Cross-linking of Li-montmorillonite by hydroxy-aluminum oligomers was performed in a specially constructed mixing apparatus. Observations on flocculation and solution composition were carried out during and after the cross-linking reaction; the dry product was studied by scanning electron microscopy.

Flocculation was most pronounced at Al/montmorillonite ratios between 0.98 and 2.45 mM/g; below and above this range, flocculation was much less intensive. These observations can be explained by heterocoagulation and protecting colloid action. A complete neutralization of the montmorillonite charge was estimated at 1.9 mM adsorbed Al per g clay, and in order to account for the electrical charge of the hydroxy-Al, polymers with an average charge of 0.5 per Al atom must be assumed on the montmorillonite surface. Assuming that the hydroxy-aluminum form in the unreacted solution is Al6(OH)3+12, the adsorbed polymer will be Al24(OH)12+60. Alternatively, assuming Al6(OH)3+15 in the unreacted solution, this form will remain unchanged upon adsorption onto the montmorillonite surface.

Differences in the microfabric of dry Al-CLM as a function of Al/montmorillonite ratio can be explained along the lines of the interpretation of the flocculation studies.

The effect of pH on the flocculation-dispersion behavior of noncrystalline aluminum and iron oxides, kaolinite, montmorillonite, and various mixtures of these materials was investigated. The clays were Na- or Ca-saturated and freeze-dried before use. Critical coagulation concentrations (CCC) of all materials and mixtures were found to be pH dependent. The Al oxide was flocculated at pH >9.5 and the iron oxide was flocculated between pH 6.0 and 8.2; i.e., flocculation occurred at pHs near the point of zero charge (PZC). The CCC of both the Na- and Ca-clay systems increased with increasing pH. The effect of pH was greater for the Na-kaolinite (flocculated at pH 5.8 and having a CCC of 55 meq/liter at pH 9.1) than the Na-montmorillonite system (having a CCC of 14 meq/liter at pH 6.4 and a CCC of 28 meq/liter at pH 9.4). A 50/50 mixture of Na-kaolinite and Na-montmorillonite behaved more like montmorillonite (having CCCs of 13 and 33 meq/liter at pH 6.2 and pH 9.0, respectively). The presence of either noncrystalline oxide decreased the CCC over that of the clay(s) alone; the decrease occurred at pHs >7 for Al oxide and at pHs >6.5 for Fe oxide. Aluminum oxide produced a greater decrease in CCC than Fe oxide, especially at pHs >8. The effect of each oxide on CCC was greatest near the PZC, 9.5 and 7.2 for Al and Fe oxide, respectively.

Novel modified clay adsorbents were prepared by blocking cation-exchange sites of an expandable clay, such as montmorillonite, with polymeric or polyvalent inorganic ions and by using cationic surfactants as sources of surface organic carbon. Electrokinetic measurements demonstrated that the adsorbed polycations were essentially nonexchangeable. Adsorption and desorption experiments revealed that about 90% of the cationic surfactant was apparently irreversibly bound to the surface. Flocculation and peptization studies were performed to establish that the adsorbed surfactant moiety was oriented with its hydrocarbon tail towards the surface. Such a configuration of simultaneously adsorbed polycations and cationic surfactants was designated as an inorgano-organo-clay (IOC). As shown in an accompanying paper, these IOCs bind priority pollutants as strongly as granulated activated carbon.

The influence of added sodium and calcium nitrate electrolyte on the particle aggregates in the colloid fraction of natural bentonite and kaolin was studied. Clays were flocculated in distilled water and various electrolyte concentrations. Aggregate size was studied by sedimentation analysis; the mean radius of the aggregates was plotted against the concentrations of Na+ and Ca2+. For bentonite, the mean radii decreased with an increase of Na+ and Ca2+ concentration, reaching a minimum; and further increases in concentration led to an increase of the mean radii of the aggregates. For kaolin, an increase in Na+ and Ca2+ concentration gave rise to an increase in the mean radii of aggregates.

Scanning electron micrographs showed different types of aggregates, depending on the physico-chemical conditions of a sedimentation process. In bentonite and kaolin sediments formed from a distilled water slurry, the dominant aggregate was an edge-face type. The small addition of salts to a bentonite slurry led to the formation of edge-edge-type aggregates; for kaolin edge-face-type aggregates formed, although within the microaggregate face-face associations were observed. The highest concentrations of electrolytes for sediments of both clays led to formation of compact, face-face-type aggregates.

Kaolin floc structures of commercial utility are produced by adsorption of hexamethylenediamine. These flocs are largely face-to-face structures with small diameter platelets of colloidal kaolinite aggregated on larger platelets of kaolinite and muscovite. Because of its higher charge density, muscovite is more effective than kaolinite in scavenging colloidal particles.

Although earlier workers have been at odds as to where amines adsorb on kaolinite, the present work indicates that both edge and basal surfaces are involved. Evidence for this contention is two-fold: (1) Face-to-face and edge-to-face flocculation of hexamethylenediamine kaolins has been observed. (2) Polyesters have been observed adsorbed on basal and edge surfaces of ethylenediamine-treated kaolins.

The mechanism by which kaolinite particles are bonded together into floc structures is unclear. Bridging by hexamethylenediammonium ions is a probable mechanism up to satisfaction of the cation-exchange capacity; further amine addition continues to promote flocculation. From this observation it is inferred that, in addition to bridging, hydrogen bonding and, perhaps, van der Waals forces are instrumental in floc formation. Although rheologically inferior to the untreated equivalent, these chemically induced flocs of kaolinite provide loosely packed, randomly oriented structures in paper coatings. Improved brightness, opacity, and printability of paper coatings arise from this structure.

Water-infiltration characteristics of soil can be improved by preventing clay dispersion. The present study determined the adsorption properties of hydroxy-Al polycations (Al-p) and their relation to the destabilization of clay suspensions. Al-p was synthesized and fractionated into nominal molecular weights between 104 and 5 × 104. The reactions of Al-p with Na-illite and Na-montmorillonite indicated a very strong affinity of Al-p to the clay surfaces. The maximum adsorptions of Al-p by Na-illite and Na-montmorillonite were found to be 0.37 and 1.7 mmole Al/g, and very close to the cation-exchange capacity of the two clays, suggesting that the adsorption was chiefly controlled by the mechanism of charge screening. Adsorption of Al-p increased the points of zero charge (PZCs) and the apparent points of zero salt effect (PZSEs) of illite and montmorillonite. PZSEs for both clays were 4.7 at their maximum Al-p adsorption, and PZCs ranged from 5.3 to 6.4, depending on solution ionic strength and the individual clay minerals. The differences in PZCs were probably due to outer-sphere complex formation between Al-p-treated illite and montmorillonite and the swamping electrolyte. Critical flocculation concentrations (CFCs) of Al-p for Na-illite and Na-montmorillonite were at 0.28 and 1.0 mmole Al/g, whereas zero electrophoretic mobilities were at about 0.36 and 1.67 mmole Al/g Al-p additions. Excessive addition of Al-p reversed this surface charge of clay colloids and restabilized the illite but not montmorillonite suspensions. This difference was probably due to the stronger and more extensive interparticle bridging of montmorillonite particles by Al-p than those of illite. The CFCs for the two clays were also found to be dependent on sodium adsorption ratio (SAR), pH, and ionic strength. Increases in SAR and pH significantly increased the CFC, whereas an increase in ionic strength decreased the CFC.

The Porters Creek Formation is mined as an absorbent clay in Illinois, Mississippi, Missouri, and Tennessee. The absorptive properties of the Porters Creek Formation are due to the high content of smectite which constitutes >50% of the minerals present. Analyses of 220 samples of the Porters Creek collected in Illinois, Missouri, and Tennessee indicate that the smectite content is highest on the western side of the Mississippi embayment and that the kaolinite content is highest on the northeastern side. The major influx of detritral clays appears to have entered the embayment from a large river on the northeast side. A major control of the distribution of clay minerals during the time of Porters Creek deposition was differential flocculation of kaolinite, illite, and smectite, as evidenced by the numerous syneresis cracks on bedding planes in the area of greatest kaolinite content. Estimates of the smectite, illite, and kaolinite contents suggest both horizontal and vertical variations among these clay minerals. In certain localities the oxidation of pyrite has created acid conditions, which apparently were conducive to the formation of authigenic halloysite.

Currently, two commercial plants, operating in the Athabasca region of Alberta, produce approximately 20 percent of Canada's petroleum requirements from oil sands. Surface mined oil sand is treated in a water based separation process that yields large volumes of clay tailings with poor settling and compaction characteristics. Clay particles, suspended in the pond water, interact with salts, dissolved from the oil sands ore, to produce mature fine tailings (MFT) containing only 20 to 50 w/w% solids. As a result, large sedimentation ponds are required to produce enough process water to recycle for the plant. Tailings pond dykes can only be constructed during a short summer season. Consequently, the capability to predict production rate and final volume of MFT is essential for mine planning and tailings disposal operations.

Previous research has demonstrated that a small fraction of nano sized clay particles (20 to 300 nm) effectively controls the bulk properties of MFT. These particles are present in the original ore and become mobilized into the water phase during the oil separation process. In this work, the nano sized particles have been separated from the bulk tailings and subjected to a fundamental study of their flocculation behavior in model tailings water.

Photon correlation spectroscopy and a deuterium NMR method were used to follow particle flocculation and gelation processes. These results were correlated with particle settling data measured under the same conditions. It was determined that the nano particles form fractal flocs that eventually interact to give a thixotropic gel. The ultimate sediment volume produced is almost entirely dependent on the original concentration of nano particles while the rate of water release is governed primarily by electrolyte concentration.

Testing shows that many of the present commercially available bentonite products used for clay liner/soil sealant applications may be susceptible to chemical degradation by certain contaminants. Testing also confirms that a recently developed contaminant resistant clay (CRC) is resistant to various contaminants that would otherwise attack and degrade the present commercially available products. The tests that were used to determine its effectiveness were American Petroleum Institute (API) fluid loss, rigid wall hydraulic conductivity, flexible wall hydraulic conductivity and a newly developed top loading filter press (TLFP) test (LSK method).

Fine kaolinite suspensions were mixed with unaged or aged FeCl3 in this experiment. The interaction between clay particles and Fe3+ hydrolysis products was studied by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The proportion of Fe adsorbed was measured and the electrical charge on the clay particles was determined by electrophoresis. The effect of this interaction on flocculation of clay suspensions was investigated in a series of sedimentation tests. The Fe3+ ions acted as counterions when their concentration was low and when unaged FeCl3 solution was used. Otherwise, their hydrolysis complexes acted as a bonding agent between kaolinite particles. The dispersion-flocculation behavior of kaolinite suspensions was found to be in agreement with the theory of Derjaguin, Landau, Verwey and Overbeek (DLVO), as the sedimentation behavior could be predicted from the data of zeta potentials (ζ).

SiO2 sols were made unstable by addition of Ca2+ ions. The resulting states of instability were classified as gelation, flocculation, and precipitation by means of observation, by checking the Tyndall effects on the supernatant or suspending solution, as appropriate, and by measuring the apparent densities of flocculated mass. The concentrations of free Ca2+ ions left in solution were measured by means of a Ca2+ ion selective electrode. The amounts sorbed onto SiO2 particles were then calculated by material balance. It was found that while the amount sorbed dictates the limit of stability, the SiO2 concentration in the mixture is an important factor deciding the state of instability. Depending on the SiO2 concentration, there were two distinct flocs with the apparent floc density of 6 ± 1 and 12 ± 1 mg SiO2/ml.

The objective of this study was to observe flocculation of montmorillonite in the presence of a glucose polymer (dextran) and to observe the effect of saturating cation and coagulant addition on the flocculation process. Flocculation of montmorillonite was dependent on polymer molecular weight, polymer/clay ratio (w/w), nature of exchangeable cation, and ionic strength of the suspension to which the polymer was added. The T500 dextran (molecular weight = 5 × 105) caused enhanced sedimentation of Ca-montmorillonite suspension at a polymer/clay ratio of ≤0.01. Increasing the polymer concentration above this level stabilized the suspension such that sedimentation was less than or equal to that of the control. The T2000 dextran (molecular weight = 2 × 106) caused a similar increase in the sedimentation of Ca-montmorillonite at polymer/clay ratios of <0.1. The ability of the T2000 polymer to cause flocculation at greater polymer/clay ratios as compared to the T500 polymer was attributed to the lower osmotic pressure between clay particles for equal concentrations of the two polymers. Flocculation of Ca-montmorillonite by dextran was enhanced when the clay had initially been coagulated by the addition of salt. Reduction of the diffuse double layer upon addition of salt permitted the polymer to extend beyond the electrostatic barrier of the clays. Dextran was not able to flocculate Mg-montmorillonite suspensions with or without the presence of coagulant. The displacement of water molecules at the clay surface rather than within the hydration shell of the more highly polarizing Mg cations by polymer segments resulted in a greater polymer collapse on the clay surface leaving fewer and shorter polymer loops and tails available for contacting adjacent clay particles.

The sedimentation behavior of a fine kaolinite, comprising a substantial proportion of colloidal particles as well as non-colloidal ones, has been studied when fresh FeCl3 or F2(SO4)3 electrolytes are added. The sedimentation behavior depends on the pH and the nature of electrolytes and can be explained qualitatively, in our study, by the theory of Derjaguin, Landau, Verwey, and Overbeek (DLVO theory). Fe helps also to aggregate the kaolinite particles in flocs. Two extreme kinds of qualitative sedimentation have been observed: flocculation-sedimentation and accumulation-sedimentation. However, the transition between the two kinds of sedimentation is quite progressive. The present results are discussed in reference to the DLVO theory and the hydrolysis behavior of Fe electrolytes.

The colloidal state (stable, coagulated, or gel-like) and the rheological properties of Na-rich montmorillonite (Wyoming) dispersions are strongly influenced by organic cations. This effect is shown for homologous organic cations: alkyl trimethylammonium ions, paraquat, diquat, alkyl bispyridinium ions, and the triphenylmethane dyes crystal violet, methyl green, and tris (tri-methylammonium phenyl) methane chloride. The critical coagulation concentrations, cK, are small (often < 1 mmol/L) because the cations are enriched in the Stern layer and influence the solvent structure near the surface. The strong adsorption of the counterions at the clay-mineral surface causes cK values to increase with the solid content. Charge reversal (recharging) of the particles was observed with the longer chain alkyl trimethyl-ammonium ions, dodecyl bispyridinium ions, and crystal violet. Other cations reduced the electrophoretic mobility to zero but positive particle charges were not observed.

The plastic viscosity increased sharply at the critical coagulation concentration and showed a minimum slightly below cK, which was caused by the electroviscous effect. Yield values were developed at concentrations above cK. In most cases, yield values reached a plateau where the amount of organic cations was ∼0.5 mmol/g, i.e., about half of the cation-exchange capacity. The cK values decreased with increasing hydrophobicity of homologous compounds, but the yield value showed maxima at intermediate chain lengths. The yield value of several 0.5% dispersions was high, e.g., dodecyl trimethylammonium ions, 71 Pa; paraquat, 100 Pa; diquat, 42 Pa; hexyl bispyridinium ions, 53 Pa (vs. Ca2+, 0.2 Pa; Al3+, 0.7 Pa). The storage modulus as a function of the number of organic cations changed in a similar way as the yield value, and high values were observed (e.g., dodecyl trimethylammonium ions, hexyl bispyridinium ions: 1000 Pa, paraquat: >4000 Pa). Thus, dispersions with high viscosity, yield value, and pronounced viscoelasticity are obtained by coagulating Na-rich montmorillonite dispersions with organic cations.

The degree of flocculation of aqueous suspensions of microcrystalline goethite was measured in salts of monovalent, divalent and trivalent cations at pH 6.0–6.5 over a range of ionic strengths using light scattering measurements at 650 nm. Varying concentrations of soluble humic material as well as the organic ligands, salicylate and citrate, were tested for their effect on flocculation. It was found that KCl and NaCl induced flocculation at lower ionic strength than CaCl2, while AlCl3 favored dispersion at all ionic strengths tested. The simple organic ligands promoted flocculation at low concentration, with citrate having a more pronounced effect than salicylate. At higher concentrations, these ligands reversed their effect, inducing a more dispersed state of the oxide. The organic ligand effect on dispersibility was modified by the particular metal cation present, with Ca2+ being more conducive to flocculation than K+. Soluble humic materials affected goethite flocculation in a qualitatively similar way to that of the simple organic ligands, that is low concentrations favored flocculation while high concentrations induced dispersion. This dispersing effect was partially suppressed by the presence of Ca2+, and completely suppressed by Al3+. Thus, soluble humic substances at relatively high concentrations appear to have a marked dispersing effect on goethite in the absence of polyvalent cations, and a strongly flocculating effect in their presence.

The results can be explained qualitatively by a simple oxide surface charge model, in which chemi-sorption of multivalent cations or organic ligands alters the surface charge. Reactions that increase the magnitude of positive or negative surface charge favor dispersion, while those that reduce the magnitude of charge favor flocculation.

This study was undertaken to investigate the changes in flocculation properties of Fe-rich smectite (nontronite, NAu-1) suspensions, including settling velocity, aggregate size and floc architecture associated with microbial Fe(III)-reduction in the smectite structure. The dissimilatory Fe-reducing bacterium Shewanella oneidensis MR-1 was incubated with lactate as the electron donor and structural Fe(III) as the sole electron acceptor for 3, 12, 24 and 48 h in an anaerobic chamber. Two controls were prepared; the first was identical to the experimental treatments except that heat-killed cells were used (non-reduced control), and the second control was the same as the first except that the incubation was carried out in an aerobic environment. The extent of Fe(III) reduction for the 48 h incubation was observed to reach up to 18%. Neither the non-reduced control nor the aerobically inoculated sample showed Fe(III) reduction. Compared with the non-reduced control, there was a 2.7 μm increase in mean aggregate size and a 30-fold increase in average settling velocity in the bioreduced smectite suspensions as measured using a Micromeritics Sedigraph®. The aerobically inoculated smectite showed a similar aggregate-size distribution to that of the non-reduced control. Significant changes in physical properties of smectite suspensions induced by microbial Fe(III) reduction were measured directly using transmission electron microscopy. The floc architecture of bioreduced smectite revealed less open structures compared to those of a non-reduced control. The aspect ratio (thickness/length) of individual smectite particle increased from 0.11 for the non-reduced control to 0.18 on average for the bioreduced smectite suspensions. The effects of pH on the clay flocculation were minimal in this study because the value of pH remained nearly constant at pH = 7.0–7.3 before and after the experiments. We therefore suggest that the increase in net negative charge caused by microbial Fe(III) reduction significantly promoted clay flocculation by increasing the electrochemical attraction in the smectite suspensions.

A major issue for the oil sand industry is the settling of thin fine tailings (TFT) which are a byproduct of the oil sand extraction process. These tailings are deposited in large ponds and settling takes decades. The aim of the present study was to increase understanding of the role of specific ion types (monovalent/divalent) present in the water in flocculation behavior, and hence the settling of flotation fine tailings of the Athabasca oil sands (which consist predominantly of kaolinite). In this study, two series of measurements were conducted and compared: one with TFT and with varying pH and salinity, and another with kaolinite suspensions with varying pH, salinity, and volume fraction. The volume fraction of kaolinite and TFT used was in the range 0.01–1% volume fraction for any ionic strength or ion. In this range the electrophoretic mobility was constant indicating that there were no particle-particle interactions, a required condition for electrophoretic mobility measurements. Electrokinetic measurements were made as a function of concentration of salt added and pH. The flocculation behavior of both TFT and kaolinite can be linked to the electrokinetic mobility at high ionic strength. The electrophoretic mobility values and therefore the electrokinetic charge of the particles were smaller for divalent salt than for monovalent salt. As a consequence, both kaolinite and fine tailings should and do flocculate more quickly in the presence of a divalent electrolyte during settling-column experiments. The electrophoretic mobility of kaolinite and tailings in electrolytes containing a majority of monovalent ions (NaCl) decreased in absolute values with decreasing pH while their electrophoretic mobility in electrolytes containing a majority of divalent ions (MgCl2) did not depend on pH. The flocculation of the fine tailings in an electrolyte where divalent ions are predominant is therefore not expected to be influenced by pH.

Particle concentration, charge, solution chemistry (i.e. ionic strength), and the nature of organic matter (OM) are the major factors controlling particle flocculation in aqueous environments. In the present study, the nature of clay fabric associated with clay—OM interaction at a range of ionic strengths was the focus. In the flocculation experiments, the aqueous suspension of montmorillonite and chitin was mixed with NaCl/MgSO4 electrolyte solution. Advanced sample-preparation techniques and visualization methods using transmission electron microscopy were used to observe directly the micro- and nano-scale clay—OM fabric of the resulting flocs. Such direct observation elucidated the role of OM in clay flocculation; few attempts have been made in the past due to the technical difficulties in preserving the original structure. A comparison of clay fabric at two different ionic strengths of 0 and 0.14 M revealed that the individual hexagonal clay particles settled slowly with little intra-aggregate void space (void ratio: 0.07) at 0 M while rapid flocculation and settling of clay particles at 0.14 M, with or without OM, resulted in a more open fabric with greater void space (void ratio: 0.33). The silver-staining technique demonstrated effectively the location of electron-transparent chitin in montmorillonite aggregates. Chitin appeared to link the face-to-face (FF) contacts of clay domains by bridging between negatively charged face surfaces. However, the resultant void ratio and the average hydrodynamic diameter (dH) values were lower than in the OM-free system after flocculation. The results indicated that the interplay between ionic strength and OM content affected the floc architecture and void ratio.