Treatment of secondary copper sulphides (chalcocite and covellite) by the BRISA process

The technical viability of the BRISA process (Biolixiviación Rápida Indirecta con Separación de Acciones: Fast Indirect Bioleaching with Actions Separation) for secondary copper sulphides has been proved. One concentrate and two ores with chalcocite and covellite as the dominant copper minerals have been leached with ferric sulphate at 12 g/L of ferric iron and pH 1.25 in agitated reactors. Effects of temperature and pulp density have been investigated. The copper extraction from the final concentrate (with 45% Cu) was 90% at 80 °C and 8 h leaching with minor jarosite precipitation. Higher degrees of recovery would require the use of a catalyst such as silver to dissolve the chalcopyrite (minor constituent) of the concentrate. An alternative treatment is proposed for this concentrate consisting of cold leaching of the concentrate (20 °C, 2 h, 34% Cu extraction) and the smelting of the leach residue. The copper extraction from ores (with 1–2% Cu) at 70 °C ranged from 77% to 98% depending on the pulp density and the size fraction of the ore. Since the ferric iron demand was very low for ores, the solid recycle could be omitted in the BRISA process and it would be possible to operate directly at high pulp densities, which represent both a technical and an economic advantage. On the other hand, as copper extraction at 25 °C is very high (up to 70% Cu), a ferric leaching in two stages, the first one at 25 °C and the second one at 70 °C, could be an interesting choice in order to minimize energy costs. ISA treatment of these ores would allow the recovery of the copper content of the fine fraction (which is not suitable for heap leaching) and the reduction of time and increase in copper extraction from the coarse fraction as compared with heap leaching treatment.