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Econ. Environ. Geol. 2023; 56(3): 301-310

Published online June 30, 2023

https://doi.org/10.9719/EEG.2023.56.3.301

© THE KOREAN SOCIETY OF ECONOMIC AND ENVIRONMENTAL GEOLOGY

Adsorption Characteristics of Oxyanions on Ferrihydrite and Mineral Phase Transformation

Gyure Kim, Yeongkyoo Kim*

Author Info. +

School of Earth System Sciences, Kyungpook National University, Daegu, 41566, Korea

Correspondence to : *ygkim@knu.ac.kr

Received: April 7, 2023; Revised: May 16, 2023; Accepted: June 12, 2023

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided original work is properly cited.

Abstract

Ferrihydrite is an iron oxide mineral that is easily found in the natural environment, including acid mine drainage, and has a low crystallinity and high specific surface area, resulting in high reactivity with other ions, and can remove environmentally hazardous substances. However, because ferrihydrite is a metastable mineral, there is a possibility of releasing adsorbed ions by phase transformation to other minerals having low surface area and high crystallinity. In this study, the adsorption characteristics of arsenate, chromate, and selenate on ferrihydrite and the oxyanion removal efficiency of ferrihydrite were studied considering mineral phase transformation. At both pH 4 and 8, the adsorption of oxyanions used in the study were in good agreement with both Langmuir and Freundlich adsorption models except for selenate at pH 8. Due to the difference in surface charge according to pH, at pH 4 a higher amount of ions were adsorbed than at pH 8. The adsorption amount were in the order of arsenate, chromate, and selenate. These different adsorption models and adsorption amounts were due to different adsorption mechanisms for each oxyanions on the surface of ferrihydrite. These adsorption characteristics were closely related to changes in the mineral phase. At pH 4, a phase transformation to goethite or hematite was observed, but only a phase transformation to hematite was observed at pH 8. Among the oxyanion species on ferrihydrite, arsenate showed the highest adsorption capacity and hardly caused phase transformation during the experimental period after adsorption. Contrary to this, chromate and selenate showed faster mineral phase transformation than arsenate, and selenate had the lowest retardation effect among the three oxyanions. Ferrihydrite can effectively remove arsenate due to its high adsorption capacity and low phase transformation rate. However, the removal efficiency for other two oxyanions were low by the low adsorption amount and additional mineral phase transformation. For chromate, the efficient removal is expected only at low concentrations in low pH environments.

Keywords ferrihydrite, oxyanion, adsorption mechanism, phase transformation, goethite

페리하이드라이트의 산화음이온 흡착 특성과 광물상 변화

김규례 · 김영규*

경북대학교 지구시스템과학부

요 약

페리하이드라이트는 산상광산배수를 포함한 자연 환경에서 쉽게 관찰되는 산화철 광물로 결정도가 낮고 높은 비표면적을 갖고 있어 다른 이온과의 반응성이 매우 우수하여 환경유해물질과의 반응을 통하여 이의 제거가 가능하다. 그러나 페리하이드라이트는 준안정성 광물이기 때문에 표면적이 작고 결정도가 높은 다른 광물로의 상변화로 흡착된 이온들의 방출 가능성도 존재한다. 본 연구에서는 비산염, 크롬산염, 셀레늄산염의 페리하이드라이트에 대한 흡착 특성과 광물상 변화까지 고려한 페리하이드라이트의 산화음이온 제거 효능을 연구하였다. 실험 시 pH 4와 8에서 연구에 사용된 산화음이온들의 흡착은 pH 8에서 셀레늄산염을 제외하고 Langmuir와 Freundlich 두 흡착 모델과 잘 일치하였다. 각 산화음이온의 흡착량은 pH에 따른 표면 전하의 차이로 인하여 pH 4의 경우 pH 8보다 더 높았다. 흡착 량은 비산염, 크롬산염, 그리고 세레늄산염의 순서를 보여주었다. 이러한 흡착모델과 흡착량은 각 산화음이온의 흡착 시 페리하이드라이트 표면에서 일어나는 서로 다른 흡착 기작을 잘 대변한다. 이러한 흡착 특성은 광물상의 변화와도 밀접한 연관성이 있었다. pH 4에서는 침철석 혹은 적철석으로의 상변화를 보여주었으나, pH 8에서는 적철석으로의 상변화만이 관찰되었다. 산화음이온 종 중 비산염은 가장 높은 흡착력을 보여주며, 흡착 후 페리하이드라이트의 실험 기간 내 거의 상변화를 일으키지 않았다. 이와 달리 크롬산염과 셀레늄산염은 비산염에 비하여 광물상 변화가더 빨랐으며 세 산화음이온 중 셀레늄산염의 지연 효과가 가장 낮았다. 페리하이드라이트는 비산염에 대하여 높은 흡착 능력과 낮은 상변화로 인하여 효과적인 제거가 가능하지만 다른 두 산화음이온 종은 낮은 흡착량과 추가적인 광물상 변화로 비산염에비하여 제거 효과가 떨어지고 크롬산염의 경우 낮은 pH 환경에서 낮은 농도의 경우에에만 효율적인 제거가 가능할 것으로 판단된다.

주요어 페리하이드라이트, 산화음이온, 흡착기작, 상변화, 침철석

Article

Research Paper

Econ. Environ. Geol. 2023; 56(3): 301-310

Published online June 30, 2023 https://doi.org/10.9719/EEG.2023.56.3.301

Copyright © THE KOREAN SOCIETY OF ECONOMIC AND ENVIRONMENTAL GEOLOGY.

Adsorption Characteristics of Oxyanions on Ferrihydrite and Mineral Phase Transformation

Gyure Kim, Yeongkyoo Kim*

School of Earth System Sciences, Kyungpook National University, Daegu, 41566, Korea

Correspondence to:*ygkim@knu.ac.kr

Received: April 7, 2023; Revised: May 16, 2023; Accepted: June 12, 2023

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided original work is properly cited.

Abstract

Ferrihydrite is an iron oxide mineral that is easily found in the natural environment, including acid mine drainage, and has a low crystallinity and high specific surface area, resulting in high reactivity with other ions, and can remove environmentally hazardous substances. However, because ferrihydrite is a metastable mineral, there is a possibility of releasing adsorbed ions by phase transformation to other minerals having low surface area and high crystallinity. In this study, the adsorption characteristics of arsenate, chromate, and selenate on ferrihydrite and the oxyanion removal efficiency of ferrihydrite were studied considering mineral phase transformation. At both pH 4 and 8, the adsorption of oxyanions used in the study were in good agreement with both Langmuir and Freundlich adsorption models except for selenate at pH 8. Due to the difference in surface charge according to pH, at pH 4 a higher amount of ions were adsorbed than at pH 8. The adsorption amount were in the order of arsenate, chromate, and selenate. These different adsorption models and adsorption amounts were due to different adsorption mechanisms for each oxyanions on the surface of ferrihydrite. These adsorption characteristics were closely related to changes in the mineral phase. At pH 4, a phase transformation to goethite or hematite was observed, but only a phase transformation to hematite was observed at pH 8. Among the oxyanion species on ferrihydrite, arsenate showed the highest adsorption capacity and hardly caused phase transformation during the experimental period after adsorption. Contrary to this, chromate and selenate showed faster mineral phase transformation than arsenate, and selenate had the lowest retardation effect among the three oxyanions. Ferrihydrite can effectively remove arsenate due to its high adsorption capacity and low phase transformation rate. However, the removal efficiency for other two oxyanions were low by the low adsorption amount and additional mineral phase transformation. For chromate, the efficient removal is expected only at low concentrations in low pH environments.

Keywords ferrihydrite, oxyanion, adsorption mechanism, phase transformation, goethite

페리하이드라이트의 산화음이온 흡착 특성과 광물상 변화

김규례 · 김영규*

경북대학교 지구시스템과학부

Received: April 7, 2023; Revised: May 16, 2023; Accepted: June 12, 2023

요 약

페리하이드라이트는 산상광산배수를 포함한 자연 환경에서 쉽게 관찰되는 산화철 광물로 결정도가 낮고 높은 비표면적을 갖고 있어 다른 이온과의 반응성이 매우 우수하여 환경유해물질과의 반응을 통하여 이의 제거가 가능하다. 그러나 페리하이드라이트는 준안정성 광물이기 때문에 표면적이 작고 결정도가 높은 다른 광물로의 상변화로 흡착된 이온들의 방출 가능성도 존재한다. 본 연구에서는 비산염, 크롬산염, 셀레늄산염의 페리하이드라이트에 대한 흡착 특성과 광물상 변화까지 고려한 페리하이드라이트의 산화음이온 제거 효능을 연구하였다. 실험 시 pH 4와 8에서 연구에 사용된 산화음이온들의 흡착은 pH 8에서 셀레늄산염을 제외하고 Langmuir와 Freundlich 두 흡착 모델과 잘 일치하였다. 각 산화음이온의 흡착량은 pH에 따른 표면 전하의 차이로 인하여 pH 4의 경우 pH 8보다 더 높았다. 흡착 량은 비산염, 크롬산염, 그리고 세레늄산염의 순서를 보여주었다. 이러한 흡착모델과 흡착량은 각 산화음이온의 흡착 시 페리하이드라이트 표면에서 일어나는 서로 다른 흡착 기작을 잘 대변한다. 이러한 흡착 특성은 광물상의 변화와도 밀접한 연관성이 있었다. pH 4에서는 침철석 혹은 적철석으로의 상변화를 보여주었으나, pH 8에서는 적철석으로의 상변화만이 관찰되었다. 산화음이온 종 중 비산염은 가장 높은 흡착력을 보여주며, 흡착 후 페리하이드라이트의 실험 기간 내 거의 상변화를 일으키지 않았다. 이와 달리 크롬산염과 셀레늄산염은 비산염에 비하여 광물상 변화가더 빨랐으며 세 산화음이온 중 셀레늄산염의 지연 효과가 가장 낮았다. 페리하이드라이트는 비산염에 대하여 높은 흡착 능력과 낮은 상변화로 인하여 효과적인 제거가 가능하지만 다른 두 산화음이온 종은 낮은 흡착량과 추가적인 광물상 변화로 비산염에비하여 제거 효과가 떨어지고 크롬산염의 경우 낮은 pH 환경에서 낮은 농도의 경우에에만 효율적인 제거가 가능할 것으로 판단된다.

주요어 페리하이드라이트, 산화음이온, 흡착기작, 상변화, 침철석

    Fig 1.

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    Figure 1.XRD pattern (A) and SEM images (B) of synthetic ferrihydrite used in this study.
    Economic and Environmental Geology 2023; 56: 301-310https://doi.org/10.9719/EEG.2023.56.3.301

    Fig 2.

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    Figure 2.Adsorption isotherms of As(V), Cr(VI), and Se(VI) on ferrihydrite. The solid line shows the result of fitting with the Langmuir isotherm and the dashed line shows the result of fitting with the Freundlich isotherm.
    Economic and Environmental Geology 2023; 56: 301-310https://doi.org/10.9719/EEG.2023.56.3.301

    Fig 3.

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    Figure 3.XRD patterns of final products of phase transformation from ferrihydrite after 40 weeks at pH 4. (A) Ferrihydrite without adsorbate, (B) AsO4-ferrihydrite, (C) CrO4-ferrihydrite, (D) SeO4-ferrihydrite. G: goethite (JCPDS No. 29-0713).
    Economic and Environmental Geology 2023; 56: 301-310https://doi.org/10.9719/EEG.2023.56.3.301

    Fig 4.

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    Figure 4.XRD patterns of final products of phase transformation from ferrihydrite after 40 weeks at pH 8. (A) Ferrihydrite without adsorbate, (B) AsO4-ferrihydrite, (C) CrO4-ferrihydrite, (D) SeO4-ferrihydrite. G: goethite (JCPDS No. 29-0713), H: hematite (JCPDS No. 33-0664).
    Economic and Environmental Geology 2023; 56: 301-310https://doi.org/10.9719/EEG.2023.56.3.301

    Table 1 . Langmuir isotherm constants of arsenate, chromate, and selenate adsorption on ferrihydrite at pH 4 and 8.

    pH 4pH 8
    Langmuirb(L/mg)qm(mg/g)qm(mol/g)R2b(L/mg)qm(mg/g)qm(mol/g)R2
    Arsenate0.48105.131.4030.96540.1556.320.7520.9920
    Chromate0.1757.621.1080.95200.0917.660.3460.9902
    Selenate0.1554.350.6330.99730.014.710.0550.9490

    Table 2 . Freundlich isotherm constants of arsenate, chromate, and selenate adsorption on ferrihydrite at pH 4 and 8.

    pH 4pH 8
    Fruendlichk(L/mg)nR2k(L/mg)nR2
    Arsenate73.7018.760.968128.508.860.9926
    Chromate33.1211.240.954212.1824.360.9676
    Selenate31.5012.750.96942.468.250.8828

    KSEEG
    Dec 31, 2024 Vol.57 No.6, pp. 665~835
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