Montana Technological University - HPSA Findings

Master’s student Mitchell Harvey at Montana Technological University is researching High-Pressure Slurry Ablation (HPSA) for improving flotation of Cu-Mo bulk concentrate, pyrite bearing gold tailings, and lead concentrate. He is about to conclude his work with Cu-Mo and is beginning testing gold tailings. His work so far with Cu-Mo has shown positive results.

Much of the world’s molybdenum is produced as a byproduct of copper mining where molybdenite (MoS2) is found alongside copper sulfide minerals. The copper and molybdenum sulfides are floated simultaneously to produce a Cu-Mo bulk concentrate, then the sulfides are separated with flotation to produce separate copper and molybdenum concentrates. Below is a diagram of a typical rougher cleaner circuit for separating copper and molybdenum sulfides. Ball mills are placed between cleaner cells to improve liberation of the molybdenite. This regrinding must be done in stages to avoid overgrinding of the soft molybdenite.

Disa’s High-Pressure Slurry Ablation Technology (HPSA) has shown potential as a more economical replacement for these regrind mills. Mitchell is using a three-factor factorial design of experiment to evaluate the effectiveness of HPSA at improving the flotation of Cu-Mo bulk concentrate. Pump speed, % solids and residence time are varied, and the change in molybdenum and copper grade and recovery with batch flotation are measured as well as particle size distribution. The best results were obtained with a high pump speed and high % solids. The batch flotation tests were conducted using Aminpro’s simple kinetic test procedure where froth is collected in logarithmic time intervals over a 30 minute period. From right to left, the points on the recovery-grade curves in the plot below represent 45 seconds, 2 minutes, 8 minutes, and 30 minutes of flotation. The recovery-grade curves improved from 7.5 minutes to 15 minutes and from 15 minutes to 22.5 minutes of HPSA time, then worsened after 30 minutes suggesting that overgrinding was beginning to occur. Particle size distribution measurements showed a steady decline in P80 during the test.

Based on this research, HPSA demonstrated it is able to increase recoveries by approximately 35% compared to currently used methods. It is believed that the results are due to HPSA’s unique application of force and the bimodal hardness of molybdenite and chalcopyrite. Molybdenite is a softer mineral with a Mohs hardness of 1.5 compared to chalcopyrite with a Mohs hardness of 3.5. The particle-to-particle collisions are thought to ablate the softer molybdenite from the chalcopyrite without overgrinding the molybdenite.