For decades, the coal float sink test has been a critical component for determining the grade of coal, especially for higher-valued metallurgical coal. Perchloroethylene (PCE) mixed with other hydrocarbons has been the fluid of choice to achieve the correct density for this test and is commonly used today. PCE is a known carcinogen and is on the EPA’s list of products to be banned in the United States. Employee safety should be a signature part of any responsible coal company and/or independent laboratory. Using PCE is a significant risk!
Additionally, recent studies have found that PCE may give inaccurate results due to its chemical reactivity with coal. Halocarbon 0.8 oil is an excellent replacement for PCE and has been proven through decades of use in float sink testing. Halocarbon 0.8 oil is inert and nonhazardous in nature, which translates to a very safe alternative that can also achieve the exact same specific gravity necessary for this critical test.
The Process: From Coal to High-Quality Steel
Metallurgical coal, also referred to as met coal or coking coal, is an important raw material for steelmaking due to its specific quality characteristics, which can be converted into “coke.” Turning met coal into coke involves a thermochemical process that converts coal into a hard, porous, high-carbon content product. In the blast furnace, coke is used as a reducing agent to extract iron from the iron ore. The value of coal is determined by its ability to convert into this important resource that allows for the production of high-quality steel from iron ore.
A simplified explanation of this process is:
Metallurgical coal (steelmaking coal or coking coal) is purchased by integrated steel companies and loaded into coke ovens, which heats the coal in the absence of oxygen. This process removes volatile components. This process turns coal into coke, a substance that is predominantly comprised of pure carbon with small amounts of mineral matter. Coke is a lightweight, porous substance with the feel and consistency of pumice, but it maintains its physical strength and integrity during handling.
The coke, along with iron ore, flux, and typically some limestone, are continuously loaded into a blast furnace, which is injected with hot air and heated to extreme temperatures (up to 2300 oF). In this process, the coke serves as an electrochemical reductant, reducing iron ore (Fe2O3 – iron oxide) into molten iron (Fe0). It also serves as a fuel source to keep the interior of the blast furnace hot and acts as a physical support for the iron ore pellets as they convert from iron oxide to molten iron (or pig iron). The limestone captures mineral impurities from the burden, which turns into slag and is removed from the molten pig iron.
The pig iron is then extracted from the bottom of the blast furnace and separated from the limestone portion, which is called slag. The pig iron is then transferred to a basic oxygen furnace, whereby pure oxygen is injected into the process to further enhance the steel by removing any remaining impurities, including unreacted carbon. At the end of this process, you are left with high-quality refined slabs of steel to be further processed.
High-quality metallurgical coal is a natural resource available in Canada, Australia, the United States, and many other parts of the world. Integrated steel companies (70% of steel mills globally) are willing to pay a price premium for metallurgical coal compared to lesser quality coals (e.g. thermal coal).
Protecting Employee Health and Ensuring Accurate Results
When metallurgical coal is mined, it is frequently contaminated with waste rock (sandstone, siltstone, claystone) and must be “washed” to remove the rock to make a product that is lower in mineral matter. At mining sites, this process is done in a coal preparation plant. During the early stages of coal project studies, exploration drill cores are analyzed to determine the quality of the coal and to design the coal preparation plant.
The Float-Sink Test (also called the Washability Test) provides analysis that aids in the wash plant design. The coal, within different size fractions, is dipped into baths of different specific gravities (SG) where the coal that has a lower SG will float, and the coal or rock with a higher SG will sink. By measuring the weight, weight % and ash (at minimum), a wash table is created and used for designing the plant. Several of the floats can also be combined to create a “clean coal composite,” where various analyses are completed to determine coal product quality.
A further step can also be taken, which involves using a laboratory-scale coke oven to test the clean coal composite for its ability to form coke and test the resultant coke properties. The coal float testing is critical in determining the design of the coal processing plant (critical for engineers) and an important step in establishing the coal’s economic value.
The most common fluid currently used in this density float method is perchloroethylene (PCE). Though this fluid is inexpensive and widely used throughout the world, the United States Environmental Protection Agency (EPA) has recently proposed a ban for most uses of this chemical as it is “known to cause serious health risks as in neurotoxicity and cancer.”
“…EPA determined that PCE presents an unreasonable risk to health, driven by risks associated with exposure to the chemical by workers, occupational non-users (workers nearby but not in direct contact with this chemical), consumers, and those in close proximity to consumer use. EPA identified risks for adverse human health effects, including neurotoxicity from inhalation and dermal exposures as well as cancer effects from chronic inhalation exposure.”
During the float sink test, where PCE is used, workers have to wear respiratory masks as personal protective equipment because the float sink baths are open to the atmosphere in the laboratories where workers are present. The float sink laboratory must be equipped with industrial ventilation, but vapors are still present throughout the testing and can remain in the laboratory for several hours after test completion.
One major coal company in Canada eliminated perchloroethylene as the fluid in float sink baths in order to protect employee health and safety in the 1980s. They identified Halocarbon 0.8 oil (available online as InfinX Calibration Fluid 0.8) as a highly effective and safe alternative to PCE. Halocarbon 0.8 oil has been used in this application for over 30 years. In their Float-Sink laboratory, no respiratory masks are required because Halocarbon 0.8 oil is non-toxic to humans and is nonhazardous, nonflammable, and chemically inert. By eliminating PCE in their facility, they have established a safe and sustainable work environment that not only directly protects their employees from exposure to PCE but also gets ahead of regulatory bans on PCE.
In addition to the health risks, perchloroethylene has been found by other Canadian studies to have the potential to cause a chemical reaction with coal and could potentially produce inaccurate results in determining the coal’s chemical composition. Halocarbon 0.8 oil is chemically inert and does not react with coal during the Float-Sink Test, providing highly accurate results.
The conclusion of this report stated that perchloroethylene produced a “solvent-induced reaction” that was highly reactive.
The report goes on to state that “the ramifications of using the wrong numbers for the above-mentioned parameters when determining product characteristics for sale are severe and could result in project abandonment or farce overvaluing of property.”
In conclusion, perchloroethylene is a dangerous toxic chemical that is undergoing a ban in the United States because of its dangerous effects on workers exposed to this chemical. In addition, some studies have determined that perchloroethylene could potentially chemically alter the effects of coal samples and potentially produce inaccurate test results.
Halocarbon 0.8 oil, manufactured in the USA, has been safely used as a float sink alternative for decades in the coal industry. We encourage responsible laboratories and coal companies throughout the world to consider this fluid as an alternative to help protect their employees and potentially eliminate inaccurate results in coal sampling. Contact us for more information, and let’s create your next breakthrough.