Politehnica University Timisoara, Faculty of Industrial Chemistry and Environmental Engineering, Bd. V. Parvan Nr. 6, 300223 Timisoara, Romania.
National Institute for Research and Development in Electrochemistry and Condensed Matter, Str. Dr. Aurel Paunescu Podeanu Nr. 144, 300587 Timisoara, Romania.
J Hazard Mater. 2016 Jun 5;310:270-7. doi: 10.1016/j.jhazmat.2016.02.042. Epub 2016 Feb 23.
Adsorption of Cr(VI) on MnO2 was investigated with respect to effect of pH, temperature, ionic strength, initial Cr(VI) concentration, co-presence of different anions (HCO3(-), SO4(2-), H2PO4(-), NO3(-) and Cl(-)) and of low molecular weight natural organic materials (LMWNOM) (acetate, oxalate and citrate). The process was rapid during the first 3-5min, reaching equilibrium after one hour. Adsorption decreased with increasing pH, temperature and Cr(VI) initial concentration, and increased with increasing ionic strength. Co-presence of phosphate, sulfate, bicarbonate, citrate and oxalate hindered Cr(VI) adsorption, whereas nitrate, chloride and acetate did not exert any notable influence. The overall order of Cr(VI) adsorption suppression due to co-presence of anions and LMWNOM was H2PO4(-)>HCO3(-)>SO4(2-), and oxalate>citrate, respectively. Highest experimental equilibrium sorption capacity (0.83mgg(-1)) was obtained at 20°C and pH 5.9, while lowest (0.18mgg(-1)) was noticed in the co-presence of H2PO4(-), at 20°C and pH 6.9. Adsorption kinetics was successfully fitted by pseudo-second-order model. Mechanisms for both specific and non-specific adsorption are likely to be involved, while rate-controlling step involved both intra-particle and film diffusion processes. Cr(VI) was strongly bound to MnO2, which makes risks of its subsequent liberation into the environment to be low.
研究了 pH 值、温度、离子强度、初始 Cr(VI) 浓度、共存不同阴离子（HCO3(-)、SO4(2-)、H2PO4(-)、NO3(-) 和 Cl(-)）和低相对分子质量天然有机物质（LMWNOM）（醋酸盐、草酸盐和柠檬酸盐）对 MnO2 上 Cr(VI) 吸附的影响。在最初的 3-5 分钟内，吸附过程迅速，1 小时后达到平衡。吸附随 pH 值、温度和 Cr(VI) 初始浓度的升高而降低，随离子强度的升高而增加。磷酸盐、硫酸盐、碳酸氢盐、柠檬酸盐和草酸盐的共存会阻碍 Cr(VI) 的吸附，而硝酸盐、氯化物和醋酸盐则没有明显的影响。阴离子和 LMWNOM 共存对 Cr(VI) 吸附的抑制总体顺序为 H2PO4(-)>HCO3(-)>SO4(2-)和草酸盐>柠檬酸盐。在 20°C 和 pH 5.9 下，实验获得的最大平衡吸附容量（0.83mgg(-1)），而在 20°C 和 pH 6.9 下共存 H2PO4(-)时，观察到的最小吸附容量（0.18mgg(-1)）。吸附动力学很好地符合伪二级模型。可能涉及到特异性和非特异性吸附的机制，而控制步骤涉及到内颗粒和膜扩散过程。Cr(VI) 与 MnO2 结合紧密，使其随后释放到环境中的风险较低。
