Introduction
Chromite is an important mineral used in the metallurgy, chemistry and refractory industries. Chromite ores contain a variety of gangue minerals such as serpentine and olivine. Therefore, some kind of ore Beneficiation is required. The most commonly used Beneficiation methods for chromite ores are the gravity methods, such as the shaking table, jig, spiral and Reichert cone methods. Beneficiation with heavy medium is also utilised for preconcentration purposes. In addition, magnetic separation may be preferred, depending on the ore characteristics. Flotation is also used for the Beneficiation of finely grained ores. With these conventional methods depending on the liberation particle size of the ore, significant amounts of fine chromite are lost to the tailings. For this reason, all of these methods are only partly successful in the fine particle size range .
Sample, Equipment and Method
The chromite sample used for MGS studies was taken from the Gulin chromite plant. The sample was ground to minus 0.150 mm before MGS tests. The chemical analysis of the chromite ore sample is given in Table 1.
A series of batch tests was run in order to determine the optimum operational parameters for the maximum concentrate grade and chromite recovery. The operational variables are the washwater flowrate, the rotational speed of the drum, the shake amplitude, the shake frequency and tilt angle of the drum.
A laboratory/pilot MGS of type C900 was used in the tests. The MGS consists of a slightly tapered open-ended drum that rotates in a clockwise direction and is shaken in a sinusoidal form in an axial direction. The parameters a ecting the eciency of separation of the MGS are the drum speed (100 to 300rpm), tilt angle (0 to 9), shake amplitude (10/15/20mm), shake frequency (4.0/4.8/5.7cps), amount of washwater (0 to 10 liters per minute) and feed pulp density (10% to 50% solids by weight).
Feed slurry is introduced continuously midway onto the internal surface of the drum via a perforated ring. Washwater is added via a similar ring positioned near the open end of the drum. The dense particles migrate through the slurry lm to form a semisolid layer against the wall of the drum as a result of the high centrifugal forces and the added shearing e ect of the shake. The scrapers towards the open end of the drum convey this dense layer where it discharges into the concentrate launder. The less dense particles are carried by the flow of washwater into the tailing launder at the rear end of the drum.
The shake amplitude and frequency drum speed, tilt angle and amount of washwater were adjusted, and the MGS was operated.
A sample bucket was placed under the tailing discharge pipe, another under the concentrate discharge pipe and another one was placed under the center spillage discharge pipe. 500 grams of dry sample was mixed with one liter of water, giving a feed density of 33% solids by weight. The solids were kept in suspension during the test by manual stirring. The feed pulp was poured into the MGS feed vessel at a steady rate of 1.2 liters/minute, giving a feed rate of 40kg/h of dry sample whilst stirring continuously. In all the tests, the total feeding time was 45 seconds. At the end of the feed period, the separator was kept running until the material flow was finished and the washwater was allowed to run for a further 2 or 3 minutes. The washwater was turned off and the MGS was stopped.
Scraper or conveyed product, which collected via the front launder during the feed and the wash period, were referred to as concentrate. Another product, which collected during the feed period was referred to as Tailing 1, and another product, which collected during the wash period was slightly higher in grade and was referred to as Tailing 2. These samples were dried at 105 °C, weighed and analysed in order to determine the chromite grade and recovery rate. Throughout the tests, Middling and Tailing 2 were combined with concentrate and Tailing 1, respectively.
Results and Discussion
A series of batch tests was run in order to upgrade the ore to over 48.0% Cr2O3 with maximum chromite recovery. In order to determine the e ects of operational parameters in the equipment, several variables were tested.