Kinetic Investigation on Leaching of Copper from a Low-Grade Copper Oxide Deposit in Sulfuric Acid Solution: A Case Study of the Crushing Circuit Reject of a Copper Heap Leaching Plant

In this study, the reject fraction of the jaw crusher, located in the first part of the crushing circuit, is used as a considerable stock in copper tank-leaching plant. High market value of copper and ease of practice were the motivating forces on studying the leaching kinetics under controlled conditions. In this regard, first, the influencing parameters such as the acid concentration, solid-to-liquid ratio, agitation speed, particle size, and temperature were assessed on the leaching fraction of copper. The findings showed that the leaching rate is nearly independent of the agitation rate at the high values of 300 rpm. The recovery of copper strongly promoted from 2 to 90% by increasing sulfuric acid concentration from 0.3 to 1.8 M. The increase in the solid-to-liquid ratio and temperature were found to be beneficial as well. Additionally, it was found that above 71% copper could be leached from the reject samples in the size range of 0-2 mm by 0.9 M sulfuric acid after 30 min contact time at 25 degrees C temperature. In the second stage, the leaching kinetics was studied by shrinking core models to gain a better description of the dissolution process of copper from crushing circuit reject. The results indicated that the dissolution rate could be controlled by both chemical reaction and diffusion process. However, diffusion process was the dominant mechanism in the system investigated. Ultimately, a mixed kinetic model with an activation energy of 11.72 kJ/mol was proposed as the leaching rate-controlling step.