F. González

SEM and AES studies of a lead sulphide bioleaching in presence of catalytic ions

Abstract Scanning electron microscopy (SEM) and Auger electron spectroscopy (AES) were used to follow the surface changes occurring in galena when the bioleaching medium contained Ag(I), Hg(II) and Bi(III) ions. The results showed that the catalyst ions Ag(I), Hg(II) and Bi(III) are incorporated into the surface irrespectively of the presence of bacteria, and different reactions take place on the surface of galena depending on the cation added to the leaching medium. When the bioleaching process takes place without catalyst or with Bi(III) the galena is transformed into PbSO4 and the growth of oxidation products is characterized by needles. Ag(I) and Hg(II) ions form a layer on the galena surface, which prevents the transformation of such surface into PbSO4. The layer formed in this process can be like a silver sulphide and a mercury sulphide depending on the ion species. Microorganisms oxidize the surface sulphur of this layer and thus decrease the S/Ag and S/HG ratios at the surface.

Effect of silver and bismuth on bioleaching of copper sulphide concentrates with thermophilic microorganisms

Silver ion has been used successfully as catalytic agent in chalcopyrite leaching with mesophilic microorganisms to increase the copper dissolution rate. Although it could appear logical to add Ag+ to accelerate the process at high temperatures, thermophilic bacteria are less resistant than mesophilic microorganims to silver and so its application is limited. Therefore other cations must be studied to increase dissolution efficiency at high temperatures. In this work, a comparative study is performed using silver and bismuth in the bioleaching of a copper concentrate with thermophilic (68 °C) and mesophilic (35 °C) bacteria. The experiments were carried out in shake flasks at 1 % pulp density.

Mechanisms involved in sorption of metals by chemically treated waste biomass from irrigation pond

Abstract Several analytical techniques (FTIR, SEM–EDS and acid–base titration) have been used to characterize an irrigation pond biomass after chemical modification with different pretreatment agents (NaHCO3, Na2CO3 and NaOH, with and without a subsequent washing treatment) in order to explain the observed increase in different metals sorption uptake (Cd2+, Cu2+, Ni2+, Pb2+ and Zn2+). It was found that chemical pretreatments favoured anchoring of Na+ on the active sites of the biomass and in turn metal uptake by ion exchange. In addition, higher cell wall porosity was observed, which increased the availability of new innermost active centres in the biomass. The active sites were loaded with Ca2+, which was also involved in the metal ion exchange process.

Bioleaching of complex sulphides with different cultures of mesophilic microorganisms

Complex sulphides are extensively studied to find the best process permitting total recovery of contained metals. The worldwide reserves are very important. Spain has 250 millions t. and this country and Portugal have approximately 70% of EEC reserves in copper, zinc and lead.

Bioremediation of Sulfide Mine Tailings: Response of Different Soil Fractions

Bioremediation phenomena of soils contaminated with heavy metals have not been considered a key sustainability issue for the mining industry until recently. At least, this is what can be deduced from the huge amount of mining activities spread out worldwide. Nevertheless, mine wastes accumulated over long periods of time have a negative impact on the landscape and pose serious threats to ecosystems. Far from being solved, this issue is becoming more acute as the metalliferous mining industry is seriously affected by the cutoff grades decline of natural resources. The mining district of Sierra Cartagena-La Union in southeast Spain, with a total area of 100 km2, is a good example of poor mine practices. Metal extraction (Ag, Pb, and Zn) from sulfide mineral ores in this mining area dates back before Roman times. Consequently, large amounts of mining wastes have been accumulated over the centuries close to human settlements. Facts like this, underestimated in the past, could be a potential source of metal propagation with possible detrimental effects on human health. In this work, a bioremediation study has been accomplished in a metalliferous contaminated soil considering different particle size fractions. Each fraction, including the global material waste, has been chemically characterized using an ad hoc approach, followed by its mineralogical characterization. The investigation has been focused on the effect of bioaugmentation on metal mobilization and redistribution of heavy metals (Zn, Pb, Cu, Fe) among different soil fractions.