BME takes a pro-active approach to reactive ground
- Published: Friday, 08 December 2017 08:16
“Reactive ground” is a situation that can lead to an unexpected blast which is why blasting and explosives specialist BME, understand that blast areas always need to be tested first to see if they are reactive.
Nitrates (typically used in explosives) react with rock that contains certain sulphides which can lead to an auto-catalysed process that in in severe cases will lead to an exothermic decomposition and an unwanted explosion. Some of the typical nitrates in the explosives industry are ammonium, sodium and calcium nitrate.
Oxidation occurs naturally in the weathering process where iron sulphides like pyrites react with air to form ferrous ions and acid. This can also be accelerated through the drilling and loading processes that that create sulphides fines thus increasing the surface area of the sulphides for reaction. Simply put:
Iron sulphides + atmosphere (H20 + air) = ferrous ions + sulphuric acid
When a nitrate is added the following occurs:
Nitrates + iron sulphides + ferrous ions + sulphuric acid = nitrous oxide + ferrous ions + heat
The reaction slowly intensifies until it speeds up and leads to a violent reaction i.e. an explosion.
Not all sulphides are reactive however; therefore, the first step is to test the explosives with the sulphides from a mine. BME has test procedures for this and if the sulphides are found to be reactive, there are a number of charging procedures that need to be observed.
“BME has also developed a special emulsion formulation specifically for reactive ground which contains inhibitors that slow down reaction rates with sulphides and has been successfully and safely used in mines that have reactive ground,” says Charles Hurly marketing manager, BME.
When considering reactive ground, the following guidelines should be noted:
- Training of all personnel in mines with reactive sulphides is important in these procedures, especially for the planning and production teams.
- Sleep times need to be kept to an absolute minimum while in severe cases blasts will need to be fired on the same day as they are charged.
- Drill cuttings may contain a high quantity of finely ground reactive sulphides and must not be used.
- Importation of material for stemming is advisable.
- Product spillage also needs to be controlled given the possibility of reactions with the surface drill chippings.
“At BME we are committed to safe blasting and have found the combination of BME’s emulsion product combined with stringent charging procedures a very successful strategy when dealing with reactive ground.
“We will continue to conduct cutting edge research and development into products and procedures for reactive ground blasting conditions which will benefit our customers in the future,” concludes Hurly.