Emulsion Explosives are Rapidly Gaining Popularity Because of Their Water-Resistance and Higher Density.
By Anthony Konya and Dr. Calvin J. Konya
Emulsion explosives are rapidly gaining popularity because of their water-resistance and higher density than products like ANFO. While these emulsions are more costly than ANFO they provide a stable approach for the blaster who does not want to contend with the many aspects of water in blastholes.
In addition, since they are higher-density explosives. Many more pounds can go into a blasthole allowing burden and spacing to be stretched. While in most cases the pattern expansion alone is not large enough to make them the same cost as ANFO, the ease of loading and water resistance have many sites switching to an emulsion product.
The reason emulsions are more costly than an ANFO is because they are orders of magnitude more complex to make. In addition to heavy mixing and a larger process for the creation of an emulsion, they require many more chemicals compared to an ANFO.
This complicated process of making emulsions can be very confusing to many people and the purpose of this article is to provide valuable knowledge to emulsion users about important parameters to know when ordering and how to run quick field testing to determine if the emulsion has any major problems.
These major problems can result in large formations of NOx, minimal fragmentation of rock, and increased ground vibration. The reason these problems occur is rarely because of geology, and normally because of inaccuracies or errors in the emulsion product.
|Figure 1 - Emulsion Micelle Size.|
Explosive emulsions are, in most cases, a mixture of water, oil, emulsifier and ammonium nitrate. In certain cases these emulsions may have other “salts” such as sodium nitrate and calcium nitrate to help allow for easier manufacturing.
These additional salts will lower the total explosive energy of the emulsion. When purchasing or comparing emulsions it is extremely important to ask the manufacturer what salts are used in the emulsion.
Another critical parameter of emulsions is the micelle size. The micelle size is the size of the bubble in the emulsion and will directly affect the shelf life and performance of the emulsion. The smaller this micelle size, the better performing the emulsion will be and the longer shelf life it will have.
The next major consideration for the purchasing of an emulsion is the method of sensitization. This is primarily done with either chemical gassing or microsphere. Chemical gassing is the more often used technique because it is cheaper, however chemically gassed emulsions typically underperform emulsions sensitized with microspheres.
Microsphere emulsions will not only contain more energy, but also have shelf lives up to double the length of a chemically gassed emulsion. The chemically gassed emulsions will also degrade over time and shoot with less explosive energy six months after manufacturing than one month after manufacturing. If using packaged product it is extremely important to not receive any product that is over halfway through its shelf life.
The last important parameter is the proper oxygen balance. While this can vary for emulsions it is generally more uniform than ANFO. Testing the oxygen balance of emulsions generally requires a more intensive laboratory study and will not be discussed here.
Emulsion Field Testing
|Figure 2 - Emulsion Crystals (crystals so large individual bubbles cannot be seen).|
The major problems most emulsions experience is the crystallization of the ammonium nitrate (or other salts). This crystallization means that the emulsion is breaking down and the emulsion has a high probability of misfiring, producing NOx, and firing very weakly causing minimal fragmentation and increased ground vibration. This can be caused by improper chemicals, poor mixing, and aging of the product but can lead to very large ramifications for a mine.
The simplest way to test for this is to take a small amount of emulsion and rub it between your fingers, if the emulsion feels gritty than it has begun to crystalize and should not be used for blasting. A proper emulsion that is ready to blast should feel greasy with no grit.
Another important factor is how likely the emulsion is to crystallization during the blasting. This crystallization can be easily tested with packaged product by smacking the package with your hand and rubbing it between your fingers, again feeling for grit.
If the product has a gritty feeling after a minor shock has been applied, it will likely break down during the blast in holes adjacent to the blasthole detonating. With bulk product this test can be completed by putting some of the product into an empty water bottle or bag and further testing in a laboratory.
The final field test should be done with all gassed emulsions and is a common test done by the blaster, this is called the cup-density test. When an emulsion is sensitized by chemical gassing, it will slowly rise achieving a certain density after 20 minutes (or other set amount of time).
The most important part of this test to take the weight and volume both before and after the set time and write down the density of the explosive in the blast report. Commonly, if the emulsion rises at all it will be considered good product when in many cases it has not reached its proper density. This is due to improper gassing and can result in large formation of NOx and poor explosive energy.
Many times, this is why after a blast has cleared NOx will bubble up from the muckpile as the bottom of the blastholes. An emulsion with too high a density (as is common in the bottom of blastholes with chemical gassing) will improperly detonate and commonly leave toes in the shot.