Role of indigenous microbial communities in the mobilization of potentially toxic elements and rare-earth elements from alkaline mine waste.

This study aims to evaluate the role of indigenous microorganisms in the mobilization of potentially toxic elements (PTE) and rare-earth elements (REE), the influence of the bioavailability of carbon sources that might boost microbial leaching, and the generation of neutral/alkaline mine drainage from alkaline tailings. These tailings, with significant concentrations of total organic carbon (TOC), were mainly colonized by bacteria belonging to the genera Sphingomonas, Novosphingobium and Solirubrobacter, and fungi of the genera Alternaria, Sarocladium and Aspergillus. Functionality analysis suggests the capability of these microorganisms to leach PTE and REE. Bio-/leaching tests confirmed the generation of neutral mine drainage, the influence of organic substrate, and the leaching of higher concentrations of PTE and REE due to the production of organic acids and siderophores by indigenous microorganisms. In addition, this study offers some insights into a sustainable alternative for reprocessing PMC alkaline tailings to recover REE.

Bacterial communities shift and influence in an acid mine drainage treatment using barium carbonate disperse alkaline substrate system.

Chemical passive treatment systems used to remediate acid mine drainage has been evaluated based mainly on the reactivity of the chemical alkaline reagents, overlooking the activity of the microorganisms that proliferate in these artificial ecosystems. In this study, the bacterial communities of a unique passive treatment system known as BDAS (Barium carbonate Dispersed Alkaline Substrate) were investigated using 16S rRNA gene metagenomic sequencing combined with hydrochemical characterization of the AMD and phenotypic characterization of biogenic precipitates. According to the hydrochemical characterization, the water quality improved as the water progressed through the system, with a drastic increase in the pH (up to alkaline conditions) and total organic carbon, as well as the removal of main contaminants such as Ca2+, SO42-, Fe3+, Al3+, and Mn2+. These environmental changes resulted in an increase in bacterial diversity (richness) after the inlet and in the shift of the bacterial communities from chemoautotrophs (e.g., Ferrovum and Acidiphilum) to chemoheterotrophs (e.g., Brevundimonas and Geobacter). Some of these taxa harbour potential to immobilize metals, aiding in the treatment of the water. One of the mechanisms involved in the immobilization of metals is microbially induced calcium carbonate precipitation, which seems to occur spontaneously in BDAS. The production of biofilm was also observed in most parts of the system, except in the inlet, helping with the removal of metals. However, in the long run, the build-up of biofilm and precipitation of metals could clog (i.e., biofouling) the pores of the matrix, reducing the treatment efficiency. Potential human pathogens (e.g. Legionella) were also detected in BDAS indicating the need for a treatment step at the end of the system to remove pathogenic microorganisms. These findings present a new perspective of the bacterial communities and their effects (both positively and negatively) in a chemical passive treatment system.

Structure and Mechanical Properties of the New Ti30Ta20Nb Biomedical Alloy.

In order to better understand the relationship between parameters of a mechanical alloying process and microstructure, especially the structure of porosity, some research and studies were carried out. The current study investigates the possibility to prepare the porous materials by mechanical alloying and annealing. A high-energy ball-milling process in the planetary ball mill Fritch PULVERISETTE 7 premium line was used for the solid-state synthesis of the single phase powders for titanium based biomedical alloy. The influence of the high-energy ball-milling time on the structure and morphology of the synthesized precursors after annealing was investigated. Additionally, the effect of the variable time of the ball-milling on the structural characteristics, pore morphology and mechanical properties of a biomedical Ti30Ta20Nb (wt.%) was investigated as well. This study confirms the predominance of the titanium ß phase and also the presence of the titanium α phase. The analysis of the diffraction patters obtained using the Rietveld method showed that when the milling time increases, the lattice parameters for the tested samples become reduced. Summing up, it should be pointed out that the areas of pure unreacted titanium still exist in the material. These areas were correlated to the results of an X-ray diffraction analysis. This research starts the process of converting mechanical alloying into a production method which could become an alternative to the space holder technique for the new titanium alloys used for medical applications.