N. Iglesias

Refractory gold-bearing ores: a review of treatment methods and recent advances in biotechnological techniques

The problem of the refractory nature of gold-bearing sulphide ores is described and possible pretreatments are reviewed. Among them, bioleaching is an interesting one from an environmental point of view, but up to the present the process has been too slow. The IBES (Indirect Bioleaching with Effect Separation) process improves the kinetics of the bioleaching by means of a physical separation of the chemical and biological effects involved in what we call the indirect contact mechanism. This permits the enhancement of each stage. This process, which has been developed for the treatment of high-grade sulphide flotation concentrates, is proposed for the pretreatment of gold-bearing sulphide ores.

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.

Treatment of a gold bearing arsenopyrite concentrate by ferric sulphate leaching

Abstract Biooxidation can be used as a pretreatment for gold-bearing sulphide ores; it has low reagent costs and is very interesting from an enviromental point of view. However the kinetics of this process is slow. Long residence times (several days, even weeks) cause excessive operational costs. If biooxidation proceeds through an indirect contact mechanism, its kinetics may be improved by means of the physical separation of the two operations relating the two effects involved: the chemical attack of sulphides by ferric iron and the biological oxidation of the ferrous iron produced (chemical and biological effects). The separation of the two effects allows the individual enhancement of both stages. In this paper the ferric sulphate leaching of an arsenopyrite concentrate is studied as an example of the Indirect Biooxidation with Effects Separation Process. This method of chemical oxidation has been taken to represent the separation of the chemical and the biological effects within a biooxidation system. The results are very satisfactory. The kinetics of the chemical oxidation stage (ferric sulphate leaching) is enhanced by the use of silver as a catalyst and moderate high temperature. Taking into account that the kinetic activation of the biological ferrous iron oxidation (biological stage) has been already proved, the enhancement of the chemical oxidation stage leads to the whole process improvement.

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.

Bacterial leaching of a copper ore rich in gold and silver: study of the chemical stage

Abstract In this paper the treatment of a copper sulphide ore rich in gold and silver is studied. The selected treatment for dissolving copper has been bacterial leaching. Since, in this case, bioleaching proceeds through an indirect contact mechanism, it is possible to separate the chemical and biological stages, in order to improve the kinetics of the whole process. Following copper removal by leaching, elemental sulphur was extracted and the treated sample was then leached with cyanide. This method allows copper, gold and silver dissolution at moderate operational conditions.

Application of IBES process to a zn sulphide concentrate: Effect of Cu2+ ion

Abstract The IBES (Indirect Bioleaching with Effects Separation) process has been developed for the bioleaching of CuZn sulphide concentrate, Zn concentrate, and as a pretreatment for refractory gold ores. In this work the influence of copper ion on the application of this process to a Zn sulphide concentrate was studied. A negative effect of Cu 2+ ions on the rate of zinc dissolution was observed Kinetic curves of ferric leaching have been combined with the residence time distribution for n CSTRs (Continuous Stirred Tank Reactors) in series, in order to predict the mean residence time and the number of reactors required in the ferric sulphate leaching of this Zn concentrate for different copper concentrations. Results indicate that some modifications on the IBES process flowsheet are needed.

Process options in the treatment of a mixed atacamite, secondary copper sulphides mineral. Heap leaching and BRISA process.

Two leaching systems have been investigated to recover copper from a mixed atacamite, secondary copper sulphides mineral: heap leaching and BRISA process. The mineral contains 3.13% Cu, 0.32% C1, a copper as sulphide/copper as oxide ratio of 1.75, and a composition of the different particle size fractions quite close to each other. The treatment of this mineral by heap leaching with acid salt water (current practice) would yield 50% of copper recovery. This leaching system fails to recover the copper present as sulphide. The reason for this is the presence of chloride ions in the medium (coming from the acid leaching of atacamite) that hinders the bioleaching of copper sulphides. In order to solve this problem a two-stage leaching system has been tested, the first stage with acid salt water and the second stage with ferric sulphate (which is biologically regenerated) as leaching agents. The technical feasibility of the two-stage leaching has been proved and the optimum operating conditions have been determined. On the other hand, plugging of heaps caused by breaking of pellets leads to lack of solution contact with particles and oxygen supply for bacterial growth. The separation of the fine fraction (

Validation of Smart Nanoparticles as Controlled Drug Delivery Systems: Loading and pH-Dependent Release of Pilocarpine

Micelles are good devices for use as controlled drug delivery systems because they exhibit the ability to protect the encapsulated substance from the routes of degradation until they reach the site of action. The present work assesses loading kinetics of a hydrophobic drug, pilocarpine, in polymeric micellar nanoparticles (NPs) and its pH-dependent release in hydrophilic environments. The trigger pH stimulus, pH 5.5, was the value encountered in damaged tissues in solid tumors. The new nanoparticles were prepared from an amphiphilic block copolymer, [(HEMA19%-DMA31%)-(FMA5%-DEA45%)]. For the present research, three systems were validated, two of them with cross-linked cores and the other without chemical stabilization. A comparison of their loading kinetics and release profiles is discussed, with the support of additional data obtained by scanning electron microscopy and dynamic light scattering. The drug was loaded into the NPs within the first minutes; the load was dependent on the degree of cross-linking. All of the systems experienced a boost in drug release at acidic pH, ranging from 50 to 80% within the first 48 h. NPs with the highest degree (20%) of core cross-linking delivered the highest percentage of drug at fixed times. The studied systems exhibited fine-tuned sustained release features, which may provide a continuous delivery of the drug at specific acidic locations, thereby diminishing side effects and increasing therapeutic rates. Hence, the studied NPs proved to behave as smart controlled drug delivery systems capable of responding to changes in pH.