Open Cut » Environment
The overall objective of the project was to develop a set of tests for reliably predicting acid rock drainage (ARD) potential of coal rejects and tailings. Standard test methods for predicting their ARD potential are unreliable due to interferences associated with organic matter and mineralogy common in these types of materials. The project involved three main components:
- Geochemical characterisation and kinetic testing of coal and coal washery samples from a variety of coal operations and projects;
- Modified net acid generation (NAG) test development; and
- Sulphur speciation test evaluation and development.
Geochemical characterisation of all samples was used to better define the geochemical variability of coal washery wastes, and provide a sample set to validate test development work. Samples of coal and coal process waste were provided from a number of coal operations and projects from Queensland, New South Wales and one site in Indonesia. The resulting case study sample set comprised a total of 125 samples, including coal, rejects and tailings from a range of locations, with varying geochemical properties and coal rank.
Modified NAG and sulphur speciation test development work involved more specialised tests and investigations on standard compounds and materials followed by validation and refinement using case study coal and washery waste samples.
Results show that the calculated NAG test is the most reliable indicator of acid potential of the geochemical characterisation tests evaluated, but its use is enhanced by the knowledge of the likely proportion of acid generating S forms in a sample.
The report details comparisons of ARD classification from different test methods across different case study samples.