.