Richard R. Klimpel

Laboratory studies of the grinding and rheology of coal—water slurries☆

Abstract The laboratory ball mill grinding of coal—water slurries is described for three coals. Emphasis is placed on the measurement of specific rates of breakage for various operating conditions. Corresponding rheological information is also presented based on data collected using a rotational viscometer. A rheological explanation of the influence of various slurry fluidity conditions on the specific rates of breakage is presented. This rheological approach has proved useful in both the identification of suitable chemicals for increasing breakage rates in coal—mineral slurry grinding and in the plant scale implementation of dense slurry grinding systems.

Chemical additives for wet grinding of minerals

Abstract This paper reviews the recent work on the use of low molecular weight anionic polymers as grinding additives for wet grinding of minerals. Laboratory results on the increase of breakage rates are given, and conclusions drawn regarding the mechanism of the effect. An experimental procedure is given for testing additives in a laboratory ball mill. Application of the additives to industrial ball mill and rod mill circuits is discussed. Experience suggests that additive costs of 12 – 30 c (U.S., 1980) per ton of dry ore are economically justifiable.

The back-calculation of specific rates of breakage from continuous mill data

Abstract Computer programs for back-calculation of specific rates of breakage Si from continuous mill data, or batch grinding data, are described. A series of statistical tests to determine the statistically acceptable ranges of values are presented. The most reliable test uses independent estimates of error variance calculated from replicated data. It is shown that the interval-by-interval method of calculating Si values is especially subject to errors in the top sizes. Back-calculation methods which use only the circuit product in the calculation give different ranges of statistically acceptable values than those which use all the size distributions round the circuit. The statistically acceptable ranges of values from using only the circuit product often do not include the values determined by direct laboratory investigation, and tend to be wider than the ranges given by using all the size distributions; thus, using only circuit product is a non-preferred method. The use of a fully-mixed residence time distribution (RTD) instead of a true RTD leads to radically incorrect values, which cannot be detected by statistical analysis except in the presence of unrealistically low experimental error. It must be realized that a set of breakage parameters which reproduce the data used in their back-calculation with good accuracy are not necessarily real, and statistical analysis is essential to define the statistically acceptable ranges of the parameters.

Frothers: Plant Practice

Abstract This paper summarizes current plant practice involving frothers. Included is a brief review of the several mechanisms proposed for froth formation and particle-bubble attachment and discussion of frother-collector surface complexes, important practical attributes of frothers, the effect of collector on froth properties, the importance of frother chemistry and dosage on the rate of flotation, and an introduction to recently developed new frother chemistry. Finally, a summary is given of typical industrial scale froth practice and usage levels.

An improved method for analyzing classifier data

Abstract A common problem in calculating classifier selectivity values occurs when experimentally measured size distributions of the three streams around the classifier do not extend to small enough sizes to obtain a direct value for the bypass fraction. For hydrocyclones, it is sometimes assumed that the bypass fraction equals the water split, but this is not in agreement with test results reported here. A mathematical procedure is outlined for obtaining the complete selectivity curve based on extra-polation of the smaller sizes of the feed size distribution on a Schuhmann plot, and fitting the selectivity curve to a three-parameter function (bypass, d 50 and steepness parameters). This procedure uses the information contained in the percentages less than the smallest measured size, whereas the normal calculation technique wastes this information. An example is given of the new procedure applied to hydrocyclone data.

Ball wear and ball size distributions in tumbling ball mills

Abstract The theory of the calculation of the size distribution of the equilibrium mixture of balls in a ball mill is developed. The differential equation is solved for wear laws of the form wear rate per ball ∝ r2 + Δ where r is ball radius. Δ = 0 gives the Bond wear law and Δ = 1 gives the Davis wear law. Methods of determining Δ are illustrated. Experimental data are presented which show that Δ = 0 for some cases of wet milling, Δ = 1 for the two mills reported by Davis, and Δ = 2 for a case of wet milling. The reason for this wide divergence is not known.

A preliminary model of liberation from a binary system

Abstract In this first report, we present a preliminary model based on the simple binary system of component B occluded in a matrix of component A, for the case where fracture planes can pass with equal ease through A or B. By assuming that the volume fraction of B in AB in the overall matrix is small, which is realistic for many practical systems, the problem is reduced to a one-dimensional treatment which is conceptually easy to understand. The model was programmed for Monte Carlo simulation, and an analytical solution also developed based on the assumption using a synthetic ‘mineral—host matrix’ particle. Preliminary experimental confirmation using a synthetic ‘mineral—host matrix’ of known amount and size of B in AB is presented.

The influence of a chemical dispersant on the sizing performance of a 24-in. hydrocyclone☆

The influence of a chemical dispersant on the hydrocycloning of a copper ore slurry and a slurry mixture of copper and magnetic iron ores was investigated. In the percent solids and slurry feed size ranges associated with industrial practice, the classification parameters of mass by-pass fraction ‘a’ to coarse stream, d50, and Sharpness Index were measured on a 24-in.-diam. cyclone under ‘stand-alone’ conditions, with and without the dispersant. With chemical use, there were significant increases in ‘a’, d50, and S.I. in the copper ore slurry tests. However, the results of chemical use in the slurry mixture tests were not as significant because the influence of the two components of widely different specific gravities obscured the effect of the chemical.

THE INFLUENCE OF MATERIAL BREAKAGE PROPERTIES AND ASSOCIATED SLURRY RHEOLOGY ON BREAKAGE RATES IN THE WET GRINDING OF COAL/ORES IN TUMBLING MEDIA MILLS

ABSTRACT Recent work has shown that wet grinding rates of minerals and coals in tumbling media mills is strongly influenced by the type of slurry rheology condition present in the mills. A number of factors such as percent solids, particle size, temperature, and the use of chemicals have been identified as having consistent and predictable influence on rheology, hence on grinding performance. This paper particularly addresses another rheology related factor influencing grinding rates; the nature in which different materials inherently break in tumbling media mills.