Advanced Materials Research Vol. 825

Abstract: The quantification of microbial colonisation and growth rate kinetics is essential in the characterisation of bioleaching systems for modelling heap performance. An experimental system, designed to simulate heap bioleaching conditions at the agglomerate scale, was used to quantify the microbial growth kinetics of a pure culture of Acidithiobacillus ferrooxidans in the PLS, the interstitial phase and attached to the mineral ore. Conventional methods for the quantification of microbial growth rate kinetics associated with the ore and in the flowing PLS have been found to be inadequate in the characterisation of whole ore systems owing to microbial transport between these regions. Growth within the whole ore system was dominated by the microbial communities associated with the ore. Two models were used to estimate the true growth rate kinetics of Acidithiobacillus ferrooxidans on whole low grade ore as a function of growth and transport between the identified phases. The “hydrodynamics” model assumed that microbial transport was promoted by fluid flow dynamics whilst the “biomass balance” model assumed that the microbial concentration gradient across identified phases was the driving force for transport.

Abstract: The electrochemical behavior of massive chalcopyrite in presence of Acidithiobacillus caldus, Acidithiobacillus ferrooxidans, Leptospirillum ferrooxidans and Sulfobacillus thermosulfidooxidans has been studied by cyclic voltammetry. The effect of Fe²⁺ and Cu²⁺ ion addition on the electrochemical behavior of massive chalcopyrite in bioleaching system were also investigated. The voltammograms illustrated that current densities of peaks were obviously increased with adding Fe²⁺ into the electrolyte. A series of anodic peaks were observed at more than 0 V when adding Fe²⁺ and Cu²⁺ ions, and these peaks are similar to the peaks of the step oxidation of chalcocite, thus proving that the formation of intermediate CuS₂. Especially, the 9 g/L Fe²⁺ and 1.5 g/L Cu²⁺ were added. Therefore, appropriate ferrous and cupric ions concentration could enhance the formation of intermediate CuS₂ leading to accelerate dissolution of chalcopyrite.

Abstract: Mine drainage waters are widely regarded as environmental pollutants, but they are also potential sources of valuable transition metals, such as zinc, copper and cobalt. This article describes the laboratory application of continuous flow modular bioreactor systems, one oxidative and the other reductive, for the selective precipitation of metals from metal-rich acidic mine waters.

Abstract: An integrated bio-processing scheme was devised and tested in the laboratory for recovering copper, or other base metals, from pregnant leach solutions (PLS) using a two-step process involving both iron-reduction, and sulfate-reduction for H₂S generation and sulfide precipitation, as a potential alternative to conventional SX-EW. Reduction of ferric iron in the PLS was achieved using iron-reducing Acidithiobacillus spp. and Sulfobacillus thermosulfidooxidans in column reactors containing elemental sulfur as electron donor. Analysis of the column reactor effluents showed not only that most of the ferric iron was reduced to ferrous, but also that all of the copper (II) had been reduced to copper (I), i.e. cuprous copper. This copper (I) appeared to be complexed as it was not oxidized when exposed to ferric iron nor precipitated as a copper-sulfide when exposed to either sodium sulfide or H₂S. The data suggested that copper (II) was reduced and the resulting copper (I) complexed, with both reactions probably mediated by sulfur oxy-anions produced indirectly by the bacteria, in the anoxic sulfur column bioreactors. It was also noted that copper (I) produced chemically by reduction of copper (II) by hydroxylamine was more toxic to axenic cultures of Acidithiobacillus spp. and Sb. thermosulfidooxidans than was the copper (I) in the column effluent liquors.

Abstract: A low pH sulfidogenic bioreactor, maintained between pH 2.8 and 4.0, was used to lower sulfate concentrations in two extremely acidic (pH 1.3 to 3.0) synthetic mine waters that contained ferrous iron but no other chalcophilic metals. Tests with water carried out with synthetic mine water from a German site showed that 98% of the sulfate present could be removed by manipulating the water pH and concentration of electron donor (glycerol) for the sulfate-reducing bacteria. While more sulfate was removed with synthetic Chilean mine water (up to 35 mmoles L^-1), this only accounted for between 50-60% of the total present. There was close agreement between the stoichiometry of glycerol used and the amount of sulfate removed, particularly with the German mine water.

Abstract: Reactors hydrodynamic condition and the choice of substrate are important factors for the optimization and implementation of this sulphate-reducing biological process. This study evaluated two continuous anaerobic reactors, UASB and fluidized bed. The maximum removal achieved by the UASB reactor when operated without recirculation was 65% for a substrate load applied to 3.55 kg/m3 d. When the mass transfer conditions of the reactor were improved by recirculating the biomass, the sulphate removal efficiency increased to 89%, representing a removal rate of 1.94 kg SO₄^2-/m^-3 .d^-1. Glycerol was used with the carbon and electron source for SRB in the fluidized bed reactor and was compared to the performance with lactate. For the same sulphate load applied, a removal efficiency of 70%-90% was observed, resulting in a residual concentration average of 254 mg/L sulphate. Glycerol, which is a by-product from biodiesel production, is a potential choice as substrate for sulphate reduction.

Abstract: Sediments from polluted urban streams act as a sink of contaminants. The high content of organic matter and sulphides makes the system appropriate for binding heavy metals. However, changes in the redox potential leads to processes in which sediments acts like a low sulphidic ore in an oxidizing environment, and could generate acid drainages. Human and not human disturbances of the sediments could derive in its oxidation catalyzed by sulphur oxidizing bacteria (SOB). This process leads to acidification and metal release. In this study we analyze the acidification potential of anaerobic sediments of polluted streams near Buenos Aires with static and kinetic methods. The results remark the necessity to consider this process before any sediment management action.

Abstract: Thespreading of nitrogenous compounds into the environment is a common challenge duringmining industries. Typical explosives used in mining are N-based compoundswhich lead to nitrogen contamination of groundwater and water bodies. In goldextraction, cyanide used as lixiviant is also another source of nitrogen pollution.The present work aims to investigate the effect of heavy metals ondenitrification using batch bioassays. Cu, Ni, Co and Fe influence ondenitrification process was studied at pH 7.0. Below the soluble concentrationof 62 mg/L, Ni did not inhibit denitrification, whereas denitrification wasrepressed at soluble Ni concentration above 62 mg/L. At 122 mg/L of soluble Ni,50% inhibition of denitrification was observed. Below soluble concentration of86 mg/L, Co exerted no inhibitory effect on nitrate removal but moderatelydecreased the denitrification rate. Cu slowed denitrification down resulting in40% of nitrate removal averagely at the soluble concentration below 1 mg/L. Onthe contrary, Fe supplementationresulted in iron oxidation and soluble Fe concentrations ranging from 0.4-1.6mg/L that stimulated denitrification. Thepresent work indicates that denitrification can tolerate heavy metals and canbe suitable for acid mine drainage remediation.

Abstract: Samples of anaerobically digested sludges from municipal wastewater treatment installations containing several toxic heavy metals (Cu, Zn, Ni, Co, Cr, Mn, Fe), different organochemicals and biological pollutants (mainly bacteria of the genera Escherichia, Klebsiella, Streptococcus and Clostridium) were subjected to different procedures for detoxification to make possible their use in agriculture. It was found that the bioleaching of these sludges at 70 °C by mixed cultures of extremely thermophilic chemolithotrophic bacteria was the most efficient way to decrease below the relevant permissible levels all above-mentioned pollutants. The bioleaching was carried out in reactors with mechanical stirring and enhanced aeration (by CO₂ enriched air) under batch and continuous-flow conditions. The extraction of some metals (mainly of Cu and Zn) which were present in relatively high concentrations in some sludge samples was very efficient and exceeded 90 % within residence times of about 96 - 120 hours. The dissolved copper and zinc were recovered from the pregnant solutions after bioleaching by means of solvent extraction plus electrolysis. At the same time, the bioassimilable forms of N, P, K and the essential microelements were still present in sufficient concentrations in the pretreated sludges making them suitable for use in agriculture. This was confirmed by experiments in green-houses with plants intended for use in the bioremediation of post-mining landscapes.

Abstract: More than 90% of metal sulfides in vanadium-bearing titanomagnetite concentrates in Panzhihua (China) are pyrrhotite. It is difficult to remove pyrrhotite from iron ores through conventional mineral processing technologies as magnetic separation and flotation. Desulfurization with the help of microorganisms is a promising alternative way relating to the implementation in dissolution. The effects of pH buffers on growth of Acidithiobacillus thiooxidans and biodesulfurization efficiency of vanadium-bearing titanomagnetite concentrates were investigated. 61.86% of sulfur can be removed from the concentrates after bioleaching for 15 days for a 10% pulp density. While 10% of citric-disodium hydrogen phosphate buffer was added into the solution, Acidithiobacillus thiooxidans grew significantly faster and the biodesulfurization rate was increased by 12.34%, accompanying with pH stabilised at ~ 3.0. Boruitan-Luobisen buffer was helpful to keep pH in a good situation, whereas it inhibited the growth of Acidithiobacillus thiooxidans seriously and brought down the biodesulfurization efficiency.