THE ALTERNATIVE APPROACHES FOR TAILINGS DISPOSAL OF THAILAND’S POTASH MINES

Abstract

This study involves the two alternative approaches to dispose of solid and liquid brine wastes which is one of the biggest environmental challenge in potash industry. The first alternative approach is solidification method that can solidify the solid tailing into the concrete block by mixing with binder as cement, and additional fine and coarse aggregates. The design provides the optimizing mixing ratio for concrete block mixture materials in relation to the uniaxial compressive strength (UCS). The expected result is the optimal mixture that maximize the solid tailing concentration and archives the minimum UCS strength requirement of backfilling materials in Thailand Potash mine. The solidified concrete blocks are then used as backfill materials into the mine-out room of the underground potash mine to minimize significantly the environmental impact and stabilize excavations and minimize convergences and subsidence of the underground mine. The second alternative approach is deep well injection of liquid brine waste into the Khok Kruat Formation. The base case simulation was modeled with one injection well at rate of 165 m3/day. To annually dispose brine waste, the operational optimum conceptual model was designed of eight injection wells at different injection rates and time following the brine volume discharged. The results from the experimental work show that the UCS values of the concrete blocks are affected by the following factors; cement content, water to cement ratio, and curing time. The mixture ID 20/5/5/70T which made from 20% cement, 5% fine aggregate, 5% coarse aggregate and 70% solid tailing, is the optimum mixture that satisfy the maximum solid waste concentration of 70%. It generates the compressive strength of 6.17 MPa, which is greater than the requirement of 5 MPa. Approximately 54.5 million tons of solid tailing can be disposed into the mine-out panels for the entire mine life. The pillar strength increases about 1.49 times, and thus minimize the subsidence of the underground mine. According to the results of waste brine injection, the base case simulation model at maximum injection rate of 165 m3/day increases the bottom-hole pressure to 842 KPa, and not exceeding the formation fracture pressure during the 21-years injection period. The brine salinity moves downward from the injection point to the bottom of the sand layer, and the plume migration of covers the area of 0.142 km2 (radius of plume migration = 212.5 m) at the bottom layer. The operational conceptual model of eight wells was designed to accommodate the disposed brine volume from the plant. The cumulative injected brine volume of 2.8 million cubic meters is recorded through 21-years injection program. The two conjunctive potash mine waste disposal programs take care of both solid and liquid potash mine wastes. These approaches will achieve the close to zero waste potash mining operation, and consequentially provide the benefits of technical aspects and reduce the environmental impacts in Potash industry in Thailand.