Improved experimental and computational methodology for determining the kinetic equation and the extant kinetic constants of Fe(II) oxidation by Acidithiobacillus ferrooxidans

H2S(g) removal using a modified, low-ph liquid redox sulfur recovery (LRSR) process with electrochemical regeneration of the Fe catalyst couple

A modified pH 1.0 liquid redox sulfur recovery (LRSR) process, based on reactive absorption of H(2)S((g)) in an acidic (pH 1.0) iron solution ([Fe(III)] = 9-8 g L(-1), [Fe(II)] = 1-2 g L(-1)) and electrochemical regeneration of the Fe(III)/Fe(II) catalyst couple, is introduced. Fe(II) was oxidized in a flow-through electrolytic cell by Cl(2(aq)) formed on a Ti/RuO(2) anode. pH 1.0 was applied to retard the potential precipitation of predominantly jarosite group Fe(III) species. At pH 1.0, the presence of chloride ions at [Cl(-)] = 30 g L(-1) allows for both efficient (indirect) electrochemical oxidation of Fe(II) and efficient H(2)S((g)) reactive absorption. The latter observation was hypothesized to be associated with higher concentrations of Fe(III)-Cl complexes that are more highly reactive toward H(2)S((aq)) than are free Fe(III) ions and Fe-SO(4) complexes that otherwise dominate pH 1.0 Fe(III) solutions in the absence of a significant Cl(-) concentration. At the described operational conditions the rate of Fe(II) oxidation in the experimental system was 0.793 kg Fe h(-1) per m(2) anode surface area, at a current efficiency of 58%. Electricity cost within the electrochemical step was approximated at $0.9 per kg H(2)S((g)) removed.

The Effect of Nutrient Supplementation on Growth and Leaching Performance of Bioleaching Bacteria

Heap bioleaching operations are often faced with extended and unpredictable lag periods after inoculation, prior to the establishment of a stable oxidising environment, during which the heap is fully colonised or the inoculum overcomes the sub-optimal conditions resulting from acid agglomeration. Supplementation of laboratory scale (4kg ore) leach columns with soluble nitrogen, particularly as yeast extract, significantly reduced the lag time and promoted bacterial growth, resulting in a 50-95% increase in copper recovery post-inoculation. The effect of yeast extract addition to Acidithiobacillus ferrooxidans in controlled oxidation tests was investigated. Initial exposure of a stock culture to yeast extract resulted in a transient, dose dependent inhibition at concentrations of 0.5 g.l-1 and below. At 1.25 g.l-1 inhibition was complete over the time scale of the experiment. The inhibition phase was characterised by observable changes in cell morphology and ultrastructure. Despite the initial inhibition, the biomass yield at the end of the experiments was equivalent, or higher, in the presence of yeast extract. Cultures were adapted to growth on yeast extract as the sole nitrogen source and adapted cultures showed the highest rates of iron oxidation and cell growth, in the presence of 0.5 and 1 g.l-1 of yeast extract.

Genomic and phenotypic heterogeneity of Acidithiobacillus spp. strains isolated from diverse habitats in China

The genetic variability among 32 Chinese Acidithiobacillus spp. environmental isolates and four reference strains representing three recognized species of the genus Acidithiobacillus was characterized by using a combination of molecular methods, namely restriction fragment length polymorphisms of PCR-amplified 16S rRNA genes and 16S-23S rRNA gene intergenic spacers, repetitive element PCR, arbitrarily primed PCR and 16S rRNA gene sequence analyses. 16S rRNA gene sequences revealed that all Acidithiobacillus spp. strains could be assigned to seven groups, three of which encompassed the Acidithiobacillus ferrooxidans strains from various parts of the world. A comparative analysis of the phylogenetic Group 1 and 2 was undertaken. Restriction fragment length polymorphism results allowed us to separate the 35 Acidithiobacillus strains into 15 different genotypes. An integrated phenotypic and genotypic analysis indicated that the distribution of A. ferrooxidans strains among the physiological groups were in agreement with their distribution among the genomic groups, and that no clear correlation was found between the genetic polymorphism of the Acidithiobacillus spp. strains and either the geographic location or type of habitats from which the strains were isolated. In addition, five unidentified sulfur-oxidizing isolates may represent one or two novel species of the genus Acidithiobacillus. The results showed that the Chinese Acidithiobacillus spp. isolates exhibited a high degree of genomic and phenotypic heterogeneity.