Enhanced rock weathering in acid mine drainage systems: Field evidence and passive treatment implications

[Geoengineering News]

https://www.sciencedirect.com/science/article/pii/S2666790826000625

Authors: Htut San Hkaung, Naito Yamashita, Nono Kimotsuki, Fugo Nakamura, Frances Chikanda, Ryosuke Kikuchi, Yoko Ohtomo, Tsubasa Otake, Tsutomu Sato

31 March 2026

https://doi.org/10.1016/j.clet.2026.101203

Highlights

•First field-scale ERW application in AMD systems.

•AMD ERW accelerates basaltic waste rock dissolution under naturally acidic, flow-through conditions.

•Basaltic rocks dissolution persisted for >1 yr, driven by textural breakdown in matrix-phases.

•Congruent dissolution of silicates led to the continue release of Ca2+–Mg2+ and pH increase.

•Schwertmannite formation enabled passive arsenic and sulfate attenuation without surface passivation.

Abstract

Despite basalt-based Enhanced Rock Weathering (ERW) showing promise in croplands, identifying alternative application sites is crucial for scaling carbon dioxide removal (CDR) and maximizing co-benefits. This study investigated acid mine drainage (AMD) systems as potential ERW sites, emphasizing the use of mining waste rock as reactive material. AMD environments are naturally acidic and characterized by continuous flow, conditions that accelerate mineral dissolution and enhance ERW effectiveness. Field-scale ERW trials were conducted in two AMD-impacted rivers in Japan using locally sourced basaltic waste rock (1–2 mm). At each site, one ton of crushed rock was deployed: (1) Yoshioka basaltic andesite (Yk) in the Amemasu River, and (2) Tetsuzan basalt (Tz) in the Shojin River. After one year, ∼0.79 tons of Yk and ∼0.36 tons of Tz remained, reflecting substantial dissolution. Rapid weathering of volcanic glass in matrix phases caused particle fragmentation and increased reactive surface area, while the absence of alteration rinds confirmed congruent dissolution. Hydrochemical monitoring revealed sustained Ca2+ and Mg2+ release, pH elevation, and schwertmannite precipitation. Schwertmannite co-precipitated arsenic without passivating rock surfaces, while proton release during its formation partly preserved acidic conditions that favor continued dissolution. These results highlight AMD systems as strategic ERW sites, offering a dual cleaner-production pathway: (i) rapid and sustained weathering ensures CDR potential, and (ii) passive treatment of contaminated mine waters provides remediation benefits. Leveraging mining by-products for ERW not only reduces the environmental burden of rock extraction but also creates opportunities for integrated waste valorization, climate mitigation, and sustainable mine-site management.

Source: ScienceDirect 

[Renaud de RICHTER]

I don't understand how  "(i) rapid and sustained weathering ensures CDR potential". If for instance the 

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[Renaud de RICHTER]

I don't understand how  "(i) rapid and sustained weathering ensures CDR potential".  If, for example, the acidity of acid mine drainage comes from H2SO4, how can the CaSO4 or MgSO4 resulting from the alteration of minerals capture CO2?

[Michael Tyka]

On Mon, Apr 6, 2026 at 2:35 PM Renaud de RICHTER <renaud.d...@gmail.com> wrote:

I don't understand how  "(i) rapid and sustained weathering ensures CDR potential".  If, for example, the acidity of acid mine drainage comes from H2SO4, how can the CaSO4 or MgSO4 resulting from the alteration of minerals capture CO2?

I havn't read the paper, just the abstract. But my assumption is that, if we include the ocean in the system boundary, any acid drainage eventually causes outgassing of CO2 (of around 0.8mol CO2/ mol H+) once reaching the ocean. Therefore neutralizing this acidity through an engineered interaction with crushed silicate rocks reduces this outgassing. So relative to the baseline of doing nothing, placing those rocks there could be seen as CDR, similarly to enhanced river weathering in acidic rivers.

M

 

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[Greg Rau]

The authors seem to argue that SO4-- is removed/reduced from solutiom via Schwertmannite precipitation (eq 2), thus apparently leavig Ca++ balanced by 2OH-?  Curiously, I don't see any effort to quantify CDR and downstream pH's of the rivers remain <3.6. They show Schwertmannite precipitation as being acid-producing(!?)

Greg

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