pH dependence of bentonite aggregate size and morphology on polymer-clay flocculation

The coagulation process for enveloped and non-enveloped virus removal in turbid water: Removal efficiencies, mechanisms and its application to SARS-CoV-2 Omicron BA.2

The coagulation process has a high potential as a treatment method that can handle pathogenic viruses including emerging enveloped viruses in drinking water treatment process which can lower infection risk through drinking water consumption. In this study, a surrogate enveloped virus, bacteriophage Փ6, and surrogate non-enveloped viruses, including bacteriophage MS-2, T4, ՓX174, were used to evaluate removal efficiencies and mechanisms by the conventional coagulation process with alum, poly‑aluminum chloride, and ferric chloride at pH 5, 7, and 9 in turbid water. Also, treatability of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), a recent virus of global concern by coagulation was evaluated as SARS-CoV-2 can presence in drinking water sources. It was observed that an increase in the coagulant dose enhanced the removal efficiency of turbidity and viruses, and the condition that provided the highest removal efficiency of enveloped and non-enveloped viruses was 50 mg/L of coagulants at pH 5. In addition, the coagulation process was more effective for enveloped virus removal than for the non-enveloped viruses, and it demonstrated reduction of SARS-CoV-2 Omicron BA.2 over 0.83-log with alum. According to culture- and molecular-based assays (qPCR and CDDP-qPCR), the virus removal mechanisms were floc adsorption and coagulant inactivation. Through inactivation with coagulants, coagulants caused capsid destruction, followed by genome damage in non-enveloped viruses; however, damage to a lipid envelope is suggested to contribute to a great extend for enveloped virus inactivation. We demonstrated that conventional coagulation is a promising method for controlling emerging and re-emerging viruses in drinking water.

Different inhibitory mechanisms of flexible and rigid clay minerals on the transport of microplastics in marine porous media

Colloidal interactions between clay minerals and microplastics (MPs) in high salinity seawater are crucial for determining MP fate in marine environments. Montmorillonite (MMT) forms thin and pliable films that tightly cover MPs, while the thick and rigid lamellae of kaolinite (KLT) have limited contact with MPs, resulting in unstable bonding. However, a small quantity of small-sized KLT can create relatively stable heteroaggregates by embedding into the interstitial spaces of MPs. Both MMT and KLT colloids can decrease the mobility of MPs in seawater-saturated sea sand, but their breakthrough curves (BTCs) show distinct phenomena of "blocking" and "ripening", respectively. The "blocking" phenomenon occurs when flexible MMT adheres to the sand surface, depleting attachment sites quickly and inhibiting the retention of subsequent heteroaggregates of MMT-wrapped MPs. The transport of single MMT also experiences colloid competition for attachment sites, but pre-equilibration experiments reveal no competition between MMT and bare MPs for attachment sites. Instead, the attached MMT provides additional attachment sites for MPs. These results suggest that the wrapping of MPs by MMT plays a dominant role in the "blocking" of cotransport. In contrast, rigid KLT forms a three-dimensional stack on the sand surface, offering more attachment sites for subsequent MPs and heteroaggregates.

Depletion-Induced Self-Assembly of Colloidal Particles on a Solid Substrate

We investigate the depletion contributions to the self-assembly of microcolloids on solid substrates. The assembly is driven by the exclusion of nanoparticles and nonadsorbing polymers from the depletion zone between the microcolloids in the liquid and the underlying substrate. The model system consists of 1 μm polystyrene particles that we deposit on a flat glass slab in an electrolyte solution. Using polystyrene nanoparticles and poly(acrylic acid) polymers as depleting agents, we demonstrate in our experiments that nanoparticle concentrations of 0.5% (w/v) support well-ordered packing of microcolloids on glass, while the presence of polymers leads to irregular aggregate deposition structures. A mixture of nanoparticles and polymers enhances the formation of colloidal aggregate and particulate surface coverage compared to using the polymers alone as a depletion agent. Moreover, tuning the polymer ionization state from pH 4 to 9 modifies the polymer conformational state and radius of gyration, which in turn alters the microcolloid deposition from compact multilayers to flocculated structures. Our study provides entropic strategies for manipulating particulate assembly on substrates from dispersed to continuous coatings.

A new bin size index method for statistical analysis of multimodal datasets from materials characterization

This paper presents a normalized standard error-based statistical data binning method, termed "bin size index" (BSI), which yields an optimized, objective bin size for constructing a rational histogram to facilitate subsequent deconvolution of multimodal datasets from materials characterization and hence the determination of the underlying probability density functions. Totally ten datasets, including four normally-distributed synthetic ones, three normally-distributed ones on the elasticity of rocks obtained by statistical nanoindentation, and three lognormally-distributed ones on the particle size distributions of flocculated clay suspensions, were used to illustrate the BSI's concepts and algorithms. While results from the synthetic datasets prove the method's accuracy and effectiveness, analyses of other real datasets from materials characterization and measurement further demonstrate its rationale, performance, and applicability to practical problems. The BSI method also enables determination of the number of modes via the comparative evaluation of the errors returned from different trial bin sizes. The accuracy and performance of the BSI method are further compared with other widely used binning methods, and the former yields the highest BSI and smallest normalized standard errors. This new method particularly penalizes the overfitting that tends to yield too many pseudo-modes via normalizing the errors by the number of modes hidden in the datasets, and also eliminates the difficulty in specifying criteria for acceptable values of the fitting errors. The advantages and disadvantages of the new method are also discussed.

Mechanism of Rake Frame Shear Drainage during Gravity Dewatering of Ultrafine Unclassified Tailings for Paste Preparation

To study the mechanism of reverse percolation and drainage of unclassified tailings, improve the disposal concentration of tailings and solve the bottleneck in the development of filling technology, this study performed semi-industrial flocculation and sedimentation tests using macroscopic continuous thickener tests and a self-developed continuous thickener test platform to observe the evolution pattern and formation mechanism of unclassified tailings flocs. Then, in situ sampling was performed on the compressed thickener zone of tailings at the bottom of the bed with the help of industrial CT scanning tests and 3D images. Avizo software was used to establish the seepage channels and construct an evolutionary model to analyze the effect of tailings dewatering and concentration on tailings concentration from a microscopic perspective. The study shows that the distribution of seepage channels is closely related to the height of the bed. As the bed height increases, the bed concentration increases; shear has a significant effect on the water flow inside the pore space. After shear, the water between the sample pores has been discharged. Therefore, the flow rate is relatively slow. Shear produces pressure and tension effects, breaking the static equilibrium between flocs and water forming seepage channels. Shear can effectively break the floc structure and release the water so that the mutual position between flocs and water constantly changes, The concentration of the tailings bed is increased.

Influence of Zwitterionic CAPB on Flocculation of the Aqueous Cationic Guar Gum/Glauconite Suspensions at Various pH

The influence of the pseudoamphoteric zwitterionic surfactant cocamidopropylbetaine (CAPB) on the stabilizing flocculating properties of the aqueous suspensions of glauconite (GT) with cationic guar gum (CGG) at various pH values was investigated. The following techniques were used: turbidimetry, UV-VIS spectrophotometry, tensiometry, electrophoretic mobility measurements, SEM, CHN, XRD, and FT-IR. It was established that CGG is an effective glauconite flocculant. Moreover, the most probable mechanism that is responsible for flocculation is bridge flocculation resulting from polymer adsorption on the glauconite surface. The adsorption process is caused by electrostatic interactions between the negatively charged glauconite surface and the positively charged polymer. The amount of CGG adsorption increases with the increase of the pH, which was confirmed by the adsorption and zeta potential measurements. The addition of CAPB increases the amount of the polymer adsorption due to the formation of intermolecular polymer–surfactant complexes; however, it reduces flocculation effectiveness.

Chain conformation of polymers adsorbed to clay particles: effects of charge and concentration

High molecular weight polymers are used in industrially important applications where the polymers adsorb onto surfaces of inorganic particles and facilitate dispersion, stabilization or flocculation of formulations. The surface conformation of these adsorbed polymers is key to their performance, yet an understanding of the effects of polymer charge, concentration and molecular weight on polymer conformation is incomplete. Here the adsorption behavior of high molecular weight, non-ionic, polyethylene oxide (PEO) and anionic partially hydrolyzed polyacrylamide (HPAM) polymers to a model clay, LAPONITE® (a trademark of BYK Additives, Inc.), was studied by small angle neutron scattering over a range of polymer concentrations. The adsorption of PEO was dependent on polymer concentration at all molecular weights, first adsorbing onto the radial edge of the clay particles and then to the clay faces as polymer concentration increased. While similar behavior was observed at low concentrations of HPAM, above a critical concentration, HPAM desorption results in large clay aggregates, which decrease in size at higher polymer loadings. The difference in adsorption properties as a function of polymer charge and concentration is interpreted in terms of conformational differences of adsorbed polymer at the clay surface. Changes in the volume fraction of adsorbed PEO with polymer concentration indicate changes in the relative amounts of adsorbed chain segments in trains, loops and tails, with no clay aggregation. In contrast, a constant volume fraction of adsorbed HPAM at low concentrations gives way to desorption at higher concentration due to charge repulsion, and depletion aggregation of the clay.

Ionic strength and polyelectrolyte molecular weight effects on floc formation and growth in Taylor-Couette flows

Polyelectrolyte-driven flocculation of suspended particulate in solution is an important process in a variety of industrial processes such as drinking water treatment and composite material synthesis. Flocculation depends on a wide variety of physicochemical and hydrodynamic properties, which affect floc size, growth rate, and floc morphology. Floc formation and growth behavior is explored here using two different molecular weights of a cationic polyacrylamide flocculant and anisotropic Na-bentonite clay particles under a variety of solution ionic strengths. A Taylor-Couette cell with radial injection capabilities was used to study the effects of solution ionic strength and polyelectrolyte molecular weight on floc size, growth rate, and floc morphology during the flocculation process with a constant global velocity gradient. The floc size generally decreased with increasing ionic strength whereas the floc growth rate initially increased then decreased. This likely occurred due to charge screening effects, where increased bentonite aggregate size and a less expanded polyelectrolyte conformation at higher ionic strengths results in a decreased ability for the polyelectrolyte to bridge multiple bentonite aggregates. The densification of bentonite aggregates at higher ionic strengths resulted in floc morphologies that were more resistant to shear-induced breakage. With the exceptions of optimal dose concentration and dispersion coefficients, there were no clear differences in the floc growth rate behaviors for the two molecular weights studied. This work contributes to an improved understanding of the physicochemical complexities of polyelectrolyte-driven flocculation that can inform dosing requirements for more efficient industrial operations.

In situ polymer flocculation and growth in Taylor-Couette flows

Flocculation of small particulates suspended in solution is a key process in many industries, including drinking water treatment. The particles are aggregated during mixing to form larger aggregates, known as flocs, through use of a polyelectrolyte flocculant. The flocculation of these particulates in water treatment, however, are subject to a wide spatial variation of hydrodynamic flow states, which has consequences for floc size, growth rate, and microstructure. Floc assembly dynamics are explored here using a commercially available cationic polyacrylamide, commonly used in water treatment, and anisotropic Na-bentonite clay particles under a variety of hydrodynamic mixing conditions. A Taylor-Couette cell with the unique ability to radially inject fluid into the rotating annulus was used to study how specific hydrodynamic flow fields affect assembly and structure of these materials during the flocculation process. Faster floc growth rates and decreased floc fractal dimensions were observed for higher order flow states, indicating improved mass transfer of the polymer flocculant and breakage at the edges of the flocs (shear rounding), respectively. This work sheds more light on the complexities of polymer-induced flocculation, towards improving dosing and efficiency of large-scale operations.