Browsing by Author "Wiegel, Ronald L"

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    Development of an Approach to the Simulation of Size Reduction/Mineral Liberation for Magnetic Taconite Ore in Tumbling Mills and Its Implementation in a BASIC Computer Program
    (University of Minnesota Duluth, 2000-10-13) Wiegel, Ronald L
    In late '98, the Iron Ore Cooperative Research Committee decided to fund a math modeling/simulation center for magnetic taconite concentrator applications at the Coleraine Minerals Research Laboratory of the University of Minnesota. In a previous association with the iron ore industry, the writer was actively involved in early attempts at modeling and simulating the magnetic taconite beneficiation process. After returning to the University of Minnesota and the iron ore industry in 1997, I attempted to play "catch up" on developments over the past twenty years related to magnetic taconite process modeling and simulation. Based on that review, it was evident that two items that are of particular importance for magnetic taconite process simulation were still missing from the tools available in the software packages for mineral process modeling/simulation. These are: (1) a suitable technique for handling the description of mineral liberation as a function of changes in particle size resulting from size reduction steps in the process and (2) the prediction of the performance of rotating drum magnetic separators as a function of their design and their operating conditions. It was therefore decided that steps should be taken to begin to address these deficiencies very early in the life of the Taconite Concentrator Modeling Center. The more complex of these two problem areas is the development of a technique for describing how mineral liberation, and the resultant possible early rejection of minerals to waste, can be related to particle size changes resulting from crushin~ and grinding size reduction. There have been numerous approaches to this subject, 10 • 1 but none have taken it to a useful conclusion. Lacking a model of the simultaneous mineral liberation/size reduction operation, some investigators have resorted to the assumption of complete mineral liberation, that is, all mineral species are totally free of other mineral species. This is certainly not appropriate for magnetic taconite, where rejection is dependent on grinding. The approach reported here begins with an early conceptual model of a binary mineral system's liberation by size reduction, as described by A. M. Gaudin in his 1939 text "Principles of Mineral Dressing." Relationships have previously been obtained to describe the amount of liberation of either component and the quantity/composition of unliberated or "locked" middlings as a function of the "effective" mineral grain size, particle size and the original ore's volumetric composition. The new developments described in this report make use of mathematically derived "directional coefficients" to follow the gradual transfer of material from locked assemblages of dissimilar mineral grains of one composition to other locked particle compositions and eventually to liberated particles of value or waste, as particle size is reduced. Finally, a BASIC program has been developed and is presented, which permits one to calculate the simultaneous liberation/size reduction phenomena for multi-stage, perfectly mixed, tumbling mills in series. The liberation parameters of a particular crude magnetic taconite ore sample are obtained by collecting Davis tube data for individual particle size fractions and subjecting these to a "best fit" program described in an earlier report. Once the liberation parameters are defined, appropriate breakage rates of the liberated and locked middling particles can be used in combination with the geometric effects of the resultant size reduction on mineral liberation to simulate in a relatively simple and understandable way the complex operation of size reduction/liberation. This BASIC program must now be translated into an appropriate FORTRAN program for use with the BRGM USIMPAC mineral processing simulation software. It can then be used in concert with other models to simulate the entire magnetic taconite beneficiation process.
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    Fitting Of Liberation Model Parameters To Davis Tube Test Data
    (University of Minnesota Duluth, 1999-08-19) Wiegel, Ronald L
    After studying the direction work in mineral liberation has taken for the past twenty years, and in particular the more recent five to ten years, it has become apparent to me that at least for the magnetic taconite process, the use of the Davis tube ideal magnetic separator on individual size fractions of process feed can provide useful data on liberation. A study made by the writer1 of process feed samples to twelve magnetite concentrators indicated a reasonable conformity between Davis tube concentrate magnetite grade and size fraction mean particle size relationships and what was predicted using the idealized "random liberation model" formulation2 with appropriate specific gravities for magnetite and waste minerals. This then suggests that the magnetic taconite liberation behavior can be characterized by three parameters (given the two specific gravities): (1) magnetite ore feed grade; (2) an average mineral grain size; and (3) an average size fraction particle size. Of the twelve sample sets noted above, only two indicated significant deviations from the shape of the concentrate grade-particle size relationships displayed by the "random model." A BASIC computer program (LIBFIT.BAS) has therefore been written to obtain the best fit of the two parameters: magnetite feed grade of the ore and average mineral grain size for the "random model," to Davis tube data on size fractions of ground taconite. The program is relatively simple in concept, in that it first seeks a value of average mineral grain size, which minimizes the sum of squares of differences in the measured and calculated Davis tube concentrate grades for an estimated magnetite feed grade of the ore. It then holds the optimum average mineral grain size constant and searches for the optimum magnetite feed grade for that mineral grain size. It continues to switch back and forth, looking at first mineral grain size and then magnetite ore feed grade for some 18 iterations, which then provides a best fit estimate of the two parameters.
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    Fitting of Liberation Model Parameters To Davis Tube Test Data
    (University of Minnesota Duluth, 1999-08-19) Wiegel, Ronald L
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    Magnetic Taconite Concentration Modeling
    (University of Minnesota Duluth, 1999-07-29) Wiegel, Ronald L
    A greatly simplified predictive liberation model has been used to generate information about the expected quantity and composition of locked middling particles, dependent on mineral grain size, particle size, ore head grade, and mineral specific gravities. This information has then been calculated for mineral systems with head grades in the range of magnetic taconite crude ore. One special "infinite dilution" case has also been evaluated which might find use with low head grade deposits such as copper and nickel sulfides. The current plan is to use these tables and relationships in developing a new and different approach to the modeling of magnetic taconite size reduction-mineral liberation.