Alfonso Mazuelos

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.

Treatment of secondary copper sulphides (chalcocite and covellite) 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 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.

Continuous ferrous iron biooxidation in flooded packed bed reactors

Abstract In this paper the biological ferrous iron oxidation in flooded packed bed reactors is studied. Bacterial oxidation of ferrous iron is a potential industrial process for the treatment of acid mine drainage and in the regeneration of ferric iron as a leaching agent in hydrometallurgical processes. The aim of this work is the development of a reactor capable of attaining the oxidation rates demanded by industrial processes, which are higher than those shown in the literature. The bioreactor consists of a polymethylmetacrylate column randomly packed with siliceous stone particles with inlets for fresh medium and air at the bottom from where they flood the reactor. The performance of ferrous iron biooxidation reactors is strongly improved by applying this bioreactor design.

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

Abstract The technical viability of the BRISA process for copper concentrates consisting of mixtures of either chalcopyrite and secondary copper sulphides (chalcocite and covellite) or chalcopyrite and sphalerite was studied. The ferric leaching of six concentrates (different in origin, granulometric, chemical and mineralogical composition) was tested in this work. In order to speed up the process, ferric leaching was carried out in two stages. In the first one, metallic sulphides associated with chalcopyrite were leached and, in the second one, the unattacked chalcopyrite was leached with Ag + as a catalyst. Applying this sequence of leaching stages, copper extractions higher than 96% were achieved within 20 h for all the studied concentrates.

Inhibition of bioleaching processes by organics from solvent extraction

Abstract The influence of the presence of an organic phase composed of 15% LIX 64 as extractant and kerosene as solvent on ferrous iron bio-oxidation has been studied. The specific bio-oxidation rate decreased as the organic concentration increased from 0 to 60 ppm; further increase in organic concentration up to 800 ppm had no effect. The lag time increased with an increase in organic concentration over the whole range. The inhibition effect was more pronounced in shake-flasks than under static conditions, suggesting that the inhibitory effect has a chemico-biological nature instead of a physical one. Pretreatment of the liquor by activated carbon completely removed the inhibitory effect both in synthetic and real liquors.

Oxygen transfer in ferric iron biological production in a packed-bed reactor

In this paper, oxygen transfer in the ferrous iron biooxidation process in a packed-bed reactor is studied. The reactor consists of a polymethyl methacrylate column randomly packed with siliceous stone particles with inlets for liquid medium and air at the bottom from where they flood the reactor. The aim of this work is to determine the parameters that influence the oxygen transfer from air bubbles to the liquid medium, and to characterize the oxygen transport through the bulk liquid medium.

Recovery of Zn from acid mine water and electric arc furnace dust in an integrated process

In this paper, the purification of acid mine water and the treatment of electric arc furnace dust (EAFD) are integrated into one process with the aim of recovering the Zn content of both effluent and waste. Zinc recovery can reduce the cost of their environmental management: purified acid mine water is discharged after removing all metals; EAFD ceases to be hazardous waste; and Zn is valorised. The process consists of the recovery of Zn as zinc oxide and its purification into commercial products. First, EAFD is leached with acid water and the dissolved metals are selectively precipitated as hydroxides. After EADF leaching, ferrous iron is bio-oxidized and Fe and Al are then precipitated; in the following stage, Cu, Ni, Co and Cd are cemented and finally Zn is precipitated as ZnO. In order to purify water that finally is discharged to a river, lime is used as the neutralizing agent, which results in a precipitate of mainly gypsum, MnO, and ZnO. From the impure zinc oxide produced, various alternatives for the attainment of commercial products, such as basic zinc carbonate and electrolytic zinc, are studied in this work.

Biotic factor does not limit operational pH in packed-bed bioreactor for ferrous iron biooxidation

Ferrous ion biooxidation is a process with many promising industrial applications: mainly regeneration of ferric ion as an oxidizing reagent in bioleaching processes and depuration of acid mine drainage. The flooded packed-bed bioreactor (FPB) is the design that leads to the highest biooxidation rate. In this bioreactor, biomass is immobilized in a biofilm that consists of an inorganic matrix, formed by precipitated ferric compounds, in the pores of which cells are attached. This biofilm covers the surface of particles (siliceous stone) that form the bed. The chemical stability of this inorganic matrix defines the widest possible pH range in FPBs. At pH below 1, ferric matrix is dissolved and cells are washed out. At pH higher than 2, ferric ion precipitates massively, greatly hindering mass transfer to cells. Thus, among other parameters, pH is recognised as a key factor for operational control in FPBs. This paper aims to explain the effect of pH on FPB operation, with an emphasis on microbial population behaviour. FPBs seeded with mixed inocula were assayed in the pH range from 2.3 to 0.8 and the microbial population was characterised. The microbial consortium in the bioreactor is modified by pH; at pH above 1.3 Acidithiobacillus ferrooxidans is the dominant microorganism, whereas at pH below 1.3 Leptospirillum ferrooxidans dominates. Inoculum can be adapted to acidity during continuous operation by progressively decreasing the pH of the inlet solution. Thus, in the pH range from 2.3 to 1, the biotic factor does not compromise the bioreactor performance.