I. Palencia

Silver catalyzed IBES process: application to a Spanish copper-zinc sulphide concentrate

Abstract The Indirect Bioleaching with Effects Separation process (IBES process) has been applied to a chalcopyrite/sphalerite concentrate from Rio Tinto. In this paper the chemical stage of the process (ferric sulphate leaching) has been studied in agitated batch reactors. Two stages of ferric sulphate leaching are required at atmospheric pressure: primary leaching and catalytic leaching, the second one using silver ion as a catalyst for chalcopyrite dissolution. The effect of the variables such as pulp density, pH, ferric and ferrous iron concentrations, temperature and amount of catalyst have been investigated. The recovery amounts to 95% for both zinc and copper under the following experimental conditions: 70°C, 12g/l Fe 3+ , pH 1.25, 8 h of primary leaching and 8 h of catalytic leaching with 2 mg silver/g concentrate. It has been proved that, after solid/liquid separation, the ferrous iron in the leaching liquor can be bio-oxidized with Thiobacillus ferrooxidans for ferric iron regeneration (the biological stage of the IBES process) and the silver can be recovered from the residue and thus recycled to the process.

Copper recovery from chalcopyrite concentrates by the BRISA process

Abstract The technical viability of the BRISA process (Biolixiviacion Rapida Indirecta con Separacion de Acciones: Fast Indirect Bioleaching with Actions Separation) for the copper recovery from chalcopyrite concentrates has been proved. Two copper concentrates (with a copper content of 8.9 and 9.9 wt.%) with chalcopyrite as the dominant copper mineral have been leached with ferric sulphate at 12 g/L of ferric iron and pH 1.25 in agitated reactors using silver as a catalyst. Effects of temperature, amount of catalyst and catalyst addition time have been investigated. Small amounts of catalyst (from 0.5 to 2 mg Ag/g concentrate) were required to achieve high copper extractions (>95%) from concentrates at 70 °C and 8–10 h leaching. Liquors generated in the chemical leaching were biooxidized for ferrous iron oxidation and ferric regeneration with a mixed culture of ferrooxidant bacteria. No inhibition effect inherent in the liquor composition was detected. The silver added as a catalyst remained in the solid residue, and it was never detected in solution. The recovery of silver may be achieved by leaching the leach residue in an acid-brine medium with 200 g/L of NaCl and either hydrochloric or sulphuric acid, provided that elemental sulphur has been previously removed by steam hot filtration. The effect of variables such as temperature, NaCl concentration, type of acid and acidity–pulp density relationship on the silver extraction from an elemental sulphur-free residue has been examined. It is possible to obtain total recovery of the silver added as a catalyst plus 75% of the silver originally present in concentrate B (44 mg/kg) by leaching a leach residue with a 200 g/L NaCl–0.5 M H 2 SO 4 medium at 90 °C and 10 wt.% of pulp density in two stages of 2 h each. The incorporation of silver catalysis to the BRISA process allows a technology based on bioleaching capable of processing chalcopyrite concentrates with rapid kinetics.

High efficiency reactor for the biooxidation of ferrous iron

Abstract The biooxidation of ferrous iron is a potential industrial process in the regeneration of ferric iron, in hydrometallurgical leaching operations and in the removal of H 2 S in combustible gases. Another field of application is the treatment of acid mine drainage water. The aim of this work was the design of a continuous reactor for a high efficiency ferrous iron biooxidation capable of attaining the oxidation rates demanded by industrial processes for a minimum-sized reactor. Some criteria of design come from the data of former studies. The bioreactor consists of a 1249 mm high and 84 mm diameter column randomly packed with siliceous stone particles with inlets for fresh medium and air at the bottom. The present work studies the influence of air and liquid flow rates on the ferrous iron biooxidation in a flooded packed bed bioreactor. Starting from the data of this study, kinetics, and oxygen concentration in the outlet gas, it was deduced that the biooxidation process was limited by the availability of oxygen in the liquid medium. The free-swimming cells concentration was measured in the outlet solution for different operating conditions. It was observed that once the biofilm has been formed, a variation in the liquid flow rate does not alter the biomass attached to the packing. The highest ferric productivity attained was 11.25 g/L·h.

Ferric iron production in packed bed bioreactors: influence of pH, temperature, particle size, bacterial support material and type of air distributor

Abstract The biooxidation of ferrous iron in solution has industrial applications in the regeneration of ferric iron as a leaching agent for non-ferrous metallic sulphides and in the treatment of acid mine drainage. The aim of this work was the study of several variables (pH, temperature, particle size, bacterial support material and type of air distributor) for the design of a packed bed bioreactor for ferrous iron biooxidation. The basic criteria of design have been the following. • Maximum residence time of the liquid for a minimum-sized reactor. Flooded packed bed reactors have been used in order to meet this requirement. • The solid material that acts as bacterial support must allow a rapid and permanent biofilm formation and show a good chemical resistance to ferric sulphate and sulphuric acid. • Constant and homogeneous air supply in the whole bed. The bioreactor consisted of a column randomly packed with solid particles, fed with an acidic solution of ferrous sulphate. Air and fresh solution were fed in at the bottom of the column from where they flooded the reactor. The inoculum consisted of a mixed culture of bacteria isolated from Riotinto mines drainage waters, and adapted to pH 1.25 in the laboratory, composed mainly of Thiobacillus ferrooxidans and Leptospirillum ferrooxidans. A methodology for biofilm formation was established. Maximum ferric iron productivity was 11.1 g l −1 h −1 . The type of air diffusor has been an important parameter to be taken into account in the design, as the oxygen dissolved in the liquid medium limits the ferrooxidant activity of bacteria.

Silver catalyzed IBES process: application to a Spanish copper–zinc sulphide concentrate: Part 3. Selection of the operational parameters for a continuous pilot plant

Abstract The selection of the operating conditions of a continuous silver catalyzed IBES (Indirect Bioleaching with Effects Separation) process for a chalcopyrite–sphalerite concentrate from Rio Tinto is presented. The data generated from the batch tests have been used to estimate the operating parameters for the continuous system. In order to obtain metal extractions of 94% Zn and 95% Cu, two ferric sulphate leaching stages are necessary: a primary leaching at 70°C with a mean residence time of 8 h divided into five stirred reactors, and a catalytic stage at 70°C and 2.5 mg Ag g −1 concentrate with a mean residence time of 10 h divided into five stirred reactors. The approach is used to develop the complete flowsheet of a pilot plant for the treatment of 50 kg h −1 of this concentrate, including stages of chemical leaching (primary and catalytic), ferrous iron biooxidation, solvent extraction and electrowinning of zinc and copper, elemental sulphur recovery, silver recovery and effluent purification. A preliminary economic evaluation of the process indicates that for an industrial plant of 100,000 t a −1 , the direct operating cost would amount to US

Silver catalyzed IBES process: Application to a Spanish copper–zinc sulphide concentrate. Part 2. Biooxidation of the ferrous iron and catalyst recovery

141 per ton; the products, copper and zinc, would be worth US

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

450 per ton and the value of by-products (mainly elemental sulphur and silver) was estimated at US

Continuous ferrous iron biooxidation in flooded packed bed reactors

29 per ton.

Treatment of copper concentrates containing chalcopyrite and non-ferrous sulphides by the BRISA process

Abstract The indirect bioleaching with effect separation process has been applied to a chalcopyrite–sphalerite concentrate from Rio Tinto. In this paper the biooxidation of the ferrous iron generated in the chemical stage (ferric sulphate leaching) and the recovery of the silver used as a catalyst have been studied. The ferrous iron in leaching liquors can be effectively biooxidized both in static batch and packed-bed reactors. The regenerated ferric iron can be recycled to the chemical stage of the process. The recovery of silver from the leach residue requires the previous removal of the elemental sulphur. The effect of variables such as temperature, type of acid, time, acid concentration and composition of the residue on the silver extraction has been examined. It is possible to obtain total recovery of the silver added as a catalyst (2 mg/g concentrate) plus 93% of the silver originally present in the concentrate by leaching a leach residue containing 1.1% Cu with a 200 g/l NaCl–0.5 M H2SO4 medium, at 90°C for 2 h.

Leaching of a copper-zinc bulk sulphide concentrate using an aqueous ferric sulphate dilute solution in a semicontinuous system. Kinetics of dissolution of zinc

Abstract The technical viability of the BRISA process (Biolixiviacion Rapida Indirecta con Separacion 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. The BRISA 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.