Red mud or bauxite residue is a solid waste generated from the Bayer process. The disposal of red mud leads to a serious environmental threat because of its tiny particle size and high alkaline value. The utilisation and recycling of red mud is currently a crucial issue and needs to be addressed as soon as possible. This study demonstrates the different methods and techniques recently analysed or suggested for the consumption of bulk red mud to maintain a sustainable environment. The potential utilisations of red mud include valuable metal recovery, the preparation of construction materials and as an alternative catalyst for diverse processes, including hydrodechlorination, hydrogenation and hydrocarbon oxidation. In addition, the red mud can also be used to control environmental pollution, such as in wastewater treatment, soil remediation and the puriﬁcation of flue gas. However, the proper utilisation and recycling of red mud has a number of shortcomings: pyro-metallurgical recovery involves high energy costs; large volumes of acid by-product needing to be neutralised after the leaching process; the fine particle size of red mud; and the necessity of pre-treatment in some methods. Although many studies have investigated the potential utilisation of red mud, most of them have concentrated on lab-scale studies. Therefore, a large-scale investigation of the recycling and utilisation of red mud needs to be explored. Moreover, an appropriate cost-benefit analysis of the existing technologies needs to be examined in the future because of the high cost of the transportation of a large amount of red mud from alumina refineries to the point of application.

The composition, recycling and utilisation of Bayer red mud

Hidden values in bauxite residue (red mud): recovery of metals

Biomining is an increasingly applied biotechnological procedure for processing of ores in the mining industry (biohydrometallurgy). Nowadays the production of copper from low-grade ores is the most important industrial application and a significant part of world copper production already originates from heap or dump/stockpile bioleaching. Conceptual differences exist between the industrial processes of bioleaching and biooxidation. Bioleaching is a conversion of an insoluble valuable metal into a soluble form by means of microorganisms. In biooxidation, on the other hand, gold is predominantly unlocked from refractory ores in large-scale stirred-tank biooxidation arrangements for further processing steps. In addition to copper and gold production, biomining is also used to produce cobalt, nickel, zinc, and uranium. Up to now, biomining has merely been used as a procedure in the processing of sulfide ores and uranium ore, but laboratory and pilot procedures already exist for the processing of silicate and oxide ores (e.g., laterites), for leaching of processing residues or mine waste dumps (mine tailings), as well as for the extraction of metals from industrial residues and waste (recycling). This chapter estimates the world production of copper, gold, and other metals by means of biomining and chemical leaching (bio-/hydrometallurgy) compared with metal production by pyrometallurgical procedures, and describes new developments in biomining. In addition, an overview is given about metal sulfide oxidizing microorganisms, fundamentals of biomining including bioleaching mechanisms and interface processes, as well as anaerobic bioleaching and bioleaching with heterotrophic microorganisms.

Biomining: metal recovery from ores with microorganisms.

The role of microorganisms in gold processing and recovery—A review

Chemical disequilibrium in planetary atmospheres has been proposed as a generalized method for detecting life on exoplanets through remote spectroscopy. Among solar system planets with substantial atmospheres, the modern Earth has the largest thermodynamic chemical disequilibrium due to the presence of life. However, how this disequilibrium changed over time and, in particular, the biogenic disequilibria maintained in the anoxic Archean or less oxic Proterozoic eons are unknown. We calculate the atmosphere-ocean disequilibrium in the Precambrian using conservative proxy- and model-based estimates of early atmospheric and oceanic compositions. We omit crustal solids because subsurface composition is not detectable on exoplanets, unlike above-surface volatiles. We find that (i) disequilibrium increased through time in step with the rise of oxygen; (ii) both the Proterozoic and Phanerozoic may have had remotely detectable biogenic disequilibria due to the coexistence of O2, N2, and liquid water; and (iii) the Archean had a biogenic disequilibrium caused by the coexistence of N2, CH4, CO2, and liquid water, which, for an exoplanet twin, may be remotely detectable. On the basis of this disequilibrium, we argue that the simultaneous detection of abundant CH4 and CO2 in a habitable exoplanet's atmosphere is a potential biosignature. Specifically, we show that methane mixing ratios greater than 10-3 are potentially biogenic, whereas those exceeding 10-2 are likely biogenic due to the difficulty in maintaining large abiotic methane fluxes to support high methane levels in anoxic atmospheres. Biogenicity would be strengthened by the absence of abundant CO, which should not coexist in a biological scenario.

https://advances.sciencemag.org/content/advances/4/1/eaao5747.full.pdf

Disequilibrium biosignatures over Earth history and implications for detecting exoplanet life.

Bioleaching of clays and iron oxide coatings from quartz sands

Biodestruction and deferritization of quartz sands by Bacillus species

Mixed-layer illite-smectite with high degree of ordering (rectorite-like clay) and with three types of interlayer cations — K+, Na+ and ${\rm{NH}}_4^ + $
 , was determined in the high-sulfide epithermal mineralization of the Western Carpathian Mountains. The tobelitic portion of the clay comprises 5–10%. Ammonium was detected both by chemical analysis and by Fourier transform infrared analysis. Some of the ammonium can be assigned to a poorly bound form, not fully fixed in the illitic interlayer. The finest size fraction separated from the samples behaves differently from the rest of the sample. It contains two layers of water molecules in the expandable interlayers as determined by X-ray diffraction, whereas coarser fractions have only one water layer in the interlayers.

Particle properties of hydrothermal ammonium-bearing illite-smectite

Dissolution of iron from quartz sands by basin bioleaching under static in-situ conditions

/pdf/charakterizacia-bentonitu-z-loziska-hlinik-nad-hronom-17tg2rh4lo.pdf

Ivan Kraus

Papers

Bioleaching of clays and iron oxide coatings from quartz sands

Biodestruction and deferritization of quartz sands by Bacillus species

Particle properties of hydrothermal ammonium-bearing illite-smectite

Dissolution of iron from quartz sands by basin bioleaching under static in-situ conditions

Charakterizácia bentonitu z ložiska Hliník nad Hronom (jastrabská formácia štiavnického stratovulkánu, Západné Karpaty)