Understanding and predicting colloid transport and retention in water-saturated porous media is important for the protection of human and ecological health. Early applications of colloid transport research before the 1990s included the removal of pathogens in granular drinking water filters. Since then, interest has expanded significantly to include such areas as source zone protection of drinking water systems and injection of nanometals for contaminated site remediation. This review summarizes predictive tools for colloid transport from the pore to field scales. First, we review experimental breakthrough and retention of colloids under favorable and unfavorable colloid/collector interactions (i.e., no significant and significant colloid-surface repulsion, respectively). Second, we review the continuum-scale modeling strategies used to describe observed transport behavior. Third, we review the following two components of colloid filtration theory: (i) mechanistic force/torque balance models of pore-scale colloid trajectories and (ii) approximating correlation equations used to predict colloid retention. The successes and limitations of these approaches for favorable conditions are summarized, as are recent developments to predict colloid retention under the unfavorable conditions particularly relevant to environmental applications. Fourth, we summarize the influences of physical and chemical heterogeneities on colloid transport and avenues for their prediction. Fifth, we review the upscaling of mechanistic model results to rate constants for use in continuum models of colloid behavior at the column and field scales. Overall, this paper clarifies the foundation for existing knowledge of colloid transport and retention, features recent advances in the field, critically assesses where existing approaches are successful and the limits of their application, and highlights outstanding challenges and future research opportunities. These challenges and opportunities include improving mechanistic descriptions, and subsequent correlation equations, for nanoparticle (i.e., Brownian particle) transport through soil, developing mechanistic descriptions of colloid retention in so-called “unfavorable” conditions via methods such as the “discrete heterogeneity” approach, and employing imaging techniques such as X-ray tomography to develop realistic expressions for grain topology and mineral distribution that can aid the development of these mechanistic approaches.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2015WR017318

Predicting colloid transport through saturated porous media: A critical review

A comprehensive review of polysaccharide biopolymers for enhanced oil recovery (EOR) from flask to field

The soil remediation field is still in de- velopment in Brazil. Currently, it is not known how many contaminated sites exist across the country; however, due to the country's large size and its extensive urbanization and industrialization, it can be postulated that the number of contami- nated sites must be very high. To remediate these sites, new sustainable technologies should be iden- tified and evaluated. A technology that was born in the 1990s in the USA, and has been fairly investigated, is the use of nanoparticles (NPs) to degrade contaminants in soils and groundwater. This study aims to present a bibliographic review of nanotechnology application to remediation of soils and groundwater, as well as assess the po- tential of conducting research in this field in Brazil. This paper first presents an overview of the number of contaminated areas identified in the USA and Europe. The basic concepts of nanomaterials followed by classification, synthesis, and characterization of nanomaterials are ex- plained. The main types of contaminants for which the technique was already applied as well as the chemical reactions between them and NPs are pre- sented. The issues related to delivery and migra- tion of NPs in the porous media is discussed. Concerns regarding the toxicity of nanomaterials are discussed. The in situ applications of nanomaterials for contaminated site remediation are presented. It is concluded that the issues in- volving remediation of soils and groundwater are site specific and it is not possible to directly transfer knowledge gained from sedimentary soils of temperate climates for residual soils found in tropical and subtropical climate regions. The research on nano- technology for site remediation in Brazil has just begun, and more efforts are required from the technical and academic professionals to develop nanotechnology as practical technology for the remediation of contaminat- ed sites.

Review of Nanotechnology for Soil and Groundwater Remediation: Brazilian Perspectives

The injection of microscale zerovalent iron (mZVI) particles for groundwater remediation has received much interest in recent years. However, to date, monitoring of mZVI particle injection is based on chemical analysis of groundwater and soil samples and thus might be limited in its spatiotemporal resolution. To overcome this deficiency, in this study, we investigate the application of complex electrical conductivity imaging, a geophysical method, to monitor the high-pressure injection of mZVI in a field-scale application. The resulting electrical images revealed an increase in the induced electrical polarization (∼20%), upon delivery of ZVI into the targeted area, due to the accumulation of metallic surfaces at which the polarization takes place. Furthermore, larger changes (>50%) occurred in shallow sediments, a few meters away from the injection, suggesting the migration of particles through preferential flowpaths. Correlation of the electrical response and geochemical data, in particular the analysis of recovered cores from drilling after the injection, confirmed the migration of particles (and stabilizing solution) to shallow areas through fractures formed during the injection. Hence, our results demonstrate the suitability of the complex conductivity imaging method to monitor the transport of mZVI during subsurface amendment in quasi real-time.

Monitoring the Injection of Microscale Zerovalent Iron Particles for Groundwater Remediation by Means of Complex Electrical Conductivity Imaging

Guar gum solutions for improved delivery of iron particles in porous media (part 2): iron transport tests and modeling in radial geometry.

Guar gum solutions for improved delivery of iron particles in porous media (part 1): porous medium rheology and guar gum-induced clogging.

Guar gum can be used to effectively improve stability and mobility of microscale zerovalent iron particles (MZVI) used in groundwater remediation. Guar gum is a food-grade, environment friendly natural polysaccharide, which is often used as thickening agent in a broad range of food, pharmaceutical and industrial applications. Guar gum solutions are non-Newtonian, shear thinning fluids, characterized by high viscosity in static conditions and low viscosity in dynamic conditions. In particular, the high zero shear viscosity guarantees the MZVI dispersion stability, reducing the sedimentation rate of the particles thus enabling its storage and field operations. In this work, a comprehensive rheological characterization of guar gum-based slurries of MZVI particles is provided. First, we derived a model to link the bulk shear viscosity to the concentration of guar gum and then we applied it for the derivation of a modified Stokes law for the prediction of the sedimentation rate of the iron particles. The influence of the preparation procedure (cold or hot dissolution and high shear processing) on the viscosity and on the stability of the suspensions was then assessed. Finally, the dosage and concentration of enzymes - an environment friendly breaker--were studied for enhancing and controlling the degradation kinetics of the suspensions. The derived empirical relationships can be used for the implementation of an iron slurry flow and transport model and for the design of full scale injection interventions.

/pdf/green-stabilization-of-microscale-iron-particles-using-guar-xrxbrj8q8u.pdf

Green stabilization of microscale iron particles using guar gum: Bulk rheology, sedimentation rate and enzymatic degradation

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Guar gum solutions for improved delivery of iron particles in porous media (part 1): porous medium rheology and guar gum-induced clogging.

Green stabilization of microscale iron particles using guar gum: Bulk rheology, sedimentation rate and enzymatic degradation