Biostabilization of Gold Mine Tailings: Co-Inoculation of Cyanobacteria Under Sterile and Non-Sterile Conditions

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.

Performance of Centrocema grown on mercury-contaminated tailing inoculated with beneficial bacteria: Preliminary study

Low levels of major essential nutrients and high mercury (Hg) content in gold mine tailings can inhibit plant growth. An inexpensive and effective strategy to overcome these obstacles was inoculation of plant-growth promoting bacteria and planting legume cover crops (LCC). A greenhouse experiment was conducted to evaluate the effect of isolates of Nitrogen Fixing Bacteria (NFB) and Phosphate Solubilizing Bacteria (PSB) on some growth characteristics of LCC Censtrosema pubescens (butterfly pea) grown in Hg-contaminated tailing of gold mine tailing. Moreover, the research was aimed to verify the viability of two bacterial groups in tailing after inoculation. The experiment was set up in randomized block design to test single and mixed inoculation of NFB and PSB. The experiment verified that the single inoculation and mixture of two bacteria did not change plant properties compared to the control treatment. Although the statistical analysis was not significant, there were slightly increase in root length as well as NFB and PSB populations of inoculated plants.

Study on Mechanical Characteristics of Composite Alkali-activated Materials-stabilized Gold Tailings Under Direct Shear

In this study, the traditional industrial waste residue and some alkaline activators were mixed to prepare a new composite alkali-activated materials (CAAMs), which was used to stabilize gold mine tailings (GMTs). Due to emissions of greenhouse gases and solid dust, alkali-activated materials have been widely used to replace Portland cement to solidify geotechnical materials to enhance their mechanical properties. Different admixture of CAAMs (i.e., 0, 3, 5, 8% ) and gold mine tailings were prepared, and the samples were cured in saturated water and under no air conditions. In order to investigate the mechanical characteristics of CAAMs-stabilized GMTs, laboratory direct shear tests were carried out on samples after curing them for 3, 7, 14 and 28 days, respectively. The test results showed that as the curing periods increased, the brittleness of the samples increased, and the stress-displacement curves for all the cured specimens changed from plateau-type to peak-type curves. The curing periods and the content of CAAMs are both beneficial for enhancing the shear strength of CAAMs-stabilized GMTs samples, but the increase rate decreased as the vertical confining pressure increased. Furthermore, the influence of CAAMs content on shear strength increment was larger than that of curing periods. An exponential growth model could be well used to describe the change of shear strength with the curing periods at different vertical stresses.