A Cheaper and More Effective Inertant than Stone Dust

Prior to the work described in this report, SkillPro Services had invented and patented a hydrated polymer which had the potential to substantially reduce the cost of providing coal dust explosion protection underground, and at the same time, be more effective than current stone dust.  Major cost savings were expected with the ability to hydrate the dry polymer underground and improved effectiveness as an inertant, vastly reducing the material handling mass and costs when used for broadcast inerting and as an inertant in explosion barriers. Tests at SIMTARS, using the industry-standard 20 litre SIWEK chamber have proven its effectiveness as an inertant.

It was acknowledged that the hydrated polymer, however, was not immediately suitable as a direct replacement for stonedust because of its short life due to drying.  This project was intended to investigate methods of reducing moisture loss to extend the in-situ life to an acceptable length.  A number of different methods of coating, variation of polymer manufacture and direct encapsulation of water were tried without success.

The last alternative considered was to coat commercially inorganic hydrate to prevent it dissolving in mine water.  Many different inorganic hydrates were considered and most were rejected on the basis of potential toxicity or inadequate water content.  Two hydrates were selected for testing of inerting levels required being magnesium chloride hexahydrate (MgCl₂.6H₂O) and magnesium sulphate heptahydrate (Epson Salts) MgS0₄.7H₂O.  Both are non-toxic and have high moisture content but only MgCl₂.6H₂O proved substantially more effective than stonedust when tested in the Siwek spherical chamber.  Concerns arose because of the possibility that a breakdown product of (MgCl₂.6H₂O) under conditions of high temperature might be HCl.  The reference to this was scant and no specific temperature was reported in the reference but the monitors were informed and it was decided to investigate further.  Tests were undertaken in the 20 litre Siwek chamber analysis of the post explosion gases indicated that this was not the case.  Despite the positive result the project ended at this point.