These by-products are generally disposed of; however, environmentally-friendly disposal can be difficult and costly. What if, instead of disposing of these by-products, we could put them to good use? That is the question CSIRO scientists sought to answer, and which led them to discover the beneficial properties of a suite of mining and industrial by-products

When extracting the material or product of interest during considerable quantities of byproducts are often produced. These by-products are generally disposed of; however, environmentally-friendly disposal can be difficult and costly. What if, instead of disposing of these by-products, we could put them to good use? That is the question CSIRO scientists sought to answer, and which led them to discover the beneficial properties of a suite of mining and industrial by-products.

By-products as ‘designer’ contaminant adsorbents

Through a joint project with the Western Australian Department of Water, CSIRO investigated a range of mining industry byproduct materials to determine whether they could be used to filter nutrients from natural waters or to treat wastewater.

As Dr Grant Douglas, CSIRO senior research scientist, explained, the team were keen to investigate whether the use of abundant, low-cost by-products generated by industry, mining or mineral processing could be used as a potentially cost-effective solution to treating water.

“We believed that the largely unexploited byproducts we generate in Western Australia, particularly in areas such as south west Western Australia and the adjacent Yilgarn region, could be developed as ‘designer’ contaminant adsorbents,” Dr Douglas says.

The identification of suitable by-products has the added benefit of reducing mining by-product stockpiles and hence the environmental footprints of the mining and minerals processing industries.

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

Next, a wide range of by-products and other mineral-based materials that had demonstrated potential benefits during characterisation were assessed for their ability to treat nutrient-rich natural water or wastewater. This stage of the byproduct assessment was undertaken using laboratory column trials and/or field trials.

The tested materials included a by-product from the heavy mineral processing industry, a steelmaking by-product, red mud and red sand from the alumina refining industry, 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.

Water treatment and soil amendment

The major outcome of this work was the first comprehensive characterisation and assessment of a suite of by-products that have potential for use in treatment and purification of industrial and farming wastewaters and for managed aquifer recharge. Additionally, it was found that some solid by-product materials may be useful as soil amendments in rural and urban applications, with the ability to address acidity issues or increase the nutrient binding capacity of the soil to which it is applied.

Detailed physico-chemical assessment, extensive column trials and a multi-year field trial using the by-products as a soil amendment on a Western Australian turf farm were undertaken. This research showed that the heavy mineral processing by-product, a steelmaking by-product, and calcined magnesia, used either alone or in combination, had the best potential in treating water or as soil amendments. Beneficial actions in water and soil included
removal of nutrients and dissolved organic carbon (DOC), absorbing trace metals, decreasing acidity, and in the specific context of a soil amendment, improving soil structure, water holding capacity, nutrient utilisation, and turf establishment and regrowth rates.

Reducing algal blooms

The heavy mineral processing by-product, when used as a five per cent by mass soil amendment incorporated into the upper 15 cm of the soil profile, was shown to remove 97 per cent of phosphorus and 82 per cent of nitrogen from the shallow groundwaters under the turf farm over four years. With
around 400 hectares of turf farms currently under cultivation over Western Australia’s Swan Coastal Plain, use of this by-product as a soil amendment on these farms would equate to the removal of around 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,” Dr Douglas said.

What’s next?

Additional field trials may be required to further assess the performance and efficacy of the heavy mineral processing by-product or by-product blends as soil amendments under different agricultural regimes. Similarly, incorporation of byproduct mixtures into nutrient- and DOCretentive structures for water treatment, for instance from nutrient- and DOC-rich catchments, also requires additional research and optimisation.

Importantly, the scope and potential benefits of future projects are not only limited to Western Australia but could be applied anywhere in the world where similar byproducts are produced, and wastewater and similar land management problems exist.

Research in partnership

This project was delivered to the Western Australian Water Foundation through CSIRO’s Water for a Healthy Country National Research Flagship in partnership with the Western Australian Department of Water.

The Western Australian Government established the Water Foundation (formerly the Premier’s Water Foundation) in 2004 to promote and enhance water-related research and development activities within Western Australia. The grants support research and development projects that challenge boundaries and investigate innovative ways of conserving water and maximising reuse of wastewater.

CSIRO initiated the National Research Flagships to provide science-based solutions in response to Australia’s major research challenges and opportunities. The ten Flagships form multidisciplinary teams with industry and the research community to deliver impact and benefits for Australia. The Water for a Healthy Country Flagship aims to provide Australia with solutions for water resource management, creating economic gains of A$3 billion per annum by 2030, while protecting or restoring our major water ecosystems.

This project follows on from the successful Phoslock®™ product developed by CSIRO, which is being used commercially worldwide to remove phosphorus in surface water environments.

For more information about this research please go to http://www.csiro.au/science/Using-Mining-By-Products.html or contact Dr Grant Douglas, grant.douglas@csiro.au