Ore Comminution Research Articles

The influence of microwave energy delivery method on strength reduction in ore samples

Recent work has shown for the first time that high electric field strength microwave energy can facilitate comminution of ores, at energy inputs considered economically viable. However, due to difficulties in measuring stress formation inside a solid being exposed to microwave energy, the accuracy of a suggested thermal stress weakening mechanism has not been quantified. It is thought that microwave induced differential thermal expansion of certain mineral phases is sufficient to cause stresses that exceed the strength of the material. This study simulated this proposed weakening mechanism using a quasi-static thermo-mechanical 2D model of a simplified pyrite/calcite system formulated in commercial finite difference numerical modelling software. The effects of microwave power density and exposure time on simulated uniaxial compressive strength are quantified. Power densities expected in both continuous wave and pulsed microwave applications are examined, and the work concludes that pulsed treatment is more effective for weakening rocks. The paper makes recommendations as to the future operating requirements of microwave equipment for the most effective weakening at economic energy inputs.

An investigation into the influence of microwave treatment on mineral ore comminution

The influence of microwave pre-treatment on mineral ore breakage has been investigated. Samples of lead–zinc ore were microwave pre-treated prior to strength testing and change in strength with microwave exposure time determined. Comparisons of change in strength were made between microwave-treated and -untreated material. Using a multimode microwave cavity, it was found that strength could be significantly reduced in 0.5 s when using 15 kW of microwave power. Lower powers in this type of cavity were found to be less effective. Drop weight tests were used to quantify the change in strength in terms of reduction in required comminution energy. Reductions of up to 40% were achieved for particles of mean size 14.53 mm. Preliminary tests in a single-mode microwave cavity gave strength reductions of 50% at 10 kW of microwave power with a residence time of only 0.1 s, indicating that high electric field strength is important in the failure of ore. A preliminary energy balance indicating the benefits of single-mode heating is presented.

Multistage mill with flow-through classification for selective comminution of sylvinite ore

The process of sylvinite ore comminution in a multistage flow-through mill is analyzed. The potential applications of the mill in preliminary treatment of the sylvinite ore to prepare it for flotation are considered.

Loesche vertical roller mills for the comminution of ores and minerals

LOESCHE vertical roller mills are widely used for the comminution of raw materials in the cement industry, for the comminution of clinker and blast furnace slag and for the production of pulverized coal for cement kilns, blast furnaces and power plants. Recent research has shown, that the application of these vertical roller mills in dry grinding of ores and minerals can lead to significantly better recovery rates and higher grades when compared to conventional grinding. Since mid 2000 a LM 50.4 has been in operation for the comminution of a phosphate carrying pyroxenite ore with a capacity of 825 t/h at a D80 of 480 μm.

Reconstruction capability of the kernel-based stereological inversion applied to particle separation techniques

The paper tackles the problem of characterizing the particulates that derive from the comminution of ores or two-component materials in terms of fraction of particles within a narrow volumetric composition. It reports some refinements to the procedures of regularized-inversion for the solution of the kernel-based stereological model applied to the conversion of areal grade distributions (readable from polished sections by image analysis) into distributions of volumetric grades. These solutions are further exploited to infer the efficiency of separation/concentration systems treating particulates, an important information rarely obtained due to the complex experimental work required with traditional heavy liquid fractionating. The use of synthetic kernels is also discussed. Finally, one practical application with computer generated data demonstrates the resolution of the efficiency coefficients of a separation process. These are recovered solving a stereologically posed mass balance around the separator with an original regularizing strategy that allows including a priori information.

Semiautogenous mill liners: Designs, alloys, and maintenance procedures

Large-diameter autogenous and semi-autogenous grinding mills represent the primary thrust of the expanding grinding technology. In spite of initial difficulties, large autogenous and semiautogenous mills have reached an acceptable level of technology that provides the mineral engineer with a reliable, low cost means of ore comminution. A successful milling installation begins during the design stage of the grinding mill and the plant in which it is to be installed. This is particularly true in autogenous and semiautogenous mills. Critical mill and plant design factors should be considered while the mill and installation are still only “paper.” Various current liner designs will be discussed ranging from lifter bar/plate to integral types. Modes of operation such as “high-low” will be considered. Liner maintenance procedures ranging from laydown area in plant design, proper mill shutdown methods, to installation and bolt tightening complete the equation to yield optimum performance possible for any particular grinding application. The objective of this paper is to discuss trends in wear materials, designs, and operating practices, and to provide some guidelines for good practice as we move through the 1980s. We will put together concepts that relate to the designs, materials, and applications so that higher performance can be obtained by the operator for his specific application. The concepts are shown as being in series because they are dependent on each other to achieve the desired performance: designs times materials times application results in higher performance (Arnson, Parks, and Kjos, 1983).

Similarity Solutions for the Population Balance Equation Describing Particle Fragmentation

Similarity solutions are obtained to the population balance equation describing particulate systems undergoing fragmentation. The solutions are restricted only by the requirement that the breakage rate of particles of volume v be of the form φ(v) = Avb and the breakage distribution function of the form ω(u, v) = ƒ(v/u)/u, where u is the volume of the fragmenting particle. Under such conditions, the moments of the distribution asymptotically approach the form Ni(t) α t (1−i)/b , and the particle size distribution function is shown to obey a first-order linear ordinary integro-diflerential equation. For the case ƒ(v/u) = γ(v/u)γ−2, analytical solutions to the above equation were obtained. Complete solutions as well as asymptotic behavior are given. The results are potentially applicable to a wide range of particle fragmentation problems, including char/ash fragmentation during pulverized coal combustion, explosively generated aerosol formation, ore comminution, powder crushing and grinding, floe breakage, and crystallization kinetics.

A method of measuring the surface area of granular material

AbstractA method is described which permits measurement of the exterior surface areas of objects down to about 0.1 sq. in. in area. In this method, the object is coated with an adhesive and a single layer of small metal particles. The change in weight gives a measure of the external area of the object.Systematic variations in the density of the metal particle coating are discussed, and appropriate correction factors are given.This method is intended for use in research that involves objects whose exterior surface areas have an effect on the process being investigated. Examples are the drying of agricultural grains and foodstuffs, the comminution of ores and chemicals, and the hydraulic and pneumatic transport of materials.The precision of the method is adequate, the root‐mean‐square error being about 1%.

Some observations on syngenetic ores

Some of the relationships that might be used in determining whether the ores are syngenetic or epigenetic are discussed. Some experiments were run to determine the amount of comminution of silicate rocks and sulfide ores in a stream environment. The possible equations that might produce covellite, chalcopyrite and bornite are cited.