The concept of solution mining of potash is based on the high solubility of potassium containing salts in water. Rather than extracting and moving solid ore to surface for processing, as in conventional mining, solution mining uses water as the means of extraction and conveyance.
In our case this technique involves drilling a large-diameter hole to the bottom of the deepest carnallite layer at a depth of about 900 meters. Heated water is pumped into the well: the water preferentially dissolves the carnallite, and the cavern formed by dissolution expands laterally through the layer of the highly soluble carnallite. A second adjacent extraction well is then connected to the first forming a dual well cavern with a diameter of approximately 100 meters. The injection and extraction well pipes are raised from the bottom carnallite layer to the next layers after the obtainable salt has been dissolved and extracted.
The saturated salt brine is pumped up and processed at surface to crystallize out potassium chloride. The rate of mining, cavern shape, and preferential separation of various salts are determined by changing the positions of the inflow pipe at the well, the location of the brine return in the extraction well, as well as adjustment of the flow rates and the level of a non-reactive cover blanket.
An experienced engineering team will use continuous measurement techniques to monitor cavern shape and solution concentration. Control the shape of each mined cavern and the spacing of the wells virtually eliminate any possibility of surface subsidence. When finished, spent caverns are filled with surplus NaCl and MgCl2 brine from the crystallization plant to provide long term stabilisation of the abandoned caverns.
An important advantage of this mining technology is extremely low impact on the environment. Well-heads and piping systems to the processing plant are the only surface infrastructure. At a similar plant in Germany, these wells are located within cultivated fields and livestock pastures.
The solution mine well field will utilise a small area of approximately 8 square kilometers which is sufficient to supply the Mengo potash plant for 20 to 25 years of production. MagIndustries’ Mengo permit covers approximately 136 square kilometers, which our studies have shown to be underlain by thick continuous carnallite horizons.