生物炭负载纳米氯磷灰石复合材料对U(Ⅵ)的吸附性能及机理

Effect of humic acid on the removal of uranium from water by biochar-supported nano-chloroapatite and its mechanism

摘要:

试验研究了生物炭负载纳米氯磷灰石，记为BC/nClAP，对水中U(VI)的去除机制及腐殖酸对去除过程的影响。并采用XRD、SEM、FTIR和XPS对材料进行了表征。结果表明：生物炭负载纳米氯磷灰石对水中铀有很好的去除效果(当U(VI)初始浓度为5 mg/L，BC/nClAP投加量为0.1 g/L，pH值为4.0，BC/nClAP对U(VI)的去除率高达99.7%)，腐殖酸对去除效果有显著影响且会缩短吸附平衡时间(使平衡时间由30 min缩短至5 min以内)。无论腐殖酸存在与否，BC/nClAP去除U(VI)的过程均可通过准二级动力学方程及Langmuir等温吸附模型拟合。表明BC/nClAP去除铀的过程是单分子层化学吸附。去除机理主要包括溶解-沉淀以及生物炭表面含氧官能团的络合作用。腐殖酸影响吸附过程可能是因为腐殖酸会抢占吸附位点；且会与U(Ⅵ)形成游离在水中U—HA复合物，从而改变了U(VI)和HA与材料的表面相互作用。

Abstract:

The removal mechanism of U(VI) from water by biochar loaded nano chlorapatite, denoted as BC/nClAP, and the effect of humic acid on the removal process were experimentally investigated. The materials were also characterized by XRD, SEM, FTIR and XPS. The results showed that the biochar-loaded nano chlorapatite had a good removal effect on uranium in water (when the initial concentration of U(VI) was 5 mg/L, the dosage of BC/nClAP was 0.1 g/L, and the pH value was 4.0, the removal rate of U(VI) by BC/nClAP was as high as 99.7%), and the humic acid had a significant effect on the removal effect and shortened the equilibrium time of the adsorption (shortened the equilibration time from 30 min to less than 5 min). Regardless of the presence or absence of humic acid, the removal of U(VI) by BC/nClAP could be fitted by quasi-secondary kinetic equation and Langmuir isothermal adsorption model. It was shown that the process of U(VI) removal by BC/nClAP was monomolecular layer chemisorption. The removal mechanism mainly includes dissolution-precipitation and complexation of oxygen-containing functional groups on the surface of biochar. Humic acid affects the adsorption process probably because humic acid seizes the adsorption sites; and it forms a free-in-water U-HA complex with U(VI), which alters the surface interaction of U(VI) and HA with the material.