基于光谱识别技术的土壤铁锰结核对镉的吸附行为研究

铁锰结核是具有高反应活性的矿物复合体;与海洋铁锰结核不同,土壤铁锰结核常在干湿交替、水气干扰条件下存在,形成了独具特色的地球化学特征.作为土壤"新生体",不同地区铁锰结核常表现出较大差异.研究典型区域土壤铁锰结核与重金属的结合行为,有助于深入了解铁锰结核的微生态属性,对于后续土壤的开发利用、保育改良、污染修复等都具有战...

Adsorption of Cadmium on Fe-Mn Nodules Derived From Soil by Spectral Methods

As clay minerals complex with high reactivity, Fe-Mn nodules in soil, with special geochemical characteristics, different from Fe-Mn nodules in the ocean, can always be found in drying-wetting cycle condition and water-air disturbing environment. Fe-Mn nodules, the new-formed component in the pedosphere, appear the various qualities in different regions. The investigation on adsorption behavior between soil Fe-Mn nodules and metals in the representative areas is helpful to understand further the micro-ecological property of Fe-Mn nodules and is significant for soil exploitation and utilization, conservation and improvement, and contamination remediation. It currently lacks the related research on soil Fe-Mn nodules in western China, while this paper might supply unclear information and improve the research level from a spectral aspect. Water-washing method was used and spectral analysis approaches of Inductively Coupled Plasma-Optical Emission Spectrometer (ICP-OES), Ultraviolet-Visible Spectroscopy (UV-Vis), X-Ray Diffractometer (XRD) and Fourier Transform Infrared Spectroscopy (FTIR) were applied to analyze the main elemental oxides and structure of Fe-Mn nodules in western China. Batch adsorption procedures were involved in study the reaction, and the effects of time, cadmium concentration and temperature were discussed. The kinetics equation and isotherms equations were used to fit the reaction, thermodynamic parameters were calculated, and the desorption experiments were studied. The dominant elemental oxides include Fe₂O₃, SiO₂, Al₂O₃ and MnO, with the highest content of Fe₂O₃ followed by SiO₂ in Fe-Mn nodules. Similar mineral components are found between Fe-Mn nodules and soil samples, and functional groups of -OH, Si-O-Si (Al) and Fe(Mn)-O appear in the FTIR spectrum. The adsorption is fast at the beginning of the reaction and then becomes slow gradually. The adsorption capacity (Q) reaches 4.96 mg·g-1 at 6 h, and changes little after 12 h. The increased concentration of cadmium leads to higher Q values, and temperature affects little the reaction. Pseudo-second order equation fit better with a higher coefficient of R2 (0.994 3), indicating the reaction rate might be controlled by chemical adsorption. The value of R2 (0.999 1) from the Langmuir equation, is higher than that from the Freundlich equation, suggesting the reaction belongs to the monolayer chemical adsorption. The reaction is spontaneous and endothermic, and complexation might be involved during the process. Positive S value suggests an increase in randomness during the interaction. The desorption efficiency is better with HCl solution (0.1 mol·L-1, prepared with tap water). The research is significant for mechanism analysis with spectral approaches in future.