Desulfurization of the Old Tailings at the Au-Ag-Cu Tiouit Mine (Anti-Atlas Morocco)

Exploring the potential of the halotolerant bacterial strain Bacillus subtilis LN8B as an ecofriendly sulfide collector for seawater flotation

AIM

To assess the effectiveness of Bacillus subtilis strain LN8B as a biocollector for recovering pyrite (Py) and chalcopyrite (CPy) in both seawater (Sw) and deionized water (Dw), and to explore the underlying adhesion mechanism in these bioflotation experiments.

MATERIALS AND METHODS

The bioflotation test utilized B. subtilis strain LN8B as the biocollector through microflotation experiments. Additionally, frother methyl isobutyl carbinol (MIBC) and conventional collector potassium amyl xanthate (PAX) were introduced in some experiments. The zeta potential (ZP) and Fourier-transform infrared spectroscopy (FTIR) was employed to explore the adhesion mechanism of Py and CPy interacting with the biocollector in Sw and Dw. The adaptability of the B. subtilis strain to different water types and salinities was assessed through growth curves measuring optical density. Finally, antibiotic susceptibility tests were conducted to evaluate potential risks of the biocollector.

RESULTS

Superior outcomes were observed in Sw where Py and CPy recovery was ∼39.3% ± 7.7% and 41.1% ± 5.8%, respectively, without microorganisms' presence. However, B. subtilis LN8B potentiate Py and CPy recovery, reaching 72.8% ± 4.9% and 84.6% ± 1.5%, respectively. When MIBC was added, only the Py recovery was improved (89.4% ± 3.6%), depicting an adverse effect for CPy (81.8% ± 1.1%). ZP measurements indicated increased mineral surface hydrophobicity when Py and CPy interacted with the biocollector in both Sw and Dw. FTIR revealed the presence of protein-related amide peaks, highlighting the hydrophobic nature of the bacterium. The adaptability of this strain to diverse water types and salinities was assessed, demonstrating remarkable growth versatility. Antibiotic susceptibility tests indicated that B. subtilis LN8B was susceptible to 23 of the 25 antibiotics examined, suggesting it poses minimal environmental risks.

CONCLUSIONS

The study substantiates the biotechnological promise of B. subtilis strain LN8B as an efficient sulfide collector for promoting cleaner mineral production. This effectiveness is attributed to its ability to induce mineral surface hydrophobicity, a result of the distinct characteristics of proteins within its cell wall.

Environmental challenges related to cyanidation in Central American gold mining; the Remance mine (Panama)

Mine tailings are a potential source of environmental pollution because they typically contain potentially toxic elements (PTEs) and the residue of chemical compounds used during extraction processes. The Remance gold mine (NW Panama) is a decommissioned mine with mining activity records dating from the 1800s and several periods of abandonment. Very little remediation work has been performed, and waste is exposed to climatic conditions. This study aimed to evaluate the PTEs and cyanide contents in mine waste after mining operations ceased some 20 years ago, and to evaluate the degree of pollution and the environmental risks they pose with the use of the Pollution Load Index (PLI) and the Ecological Risk Index (RI). Although the total cyanide (T-CN) concentration (1.4-1.9 mg kg^-1) found in most of the study area falls within the limits of gold mining tailing values for American sites (1.5-23 mg kg^-1), it is worth noting that the values of the tailings of the last used mining operation exceed it (25.2-518 mg kg^-1) and persist at the site. The PLI and RI suggest that the tailings from the mine and mine gallery sediments represent a source of pollution for soils and surrounding areas given their high content of PTEs (As, Cu, Sb, Hg) and T-CN, which pose serious ecological risks for biota. Therefore, it is necessary to draw up a remediation plan for this area.

Effects of Galvanic Interaction between Chalcopyrite and Monoclinic Pyrrhotite on Their Flotation Separation

The galvanic interaction between chalcopyrite and monoclinic pyrrhotite and its effect on flotation separation were studied using monomineral flotation tests, adsorption capacity tests, X-ray photoelectron spectroscopy (XPS) characterization, and scanning electron microscopy (SEM) test. These results showed that the interaction promoted the reduction of O2 on the cathodic chalcopyrite surface and accelerated the generation of Fe(OH)3, which was not conducive to collector adsorption; hence, the flotation recovery decreased by 10–16%. On the other hand, galvanic interaction accelerated the oxidation of S on the anodic monoclinic pyrrhotite surface to S0 or SO42− and produced a large amount of H+, thus preventing the formation of Fe(OH)3. Meanwhile, the Cu2+ eluted from chalcopyrite surface activated monoclinic pyrrhotite; hence, the flotation recovery increased by 3–10%. Galvanic interaction reduced the floatability difference between the two minerals, and the separation difficulty was significantly increased. Even with an increase in the amount of lime, the separation could not be improved.

Geochemical Classification of Global Mine Water Drainage

This paper evaluates the geochemical distribution and classification of global Acid Mine Drainage (AMD) sources. The geochemical compositions of AMD from 72 mine water sites in 18 countries across 6 continents were referenced from literature. The secondary data were analysed for statistical distribution and mine water classification against the Hill (1968) framework. The research found that the global mine water displayed geochemical concentrations within 2%, 11%, 5%, 9% and 8% of the aluminium, sulphate, acidity, total iron and zinc distribution ranges, respectively, at the 75th percentile. The study also found that 46%, 11.1% and 2.7% of mine water sites met the criteria for Class I, Class II and Class III of the Hill (1968) framework, respectively, while the remaining 40% of sites were omitted by the framework’s geochemical specifications. The results were used to optimise the Hill (1968) framework. The revised framework was proposed for effective AMD geochemical classification, regulation and remediation.

Retention of Contaminants Elements from Tailings from Lead Mine Washing Plants in Ceramics for Bricks

Mining activity is essential for the social welfare of the population. However, this activity produces a series of mining waste. These mining wastes, if not properly treated, can produce significant environmental pollution. This study develops the incorporation of tailings from washing plants in ceramic materials for bricks in order to retain the contaminating elements in the ceramic matrix. To this end, firstly, a physical and chemical characterisation of the mining waste is carried out and different groups of samples are conformed with clay and mining waste. These conformed samples with mining waste are evaluated through different physical and mechanical tests typical in the ceramic industry, studying the variation of properties by the incorporation of the waste. In turn, the leachates from the groups of conformed samples are analyzed, confirming the retention of the contaminating elements of the mining waste in the ceramic matrix. The results of these tests showed that ceramics can be made for bricks with up to 90% mining waste, obtaining physical and mechanical properties acceptable regarding the regulations and retaining the contaminating elements in the ceramic matrix, as confirmed by the leachate tests.

Editorial for Special Issue “Towards a Sustainable Management of Mine Wastes: Reprocessing, Reuse, Revalorization, and Repository”

The mining industry continues to face many challenges due to its potential environmental impacts [...]