Adsorption Behavior And Mechanisms Of Heavy Metal Using Natural Soil Mineral Nanoparticles

Kaolinite and montmorillonite were abundant in the soil environment and their capability for heavy metal removal had been widely excavated.The main objectives of the present work were to explore the capability of two types of natural mineral NPs?i.e.,kaolinite and montmorillonite NPs?for the adsorption of a typical environmental heavy metal(i.e.,Cd²⁺)under varying environmental conditions.Briefly,the kaolinite and montmorillonite NPs were prepared by dispersing the granular kaolinite and montmorillonite in an aqueous phase,followed by the extraction of the nano-sized fractions from the suspension.The dynamics and thermodynamics adsorptions of the kaolinite and montmorillonite NPs were studied through a series of batch experiments.The pseudo-first-order and pseudo-second-order kinetics equations were used to describe the kinetic data.Langmuir and Freundlich equations were used to describe the thermodynamic data.The effects of varying environmental factors?i.e.pH,ionic strength and species?were also studied.The average particle sizes of kaolinite and montmorillonite NPs were125.6 nm and122.3 nm,respectively.The maximum adsorption capability of Cd²⁺by kaolinite NPs were0.5896 and 4.3122 mg·g^-1 at pH 5 and 7,respectively(for montmorillonite nanoparticles are 2.7012 and 6.9541 mg·g^-1).Further experiments revealed that the maximum adsorption capability of Cd²⁺by either kaolinite or montmorillonite NPs increased with increasing environmental p H.Both ionic strength and type of electrolyte are two of the important factors affecting the adsorption of Cd²⁺by kaolinite and montmorillonite NPs.In this paper,the following conclusions are drawn from the adsorption of heavy metals using natural soil mineral nanoparticles:?i?The pseudo-second-order kinetics model is more suitable for describing the adsorption of heavy metals by natural NPs.The chemisorption is found to be the predominant mechanism for the Cd²⁺adsorption by kaolinite/montmorillonite NPs.?ii?The adsorption capacities of Cd²⁺by kaolinite and montmorillonite NPs largely depended on solution pH.It is possibly due to the surface functional group of the natural NPs and competitive adsorption between H⁺and Cd²⁺in the solution.Ionic strength and species were also found to play an important role important in influencing the adsorption of Cd²⁺by kaolinite and montmorillonite NPs.?iii?Comparing with engineered NPs,kaolinite and montmorillonite NPs in environmental remediation could provide both economic and ecologic advantages because of comparable adsorption capacity,shorter equilibrium time,non-invasive property and low production costs.These advantages of the natural NPs provide the engineer with a promising alternative option in the future remediation practice.