Maria Eliza Nagel-Hassemer

The objective of this study is to obtain a more detailed assessment of particles that contain rare-earth elements (REEs) in abandoned deposits of Brazilian fine coal tailings (BFCTs), so as to aid current coal mining industries in the identification of methodologies for extracting such elements (Santa Catarina State, Brazil). The BFCT areas were sampled for traditional mineralogical analysis by X-ray Diffraction, Raman Spectroscopy and nanomineralogy by a dual beam focused ion beam (FIB) coupled with field emission scanning electron microscopy (FE-SEM) and high-resolution transmission electron microscopy (HR-TEM) coupled with an energy dispersive X-ray microanalysis system (EDS). The results show that the smaller the sampled coal fines were, the higher the proportion of rare-earth elements they contained. Although the concentration of REEs is below what would normally be considered an economic grade, the fact that these deposits are already ground and close to the surface negate the need for mining (only uncovering). This makes it significantly easier for REEs to be extracted. In addition, owing to their proximity to road and rail transport in the regions under study, the opportunity exists for such resources (BFCTs) to be utilized as a secondary market as opposed to simply being discarded as has been done in the past.

This work aimed to remove sulfate and acidity from mine-impacted water (MIW) via electrocoagulation (EC), a technique which stands as an advanced alternative to chemical coagulation in pollutant removal from wastewaters. The multiple electrochemical reactions occurring in the aluminum anode and the stainless steel cathode surfaces can form unstable flakes of metal hydroxysulfate complexes, causing coagulation, flocculation, and floatation; or, adsorption of sulfate on sorbents originated from the electrochemical process can occur, depending on pH value. Batch experiments in the continuous mode of exposition using different current densities (35, 50, and 65 A m⁻²) were tested, and a statistical difference between their sulfate removals was detected. Furthermore, the intermittent mode of exposure was also tested by performing a 2²-factorial design to verify the combination with different current densities, concluding that better efficiencies of sulfate removal were obtained in the continuous mode of exposition, even with lower current densities. After 5 h of electrocoagulation, sulfate could be removed from MIW with a mean efficiency of 70.95% (in continuous mode of exposition and 65 A m⁻² current density), and this sulfate removal follows probable third-order decay kinetics in accordance with the quick drop in sulfate concentration until 3 h of exposure time, remaining virtually constant at longer times. Graphical abstract

Iron and manganese removal is made conventionally by oxidation methods; however, when aquatic humic substances (HS) are present, they can affect the removal, with another treatment process being necessary. This study focused on performance of ultrafiltration (UF) and nanofiltration (NF), preceded by coagulation, flocculation, and sedimentation stages for iron, manganese, and HS removal, with two water sources that present superior levels of humic compounds, and measured by dissolved organic carbon (DOC) and UV absorbance at 254 nm. Coagulation, flocculation, and sedimentation combined with UF/NF efficiently removed dissolved iron, HS, apparent color, and turbidity. Almost total iron removal was already attained in the prior steps of coagulation, flocculation, and sedimentation, obtaining final values of dissolved iron of less than 0.001 mg L⁻¹ for the two types of water studied. However, the complete system did not appear effective (less than 50% efficiency) in dissolved manganese removal, although a significant reduction in the HS was achieved (approximately 80% after UF and 90% after NF measured as DOC, for two types of water). Pretreatment was shown to be effective in reducing the loss of filtration flow because of the removal of high-molecular-weight HS, thus minimizing the formation of fouling on the membrane.