Flowsheet Development for Sustainable Processing of Kukersite Waste Rock

Abstract

This thesis investigates the sustainable processing of Kukersite waste rock, a by-product of Estonia’s oil shale industry, through the development of a flotation-based flowsheet. The material, composed mainly of calcite, dolomite, kerogen, and silica, was processed using a combination of sensor-based sorting, controlled milling, and flotation. A staged methodology was applied: laboratory-scale mechanical flotation was used to establish effective reagent regimes, while laboratory-scale pneumatic flotation with Maelgwyn’s IMHOFLOT unit was conducted to study hydrodynamic effects and optimize operating conditions. Froth monitoring supported by Gaussian-mixture-model clustering provided additional insight into flotation dynamics and indicated opportunities for real-time process control. Pilot-scale pneumatic flotation trials then validated the combined reagent–hydrodynamic methodology, achieving kerogen concentrates of 42\% grade at 55\% recovery in the rougher stage and 29.5\% grade at 80.4\% recovery after scavengers, as well as calcite concentrates of 84\% CaCO$_3$ at 70\% recovery in the rougher stage and 96\% CaCO$_3$ at 40\% overall recovery after two cleaning stages and regrinding. The resulting flowsheet integrates rougher, scavenger, and cleaning stages with regrinding, producing industrially relevant concentrates and valorizing carbonate-rich tailings. Overall, this study provides the first proof of concept for Kukersite flotation, demonstrating that pneumatic flotation can deliver resource efficiency, high product quality, and reduced environmental impact within a circular economy framework.