A kinetic study of precipitate flotation of Zinc(II), Cobalt(II) and Copper(II) hydroxides

An experimental kinetic study has been completed on precipitate flotation of Zn(II), Co(II) and Cu(II) hydroxides (initial metal concentration 1 × 10^?-2M) with the anionic surfactant, sodium dodecyl benzenesulphonate (1 × 10^?-4M), at varying equilibrium pH. An original radioactive isotope procedure was applied and proved to be sufficiently accurate. Kinetic equations of Rubin and co-workers were found to be relevant for precipitate flotation of hydroxides. From the flotation rate constant (k_p) determined at varying equilibrium pH of floated suspensions it appeared that the selective flotation of individual compounds from mixed precipitate was possible as a result of the ‘kinetic effect’.     

Characterization of polyetheretherketone particle suspensions for electrophoretic deposition

Suspensions of polyetheretherketone (PEEK) using mixture of ethanol and isopropanol as solvent were prepared to carry out PEEK electrophoretic deposition (EPD). The rheological behavior and suspension structure of PEEK particles dispersed in co‐solvents were investigated over a range of pH values (1–10) and shear rates (γ = 10¹?3 × 10² s^?1). These PEEK suspensions generally exhibited a pseudoplastic flow behavior, indicating the occurrence of particle aggregation in the liquid medium. The maximum solids fraction (?_m) showed an estimated value of  ?_m = 2.9 wt %. Using a suspension with 3 wt % PEEK concentration, PEEK coatings on stainless steel substrates were obtained by EPD at constant voltage condition. The influence of the electrolyte conductivity on PEEK EPD from ethanol–isopropanol suspensions was studied. Experimental results showed that high‐conductivity ethanol‐based suspensions yield non‐uniform deposits, while low‐conductivity suspensions resulted in uniform coatings. The difference in the deposition behavior is due to the different pH of the suspensions and the relationship of pH with suspension conductivity. pH = 8 was the optimal value for this system in terms of deposition results. The surfaces of EPD PEEK coatings were homogenous and a qualitatively good adhesion between the PEEK deposits and the substrate was confirmed. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40953.     

Effect of ionic strength on bubble coalescence in inorganic salt and seawater solutions

Bubble size is of fundamental importance in the flotation process, as it provides the surface area for particle collection. Typically, weak surfactants (frothers) are added to process water to reduce bubble coalescence. Certain inorganic electrolytes, which occur naturally in some flotation process water, have been shown to mimic the role of frothers. The concentration at which bubble coalescence is inhibited, the critical coalescence concentration, was determined in a 5.5‐L mechanical flotation cell for a series of coalescence inhibiting inorganic salts. To mimic some industrial flotation process water, a synthetic sea salt solution was also tested. It was found that when the multicomponent sea salt solution was broken down into its constituent parts, the addition of the ionic strength of each ion correlated well with the overall ionic strength curve of all the salts tested. The critical coalescence ionic strength ranged from 0.22 to 0.35, with sea salt being 0.26. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2489–2496, 2015     

Porous Ni/ZrO2 Cermet from Highly Concentrated Composite Colloid

Rheology and shaping of concentrated cermet suspensions consisting of nickel (Ni) and yttria‐stabilized zirconia (YSZ) nanoparticles in water have been examined over a broad range of volumetric solids concentration (? = 0.1–0.4) and Ni fraction (f_Ni = 0.15–0.45). Preferential adsorption of pyrogallol‐poly(ethylene glycol) polymer (i.e., Gallol‐PEG) on surface of the Ni and YSZ particles imparts steric hindrance between the suspending particles so that fluidity can be obtained under shear stress. The cermet suspensions exhibit shear‐thinning flow behavior under steady‐shear measurement over shear rates of 10⁰–10³ s^?1. Yield stress and yield strain of the suspensions appear to vary pronouncedly with ? and f_Ni under oscillatory shear over a shear‐strain range of 10^?1–10³%. With the Gallol‐PEG adsorption, an apparent viscosity less than 6 × 10^?1 Pa.s at a shear rate of 10² s^?1 has been obtained for the highly concentrated composite suspension with ? of 0.40 and f_Ni of 0.25. A high solids concentration effectively prohibits phase segregation during wet‐shaping processes. Uniform green compacts have been obtained from slip casting of the concentrated cermet mixture (? = 0.30) without use of binder and are then fired at 1200°C under reducing atmosphere to form porous Ni/YSZ compacts. Relative sintered density increases from 65% to 75% of the theoretical value when f_Ni was increased from 0.15 to 0.45, due mainly to the lower sintering temperature required for the Ni phase.     

Vegetable tannin composition and its association with the leather tanning effect

Abstract

The increasing environmentally friendly approach of using renewable materials has led to vegetable tannins having an important role as tanning agents in the leather industry. Tannins are complex phenolic structures, and the literature shows that a considerable amount of chemical parameters measured through analytical techniques can be associated with their tanning ability. In the present study, five types of vegetable tannins highly used in the tanning industry were chosen for the evaluation of some of their relevant chemical parameters and the correlation with their cross-sectional penetration in the hide. Black wattle (Acacia mearnsii), quebracho (Schinopsis lorentzii), chestnut (Castanea sativa), tara (Caesalpinia spinosa), and myrobalan (Terminalia chebula) were tested. The chemical properties of the total tannin polyphenols, non-tannin polyphenols, insoluble solids, soluble solids, total solids, total phenols, non-tannin polyphenols:total phenols ratio, and residual tanning float concentration were measured and associated with the leather cross-sectional penetration results. The statistical Mann–Whitney-U test showed that the insoluble solids, non-tannin polyphenols, soluble solids, and total tannin polyphenol percentages distinguished the groups of tannins that crossed the hide from those that did not well. Hence, since the analysis of insoluble solids is the simplest and the most direct among them, it would be recommended to use this parameter to define a cutoff to distinguish the performance of tannins for leather application.     

Dimensional Analysis of Crossflow Microfiltration Data

Abstract

A new approach to correlating crossflow microfiltration (CFMF) data based on dimensional analysis is presented. The steady state flux was assumed to be a function of the trans‐membrane pressure (ΔP), the crossflow velocity (u), the particle concentration (c), filtrate viscosity (μ), and membrane resistance (R _m). Correlations of the form J/u=K(ΔP/cu ²) ^a (ΔP/μuR _m) ^b were tested on three sets of published data: one for CFMF of dried yeast suspensions in a laminar flow hollow fiber module, one for dried yeast suspensions in a turbulent flow tubular module and one for suspensions of latex particles in a laminar flow flat sheet module. The R ² values for the fits of the correlations to the data were 0.98, 0.94, and 0.91 respectively.     

A Comparison of Flow Dynamics and Flow Structure in a Riser and a Downer

Flow development and flow dynamics were systematically investigated using local solids concentration measurements in a pair consisting of a downer (0.1 m I.D., 9.3 m high) and a riser of the same diameter (0.1 m I.D., 15.1 m high). Both statistical and chaos analysis were employed. Values for the Kolmogorov entropy (K), correlation dimension (D), and Hurst exponent (H) were estimated from time series of solids concentration measurements. Axial distributions of chaos parameters were more complex in the downer than those in the riser, especially in the entrance section. Flow in the downer was more uniform with a flatter core in all the radial profiles of chaos parameters. The radial profiles of K varied significantly with increasing axial levels due to different clustering behavior in the wall region of the downer. In both the riser and the downer, anti‐persistent flow in the core region and persistent flow behavior near the wall were identified from the profiles of H. Different flow behavior in the region close to the wall in the downer and riser was characterized from the combination of the three chaos parameters. Relationships between chaos parameters and local time‐averaged solids holdup in the core and wall regions of the developed sections in both the downer and riser were also analyzed.     

The Rheology of Peat/Solvent Slurries

Slurries of finely milled Irish peat in Shell White Spirit (100F) were prepared and their rheological behaviour was evaluated in terms of shear rate, solids concentration, moisture content and particle size distribution of the solids. The moisture content of the peat was found to be of crucial significance in determining both the effective solids concentration and the stability of the suspensions. The viscosity of slurries composed of 7% moisture peat solids were almost independent of solids concentration and displayed Newtonian rheological behaviour, with a viscosity of approximately 0·012 N s m⁻². The viscosity of the suspending medium was 1·006×10⁻³ N s m⁻² at 20±1°C. The viscosity of the slurries composed of 55% moisture peat solids was observed to rise sharply, up to about 0·10 N s m⁻² with solids concentration. The shear rate dependence of these suspensions was more complex and their flow characteristics were evaluated in terms of empirical non-Newtonian models. It proved difficult to confidently distinguish between the Bingham Plastic and Casson models as each gave best fit regression curves which were almost identical. Particle size distribution analysis of the suspensions indicates the formation of peat aggregates in the 55% moisture samples which exhibited more rapid settling of the solid. © 1997 SCI     

Precipitate Flotation of Complexed Cyanide

Abstract

Precipitated cyanide, complexed with Fe(II) at a molar Fe/CN ratio of 0.550, can be floated readily from aqueous suspension with a cationic surfactant, ethylhexadecyldimethylammonium bromide. The effects of three distinct mixing times of significance in preparing the precipitate and contacting it with surfactant, of pH, of initial cyanide concentration, of initial surfactant concentration, and of ionic strength have been established experimentally. Mixing times and the initial cyanide concentration have little influence on the flotation, while increases in pH and ionic strength have a most pronounced influence, part of which can be overcome with increased surfactant concentrations. At pH 6.0, 95% of the complexed cyanide can be foam separated from distilled water suspensions 1.5 to 3.1 mM in total cyanide. About 0.04 mole surfactant/mole complexed cyanide is required; about 0.08 mole/mole is required to increase the flotation to 99% or to overcome ionic strength effects.     

Powdered Activated Carbon Separation from Water by Foam Flotation

Abstract

Powdered activated carbon was separated from dilute aqueous suspensions (200–1000 mg/L) by foam flotation using surfactants (anionic or cationic). The effects of surfactant type, pH value of the suspension, initial carbon and surfactant concentrations, flotation time, and air flow rate on the dispersed-air flotation of powdered activation carbon were investigated. In optimum conditions the powdered activated carbon separation was almost complete. The ζ-potential of powdered activated carbon was also measured in the presence and absence of surfactants. Finally, carbon flotation was examined after the carbon had adsorbed chromate ions from an acidic solution (pH 2). Almost complete separation of Cr(VI)-loaded carbon was obtained by using an anionic surfactant.     

Solids exit discontinuity in slurry bubble columns

The exit discontinuity in slurry bubble columns, i.e., the difference in the apparent solids concentration at the very top of the column (C_t) and the concentration in the effluent (C_e), was studied in a 0.3 m ID bubble column, using air as the gas phase, water, a light hydrocarbon oil (Varsol) and trichloroethylene as liquids and glass beads of different sizes and density as solids. The results showed that the drop in solids concentration occurs in a very small layer at the gas/liquid interface. By changing the column exit configuration and removing the gas/liquid interface the exit discontinuity disappeared. The extent of the exit discontinuity depended on the liquid properties and appeared to be related to the foaming tendency of the liquid. In addition, in those systems where the exit discontinuity was significant, it depended on the solids properties and the gas and liquid superficial velocities.     

Investigation of electrorheological properties of kaolin suspensions under DC fields

In this study, the electrorheological (ER) behavior of suspensions prepared from d₅₀ = 7 μm kaolin particulate, dispersed in insulating silicone oil (SO) medium, was investigated. ER activity of all the suspensions was observed to increase with increasing electric field strength (E), concentration (c), and decreasing shear rate ( ). Shear stress ( ) of kaolin suspensions increased linearly with increasing concentrations of the particles and with the applied electric field strength. The viscosity (η) of all suspensions was decreased sharply with increasing shear rate and showing a typical shear thinning non‐Newtonian viscoelastic behavior. It was observed that kaolin/silicone oil system studied in the present work was sensitive to high temperature. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3798–3802, 2007     

The distribution of serum high density lipoprotein subfractions in non-human primates

The ultracentrifugal flotation patterns in 1.2 g/ml solvent and ultracentrifugal gradient distribution of high density lipoproteins (HDL) from the primates-human, apes and monkeys-were determined, with emphasis on the gorilla species of apes and rhesus monkeys. Diets for non-human primates were commercial chow, which is low in cholesterol. Molecular weights and protein, cholesterol, phospholipid and triglyceride compositions of various density fractions were determined on human, gorilla and rhesus HDL. The HDL₂/HDL₃ ratio was determined from the two peaks observed upon flotation in high salt in the analytical ultracentrifuge. The HDL₂ of all three species of apes-gorillas (Gorilla gorilla), chimpanzees (Pan troglodytes) and orangutans (Pongo pygmaeus)—was always greater than HDL₃, while that of all six species of Old World monkeys-Rhesus (Macaca mulatta), sooty mangabeys (Cercocebus atys), cynomolgus (Macaca fascicularis), stumptails, (Macaca arctoides) patas (Erythrocebus patas) and African greens (Cercopithecus aethiops)—was less. In addition, the HDL₃ concentration in five gorillas was about 15 mg/dl as cholesterol while the HDL₂ concentration was 92 mg/dl, much lower and higher, respectively, than humans. HDL₂ of gorillas was similar in density and molecular weight to that of humans. The distribution of densities in gorilla HDL was predominantly in HDL₂, while rhesus HDL usually, but not always, was unimodal, having a density distribution similar in heterogeneity to human HDL₃, but somewhat less dense (peaking at 1.109 vs 1.129 g/ml). The molecular weight of rhesus HDL was about the same as human HDL₃ in all three density subfractions and at the peak density. Likewise, the chemical compositions were similar for the subfractions 1.10–1.125 and>1.125 g/ml for rhesus HDL and human HDL₃. Consequently most but not all chow-fed rhesus HDL was very similar to human HDL₃, but lighter in density. A preliminary report of this study was given at the American Society for Biological Chemists Meeting in New Oreleans in April 1982.     

Rapid differentiation of new isolates with MALDI-TOF mass spectrometry via discriminant function analysis based on principal components

Discriminant function analysis based on principal components was applied to the spectral outputs of whole cell suspensions of nine isolates from matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry. First, based on the salt tolerance and whole cell proteins, the similarity of the isolates to moderate halophiles was established. Intact microorganisms were then inferentially clustered by MALDI-TOF mass spectroscopy taking four type strains as precursors. Two of these type strains were moderate halophilic bacteria (Halomonas salina and Halomonas halophila), one was a mesophilic bacteria (Escherichia coli), and one was a halophilic archaea (Haloarcula vallismortis). Results showed that the isolates were significantly similar to halophiles but were different from a mesophile. This investigation demonstrates the feasibility of using whole cell suspensions for rapid differentiation prior to extensive experimentation.     

The Coagulation of Finely-Divided Ion Exchange Resins and the Use of the Coagulated Material for Rapid Ion Removal

Abstract

Finely-ground ion exchange resin particles remove ions from solution much more rapidly than the conventional-size beads. Such finely-divided solids form suspensions when added to aqueous solutions. A method was required for rapidly removing such suspensions once ion adsorption had occurred, and to this end it is shown that the particles (-400 mesh) can be completely coagulated within a few minutes by the addition of suspensions of oppositely-charged solids. Thus anion exchange resins are coagulated by cation exchange resins (200 to 400), montmorillonite (200), kaolin (30), charcoal (10), silica (10), and glass (5), the figures representing arbitrarily defined relative coagulating abilities. Coagulating power is shown to increase markedly with decreasing particle size. Most suitable for ion removal is a mixed finely-divided resin formed by coagulation of anionic and cationic resins from pure water. The mixed resin, when added to 1 liter of 3 × 10^?4 M sodium phosphate solution removes all the phosphorus within 2 min, and when added to 1 liter of 2.5 × 10^?4 M calcium chloride, removes over 90% of the calcium within 3 min.     

Nitrogen dynamics in maize-based agroforestry systems as affected by landscape position in southern Malawi

In Malawi, agroforestry is very promising for N replenishment; however, there are still large variations in the performance of these agroforestry technologies on farmers’ fields. A study was conducted on-farm to determine the influence of three landscape positions on N dynamics in maize (Zea mays L.)-based agroforestry systems. The agroforestry systems were relay fallow using Sesbania sesban (L.) Merr or Tephrosia vogelii (Hook F.), simultaneous fallow using Gliricidia sepium(Jacq.) Walp., and maize without trees as a control. Sesbania was superior to other systems in the bottom slope, producing the highest tree biomass (1,861 kg ha⁻¹), whereas, gliricidia gave the highest tree biomass production in the mid-slope (2,147 kg ha⁻¹) and upper slope (1,690 kg ha⁻¹). Preseason inorganic N, maize flag leaf N concentration, maize total N uptake and maize yields followed a similar trend to tree biomass production with tree-based cropping systems exhibiting higher productivity (P < 0.05) than the cropping systems without trees. Nitrogen leaching from gliricidia agroforestry systems was lower than in the other agroforestry systems across all landscape positions as evidenced by 17% lower amounts (P < 0.05) of inorganic N adsorbed to ionic exchange resin membranes at 60 cm soil depth most likely due to the permanent root system of gliricidia. The difference between δ¹⁵N values of the trees and the soil did not change between landscape positions suggesting that if the leguminous trees fixed atmospheric N₂, the proportion of total N uptake was identical at all locations. We concluded that landscape positions have a significant effect on tree performance with sesbania remarkably adapted to the bottom slope, gliricidia to the mid-slopes and tephrosia fairing similar in both the bottom slope and mid-slopes.     

Recovery of unburned carbon from lime calcination process using statistical technique

In this study, unburned carbon recovery from lime calcination plant tailings was investigated using diesel oil, kerosene, MIBC and pine oil. A series of laboratory experiments using 2³ full factorial designs was conducted to determine the types and dosages of collector and frother. For these tests, data were analyzed by the paired t-test. The main and interaction effects on combustible recovery were evaluated using Yates' analysis. By optimizing the flotation parameters at slurry concentration of 34% solids, flotation time of 2.5 min, pH of 7.5, collector diesel oil dosage of 2780 g/t, and frother pine oil dosage of 2620 g/t, unburned carbon (UC) has been successfully recovered with 93.07% combustible recovery (CR) and 6030 kcal/kg calorifical value.     

The effect of solids on the dense phase gas fraction and gas–liquid mass transfer at conditions close to the heterogeneous regime in a mechanically agitated vessel

In the heterogeneous regime, there is a strong literature evidence (discussed herein) that solids can supplant small bubbles in the dense phase and reduce the gas hold-up. This work examines the effects of the addition of 205 μm glass ballotini on the gas hold-up and k_La in a 0.286 m diameter stirred tank operated under intense conditions (P/V ≥ 5 kW m⁻³) close to the heterogeneous regime and above the agitator speed corresponding to the just suspended point, N_JS. The tests were carried out on two systems: air–water (coalescing) and air–0.2 M sodium sulphate (salt) solution (which resists coalescence in the bubble regime). For the air–water system it was observed that the overall gas plus solids hold-up remains approximately constant until all the small gas bubbles are supplanted and then increased in direct relation to the solids volume. The k_La mirrored the gas hold-up trend and decreased with a fall in gas hold-up. In the salt solution k_La decreased in direct relationship to the solids concentration, to 40% of the no solids value at around 19% solids by volume of dispersion. Dynamic engagement and disengagement experiments established that the salt solution behaves differently than water with the small bubbles initially growing in size rather than being coalesced directly into the large bubble population.     

Research Note: Inactivation Efficiency of Ozonated Water for Fusarium oxysporum Conidia Under Hydroponic Greenhouse Conditions

Ozonated water was used for inactivation of Fusarium oxysporum conidia in sterilized water and inorganic soil-less nutrient medium at different treatment temperatures. F. oxysporum conidia were effectively inactivated in both water and nutrient media and the inactivation curves were almost same at 15°C, 25°C and 30°C. Approximate 4-log orders of F. oxysporum conidia were killed when the ozonated water with initial ozone concentration of 1.0 ppm had been used. The surviving curves, however, were characterized by a tailing-off effect, and the effect was related to the residual ozone concentration in the ozone treated suspensions.     

Study of the flow behavior of polymer-natural fiber suspensions in the power law validity range

The melt flow properties of PVC suspensions with henequen, coconut and bovine leather, in their raw condition, and after extraction of all their low molecular weight substances were studied. The experimental results show that, at the strain rates employed, the behavior of the suspensions is described by a power law (η = mγ^n–1). It is important to mention that in the present work we do not restrict our analysis to the evolution of the suspension Newtonian viscosity with the fiber concentration (as commonly is reported in the literature), but a more complete analysis is performed by describing the evolution of the consistency (m) and the power law (n) indices with the fiber concentration. Both indices were evaluated using a technique previously developed. The flow index (n) presents an anomalous behavior, it increases when the fibers are incorporated into the melted matrix at low fiber concentrations. This unexpected behavior is very different from that commonly reported in the literature and is apparently due to the flexibility of fibers. Moreover, the influence of the fiber extractable materials on the behavior of these suspensions was also evaluated. It was found that these latter materials apparently influence the value of the consistency index (m) of suspensions, at fiber concentrations above the critical pigment volume fraction; however, they do not have a significant effect on the power law index (n). Concerning the mechanical behavior of composites molded from the previous suspensions, it was found that when the fiber content augments, their elastic modulus increases, but their tensile strength falls. This behavior, however, could be improved by increasing the adhesion between the fibers and matrix.