D.W. Fuerstenau

Mutual coagulation of colloidal dispersions

A quantitative theory is presented which describes the kinetics of coagulation of colloidal systems containing more than one dispersed species. A general expression has been derived to describe the potential energy of interaction between dissimilar spherical colloidal particles, using the linear (Debye-Huckel) approximation for low surface potentials. An overall stability ratio has been defined which takes into account the possibility of interactions between like, as well as unlike, particles in the system. The errors introduced by the use of the linear approximation have been assessed in terms of their effects on the stability ratio, and found to be quite small. The theory has been used to describe the behaviour of a hypothetical system under various conditions.

The zero point of charge of alpha-alumina

Abstract The zero point of charge of α-alumina was found to occur in aqueous solutions at pH 9.1 ± 0.1. Three independent methods of measurement were used: potentiometric titration for determination of the adsorption density of the potential-determining ions, measurement of the electrophoretic mobility, and determination of maximum subsidence rate. Potassium, chloride, perchlorate, and nitrate ions were all found to be indifferent at the surface of alumina.

Adsorption of polyacrylic acid at oxide/water interfaces

Abstract The adsorption of polyacrylic acid (PAA) on rutile (TiO3) and hematite (Fe2O3) has been studied as a function of pH. The uptake of PAA at the adsorption plateau level was observed to decrease with increasing pH until near-zero values of adsorption occurred near the isoelectric point of the oxide. Adsorption of PAA is correlated to the amount of positive surface charge on the oxide particles. Electrophoretic mobility measurements Indicate that some specific adsorption occurs at the pH of the isoelectric point of the oxides.

The effect of crystal structure on the surface properties of a series of manganese dioxides

Abstract The zero-points-of-charge for a series of manganese dioxides have been determined by both electrophoretic and coagulation-sedimentation techniques. The zpc was found to increase from pH 1.5 for the amorphous δ form of MnO 2 up to pH 7.3 for β-MnO 2 , the most well-defined crystalline form. This variation is interpreted in terms of, and is shown to be in agreement with, the electrostatic field strength concept modified to describe more complex solids. The change in cation-anion spacing, as derived from the volume per unit cell per cation in the crystal lattice, corresponds to a change in the polarization of the water dipoles and their subsequent dissociation to establish the electrochemical double layer at the oxide-water interface.

Effect of surface functional groups on the flotation of coal

Abstract The flotation behavior of a series of coals is described in terms of the predominant oxygen-containing functional groups. These groups control not only the thermodynamics, but also the kinetics of coal flotation. It is shown that the maximum flotation response occurs close to the isoelectric point of the demineralized coal. The correlation between content of phenolic and carboxylic groups and the flotation response of a range of coals was found to be excellent. Functional groups control coal wettability through the balance of hydrophobic/hydrophilic sites, and control flotation kinetics by their influence on surface charge.

Scale-up procedure for continuous grinding mill design using population balance models

Abstract This paper presents the development of a mill scale-up procedure based on population balance models of grinding circuits. Models containing various degrees of details in their representation of the kinetics of breakage, material transport through the mill, and performance of the classifier are examined; and the extent to which each may be useful for design is discussed. Special attention is given to the type of experimental information required at the bench, pilot-plant and plant scales to enable these models to be applied successfully to the design of continuous grinding mills. The grinding subprocesses: breakage, transport, and classification are taken into account in developing the present scale-up/design procedure. Utilization of the concept of specific energy consumption in kinetic models is demonstrated. The mechanics of design of a commercial-scale mill within the population balance model framework presented in this paper are illustrated using batch data obtained for the dry ball milling of limestone.

An improved class of universal collectors for the flotation of oxidized and/or low-rank coal

Ash minerals, including pyrite, can be separated from coal by flotation, primarily making use of the natural hydrophobicity of the carbonaceous matter in coal. However, to overcome the deleterious effect of oxygen functional groups on the coal surface, an organic collector is required. The most common industrial coal flotation collector is fuel oil, but the addition of oxygenated functional groups to the collector molecule markedly enhances the flotation of lower rank and oxidized coals. This paper summarizes the results of detailed study of the flotation response of two high-sulfur coals, Illinois No. 6 coal and Pittsburgh No. 8, using different non-ionic oxygenated surfactants as the collector. The performance of these reagents is compared with that of two oily collectors, namely dodecane and nonylbenzene, and mechanisms for the interaction of these compounds with coal are suggested.

The energy efficiency of ball milling in comminution

Comminution efficiency is a technical term that relates some measure of the output from a comminution machine to the energy input into it. The term has usually been encompassed in controversial arguments. The conflict in reporting comminution efficiencies has arisen from ill definition of the reference for the output energy. Surface area and surface energy have been widely used in the assessment of comminution efficiency. Review of the energy to produce new surface of quartz shows comminution efficiency ranging from about 0.1% to 1.0%, for various comminution methods, when expressed in terms of the surface free energy of quartz. However, in this paper, comminution efficiencies are based on the comparison of ball milling with single-particle comminution, either in terms of the energy to produce new surface or in terms of some size distribution parameter. If the energy to produce new surface by single-particle breakage is used as the basis for evaluating efficiency, then the efficiency of ball milling has a more realistic value of about 15% for the comminution of quartz and soda-lime glass. In a second approach, comminution efficiency is based on comparing the energy to produce some size distribution parameter of the product from ball milling with that by single-particle breakage. For both materials, dry ball milling efficiency was found to be in the range of 25%.

Interfacial processes in mineral/water systems

Factors that control the selective adsorption of both inorganic and organic ions at mineral/water interfaces are reviewed and summarized. In particular, the role of the electrical double layer in the adsorption of surface-active materials on oxides in aqueous media is stressed. The importance of interfacial processes to mineral chemistry is illustrated through the application of specific adsorption phenomena to the understanding of the physical chemistry of flotation systems.

Mechanisms of agglomerate growth in green pelletization

Abstract The mechanisms responsible for the formation and growth of agglomerates in balling or granulation can be described as nucleation, coalescence, abrasion transfer, breakage, and snowballing. These mechanisms have been identified by means of tracer studies using two calcites which have similar green pelletizing behavior but different fluorescent characteristics. Precise definitions of the growth mechanisms, so as to be useful for mathematical modeling of agglomeration processes, are given. Further, the batch balling behavior of particulate materials in terms of the growth mechanisms is discussed.