Zero-Waste Mine Reclamation: Coal + Steel + Human Wastes = Soil

by Zoe Dilles

Coal has seen a worldwide growth in production in recent decades despite health as well as environmental concerns as coal combustion is cited as the primary CO2 atmospheric source. In this age anthropogenic climate change, air emissions often overshadow the threats posed coalmine waste rock, which has far-reaching ecological effects from its metal and acid contents. Mixes of coal waste rock with other substances to balance the concentration of nutrients and minerals can order to promote plant growth. Fabricated soils have the potential to reduce landfill disposal as well as mitigate the issues attendant to reclamation reliant on borrowed soils, often leading to deforestation and hydrologic changes.
Firpo et al. (2015) puts forth a succinct procedure for producing useable manufactured soils from coal mine waste, steel slag, and sewage sludge. Soils produced through their methods were effective in promoting sorghum growth without unhealthy uptake of minerals and may have application in active mine reclamation operations pending further research into the ongoing behavior of the soils. Firpo et al. utilized coal waste from the important coal-mining district in the state of Santa Catarina in southern Brazil, along with slag from a local steel refinery and sewage sludge samples from a nearby water treatment plant. The procedure is broadly outlined into five stages, the first of which is to desulphurize the coal. It is then milled and separated by density into fractions that are characterized in terms of chemistry and texture and compared with other soil compositions, especially locally. This is followed by soil mixing, a combination of pH adjustment and addition of nutrients, organic matter. After 20 weeks, the soils had high levels of nutrients and metals with a high fertility index compared to native samples. Sorghum growth was most promoted by soils containing steel slag and in those with sewage sludge some seedlings grew nearly twice as large as those in the control. Even those fabricated soils with extremely high metal concentrations did not result in hazardous levels of absorption into the plants’ biomass. As this study shows, a combination of coal with other types of waste may improve mine reclamation as it promotes plant growth and can help neutralize the acid-generation.

Firpo, B. A., do Amaral Filho, J. R., Schneider, I. A. H. 2015. A brief procedure to fabricate soils from coal mine wastes based on mineral processing, agricultural, and environmental concepts. Minerals Engineering, 76, 81-86.

Also citing coal production trends as published on U.S. Energy Information Administration website.

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