Abstract:

Taking the desilication liquor produced during the alumina recovery of coal fly ash as raw material, mesoporous C-S-H with large specific surface area (401 m²·g^-1) was prepared by using the normal precipitation method, of which the molar ratio of calcium to silicon had been controlled. The effects of initial concentration, sorbent dosage, solution pH and ionic strength on the sorption of U(Ⅵ) by C-S-H were systematically investigated, and the sorption kinetics and thermodynamics were also studied. Moreover, the performance of C-S-H on the removal of toxic metals in actual uranium-containing wastewater was evaluated. The results indicated that the transformation of calcium silicate solid in low quality to high-value-added sorbent material had been realized by controlling the synthesis condition. C-S-H of 0.75 g·L^-1 still had a high sorption capacity in equilibrium at pH 2 (q_e=67.9 mg·g^-1), while UO₂(H₂O)₅²⁺ transformed to UO₂(CO₃)₃^4- in alkaline solution with high amount of CO₃^2-, and it was not good for the sorption of U(Ⅵ) on the negative surface of C-S-H. When C-S-H dosage increased to 2-5 g·L^-1, the removal efficiency of U(Ⅵ) by C-S-H could be maintained at a comparatively higher level (C[U(Ⅵ)]_initial=500 mg·L^-1, 88.3%-93.5%). The equilibrium of the adsorption could be reached within several hours, and the process followed the pseudo-second-order kinetic model and two-stage Weber-Morris equation model. The adsorption followed Langmuir isotherm model. Ion exchange (84.6%) and surface complexation were the main mechanisms accounting for the sorption. The material exhibited a great capacity to remove U, Zn, Hg, Mn and Cd in uranium-containing wastewater. Therefore, C-S-H had great potential to become a promising material to remove the toxic metals from wastewater.

Key words: coal fly ash, sustainability, adsorbents, porous materials, adsorption, wastewater

摘要：

以粉煤灰铝回收过程的脱硅液为原料，通过控制钙硅摩尔比的常规沉淀法制备得到大比表面积介孔C-S-H（401 m²·g^-1），系统研究了初始浓度、投加量、pH和离子强度对C-S-H吸附U（Ⅵ）过程的影响，以及吸附的热动力学特征，并评价了C-S-H去除实际含铀废水中毒性金属的性能。结果表明，通过控制合成条件实现了低品质硅钙渣向高附加值吸附材料的转变。0.75 g·L^-1 C-S-H在pH 2仍具有较高的平衡吸附容量（q_e=67.9 mg·g^-1），在富含CO₃^2-的碱性溶液中UO₂（H₂O）₅²⁺转变为UO₂（CO₃）₃^4-不利于带负电的C-S-H表面吸附U（Ⅵ）。当C-S-H投加量升高至2～5 g·L^-1，材料对U（Ⅵ）的吸附去除效率即能维持在相对较高水平（C[U（Ⅵ）]_initial=500 mg·L^-1，去除率88.3%～93.5%），吸附可在数小时内达到平衡，符合拟二级动力学模型和两阶段Weber-Morris方程模型，吸附等温线符合Langmuir模型，吸附机理主要为离子交换（84.6%）和表面络合。材料对含铀废水中的U、Zn、Hg、Mn和Cd均表现出良好的吸附去除性能，因而C-S-H可成为在废水毒性金属去除方面极具应用前景的材料。

关键词: 粉煤灰, 可持续性, 吸附剂, 多孔材料, 吸附, 废水