Magnetic separation is routinely used in the processing of titanium minerals, and the efficiency of these operations can be determined by measuring the magnetic properties of the process streams. The valuable components in the feed to a titanium minerals plant have specific magnetic susceptibilities ranging from -10-9 m3kg-1(zircon) to 10-6 m3kg-1 (ilmenite). However, in an industrial environment, in which the mineral temperature may range from 20 to 120°C, it is difficult to measure susceptibilities lower than about 10-7 m3kg-1. Hence laboratory testing of spot samples from magnetic separators is currently required to obtain accurate performance data. This is an inherently slow process and where feed grades are variable, optimum
performance of separators is generally not achieved.
This thesis describes the development of an inductance-based instrument for measuring down to low levels of magnetic susceptibility online in harsh plant environments. The major difficulties in developing this device were temperature induced changes in the resistance/ capacitance of the inductance coil and phase stability of the inductance coil excitation current. Coil temperature problems were solved by using a physical small coil in batch operation. Phase stability was overcome by designing a phase extraction system that used the coil excitation phase information as part of the phase extraction algorithm.
Investigations were made into calibration and measurement error of the instrument. Calibration at low levels of magnetic susceptibility was performed using a range of chemical salts. For higher susceptibilities no well defined calibration standards were found and a method to
measure high levels of susceptibility was formulated. The method relies on diluting the highly magnetic material with salt to prevent magnetic interaction between particles. It was found that the resolution of the electronics was the most significant error and the homogeneity of the sample the least significant.
Plant samples were tested and the device was able to determine the zircon content in a zircon magnetics circuit, determine the TiO2 content in the non-mag stream of a magnetic circuit, determine the iron content in the mag stream of a magnetic circuit and determine the metallic iron content of reduced ilmenite.
The device has also been used in a system to determine the mass distribution of the magnetic properties of a titanium mineral sample in less that 1 minute. Previously, the distribution was determined using a laboratory scale magnetic separator (e.g. an Ore Sorters Permroll), with it taking
approximately 40 minutes to process each sample. The system is best described as an hourglass with mineral flowing from a hopper through a small inductance coil. The impedance of the coil is proportional to the mean magnetic susceptibility of the number of particles within the coil (i.e. each measurement is the mean magnetic susceptibility of a fixed size group of particles). An algorithm has been developed to determine the percentage of the feed material at each level of magnetic susceptibility. Hence the results are identical to those determined using a laboratory magnetic separation. Accuracy of the device has been proven by simulation and by testing of plant samples using the new system and comparing the results with measurements made using a Permroll separator.
The thesis also presents recommendations for future work and future potential applications of magnetic susceptibility measurement to mass flow of titanium minerals, measurement of moisture content
and jigging operations.