Sustainable long-term solutions to managing tailings storage facilities (TSFs) are integral for mines to operate in a safe and environmentally responsible manner. The long-term storage of subaqueous tailings can pose significant safety, environmental, and economic risks; therefore, alternative containment strategies for maintaining geochemical stability of reactive materials must be explored. In this study, the physical and geochemical stabilization of coal tailings using microbially induced calcite precipitation (MICP) was evaluated at a laboratory pilot scale. Three application techniques simulated commonly used agricultural approaches and equipment that could be deployed for field-scale treatment: spraying on treatment solutions with irrigation sprinklers, mixing tailings and treatment solutions with a rototiller, and distributing treatment solutions via shallow trenches using an excavator ripper. Test cells containing 1.0 × 1.0 × 0.5 m of tailings were treated with ureolytic bacteria (Sporosarcina pasteurii) and cementation solutions composed of urea and calcium chloride for 28 days. Penetrometer tests were performed following incubation to evaluate the extent of cementation. The spray-on application method showed the greatest strength improvement, with in an increase in surface strength of more than 50% for the 28-day testing period. The distribution of treatment solution using trenches was found to be less effective and resulted in greater variability in particle size distribution of treated tailings and would not be recommended for use in the field. The use of rototilling equipment provided a homogenous distribution of treatment solution; however, the disruption to the tailings material was less effective for facilitating effective cementation. Bacterial plate counts of soil samples indicated that S. pasteurii cultures remained viable in a tailings environment for 28 days at 18 °C and near-neutral pH. The treatment was also found to stabilize the pH of tailings porewater sampled over the 28-day incubation period, suggesting the potential for the treatment to provide short-term geochemical stability under unsaturated conditions.

Zusammenfassung. Hilft eine kurz applizierte kognitive Technik oder ein schnell durchgeführtes Entspannungsverfahren Kletteranfängern bei der Angstbewältigung? Um dies zu untersuchen, wendeten wir bei Kletteranfängern vor dem Erklettern der ersten Route das Selbstinstruktionstraining nach Meichenbaum ( 1977a , 1977b ) oder die Deep Breathing Technik nach Lichstein, (1988) an. Die Zustandsangst wurde über ein Angst-Thermometer gemessen ( Houtman & Bakker, 1989 ), als zusätzliche Hinweise auf Angst dienten Herzfrequenz und Klettergeschwindigkeit (vgl. Pijpers, Oudejans, Holsheimer & Bakker, 2003 ). Die Herzfrequenz sank unmittelbar nach der Instruktion, was auf die Wirksamkeit der Manipulation hinweist. Beide Techniken zeigten jedoch gegenüber der Kontrollgruppe während des Kletterns keine Wirkung. Zwar stiegen die Werte auf dem Angstthermometer mit zunehmender Höhe an, die beiden Treatmentgruppen unterschieden sich aber nicht von der Kontrollgruppe. Nur kurzfristig eingesetzte Verfahren zur Angstreduktion haben also keine Wirkung. Eine langfristige Vorbereitung sowie ein Training der Intervention scheinen für die Angstreduktion nötig zu sein.

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Cyanobacterial crust formation has attracted attention for stabilizing erosion-susceptible soils in desert regions. However, limited information exists on its application in waste impoundments such as mine tailings. Identifying suitable inoculants with the ability to develop biocrusts in the more toxic conditions of mine tailings represents a challenge for exploiting this biotechnology for such applications. In this study, the performance of two nitrogen-fixing cyanobacteria (Anabaena sp. and Nostoc muscorum), individually and as a consortium, in creating biocrusts over gold mine tailings were investigated under sterile and non-sterile conditions. The results showed that Anabaena sp. and the co-inoculation of the species promoted higher synthesis of chlorophyll-a and total EPS compared to N. muscorum. The inoculated strains also exhibited different responses in the amount of the EPS fractions. The less soluble and more condensed tightly bound EPS represented a higher fraction of total EPS with co-inoculation and N. muscorum. With respect to wind erosion resistance and compressive strength of the biocrusts generated, co-inoculation showed better performance, followed by N. muscorum, while Anabaena sp. appeared to be less effective. The presence of indigenous microbial community within the tailings influenced the biostabilization performance of Anabaena sp., while the influence was insignificant under co-inoculation and N. muscorum. Overall, inoculating the cyanobacteria in a mixture with complementary traits (higher chlorophyll-a synthesis and total EPS secretion of Anabaena sp. vs. higher TB-EPS fraction and filamentous growth of N. muscorum) presented an effective strategy in the development of a resistant biocrust against wind erosion. With this inoculation strategy, the beneficial effects of the individual strains on biocrust formation could be combined, thus a comparatively stronger structure could be formed. Besides chlorophyll-a content, factors such as cyanobacteria morphology and EPS fractions would contribute to the biostabilization process. The results also suggested that sterilization of the tailings would influence the performance of cyanobacteria depending on the inoculant. Thus, the response of inoculants to other microbial communities should be considered prior to field-scale application.

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