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Chilean copper production has been growing in the last 20 years reaching an annual production of 5,557,000 tons of Cu in 2007. For each ton of copper produced, about 200 tons of sterile and low grade ore and 100 tons of tailings are discharged in the environment. Most of these wastes contain significant amounts of sulphide minerals, mainly pyrite, that once submitted to weathering, may produce acid mine drainage. On the other hand, copper high prices raised the interest for processing the low grade ore deposited in large dumps by leaching. An important part of these mining wastes and low grade ores is located in the Andes, where the mean temperature is usually ∼ 5 °C or less. The rate at which bioleaching reactions occur is directly related to the temperature at which the microorganisms (bacteria and archaea) develop. A temperature decrease causes both a decrease on the chemical reactions rates and a decrease or inhibition on microbial growth. The results for microorganism isolation from an old tailing deposit, exposed at low temperatures (5 °C) during most of the winter are presented in this work. Initially the isolated microorganisms showed a limited capacity in oxidizing Fe(II) sulfate (3 g L−1) at pH 1.6, and tetrathionate (0.01 M), with an initial pH of 4.0 at 5 °C. However, after successive cultures, microorganisms showed a low capacity to oxidize both substrates, as well as the sulphide contained in the tailing samples. The terminal Restriction Fragment Length Polymorphism (tRFLP) of the isolated cells grown in basal medium containing Fe(II) showed a nearly pure culture of Acidithiobacillus ferrooxidans. The present study indicates that, even at very low temperatures, microorganisms play an important role in the acid mine drainage generation and also during the oxidation and leaching of sulphide ores.

Arsenic, present as impurity in many sulfide ores, dissolves during the bioleaching process and the resulting high As(III) concentration can inhibit bacterial activity, compromising the whole process. Oxidation of As(III) to As(V) and its further precipitation as ferric arsenate is probably the most accurate way to face the problem. Thermodynamically, As(III) should be easily oxidized by Fe(III), but the reaction is very slow and only in the presence of pyrite, significant oxidation of As(III) to As(V) takes place. In the present study, the catalysis mechanism of arsenic oxidation on pyrite surface and the role of Acidithiobacillus ferrooxidans at 30 °C and Sulfolobus metallicus at 70 °C were analysed. Anaerobic experiments demonstrated that ferric ions participate as electron acceptors during the oxidation of As(III) to As(V) but that electron transfer only takes place at the pyrite surface. As(III) oxidation is only observed at high oxidoreduction potential (Eh > 450 mV vs. Ag/AgCl). At lower potential, As(V) is reduced to As(III), oxidising the pyrite. The role of microorganisms is mainly to maintain a high potential. Ferric ions produced by bacterial oxidation are reduced at the pyrite surface, oxidising both pyrite and As(III). Only a small fraction of electrons transferred comes from As(III).

A method for evaluating the proportion of bacteria attached to mineral sulfides is presented. The method is based on the determination of the rate of ferrous iron oxidation by attached bacteria on the mineral surfaces. The values obtained with this procedure are in agreement with measurements of attached bacteria using bacteria grown with radioactive (C 14 ) NaHCO 3 . The methodology was used to evaluate the fraction of bacteria attached to chalcopyrite during bioleaching of this sulfide. It was observed that a significant fraction of the bacteria grow attached to the mineral.

The kinetics of the bioleaching of a low-grade copper ore was studied in a pilot-scale leaching column over a period of 360 days using an open-circuit leaching regime with a fresh sulfuric acid solution at pH = 2 at the inlet of the column. The effluent solutions were periodically analyzed for Cu, total Fe and Fe(II) concentrations as well as Eh and pH values. Bacterial population was measured both in the solution (free cells) and at the surface of the ore particles. Bacterial growth parameters and the true kinetic constant for the dissolution of the sulfide minerals present in the ore were determined in independent experiments. A generalized phenomenological model for the bioleaching of sulfide ores is presented, for which practically all the required parameters can be independently measured. The model is capable of reproducing well measured values of the process variables, and the results are extended to the simulation of the process under different operating conditions.

In the thymuses of patients dying with acromegaly or with juvenile-onset diabetes mellitus, there is a significant increase in the number of Hassall's corpuscles and in the diameter of the largest Hassall's corpuscle, when compared with normal controls (traumatic deaths). There were no statistically significant thymic changes in patients dying with adultonset diabetes mellitus or with Cushing's syndrome.

A case of Friedreich's ataxia with evidence of hypertrophic obstructive cardiomyopathy involving both ventricles is reported. A review of the previously reported cases leads us to believe that this association is not merely accidental, but that Friedreich's ataxia and hypertrophic obstructive cardiomyopathy are parts of the same syndrome.