Mined rock salt
Rock salt comes from geological formations either on the surface or in a deep mine.
Mining companies crush and screen to various sizes preferred by snow removal customers.
(Left) Sample from U.S.-based deep mine. (Right) Mid-American Salt sample from its
- Sizing tends to be coarser, which creates a lasting effect that doesn’t dissolve right away.
- Typically drier than solar salt. Mined rock salt comes out of the mine very dry and doesn’t accrue moisture unless there are handling or mine flooding issues.
- Purity variances. Some mines have a high concentration of rock/shale within the salt deposit deep in the ground. This can lead to the NaCl content being 90% or lower, which creates a measurable drop in melting ability.
- Too many fines can cause clumping in spreaders.
Commercial solar salt is produced by natural evaporation of seawater or brine.
Standard solar salt evaporated from the ocean.
- Purity levels are high, usually over 99% NaCl.
- Less costly.
- Typically higher moisture content (anywhere from 2% to 5%), which can lead to product freezing and spreading issues.
- Tends to break down faster than deep-mined salts during handling, leading to a higher concentration of fines.
- Gradation is finer, which can lead to spreading issues. However, fines melt salt faster because of more surface contact with ice.
- Know what you’re buying. Don’t assume all salts are the same. Salt quality varies depending on the source, the type of salt, and the shipping and handling process.
- Are you buying salt from a domestic mine or is it imported?
- Are you buying deep mined rock salt or solar salt?
- Get what you pay for. Purity levels can vary 3% to 5% between sources, and moisture content can vary even more. Low purity or high moisture content should be considered as you analyze the price. Only sodium chloride melts ice, so why pay for shale, rock, or mud?
- Investigate the supplier. Make sure you are dealing with a reputable company based on quality and experience, not just years in the industry.
- Are you comfortable with the people you are dealing with? The supplier should be knowledgeable about the salt it is selling and be able to answer basic questions regarding moisture content, purity level, gradation, salt storage conditions, etc. Ask for references and make sure you’re comfortable before spending your money.
- Confirm the tonnage you’re buying is in inventory and available for immediate delivery. Some suppliers oversell their inventory and, in times of high demand, run out of salt. In some cases, your salt may be sold to another customer.
- Request a certificate of compliance to a recognized specification. The most common specification is ASTM D-632 Type 1 Grade 1, typically used for road salt applications. This specification outlines all the critical characteristics for a good performing road salt. If the supplier can’t verify that his salt conforms to a recognized specification, proceed with caution.
- Mark Thiele, Mid-American Salt