Pore Fluid Chemistry Research Articles

A process-based geochemical framework for shallow-marine carbonate sediments during burial diagenesis

A significant proportion of marine calcium carbonate sediments are comprised of metastable minerals that are susceptible to diagenetic alterations during burial. These reactions can reset the geochemical signature of sediments and pore fluids and influence elemental cycling in the ocean. However, the timing and mechanisms by which these reactions take place are poorly constrained. This study uses cores drilled on the slope of the Great Bahama Bank to provide quantitative constraints on important diagenetic reactions; namely respiration-driven dissolution, authigenic carbonate mineral formation, and conversion of aragonite to low Mg calcite (LMC). We perform detailed mineralogical characterization using newly acquired, high resolution X-ray diffraction (XRD) data and over 1000 reanalyzed XRD scans, characterize sediments texturally and elementally using electron microprobe data, calculate pore fluid saturation state with respect to aragonite using a Pitzer ion interaction approach, and use pore fluid chemistry and experimental distribution coefficients to predict authigenic carbonate compositions. These data suggest that aerobic organic matter oxidation, enabled by the advection of oxygenated seawater throughout the upper ∼ 30 m interval of sediment, causes undersaturation and thus dissolution of biogenic high Mg calcite (HMC) and aragonite. Deeper, anaerobic organic matter oxidation takes over and causes supersaturation, promoting authigenic precipitation in the form of HMC, which in turn decreases pore fluid Mg/Ca and promotes aragonite conversion to LMC. One novel aspect of this study is the identification of three types of calcites using the newly acquired XRD and electron microprobe data. Based on their unique crystallographic characteristics and chemical compositions, these types of calcites are interpreted to represent pelagic biogenic LMC, bank-derived biogenic HMC, and authigenic HMC precipitated from pore fluids. Notably, the composition of the authigenic calcite matches that predicted to precipitate from pore fluids using an empirical Mg partition coefficient in calcite. Calcites that form authigenically and from aragonite via replacement are suggested to recrystallize with burial as evidenced by the decrease in Mg content and micro-strain. This process-based geochemical framework assigns diagenetic processes to a specific depth window within the sediment column and paves the way for a mechanistic understanding of carbonate diagenesis, one that is rooted in thermodynamic and kinetic bases.

Geochemical indications of hydrothermal fluid through sediments within the Geolin Mounds and Mienhua Volcano hydrothermal fields, southernmost Okinawa Trough

This study focused on the chemistry of sedimentary pore fluids to clarify hydrothermal fluid migrating within sediments at the Geolin Mounds (GLM) and Mienhua Volcano (MHV) hydrothermal fields, southernmost Okinawa Trough, where are characterized by covering of thick sediment. The significant downward decrease in Mg2+ (low to 23.3 mmol L−1) and concurrent increase in Li+ (up to 2,269 μmol L−1) in sedimentary pore fluids implied a substantial influence of hydrothermal fluid, which might be associated with high-temperature (>350 °C) rock/sediment-fluid interaction. The best fitting of the 1-D advection-diffusion equation to pore-fluid Cl−, Mg2+, and Li+ concentrations further evidenced the upward hydrothermal through sediments with rates of 0.13 ∼ 124 cm yr−1. The apparently Cl-depleted and slightly Cl-enriched pore fluids in the GLM and MHV hydrothermal fields supported the occurrence of subseafloor phase separation and classified their hydrothermal fluids into vapor-rich and brine-rich phases, respectively. The low pH values (pH = 5.67 ∼ 6.21) with downward increasing trends of pore-fluid dissolved inorganic carbon (DIC, up to 60 mmol L−1) and its heavy isotopic compositions (δ13CDIC = +2.5 ∼ +7.0 ‰) inferred in-situ liquid CO2-impregnated sedimentary circumstance in the GLM and MHV hydrothermal fields. This sedimentary environment, as demonstrated, enhanced the chemical weathering of silicate and carbonate minerals, resulting in the elevated concentrations of Ca2+ and K+ in pore fluids. It highlights the impact of acidic and in-situ CO2-saturated fluids within sediments on geochemical alterations of bulk solids/sediments and interstitial fluids.

THEORETICAL FRAMEWORK FOR LARGE-STRAIN SHEAR RESISTANCE OF KAOLIN CLAYS UNDER CHEMO-MECHANICAL LOADINGS

The normal stress, strain rate, and pore-fluid chemistry significantly influence the large-strain shear response of clays and received great attention for engineering practice. The effect of inundation pressure, consolidation pressure, pH of aqueous solutions, and di-electric on the shear response of kaolin was experimentally investigated. The strain-softening behaviour was observed under normally consolidated (NC) conditions as observed in the past studies on different clays. However, this anomalous shear response with volumetric contraction is not understood. Thus, for the first time, the strain-softening behaviour of NC clays was addressed from an effective stress approach using physico-chemical analysis of kaolin. In this study, the drained shear strength response of NC kaolin was investigated under physico-chemical influence using ring shear tests. A theoretical framework was developed by including micro-mechanism of clay fabric evolution during shear and explicit expressions for electro-chemical forces. The proposed framework provides useful expressions for predicting the shear strength behaviour of kaolin clays, which were validated with experimental data from the present study and literature studies. The new conceptual framework satisfactorily explained the peak and residual shear strength variations under different chemo-mechanical loading for NC conditions. The proposed model adequately predicted the effective stress paths, peak, and residual envelopes in ring shear stress conditions for normally consolidated kaolin soils

Effect of pore water chemistry on the ring shear behavior and the rate dependency of residual strength

The rate dependency of residual strength plays an important role in the selection of residual strength parameters to design the remediation works for reactivated landslides. In the literature, it is shown that the rate dependency of residual strength depends on some factors such as types of soil, range of shear rates, range of effective normal stresses, and pore water chemistry. Recently, the effect of pore water chemistry on the rate dependency of residual strength soil has been examined. However, the ring shear behavior and the rate dependency of residual strength of soil having different pore fluids should be more evaluated. In this study, the effect of the pore fluids of distilled water and 1 M NaCl on the rate dependency of residual strength of kaolin clay was investigated in the Bishop ring shear apparatus. The ring shear tests were conducted at different shearing rates from 0.02 mm/min to 20 mm/min under the effective normal stress of 98 kPa. The research results showed that the pore fluid chemistry affected the shear displacement required to reach the peak strength, the vertical displacement, and the peak strength of kaolin clay. These parameters also exhibited rate dependency, especially at the fast shear rates. The research also indicated that the pore fluid chemistry had a significant effect on the rate dependency of residual strength. Accordingly, the rate dependency of residual strength of kaolin mixed with distilled water showed a positive tendency while that of kaolin with 1 M NaCl as the pore fluid was the neutral tendency.

Numerical simulation of creep behavior of clay using discrete element method

The current study examined the creep behavior of clay in terms of particle sliding using samples containing montmorillonite and kaolinite by modeling all interparticle forces using the discrete element method. The effects of the stress level, pore fluid chemistry, fabric structure and mineral compositions of clay on creep behavior have been studied. The results show that creep mechanisms emerged as a result of clay particle slippage at their points of contact and deformation of the particles themselves. It was also observed that interparticle physicochemical interactions affected the creep behavior of clay minerals. Generally, the rate of secondary consolidation declined with an increase in loading due to densification of the soil. Additionally, a stronger DDL repulsive force led to the neutralization of applied stress at higher compressions, resulting in sooner completion of primary consolidation and initiation of creep.

Pore fluid chemistry effects on homogenization of compacted bentonite specimen with technological voids

Pore fluid chemistry effects on homogenization of compacted bentonite specimen with technological voids

Sedimentation Behavior of Clays in Response to Pore-Fluid Chemistry: Effect of Ionic Concentration and pH on Its Trends

Sedimentation Behavior of Clays in Response to Pore-Fluid Chemistry: Effect of Ionic Concentration and pH on Its Trends

Reconstruction of the Diagenetic Environments of Tight Sandstone Reservoirs: A Case Study from the Tengger Formation in the Baiyinchagan Sag, Erlian Basin, Northern China

Abstract The Lower Cretaceous Tengger Formation located in the Baiyinchagan Sag of the Erlian Basin comprises mainly deeply buried tight sandstone. The identification of high-quality reservoirs in these thickly stacked and heterogeneous units requires a comprehensive understanding of the diagenetic environmental history of the rocks. This paper reports an integrated study involving thin-section petrography, scanning electron microscopy, X-ray diffraction, fluid-inclusion analysis, and vitrinite reflectance analysis of Tengger Formation sandstones with the aim of characterizing the diagenetic conditions of the reservoir rocks and providing guidance for future petroleum exploration. Observed mineral assemblages, the distribution of authigenic minerals, and the distribution and nature of pores suggest the presence of two types of diagenetic environment, acidic and alkaline, which have varied over time and vertically through the rock column. Acidic conditions are indicated by quartz overgrowths and dissolution of both feldspar and carbonate cement. In contrast, alkaline conditions are indicated by the precipitation of carbonate cement, feldspar overgrowths, quartz dissolution, and occurrences of authigenic illite and chlorite. Changes in pore fluid chemistry controlled the evolution of the diagenetic environment. The early diagenetic environment from 110 Ma to 107 Ma was syndepositional and thus controlled by the chemistry of water in depositional centers, which is interpreted to have been weakly alkaline. Significant burial that occurred at 107 Ma induced pulses of hydrothermal fluids and petroleum into the reservoir rocks, which caused a shift to an acidic diagenetic environment. From 103 Ma to 70 Ma, subsequent episodes of uplift and burial caused periodic alternation between acidic and alkaline diagenetic environments. Three distinct episodes of oil and gas charging interpreted from petrography and the homogenization temperatures of fluid inclusions played a critical role in the enhancement of porosity through time. From 70 Ma to the present, acidic diagenesis gradually weakened because of the consumption of organic acids during the process of interaction between rocks and fluids. This study demonstrates the importance of understanding the diagenetic history of reservoir rocks and provides the basis for improved reservoir characterization and optimized hydrocarbon exploration of the Tengger Formation.

Early-age characterisation of Portland cement by impedance spectroscopy

Alternating current impedance spectroscopy (ACIS) was used to assess the effect of different sand, anhydrite and water contents on the electrochemical response of Portland cement paste in the early stages of hydration. Potential factors that may affect impedance measurements and data interpretation are also discussed, such as the complexity of the chemical composition of cement, its physical properties and hydration kinetics, and technique limitations. The impedance data obtained were benchmarked against different supporting techniques and literature data, showing a strong relationship among hydration rates as determined by thermochemistry, setting time measurements by physical approaches, pore fluid chemistry, electrical conductivity and the observed impedance behaviour. The results demonstrate that ACIS is a sensitive technique for assessing cement paste hydration, enabling differentiation of changes in the water and cement content, hydration degree and microstructural development during the first 24 h after mixing.

Physicochemical effects of pore fluid on the dynamic behavior of reconstituted marine clay

An experimental investigation was conducted to study the effect of pore fluid chemistry on the dynamic behavior of reconstituted marine clay. Sodium chloride solution of 0.4 M and 1 M concentrations was used to induce the physicochemical changes. Strain-controlled undrained cyclic triaxial tests were carried out to evaluate the most important parameters such as shear modulus and damping ratio at a large strain range. The results showed that the effect of pore fluid was more pronounced on cyclic shear modulus values at a strain amplitude of 0.3–1%. Tests were also conducted to study the effect of physicochemical factors on the degradation of normalized modulus G N/G 1 of marine clay specimens reconstituted with distilled water and salt solutions.

Impact of High Methane Flux on the Properties of Pore Fluid and Methane-Derived Authigenic Carbonate in the ARAON Mounds, Chukchi Sea

We investigated the pore fluid and methane-derived authigenic carbonate (MDAC) chemistry from the ARAON Mounds in the Chukchi Sea to reveal how methane (CH4) seepage impacts their compositional and isotopic properties. During the ARA07C and ARA09C Expeditions, many in situ gas hydrates (GHs) and MDACs were found near the seafloor. The fluid chemistry has been considerably modified in association with the high CH4 flux and its related byproducts (GHs and MDACs). Compared to Site ARA09C-St 08 (reference site), which displays a linear SO42- downcore profile, the other sites (e.g., ARA07C-St 13, ARA07C-St 14, ARA09C-St 04, ARA09C-St 07, and ARA09C-St 12) that are found byproducts exhibit concave-up and/or kink type SO42- profiles. The physical properties and fluid pathways in sediment columns have been altered by these byproducts, which prevents the steady state condition of the dissolved species through them. Consequently, chemical zones are separated between bearing and non-bearing byproducts intervals under non-steady state condition from the seafloor to the sulfate-methane transition (SMT). GH dissociation also significantly impacts pore fluid properties (e.g., low Cl-, enriched δD and δ18O). The upward CH4 with depleted δ13C from the thermogenic origin affects the chemical signatures of MDACs. The enriched δ18O fluid from GH dissociation also influences the properties of MDACs. Thus, in the ARAON Mounds, the chemistry of the fluid and MDAC has significantly changed, most likely responding to the CH4 flux and GH dissociation through geological time. Overall, our findings will improve the understanding and prediction of the pore fluid and MDAC chemistry in the Arctic Ocean related to CH4 seepage by global climate change.

Tunnel cation and water structures of todorokite: Insights into metal partitioning and isotopic fractionation

Tectomanganate todorokite and phyllomanganate vernadite are the two major manganese minerals in marine ferromanganese sediments that contain large quantities of trace metals. Todorokite has a less clear metal partitioning mechanism than vernadite, mainly because the metal cation and water structures in the tunnel cavities remain poorly understood. Here, we report the composition-dependent tunnel-cation site disorder of todorokite obtained from molecular dynamics (MD) simulations. Our simulations of homocationic Ni2+-, Zn2+-, Mg2+-, Ca2+-, or Na+-todorokite revealed that tunnel cations form inner-sphere (IS) complexes with Mn octahedral surface at low hydration states, but at higher hydration states, outer-sphere (OS) complexes are the dominant cation species located at the center of the tunnel. However, K+ and Cs+ form only IS complexes regardless of the tunnel hydration state. Optimum water contents were determined based on the free energy changes associated with water intercalation into the tunnel cavities calculated as a function of water content for two heterocationic todorokite models: Mg0.5Na0.4Ca0.1Mn6O12·nH2O (Mg/Mn = 0.08, average Mn oxidation state = +3.73) and Mg1.1K0.1Ca0.1Mn6O12·nH2O (Mg/Mn = 0.18, average Mn oxidation state = +3.58). These models emulate the chemical compositions of well-characterized terrestrial and marine todorokite samples, respectively. At each optimum water content, MD simulations revealed that OS complexes are the major Mg2+ species in the former model. However, IS complexes are the major Mg2+ species in the latter model, indicating that the tunnel cation speciation of diagenetic todorokite can be influenced by the sediment pore-fluid chemistry. The atomic tunnel cation and water structures of todorokite provide a molecular basis for understanding of metal partitioning to Mn oxides and interpretation of metal stable isotopes recorded in ferromanganese nodules.

Influence of Pore Fluid Chemistry on Electrical Force-Dominated Fabrics of Fine-Grained Soils: Implications in Submerged Sediments

Structures to mitigate the climate change such as offshore wind farms and geological CO<sub>2</sub> sequestration would be located on coastal regions and offshores. Understanding of fine-grained soil fabrics in submerged conditions can help evaluate the safety of coastal underground constructions such as submarine excavation and slope stability. Fall cone tests for the liquid limit, grain-settling-based sedimentation tests, and ball penetration tests were conducted to investigate soil fabrics in different pore fluids with changes in ionic concentration and permittivity. Based on particle morphology and mineralogy, fine-grained soils were influenced by pore fluid chemistry. Fall cone tests showed the influence of pore fluid chemistry on uniformly mixed soil samples. Fine-grained soils that contained clay minerals such as kaolinite and bentonite showed significant liquid limit changes. Sedimentation tests and ball penetration tests induced fabrics with particle segregation and identified the type of fine-grained soils that could form gravitational force-dominated fabric or electrical force-dominated fabric during natural sedimentation process in submerged conditions.

Numerical Simulation of Cool Hydrothermal Processes in the Upper Volcanic Crust Beneath a Marine Sediment Pond: North Pond, North Atlantic Ocean

AbstractLow temperature hydrothermal systems hosted in the volcanic oceanic crust are responsible for ∼20% of Earth's global heat loss. Marine sediment ponds comprise an important type setting on young ridge flanks where hydrothermal circulation advectively extracts lithospheric heat, but the nature of coupled fluid‐heat transport in these settings remains poorly understood. Here we present coupled (fluid‐heat) numerical simulations of ocean crustal hydrogeology in and below North Pond, a sediment pond on ∼8 Ma seafloor of the North Atlantic Ocean. Two‐ and three‐dimensional simulations show that advective transport beneath North Pond is complex and time varying, with multiple spatial and temporal scales, consistent with seafloor and borehole observations. A unidirectional, single‐pass flow system is neither favored nor needed to match the spatial distribution of seafloor heat flux through North Pond sediments. When the permeability of the crustal aquifer is relatively high (10−10–10−9 m2), simulations can replicate much of the observed variability and suppression of seafloor heat flux and can explain basement overpressures and transient perturbations in pressure and temperature in the upper volcanic crust. Simulation results can also help explain heterogeneity in pore fluid chemistry and microbiology in the crust. Although driven by the same physical processes, the dynamics of hydrothermal circulation below North Pond are different from those seen on "discharge‐dominated" ridge flanks, where the permeability and exposed area of isolated basement outcrops control the extent of regional heat extraction.

Effect of Pore–Fluid Chemistry on the Undrained Shear Strength of Xanthan Gum Biopolymer-Treated Clays

Xanthan gum (XG) biopolymer-based soil treatment is an effective soil improvement method. In this study, we explored the effect of XG on the undrained shear strength of clays (kaolinite and montmorillonite) in chemically distinct pore fluids. Among the pore fluids tested, the undrained shear strength of kaolinite was the highest in kerosene, followed by deionized (DI) water and brine. This study hypothesized that the interparticle forces and interactions dominated the undrained shear strength of the kaolinite clay. In contrast, montmorillonite showed the highest undrained shear strength with DI water, followed by brine and kerosene, likely due to the increase in thickness of the viscous double layer that reduced the undrained strength of the montmorillonite clay. XG also affected the undrained shear strength of the clays, possibly due to the increase in viscosity of the pore fluids and modification of the clay interparticle fabrics. In DI water, XG increased the undrained shear strength of kaolinite (maximum shear strength was observed in the sample with an XG-to-soil mass ratio of 0.5%) via water absorption. Simultaneously, XG decreased the undrained shear strength of montmorillonite, likely due to XG-induced particle aggregation resulting from the changes in the montmorillonite particle surface charges. In 2-M-NaCl brine, the undrained shear strength increased with the increase in XG content, regardless of the mineral types, owing to the salt-induced double-layer compression and increase in concurrent XG-induced pore–fluid viscosity. However, the unaffected and constant undrained shear strength of both clays in nonpolar kerosene suggests that hydrating XG is a prerequisite for its application in soil treatment.

Impact of Particle Sizes, Mineralogy and Pore Fluid Chemistry on the Plasticity of Clayey Soils

The current classification of clayey soils does not entail information of pore fluid chemistry and particle size less than 75 µm. However, the pore fluid chemistry and particle size (at given mineralogy) are critical in the plasticity of clayey soils because of their impact on negative charge density. Therefore, this study extensively discusses the description of clay with respect to mineralogy, particle sizes, and pore fluid chemistry based on liquid and plastic limits of kaolinite, illite, and bentonite, and estimates undrained shear strength from the observed liquid limits. The liquid limits and undrained shear strength estimated from the observed liquid limits as a function of mineralogy (clay type), particle size, and ionic concentration reveal the need of incorporating pore fluid chemistry and particle size into the fines classification system. Furthermore, multiple linear regression models developed in this study demonstrate the importance of particle size and ionic concentration in predicting the liquid limit of clayey soils. This study also discusses the need for a comprehensive understanding of fines classification for proper interpretation of natural phenomena and engineering applications for fine-grained sediments.

Sedimentation rate and organic matter dynamics shape microbiomes across a continental margin

Abstract. Marine sedimentation rate and bottom-water O2 concentration control organic carbon remineralization and sequestration across continental margins, but whether and how they shape microbiome architecture (the ultimate effector of all biogeochemical phenomena) across shelf and slope sediments is still unclear. Here we reveal distinct microbiome structures and functions, amidst comparable pore fluid chemistries, along 300 cm sediment horizons underlying the seasonal (shallow coastal; water depth: 31 m) and perennial (deep sea; water depths: 530 and 580 m) oxygen minimum zones (OMZs) of the Arabian Sea, situated across the western Indian margin. The sedimentary geomicrobiology was elucidated by analyzing metagenomes, metatranscriptomes, enrichment cultures, and depositional rates measured via radiocarbon and lead excess dating; the findings were then evaluated in light of the other geochemical data available for the cores. Along the perennial-OMZ sediment cores, microbial communities were dominated by Gammaproteobacteria and Alphaproteobacteria, but in the seasonal-OMZ core communities were dominated by Euryarchaeota and Firmicutes. As a perennial-OMZ signature, a cryptic methane production–consumption cycle was found to operate near the sediment surface, within the sulfate reduction zone; overall diversity, as well as the relative abundances of anaerobes requiring simple fatty acids (methanogens, anaerobic methane oxidizers, sulfate reducers, and acetogens), peaked in the topmost sediment layer and then declined via synchronized fluctuations until the sulfate–methane transition zone was reached. The microbiome profile was completely reversed in the seasonal-OMZ sediment horizon. In the perennial-OMZ sediments, deposited organic carbon was higher in concentration and rich in marine components that degrade readily to simple fatty acids; simultaneously, lower sedimentation rate afforded higher O2 exposure time for organic matter degradation despite perennial hypoxia in the bottom water. The resultant abundance of reduced carbon substrates eventually sustained multiple inter-competing microbial processes in the upper sediment layers. The entire geomicrobial scenario was opposite in the sediments of the seasonal OMZ. These findings create a microbiological baseline for understanding carbon–sulfur cycling in distinct depositional settings and water column oxygenation regimes across the continental margins.

Effect of pore fluid chemistry on uniaxial compaction creep of Bentheim sandstone and implications for reservoir injection operations

In the transition to a sustainable energy system, natural gas may be an interim source for relatively low-carbon energy production. However, hydrocarbon production worldwide is leading to reservoir compaction and, consequently, surface subsidence and induced seismicity, hampering the potential of natural gas. Reservoir compaction may potentially be mitigated by fluid injection. Fluid injection into porous subsurface reservoirs is also required in other technologies envisioned in a sustainable energy system, such as geothermal energy production and temporary storage of renewable energy. However, fluid injection into porous reservoirs may create a chemical disequilibrium between the pore fluid and host rock, potentially activating fluid–rock interactions that can cause compaction of the reservoir. These chemically activated fluid–rock interactions are not well-understood, and, therefore, we performed uniaxial compaction experiments at 35, 75 and 100 MPa effective stress, employing samples of Bentheim sandstone saturated with supercritical phases (i.e. N2, CO2, wet-N2 and wet-CO2), distilled water and aqueous solutions (i.e. 3.7 pH HCl solution, AMP solution and AlCl3 solution), as well as low-vacuum (dry) conditions. Creep strain and acoustic emissions (AEs) accumulated with increasing stress and sample porosity. While saturation with supercritical fluids produced slightly less creep strain than dry conditions, flooding with distilled water doubled the creep strain. The acidic solutions inhibited compaction creep compared to distilled water saturation. AE activity and microstructural analysis revealed that microcracking controlled deformation, presumably via stress corrosion cracking. While the supercritical fluids may have dried crack tips, distilled water likely reduced the stress required for Si-O bond breakage. The acidic solutions inhibited microcracking through, presumably, a change in surface energy. Our results suggest that fluids devoid of water, with low water content or acidic in nature can be injected into quartz-rich porous reservoirs without increasing reservoir compaction rates.

Improvement and Soil Consistency of Sand-Clay Mixtures Treated with Enzymatic-Induced Carbonate Precipitation.

Recently, microbially induced carbonate precipitation (MICP) has been studied as an alternative for the improvement of sand–clay mixtures. However, the cementing uniformity of MICP-treated sand–clay mixtures cannot be guaranteed. In this present study, enzymatic-induced carbonate precipitation (EICP) was used to deal with it. The ions used in kaolin clay was predicted to affect the production rate for calcium carbonate (CaCO3), which was studied using the calcification test. The solidification test was conducted using two different methods (the premixing method and the diffusion method). The permeability, unconfined compressive strength and the content of CaCO3 of treated samples were obtained to evaluate the solidification effect of the EICP method. Moreover, in EICP treatment, the particle aggregation decreased the liquid limit, but the addition of solution increased it. Therefore, there were contrary effects to the soil consistency. In this study, the two types of liquid limits of treated samples were measured with deionized water and 2M-NaCl brine, respectively. The results show that the Al2O3, NaCl and MgCl2 in the kaolin clay had a slight impact on the production rate for CaCO3, while FeCl3 significantly inhibited it. The EICP method can improve sand–clay mixtures and decrease their permeability. Different from MICP, the EICP method can guarantee the uniformity of treated samples. Moreover, the liquid limit of the sample treated with the premixing method decreased, while that of the sample treated with the diffusion method increased firstly and then decreased with the increasing treatment cycles. Different from the deionized water, the pore-fluid chemistry had a larger effect on the liquid limit with 2M-NaCl brine.

On the utilization of mica waste: The pore-fluid chemistry of mica soils and its implication for erosion susceptibility

Soil is a vital resource which is limited in availability and must be adequately managed for sustainable development. Despite the importance of soil and its limited availability, a huge amount of soil is classified as waste. As one of the world’s largest soil waste generators, the mining industry must transition to a circular economy model to meet sustainability requirements. As a readily available, large-volume waste material (about 10 million tonnes each year), waste mica has been considered for re-use as an alternative soil potassium source for plants, as landscaping material etc. One of the problems with mica waste is its susceptibility to erosion. To use mica as an agricultural or landscaping material, it is therefore important to understand the erodibility of mica and how its erodibility can be reduced. This study presents an experimental campaign to characterize mica erosion susceptibility. Mica particle-to-particle interaction forces and their effect on the macroscopic material behaviour were systematically investigated by changing pore fluid pH and ionic concentration. Sedimentation and liquid limit tests were first carried out to inform a conceptual model of the mica fabric. Triplets of 12 mica samples, compacted at different water contents and with different pore chemistry, were tested for erosion susceptibility using a Jet Erosion Test (JET) apparatus. The particle configuration of mica samples consistently varied with the pore water chemistry, regardless of whether the samples being tested were suspension sediments or compacted samples. For mica samples formed with neutral water at low ionic concentration, the particles are in a dispersed configuration. This implies a poor mechanical behaviour and high erosion susceptibility, as particles are eroded one by one. For porewater samples formed with an increased ionic strength or within the acidic pH range, particles tend to cluster together and organize in a non-dispersed configuration. This results in an improved mechanical behaviour and less erosion susceptibility, as group of particles must be eroded as opposed to individual ones. Similarly, the Jet erosion test results reinforced these observations showing that mica erodibility varies with porewater chemistry. Considering that mica erodibility varies with pore fluid chemistry and mica waste derived from mining operations are often slightly acidic, this paper paves the way for tailored assessments of individual mica waste materials to determine the appropriateness of their use.