M.L. Blázquez

New information on the chalcopyrite bioleaching mechanism at low and high temperature

Abstract The chalcopyrite bioleaching mechanism was studied to determine its direct or indirect nature. At the same time, a study of possible causes that diminish the dissolution rate and inhibit the attack of this sulphide mineral was carried out. An electrochemical study of the mineral was also performed, which included the elimination or dissolution of possible diffusion barriers formed on the mineral surface. Results of these studies showed that the oxidation state of the dissolved iron (Fe3+) was fundamental to chalcopyrite bioleaching because Fe3+ controlled the relative rate of the oxidation reactions. In addition, the attack of chalcopyrite was controlled by elemental sulphur and intermediate, nonstoichiometric, copper sulphides forming on the chalcopyrite surface, which are less reactive than the original sulphide. Intermediate sulphides caused an important barrier effect at low temperature (35 °C). At higher temperature (68 °C), these intermediate sulphides do not constitute a diffusion barrier due to their dissolution. Microbial attachment to the pyritic phase of the copper ore was related to the dissolution rate of the mineral due to the liberation of Fe2+ after the attack of the pyrite by contact bioleaching. It was concluded that the bioleaching of chalcopyrite concentrate is a cooperative effort involving the simultaneous contact bioleaching of the pyritic phase of the mineral, possibly by an indirect mechanism via thiosulphate, and the indirect bioleaching of chalcopyrite, probably by a mechanism by way of polysulphide and elemental sulphur.

Biosorption with Algae: A Statistical Review

ABSTRACT The state of the art in the field of biosorption using algae as biomass is reviewed. The available data of maximum sorption uptake (qmax) and biomass-metal affinity (b) for Cd2 +, Cu2 +, Ni2 +, Pb2 + and Zn2 + were statistically analyzed using 37 different algae (20 brown algae, 9 red algae and 8 green algae). Metal biosorption research with algae has used mainly brown algae in pursuit of treatments, which improve its sorption uptake. The information available in connection with multimetallic systems is very poor. Values of qmax were close to 1 mmol/g for copper and lead and smaller for the other metals. Metal recovery performance was worse for nickel and zinc, but the number of samples for zinc was very small. All the metals except lead present a similar affinity for brown algae. The difference in the behavior of lead may be due to a different uptake mechanism. Brown algae stand out as very good biosorbents of heavy metals. The best performer for metal biosorption is lead.

Gold(III) biosorption and bioreduction with the brown alga Fucus vesiculosus

In this paper, the bioreduction of Au(III) to Au(0) using biomass of the brown alga Fucus vesiculosus was investigated. The recovery and reduction process took place in two stages with an optimum pH range of 4-9 with a maximum uptake obtained at pH 7. In the first stage, an induction period previous to gold reduction, the variation of pH, redox potential and gold concentration in solution was practically negligible and no color change was observed. In the second stage, the gold reduction was followed by a sharp decrease of gold concentration, pH and redox potential of solution and a color change from yellow to reddish purple. Hydroxyl groups present in the algal polysaccharides were involved in the gold bioreduction. Metallic gold was detected as microprecipitates on the biomass surface and in colloidal form as nanoparticles in the solution. Bioreduction with F. vesiculosus could be an alternative and environmentally friendly process that can be used for recovering gold from dilute hydrometallurgical solutions and leachates of electronic scraps, and for the synthesis of gold nanoparticles of different size and shape.

Characterization of the biosorption of cadmium, lead and copper with the brown alga Fucus vesiculosus.

The recovery of cadmium, lead and copper with the brown alga Fucus vesiculosus was characterized and quantified. The biosorption data fitted the pseudo-second order and Langmuir isotherm models, but did not adjust to the intraparticle diffusion model. The metal uptakes deduced from the pseudo-second order kinetic model and the Langmuir isotherm model followed a similar sequence: Cu>Cd approximately Pb. The Langmuir maximum metal uptakes were: 0.9626 mmol/g, Pb 1.02 mmol/g, and Cu 1.66 mmol/g. According to the equilibrium constants of this isotherm model, the affinity of metals for the biomass followed this order: Pb>Cu>Cd. Biosorption was accomplished by ion exchange between metals in solution and algal protons, calcium and other light metals, and by complexation of the adsorbed metals with algal carboxyl groups. FTIR spectra showed a shift in the bands of carboxyl, hydroxyl and sulfonate groups.

Bioremediation of an industrial acid mine water by metal-tolerant sulphate-reducing bacteria

The microbiological diversity associated with mining environments is a very well proven fact. One of the communities appearing in these environments is that formed by anaerobic sulphate-reducing bacteria (SRB) which can be used for the decontamination of acid mine drainage waters. In this work, the potential of a mixed population of SRB, isolated from the bottom of a pyritic tailing pond situated in the Spanish pyritic Belt, has been investigated with the main objective of treating the effluent generated in the same disposal site. The efficiency of the system is based on the presence of an important amount of reducing agents contained in the acid mine drainage received in the pond. Results showed that this option is effective for the precipitation of the dissolved metals (copper and iron), for the reduction and removal of sulphates and even for the alkalising of the waters. SRB were able to remove up to 9,000 ppm of sulphate ion efficiently, to grow in the presence of up to 100 ppm of copper and 30 ppm of iron, and alkalise the medium, provided that this was not extremely acidic (pH>4). Finally, according to the results obtained, the possibility of applying this method to the treatment of a real effluent is discussed.

Study of cadmium, zinc and lead biosorption by orange wastes using the subsequent addition method

The biosorption of several metals (Cd2+, Zn2+ and Pb2+) by orange wastes has been investigated in binary systems. Multicomponent sorption isotherms were obtained using an original procedure, similar to that proposed by Pagnanelli et al. [Pagnanelli, F., Petrangeli, M.P., Toro, L., Trifoni, M., Veglio, F., 2001a. Biosorption of metal ions on Arthrobacter sp.: biomass characterization and biosorption modelling. Environ. Sci. Technol. 34, 2773-2778] for monoelement systems, known as subsequent addition method (SAM). Experimental sorption data were analysed using an extended multicomponent Langmuir equation. The maximum sorption uptake was approximately 0.25mmol/g for the three binary systems studied. The reliability of the proposed procedure for obtaining the equilibrium data in binary systems was verified by means of a statistical F-test.

Silver-catalysed bioleaching of a chalcopyrite concentrate with mixed cultures of moderately thermophilic microorganisms

Abstract Bioleaching of a chalcopyrite concentrate was studied using two mixed cultures of moderately thermophilic microorganisms, one from the drainage of Rio Tinto mines and the other obtained by raising the growth temperature of a mixed culture of mesophilic bacteria. Both cultures were adapted to different concentrations of silver (0.1–0.5 g of silver/kg of concentrate) to test their leaching capacity in the presence of this catalyst. The results showed the important role of silver in the chalcopyrite leaching process carried out at 45°C. Copper yields increased around 3-fold over the control experiment without silver. At 50°C, however, only one of the cultures remained active and the effect of silver was masked by strong jarosite precipitation, which increased with the amount of silver used. The 9K medium played a key role in this respect, and it was clear that more diluted media should be used to avoid this problem. Despite this drawback, the amount of copper extracted using the catalyst was double than that obtained without it.

Electrochemistry of chalcopyrite

Abstract The electrochemical response of a massive chalcopyrite electrode at two different temperatures, 25°C and 68°C, were compared. The electrolyte used in the experiments was an acidic medium (0.4 g ·1 −1 (NH 4 ) 2 SO 4 , 0.5 g ·1 −1 MgSO 4 · 7H 2 O, 0.2 g ·1 −1 K 2 HPO 4 at pH = 2) which is suitable for the growth of the microorganisms involved in the bioleaching process. The chosen temperatures were optimum for the growth of the mesophilic ( Thiobacillus ferrooxidans ) and thermophilic ( Sulfolobus ) microorganisms. The experimental results at both temperatures were similar and confirmed that, during the anodic dissolution of chalcopyrite, a passive film is formed on the surface which restricts the oxidation reactions in the medium by diffusional control of the film. The different responses at the temperatures tested were due to the differing physical structure of the complex films of the electrochemically formed sulphides, polysulphides and elemental sulphur.

Study of Bacterial Attachment During the Bioleaching of Pyrite, Chalcopyrite, and Sphalerite

In this study the degree of bacterial attachment of the main microorganisms involved in the bioleaching of metal sulfides and their influence on the dissolution rate and final metal extractions were determined. Three different mineral sulfides were bioleached: chalcopyrite (CuFeS 2 ), sphalerite (ZnS) and pyrite (FeS 2 ). A mixed culture of mesophilic bacteria ( Acidithiobacillus and Leptospirillum spp.) was tested at 35°C and thermophilic bacteria ( Sulfolobus spp.) were tested at 68°C. The results confirmed that a relationship exists between attachment and mineral dissolution rates. The bioleaching process can be divided into three stages. An initial stage with extensive bacterial attachment to the pyritic phase, which is of major importance in order to obtain high dissolution rates (since attached cells liberate Fe 2+ by contact bioleaching and oxidize Fe 2+ to Fe 3+ avoiding iron accumulation at the surface). In a second stage the bacterial attachment diminishes due to the saturation of the surface by the attached cells. This limitation, together with the presence of Fe 2+ in solution, produces an increase in the concentration of free cells, which use Fe 2+ as an energy source. Finally, in a third stage, a balance between free and attached cells is reached, giving rise to a cooperative mechanism. In this case, the attached cells attack the pyrite phase of the mineral generating Fe 2+ . This in turn is oxidized by the free cells in solution, regenerating the oxidizing agent (Fe 3+ ) for the indirect bioleaching of the mineral.

Bioleaching of a Spanish complex sulphide ore bulk concentrate

Abstract In the present work the applicability of bioleaching using a mixed culture of mesophilic microorganisms (Thiobacillus ferrooxidans, Thiobacillus thiooxidans and Leptospirilum ferrooxidans) on a bulk concentrate of a Spanish complex sulphide ore was studied. The bulk concentrate mainly consisted of by chalcopyrite, sphalerite and pyrite. Effects of nutrient medium, stirring, pulp density, temperature and the addition of CO 2 (1% v/v) to the air flow were also studied. The highest leaching rates and recoveries were obtained with mechanically stirred reactors at 5% pulp density and 9K medium. However, by using 9K medium higher jarosite precipitation was observed. Results showed that the optimum temperature for copper bioleaching was 30°C, whereas zinc dissolution increased with a rise in the temperature.