Cause, effect and control of potash dissolution by brine

A number of potash mines around the world experience brine inflow occurrences and various associated structural and stability problems, as brine tends to dissolve the potash and salt strata. Potash mining carries a distinctive risk because potash rock is highly soluble in water. The initial ventures of mining potash in Canada failed due to flooding five decades ago. Billions of dollars are lost due to partial or complete closures of potash mines as a result of flooding ranging in volume from a few milliliters to thousands of liters per minute.; A novel research program was developed to simulate the effect of brine on the performance of mine supports with and without dissolution control measures (DCM) in uniaxial and triaxial loading conditions. Acoustic emission (AE), as a nondestructive testing technique, was used to evaluate the dissolution chemistry processes and the time dependent behaviour of potash rock.; In the first stage, studies were carried out to understand the causes and effects of brine on potash dissolution and strength characteristics. The uniaxial testing program consisted of loading potash specimens in a creep frame to reproduce pillar loading, and then to simulate the presence of brine using three different brine inflow scenarios, increasing, stagnant and continuously refreshing brine conditions. Brine temperature ranged between 20°C and 60°C, and pillar load conditions varied from unloaded to 50% of the unconfined compressive strength (UCS) of the rock. Potash specimens were fitted with AE transducers to monitor energy emission and brine sampling was used to assess dissolution reactions.; The triaxial testing program consisted of loading potash specimens in a creep frame to simulate axial loading, and then simulating the confining effect using brine as the confining medium, thus achieving triaxial loading conditions. The axial stress settings were set at 25% and 50% UCS, and the confining pressure was varied from 10% to 25% UCS in increments of 5% UCS. Ambient brine temperatures were used for all tests.; Dissolution control studies comprised loading of potash specimens treated with DCM under uniaxial and triaxial loading conditions and then simulating the presence of stagnant brine conditions. Three DCM, cement grout, Mineguard™ (polymer lining) and chemical suppressant, were used.; The results of uniaxial testing without DCM indicated that dissolution rates and strength characteristics are highly dependent on the brine inflow pattern, brine temperature and load conditions. Loads approaching 50% UCS tend to generate very high rates of energy emission, often leading to the failure of the simulated pillars. It was demonstrated that AE could be effectively used for predicting the strength behaviour and failure progression of pillars when exposed to brine inflow under uniaxial loading conditions. (Abstract shortened by UMI.)...