C.C. Harris

A study on grinding and energy input in stirred media mills

Grinding and energy input in stirred media mills are studied as functions of grinding time, stirring speed, media size and density, solid concentration, impeller and tank dimensions and design, and other relevant variables. Ground product size and surface area are determined with respect to the above variables. Changes in energy input and media/pulp rheological properties during grinding are described. The best conditions for grinding limestone in the laboratory stirred media mills have been identified. Equations for correlations involving power and modified Reynolds numbers have been established.

Multiphase models of flotation machine behaviour

Abstract Models in which the cell contents are partitioned into distinct pulp and froth phases are reviewed critically. The nature of the mixing within the phases is discussed. Multiphase models describing froth column concentration gradients and pulp residence time effects are mentioned. It is shown that at steady state multiphase models can be reduced to the two-phase case. Deficiencies in the models and topics requiring further development are outlined.

The effect of additives on stirred media milling of limestone

The effects of additives (sodium hydroxide, sodium carbonate, sodium oleate, oleic acid and poly(acrylic) acid), on stirred media milling of limestone have been investigated. The results are evaluated in terms of specific surface area, specific energy and energy efficiency as a function of additive dosage, polymer molecular weight, solids concentration and relevant operating variables. Use of additives generally results in changes in specific surface area and energy efficiency, while under certain conditions a more than 100% increase in these parameters can occur. Relevant interfacial properties have been measured and the milling mechanisms involved are explored, particularly in terms of the effect of additives on the flow patterns at higher solids concentration.

The air flow number in flotation machine scale-up

Abstract The flotation cell is quantified as a mixing device for one, two, and three phase systems using combinations of water, air, and solids. To do this, power consumption was measured as a function of impeller speed, rate of aeration, and solids concentration. Initial suspension of solids and dispersion of suspended solids throughout the water or water/air system were also studied as influenced by impeller speed, particle size and solids concentration. The power number and air flow number were used to correlate the data. Flotation studies with a zinc ore using three sizes of cells of the same design, showed that aeration had to be controlled in the smaller cells to duplicate the results in the cell of commercial size. For optimum results the flow number range in the smallest cell was less than the critical value for suspension of coarse particles. Operating flow numbers for the three cell sizes under optimum conditions were close; commercial cells of the same size operating elsewhere appear to have two to three times higher flow numbers. The general relationships among air flow, impeller speed, particle suspension and flotation are discussed with particular reference to scale-up problems and coarse particle flotation. Both impeller speed and aeration should be considered as variables requiring systematic study and independent adjustment.

Grinding Mill Power Consumption

Equations and associated procedures for estimating power draw are inconsistent. The various methods are discussed critically. Topics discussed are: diameter exponent; loading; speed correction factors; buoyancy effects; liner wear, and effect of load dilation. Balance between effective load weight and torque-arm length determines direction of power change at critical operating points (e.g. incipient overloading). Consistent procedures for calculating the effect of charge weight on power draw in different mill types are given. Error analysis shows that the accuracy of power estimation and data correlation may depend as much on the accuracy of measurement of mill dimensions and operating variables as on the particular equation used. An equation based on the torque-arm model, and providing a compromise between existing equations, is proposed. It is simple and suitable for correlating data and estimating power draw. A data-base of power related parameters documenting mill scale-up during the past few decades ...

A multi-purpose Alyavdin—Rosin-Rammler—Weibull chart

Abstract The chart described enables size distribution and kinetic data to be presented graphically without the kind of congestion frequently observed with log versus log and semi-log plotting. It is especially useful for comparing sets of data, for example, experimental with simulated. The chart can also be used for fitting equations to data.

Species interaction in flotation: A laboratory-scale semi-batch study

Abstract Semi-batch flotation tests were performed using different narrow size fractions of three different xanthate-conditioned sulphides floated singly and together in all possible combinations. To ensure proper selective flotation conditions a gangue mineral was included in all tests. Within the reproducibility of the experimentation no significant interaction among the mineral species is indicated, a result which has useful implications in distributed rate coefficient models of flotation kinetics. The conditions under which the present findings may be valid in industrial flotation are discussed, and suggestions are made for further work.

Impeller speed, air, and power requirements in flotation machine scale-up

Abstract Experimental and operational data, flotation criteria, machine design and scale-up principles are reviewed and combined in a chart encompassing scale-up detail for various machine types. Topics requiring further study are mentioned.

Role of pH and dissolved mineral species in Pittsburgh no. 8 coal flotation system — I. Floatability of coal

Abstract The roles of pH and of dissolved mineral species on the floatability of Pittsburgh No. 8 coal was investigated. Isolation of the direct effect of pH from that of the interaction of the dissolved mineral species with OH − was achieved by the appropriate design of the experimental procedure. The effect of pH on flotation, determined using a washed coal sample, was found to be significant, especially above pH 8, with the floatability falling sharply with pH increase. The effect of interaction of the dissolved mineral species with OH − depended on the path of approach to the flotation pH. Under the conditions of increasing pH , precipitation/adsorption of Fe, Al, Ca and Mg species occurred, and the effect of interaction was marked with the floatability decreasing with pH increase. This was shown to be mainly due to precipitation/adsorption on the coal surface of dissolved Fe species which were the predominant inorganic species in the supernatant of the coal slurry. Under the conditions of decreasing pH , dissolution of Fe, Ca and Mg species and precipitation of Al species occurred as the pH is lowered, and the effect of the interaction between pH and the dissolved mineral species was marginal.

A recycle flow flotation machine model

Abstract Residence time measurements were made on a Denver laboratory flotation machine with and without the DR ring assembly. Soluble and insoluble tracers were used (a dye and fine quartz, respectively), and the variables studied were tank liquid volume, V , water and air volumetric flow rates, Q and QA respectively, and some geometric and design variables. By analogy with nominal residence time, t N (= V Q ) , a term “effective residence time” t E is defined by: f (t)= exp [− t t E where f(t) is the fraction of tracer remaining in the tank at time t. Perfect mixing is indicated if and only if: (i) data satisfies the exponential relationship; and (ii) t E t N = 1 . Using the soluble tracer the machine behaved substantially as a perfect mixer under all operating conditions, except with the DR ring at values of QA nearly double the natural aeration capacity of the machine; condition (i) above was satisfied, but t E t N ∼ 1.1 . With the insoluble tracer the machine behaved as a perfect mixer only without air. As QA increased, t E t N increased from unity to about 1.2, and the effect was emphasized by the DR ring. In all cases condition (i) above was satisfied. A model in which the flow pattern in the tank includes a large component of pulp recirculation through the impeller region is developed. This model can account for the experimental findings but the details remain to be elucidated.