L. Liao^1,2, Y.J. Zheng¹, S.C. Duan^1,2, Z.Q. Yu¹, P.A. Peng^1,2

(1. State Key Laboratory of Advanced Environmental Technology, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, 

Guangzhou 510640, China

2. University of Chinese Academy of Sciences, Beijing, 100049, China)

Abstract: The “orange hydrogen” concept, injecting water into Fe-rich basalts to stimulate coupled H₂ generation and permanent CO₂ mineralization, offers a synergistic pathway for carbon-neutral energy production, yet the influence of fluid chemistry on these coupled reactions remains poorly quantified. In this study, we conducted 7-day batch experiments under simulated reservoir conditions (45 ℃, 5 MPa) using deionized water, artificial seawater (ASW), and ASW amended with biodegradable chelating agents (tetrasodium iminodisuccinate, IDS; and tetrasodium glutamic acid-N,N-diacetate, GLDA). Gas chromatography, ICP‑OES, thermogravimetric analysis (TGA), and FT‑IR spectroscopy were employed to quantify H₂ yields, elemental release, and CO₂ mineralization efficiency. Artificial seawater enhanced H₂ production by 3.4‑fold over deionized water (117.1 vs. 34.2 μmol H₂/g rock), attributed to synergistic carbonate buffering (maintaining pH 6.5–7.0), elevated ionic strength (I ≈ 0.7 mol/kg), and SO₄²⁻ catalysis. Biodegradable chelating agents dramatically mobilized Fe (up to 1798 mg/L, a 1762‑fold increase) but reduced immediate H₂ yields to 37–77% of seawater levels due to Fe²⁺ complexation, which limits free‑ion availability for the redox reaction (2Fe²⁺ + 2H⁺ → 2Fe³⁺ + H₂). Conversely, chelant systems promoted net CO₂ mineralization, with GLDA achieving a 0.27% net carbonate increase (vs. net dissolution in seawater controls), corroborated by alkalinity rises up to 28,150 mg/L and a diagnostic 23 cm⁻¹ blue shift in carbonate FT‑IR bands, suggesting organic ligand–carbonate interactions that may enhance storage stability. These findings identify seawater as the optimal injection fluid for maximizing immediate H₂ yields in coastal basalt formations, while biodegradable chelating agents enable a conceptual temporal decoupling strategy—initial chelant injection accelerates Fe mobilization, and subsequent biodegradation could release Fe²⁺ for sustained H₂ generation from the accumulated iron pool. This approach addresses freshwater scarcity in large‑scale CO₂ storage and offers a geochemical basis for designing injection fluids in orange hydrogen projects, contributing to carbon neutrality through integrated gas–rock–fluid interactions in basaltic reservoirs.

Keywords: Orange hydrogen; CO₂ mineralization; Basalt-water interaction; Biodegradable chelating agents; Seawater chemistry; Carbon neutrality

Author Profile:

Yijun ZHENG, Male, Assistant Professor, mainly engaged in (1) site screening and assessment for CO₂ storage; (2) suitability evaluation and monitoring of CO₂ storage. E-mail: zhengyijun@gig.ac.cn