Optimization Of Grinding Circuit Research Articles

Analytical solution for the dynamic model of tumbling mills

Optimisation of grinding circuits is invariably dependent on sound process models together with process simulators that can solve the process models accurately. Most of the process models are solved numerically because analytical solutions are not available, which can lead to errors in the results due to the numerical approximation of mathematical equations. Whiten [1], and Valery Jnr & Morrell [2,3] have developed a dynamic model with numerical simulation for autogenous and semi-autogenous mills, and validated the model with dynamic response of mills in terms of power draw, grinding charge level, slurry level and product size distribution to changes in feed rate, feed size, feed hardness and water addition [2,3]. In this work, an analytical solution for their dynamic model of tumbling mills has been developed based on the knowledge of solutions to the first-order nonhomogeneous linear differential equations. Two algorithms, Direct Single Time method (DST) and Direct Multiple Time method (DMT), were applied to obtain the analytical solutions respectively. It was found that analytical solutions are more accurate than the traditional finite difference numerical methods. However, the DST analytical method has a drawback of numerical instability due to the accumulation of round-off errors which are amplified by exponential functions, whilst the DMT method can provide stable solutions. To test the DMT analytical method, two cases of SAG mill dynamic operation were studied with both the traditional numerical method and the newly developed analytical method, further proving the robustness and feasibility of the analytical solutions.

An alternative energy–size relationship to that proposed by Bond for the design and optimisation of grinding circuits

Despite reservations of a number of researchers concerning the applicability of Bond's equation for relating specific energy to the size reduction of rocks, his approach has become an industry standard. Data from a large number of pilot and full-scale autogenous (AG), semi-autogenous (SAG) and ball mill circuits are used to show that Bond's equation does not hold over the particle size range −100 mm+0.1 mm. However, if suitable correction factors are applied its results can be made to approximate observed values. It is shown that a more appropriate relationship relies on a particle size exponent that is a function of size. This new relationship, which does not rely on the need for correction factors, is used to predict the specific energy requirements of a number of autogenous, semi-autogenous and ball mill grinding circuits. The results are compared to those obtained using Bond's equation and are shown to provide a more precise prediction of specific power requirements.

Optimisation of Grinding Circuits at the Lead/Zinc Concentrator, Mount Isa Mines Limited

Abstract This paper describes the use of modelling and simulation techniques in the analysis and optimisation of grinding circuits at the Lead/Zinc Concentrator of Mount Isa Nines Limited. The objectives of the studies were to:- 1. improve primary grinding circuit performance by reducing the production of -0.006 mm galena fines. 2. maximise the fineness of grind in the secondary grinding circuit using the existing grinding power and pumping capacities. The study has shown that quantitative models can be useful in analysing plant operations. The models described plant operations, planned pilot scalc tests and simulated the effect of process changes on plant performance. The use of automated scanning electron microscope technology to understand the liberation characteristics of the major minerals in the Mount Isa Lead/Zinc ore is also described.