- Title
- Coal tailings for soil improvement
- Creator
- Bradney, Lauren Margaret
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2023
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- Tailings are unavoidable during coal beneficiation, yet their disposal comes with economic, environmental, and social costs. Tailings predominantly consist of fine (<2 mm) minerals (e.g., clays, silt, and coal particles) in a water suspension and are conventionally stored in embankment dams. However, there has been a shift over the years towards alternative storage solutions for mine tailings and more sustainable mining practices, such as reducing and reusing waste material. Because tailings are rich in silt and coal-derived carbon, one reuse option is to use raw or modified coal tailings as a soil additive or soil-based material. Consequently, the purpose of this thesis was to assess the feasibility of using coal tailings as a soil additive for mine site rehabilitation and beyond. Firstly, the physical and chemical characteristics of 21 coal tailings sampled from two mine sites located in the Hunter Coalfields of New South Wales (NSW) were undertaken, testing for standard soil parameters considered to be important for plant productivity and soil-resource quality. The results indicated that the coal tailings had a high total carbon content and had a soil texture that corresponded to a silt-like or silt-loam-like soil. Both characteristics are beneficial attributes for a soil additive, especially when used on sandier textured soils. However, the coal tailings were also found to have a high sodicity, which is known to restrict plant growth, especially in salt-sensitive species. Consequently, modification of coal tailings may be needed to increase its beneficial potential as a soil additive. Unlike other types of tailings produced from metal mining, one of the benefits of coal tailings is that it is generally lower in potentially toxic trace metal(loid)s (i.e., cadmium, chromium, lead, mercury, or arsenic). This was found to be the case for the coal tailings characterised in this study, as all samples were below threshold levels for soil application. Secondly, to understand the feasibility of using coal tailings within mine sites, different levels of tailings were combined with native mine topsoil, and these were assessed by examining the chemical and mineralogical characteristics, microbial activity, and its ability to support the growth of native mine rehabilitation plant species. Dehydrogenase activity and basal microbial respiration were reduced by the application of coal tailings, while substrate-induced respiration was reduced at higher levels above 50:50 tailings:soil. The results from the microbial activity tests suggest that the carbon within coal tailings may not initially be readily available to microorganisms. However, the carbon could become more available through time and weathering processes. Both Bothriochloa macra (Red Grass) and Acacia decora (Western Silver Wattle) grew in 25:75 and 50:50 tailings:soil. While the control showed the best growth for the Bothriochloa macra, no significant difference in growth was observed for Acacia decora among levels. Overall, the results indicate that there could be future potential to use coal tailings at low levels to help lessen issues surrounding topsoil scarcities at mine sites. However, more work would need to be conducted to assess coal tailings as an additive under field conditions, and modification may be required to improve coal tailings soil-health-promoting qualities. Thirdly, the work explored the feasibility of utilising coal tailings beyond mine rehabilitation through a series of threshold germination or seedling emergence trials using four crop species (lettuce, canola, onion, and maize). It was observed that the coal tailings reduced the full emergence and initial growth of lettuce, onion, and canola at higher levels (>30:70 tailings:soil), but no significant decrease was observed at lower levels. Furthermore, seedling emergence and initial growth of maize was not reduced by the application of coal tailings at any level. Overall, it was suggested that target levels for coal tailings remain below 30:70 tailings:soil. Finally, agricultural gypsum and manure (cow, sheep, and poultry) were combined with coal tailings to alleviate high sodicity and improve microbial activity, respectively. Gypsum application was shown to reduce the exchangeable sodium percentage (ESP) of coal tailings. Furthermore, the addition of gypsum also increased the Ca:Mg ratio, which is known to improve soil stability. A small-scale column leaching experiment and pore water experiment was also conducted for the gypsum-modified coal tailings. It was found that sodium leached out of the coal tailings, however, this occurred with and without the addition of gypsum. As expected, the addition of manure was also shown to increase the microbial activity (assessed through basal respiration) of the coal tailings. Overall, the results demonstrated that there is scope to beneficially use coal tailings as a soil additive at levels around 25:75 tailings:soil or below. With vast quantities of mine waste, including tailings, produced each year in the coal industry, future research must find ways to reduce the volume of mineral waste sent to storage facilities through beneficial utilisation.
- Subject
- soil additive; coal tailings; mine rehabilitation; sustainable mining
- Identifier
- http://hdl.handle.net/1959.13/1495258
- Identifier
- uon:53975
- Rights
- This thesis is currently under embargo and will be available from 27.10.2024, Copyright 2023 Lauren Margaret Bradney
- Language
- eng
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