D.W. Shiers

Metals tolerance in moderately thermophilic isolates from a spent copper sulfide heap, closely related to Acidithiobacillus caldus, Acidimicrobium ferrooxidans and Sulfobacillus thermosulfidooxidans

Selective enrichments enabled the recovery of moderately thermophilic isolates with copper bioleaching ability from a spent copper sulfide heap. Phylogenetic and physiological characterization revealed that the isolates were closely related to Sulfobacillus thermosulfidooxidans, Acidithiobacillus caldus and Acidimicrobium ferrooxidans. While isolates exhibited similar physiological characteristics to their corresponding type strains, in general they displayed similar or greater tolerance of high copper, zinc, nickel and cobalt concentrations. Considerable variation was found between species and between several strains related to S. thermosulfidooxidans. It is concluded that adaptation to metals present in the bioleaching heap from which they were isolated contributed to but did not entirely explain high metals tolerances. Higher metals tolerance did not confer stronger bioleaching performance, suggesting that a physical, mineralogical or chemical process is rate limiting for a specific ore or concentrate.

Saline-water bioleaching of chalcopyrite with thermophilic, iron(II)- and sulfur-oxidizing microorganisms

The application of thermoacidophiles for chalcopyrite (CuFeS2) bioleaching in hot, acidic, saline solution was investigated as a possible process route for rapid Cu extraction. The study comprised a discussion of protective mechanisms employed for the survival and/or adaptation of thermoacidophiles to osmotic stress, a compilation of chloride tolerances for three genera of thermoacidophiles applied in bioleaching and an experimental study of the activities of three species in a saline bioleaching system. The data showed that the oxidation rates of iron(II) and reduced inorganic sulfur compounds (tetrathionate) were reduced in the presence of chloride levels well below chloride concentrations in seawater, limiting the applicability of these microorganisms in the bioleaching of CuFeS2 in saline water.

Life in heaps: a review of microbial responses to variable acidity in sulfide mineral bioleaching heaps for metal extraction.

Industrial heap leaching of low grade mineral sulfide ores is catalysed by the use of acidophilic microorganisms. These microorganisms obtain energy for growth from the oxidation of reduced inorganic or organic compounds, including soluble ferrous ion, reduced inorganic sulfur compounds (RISC) and acid-stable organic compounds. By-products of these oxidative processes, such as soluble ferric ion and sulfuric acid create favourable chemical conditions for leaching. This review is focused on the behaviour of common bioleaching microorganisms, their responses to changing pH in an industrial setting, and how both changes and microbial responses can impact the micro and macro environment.

Extremophiles in Mineral Sulphide Heaps: Some Bacterial Responses to Variable Temperature, Acidity and Solution Composition

In heap bioleaching, acidophilic extremophiles contribute to enhanced metal extraction from mineral sulphides through the oxidation of Fe(II) and/or reduced inorganic sulphur compounds (RISC), such as elemental sulphur or mineral sulphides, or the degradation of organic compounds derived from the ore, biota or reagents used during mineral processing. The impacts of variable solution acidity and composition, as well as temperature on the three microbiological functions have been examined for up to four bacterial species found in mineral sulphide heaps. The results indicate that bacteria adapt to sufficiently high metal concentrations (Cu, Ni, Co, Zn, As) to allow them to function in mineral sulphide heaps and, by engaging alternative metabolic pathways, to extend the solution pH range over which growth is sustained. Fluctuating temperatures during start up in sulphide heaps pose the greatest threat to efficient bacterial colonisation. The large masses of ores in bioleaching heaps mean that high temperatures arising from sulphide oxidation are hard to control initially, when the sulphide content of the ore is greatest. During that period, mesophilic and moderately thermophilic bacteria are markedly reduced in both numbers and activity.

The Effect of LIX 63 Hydroxyoxime Degradation Products on Kinetics-Based Metal Extraction

The potential of the LIX® 63 hydroxyoxime/Versatic 10 combination to kinetically directly separate cobalt (1 g/L) from a nickel rich (20 g/L) synthetic leach solution while rejecting impurities has been highlighted previously. In the present work, the stability of the LIX 63 hydroxyoxime has been assessed under conditions relevant to a commercially prospective kinetics-based operation, and the results compared with those obtained in previously investigated equilibrium-based systems. Importantly, no adverse effect of the four main hydroxyoxime degradation products on metal extraction and stripping kinetics was found, even when these were added at high concentrations.

The Impact of Heap Self-Heating on Microbial Activity during the Bioleaching of Low-Grade Copper Sulfide Ores

In this study, a dynamically-controlled column was used to evaluate two ores known to cause heap overheating. This enabled the simulation of heap self-heating under controlled conditions. The lixiviant was inoculated with a consortia of mesophilic and moderately thermophilic microorgaisms, and the impact of rapid temperature increases on biological activity and cell numbers was evaluated. During the leaching of ore sample A, the temperature lagged for 29 days before increasing rapidly from 26 to 88 °C. Cell numbers and solution potential increased concomitantly, before both were reduced as the temperature increased past maximum microbial tolerances. Cell numbers began increasing again within 10 days of reaching temperatures that would facilitate mesophilic growth being restored. During the leaching of ore B, the temperature lagged for 4 days before exhibiting a rapid increase in temperature, increasing from 30 to 76 °C over a six-day period. Cell numbers were reduced with the sudden temperature increase, and did not recover over the remainder of the experiment.

Synthesis of a t-α-Hydroxy Oxime and its Synergistic Behavior with Versatic 10

The aliphatic α-hydroxyoxime LIX® 63 contains a secondary hydroxyl group that is susceptible to oxidation. In the present work, an alternative oxidation-resistant α-hydroxyoxime containing a tertiary hydroxyl group, namely (1-hydroxycyclohexyl)-phenyl ketone oxime (“phenyl oxime”), has been synthesized and characterized. Combining phenyl oxime with Versatic 10 results in synergistic metal extraction behavior. The ability of this ligand to withstand oxidation is demonstrated. Other benefits are also evident, including its existing wholly in the active anti isomeric form and exhibiting fast nickel kinetics in the synergistic system. Phenyl oxime readily undergoes aqueous acid-catalyzed hydrolysis and so is not commercially practical. Addition of carbon side-chains could help to overcome this.

The Effect of Ferrous Iron Addition during Tetrathionate Utilisation by Some Sulfobacillus Species

Ferrous sulfate was added to batch cultures of Sulfobacillus (Sb.) acidophilus, Sb. thermosulfidooxidans and Sb. sibiricus during growth on tetrathionate. Soluble ferrous ion and polythionate concentrations were used as a measure of substrate utilisation. Sb. thermosulfidooxidans switched from utilising polythionates to exclusively oxidising ferrous ions, only then oxidising the remainder of the polythionates. Sb. sibiricus and Sb. acidophilus did not cease polythionate oxidation but utilised both substrates concurrently after ferrous ion addition. None of the cultures tested exhibited preferential polythionate utilisation, even though they were utilising polythionate prior to the addition of ferrous ions.

Impacts of Mineralogy on the Chemistry and Microbiology of Heap Bioleaching

The microbial microenvironment in heaps is strongly influenced by ore mineralogy. While laboratory studies on microbial activity under controlled conditions provide a good understanding how bioleaching organisms might assist in metal extraction, examination of the ore, its mineralogy and leaching chemistry offer additional valuable insights. Some examples are discussed and illustrated with data for a copper-nickel sulfide ore.

Chemical Reactivity of Tributyl Phosphate with Selected Solvent Extraction Reagents

It has recently been shown that Cyanex 272 can react with tributyl phosphate (TBP) to form the corresponding butyl ester species under both commercial and anhydrous operating conditions. The present work found that acidic organic extractants MEHPA, DEHPA, Ionquest 801, Cyanex 302, Cyanex 301, and decanoic acid also react with TBP to form the corresponding butyl ester species and dibutyl phosphate under anhydrous conditions at 65°C, whereas non-acidic reagents Alamine 308, LIX 84, LIX 63, and Acorga M5640 do not. Excluding MEHPA, the rate of ester formation appears inversely correlated with the pKa of the organic acid used.