Abstract
Water scarcity in semi-arid/arid regions is driving the use of salt water in mining operations. A consequence of this shift, is the potentially unheeded effect upon Mine Tailing (MT) management. With existing stabilization/solidification methodologies exhibiting vulnerability to MT toxicity and salinity effects, it is essential to explore the scope for more environmentally durable sustainable alternatives under these conditions. Within this study we investigate the effects of salinity (NaCl, 0–2.5 M) and temperatures associated with arid regions (25 °C, 40 °C), on Locust Bean Gum (LB) biopolymer stabilization of MT exemplar and sand (control) soil systems. A cross-disciplinary ‘micro to macro’ pipeline is employed, from a Membrane Enabled Bio-mineral Affinity Screen (MEBAS), to Mineral Binding Characterisation (MBC), leading finally to Geotechnical Verification (GV). As predicted by higher Fe2O3 LB binding affinity in saline in the MEBAS studies, LB with 1.25 M NaCl, results in the greatest soil strength in the MT exemplar after 7 days of curing at 40 °C. Under these most challenging conditions for other soil strengthening systems, an overall UCS peak of 5033 kPa is achieved. MBC shows the critical and direct relationship between Fe2O3-LB in saltwater to be ‘high-affinity’ at the molecular level and ‘high-strength’ achieved at the geotechnical level. This is attributed to biopolymer binding group’s increased availability, with their ‘salting-in’ as NaCl concentrations rises to 1.25 M and then ‘salting-out’ at higher concentrations. This study highlights the potential of biopolymers as robust, sustainable, soil stabilization additives in challenging environments.
Highlights
Reactions between salt anions (Cl−) and cement matrices cause the formation of voluminous, Friedls salt compounds, resulting in the expansion and cracking of cements rigid microstructure, reducing soil strength over time[19,20]
The effect of salinity/aridity on biopolymer stabilized soil properties has been investigated through the micro and macro-scales, utilizing Membrane enabled bio‐mineral affinity screen (MEBAS)-Mineral Binding Characterisation (MBC)-Geotechnical Verification (GV) methodology optimized in our previous study[42]
For the Mine Tailing (MT) series, MEBAS and MBC points to the strong affinity between the Fe surface and Locust Bean Gum (LB) which is improved with salinity
Summary
Stabilization/solidification is used by engineers to improve the geotechnical characteristics of soils for a range of purposes (slope stabilization, low carbon building materials, road/building foundations). OPC further consumes huge quantities of resources, such as raw materials (limestone, clay and sand), water and e nergy[6,7] This is accompanied by emissions of SOx, NOx, toxic particulate matter, carbon oxides, metals, hydrogen fluoride/chloride and carbon monoxide by cement production plants, resulting in numerous local and global detrimental environmental e ffects[8]. As a global community, we critically requires a more sustainable, scalable alternative to OPC, that functions optimally for the range of challenging environments that mining facilities operate, with saline-arid conditions being a principle environment of interest. Chemical and physical approaches create their own environmental and effectivity concerns[27,28] Biological based methodologies, such as microbial/enzyme induced cementation (MIC/EIC), have attracted increasing attention due to desirable qualities, such as; renewable, low carbon production, low toxicity and their increasing economic viability[29,30]. Further exploration is required to discover a more environmentally durable solution, whilst retaining the sustainability benefits biological stabilization offers
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