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| Facet-dependent Cr(Ⅵ) adsorption and transport on hematite nano-particles |
| Received:March 31, 2021 |
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| KeyWord:hematite;facet-dependent adsorption;Cr(Ⅵ);breakthrough curve |
| Author Name | Affiliation | E-mail | | ZHOU Yiyi | Key Laboratory of Soil Environment and Pollution Remediation, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China
University of Chinese Academy of Sciences, Beijing 100864, China | | | LIU Cun | Key Laboratory of Soil Environment and Pollution Remediation, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China | liucun@issas.ac.cn | | WANG Yujun | Key Laboratory of Soil Environment and Pollution Remediation, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China
University of Chinese Academy of Sciences, Beijing 100864, China | yjwang@issas.ac.cn |
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| Abstract: |
| This study investigated the facet-dependent Cr(Ⅵ) adsorption and transport on hematite nanoparticles using batch and column experiments, respectively. Two hematite nanoparticles were characterized as nano-plates(HNPs) with dominant-exposed {001} facets and nano-rods(HNRs) with dominant-exposed {110} facets. We determined how the flow conditions, including pH, inflow concentration, flow velocity, and ionic strength, could impact Cr(Ⅵ) transport. The batch experiments showed that the HNR- and HNP-related isothermal and kinetic adsorption of Cr(Ⅵ) could be described well by the Langmuir and the pseudo-second-order kinetic models, respectively. The maximum Cr(Ⅵ) adsorption capacities of the HNPs and HNRs were 2.97 mg·g-1 and 4.95 mg·g-1, respectively. The increase in the pH and ionic strength reduced both the HNP- and HNR-related Cr(Ⅵ) adsorption, indicating both chemical and electrostatic adsorption mechanisms. The column experiments showed that the pH increase augmented the electronegativity in the packed columns and reduced the Cr(Ⅵ) retention. The initial concentration increase accelerated the site occupation, while the increase in the flow rate reduced the Cr(Ⅵ) residence time in the columns. The increasing ionic strength increased the competition for the surface sites from the competing anions and promoted the Cr(Ⅵ) transport. The retention of the HNPs is less than that of the HNRs due to the lower adsorption site density of the {001} facets. Results indicated that the different binding modes on hematite facets significantly influence the adsorption and transport behaviors of Cr (Ⅵ). |
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