Slag Made from New Sedimentary Rock

By The Study IAS

Oct 11, 2024

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Slag Made from New Sedimentary Rock

Context:

Researchers documented a new type of sedimentary rock formed from coastal slag deposits in the U.K., showcasing how human waste can lead to unusual geological formations.

Slag Overview:

A by-product of steelmaking is a composite material composed of metal oxides and silicon dioxide. It plays a significant role in the creation of artificial ground.
- In areas like Warton, England, researchers are investigating the process of slag hardening, or lithification, which transforms industrial waste into sedimentary rock.
Over time, as these rocks weather, they release sediments into the environment, often containing toxic metals that can contaminate soil, water, and air.
Despite these concerns, slag also presents opportunities. It is chemically stable and has the unique ability to neutralise acidity, storing greenhouse gases like carbon dioxide through mineral carbonation.
- This process mimics natural weathering and could be crucial in rising slag production, which is projected to increase by 10.5% worldwide by 2031.

Methodology

The research team collected slag samples from the Warton slag heap, an area with historical iron and steel operations from 1864 to 1929.
To analyse the slag, they employed a multi-step preparation process involving cutting, grinding, and sieving the samples.
They also investigated variations in exposure to seawater and rainwater across the deposit.

Key Findings:

The researchers identified various minerals, including a form of calcium silicate called larnite, and the presence of calcite, a form of calcium carbonate that aids in the lithification process.
Stable isotope analysis revealed variations in carbon and oxygen isotopes, shedding light on the origins and dynamics of carbonate reactions in the environment.
Two lithification mechanisms:
- Calcite cement precipitation: Dominated on the top surface and the sea-facing side above average water levels.
- This process occurs when minerals dissolve, releasing calcium that reacts with atmospheric carbon dioxide to form calcite.
- Calcium-silicate-hydrate (CSH) cement precipitation: The presence of saltwater prevented the dissolution of slag minerals, leading to the formation of CSH minerals with varying textures and elemental distributions.

Implications:

Carbon Capture: Understanding these lithification processes can inform strategies for repurposing slag deposits for carbon capture.
The calcite cement mechanism, in particular, can sequester atmospheric carbon dioxide without the need for transporting carbon to additional processing facilities.
The precipitation of CSH minerals may help limit the release of potentially toxic metals like vanadium and chromium into the environment.
Environmental Protection: The research also opens avenues for recovering valuable resources from slag deposits, increasing recycled materials in steelmaking.
Additionally, the hardened slag could serve as a natural barrier against coastal erosion, marrying environmental protection with effective waste management strategies.