The development of frother optimisation techniques in full scale flotation plants
Master Thesis
2013
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University of Cape Town
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In 2012, Anglo American Platinum assembled a technical task team of metallurgists for their concentrator operations. Although there has been extensive research in literature regarding the flotation response and behaviour of reagents, there still exists a gap between fundamental laboratory scale research and plant scale application. This thesis will focus on the development of techniques for optimising and characterising frother on a full scale plant using the Anglo American Platinum Bubble Sizer (AAPBS) which is a commonly used tool by the plant metallurgist. The techniques developed have been based on the application of fundamental research of frothers in literature. This thesis consists of three main focus areas: 1) Developing a technique for measuring the relationship between sauter mean bubble diameter and frother concentration on a full scale plant. 2) Developing a technique for estimating frother concentrations in process streams in full scale plant 3) Establishing whether the relationship between sauter mean bubble diameter and superficial gas velocity in a flotation bank of identical cells in series in a plant operating at frother concentration above the CCC is identical, and whether this can be used to detect the decrease of frother concentration to below the CCC at any point in the bank. Furthermore, the metallurgical performance of a bank with a decrease in frother concentration below the CCC midway through the bank was determined before and after the addition of frother, which was added as such that all the cells in the bank operate with a frother concentration above the CCC. There were two techniques investigated for measuring the relationship between sauter mean bubble diameter and frother concentration. Both techniques involved using the AAPBS and the use of forced air mechanically agitated tank cells. Technique 1 involved using the first rougher cell on a flotation plant, dosing frother at different rates into the cell to target different frother concentrations and then measuring the resultant bubble size whilst operating at a fixed air rate. The coalescence mechanism here was occurring in a three phase solids/aqueous/air system occurring in a continuous stirred tank. Similarly Technique 2 involved using the first rougher cell; however, the first cell was depleted of frother by bypassing the frother dosage line into the next cell. This was done to isolate the first rougher cell and to minimise disturbance to the rest of the rougher bank. Known concentrations offrother were made up in potable water and these were added into the AAPBS. Bubbles from the pulp phase enter the bubble riser tube which is long and narrow (3m x 25mm diameter) which is representative of two phase aqueous/air “plug flow” system. These bubbles coalesce to different degrees based on the known frother concentration. The resulting bubble size distribution was then be measured by taking photographs at the viewing pane of the AAPBS. The air rate in the cell was kept constant to within 0.7-0.9 cm/s and the photographs were analysed using software provided by stone three to determine the sauter mean bubble diameter and the bubble size distribution. Technique 1 was applied to Plant A UG2 concentrator which was using a polyglycol type frother called Betafroth 206C which has an undisclosed composition and a molecular weight of approximately 200 g/mol. The first rougher cell used was an Outokumpu 70 m3 forced air mechanically agitated tank cell. The results showed no clear relationship between sauter mean bubble diameter and frother concentration. Furthermore, the sauter mean bubble diameter was already very small and it appeared that the changes in between runs were more strongly linked to the superficial gas velocity than frother concentration. The fact that the sauter mean bubble diameter obtained was already small implied that the frother concentration in the cell was already high. This could have been due to an additional source of frother due to spillage or in the process water that potentially elevated the actual frother concentrations in the cell. Technique 1 also resulted in significant disturbances to the entire rougher bank because it involved changing the frother dosages to the bank. This would affect the flotation performance of the bank for a prolonged period and affect plant performance. Hence it was decided that technique 1 would not be suitable.
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Venkatesan, L. 2013. The development of frother optimisation techniques in full scale flotation plants. University of Cape Town.