Open Cut » Geology
Exploration and development of a new coal mine and mine plan strategy depend on the characterization of borehole coal samples. Their washability characterization is one of the important, well-defined steps to be followed and has been achieved by conducting Float and Sink (FaS) testing as outlined in AS 4156.1-1994. The FaS testing is an environmentally hazardous, time-consuming and expensive exercise. This proposal aims to develop a novel technique using X-ray Computed Tomography (XCT) technology for fast and cost-effective characterization of washability of borehole coal samples. The XCT technique is non-destructive, environmentally safe and rapid. With the latest advances in XCT hardware and software, computing power and the associated cost reduction, the application of XCT technology in the industry has become economically feasible. The XCT technique is much better than the FaS technique in all aspects.
This project is based on the successfully executed ACARP (C20150) project on the washability curves for selected DMC (Dense Medium Cyclone) samples of various particle sizes which were accurately determined using XCT technology. Further application of XCT technology can be extended for the evaluation of the washability characteristics of borehole coal samples without destroying their compact internal structure. In this regard, reconstruction of the 3D density map of borehole samples from CT scans provides basic data for sedimentological characterization of coal seams, as vertical and lateral variations of coal constituents can be described in 3D. Once the 3D density image of the borehole sample is obtained from XCT analysis, the washability characteristics information regarding the structure of the coal constituents of the drill core can be determined based on a semivariogram operator.
The overall objective of this project is to apply XCT technology to obtain washability characteristics from borehole samples. However, since these samples are expensive and retained by mining companies as reference material, they were unavailable for the destructive testing required in this project for methodological validation. Thus to achieve the project objectives large chunks of two ROM coal samples were obtained from two different operating coal mines. The first sample was used to enable an effective analysis methodology to be developed while the purpose of analysing the second sample was to confirm the application and enable validation of the methodology developed for the first sample.
XCT imaging was carried out, and 3D CT density maps of these samples were prepared. Using this data a methodology for determining washability characteristics from borehole samples based on semivariogram analysis to establish with statistical significance the washability characteristics from certain features of the breakage process (size and direction) was developed. Based on this information, fragmentation of the unbroken samples was performed, and FaS analysis was also carried out to obtain independent sets of washability data which were compared with the results from XCT analysis of the corresponding sample.
Based on the outcomes of this work, the objectives of the project were successfully achieved, namely:
· A novel, non-destructive methodology for coal characterization from borehole samples was developed;
· XCT instrumentation capability of analysing washability of borehole samples was demonstrated;
· An alternative to FaS analysis of washability of borehole/unbroken coal samples which does not destroy these expensive samples and preserves them for further use and applications was demonstrated;
· An alternative to FaS analysis of washability of borehole coal samples which is not toxic and not harmful to people and the environment was demonstrated;
· Fast, cost-effective evaluation and optimization of exploration and development of new coal mines and mine planning strategy based on the fragmentation parameters (particle size and direction) and washability parameters (density and ash), could be achieved using non-destructive XCT technology.
The outcomes of this project show that use of XCT provides benefits to the coal industry, including a novel non-destructive technique to characterize borehole coal samples for mine planning and processing strategy, and exploration and development of new coal mines. The technique is environmentally safe, fast and cost-effective. However, many challenges remain if the XCT technique can be routinely utilized to save time, human resources and money for the coal industry. Some of the challenges include the XCT signal calibration using standard samples and databases, X-ray beam hardening and user-friendly software.