The extraction industry-from shiny diamonds to black-as-night coal-hasnt earned a shining environmental reputation. It is seen as dirty, unsafe and sometimes even toxic. But the industry has made great strides over the years, and the lubricants used in some mining applications are lending a bit of spit and polish to its standing.
An estimated $82.2 billion of raw minerals were mined in the United States in 2018, a 3 percent increase over 2017, according to the U.S. Geological Surveys Mineral Commodity Summaries 2019. The top producing states, in descending order of production value, were Nevada, Arizona, Texas, California, Minnesota, Florida, Alaska, Utah, Missouri, Wisconsin, Michigan and Wyoming.
Mining equipment is extremely varied, encompassing many massive machines, both mobile and stationary, working above and below ground. These expensive investments are protected by lubricants ranging from open gear lubes and wire rope greases to heavy-duty diesel engine oil, transmission oil and hydraulic fluids, according to David Gamble of mining company AngloAmerican, speaking at the ICIS African Base Oils & Lubricants Conference in November.
The appetites of these machines are as impressive as their size: A Caterpillar 797 F-the OEMs largest haul truck-takes about 320 liters of lubricant in its crankcase, 1,675 liters in its brake and hoist system, 1,180 liters in the differentials, 630 liters in the transmissions, 360 liters in the steering system and 186 liters in the final drives, Gamble said.
These lubricants must combat moisture and dirt in addition to heavy loads, shock loads, extreme pressures and continuous operation. Mobile equipment that tilts and sways causes oil to slosh around in the sump, creating aeration problems.
Mining equipment operators demand quality, high-performance lubricants based on API Group II or higher base oils with premium additive packages as well as energy-efficient synthetic options, he continued. Original equipment manufacturer approvals are important, such as Caterpillars TO-4 and Allisons C4 transmission oil specifications.
Protecting Water Sources
In countries around the world, there is a concern that spilled lubricants can leach into ground water and contaminate aquifers, streams and lakes, says Kluber Lubrications website. The company points to regulations in some Canadian lake regions that require mines to use biodegradable lubricants. Many regions require operators to report any lubricant spills over a certain volume.
Currently, only one U.S. state, Montana, has a law mandating the use of biodegradable lubricants in mining, according to Larry Ludwig, chief chemist and technical director at Schaffer Manufacturing in St. Louis, Missouri. That law requires any underground mining done near water to use environmentally acceptable lubricants. EALs are defined by the Environmental Protection Agencys Vessel General Permit regulation, which sets specific standards for the fluids to be biodegradable, minimally toxic and non-bioaccumulative. They can be either biobased, such as vegetable oils, or synthetic, such as polyalphaolefins, diesters or polyalkylene glycols.
While reliable figures are difficult to find on the amount of biobased lubricants used specifically in the mining industry, the Freedonia Groups figures indicate that in 2022, demand for biobased base stocks will reach 40 million gallons, based on annual growth of 5.9 percent. Going forward, growth is projected to be somewhat less intense, and biobased oils will remain a small portion of total lubricant base stocks by volume.
The use of biobased lubricants in the mining industry has been limited in the past decade. However, Ludwig said more mining companies are employing biobased and biodegradable lubricants than before. Theyre beginning to understand the consequences of cleanup costs, especially if [the spill] gets close to a watershed, he said.
Most vegetable oils have good lubricating qualities due to their polar nature. They provide good wetting properties and act as solvents that help keep particulates away from metal surfaces, where they could cause wear.
Biobased oils also have naturally high viscosity and viscosity index, adding to their ability to form a protective lubricating film and resist evaporating. Additionally, genetic modifications have brought improvements in thermal and oxidative stability, particularly with soybean and canola oils.
However, biobased lubricants decompose easily when mixed with water, which is what makes them highly biodegradable compared with conventional lubricants, said Ludwig. He stressed there is a downside to using biobased lubricants in mining applications, as vegetable oil is not as oxidatively stable as regular lubricants. Performance could also be hindered during cold snaps, he said, as low temperatures can affect pumpability.
Hind Abi-Akar, fluid technical expert with Caterpillar, pointed out that biodegradable fluids must pass the same rigorous testing as mineral oils before they can hit the market. Bio-hydraulic oils, for example, have to pass stringent and demanding pump tests to qualify for mobile machines and equipment (not just mining-but the entire machine sector).
This may require different antiwear additives than oils used in the industrial sector and more robust additive systems, she wrote in an email.
Biobased fluids are currently being used in mining equipment such as crushers that smash large rocks, drill rigs that bore deep into the earth, and loaders and trucks. These pricy pieces of equipment operate using highly formulated biodegradable antifreeze, gear oils, hydraulic fluids and greases, said Ludwig. He added that a number of OEMs are currently considering biobased lubricants for use in open gears and bearings.
A quick review of lubricant marketers websites indicates that biodegradable lubes are available for most, if not all, mining applications.
One remaining drawback is price. According to Shell, lubricants account for about 5 percent of maintenance expenditures in the mining industry. Ludwig indicated that cost is a drawback for biobased lubricants within mining, where some sectors, especially coal, are operating on the continual cusp of insolvency. The markup comes from the chemistry involved, he said, as ester formulations and biodegradable hydrocarbons are costly.