Enhanced weathering of kimberlite residues in a field experiment - implications for carbon removal quantification and mine waste valorization

At a Glance

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

Technical Documentation & Analysis: MPCVD Diamond for Enhanced Rock Weathering (ERW) Monitoring

Executive Summary

This document analyzes the research on Enhanced Rock Weathering (ERW) using kimberlite residues, focusing on the material science challenges and opportunities for advanced monitoring solutions provided by 6CCVD’s specialized diamond materials.

Application Validation: Fine processed kimberlite (FPK) residues from diamond mining are confirmed as a viable feedstock for large-scale Carbon Dioxide Removal (CDR) via ERW, leveraging abundant Mg-silicates (Lizardite, Forsterite).
CDR Performance: Field experiments demonstrated significant CDR rates via solubility trapping, achieving up to 2.6 t CO₂/ha over 3 years at a cumulative dosage of 400 t/ha (K10+30 plot).
Mineralogy & Reactivity: The primary weathering contributions were partitioned into kimberlite-derived carbonate (~75%) and silicate (~25%) dissolution, releasing key cations (Mg, Si, Ca) into porewater.
Monitoring Challenge: Traditional CO₂ flux measurements proved ineffective for CDR quantification due to overwhelming background noise from soil respiration, necessitating reliance on porewater Dissolved Inorganic Carbon (DIC) and hydrological modeling.
Material Safety: Despite high initial concentrations of metals of concern (Ni: 1,151 mg/kg, Cr: 704 mg/kg) in the FPK, porewater concentrations remained within safe Canadian water quality guidelines, validating kimberlite as a safe soil amendment.
6CCVD Value Proposition: The complexity of in-situ monitoring in chemically variable soil environments highlights the critical need for robust, high-stability sensor materials. Boron-Doped Diamond (BDD) offers an ideal platform for next-generation electrochemical sensors to accurately measure DIC, alkalinity, and trace metals, overcoming limitations identified in the study.

Technical Specifications

The following table summarizes the key material and performance data extracted from the research paper:

Parameter	Value	Unit	Context
Maximum CDR Rate (K10+30)	2.6	t CO₂/ha	Over 3 years, solubility trapping
FPK Application Dosage (K10+30)	400	t/ha	Cumulative dosage (100 + 300 t/ha)
FPK Application Dosage (K20)	200	t/ha	Single high dosage
FPK Specific Surface Area (SSA)	20.6	m²/g	High reactivity potential
FPK D80 Particle Size	175	µm	Fine processed kimberlite
Primary Silicate (Lizardite)	29.4	wt.%	Mg₃Si₂O₅(OH)₄ content
Secondary Silicate (Forsterite)	9.2	wt.%	Mg₂SiO₄ content
Initial Carbonate (Calcite)	1.9	wt.%	CaCO₃ content
Porewater DIC Range (Amended)	64-118	mg C/L	Demonstrating CO₂ solubility trapping
Soil pH Range (Amended/Control)	7.2-8.2	N/A	Circumneutral conditions
Maximum Porewater Ni Concentration	11.3	µg/L	Below Canadian water quality threshold (25 µg/L)

Key Methodologies

The field experiment utilized a multi-proxy approach focusing on hydrological and geochemical monitoring over a three-year period.

Material Characterization: FPK residues were analyzed for mineralogy (XRD), bulk chemistry (XRF, ICP-OES), and physical properties (D80, SSA, CEC).
Batch Reactivity Tests: FPK/soil mixtures were incubated under elevated CO₂ (10% CO₂) at 35°C for 2 weeks to assess initial cation (Ca, Mg, Si) and metal (Ni, Cr) release potential.
Field Plot Setup: Meter-scale (1 m²) plots were amended with FPK (K10+30, K20) and monitored alongside a control plot in Brunisolic soil (Ontario, Canada).
Hydrological Monitoring: Continuous soil volumetric water content (m³/m³) and temperature (°C) were recorded at 15 cm and 30 cm depths using TEROS 12 probes and ZL6 data loggers to establish a site-specific water budget and calculate percolation (V_p).
Solubility Trapping Quantification: Porewater samplers (15 cm and 30 cm depths) were used to collect samples for immediate pH measurement, followed by analysis of alkalinity and Dissolved Inorganic Carbon (DIC) via carbon coulometry.
Mineral Trapping Quantification: Triplicate soil cores (0-25 cm) were sampled and analyzed for Total Inorganic Carbon (TIC) to detect pedogenic carbonate precipitation.
Isotopic Tracing: Stable carbon isotope analysis (δ¹³C and δ¹⁸O) of pore CO₂ and porewater DIC was used to distinguish the source of sequestered carbon (biogenic soil respiration vs. atmospheric CO₂).

6CCVD Solutions & Capabilities

The challenges encountered in accurately quantifying CDR, particularly the masking of CO₂ fluxes by soil respiration and the need for high-precision, stable in-situ chemical sensing in complex porewater, present a direct opportunity for 6CCVD’s advanced diamond materials.

Applicable Materials for ERW Monitoring & Research

Research Requirement	6CCVD Material Solution	Technical Advantage
High-Stability Electrochemical Sensing	Boron-Doped Diamond (BDD)	Extreme chemical inertness and wide electrochemical window for stable, long-term in-situ measurement of DIC, alkalinity, and trace metals (Ni, Cr) in highly variable soil porewaters (pH 7.2-8.2).
High-Purity Optical Windows	Optical Grade Single Crystal Diamond (SCD)	Superior transparency and thermal conductivity for integration into advanced spectroscopic monitoring systems (e.g., Raman or FTIR) used for real-time analysis of mineral dissolution products (Mg, Si, Ca) or carbonate phases.
High-Pressure/High-Temperature (HPHT) Simulation	SCD Substrates (up to 500 µm thickness)	Ideal for high-pressure diamond anvil cell (DAC) or HPHT synthesis experiments, enabling precise simulation of deep earth or engineered carbonation conditions relevant to ERW feedstock analysis.

Customization Potential for ERW Field Trials

6CCVD offers specialized manufacturing capabilities essential for developing and deploying next-generation ERW monitoring equipment:

Custom Dimensions & Integration: We provide PCD plates/wafers up to 125mm and SCD substrates with custom geometries, allowing seamless integration of BDD sensor arrays into existing field equipment (e.g., porewater samplers, soil gas lances, or LI-COR chambers).
Precision Metalization: The study required precise measurement of trace metals (Ni, Cr). 6CCVD offers custom metalization (Au, Pt, Ti, W) on BDD surfaces, enabling the fabrication of highly sensitive micro-electrodes optimized for specific heavy metal detection in porewater, surpassing the limits of conventional ICP-MS analysis noise.
Advanced Polishing: Our capability to achieve surface roughness of Ra < 1nm (SCD) and Ra < 5nm (Inch-size PCD) ensures optimal performance for optical components and minimizes fouling on electrochemical sensor surfaces during long-term field deployment.

Engineering Support

The research highlights the difficulty in distinguishing CDR signals from background noise and the necessity of complex stoichiometric modeling. 6CCVD’s in-house PhD team specializes in high-purity material science and electrochemistry.

Material Selection Consultation: We assist researchers in selecting the optimal diamond material (SCD, PCD, BDD) and geometry for developing robust sensors tailored to specific ERW environments (e.g., high alkalinity, high metal loading, or extreme temperature ranges).
Next-Generation Sensor Design: We support projects aiming to develop diamond-based sensors for accurate in-situ DIC/TIC quantification, providing a direct, reliable measurement pathway that bypasses the inherent inaccuracies and masking issues associated with traditional CO₂ flux and hydrological modeling methods.

Call to Action: For custom specifications or material consultation regarding advanced ERW monitoring, sensor development, or high-pressure mineral synthesis, visit 6ccvd.com or contact our engineering team directly.

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.

Tech Support

Original Source

DOI: https://doi.org/10.3389/fclim.2025.1592626

References

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]
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