Salt production/logistics & the environment
Any extractive industry necessarily disturbs the natural environment. Removing salt from the sea makes no virtual change in the vast volume or salinity levels of the ocean; nor does a rock salt mine or solution mining operation significantly alter the landscape, though underground operations must be carefully managed for structural stability. Both solar saltworks and solution mine/vacuum pan-refining plants produce a saline waste stream that also requires proper management. Stockpiling and shipping salt also requires proper handling.
When a rock salt mine blasts away the solid seam of salt, the explosion leaves pieces ranging from boulders of salt to fine salt dust. As the salt is crushed to the size specified by each customer, further unusable fine salt dust is created. These “fines” are routinely used to fill some of the vast expanse created when the usable salt is hoisted to the surface.
In the final production of salt, to prevent the crystallization of other minerals which would degrade the purity of the sodium chloride, the crystallizing pond is drained of the concentrated solution containing salt and other minerals, termed “bitterns.” Sometimes, the salt producer further processes the bitterns to extract other salable materials before returning the all-natural remains to the sea.
In producing evaporated salt, the process water is re-used until all salt is removed that is economically recoverable and the remainder is generally deep well-injected (in the U.S., under a Class IV underground injection well permit from the U.S. Environmental Protection Agency). The size and shape of solution-mined caverns is also regulated by environmental permits. When a cavity has reached its planned size, it is closed and sealed under the terms of another environmental permit or, as is increasingly the case, is used to store petroleum or natural gas reserve supplies. The Salt Institute has been deeply involved working with environmental regulators to ensure that regulations are both environmentally-protective and conducive to economical salt production. Current U.S. federal standards for the mechanical integrity of solution wells, for example, reflect the expertise of the Salt Institute working with U.S. EPA.
Moving salt from its production site to salt users can also impose environmental stress. A 2008 study conducted for the Port of Toronto documented that waterborne salt deliveries offer significant reduction in the “carbon footprint” of salt deliveries over land-based delivery options.