The Integration of These Two Processes Can Lead to Sizeable Cost Savings as Well as a Diminishing Environmental Impact.
By Anthony Konya and Dr. Calvin J. Konya
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| Used oil in ammonium nitrate explosives (ANFOs and Emulsions) can provide an environmental friendly remedy for disposing of used oils and cut costs at most operations that use heavy equipment. |
Today’s aggregates industry seeks cost-reducing technologies to enable more efficient operations. In addition to worrying about costs, mines must balance environmental considerations, quality of product, health and safety of workers, and strict government regulations on many facets of their operation.
A mine that does not meet these stringent criteria will either be forced to close with the loss of their social license to operate, or will be pushed out by other competition that can produce at lower cost. Two factors used at nearly every mine that affect all of these situations is oil and explosives, and with proper management mines can realize cost-reduction and a viable solution to reduce waste.
Mines and construction projects alike use massive machines that expend sizeable amounts of oil in daily operations. This oil is then changed on a regular basis during preventative maintenance procedures and is then sent away for recycling or waste. This typically is an added expense, as the mine will pay a company to handle these used oil products in an environmentally friendly manner.
At the same time, mines use ammonium nitrate-based explosives such as ANFO or Emulsions to fragment and move rock in the blasting processes. These explosives combine oil and ammonium nitrate (and some other chemicals in minor amount) to achieve oxygen balance for minimal production of toxic gasses when blasting. Most mines will fuel their ANFO with diesel oil which is either purchased and provided by the mine or brought in by the explosive supplier.
When this process is analyzed one can observe that the mine will pay to have used oil removed from their site and at the same time purchase another oil (or other petroleum product) to sensitize the explosives. Not only is cost associated with the purchase of new oil and recycling of used oil, but major shipment costs can be incurred where oil is shipped away and new oil is shipped in.
The integration of these two processes can lead to sizeable cost savings as well as a diminishing environmental impact. However, the combination of these processes can involve some basic understanding of explosives, MSHA safety concerns, and government regulations. This article will detail and provide information that will be needed for a mine pursuing this effective cost-reduction technique.
Risks of Used Oil in Explosives
As previously mentioned, explosives that are ammonium nitrate-based typically use petroleum products (oils) to provide proper oxygen balance. This ensures good velocity of detonation, proper combustion, minimal gasses, and good performance.
Oils that have then been previously used around the site, particularly in equipment can then be used in these explosive products. This combines good recycling and environmental habits with cost-reduction in the price of explosive products.
While these used oils can be used in emulsion formulations, emulsion matrix is typically made in a plant setting and would need to be used by explosive companies – not a mine. For this reason, we will center this discussion primarily on ANFO, noting that similar principles would apply to emulsions with proper percentages. Many explosive companies use a used or recycled oil in their emulsions, with some companies using entirely used oil to sensitize their emulsions.
Ammonium Nitrate and Fuel Oil (ANFO) typically has around 6 percent oil with an optimal balance of 5.7 percent oil to 94.3 percent ammonium nitrate. Other substances may be present in small quantities to achieve proper prill properties.
Two methods exist then for adding used oil to the ANFO. The first method would be to use the entire amount of oil as a used oil. This can work at larger sites that produce enough oil for complete sensitization, but will require more careful monitoring and testing. The second method would be to use a percent of the total oil in the explosive as used oil. This way the used oil is diluted and any impurities are also diluted, leading to more consistently meeting the used oil standards.
It is important to note, with proper preventative maintenance schedules most operations will not use oil in the equipment long enough to have oil that consistently fails to meet required standards.
The major risks associated with used oil in ANFO is in blasting safety and environmental concerns. The first of these risks, blasting safety, will be considered in extreme conditions such as very low ambient temperatures and very high ambient temperatures. These safety issues include the ability to change the ANFO to a cap-sensitive state and in the storage of these used oil ANFOs (UOANFO) in contact with different metals.
One such study (Ruhe & Bajpayee) observed the properties that different oil mixtures would exhibit in contact with different metals at high ambient temperatures. There tests included 100 percent recycled “used” oil mixtures, mixes of used oil and other petroleum products, synthetic oils, and used oils mixed with graphite.
Graphite is sometimes used as a motor oil additive and can cause sensitivity issues. All these mixtures proved to be stable at 140 F (60 C) in steel, stainless steel, and galvanized steel contained. At 176 F (80 C) all samples, besides that containing 1 percent graphite, had limited reactions with galvanized steel. None of these samples proved to be cap sensitize at 75 F (24 C).
In addition, small hazards can arise at very low temperatures due to increase in used oil viscosity. Tests have been run (Ruhe & Bajpayee, 1996) with mixes of diesel No. 1 and No. 2 and used oils to quantify these risks at these low temperatures.
Blends of No. 2 Diesel and Used Oil in a 50 percent to 50 percent quantity were made down to 0 F (-18 C) and the same blend with No. 1 Diesel was made down to -20 F (-29 C) with minimal changes in detonation velocity, compared to a ANFO made with 100 percent No. 1 Diesel. All tests run at low ambient temperatures, some as low as -40 F (-40 C) have proved that USANFO present minimal risks in blasting safety, as long as proper guidelines are followed for quality of used oil. The oil blends that have a greater percentage used oil than diesel will have slightly lower velocities of detonation.
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| Oils that have then been previously used around the site, particularly in heavy equipment, can be used in explosive products. |
Regulatory Standards
The Mine Safety and Health Administration (MSHA) along with the Bureau of Alcohol, Firearms, and Tobacco (ATF) regulate the use of explosives at mines. The ATF has almost no mention of used oil with ammonium nitrate explosives, and when asked for comment responded that “in general, ATF does not regulate the components used to manufacture explosive materials.” Therefore, if the proper ATF manufacturing permits are held, a USANFO is not viewed differently by the ATF.
MSHA does regulate the components to make ANFO and has specific standards (30CFR Part 56.6309) which specifies the minimum flash point of oils in explosives (125 F) and that waste oils shall not be used to prepare ammonium nitrate-fuel oil (ANFO). MSHA has not responded as of this writing to further clarification. However, in response to frequent requests for exemptions from this rule, MSHA released the “MSHA Generic Petition” on Sept. 1, 1994, to provide a simple method for mines to legally begin this process.
This standard addresses the use, system and type of used oils allowed for USANFO. Two of the major topics included in the basis of this is that only petroleum-based lubrication oils recycled from equipment can be used and a maximum of 10 percent of 90W oil can be used in USANFO.
Additional regulations require testing of the used oil for Arsenic, Cadmium, Chromium, Lead, Halogens, and Flash Point before mixing with fuel oils. The chemical testing is primarily to ensure environmental compliance (non-hazardous waste requirements) which are derived in 40 CFR 279.11.
Flash Point testing must follow either closed-cup ASTM D3941-90 tests or open-cup ASTM D1310-86 tests. MSHA also mandates a maximum of 50 percent by volume of used oil in an ANFO product and when used oil exceeds 30 percent, absorption tests must be performed prior to blending. Other requirements are also listed in the generic petition, which must then be submitted to MSHA for approval for each individual mine.
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Tested Component |
Limit |
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Arsenic |
5 ppm maximum |
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Cadmium |
2 ppm maximum |
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Chromium |
10 ppm maximum |
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Lead |
100 ppm maximum |
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Total Halogens |
1,000 ppm maximum |
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Flash Point |
100° minimum |
The Mixing Process
After the oil has been drained from equipment, it must first be placed into a tank that will store all used oil on-site. Oils of varying grades can be mixed, as long as under 10 percent total volume of 90W oil is used. Oil must then be tested on a re-occurring basis to ensure proper quality is met. One important note, if testing off-site it is best practice to not use the oil until after tests return as failed tests may result in consequences to the mine.
After the storage and testing stage, the oil may be drawn from the tank to a truck for mixing into explosives. While the oil is in the tank, it is considered by MSHA as a “used oil” and upon filtering through a 60 mesh and 100 mesh (in series) filter system the oil is then treated as “recycled oil”. This oil can now be diluted and mixed with diesel oil and must be used within 24 hours of being drawn into a bulk vehicle.
After blending this oil mixture can be used from a bulk truck and is mixed with blasting grade ammonium nitrate prills. With proper oxygen balance and a good truck this USANFO will perform almost identically to regular ANFO.
One word of caution, different state Environmental Protection Agencies require different testing and modelling of fumes generated from blasting. Suppose that this oil had a lead content of 40 ppm (40 percent of limit to hazardous waste), with the proper MSHA paperwork and generic petition it could be used in ANFO with up to a 50 percent of the oil mixture.
This would then reduce the lead content to 20 ppm for what would be mixed into the ANFO. During the detonation, this oil would be exposed anywhere from 3,000 F to 7,000 F and a chemical reaction would take place that could create some lead components, such as lead oxides, which is a solid at normal state and has a boiling point of about 2,700 F.
This means that at a point in the detonation, the lead oxide would be gas and turn to a liquid, then solid normally within milliseconds or less. However, some state EPAs will require “gas modeling” to incorporate this and updating of permits, even though these gasses will not leave the property.
The EPA has not responded to requests for more information or federal guidelines on this matter. In this case, best practice is to check with the local EPA office to detail exactly what will be required to allow this. The authors have seen projects in the past that would have saved large amount of money ruined because of such stringent EPA testing and modeling requirements, especially in terms of air pollution.
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| Most mines will fuel their ANFO with diesel oil, which is either purchased and provided by the mine or brought in by the explosive supplier. |
Conclusion
Used oil in ammonium nitrate explosives (ANFOs and Emulsions) can provide an environmental friendly remedy for disposing of used oils and cut costs at most operations that use heavy equipment. While specific regulations exist to stop this process, exemptions from MSHA can be obtained following generic petitions and proper testing standards.
These testing standards, filtering processes, and maximum blend limitations ensure that used oil does not pose significant risks to blasting safety or the environment. State EPAs can have significant say in the use of used oil in these explosives products and must be contacted in any feasibility study to determine exact regulations of each mine.
With proper management of oil and explosives, mines can efficiently reduce costs and see increases in their social license to operate by removing normally waste oils from site.
Dr. Calvin Konya is the president of Precision Blasting Services, and Anthony Konya is a project engineer for the company. They can be reached at 440-823-2263, or [email protected].