Rock Products

MAR 2017

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60 • ROCK products • March 2017 nitrate is used, not ANFO. Without the use of ANFO, one of two situations must occur: 1. The emulsion must be over-oiled, this can lead to problems with the emulsion and creation of both carbon monoxide (CO) and nitrous oxides (NO x ). 2. The emulsion is not over-oiled, leading to improper oxygen balance and creation of large amount of nitrous oxides (NO x ). In addition, either of these situations can lead to a decrease in explosive energy and additional variability in the blast- ing. Worse yet, many times hard-fertilizer grade AN prills are used to reduce cost of production further increasing the problems with this product. In one case the authors investigated where a 70/30 blend was being used with hard prills, the entire pit would be smoked out for hours after each blast from large amounts of visible NO x . In order to improve this situation, ensure that if a blend is being used for water resistance, ANFO is fueled properly and being mixed with the emulsion. Furthermore, in some places in the world these blends are being sold mixing hard fertilizer prill AN with emulsion, yet selling the hard prill AN for the price of an ANFO. This dra- matically increases the cost of the product, for example let's assume that ANFO sells for $0.30 per pound and hard-prill sells for $0.18 per pound. In a 70/30 blend, a mine would be overcharged $0.036 per lb. At one large aggregate operation this overcharge equates to more than $150,000 per year and in many large metals mines can result in over $750,000 per year overcharge. 50/50 Blends The 50/50 category of blends is those that contain approxi- mately even amount, by weight, of emulsion and ammonium nitrate. These blends are generally water resistance with a proper emulsion but can break down if water is flowing through the blasthole. This blend is generally augured into the borehole, requir- ing the need for dewatering, pumping, and has increased explosive energy cost. These blends become much easier to recognize, as the prills can be seen but the mixture is still retaining the look of the emulsion. The 50/50 blend, when improperly made can create large problems for the mine especially with the increase of blast- ing fumes (CO, NO x ). It is critical for this blend that both the emulsion and ammonium nitrate be sensitized. This means that the emulsion should either be gassed or contain micro- spheres and a proper ANFO with 6 percent oil should be used for maximum energy release. Figure 2 – Straight Emulsion. Figure 3 – 70 percent emulsion and 30 percent ammo- nium nitrate blend. FIELD TESTING

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