Probing the whole ore chalcopyrite–bacteria interactions and jarosite biosynthesis

Significance Statement

Chalcopyrite is considered the most abundant ore of copper sulfide. The ore has received significant attention owing to its vast ores with exploitation potential. Bioleaching that is environment friendly can be implemented for leaching copper ores employing sulfur and mesophilic oxidizing bacteria including Acidithiobacillus thiooxidans. The major oxidation product of chalcopyrite leaching has been found to be chalcocite that is further oxidized to yield covellite.

Chalcopyrite bioleaching initiates iron hydrosulfates precipitation coupled with metal-deficient layers that tend to minimize the entry of leaching components and bacteria to mineral surfaces. This in turn makes bioleaching inefficient. For this reason, finding a clarification of the approaches is necessary for optimizing chalcopyrite leaching and lessening the formation of jarosite passivation layers. Above all, researchers are yet to reach a consensus on the appropriate control procedures that must be followed in the bioleaching process.

Researchers led by professor Constantinos Varotsis from Cyprus University of Technology, Cyprus in collaboration with scientists at Hellenic Copper Mines, studied, for the first time, the formation of covellite from the bioleached surface of chalcopyrite, potassium, ammonia, ammonium ions, jarosites, and extracellular polymeric substances. They did the study in the microbial setting of the mines of copper. They applied FTIR micro-spectroscopies and Raman methods in a bid to establish a simple approach for assessing the formation of secondary minerals. Their work is published in peer-reviewed journal, Bioresource Technology.

The authors collected specimens from the copper mines of Hellenic and analyzed them by microscopy. They did bioleaching experiments in compact columns that were filled with solutions from the copper mines. The solutions contained microorganisms including Acidithiobacillus thiooxidans and Leptospirillum ferriphilum. They attached heating tapes around the testing columns in a bid to maintain the experiment at 350C and this was done for four months. The authors performed infrared microscopies tests and collected Raman data.

The authors observed that the Raman spectra of chalcopyrite grain had a weak band of approximately 292cm-1. In the spectra, this zone was obscured by light scattering because of focusing of the laser beam on the mineral surface, therefore, the authors were unable to detect this weak band. After one month of bioleaching, the authors recorded new bands of 469 and 226 cm-1, which they assigned to Cu-S of covellite and FeO of K+ jarosite respectively.

At the end of two months of bioleaching, the authors recorded six more bands. However, by the end of the third month, they observed a drop in the intensity of the 469 cm-1 band. This indicated that there was a drop in covellite concentration. However, at the fourth month, this band had disappeared altogether, and there was the formation of new marker bands.

From Raman data, the authors observed the formation of K+ Jarosite, which was then followed by NH4+. They observed a color variation in the FTIR data, which indicated that microorganisms were attached on the surface of the mineral. A change in the intensity of the bands in the frequency range of 900-1140 cm-1 confirmed the presence of biofilm conformations.

By analyzing the FTIR maker bands, the authors were able to understand the purpose of the extracellular polymeric substances to copper bioleaching.

Reference

Anastasia Adamou, Giorgos Manos, Nicholas Messios, Lazaros Georgiou, Constantinos Xydas, and Constantinos Varotsis. Probing the whole ore chalcopyrite–bacteria interactions and jarosite biosynthesis by Raman and FTIR micro spectroscopies. Bioresource Technology, volume 214 (2016), pages 852–855.

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