Kaolin Slurry Research Articles

Stokes layers in complex fluids

Stokes’s second problem is reconsidered for three models of complex fluids: an elasto-viscoplastic fluid, a thixotropic viscoplastic fluid and a discontinuously shear-thickening fluid. In each case, the Stokes-layer dynamics is interrogated with a view to examining the signatures of the detailed rheology. Significant deformations are possible below the yield stress for elasto-viscoplastic fluids as a result of the excitation of elastic waves, particularly near resonances. Thixotropic fluids with viscosity bifurcations layer internally, but surface-speed signatures mostly appear similar to those for simple yield-stress fluids. Stokes-layer oscillations of discontinuous shear thickening fluids can prompt abrupt increases in viscosity, introducing sudden jumps in surface speed. Pre-existing experimental results for layers of kaolin slurries in a motorized, oscillating tray are reconsidered and compared with the results for elasto-viscoplastic and thixotropic fluids.

Corrosion Behavior of 30 ppi TAD3D/5A05Al Composite in Neutral Salt Spray Corrosion

This study created ceramic preforms with a 3D network structure (TAD3D) by using treated aluminum dross (TAD) and kaolin slurry, with 30 ppi polyurethane foam as a template via the sacrificial template method. TAD3D/5A05Al composites were then produced via pressureless infiltration of 5A05Al aluminum alloy into TAD3D. The corrosion behavior and resistance of TAD3D/5A05Al in salt spray were assessed via neutral salt spray corrosion (NSS), scanning electron microscopy (SEM), potentiodynamic polarization (PDP), and electrochemical impedance spectroscopy (EIS) tests. The results showed that after 24 to 360 h of NSS corrosion, the corrosion of the 5A05 matrix was primarily pitting, with pits expanding and deepening over time, and showing a tendency to interconnect. The main corrosion products were MgAl2O4, Al(OH)3, and Al2O3. As corrosion progressed, these products increased and filled cracks, pits, and grooves at the composite interface on the material’s surface. Corrosion products transferred to the grooves at the composite interface and grew on the ceramic surface. Corrosion products on the ceramic framework and the Al matrix can form a continuous passivation film covering the composite surface. PDP and EIS results indicated that the composite’s corrosion resistance decreased by 240 h but increased after that time. After 240 h, the surface passivation film can weaken corrosion effects and enhance the composite’s resistance, although it remained weaker than that of the uncorroded samples. Additionally, grooves at the composite interface deepened over time, with loosely structured corrosion products inside, potentially leading to severe localized corrosion.

Flocculation and dewatering of the Kaolin slurry treated by single- and dual-polymer flocculants

To mitigate the sudden increase in the production of waste engineering slurry, predominantly composed of Kaolinite, this study investigated the flocculation and dewatering of Kaolin slurry treated with single- and dual-polymer flocculants. The influence of the flocculant type and dosage, under single- and dual-dose conditions, on slurry's sedimentation and the filtration characteristics, were thoroughly discussed. The results reveal that the adsorption bridging of the polymeric flocculant, resulting from hydrogen bonds, exerts a more significant effect than electrical neutralization on forming a large floc. Under single-dose conditions, nonionic polyacrylamides (NPAMs) with the strongest adsorption bridging leads to biggest flocs and the maximum settling rate of 21.55 mm/s. Under the dual-dose conditions of polymeric aluminium chloride (PAC) and PAM, the size of the slurry's floc decreases with an increase in PAC dosage. Nevertheless, the filtration performance of the slurry improves, with the lowest SRF value of the flocculated slurry being 1.58 × 1011 m/kg as 3‰ PAC and 3‰ NPAM is dosed. The improvement is explained by the micro-pore distribution of sludge. According to Mercury intrusion porosimetry (MIP) test, the slurry treated with the optimal dosage of dual-polymer flocculant exhibits the greatest sludge pore size and connected porosity (with a maximum value of 20.99%). Furthermore, the study discusses and compares the flocculation mechanism of single- and dual-polymer flocculants. The obtained results provide guidance for selecting appropriate flocculants for dewatering inorganic slurries, using different dewatering methods, such as gravitational thickening or filter pressing.

Compressive Yield Stress of Flocculated Kaolin Suspensions in Seawater.

The mining industry has resorted to using seawater while trying to find a solution to the water shortage, which is severe in some regions. Today, the industry looks to tailings dams to recover more water and, thus, increase recirculation. The migration of interstitial water due to the consolidation of particle networks can give rise to large water mirrors in different dam areas. These pools can contain enough water to be recovered and recirculated if the external stress caused by the weight of the pulp exceeds the compressive yield stress. The density and rheological properties of the discarded pulps determine the feasibility of water expulsion during tailings consolidation. As these conditions are largely established in the thickening stage, it is necessary to revisit operations, looking at the dam as a water source. Thus, a thorough understanding of the compressive properties that determine the level of consolidation of typical pulps and their relationships to aggregate properties, such as size and fractal dimension, is crucial. Here, the effect of two types of water, industrial water and synthetic seawater, on kaolin flocculation, sedimentation rate, yield stress, and compressive yield stress were studied. In addition, the relationship of these properties with the flocculant dose and the resulting aggregate size and fractal dimension was examined. One promising finding to practitioners was that salt and small doses of high molecular weight flocculant improved the consolidation of kaolin slurries under compression. These conditions generated low compressive yield stress compared to fresh water and water with low salt content, favoring the consolidation of the pulps and the release of water.

Dewatering Characteristics of the Kaolin Slurry Treated by Single and Dual Polymer Flocculants

Dewatering Characteristics of the Kaolin Slurry Treated by Single and Dual Polymer Flocculants

Use of Multi-Anionic Sodium Tripolyphosphate to Enhance Dispersion of Concentrated Kaolin Slurries in Seawater

This research aims to analyze the impact of sodium tripolyphosphate (STPP) as a rheological modifier of concentrated kaolin slurries in seawater at pH 8, which is characteristic of copper sulfide processing operations. The dispersion phenomenon was analyzed through chord length measurements using the focused beam reflectance measurement (FBRM) technique, complementing size distributions in unweighted and square-weighted modes. The reduction of the rheological properties was significant, decreasing from 231 Pa in a reagent-free environment to 80 Pa after the application of STPP. A frequency sweep in a linear viscoelastic regime indicated that by applying a characteristic dosage of 0.53 kg/t of STPP, the pulp before yielding increases its phase angle, which increases its liquid-like character. Measurements of the chord length verified the dispersion of particles, which showed an apparent increase in the proportion of fine particles and a reduction of the coarser aggregates when STPP was applied. Measurements of the zeta potential suggested that the high anionic charge of the reagent (pentavalent) increases the electrostatic repulsions between particles, overcoming the effect of cations in seawater. The results are relevant for the mining industry, especially when the deposits have high contents of complex gangues, such as clays, that increase the rheological properties. This increases the energy costs and water consumption needed for pumping the tailings from thickeners to the tailing storages facilities. The strategies that allow for the improvement of the fluidity and deformation of the tailings generate slack in order to maximize water recovery in the thickening stages.

Corrosion Protection of Copper Foil by Ni-W Electrodeposited Coating in Kaolin Slurry

Corrosion Protection of Copper Foil by Ni-W Electrodeposited Coating in Kaolin Slurry

Temporal evolution of the structure of tailings aggregates flocculated in seawater

Mineral processing produces large volumes of dilute tailings that are flocculated and thickened, returning water to the process. The drive towards more sustainable processing has seen seawater considered to replace fresh water usage and an increased focus on how flocculation conditions can influence the fractal-like aggregates formed. The fragility of such structures and the likelihood that they change with time makes their study challenging.A synthetic tailings slurry of quartz and kaolin in seawater was flocculated at different mixing times and flocculant dosages, with aggregate size monitored over time by focused beam reflectance measurement (FBRM) and hindered settling rates determined after set reaction times. A model relating hindered settling rate to size as estimated by FBRM was used to derive an aggregate fractal dimension (Df) at each time. With flocculation at typical tailings solids concentrations rapid, aggregate breakage will normally dominate after very short reaction times. Under mild mixing conditions, settling rates are higher than expected from sizes measured in real time due to aggregate growth continuing after mixing ceases, leading to inflated Df estimates. An apparent decline in Df under more intense mixing was consistent with an increased presence of high aspect ratio (low effective porosity) aggregate fragments, supported by in situ aggregate imaging at different reaction times. In contrast, the observed trends for a reduction in Df with mixing intensity and an increase with dosage are both thought to represent the expected aggregate structure changes for the synthetic tailings.While estimating aggregate structural properties by relating FBRM sizes to settling rates can offer useful insights, it is important to recognise the aggregation state observed by FBRM under mixing applied to induce flocculation may differ from that which exists during hindered settling. Values of Df derived in this manner must therefore be viewed with caution.

Analysis of Kaolin Flocculation in Seawater by Optical Backscattering Measurements: Effect of Flocculant Management and Liquor Conditions

Optical backscattering (OBS) signal values were used to evaluate the flocculation of kaolin slurries and seek the implications of using seawater. Two anionic flocculants were applied to kaolin suspensions at several dosages and in water of varying pH and electrolyte concentration. An OBS height scan method was used to estimate the degree of aggregation, supernatant quality, and solids concentration of the sediments. The residual solids of the supernatant depended of the extent of particle coagulation before flocculant was added, where the pH and salinity displayed a significant impact on flocculation. The OBS results were highly sensitive to the presence of fine particles, which was estimated in parallel from the focused beam reflectance measurements (FBRM.) In seawater, without flocculant added, the samples had increased root-mean-square scattering (Frms) values and larger final sediment volume than samples prepared in water with lower electrolyte concentration. This indicates a higher initial state of aggregation of the particles in seawater. Then, the aggregation degree was best linked to the square-weighted chord length distribution of the FBRM data, which intensifies the sensitivity to coarse aggregates.

Enhanced Flocculation Efficiency in a High-Ionic-Strength Environment by the Aid of Anionic ABA Triblock Copolymers.

The flocculation efficiency of polyelectrolytes in a high-ionic-strength environment is often affected and reduced due to shielding of the active ionizable functional groups, as well as changes in the surface chemistry of the solid slurry. To address this problem, a series of well-defined novel ABA triblock copolymers were employed for the flocculation of high-ionic-strength kaolin slurries at three different Ca2+ concentrations (0.05, 0.10, and 0.50 M). The primary focus was on the advancement in the polymer architecture, where the anionic functionalities were localized at the terminal ends. Typical commercial flocculants tend to have anionic functionalities randomly distributed throughout the polymer chain and hence a higher propensity toward condensed conformation and formation of insoluble species. In comparison to a control random copolymer, the ABA triblock copolymers were able to flocculate kaolin slurries to give faster settlement rates, particularly at the high Ca2+ concentrations of 0.10 and 0.50 M. In addition, these polymers had significantly better clarification ability at higher Ca2+ concentrations compared to the control random copolymer. The ABA triblock copolymer architecture may therefore have potential as a flocculant in high-ionic-strength applications.

Viscoelasticity of Quartz and Kaolin Slurries in Seawater: Importance of Magnesium Precipitates

In this study, the viscoelastic properties of quartz and kaolin suspensions in seawater were analysed considering two distinct conditions: pH 8 and 10.7. Creep and oscillatory sweep tests provided the rheological parameters. An Anton Paar MCR 102 rheometer (ANAMIN Group, Santiago, Chile) was used with a vane-in-cup configuration, and the data were processed with RheoCompassTM Light software (ANAMIN Group, Santiago, Chile). The outcomes were associated with the formation of solid species principally composed of magnesium precipitates. The magnesium in solution reduced in the presence of quartz (68 wt %), from 1380 to 1280 mg/L. Since the difference was not large regarding the solid-free seawater, the disposition of solid complexes at pH 10.7 was expected to be similar. The jump in pH caused both yield stress and viscoelastic moduli to drop, suggesting that the solid precipitates diminished the strength of the particle networks that made up the suspension. For the kaolin slurries (37 wt %), the yield stress raised when the pH increased, but unlike quartz, there was significant adsorption of magnesium cations. In fact, the concentration of magnesium in solution fell from 1380 to 658 mg/L. Dynamic oscillatory assays revealed structural changes in both pulps; in particular, the phase angle was greater at pH 8 than at pH 10.7, which indicates that at more alkaline conditions, the suspension exhibits a more solid-like character.

Surface modification and stabilisation of kaolin part 1: effects of CTAC-PP fibre composites

ABSTRACTThis paper presents an experimental study of the effects of surface modification and fibre types on the stabilisation of kaolin slurry. A pre-mixed solution of cationic surfactant – cetyltrimethylammonium chloride (CTAC), selected after preliminary screening based on the knowledge of the substrate, have been used for the surface modification of kaolin prior to stabilisation with different types of synthetic polypropylene (PP) fibres. The results show an improvement in the shearing resistance of kaolin when stabilised with different types, proportions, and lengths of fibres. At higher fibre content, there is an increase in the shearing resistance of the fibre-stabilised kaolin composites for the three categories of fibres tested. Furthermore, the shearing resistance of the CTAC-PP fibre composites converges as the confining stress increases from 160kPa to 480kPa. In general, the shearing resistance of surface modified kaolin stabilised with 5% fibre length is slightly higher than corresponding composites containing unmodified kaolin.

An experimental investigation of the cyclic response of bucket foundations in soft clay under one-way cyclic horizontal loads

This study conducted 1 g laboratory tests to investigate the accumulated rotation and unloading stiffness of two model bucket foundations embedded in soft clay under one-way cyclic horizontal loads. The model bucket foundations were specifically designed to have embedment ratios of 0.5 and 1. Ground models were prepared by consolidating the kaolin slurry. One-way cyclic horizontal loads of up to 104 cycles were applied varying loading magnitudes. Test results showed that the accumulated rotations of the bucket foundations increased with increased number of load cycles and cyclic horizontal load magnitudes. The unloading stiffness of the bucket foundations increased with increasing number of cycles and embedment ratios but decreased with increasing cyclic horizontal load magnitude. Based on the model test results, empirical equations were proposed to evaluate the accumulated rotation and unloading stiffness of the bucket foundations in soft clay under one-way cyclic horizontal loads.

Variations in the molecular weight response of anionic polyacrylamides under different flocculation conditions

The influence of applied mixing (intensity and duration), solids concentration, and liquor chemistry on the molecular weight (MW) response of seven anionic (30%) polyacrylamides was investigated in the flocculation of standard kaolin slurry at pH 8. Continuous flocculation was achieved in a Couette mixing device (CSIRO Shear Vessel) with a vertical flow-through arrangement allowing operator-independent settling rate measurements to be made under tightly controlled mixing conditions. It was found that the relative performance of the flocculants was strongly dependent on the hydrodynamic conditions prevailing during flocculation. The lower MWs gave a more dosage-effective response under mild mixing, producing denser, faster-settling aggregates than equivalent sizes produced with the higher MWs. Conversely, the larger sizes created by the higher MWs gave access to faster settling rates under intense mixing, except in the instance where polymer size and concentration led to chain entanglements. Sodium cations (<0.01 M) in the slurry favoured some degree of particle coagulation, whereas calcium cations had an adverse effect on settling rates even at low concentrations (<0.002 M), with the effects of a reduced bridging capacity most apparent in the lower MWs. The results advance the fundamental understanding of how chain length can substantially alter inter-particle bridging behaviour under different conditions, and thus provide a more robust basis for enhanced dewatering of clay suspensions through flocculant MW selection.

Effects of sand and flocculation on dewaterability of kaolin slurries aimed at treating mature oil sands tailings

In guiding dewatering of oil sands tailings we measured dewaterability of as-mined kaolin when sand was added as a process aid to both the dispersed and flocculated kaolin slurries. In batch tests, gravitational settling, inverse permeability R, and compressive yield stress Py were measured as functions of solids volume fractions Φ, as sand increased in the mixtures. We measured Py(Φ) for flocculated kaolin with an equal sand fraction, a flocculated diluted kaolin, flocculated diluted mature fine tailings (MFT), gel-point kaolin and MFT. Results indicated that an optimal quantity of sand in mixtures with kaolin increased the consolidated volume fraction of solids at equivalent compressive yield stress, reduced hindered settling function values, and enhanced gravitational settling rate. Py(Φ) vs Φ plots for gel-point volume fractions of kaolin and MFT showed MFT to be more compressible, but needed a much longer time to dewater. Two flocculants had similar Py(Φ) vs Φ responses when tested with either kaolin or MFT. Flocculated kaolin and MFT exhibited rapid settling, but flocculated was less compressible than unflocculated. Py(Φ) vs Φ plots for both kaolin and MFT that were flocculated after dilution produced a crossover at Py=121kPa and Φ=0.41. The Py(Φ) vs Φ data from all tests followed power law.

Stabilization of kaolin clay slurry with sodium silicate of different silicate moduli

In the ceramic technological processes, the suspensions with high concentration of ceramic particles (>60%) play a very important role because this let to obtain inter alia reasonable casting rates what is one of the most important steps during the ceramics manufacturing. The article shows the attempts to modify the rheological properties of concentrated ceramic slurries, based on kaolin KOC. Different alkali sodium silicate based stabilizers, i.e. sodium water glasses ((Na2SiO2)nO) of silicate moduli in the range 1.74–3.25, were used for the research. The flow curves were analyzed and the technological parameters of slurries were described. Special attention was paid to the stabilization of slurries with the use of sodium water glasses of higher silicate moduli (>2). It was found that the best results of the stabilization of the kaolin slurry can be obtained while using sodium water glass of silicate moduli 2–2.5. Sodium water glasses of the moduli smaller than 2 precipitated free silica in the suspension and increased the alkalinity of ceramic slurry while those larger than 2.5 created independent silicate micelles, co-existing with the dispersed kaolin grains. The mechanisms appearing during the stabilization of ceramic slurry with the use of sodium water glass were ion exchange and, the so called depleted stabilization.

The efficacy and use of small centrifuge for evaluating geotextile tube dewatering performance

Geotextile tube dewatering technology has been widely used over the past two decades for dewatering high water content slurries. The dewatering process in geotextile tubes aims to decrease the volume of the dewatered slurry, which helps in the transportation, disposal, and reuse of the dewatered material. Several researchers have emphasized the effect of the retained sediment (filter cake) properties, in particular final solids content and volume (height) change, on the feasibility of geotextile tube dewatering projects. Retained sediment properties are often evaluated using small scale tests such as rapid dewatering test, falling head test, pressure filtration test (PFT), and field scale tests such as hanging bag test (HBT) and geotextile tube demonstrations test (GDT). In this study, centrifuge test is introduced as an alternative for the widely used pressure filtration and falling head tests to evaluate retained sediments properties. Centrifuge test provides a mechanism for understanding the response of slurries to externally applied pressure in geotextile tube environment. Centrifuge test was used to evaluate maximal solids content of the retained sediments and change in slurry volume of four soils that represent typical dredged soils. Tully sand, Tully fines, Elliott silt loam, and kaolin slurries were used at varying solids concentrations. Slurries were subjected to external stresses between 0.1 and 40 kPa by applying centrifugal speeds between 300 rotation per minute (rpm) and 1800 rpm. Both centrifuge test and PFT were conducted with unconditioned and cationic polyacrylamide conditioned slurries. Centrifuge tests results were compared with PFT results with respect to retained sediments final solids content and volume change. Tests results indicated that the maximal solids concentration of the retained sediments in saturated conditions is unique for each soil and is independent of the initial slurry solids concentration. Tests results also indicated that there is linear relationship between the initial concentration of the slurry and the final volume change at any externally applied stress. Finally, a relationship between the total pumped slurry volume and the final height of the dewatered sediments in a geotextile tube is presented.

Viscosity of kaolin slurries: Effects of dispersant and urea-intercalation

Good fluidity (low viscosity) of highly concentrated kaolin is highly needed in paper-coating industry. We put forward an effective route to improve the viscosity concentration of Beihai kaolin slurries. The effects of various factors such as solid content, pH, dispersant content, and urea-intercalation on the viscosity of kaolin slurries were investigated. The results revealed that the viscosity of kaolin slurries significantly decreased with decreasing solid content or with increasing pH and dispersant content. It was worth noting that urea-intercalation was proven to be an efficient method for promoting the dispersion of highly concentrated kaolin as compared with adding dispersant. The intercalation ratio of urea-intercalated kaolin was increased from 17.36% with 2% of urea addition to 81.30% with 6% of urea addition. Meanwhile, the viscosity concentration of raw kaolin slurry was improved from 65.0% to 70.13% after the intercalation of urea with 6% addition, which was attributed to finer particle size, increased pH value and more negative charges of urea-intercalated kaolin. Therefore, the route is effective to improve the dispersion of highly concentrated kaolin for paper-coating.

Secondary consolidation of a consolidated kaolin slurry during electrokinetic treatment

The increment of secondary deformations due to electrokinetic treatment (EKT) was studied considering that these deformations are associated to the mobilization of the water adsorbed by the clay minerals. This water is at the level of microstructure, and therefore volume changes occur while water is flowing from the micro to the macropores. Water transference can be explained based on the unbalance of the chemical potentials of microwater (at the surface of the clay minerals) and bulk water. Electrical potential increases this transfer of water, increasing the rate of secondary consolidation and therefore increasing the deformations. The comparison of secondary consolidation coefficients measured in consolidated kaolin slurry samples with and without electrical potential applied only during secondary consolidation made possible to understand that the flow due to electrical gradients appeared to be independent from the vertical stresses applied, unlike the flow due to hydraulic gradients. Under the same stresses, however, the application of electric current increases the amount of creep. Considering the total duration of each loading step, the electrical potential increased the elastic compressibility index defined at the level of the microstructure, but almost had no effect on global compressibility. This increment in the compressibility was explained by the mobilization of adsorbed water reducing repulsive forces between the clay minerals. A deeper knowledge of the electro-hydro-mechanical behaviour of clays will be useful for optimizing in-situ application of EKT in terms of its duration and consequences.

Compression and expansion properties of filter cake accompanied with step change in applied pressure in membrane filtration

Abstract In order to well elucidate the true nature of filter cake formed in membrane filtration of aqueous colloids, the transient flux decline behaviors accompanied with step-up and step-down changes in the applied filtration pressure during the course of constant pressure filtration were investigated by carrying out both microfiltration experiments of kaolin slurry and ultrafiltration experiments of nanosilica sol under various experimental conditions. When the applied pressure was increased stepwise, for each colloid the plot of the reciprocal filtration rate vs. the filtrate volume per unit membrane area referred to as the Ruth plot tends to approach a linear relationship obtained in constant pressure filtration conducted under the increased pressure condition from the beginning of filtration, after a transient period when the preformed cake under the initial pressure was compressed. In contrast, in the case of the step-down change in the applied pressure, when the volume of the preformed cake is adequate, the plot after a transient period tends to approach a higher straight line parallel to a linear relationship for constant pressure filtration conducted under the decreased pressure condition from the beginning. Such flux decay behaviors were well described by the expression having two constants: one is the constant representing the final filterability for the preformed filter cake, and the other is the rate constant describing the change rate in the structure of preformed cake resulting from a pressure jump. Moreover, the influence of experimental conditions on the cake reversibility and the rate constant was revealed both for kaolin slurry and for nanosilica sol.