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<p>Hexavalent chromium (Cr(VI)) contamination in groundwater poses serious threats to human health and the environment. This study synthesized sodium alginate-encapsulated nano-zero-valent iron supported on graphene oxide gel beads (SA/NZVI-rGO) for Cr(VI) removal and systematically investigated the effect of humic acid (HA) on its removal performance, revealing in depth the pH-dependent mechanism by which HA enhances Cr(VI) removal. Under acidic conditions, HA significantly increased the Cr(VI) removal rate by enhancing electrostatic adsorption. Under neutral and alkaline conditions, although electrostatic repulsion existed, HA still accelerated the reaction rate and improved the final removal efficiency. This is because the quinone/hydroquinone groups in HA act as electron shuttles, facilitating electron transfer from NZVI to Cr(VI). In addition, the resulting Cr(III) can form stable complexes with HA, which synergistically promote Cr(VI) removal. Kinetic analysis indicated that the process followed the pseudo-second-order model (R<sup>2</sup> = 0.999), and the adsorption isotherm conformed to the Freundlich model (R<sup>2</sup> = 0.974). Response surface methodology (RSM) was applied to optimize four parameters: pH, Cr(VI) concentration, HA concentration, and reaction time. The RSM model was highly reliable (P &lt; 0.0001, R<sup>2</sup> = 0.9936), predicting optimal removal conditions were: pH 3.14, initial Cr(VI) concentration 15.14&#xa0;mg/L, HA concentration 12.79&#xa0;mg/L, reaction time 33&#xa0;min, and SA/NZVI-rGO achieved 100% Cr(VI) removal. Study reveals the mechanisms of HA affecting the Cr(VI) removal by gel beads, and optimizes the key parameters through RSM, laying a theoretical foundation for the practical application of gel beads in groundwater remediation.</p>

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In-Depth Analysis of Humic Acid Involvement and Impact in the ElimiNation of Cr(VI) from Groundwater by SA/NZVI-rGO Gel Beads and Its Optimization via Response Surface Methodology

  • 期刊论文

  • 发表日期：

    2026年2月18日

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  • Qi Jing,
  • Xi Wang,
  • Bingjie Wang,
  • Wenxiu Xie,
  • Xueyang Feng,
  • Zhongyu Ren

摘要

Hexavalent chromium (Cr(VI)) contamination in groundwater poses serious threats to human health and the environment. This study synthesized sodium alginate-encapsulated nano-zero-valent iron supported on graphene oxide gel beads (SA/NZVI-rGO) for Cr(VI) removal and systematically investigated the effect of humic acid (HA) on its removal performance, revealing in depth the pH-dependent mechanism by which HA enhances Cr(VI) removal. Under acidic conditions, HA significantly increased the Cr(VI) removal rate by enhancing electrostatic adsorption. Under neutral and alkaline conditions, although electrostatic repulsion existed, HA still accelerated the reaction rate and improved the final removal efficiency. This is because the quinone/hydroquinone groups in HA act as electron shuttles, facilitating electron transfer from NZVI to Cr(VI). In addition, the resulting Cr(III) can form stable complexes with HA, which synergistically promote Cr(VI) removal. Kinetic analysis indicated that the process followed the pseudo-second-order model (R2 = 0.999), and the adsorption isotherm conformed to the Freundlich model (R2 = 0.974). Response surface methodology (RSM) was applied to optimize four parameters: pH, Cr(VI) concentration, HA concentration, and reaction time. The RSM model was highly reliable (P < 0.0001, R2 = 0.9936), predicting optimal removal conditions were: pH 3.14, initial Cr(VI) concentration 15.14 mg/L, HA concentration 12.79 mg/L, reaction time 33 min, and SA/NZVI-rGO achieved 100% Cr(VI) removal. Study reveals the mechanisms of HA affecting the Cr(VI) removal by gel beads, and optimizes the key parameters through RSM, laying a theoretical foundation for the practical application of gel beads in groundwater remediation.