An investigation into the effect of cementation on self-heating of backfill

Authors: Zarassi, A; Hassani, FP

DOI https://doi.org/10.36487/ACG_rep/1404_20_Zarassi

Cite As:
Zarassi, A & Hassani, FP 2014, 'An investigation into the effect of cementation on self-heating of backfill', in Y Potvin & T Grice (eds), Mine Fill 2014: Proceedings of the Eleventh International Symposium on Mining with Backfill, Australian Centre for Geomechanics, Perth, pp. 259-270, https://doi.org/10.36487/ACG_rep/1404_20_Zarassi

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Abstract:
The use of high sulphide content mine tailings as backfill could pose technical and environmental challenges during mining operations or the post-mining cycle. This paper describes one of these challenges: the self−heating of high sulphide content backfills, and proposes a mitigation method involving the use of different amounts of binders and additives. Tailings rich in sulphide minerals, and in particular pyrrhotite, may self-heat, defined as the spontaneous oxidation of materials resulting in excessive heat generation. This phenomenon has led to mine fires, elevated toxic gas levels, oxygen depletion in the stopes, acid mine drainage and even mine closure in some cases. The self-heating cycle can be described in three stages, defined by increasing heating rates: stage A from ambient temperature to 100°C, at which point free moisture is driven off; stage B continues to 350-400°C (the ignition point of sulphides) if sustained by the reactions; and Stage C starts at the ignition point, and effectively represents roasting of the material. A unique apparatus for measuring stage A and stage B self-heating rates, which was originally developed at the Noranda Technology Centre in the 1980s, and now resides at McGill University, was used for this work. Results are reported as self-heating capacity (SHC) for backfill samples (joules/gram). Interpretation of SHC values is done by using a risk-assessment chart that delineates five regions of increasing risk. The experimental program reported here involved adding different amounts of cement, slag and sodium silicate to high-pyrrhotite tailings to investigate the mitigating effect of cementation on self-heating. Findings clearly demonstrate that cementation significantly reduces the SHC values of backfill samples and effectively removes their associated data points from the high risk region in the assessment chart. In addition, the SHC values are highly sensitive to the amount of binders and additives added to the backfill.

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