Framework for the integration of coal ash–brine encapsulation into cemented paste backfill design

Authors: Hareeparsad, S; Longo, S

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DOI https://doi.org/10.36487/ACG_repo/2655_29

Cite As:
Hareeparsad, S & Longo, S 2026, 'Framework for the integration of coal ash–brine encapsulation into cemented paste backfill design', in AB Fourie, M Horta, M Oliveira & S Wilson (eds), Paste 2026: Proceedings of the 28th International Conference on Paste, Thickened and Filtered Tailings, Australian Centre for Geomechanics, Perth, pp. 1-13, https://doi.org/10.36487/ACG_repo/2655_29

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Abstract:
The incorporation of coal ash and saline brines into cemented paste backfill (CPB) presents an opportunity to combine underground structural support with the secure disposal of high-volume industrial wastes. This paper outlines a practical framework for assessing, designing, and implementing coal ash–brine encapsulation within CPB, with the dual objective of meeting backfill performance requirements and immobilising dissolved salts. The approach draws on established mineralogical, geochemical, and engineering principles, and is adaptable to site-specific materials and operational constraints. The framework begins with systematic characterisation of coal ash and brine, including chemical composition, mineralogy, and leach potential, to evaluate reactivity and compatibility. Encapsulation mechanisms are linked to pozzolanic and cementitious reactions, with the formation of secondary phases such as calcium silicate hydrates, layered double hydroxides, and Friedel’s salt contributing to long-term stability. Mix design development considers ash–brine ratios, binder type and dosage, water–binder ratios, and additive use. Laboratory testing for unconfined compressive strength, permeability, and leachate chemistry supports optimisation of mix performance. This integrated approach is relevant to coal-fired power stations seeking to reduce surface storage of ash and brine, and to coal mines with suitable underground workings for placement. By functioning both as a structural fill and a secure containment medium, CPB can deliver operational, environmental, and cost benefits. Although the focus is on coal ash–brine systems, the methodology can be extended to other compatible industrial by-products and saline waste streams.

Keywords: cemented paste backfill, coal ash, saline brine, encapsulation, co-disposal, waste management

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