Papers by Author: Cecilia Demergasso

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Authors: Víctor J. Zepeda, Ivan Nancucheo, Milton Guillen, Enrique Becerra, Camila Escuti, Dina Cautivo, Daniella González, C. Colipai, Cecilia Demergasso, Pedro A. Galleguillos
Abstract: Flotation tailings are hazardous due to physical and chemical instability and are currently considered one of the main pollution concerns of mining industry. Most of these tailings are fine-grained residues with low copper content (0.1-0.8%) and include toxic compounds, such as heavy metals, arsenic, and flotation reagents, among others. Another hazard is the generation of acid mine drainage (AMD) due to biological oxidation of tailings. On the other hand, low-grade ore is challenging the mining industry to commercially produce copper.The main objective of this work was to assess the use of flotation tailings and low-grade ore to produce a biologically-produced copper sulfide, as a product for further pyrometallurgical or fine chemistry processing. Low-grade ore and flotation tailings were first agglomerated at different proportions and leaching tests were performed in 1m columns, using either industrial or synthetic raffinate solution. Then, the PLS solution obtained from the column tests was subjected to selective precipitation of copper by using biogenic hydrogen sulfide (H2S) generated by a mixed culture of neutrophilic sulfate reducing bacteria (SRB), enriched from sediments of Caracarani river (located at 4,600 m over sea level in northern Chile).Over 91% of the copper soluble present in the PLS was recovered as copper sulfide in 28 days, while ferrous iron, other metals and arsenic remained in solution. Analysis performed by XRD confirmed the presence of copper in the precipitate (58% as covellite). This work demonstrates the possibility to apply bioleaching and bio-precipitation technologies to treat tailings and low-grade copper ore to produce a high quality copper sulfide.
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Authors: Mauricio Acosta, Pedro A. Galleguillos, Sabrina Marín, Clement Chibwana, Hannes Strauss, Cecilia Demergasso
Abstract: In bioleaching, the chemiolithotrophic community plays an important role as oxidizers of sulfur compounds and ferrous iron. Ferrous iron oxiding microorganisms are key players in the process, as ferric iron is absolutely required to solubilize metal sulfide ores. Members of the Sulfobacillus genus (able to oxidize ferrous iron) were predominant (22 - 95%) in a chalcopyrite bioleaching columns test. In order to obtain new insight about the mechanism of iron oxidation in Sulfobacillus we investigated the presence and expression of genes potentially related to iron oxidation by Sulfobacillus, especially the group of the so-called blue-copper proteins rusticyanin (rus) and sulfocyanin (soxE) in the course of the experiment. The physicochemical parameters and the population dynamics were monitored periodically in the columns and the metatranscriptome was analyzed by using pyro-sequencing. The average temperature inside the column ranged from 22 to 57 °C and the Fe(II) oxidation rate at 45 °C varied between 8 and 42 mg L-1h-1 along 300 days of operation. The metatranscriptomic analysis reveals an over-expression of 9-13 folds of the putative rus and soxE genes in four strains of Sulfobacillus spp. when the Sulfobacillus proportion in the column was >80% and the Fe(II) oxidation rate measured at 45 °C reached 10 mg L-1h-1. Some cytochromes from the electron transport chain were also over-expressed, on a range of 7 - 10 folds under those operational conditions. These results support the hypothetical participation of blue-copper proteins in the iron oxidation pathway of Sulfobacilli. Culture assays and more specific expression analysis are necessary in order to confirm this hypothesis. In addition, we attempt to establish the relationship between rusticyanin and sulfocyanin genes and perform a protein sequence analysis that allows us to infer the actual function of these proteins in Sulfobacillus species.
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Authors: Cecilia Demergasso, Roberto Véliz, Pedro A. Galleguillos, Sabrina Marín, Mauricio Acosta, Víctor J. Zepeda, Juan Bekios, Jaqueline Zeballos
Abstract: The huge industrial data recorded by several years in copper bioleaching operations represents an opportunity for the technology improvement. A systematic approach is being developed to get insights from the field data from an industrial process and to deliver the obtained knowledge with the aim to serve as the foundation for optimal industrial decision making even in presence of inherent process variations. The development of this Decision Support System (DSS) considers a Q-PCR array, a database for data logging and storage, the application of suitable statistical and computational tools for data analyses and knowledge acquiring and finally the creation of a system of knowledge translation to transform it into action (operational suggestions). The user can accurately retrieve data and design similar matches to the historic operation to get e.g. the expected metallurgical performance of a strip based on its mineralogical parameters. In addition, the user can get computed information and recommendations that should be analyzed. We will discuss the process followed to construct the base of knowledge of the DSS.
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Authors: Sabrina Marín, Mauricio Acosta, Pedro Galleguillos, Clement Chibwana, Hannes Strauss, Cecilia Demergasso
Abstract: Recently, a preliminary model has been proposed for relating the microbial succession of bioleaching heaps with the activity of different CO2 fixation pathways. In order to confirm this hypothesis and to understand the impact of the carbon metabolism in the metallurgical performance, the expression levels of carbon fixation pathways were investigated in a chalcopyrite bioleaching column test by transcriptomic analysis. The community structure, the physicochemical conditions and the metallurgical parameters were also analyzed. Gene expression profiles obtained by microarrays confirmed the temporal distribution of microorganisms as a function of the temperature and the different pathways for CO2 fixation. These results revealed the impact of the different CO2 fixation pathways in the composition of the microbial assemblage as the bioleaching proceeds.
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Authors: Mauricio Acosta, Pedro A. Galleguillos, Mariela Guajardo, Cecilia Demergasso
Abstract: Bioleaching processes are usually open systems where introduced and native microorganisms survive to changes in pH, temperature, salt and metal concentration, among others. Spatial and temporal description of the microbial community could be relevant for better comprehension of copper extraction process and help in the development of operative procedures to improve the metal extraction. We performed metagenomics and high-throughput sequencing of 16S rRNA genes analyses on samples from Escondida mine bioleaching heap and laboratory columns tests. Archaeal community structure in samples was assessed using three pairs of Archaea-specific primers, and results were highly depending on the primers pairs used. Similarly, three pairs of Bacteria-specific primers were used to assess the bacterial community. Moreover, according to the metagenomics analysis, At. thiooxidans, F. acidarmanus, Leptospirillum spp., Acidiphilium sp. JA12-A1, Acidiphilium spp., At. ferrivorans, and Leptospirillum ferriphilum were the most representative microorganisms. The repercussion of the different methodologies and outputs in the characterization of the bioleaching microbial community is discussed. A better understanding of the microbial community in bioleaching processes could improve the analysis regarding environmental changes in the heap process, its metallurgical performance and, can be used to assist in the decision-making process.
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Authors: Lorena Escudero, Jonathan Bijman, Guajardo M. Mariela, Juan José Pueyo Mur, Guillermo Chong, Cecilia Demergasso
Abstract: To understand the microbial community inhabiting in an acidic salt flat the phylogenetic diversity and the geochemistry of this system was compared to acid mine drainage (AMD) systems. The microbial community structure was assessed by DNA extraction/PCR/DGGE and secuencing for the 16S rRNA gene and the geochemistry was analyzed using several approaches. Prediction of metagenome functional content was performed from the 16S rRNA gene survey using the bioinformatics software package Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt). The geochemical results revealed a much lower iron concentration in the salt flat than in AMD systems (39 and 21804 mg L-1, respectively) and a significant difference in chloride levels. Sequences inferred to be from potential sulfur metabolizing organisms constituted up to 70% of the microbial community in the acidic salt flat meanwhile predominat iron-metabolizing acidophile populations were reported in AMD systems. Interestingly, the microbial assemblage in the acidic salt flat was dominated by mixotrophic and organotrophic sulfur oxidizers as well as by photoautotrophic acidophiles. Our results suggests that the salt concentration in Salar de Gorbea (average Cl-= 40 gL-1) is in the limit for the occurrence of chemolithotrophic oxidation of sulfur compounds. In addition, the investigation allows concluding that salinity rather than extremes of pH is the major environmental determinant of microbial community composition.
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Authors: Sabrina Marín, Mauricio Acosta, Pedro A. Galleguillos, Yohan Villegas, Dina Cautivo, Víctor J. Zepeda, Cecilia Demergasso
Abstract: Acidithiobacillus thiooxidans is one of the most stable components in the consortium of microorganisms inhabiting the copper bioleaching heap of Minera Escondida Limitada. CalvinBenson-Bassham (CBB) is the CO2 fixation pathway most used by aerobic bacteria, and is the exclusive pathway used by A. thiooxidans. In this work, the population dynamics and the transcriptomic dynamics of five key genes involved in the A. thiooxidans CBB pathway were studied in bioleaching column and pure culture tests at different concentrations of CO2 availability. Association between CO2 level, population dynamics and relative expression of CBB-genes was discovered. Differences between CBB pathways from closely related species were reported. The transcription profile modelling could provide useful knowledge for improving industrial bioleaching operations.
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