Inhibition of spontaneous combustion of sulfide ores by thermopile sulfide oxidation
Introduction
The fire caused by spontaneous combustion due to the oxidation of sulfide ore is one of the major disasters in mining high sulfur content ores (HSO), which affects about 30% of metalliferous mines in China (Qian, 2005). Traditional fire-fighting technologies mainly focus on removing the oxygen from the heap or decreasing the temperature by some heat dissipation procedures (Wu et al., 2004 and Li, 2003). However, the sulfur element contained in the ore, the real cause of the problem, is in general not given enough attention in the fire-fighting process, which makes it difficult to eradicate the problem completely.
Based on past studies of the mechanism of spontaneous combustions in HSO mines, the authors believe that the bio-oxidation technology using certain type of bacteria to remove the sulfide at the ore surface can be used as an effective measure to lower significantly the risk of ore spontaneous combustions (Luo et al., 2012). Published relevant applications, however, mainly focus on coal desulphurization and pyrite cinder desulphurization (Komnitsas and Pooley, 1991, Komnitsas et al., 1995, Aller et al., 2001, Zilberchmidt et al., 2004, Cardona and Márquez, 2009 and Adamus et al., 2011), aiming to improve either the coal quality or the re-usability of solid wastes. There has been little research on using the technology to deal directly with the problem of spontaneous combustions in HSO mining operations.
Previous laboratory tests show that normal mesophilic bacteria (Thiobacillus ferrooxidans), which can only work at ambient temperature of about 30 °C, is not very effective to remove sulfur at ore surfaces. It can only manage to achieve the degree of oxidation between 12.89% and 15.25% in a shake flask environment (Wang et al., 2012). Considering the high temperature condition in the heap of HSO due to the accumulation of heat generated by ore oxidation (D’Hugues et al., 2002), we focus our work in this research on investigating the effect of thermophiles on the desulphurization process. Experiments were carried out to study the desulphurization effect of thermopile on various parameters related to the spontaneous combustion tendency of HSO. The application of the thermophile treatment will increase the mining cost, however safety of the mining operation is the major concern here. The results are useful in helping derive an effective procedure to prevent HSO spontaneous combustion using the proposed bacteria oxidation technology. Detailed discussions about how to apply this technology for HSO mining operations are beyond the scope of this paper, but potential applications include spraying the solution that contains thermopiles over blasted stope, ROM (run of mine) stockpile and waste dump to inhibit the oxidation process so as to reduce the self-heating and the potential of spontaneous combustion. The results reported here can help derive an effective monitoring process based on bacterial concentration, sulfur content, PH value and E value after spraying the solution to ensure a safe mining operation.
Section snippets
Ore samples
The sulfide ore used in this experiment contains 45.87% of sulfur so it can be classified as HSO with high spontaneous combustion tendency level (Level I, see below). The ore particles have the size of −12 mm after crushing and were separated by sieving according to different size requirements set by the experimental program. Ore particles were sealed in plastic bags and stored in a dry place before the test.
Thermophile
The bacteria (thermophiles) used in this research were sourced from the hot spring of
Adaptation, growth cycle and strain identification of the bacteria
During the bacteria growth process, the pH value of the medium decreases over generations. This is caused by thermophiles digesting the sulfur powder and converting it into H2SO4. The bacteria solution will have high oxidation ability after 3–5 generations when it is suitable for the oxidation operation (Mikkelsen et al., 2007).
As illustrated in Fig. 1, there is a slight increase in the value of OD in the initial 15 days of cultivation, with the value range from 0.008 to 0.155. But there is an
Conclusions
The following conclusions can be drawn based on the experiment and the analyses of the test results:
- (1)
The measured OD values show that the growth cycle of the thermophiles is 17 days. This bacterial strain is identified to be thiobacillus.
- (2)
The average oxidation weight gain rate in 5 days of the original ore sample before the desulphurization treatment is four times of that of the ore sample obtained after the treatment.
- (3)
The spontaneous combustion point of the sample obtained after the
Acknowledgments
The authors would like to acknowledge the financial support for this work provided by Natural Science Foundation of China (50774011, 51074013), the Key Project in The National Natural Science Foundation (50934002), The Yangtze River Scholars and Innovation Team Development Plan (IRT0950) and PhD Programs Focusing on Developing Fields (20110006130003).
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