| Metadata | Details |
|---|
| Publication Date | 2025-07-01 |
| Journal | Frontiers in Climate |
| Authors | Zivi Schaffer, Kwon Rausis, Ian Power, Carlos Paulo |
| Citations | 1 |
| Analysis | Full AI Review Included |
- Value Proposition: Fine processed kimberlite (FPK) residues from diamond mining (estimated 3.9 Gt global reserve) are validated as an environmentally safe and effective feedstock for Enhanced Rock Weathering (ERW) and Carbon Dioxide Removal (CDR).
- Performance Metrics: CDR rates achieved up to 1.4 t CO2/ha over 3 years via solubility trapping in field plots amended with 400 t/ha cumulative dosage (K10+30 plot).
- Feedstock Composition: Gahcho Kué FPK is rich in fast-weathering Mg-silicates, primarily lizardite (29.4 wt.%) and forsterite (9.2 wt.%), providing high CDR potential compared to average basalt.
- Weathering Mechanism: CDR was successfully partitioned, showing that kimberlite-derived weathering contributed approximately 75% via carbonate dissolution and 25% via silicate dissolution.
- Quantification Methodology: CDR was quantified using porewater Dissolved Inorganic Carbon (DIC) and alkalinity coupled with a site-specific water budget derived from continuous soil moisture monitoring.
- Monitoring Challenge: Direct CO2 flux measurements were ineffective for CDR quantification due to high background effluxes from soil respiration, which masked the minimal CO2 drawdown signal.
- Environmental Safety: Concentrations of metals of concern (Ni, Cr) in porewater remained below strict Canadian water quality guidelines throughout the 3-year experiment.
| Parameter | Value | Unit | Context |
|---|
| Kimberlite Residue (FPK) D80 | 175 | ”m | Particle Size Distribution |
| FPK Specific Surface Area (SSA) | 20.6 | m2/g | BET N2 adsorption |
| FPK Lizardite Content | 29.4 | wt.% | Primary Mg-silicate phase |
| FPK Forsterite Content | 9.2 | wt.% | Primary Mg-silicate phase |
| FPK Total Inorganic Carbon (TIC) | 0.25 ± 0.01 | % | Carbonate content |
| FPK Ni Concentration (Solid) | 1,151 | mg/kg | Metal of concern in solid residue |
| FPK Cr Concentration (Solid) | 704 | mg/kg | Metal of concern in solid residue |
| Maximum Porewater Ni | 11.3 | ”g/L | Amended plots (Below 25 ”g/L threshold) |
| Maximum CDR Rate (K10+30) | 1.4 | t CO2/ha | Over 3 years, kimberlite contribution via solubility trapping |
| Control Porewater DIC (Avg) | 56 ± 14 | mg C/L | Background weathering rate |
| Amended Porewater DIC (Avg) | 64-118 | mg C/L | Range observed in K10+30 and K20 plots |
| Soil pH Range (Field) | 7.2-8.2 | - | Circumneutral conditions |
| Soil Calcite Content (Control) | 16.1 | wt.% | High background carbonate content |
| Percolation Factor (Estimated) | 25-100 | % of rainfall | Range used for uncertainty bounds in CDR calculation |
- Feedstock Preparation and Characterization: Fine processed kimberlite (FPK) residues were characterized for mineralogy (XRD Rietveld refinement), geochemistry (XRF, ICP-OES), and physical properties (SSA via BET, PSD via laser scattering).
- Batch Leaching Reactivity Assessment: FPK/soil mixtures (0.5 to 100 wt.% FPK) were leached in deionized water under elevated CO2 (10% CO2) and temperature (35 °C) for 2 weeks to assess initial cation release (Ca, Mg, Si) and metal leaching potential (Ni, Cr).
- Field Plot Setup: Three 1 m2 plots (Control, K20, K10+30) were established on calcareous Brunisolic soil. FPK was applied at 200 t/ha (K20) and 100 t/ha, re-amended to 400 t/ha (K10+30), and mixed into the top ~3 cm of soil.
- Hydrological Monitoring and Water Budget: Soil volumetric water content and temperature were continuously monitored at 15 cm and 30 cm depths using TEROS 12 probes. Percolation values (Vp) were calculated from the difference in average soil water content over 2-hour intervals, enabling the calculation of water loading.
- Solubility Trapping Quantification (CDRtotal): Porewater was collected weekly/opportunistically from samplers at 15 cm and 30 cm depths. Samples were analyzed for DIC and alkalinity via carbon coulometry. CDR rates were calculated by multiplying DIC concentration by Vp and extrapolating monthly data to annual rates.
- CDR Partitioning (Silicate vs. Carbonate): Cation loadings (Ca and Si) in porewater were used with stoichiometric mineral reaction equations (forsterite, lizardite, calcite) to partition the total CDR into contributions from kimberlite silicate weathering and kimberlite carbonate weathering.
- Mineral Trapping Assessment: Triplicate soil cores were sampled (0-25 cm) and analyzed for Total Inorganic Carbon (TIC) via carbon coulometry to detect pedogenic carbonate precipitation.
- CO2 Source Identification: Stable carbon isotope analysis (ÎŽ13C and ÎŽ18O) was performed on soil organic carbon, bulk kimberlite, pore CO2 gas, and porewater DIC to confirm that the sequestered carbon originated from biogenic sources (soil respiration).
- Mine Waste Valorization: Repurposing fine processed kimberlite (FPK) residues, a major industrial waste stream, as a high-performance ERW feedstock, reducing containment and remediation costs for mining companies.
- Carbon Dioxide Removal (CDR) Projects: Utilizing FPK as a viable, high-Mg ERW material for large-scale CDR deployment, particularly in non-agricultural settings (e.g., mine sites, degraded lands) where metal accumulation thresholds are less restrictive.
- Accurate MRV for CDR Credits: Implementing the validated monitoring approach (DIC/Alkalinity + Water Budget) to accurately quantify CDR rates and distinguish between silicate and carbonate weathering contributions, crucial for securing carbon credits in the voluntary carbon market.
- Mine Site Reclamation: Using FPK as a soil amendment during mine closure to build technosols, leveraging the materialâs ability to supply essential nutrients (e.g., K) and improve soil stability, thereby aiding revegetation efforts.
- Industrial By-product Utilization: Advocating for the use of other processed rock and industrial silicate wastes (e.g., steel slag, returned concrete) in ERW, applying the developed monitoring protocols to ensure accurate CDR accounting across diverse feedstocks.
View Original Abstract
Scaling up enhanced rock weathering (ERW) will require gigatonnes of suitable rock, which could include mine wastes such as the estimated 3.9 Gt of kimberlite residues from historic diamond mining. Here, we conducted meter-scale field experiments (2021-2023) in Ontario, Canada, to assess fine processed kimberlite residues for ERW and test carbon-based methods for CO 2 removal (CDR) quantification, including CO 2 fluxes, and measurements of soil and porewater inorganic carbon. A control plot consisted of local calcareous (16.1 wt.% calcite) Brunisolic soil to assess background weathering rates. Two soil plots were amended with 20 and 40 kg of kimberlite residues from the Gahcho Kué Diamond Mine (Northwest Territories, Canada) that contained 30.2 wt.% lizardite [Mg 3 Si 2 O 5 (OH) 4 ], 9.4 wt.% forsterite (Mg 2 SiO 4 ), and 1.9 wt.% calcite (CaCO 3 ). Coinciding with increases in Mg and Si, dissolved inorganic carbon increased in porewaters with kimberlite dosage (amended: 64-118 mg C/L, control: 56 ± 14 mg C/L), demonstrating CO 2 solubility trapping. Water chemistry data, coupled with a water budget derived from weather and soil moisture data, were used to determine CDR rates. The removal rates by the kimberlite residues were up to 1.4 t CO 2 /ha over 3 years calculated using porewater inorganic carbon loadings, with Ca and Si loadings allowing for partitioning of rates into removal contributions by kimberlite-derived carbonate weathering (~75%) and silicate weathering (~25%), respectively. CO 2 fluxes and soil inorganic carbon proved ineffective for CDR quantification, given the high effluxes due to soil respiration and high and variable carbonate content of the soils, respectively. Stable carbon isotope data demonstrated that the removed CO 2 was derived from organic carbon, suppressing soil CO 2 effluxes to the atmosphere. This study has implications for repurposing environmentally safe mine wastes for ERW with the potential to reduce net CO 2 emissions and storage and remediation costs in the mining industry. We highlight similarities between kimberlite residues and basalt fines, a common quarry by-product used in ERW, advocating for the use of processed rock from current and legacy mining operations for CDR. Further, our CDR monitoring approaches that effectively distinguish between silicate and carbonate weathering may be utilized in other ERW applications.
- 2022 - A meta-analysis of carbon content and stocks in technosols and identification of the main governing factors [Crossref]
- 2022 - Methods for determining the CO2 removal capacity of enhanced weathering in agronomic settings [Crossref]
- 2022 - Carbon accounting for enhanced weathering [Crossref]
- 2020 - Enhanced weathering and related element fluxes - a cropland mesocosm approach [Crossref]
- 2000 - Crushed rocks and mine tailings applied as K fertilizers on grassland [Crossref]
- 2019 - Reuse of dunite mining waste and subproducts for the stabilization of metal(oid)s in polluted soils [Crossref]
- 2024 - Enhanced weathering in the US Corn Belt delivers carbon removal with agronomic benefits [Crossref]
- 2020 - Potential for large-scale CO2 removal via enhanced rock weathering with croplands [Crossref]
- 2018 - Farming with crops and rocks to address global climate, food and soil security [Crossref]
- 2014 - Reaction kinetics of primary rock-forming minerals under ambient conditions [Crossref]