Reducing mining’s environmental impact

Researchers have found a way to reduce the environmental footprint from mining by lowering by-product stockpiles.

Researchers have found a way to reduce the environmental footprint from mining by lowering by-product stockpiles.

In a joint project with the CSIRO, the Western Australian Department of Water investigated a range of currently unused mining industry by-product materials to determine whether they could be used to filter nutrients from natural waters to treat wastewater that would otherwise be discarded.

CSIRO project leader, Dr Grant Douglas said using the low-cost by-products generated from minerals processing offers a solution that is both cost-effective and environmentally friendly for the removal of nutrients.

“The largely unexploited by-product materials we generate in Western Australia could be developed as ‘designer’ contaminant absorbents,” Douglas said.

The research showed that some mining by-products can be effective in preventing nutrients from entering river systems, thereby reducing the potential for algal blooms.

They assessed a range of potentially suitable by-products to establish their efficacy in removing nutrients or reducing acidity.

“After identification and procurement, basic characterisation of by-products included major and trace element geochemistry, mineralogy, radioactivity, geochemical modelling, and leachate chemistry and toxicity. These inherent properties and suitability of by-products for potential environmental use were then classified,” according to the CSIRO.

The suitable by-product was then used in a four year trial.

The range of by-products or other potentially beneficial mineral-based materials assessed included neutralised used acid (NUA) from the heavy minerals processing industry, a steel making by-product.

Red mud and red sand from the alumina refining industry was also used, as well as activated carbon, calcined magnesia, attapulgite, zeolite, fly ash, laterite, groundwater treatment residues, carbonate minerals and a range of rocks common in south-west Western Australia.

Assessments and trials of NUA as a turf farm soil amendment showed when used, either alone or with calcined magnesia, it possessed the best potential as environmental water or soil amendments in terms of one or more of nutrient and dissolved organic carbon (DOC) removal, acidity attenuation and trace metal adsorption.

Various combinations of NUA and calcined magnesia also showed a vast range of characteristics indicating potential for environmental application.

“Combinations of NUA, steelmaking by-product and calcined magnesia exhibited effective removal of a range of nutrient species and trace elements while also retaining a capacity to attenuate acidity, buffer pH, or in the specific context of a soil amendment, improve soil structure, water holding capacity, nutrient utilisation, and turf (re)growth rates,” the CSIRO said.
“The long-term turf farm soil amendment trial undertaken as part of this Water Foundation project demonstrated the efficacy of NUA application as a soil amendment under conditions common to many turf farms currently operating on the Swan Coastal Plain.”

When added to the soil in the Swan Canning catchment, the by-product removed 97 per cent of phosphorus and over 80 per cent of nitrogen from the shallow ground waters.

Adding the by-product also reduced water use and improved turf health.

With around 400 hectares of turf farms currently under cultivation over the Swan Coastal Plain, the use of the by-product as a soil amendment on turf farms would equate to the removal of about two tonnes of phosphorus and nitrogen from groundwater each year.

“This is good news for the health of Perth’s waterways, as it could lead to a substantial reduction in the key nutrients that eventually contribute to algal blooms,” Douglas said.

“The productive use of the by-products also has the potential to reduce the environmental footprint of mining and mineral processing industries by lowering by-product stockpiles.”

The researchers say the benefits of the project could be realised anywhere in the world where similar by-product materials are produced and similar water management issues exist.

The CSIRO say additional field trials may be needed to further analyse performance and appropriateness of the application of NUA or NUA mixtures as soil amendments under different agricultural regimes.

Incorporation of NUA-based by-product mixtures into nutrient and DOC-retentive structures for water treatment also requires considerable research and optimization.

It says while the trials have shown considerable potential of some by-products, further research is necessary to fully validate the performance of NUA and calcined magnesia under varying environmental conditions.

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