Removal Of Heavy Metal Ions From Wastewater By Modified Halloysite Mineral

Heavy metal wastewater can enter into the ecosystem from mining, metallurgy operations, metal finishing, chemical wastewater, electroplating etc. The adsorption process is generally known to be one of the most promising techniques for the removal of heavy metals from the waste streams.·In recent years, natural mineral materials, due to their large surface area, high cation exchange capacity and low costs, have been studied for potential applications as environmental remediation agents to remove heavy metals from wastewater. And mineral materials that have been often used to remove heavy metals include zelolite, bentonite and so on. However, there are few relevant literatures of heavy metals adsorption by halloysite. Halloysite is a kind of aluminosilicate with a predominantly nanosized hollow tubular structure. It is also found to contain adequate hydroxyl functional groups that make it a potential candidate for the modification with organic matter. Raw halloysite presents low metal ion adsorption capacity, so it is necessary to study chemical modification of halloysite to enhance its adsorption capacity. One technique is the grafting of functional groups onto the adsorbent surface via direct grafting.Modified halloysite nanotubes were prepared with halloysite and various organic compounds as raw materials using solution blended method. The as-prepared adsorbents were characterized by the FTIR, thermogravimetric analysis, transmission electron microscope and N2 adsorption-desorption isotherms. By single factor experiment, the influence of the initial concentration of heavy metal ions, adsorption time, adsorption temperature, pH value on adsorption properties were investigated. Finally, adsorption kinetics and adsorption isotherm model were studied. We obtain the following results.(1) The natural halloysite nanotubes (HNTs) were modified with y-thiopropyl trimethoxy silane (KH-590) to form nano-composite which named as SH-HNTs. The characterization results of original and modified hanlloysite show that thiopropyl groups were grafted successfully onto the nanotubes surface and the grafted amount is 0.0235 g/g. Then the SH-HNTs was used as adsorbent for Ag(Ⅰ) removal from its aqueous solution. The results showed that SH-HNTs exhibited rapid adsorption rate. And the adsorption capacity increased with increasing Ag(Ⅰ) initial concentration and achieved maximum adsorption capacity finally. Moreover, the adsorption capacity of SH-HNTs almost unchanged when the pH varies. Pseudo-second-order model was found to explain the kinetics of Ag(Ⅰ) adsorption of SH-HNTs most effectively. And the adsorption data of Ag(Ⅰ) on SH-HNTs were all well consistent with Langmuir and Freundlich model. According to Langmuir model, the maximum adsorption capacity (Qmax) can be calculated as 25.51mg/g.(2) The natural halloysite nanotubes (HNTs) were modified with hexadecyl trimethyl ammonium bromide (HDTMA) to form nano-composite which named as HDTMA-HNTs. The characterization results of original and modified hanlloysite show that quaternary ammonium cations were grafted successfully onto the nanotubes surface and the grafted amount is 0.0769 g/g. Then the HDTMA-HNTs was used as adsorbent for Cr(Ⅵ) removal from its aqueous solution. The results showed that HDTMA-HNTs exhibited rapid adsorption rate. And the adsorption capacity increased with increasing heavy metal initial concentration and achieved maximum adsorption capacity finally. Moreover, the adsorption capacity of HDTMA-HNTs changed significantly with the increase of pH. Pseudo-second-order model was found to explain the kinetics of Cr(Ⅵ) adsorption of HDTMA-HNTs most effectively. And the adsorption data of Cr(Ⅵ) on HDTMA-HNTs was well consistent with Langmuir model, which showed the monolayer coverage of the adsorbate on the surface of modified halloysite. According to Langmuir model, the maximum adsorption capacity (Qmax) can be calculated as 6.892 mg/g.(3) The natural halloysite nanotubes (HNTs) were modified with 3-aminopropyl trimethoxy silane (KH-792) to form nano-composite which named as NH2-HNTs. The characterization results of original and modified hanlloysite show that amino groups were grafted successfully onto the nanotubes surface and the grafted amount is 0.0187 g/g. Then the NH2-HNTs was used as adsorbent for Cr(Ⅵ) removal from its aqueous solution. The results showed that NH2-HNTs exhibited rapid adsorption rate. And the adsorption capacity increased with increasing heavy metal initial concentration and achieved maximum adsorption capacity finally. Moreover, the NH2-HNTs had good adsorption capacity at pH 3 to 5. Pseudo-second-order model was found to explain the kinetics of Cr(VI) adsorption of NH2-HNTs most effectively. And the adsorption data of Cr(VI) on NH2-HNTs was well consistent with Langmuir model, which showed the monolayer coverage of the adsorbate on the surface of modified halloysite. According to Langmuir model, the maximum adsorption capacity (Qmax) can be calculated as 47.6 mg/g.