Abstract

Freeport-McMoRan Inc. (FMI) is the majority owner and operator of the Morenci copper mine. The mine process facilities include two flotation concentrators, four solvent extraction plants, 3 electrowinning plants and a concentrate leach plant (CLP). The CLP applies a pressure oxidative leach process to leach copper concentrate into solution for recovery to copper cathode at Morenci. The leach process is applied in two pressure leach vessels (PLV) operating at elevated temperature and pressure. The CLP was designed, constructed and commissioned in 2007 under partial leach and direct electrowinning conditions. The circuit was restarted in 2015 under full oxidation conditions. An expansion project was completed in 2025 to utilize PLV process volume at full oxidation conditions.  The expansion required an increase in gas flow rates and during the investigation phase of the project the installed SPX FLOW agitators were evaluated for dispersion performance and handling of the increased gas flow.  The original agitator utilized dual up pumping wide blade A340 Hydrofoils to disperse gas and suspend solids.

At the increased throughput and oxygen flow rates, the agitator system faced challenges to meet process requirements, so a new design was proposed and evaluated. The new design involved inverting the upper A340 to a down pumping A320 and maintaining the lower A340 impeller. The two impellers produce an impinging axial flow which increases power transfer and subsequently the gas handling ability of the system.  The pilot design was developed to a commercial scale and installed in both of the Morenci PLVs in mid-2024. The agitators have achieved the target power transfer and gas dispersion since installation and have provided an additional benefit of reducing the headspace fouling and scale buildup of precipitated solids present with the prior agitator configuration.

The success of this novel hydrofoil agitator configuration has been encouraging, and further study has progressed to assess other pressure oxidation applications. This paper discusses the evaluation and development of the novel up/down pumping hydrofoil system with a focus on gas-liquid mass transfer and gas handling ability as well as power consumption vs. various geometric parameters characterization to optimize the configuration. Erosion characteristics have been measured and compared with standard Rushton-style impeller performance at similar power input for blade-life analysis. This characterization effort will help define the optimum operating envelope for this new style of pressure oxidation agitator for future applications.