Valorization of Kimberlite Tailings by Carbon Capture and Utilization (CCU) Method

At a Glance

Metadata	Details
Publication Date	2020-07-08
Journal	Minerals
Authors	C. N. Chakravarthy, Salma Chalouati, Ye Eun Chai, Hugo Fantucci, Rafael M. Santos
Institutions	University of Guelph
Citations	12
Analysis	Full AI Review Included

Executive Summary

This study demonstrates the technical feasibility of utilizing carbonated kimberlite tailings (a diamond mining waste product) as a partial cement replacement in concrete brick manufacturing, effectively integrating Carbon Capture and Utilization (CCU) into sustainable construction.

Value Proposition: Converts high-volume mining waste into a durable building material while permanently sequestering CO₂, addressing both waste management and the cement industry’s significant greenhouse gas emissions (8% of global CO₂).
Carbonation Mechanism: Kimberlite, rich in magnesium and calcium silicates, was subjected to mild thin-film carbonation, resulting in the formation of hydrated magnesium carbonates, specifically nesquehonite (MgCO₃.3H₂O) and lansfordite (MgCO₃.5H₂O).
CO₂ Uptake: The maximum CO₂ uptake achieved was approximately 3.7 wt% (dry basis) above the material’s pre-existing carbonate content.
Mechanical Performance: Bricks incorporating carbonated kimberlite (10% to 20% cement replacement) showed significantly improved compressive strength compared to bricks using unreacted kimberlite, confirming the binding benefit of the newly formed carbonates.
Durability Metrics: All tested bricks exhibited low initial water absorption (less than 2%), indicating high density, low air voids, and expected durability against freeze-thaw cycles.
Process Optimization: Optimal strength was generally achieved using kimberlite carbonated at the highest tested CO₂ concentration (20%) and moisture content (20%), conditions that accelerate mineral dissolution and subsequent carbonate precipitation.

Technical Specifications

Parameter	Value	Unit	Context
FPK Grain Size Range	3.9 to 62.5	µm	Fine Processed Kimberlite (FPK)
Cement Replacement Ratio	10% to 20%	%	Kimberlite used as partial cement substitute
Water-to-Binder Ratio	0.6:1	Dimensionless	Constant for all brick mixes
Cementitious Material-to-Sand Ratio	1:3	Dimensionless	Constant for all brick mixes
Unreacted Kimberlite CO₂ Content	4.32	wt% (d.b.)	Pre-existing carbonates (mainly calcite)
Maximum Sequestered CO₂ Gain	3.7	wt%	Achieved at 35 °C, 20% CO₂, 20% moisture
Initial Water Absorption (Max)	< 2	%	Durability criterion (Standard requires < 7%)
Kimberlite SiO₂ Content	48.4	%	Elemental composition (WDXRF)
Kimberlite MgO Content	27.5	%	Elemental composition (WDXRF)
Kimberlite Fe₂O₃ Content	9.42	%	Elemental composition (WDXRF)
Kimberlite CaO Content	3.0	%	Elemental composition (WDXRF)
Target 28-Day Compressive Strength	15 to 40	MPa	Typical Canadian masonry brick standard
Strength Difference (28 vs 7 days)	~33.33	%	Expected strength gain trend (ASTM standard)

Key Methodologies

The study utilized a mild, low-energy thin-film carbonation process followed by standard concrete brick casting and testing procedures.

Kimberlite Preparation: Fine Processed Kimberlite (FPK) was dried at 50 °C for 24 h and ground to a powder.
Thin-Film Carbonation (TFC):
- Duration: 144 hours (6 days).
- Temperature Range: 35 °C and 50 °C.
- CO₂ Concentration: 10 vol% and 20 vol% (ambient pressure).
- Moisture Control: Paste moisture content (MC) was tested at 10 wt%, 15 wt%, and 20 wt%. MC was monitored every 24 h (via oven drying of a small crucible sample) and adjusted with ultrapure water.
Mineralogical Analysis:
- XRD: Confirmed the formation of hydrated magnesium carbonates: nesquehonite (thermodynamically stable) and lansfordite (kinetically favored precursor).
- Furnace Test (LOI): Quantified total CO₂ content by measuring weight loss between 300 °C and 950 °C (attributable to Ca- and Mg-carbonates).
Brick Mix Design:
- Ratios: Fixed water-to-binder ratio (0.6:1) and cementitious material-to-sand ratio (1:3).
- Replacement: Carbonated kimberlite replaced cement at 10% and 20% by weight.
Initial Curing: Molded bricks were placed in a CO₂ incubator (35 °C, 10% CO₂) for 24 h prior to demolding to promote early strength-producing carbonation.
Testing: Initial water absorption (24 h immersion) and compressive strength (MTS® compression machine, ASTM C 67) were measured after 7 and 28 days of immersion curing.

Commercial Applications

This CCU methodology and the resulting material are highly relevant to industries focused on sustainability, waste management, and construction material innovation.

Sustainable Construction: Direct use in the production of low-carbon masonry units (bricks, blocks) and pre-cast concrete products, providing a durable, cement-reduced alternative.
Carbon Capture and Utilization (CCU): Implementation of accelerated mineral carbonation as a commercial process for permanent, long-term CO₂ storage, particularly suitable for alkaline industrial wastes.
Mining and Tailings Management: Provides a high-volume valorization pathway for magnesium-rich silicate tailings (e.g., kimberlite, serpentinite), transforming waste liabilities into revenue streams.
Supplementary Cementitious Materials (SCMs): The fine, silicate-rich nature of kimberlite, enhanced by carbonation (which produces amorphous silica and small carbonate crystals), positions it as a potential SCM to improve concrete matrix density and strength.
Infrastructure Development: Use of carbonated kimberlite bricks in housing and infrastructure projects, particularly in regions near diamond mining operations (e.g., Northwest Territories, Canada), reducing transportation costs and environmental impact.

View Original Abstract

In the world of construction, cement plays a vital role, but despite its reputation and affordable prices, the cement industry faces multiple challenges due to pollution and sustainability concerns. This study aimed to assess the possibility of utilizing carbonated kimberlite tailings, a waste product from diamond mining, as a partial cement substitute in the preparation of concrete bricks. This is a unique opportunity to help close the gap between fundamental research in mineral carbonation and its industrial implementation to generate commercial products. Kimberlite was subjected to a mild thin-film carbonation process in a CO2 incubator at varying levels of CO2 concentration (10 vol% and 20 vol% at ambient pressure), kimberlite paste moisture content (10 wt% to 20 wt%), and chamber temperature (35 and 50 °C). The formation of magnesium carbonates, in the form of nesquehonite and lansfordite, was verified by X-ray diffraction analysis, and total CO2 uptake was quantified by thermal decomposition in furnace testing. Carbonated kimberlite tailings were then used to cast bricks. Replacement of cement between 10% and 20% were tested, with a constant water-to-binder ratio of 0.6:1, and a cementitious material-to-sand ratio of 1:3. Initial water absorption and 7- and 28-days compressive strength tests were carried out. The results obtained confirm the possibility of using carbonated kimberlite to replace cement partially, and highlight the benefits of carbonating the kimberlite for such application, and recommendations for future research are suggested. This study demonstrates the potential use of mining tailings to prototype the sequestration of CO2 into sustainable building materials to positively impact the increasing demand for cement-based products.

Tech Support

Original Source

DOI: https://doi.org/10.3390/min10070611

References

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