solution mining of deep potash

everything thing you need to know about removal of potash.
Solution Mining is defined as the extraction of the valuable components from a mineral deposit using an aqueous leaching solution. In its original sense, solution mining refers to evaporite mining, the dissolution of soluble rock material such as salt by using borehole wells to pump water into the deposit and remove the resulting saturated brine. In its current usage, solution mining also includes ore leaching, the in-place (in-situ) leaching of valuable metal components from an orebody, and the mine-site procedures of heap leaching and dump leaching. Often included is the Frasch process of using superheated water to melt sulfur in its deep deposits and recover the molten sulfur in borehole wells.

Evaporites represent a broad class of water-soluble minerals (salts). Commercially important evaporites include halite (sodium chloride), sylvite and silvinite (potash), bischofite(magnesium chloride), nahcolite (sodium bicarbonate), trona (raw soda ash), and langbeinite and carnallite [both sources of potash and magnesia (magnesium oxide)].

Solution mining involves injecting a solvent into the pay zone of the deposit through a cased borehole. For evaporites, the solvent is hot water, which forms brine as the soluble minerals dissolve. The brine is brought to the surface via the casing system in the same or another borehole and sent to a processing facility for recovery by the controlled crystallization of the desired product, followed by dewatering and drying. Some minerals may require additional purification steps, such as the flotation of potash crystals. The depleted brine is chemically reconditioned and injected back into the deposit. Thus, solution mining creates minimal surface disturbance and little waste, compared to conventional mining.
Geology

Saskatchewan is underlain by a vast deposit of evaporite minerals of Middle Devonian age, including the economically valuable fertilizer mineral sylvite (KCl). The beds are generally flat-lying, mineralogically simple, and of high grade, leading to economic exploitation by either underground mining methods or by solution mining methods. The key constraint in determining mining method is depth of burial ? underground mining is not considered feasible if the deposit is deeper than some 1100m below surface. At greater depths solution mining is the only applicable technique, and even in this circumstance, it is generally regarded that the deposit should be hotter than 50 degrees C and/or deeper than 1,450m burial depth for solution mining to be effective and economically efficient. Much more of the potential Saskatchewan potash deposit is amenable to solution mining than to conventional underground mining
Key Parameters

Thickness of Mineralization - As the solution mining method would allow for the selective removal of each of the mineralized members.
Potash Bed - This can control the concentration of the product liquor, the rate of solution mining, and the effectiveness of secondary mining.
Depth of Burial - As temperature increases with depth, thus, making the solution process more efficient.
Carnallite Content - As increased amounts of carnallite decrease the efficiency of cavern dissolution and potash recovery. Presence of depositional anomalies that reduce the thickness or grade of the potash zones.
Presence of faults or similar geologic features that displace the potash beds.
The Dip of the Potash Beds - Excessive dip can limit the size of the caverns and the resource recovery.
The presence of clay layers in the immediate roof as they can lead to premature roof fallout and limit the size of the cavern.

Advantages

Capital Costs - As it is cheaper to drill a series of production wells to handle solutions than to construction a pair of conventional shafts, undertake the initial underground development work and install mining machinery, there should be a significant saving in the initial capital cost of a solution mine. However, the need to develop new cavities results in an on-going need for small-scale investment.
Operating Costs - Solution mines use hot brine instead of mining machines to extract the potash values from underground deposits and for this reason their operating costs are very sensitive to the price of fuel. When natural gas prices were low, solution mining was very competitive, but the rise in fuel prices since 2000 has changed this situation. However, any potash project with access to cheap natural gas, possibly from an isolated source, could find it interesting to employ the solution route.
Environmental Benefits - Conventional potash operations yield large amounts of waste salt (NaCl) that is usually stacked at the mine site, as back filling of the salt is costly and difficult to undertake. Solution mines can avoid this problem, pumping back underground any solid waste in the form of a slurry. As environmental pressures increase, this is clearly an advantage for the solution-mining route.
Absence of Flooding Risk - Solution mines do not have the specific problem of water inflow that threatens conventional underground mines ? an issue that has received more than its usual share of publicity in recent months.
Other Advantages of Solution Mining include the ability to access deep reserves and the option of making a high grade of final product.

Solution Mining



Dry Shaft Mining