Outotec copper concentrate pressure leaching process

The complete copper pressure leaching process concept includes pressure leaching in an autoclave to produce copper-containing pregnant leach solution. Leaching is followed by a neutralization step and then copper solvent extraction and electrowinning. Gold and silver can be recovered by adding a lime boil step before cyanide leaching.

The Copper Pressure Oxidation Plant is an Outotec proprietary technology for impure concentrate refining. The new process offers an effective way to dissolve concentrate, remove impurities, and recover copper as LME A-grade cathodes. In addition, the flowsheet can be modified to recover silver and gold. It is an easy-to-operate, self-optimizing plant that provides high availability and fast ramp-up to production.

The process uses proven proprietary equipment and plant units for all process unit operations. Productization of the process and pre-designed plant units together with modular equipment design reduces both project delivery lead time and CAPEX.

The plant concept enables customers to utilize existing SX/EW infrastructure while maintaining or even increasing copper production levels.

Case: Copper concentrate leaching with existing heap leaching operation

In this flowsheet the feed is copper concentrate. The main minerals in the concentrate are pyrite (39%) and chalcopyrite (36 %); sulfur content is 39%. High-temperature POX (220°C) provides fast oxidation kinetics, almost complete sulfide sulfur oxidation, and high copper extraction (>99%). Medium-temperature POX (150°C) results in 87% copper extraction in three hours and low-temperature (105°C) POX in 87% copper extraction in five hours.

According to test work, gold recovery in carbon in leach (CIL) after high-temperature POX is approximately 90%. Figure 2 illustrates the test-work results for copper, iron, and sulfur recoveries in pressure leaching tests.

Based on test-work results, pressure leaching is operating at 220°C and 7 bar oxygen overpressure.  Copper from is recovered by SX-EW. The client in this case has an existing heap leaching operation, and this was used to neutralize part of the PLS solution that contained acid. Leach residue from POX was fed to a conditioning stage where basic iron sulfates are leached back into the solution. After conditioning (residence time four hours at 95°C) the leach residue was sent to the existing CIL circuit in order to recover gold.