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Accueil du site → Doctorat → Australie → 2020 → Predicting salt generation from coal mine spoil heaps in a semi-arid climate, Central Queensland, Australia

University of Queensland (2020)

Predicting salt generation from coal mine spoil heaps in a semi-arid climate, Central Queensland, Australia

Hilton, Melinda

Titre : Predicting salt generation from coal mine spoil heaps in a semi-arid climate, Central Queensland, Australia

Auteur : Hilton, Melinda

Université de soutenance : University of Queensland

Grade : Doctor of Philosophy (PhD) 2020

Résumé partiel
Coal spoil constitutes a highly heterogeneous mining waste material that varies greatly in particle size, hydraulic conductivity, and mineral solubility. It is difficult to fully prevent water entry into spoil heaps, and the salt-leaching of mine spoil into mine pits and other final voids is almost inevitable. In geochemical and water balance modelling, the rate of salt generation from spoil is generally assumed to be constant and based upon the total intrinsic salt content. However, in theory the rate of salt generation from spoil will decrease over time due to an initial flushing of soluble salts followed by mineral weathering, until a quasi-steady state equilibrium is reached. The factors which influence the rate of salt release from spoil have not yet been investigated in detail, making it difficult to predict, for example, the salt contribution from spoil to final voids. This research aims to quantify and characterise changes in salt concentration over time for leachates from spoils of different compositions.

Spoil samples were selected from the Burton, Moorvale, and Oaky Creek mines in the Bowen Basin of Central Queensland, Australia to represent dominant but different types of lithology (mineralogy and texture). The case study area has a semi-arid climate, and the geological age of local sedimentary coal seam measures is commonly Late Permian to Tertiary. Spoil samples varied from matrix-dominated (‘soil-like’) to framework-dominated (‘rock-like’). Based on a series of short-term characterisation tests, including degradation tests, patterns were established to assign the spoil samples into groups in a spoil salinity classification system. Small-scale free-draining funnel leaching was carried out using mixed, and controlled particle size fractions to assess the effect of particle size as a proxy for a range of void spaces inside spoil heaps. Changes in spoil composition, degradation, and hydrology were measured, as well as leachate salt concentration and geochemistry. Additionally, upscaled leaching experiments on 1-1.5 tonnes spoil samples in 1 m3 medium-scale containers (‘mesocosms’) were conducted to simulate the moisture regimes of the upper, middle and lower zones of a full-scale spoil heap. Typical soil-like and rock-like spoil samples were leached over a 15-month period in the mesocosms.

Spoil physical degradation was identified as a key factor influencing the rate of salt release. Spoil groups were described as having a rapid, episodic, or slow degradation rate. A rapid degradation rate was associated with matrix-only or matrix-supported spoil, while framework-supported and framework-only spoils were generally showed episodic or slow degradation. Degradation changed the particle size distribution of the spoil, which influenced its hydrological properties and ability to generate salt. Rapidly degrading soil-like spoil types produced the highest initial salt concentrations with a sharp decay curve, while competent, slowly-degrading rock-like spoil types produced a relatively gradual decay

Mots clés : Spoil Salinity Coal mining Leachate Geochemistry Spoil characterisation Spoil hydrology Final voids


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