Biopolymer Stabilization/Solidification of Soils: A Rapid, Micro-Macro, Cross-Disciplinary Approach

Abstract

In this study we describe a novel high throughput, micro-macro approach for the identification and efficient design of biopolymer stabilised soil systems. At the 'microscopic' scale we propose a rapid Membrane Enabled Bio-Mineral Affinity Screening (MEBAS) approach supported by Mineral Binding Characterization (MBC) (TGA, ATR-FTIR and Zeta Potential), while at the 'macroscopic' scale, micro scale results are confirmed by Geotechnical Verification (GV) through unconfined compression testing. We illustrate the methodology using an exemplar mine tailings Fe2O3 -SiO2 system. Five different biopolymers were tested against Fe2O3: Locust Bean Gum, Guar Gum, Gellan Gum, Xanthan Gum and Sodium Carboxymethyl Cellulose. The screening revealed that Locust Bean Gum and Guar Gum have the highest affinity for Fe2O3, which was confirmed by MBC and GV. This affinity is attributed to the biopolymer's ability to form covalent C-O-Fe bonds through β-(1-4)-D-Mannan groups.Upon their 1% addition to a 'macroscopic' Fe2O3 based exemplar MT system, unconfined compressive strengths of 5171 kPa and 3848 kPa were obtained, significantly higher than for the other biopolymers and non-Fe systems. In the current study MEBAS gave an approximately 50-fold increase in rate of assessment compared to GV alone. Application of the proposed MEBAS -MBC -GV approach to a broad range of soil/earthwork components and additives is discussed.

Sustainable Biopolymer Soil Stabilization in Saline Rich, Arid Conditions – A ‘Micro to Macro’ Approach.

“…Fe2O3 (abbreviated to Fe in sample names) was selected as the mineral of focus, due to its universal and consistence abundance in MT, and the relative activity of iron minerals within fresh MT material conditions. 29 The MT exemplar soil system (abbreviated to MT in sample names) is composed of SiO2 (90% by weight, 90 -150 m) and Fe2O3 (10% by weight, 224 nm ± 119 nm) to emulate typical chemical and physical characteristics 30 found within real MT systems (Supplementary Table S1). Furthermore, surprisingly, little research has focussed on utilising abundant Fe minerals for soil stabilisation mechanisms.…”

“…In order to keep the experiments equivalent, the ratio of LB:S was kept the same (see methods). 29 Micro-scale sample names have the addition of equivalent (eq.) to make this clear e.g.…”

“…Previously, the biopolymer Locust Bean Gum (LB) was found to vastly strengthen a MT exemplar soil matrix (containing 10% Fe2O3). 29 Here we expand this work to test the applicability of this biopolymer in a range of environments including in saline (0.5-2.5M NaCl) and arid (25 ℃, 40 ℃) mining conditions, emulating environmental conditions found for many MT facilities operating in water scarce regions. This study highlights the potential of biopolymer additives as next generation, sustainable geotechnical solutions.…”

“…28 In previous work we have introduced a 'micro to macro' methodology to assist in the rapid development of biopolymer soil stabilization additives. 29 At the microscale, Membrane Enabled Bio-mineral Affinity Screen (MEBAS) is a fast method to assess a large number of bio-mineral binding molecules. Mineral Binding Characterisation (MBC) can then be performed on a smaller number of candidates to help understand the micro-scale driving mechanism.…”

“…This pipeline has shown the capability to identify 'high-affinity, high-strength' bio-mineral composites, showing how this binding affinity at the microscale directly translates into highly increased unconfined compressional strength (UCS) of the soil at the macroscale, MEBAS assessment is ~ 50 fold quicker, when compared to a typical trial and error 'top down' methodology. 29 The ability to rapidly identify, understand and verify suitable biopolymer additives dramatically catalyses progression in the field.…”