Papers by Keyword: Heap Leaching

Abstract: The present work relates to hydrometallurgy, in particular, to gold-bearing clay ores leaching processes. The initial and agglomerated material filterability was studied. Filterability varies in different agglomeration conditions. Influence of cement, lignosulfonate, plastizer (Cemmix CemPlast), lime consumption was investigated. The negative effect of organic reagents additives, such as plasticizer (Cemmix CemPlast) and lignosulfonate, on the filtration process was established. Colmatation of agglomerated ore minimizes at CaO and Ca (OH)2 using as a modifier of the system, also phase separation in the percolation regime and under pressure proceeds without difficulty. Lime and cement joint use in the optimum proportion at clay ore agglomeration under the studied conditions reduces the filtration duration from a few hours to 2-5 minutes.

Abstract: Heap and dump leaching of sulphide minerals have become well-established techniques for the processing of low grade ores, especially of copper, over the past 30 years. The oxidative dissolution of sulphides in heaps can be significantly enhanced by microbial colonies, but the complexities of the heap leach process overall often counteract the potential advantages, or prevent microbial colonisation and bioleaching in the first place. This overview discusses the multiple layers of complexities that govern percolation leaching processes, such as the interactions between mineral grains, particle pores and leach solution, microbial responses to solution chemistry typical of heaps, solution and solute transport in heterogeneous unsaturated ore beds, as well as heap aeration and microbial response to CO₂ supply. It becomes clear that economically successful heap bioleaching hinges on careful engineering and operation of the heap process as a whole to create an environment in which microbial colonies can thrive and the value metal is released sufficiently rapidly into solution.

Abstract: The aim of this study was to investigate the microbial colonization and arsenic leaching kinetics of South Korean mine tailings containing arsenopyrite at fixed temperatures (20°C, 30°C and 45°C) and at ramped up temperatures (25 to 45°C, with a 2°C daily increase). The experiments were conducted in a packed bed of inert granite pebbles coated with the tailings material and leached with a mesophilic culture dominated by Acidithiobacillus caldus (56%), a lesser percentage of Leptospirillum ferriphilum (29%) and Archaea (15%), using 1 g/L ferrous-enriched 0K medium. The ramped-up temperature experiment was conducted in triplicate and columns were sacrificed after different leach periods to study the evolution of microbial species dominating the colonization. The leaching performance was evaluated using the arsenic released into solution, the iron oxidation rates, the pH and the redox potential. The microbial speciation of the culture attached to the solids during the leach experiment was determined upon completion of each experiment. A steady arsenic solubilisation of between 94 and 97% was observed among the various column experiment after 88 days post inoculation. Microbial speciation performed following the leaching of the mineral indicated a shift of microbial communities in the columns when compared to the initial inoculum.

Abstract: Two samples, a Platreef flotation concentrate and coarse ore (<6 mm), were column bioleached at 65°C using a culture dominated by Metallosphaera hakonensis. Based on solution assays, extractions in excess of 90% Cu and Ni were achieved from the flotation concentrate, while from the coarse ore 96% Cu and 67% Ni extractions were achieved. The difference in extraction levels and leaching patterns despite identical conditions used for both samples is discussed, as is the performance of the samples during a follow-up leach step using cyanide to extract the PGMs in a separate column leach experiment. While the recovery of Pd and Au was excellent during these steps, recovery of Pt was limited to 35% after 45 days for the concentrate and 56% after 60 days for the whole ore material, primarily due to the presence of a refractory Pt mineral. Recovery from a concentrate without pre-treatment was substantially lower.

Abstract: Previous agglomerate-scale heap bioleaching studies have outlined the variations in cell numbers of the liquid and attached phases during colonisation of sterilised ore by a pure culture. In this study, a mixed mesophilic culture was used in agglomerate-scale columns containing non-sterilised low-grade copper ore. Over a six - month period, columns were harvested at various intervals to provide snapshots of the metal distribution and the quantity, location, and ecological variations of mineral-oxidizing microbes within the ore bed. The initial colonisation period in this experiment was dissimilar to previous work, as the indigenous community was retained within the ore-bed throughout acid agglomeration. The overall colonisation phase lasted for approximately 1,000 hours until cell concentrations stabilised. In each column, less than 0.05% of the total cells were found in the leachate, 15-20% in the interstitial phase and the remaining ~80% were attached to the mineral surface. Once cell numbers had stabilised, interstitial cell concentrations were approximately 2,000× greater than those in the leachate. This difference persisted for the duration of the experiment. Copper concentrations in the two liquid phases generally decreased over time, but were on average 50× higher in the interstitial phase. Iron concentrations were more stable, but again were 30× higher in the interstitial phase. This demonstrates that that the difference in cell concentration between the leachate and interstitial phases cannot be explained through diffusion gradients within the system as it is much greater than those observed for the dissolved metals. It also shows that the specific environmental conditions of the interstitial and attached cells are very different to those inferred through analysis of leachates alone.

Abstract: JOGMEC has been carrying out the study on primary copper sulfide ores leaching for recovering copper economically and efficiently by heap leaching. In our study, we have been using the primary copper sulfide ore produced in an IOCG deposit. The ore is characterized by high iron content and high acid consumption in leaching. For the optimization of the leaching, the conditions such as ore size, agglomeration, pH and irrigation rate of leaching solution were examined with column leach tests. The best result was over 80 % extraction of copper in 150 days with leaching solution of 1 M sulfuric acid and temperature of 45 °C. In this experiment, the fines of the ore sample were removed before putting it into the column to keep the permeability of the ore bed. In these column leach tests, the Fe²⁺/total-Fe ratio of PLS decreased gradually by the activity of naturally grown iron-oxidizing bacteria. The bacteria in PLS, which have the ability of iron-oxidizing and sulfur-oxidizing, were identified by next-generation sequencing as Acidithiobacillus caldus and Sulfobacillus thermosulfidooxidans. We also carried out bench-scale tests with about 200 tons of the primary copper sulfide ores. Iron-oxidizing and sulfur-oxidizing bacteria were identified in the leaching solution as same with column leach tests. It is considered that the bacteria worked in the leaching solution and on the surface of the ores.

Abstract: In a mine owned by the company Orenas S.A. (Equador), a biooxidation process for gold recovery has been developed. Refractory gold ore was crushed, milled and 500 ton of flotation concentrate was agglomerated by coating a support rock. This was piled up on a liner and the biooxidation process in the heap of 35x25x6 m³ was run for approximately 150 days. The oxidized material was subsequently removed for further processing. An outcrop allowed for depth dependent sampling of altogether 36 samples at three sites over the complete depth of 6 m. The fine fraction was removed from the host rock and sent to the laboratory for analysis of the microbial community. The pH ranged between 2.2 and 2.9. Total cell counts determined via counting under a fluorescence microscope after SYBR Green staining indicated a high microbial colonialization of the heap in all depths between 10⁶ to 10⁹ cells per g concentrate, however the highest cell numbers were mainly found in the upper 50 cm. Most-probable-number determination of living, acidophilic iron (II)-oxidizers for one site also revealed a decrease of cell numbers with depth (between 10⁴ to 10⁸ cells per g concentrate). Further molecular analyses of the community composition based on extracted DNA and 16S rRNA gene analyses by TRFLP and qPCR revealed a complex archaeal and bacterial community within the heap. It can be stated that an active community of acidophiles runs the biooxidation process in all sampled parts of the heap.

Abstract: Heap biooxidation is the most economic option of treating processing plants tailings and refractory ores containing non-ferrous and precious metals and sulphides.Pyrite tailings of copper ore processing (Sample 1), tailings of sulphide copper-nickel ore processing (Sample 2) and double refractory gold-bearing ore (Sample 3) were studied.Autotrophic microorganisms Acidithiobacillus thiooxidans and Acidithiobacillus ferrooxidans were used for the tests. The duration of heap biooxidation tests for Samples 1, 2 and 3 was 6, 10 and 16 months, respectively. The rates of copper and zinc recovery into solution during heap biooxidation of Sample 1 were 68% and 71%, respectively; the rates of copper and nickel recovery from Sample 2 were 50% and 75%, respectively. Base metals were extracted from solution to selective high-grade concentrates after biooxidation.Biooxidation tailings of Samples 1 and 3 were leached using an alkaline sodium cyanide solution. The recovery of gold from Sample 1 and Sample 2 was 65% and 85%, respectively.

Abstract: The Sawayardun Gold Mine, the first Muruntau type gold mine in China, was located in the south Tianshan Mountain, Xinjiang Province. The gold reserve was 127 t with an average gold grade of 2.36 g/t. Due to the high content of arsenic and antimony, the traditional flotation-roasting-cyanidation process was not suitable. The direct cyanidation gold extraction for the raw ore was 44.70 %. Thus, biooxidation experiments in shaker flasks were conducted for this ore. The optimum conditions were obtained as inoculation volume 10 %, initial pH 1.7, pulp density 15 %, temperature 33 °C, leaching time 10 days, with the arsenic oxidation rate of 75.12 %. Then the biooxidation residues were test for gold leaching using NaCN, green gold leaching agent and thiourea. After 24 h leaching rate at pulp density of 33%, gold leaching agent dosage of 2 kg/t ore, the gold extraction for NaCN, green gold leaching agent and thiourea were 91.50 %, 86.23 % and 91.09 %, respectively. The high gold extraction showed a bright future for the whole-ore heap biooxidation of this refractory gold ore.

Abstract: Strains of Sulfobacillus (S.) and Alicyclobacillus species have been identified/detected in managed bioleaching heaps and agitated tanks using culture-dependent and culture-independent methods. S thermosulfidooxidans oxidises both iron(II) and reduced inorganic sulfur compounds (RISC). Several strains were isolated from a copper sulfide heap in North Western Australia. Alicyclobacillus strain FP1 (FP1) was also isolated from the heap and oxidises iron(II) but not RISC. However, the species exhibit differentiating characteristics during growth on D-glucose, which has been explored using a suite of monitoring and measurement techniques. As examples, a growth factor (yeast extract) is essential for FP1 but not for S. thermosulfidooxidans, although yeast extract is beneficial to the latter. FP1 grows well on glucose, compared with the poor-to-no growth of S. thermosulfidooxidans on the substrate. Solution pH strongly influences the activity of both species when grown on organic substrates, suggesting a pivotal role for solution acidity in the growth and activity of heterotrophs or mixotrophs in heap leach systems. This research forms part of an ongoing development of a data base with which to interpret the impacts of leaching conditions in heaps on microbial activity without having to disrupt metal production by invasive sampling campaigns. The insights gained will assist in understanding the effects that changing conditions in heaps due to acid consumption and/or increased element concentrations in process water may have on microbial activity.