Stone Dusting Process Advance

The coal mining industry has, for many years, used dry stone dust or calcium carbonate (CaCO₃) in the prevention of the propagation of coal dust explosions throughout their underground mines in Australia.

One of the major limitations of dry stone is the interruption to production when applied in intake airways. The stone dust is blown or flung in its dried powder form utilising compressed air and or other mechanical means. These methods lead to the generation of large quantities of fugitive dust in the downstream airflow. The immediate roadways along this airflow are unsuitable for human respiration requiring the evacuation of all personnel. This causing disruptions to production and other associated panel activities.

Attempts to address this issue were made in the last decade with the introduction of wet stone dusting. This is where stone dust and water are mixed together to form a paste like slurry. This mixture is pumped and sprayed on to the underground roadway surfaces.  

This method solved the contamination of the intake airways but brought with it a new problem known as “caking”. Caking is the hardened layer that is formed as the stone dust slurry dries. It was proven that this hardened layer compromises the dispersal characteristics of the stone dust and therefore its ability to suppress a coal dust explosion. Further, it was found that subsequent roadway dust deposits could be lifted in an explosion without disturbance of the caked stone dust below negating the original intent of roadway stone dusting.

This project set out to prove a specially formulated, non toxic slurry additive and process that could overcome the caking effect. The slurry additive process combines dry stone dust with water to form a slurry. The slurry is then treated with the additive and compressed air to create a highly vesicular foam like stone dusted surface.

This process retains all the benefits of traditional wet stone dusting. It greatly reduces the caking effect and as was proven, returns to dust when exposed to a shock wave or when sampled.

Over this two year project, work to trial and test the slurry additive process spanned a range of locations, mines sites and international testing facilities. The initial testing on a range of additives and the effectiveness in minimising the caking effect of wet dusting were performed at Applied Chemical's research laboratory in Melbourne, Victoria and independently tested at the SGS laboratory in Paget, Queensland. The results from these tests provided the platform to conduct full scale spraying trials at the Queensland Mines Rescue Station and Caledon Coal's Cook Colliery, Blackwater.

Successful testing results and a growing industry support network provided the confidence that allowed ACARP to approve the extension to this project. The project moved into the final stage of completion with the collection of data. The intent was to compare the slurry additive process to dry stone dusting in full-scale methane explosions at the CSIR Kloppersbos explosion facility in Kloppersbos, South Africa.