Tailings to Topsoil

This project targets a co-utilisation and soil improvement program that addresses the environmental challenges associated with tailings management within mining operations. This transformational alternative for tailings management optimises existing technologies connected with dewatering, delivery, and soil remediation processes, and transforms it into an integrated pit-to-paddock mobile plant emplacement and cultivation system. It is a cost effective solution for tailings utilisation, with the target goal being the creation of a valuable topsoil supplement for restoration of native flora, or for the establishment of biomass crops for utilisation in next generation alternative energy technologies. Transforming coal tailings into a valuable resource will not only help reduce tailings dam requirements (and subsequent risks) but will also create re-vegetative land use opportunities.

The work within this project centres on four major processes relating to coal tailings; collection, characterisation, and pre-treatment; delivery to site; de-watering and emplacement; and assessment for mine site rehabilitation, focusing on improved soil health and plant productivity.

Forty-six coal tailings sampled from ten mines across New South Wales and Queensland were analysed for several chemical characteristics known to be important for soil health and plant productivity. Characterisation results were assessed for beneficial attributes and potential modification requirements. Findings showed the coal tailings to be alkaline, with a high total carbon content, and low levels of potentially toxic metals and metalloids. However, sulfur and sodium concentrations were elevated in some tailings, and thus, may require modification before use as a soil supplement.

Preliminary ex-situ (glasshouse) plant growth trials were conducted to help identify the types of coal tailings that could be used to supplement topsoil. Although the results from the trials were varied, there is potential that certain coal tailings could be used. The glasshouse trails were expanded upon through two in-situ field trials. These trials allowed for a more realistic assessment of coal tailings on plant growth, and also allowed for changes to the soil profile to be assessed. Plant growth results were varied, however, no obvious difference was observed between the plots with and without coal tailings. The soil profile assessment showed an increase in total organic carbon, which is a fundamental property for improved soil physical structure and the establishment of microorganisms.

An assessment of the emplacement rate of coal tailings was also conducted. It was calculated that for dry tailings production of 1.05 Mtpa with a tailings emplacement depth of 0.15m, that approximately 438 Ha of land could be covered. Subsequently, a mobile emplacement concept was developed based on a slurry feeding scenario. This included determining the design requirements associated with slurry flow and likely terrain scenarios. The final design incorporated a two-element machine system. Initially the slurry is fed into a drag wheel system, which allows slurry pipelines to be elongated and retracted as required. This system is attached to a to a mobile tracked “panther” prime mover, which houses a belt press filter to dewater and return the excess water to the drag wheel. The excess water is returned to the mine for use.

To identify the constituent coal tailings properties at real time, hyperspectroscopy (coupled with machine learning) offers a powerful toolset for tailings management and material property prediction. It has the potential to enhance the understanding of tailings characteristics and allows for a faster more streamline system by eliminating the need for traditional laboratory analysis. Furthermore, it facilitates responsible mining practices and enables sustainable resource management. Hyperspectral analysis was conducted on a selection of coal tailings samples and the predictive capability for several pre-determined characteristics was made.

The national benefits of this novel initiative are significant not only for its environmental solutions but also its commercial potential as a soil health enhancement product. The outcomes of the work could help reduce the need for tailings storage facilities, reduce costs and environmental risks of tailings management, generate productive and innovative uses of mined land, buffer zones, or land offsets, help convert mineral residue into a value-added soil improvement additive, and develop improved rehabilitated land or a new agribusiness.

The work presents a compelling opportunity to establish one form of large-scale tailings utilisation and has identified a solution to a major economic cost and environmental challenge related to tailings. A key feature of this work was the combination of research in several areas critical to achieving a successful cost-effective outcome in converting mine tailings into agricultural commodities for developing soil resources. The project provides a resourceful framework to transform tailings management into an effective usage for regional and national innovative advancements, and ultimately, allow for the utilisation of this product for energy crop production and revegetation of mine impacted sites.