Electrokinetics couples with the adsorption of activated carbon-supported hydroxycarbonate green rust that enhances the removal of Sr cations from the stock solution in batch and column

https://doi.org/10.1016/j.seppur.2021.118531Get rights and content

Highlights

  • Activated carbon-supported hydroxycarbonate green rust was prepared to remove Sr2+.

  • Electrokinetics coupling with GR-AC was designed to enhance column-mode Sr2+ uptake.

  • Sr2+ cations experienced different reaction pathways in the column electrokinetics.

  • Thomas breakthrough model was suitable for describing the Sr2+ removal in the column.

  • The research supplies a reference for removing other radioactive cations from wastewater.

Abstract

Activated carbon-supported hydroxycarbonate green rust (GR-AC) was prepared, characterized, and used to remove Sr2+ ions from stock solutions. The electrokinetics coupling with the adsorption was further designed to enhance the uptake of Sr2+ ions in the fixed-bed column. The adsorption capacities (mg/g) of GR-AC experienced a U-shaped change over the pH of 2–13 for each concentration of Sr2+. The equilibrium adsorption capacities for the adsorbent in the initial concentrations of Sr2+ of 50, 100, 150, 200, and 250 mg/g were 48.36, 67.42, 73.25, 81.59, and 84.47, respectively. The pseudo-first-order and Elovich kinetic models were appropriate for modeling the adsorption of Sr2+ onto the GR-AC in the static equilibrium-adsorption experiments in terms of the whole pH range, while the intraparticle model was only suitable for the modeling in the alkaline aqueous environment. For the column-mode experiments, the changes in the voltage gradients, flow rates, and initial pH all had a significant effect on the removal of Sr2+ cations. A maximum breakthrough volume of 26.52 L was obtained in the orthogonal design. The correspondingly optimal combination of parameters determined for the column-mode experiments included the voltage gradient of 1.0 V/cm, the initial pH of 10, and a relatively slow flow rate of 5–15 mL/min. The application of EK enhanced the removal kinetics of Sr2+ from the stock solutions while had not significantly affected the interactions between Sr2+ and GR-AC. The specific reaction pathways determined for the Sr2+ removal was different with different pH ranges. The research provides an efficient method for removing radioactive Sr from wastewater in the future.

Introduction

The dependence of economic development on energy consumption and the shortcomings highlighted in traditional energy sources have accelerated the utilization of nuclear energy in many countries including both developed and developing countries [1]. The discharge of wastewater containing radioactive ions and the disposal of nuclear wastes have become major technical problems limiting the sustainable development of the nuclear industry [2], [3]. Moreover, the accidental release of some radionuclides not only threatens food supplies for human also sustains a negative impact on natural ecosystems. In March 2011, an earthquake measuring 9.0 on the Richter scale caused the failure of two nuclear power plant reactors in Fukushima Prefecture, in which an abnormality occurred in a reactor in the first nuclear power plant, causing nuclear steam leakage [4], [5]. The accident caused a large area of contamination with the radionuclides of 137Cs, 134Cs, 131I, and 90Sr [6], [7], [8], [9]. Among these radionuclides, 90Sr isotope having a half-life of approximately 29 years, as a beta emitter, has attracted wide attention from researchers and environmentalists [10], [11]. strontium ions (i.e., Sr2+) have strong mobility in the water environment and can be easily incorporated into terrestrial and aquatic organisms. Therefore, it is critical to explore new materials and invent new techniques for the selective uptake or efficient removal of Sr2+ ions from the solution [11], [12].

There are several methods used to remove Sr ions from wastewater, such as evaporation, filtration (e.g., microfiltration and ultrafiltration), chemical precipitation or coprecipitation, chromatography, solvent extraction, reverse osmoses, adsorption, and ion exchange [13], [14], [15], [16]. Among these techniques, the adsorption method is more desired to remediate the wastewater with high volumes to guarantee the removal performance and to cause minimal disposal wastes. Besides, the adsorption of Sr2+ presents some unique advantages compared to the others including high efficiency, excellent selectivity, simple processing, and convenient operation [2], [15], [17], [18]. Commonly, for a specific pollutant, the adsorption performance depends largely on the physicochemical properties of the adsorbent and the changes in the competitive environments. Some traditional adsorbents such as zeolite, bentonite montmorillonite, biomass-carbonized materials, and chitosan, etc., and some synthesized adsorbents silicotitanate, WO3, niobate nanofibers, and metal hexacyanoferrates, etc., have developed and applied for the removal of Sr2+ ions [19], [20], [21], [22], [23], [24], [25], [26]. However, some existing issues which include the stability drawbacks of the organic-based materials, the complexity of the synthetic process, the high sensitivity to solution conditions, and the inapplicability of adsorbents in the column mode have restricted the industrial applications of these materials. It is essential to test and investigate more efficient and cheaper materials [2], [15], [27].

Over recent decades, the wide application of the mixed-valent iron minerals in processing environmental pollutions has drawn a significant amount of attention due to their important roles in influencing the transformation, toxicity, and mobility of inorganic pollutants in the engineered systems. The mixed-valent iron oxides mainly include magnetite and green rust (GR) [28], [29]. GRs are layered double hydroxides, containing both Fe(II) and Fe(III) cations in the brucite-like structures [30]. Following the type of intercalated anions (e.g., CO32-, SO42-, and Cl-), there are some common types of GRs such as hydroxycarbonate GR (i.e., GR(CO32-)), hydroxysulfate GR (i.e., GR(SO42-)), and hydroxychloride GR (i.e., GR(Cl-)) [31], [32]. GR can theoretically adsorb both inorganic anions and cationic metals based on its amphoteric surface hydroxyl groups. GRs have been used to transform several inorganic contaminants through redox processes [33], [34], [35], [36], [37], [38]. The cycling of 35 elements highlighting the involvement of GR has been reported in a comprehensive investigation [31], [32]. Generally, the interaction between cations and GR mainly experiences three major pathways: 1) the adsorption of cations onto the external surfaces of GR; 2) the incorporation of cations (e.g., divalent and trivalent metals) into the octahedral sheets of the GR interlayer; 3) redox transformations or chemical immobilization through anion exchange, complexation, and chemical precipitation [28], [29], [31], [32], [39], [40], [41]. The redox processes caused by GRs for the transformation of inorganic contaminants have been widely investigated [32]. However, the adsorption capabilities of GRs for cations in the solution environment have been rarely studied, which increases the uncertainty of the application of GR on the uptake of Sr2+ ions. To enhance the adsorption performance of GR on Sr2+, some other techniques are needed to improve the whole removal process.

Electrokinetic (EK) remediation is considered an outstanding method for the remediation of contaminated soil and solid wastes, which is effective in achieving the migration and accumulation of inorganic contaminants in a specific area by electrolysis (i.e., decomposition of water) and electromigration [42], [43], [44], [45]. The H+ and OH ions generated in electrolysis can affect the adsorption and desorption of Sr2+ in the electrolyzer [46], [47]. The Sr2+ ions will be continuously migrated to the cathode area through electromigration during the EK process. In this study, the hydroxycarbonate GR loading on activated carbon (GR-AC) was synthesized to remove Sr2+ ions from the stock solution. The EK technique coupling with the adsorption was further designed to conduct the uptake of Sr2+ ions in the column-mode experiments. The parameters including the molar ratios of Fe(II) to Fe(III), the ratios of solid to liquid (g/mL), the molar ratios of OH to Fe(II) + Fe(III), and the molar ratios of CO32- to Fe(II) + Fe(III) were comprehensively adjusted based on the adsorption results of Sr2+ in the static equilibrium-adsorption tests to choose an appropriate type of GR-AC for further experiments. Five kinetic models including the pseudo-first-order, pseudo-second-order, intraparticle diffusion, Elovich, and Chrastil’s models were employed to obtain reaction kinetic parameters in different pH ranges and elucidate mechanism pathways corresponding to the equilibrium adsorption. The factors in the column experiments including the voltage gradients (V/cm), the flow rates of feed solutions (mL/min), and the initial pH were changed within four levels in the form of orthogonal design to optimize the running performance of the EK system. Two models including Thomas and Bohart–Adams were further applied for the prediction of breakthrough curves. The mechanisms of Sr2+ removal from the stock solution in the column-mode experiments were comprehensively discussed and analyzed by combining the results of pH, minerals, and morphologies. The research provides an efficient method for removing radioactive Sr from water and also supplying a reference for removing other radioactive cations from wastewater.

Section snippets

Synthesis of GR-AC

Hydroxycarbonate GR loading on AC was synthesized under a coprecipitation method [32]. The AC powders were commercially purchased and were washed several times using ultrapure water, separated by centrifugation at 5000 rpm, dried at 100 °C, and immediately stored in a chamber (150 mbar) pumped by a vacuum machine (VT4.8, BEAKER, Germany) to remove some dissolvable impurities and oxygen gas (O2) before being employed for the synthesis process. The ultrapure water was boiled under atmospheric

Characterization of GR-AC

Characterizations of AC and GR-AC referring to SEM images, EDS, and FTIR spectra are shown in Fig. 2. The distribution of elements on the adsorbents that includes AC and GR-AC are correspondingly listed in Table S2 in the SI. As seen, for the morphology of AC (Fig. 2 a), the surface was rough and uneven with the random distributions of some small pores and cracks. Differently, for the morphology of GR-AC (Fig. 2 b), the brucite-like structures were observed, which demonstrated the layered

CRediT authorship contribution statement

Tao Huang: Conceptualization, Methodology, Formal analysis, Writing - original draft, Writing - review & editing. Shu-wen Zhang: Validation, Resources, Supervision. Lulu Zhou: Data curation, Writing - review & editing. Long-fei Liu: Resources, Project administration.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

This work was supported by the China Postdoctoral Science Foundation (No. 2020M681774) and the Natural Science Foundation of the Jiangsu Higher Education institutions of China (No. 20KJB490001).

References (79)

  • A.M. Ganan-Calvo et al.

    Review on the physics of electrospray: From electrokinetics to the operating conditions of single and coaxial Taylor cone-jets, and AC electrospray

    J. Aerosol Sci.

    (2018)
  • E.M. Laux et al.

    Electrode-based AC electrokinetics of proteins: A mini-review

    Bioelectrochemistry

    (2018)
  • Y.Z. He et al.

    Selenium contamination, consequences and remediation techniques in water and soils: A review

    Environ. Res.

    (2018)
  • A. Ramos et al.

    AC electrokinetics of conducting microparticles: A review

    Curr. Opin Colloid Interface

    (2016)
  • Y.C. Wu et al.

    Recent advances in microbial electrochemical system for soil bioremediation

    Chemosphere

    (2018)
  • B.S. Ramadan et al.

    Hadrah, An overview of electrokinetic soil flushing and its effect on bioremediation of hydrocarbon contaminated soil

    J. Environ. Manage.

    (2018)
  • J.C. Mendez et al.

    High and low affinity sites of ferrihydrite for metal ion adsorption: Data and modeling of the alkaline-earth ions Be, Mg, Ca, Sr, Ba, and Ra

    Geochim. Cosmochim. Acta

    (2020)
  • X.H. Feng et al.

    Effects of phosphate and silicate on the transformation of hydroxycarbonate green rust to ferric oxyhydroxides

    Geochim. Cosmochim. Acta

    (2015)
  • T. Huang et al.

    Ultrasound-enhanced electrokinetic remediation for removal of Zn, Pb, Cu and Cd in municipal solid waste incineration fly ashes

    Waste Manage.

    (2018)
  • R. Chakravarty et al.

    Facile radiochemical separation of clinical-grade (90)Y from (90)Sr by selective precipitation for targeted radionuclide therapy

    Nucl. Med. Biol.

    (2019)
  • T. Huang et al.

    Electrokinetic removal of chromium from chromite ore-processing residue using graphite particle-supported nanoscale zero-valent iron as the three-dimensional electrode

    Chem. Eng. J.

    (2018)
  • T. Huang et al.

    Graphite particle electrodes that enhance the detoxification of municipal solid waste incineration fly ashes in a three-dimensional electrokinetic platform and its mechanisms

    Environ. Pollut.

    (2018)
  • P. Ammendola et al.

    Insights into utilization of strontium carbonate for thermochemical energy storage

    Renew. Energy

    (2020)
  • R. Pinsky et al.

    Comparative review of hydrogen production technologies for nuclear hybrid energy systems

    Prog. Nucl. Energy

    (2020)
  • W.J. Mu et al.

    Bonding of crown ethers to alpha-zirconium phosphate-Novel layered adsorbent for radioactive strontium separation

    Sep. Purif. Technol.

    (2020)
  • M.D. Zhang et al.

    Na/Zn/Sn/S (NaZTS): Quaternary metal sulfide nanosheets for efficient adsorption of radioactive strontium ions

    Chem. Eng. J.

    (2020)
  • S. Salminen-Paatero et al.

    Nuclear contamination sources in surface air of Finnish Lapland in 1965–2011 studied by means of (137)Cs, (90)Sr, and total beta activity

    Environ. Sci. Pollut. Res. Int.

    (2019)
  • C. Ory et al.

    Consequences of atmospheric contamination by radioiodine: the Chernobyl and Fukushima accidents

    Endocrine

    (2020)
  • M. Hori et al.

    Source evaluation of Cs-137 in foodstuffs based on trace Cs-134 radioactivity measurements following the Fukushima nuclear accident

    Sci. Rep.-Uk

    (2018)
  • S. Nakamura et al.

    Measurement of Sr-90 radioactivity in cesium hot particles originating from the Fukushima Nuclear Power Plant Accident

    J. Radiat. Res.

    (2018)
  • S. Nakamura et al.

    Measurement of 90Sr radioactivity in cesium hot particles originating from the Fukushima Nuclear Power Plant Accident

    J. Radiat. Res.

    (2018)
  • H. Ashworth et al.

    Effect of humic acid & bacterial exudates on sorption-desorption interactions of (90)Sr with brucite

    Environ. Sci. Processes Impacts

    (2018)
  • V. Vicente Vilas, S. Millet, M. Sandow, L. Aldave de Las Heras, Automated 90Sr separation and preconcentration in a...
  • B. McDevitt et al.

    Maximum removal efficiency of barium, strontium, radium, and sulfate with optimum AMD-marcellus flowback mixing ratios for beneficial use in the northern appalachian basin

    Environ. Sci. Technol.

    (2020)
  • M.Y. Prajitno et al.

    The effect of pre-activation and milling on improving natural clinoptilolite for ion exchange of cesium and strontium

    J. Environ. Chem. Eng.

    (2020)
  • M.D. Zhang et al.

    A novel nanomaterial and its new application for efficient radioactive strontium removal from tap water: KZTS-NS metal sulfide adsorbent versus CTA-F-MF process

    Chem. Eng. J.

    (2020)
  • T. Huang et al.

    Microwave irradiation assisted sodium hexametaphosphate modification on the alkali-activated blast furnace slag for enhancing immobilization of strontium

    Chemosphere

    (2020)
  • H. Kunishi et al.

    Investigation on strontium adsorption selectivity of hydrothermally synthesized layered sodium titanates

    Sci. Adv. Mater.

    (2020)
  • A. Ermolenko et al.

    Wastewater treatment from lead and strontium by potassium polytitanates: kinetic analysis and adsorption mechanism

    Processes

    (2020)
  • Cited by (12)

    • A comprehensive investigation of zeolite-rich tuff functionalized with 3-mercaptopropionic acid intercalated green rust for the efficient removal of Hg<sup>II</sup> and Cr<sup>VI</sup> in a binary system

      2022, Journal of Environmental Management
      Citation Excerpt :

      Although CrVI is indispensable for the growth of some plants, excessive Cr in the soil would poison the plant root and thwart the adsorption and transportation of some nutrients to the botanical issues (Apollaro et al., 2019; Zhang et al., 2019). Some techniques including ion exchange, chemical precipitation, chemical reduction, electrokinetics, electroplating, adsorption, and microbial disposal have been used to remove heavy metals (HMs) from the wastewater (Bilal et al., 2020; Egbosiuba et al., 2020; Huang et al., 2021e; Qin et al., 2020; Zeng et al., 2020). The adsorption method among these choices has its advantages for the treatment of HM-contaminated wastewater such as operation simplicity, lower secondary pollution, and adsorbent recyclability (Egbosiuba et al., 2020; Jeon et al., 2020; Rasheed et al., 2020).

    View all citing articles on Scopus
    View full text