Mining Contract: Development of an Anti-Caking Rock Dust
When exposed to moisture, limestone-based rock dusts have a tendency to cake and do not disperse easily. Caked rock dusts offer less protection against propagating coal dust explosions in mines. The focus of this contract is to develop anti-caking rock dusts.
Contract Status & Impact
This contract is complete. To receive a copy of the final report, send a request to OMSHR@cdc.gov.
Adding reagents to pulverized limestone for anti-caking purposes has been done commercially since the 1980s. The measurement of the amount of anti-caking reagent on the treated products after manufacture has been a great asset in determining the ability of the treated products to perform as intended in end-use applications. This technology was applied to the development of anti-caking rock dust for use in the underground coal mines. Currently, no commercially available rock dusts meet the dispersibility requirements of 30 CFR 75.2., which call for a rock dust, “the particles of which when wetted and dried will not cohere to form a cake which will not be dispersed into separate particles by a light blast of air.”
This contract had three phases: two different commercially available treated ultrafine limestone products were evaluated in relation to their particle size, chemical make-up, stearic acid treatment levels, and contact angles (Phase 1); from the results of this evaluation, a series of blends were made where various untreated ground limestone products with different median particle sizes were blended with the two products mentioned above (Phase 2); the samples from Phase 2 that were found to meet the desired properties for anti-caking rock dust were then re-evaluated (Phase 3). During each phase, explosibility testing was also conducted within the OMSHR 20-L chamber to determine the inerting effectiveness of the blend when mixed with an explosible concentration of pulverized coal dust.
Following Phase 3, the most economically viable, successful blend was selected for a pilot scale-up that did confirm through testing that the blend could be accurately reproduced during large-scale production. Subsequently, large-scale evaluations within the OMSHR experimental mine of the production blend showed that this anti-caking rock dust will disperse and not cake even under damp underground conditions.
The technology and approach used in this contract were successful in developing an anti-caking rock dust blend that would meet the specifications of the 30 CFR 75.2 rock dust definition. Specifically and in the event of an explosion, the rock dust would be dispersible under all mining conditions, including areas that are wet, and thereby be capable of meeting its intended function of inerting coal dust.