Importance of Initial Interfacial Steps during Chalcopyrite Bioleaching by a Thermoacidophilic Archaeon

Studies of thermophilic microorganisms have shown that they have a considerable biotechnological potential due to their optimum growth and metabolism at high temperatures. Thermophilic archaea have unique characteristics with important biotechnological applications; many of these species could be used in bioleaching processes to recover valuable metals from mineral ores. Particularly, bioleaching at high temperatures using thermoacidophilic microorganisms can greatly improve metal solubilization from refractory mineral species such as chalcopyrite (CuFeS2), one of the most abundant and widespread copper-bearing minerals. Interfacial processes such as early cell adhesion, biofilm development, and the formation of passive layers on the mineral surface play important roles in the initial steps of bioleaching processes. The present work focused on the investigation of different bioleaching conditions using the thermoacidophilic archaeon Acidianus copahuensis DSM 29038 to elucidate which steps are pivotal during the chalcopyrite bioleaching. Fluorescent in situ hybridization (FISH) and confocal laser scanning microscopy (CLSM) were used to visualize the microorganism–mineral interaction. Results showed that up to 85% of copper recovery from chalcopyrite could be achieved using A. copahuensis. Improvements in these yields are intimately related to an early contact between cells and the mineral surface. On the other hand, surface coverage by inactivated cells as well as precipitates significantly reduced copper recoveries.

Caliche and Seawater, Sources of Nitrate and Chloride Ions to Chalcopyrite Leaching in Acid Media

Hydrometallurgical processing of chalcopyrite is of great interest today due to the depletion of oxidized copper minerals. This will also enable existing plants to continue operation. The objective of this work is to study the behavior of chalcopyrite leaching by stirring in an acid-nitrate-chloride media where seawater and brines provide chloride ions and nitrate ions can be provided from the caliche industry. The variables studied were sulfuric acid, nitrate and chloride concentration, source of water (dissolvent), temperature, solid/liquid ratio, particle size, mineral sample, and pretreatment before the leaching process. Despite being a refractory mineral, chalcopyrite can be leached in this system obtaining favorable recoveries at the conditions studied. It was possible to obtain 50% Cu in 0.7 M of H2SO4 and NaNO3, using brine at 45 °C. The nitrate-chloride-acid system was highly temperature dependent, with an activation energy of 82.6 kJ/mol, indicative of chemical reaction control of leaching kinetics. SEM/EDS indicated the presence of sulfur on the surface of the mineral after leaching. This study demonstrates that sources such as seawater or discard brines (such as from the reverse osmosis process) and waste (solid or solutions) from the caliche industry can provide a highly oxidative system for the dissolution of chalcopyrite.

Geochemical fingerprints of brannerite (UTi2O6): an integrated study

Brannerite (UTi2O6) is among the major uranium-bearing minerals found in ore deposits, however as it has been long considered as a refractory mineral for leaching it is currently disregarded in ore deposits. Brannerite is found in a variety of geological environments with the most common occurrences being hydrothermal and pegmatitic. On the basis of scanning electron microscopy observations coupled with electron probe micro-analyses and laser ablation inductively-coupled plasma mass spectrometer analyses, this study describes the morphological features and the major- and trace-element abundances of brannerite samples from five hydrothermal and five pegmatitic localities across the world. Mineral compositions are also compared with observations from transmission electron microscopy and Raman spectrometry showing that brannerite is amorphous. Significant results include the definition of substitution trends and REE patterns, which are characteristics of either an occurrence or genetic type (hydrothermal and pegmatitic). Hence, in combination, it is possible to obtain reliable constraints for establishing a geochemical classification of brannerite. Inferred fingerprints have direct implications for forensic science and the exploration industry; they also contribute to a better understanding of metallogenic processes and to optimising the extraction of uranium.

This New Mineral is Out of This World!

In 1969 a meteorite exploded over Pueblito de Allende in northern Mexico. Many of the fragments were recovered and have provided a wealth of information about the chemical composition of our early universe. Most recently, Chi Ma, Oliver Tschauner, John Beckett, George Rossman, and Wenjun Liu have reported a new mineral in one of these meteorite fragments. Ma et al. named this new form of titanium oxide “panguite” for Pan Gu, the giant in Chinese mythology who, in the beginning, created the world by separating the heaven and earth from chaos. This is an allusion to this ultra-refractory mineral, stable at high temperatures and in extreme environments, being among the first solid materials in our solar system.