Potash is commercially mined through two methods, conventional underground mining and solution mining techniques. The geology of the deposit dictates what method is best suited for resource extraction. Conventional mining methods have a depth limitation, once potash reserves are deeper than 1200 meters, solution mining must be employed. For the most part, the solution method of mining is due to the fact that potash is found in sedimentary rocks. Sedentary rocks tend to collapse when they are dug too deep, and deep mine shafts are also prone to flooding due to the porosity of these rocks. Solution mining offers a few advantages compared to conventional underground mining including lower up-front capital cost and a shorter ramp-up time. As all mining methods, the profitability of a solution mine is affected by the mineralogy, grade and tonnage of the potash reserve.
Solution mining costs are directly related to drilling cost and the quantity of potash produced from each well. A variety of production well configurations for solution mining are available dependent upon the geology of the deposit. Most solution mining has involved extracting potash-bearing solutions from flooded underground mines or used well designs which access the potash with vertical drill holes. Improvements in drilling techniques, particularly the ability to drill horizontally have enabled the cost effective extract ion of a variety of deposits, including those with thinner potash beds.
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The minerals from which potash is extracted include carnallite and sylvinite. Carnallite is hydrated potassium magnesium chloride. It dissolves fast- a benefit to the potash mining timeline, and therefore mining economics, and it has easy simple process chemistry. Sylvinite is a high-potassium chloride salt containing 63 percent potassium by weight. Sylvinite typically contains about 10-50 percent sylvinite mixed with halite, minor shale beds and other salts. The main product after mining and processing sylvinite is muriate of potassium (MOP)- a sylvinite and halite mix containing greater than 95 percent sylvinite.
The solution mining process
The first phase of solution mining is to access the potash reserve. This may be completed with a combination of machines and labour. Often, access is provided through an old conventional potash mine, with a mine pit held up by pillars of potash. Solution mining can extract the remaining potash in the pillars and mine walls. In other cases, drill holes are drilled to access the potash containing rock. The next step is to inject a saltwater into the potash bearing rock feeder, whether it’s a drill hole or a cavern. Salt saturated brine is used so only the potash is dissolved and extracted from the existing pillars and surrounding walls. The existing salt is left largely undisturbed in the underground mining works, which will reduce potential surface disturbance and prevent the creation of sink holes. Once the brine is enriched with potash, the brine is pumped out of the cavern. The potash saturated salt solution may be pumped to lined solar evaporation ponds. The water evaporates, leaving behind salt and potash. This “left-over” salt and potash is then removed from the pond and transported to a processing facility where the potash is separated from the salt and refined for sale.
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A sample of explorers and miners
As the world’s largest potash producer, Potash Corp has both conventional and solution mining projects. Their Patience Lake Mine was originally an underground operation, however, it was converted to a solution mine in 1998 after flooding hampered conventional mining operations
Utilizes solution mining and solar evaporation at their Cane Creek Project in the high-altitude Moab desert in Utah.
A potash development company, their Milestone Property has the characteristics of a potash deposit amenable to solution mining .
Mosaic operates a potash solution mine in Belle Plaine, Saskatchewan. This mine produces Muriate of Potash (MOP), including Fine, Standard, Coarse, Ag Granular, HQ Granular, Special Granular and Water Softener.
Karnalyte Resources is engaged in the business of exploration and development of agricultural and industrial potash and magnesium products. Karnalyte’s primary objective is to become a leading low-cost producer of high quality potash using proprietary improvements to a known solution mining process.
Allana Potash is a Canadian company with an focus on the international acquisition and development of potash properties. The company is currently focused on developing its Ethiopian Dallol Project, where it has completed a Feasibility Study for the project using solution mining and solar evaporation.