A comparison between column and mechanical cell performance in platinum flotation.
Froth flotation has been used to concentrate minerals for over a century (Finch and Dobby, 1990) and it is essential for the economical recovery of metals which are present at low concentrations. The traditional flotation cell consists of a stirred tank incorporating air injection. In recent decades columns have appeared to offer advantages for platinum flotation. This project is a comparative study of the use of column and mechanical cells as cleaners for the flotation of an UG-2 (Upper Group 2) platinum ore. A laboratory column cell, 1.8 m high and 60 mm in diameter, was constructed to have the same volume as a conventional 5L Denver mechanical cell. Batch cleaning tests were used to compare the two types of cells, while varying the depressant dosage and conditioning technique. The performance of the column cell when the pulp was recycled was also compared. Finally the effect of doubling the column height, whilst maintaining the same mass percent of solids as in the original column, was investigated. Samples were subjected to acid digestion to determine Copper (Cu) and Nickel (Ni) recovery as an indicator of platinum recovery. Platinum Group Metals and Gold (PGM+Au) assays were performed on samples from a final series of tests that used a different but similar ore sample. The investigations showed that the mechanical cell performed better than the column. The PGM grade in the mechanical cell was 6.5ppm higher for a common recovery of 80% PGM in both cells. The performance of the column cell was only marginally improved when the pulp was recycled. Mass recovery data indicated that the column cell required less depressant for reducing the mass recovery. The corresponding grade recovery curves showed that for a 10 g/t depressant addition, the grade of the concentrate produced in the column cell doubled whilst that of the mechanical cell revealed no significant change. It was suggested in literature (Whitney and Yan, 1996) that the depressant was more effective in a column cell, due to the absence of agitation by an impeller. Platinum recovery data from the final series did not confirm the interesting trend observed with the preliminary tests (Cu/Ni) at a low depressant dosage (10g/t), but marginal improvements were noted at higher dosages. The effect of agitation during conditioning with depressant was also investigated. Gentle conditioning of the depressant, prior to column flotation, resulted in a higher grade and recovery of PGM as compared to conditioning by means of the recirculation pump. The PGM grade when gentle conditioning was employed was 9 ppm higher for a common PGM recovery of 80% for both conditioning techniques. Finally it was found that increasing the column height improved the grade-recovery relationship. The PGM grade obtained by the longer column was 8 ppm higher for a common PGM recovery of 75% in both columns. The performance of the longer column was similar to that of the mechanical cell. Tests were also conducted at a platinum concentrator, to compare the performance of a 378L pilot-plant column (5.5m high and 0.3m diameter), to that of a pilot-plant consisting of six mechanical cells. The pilot test rig of mechanical cells (FCTR) achieved a significantly better recovery than a pilot column. However, by decreasing the column feed flowrate and thereby increasing the residence time, a substantial improvement in the PGM grade and recovery was obtained by the column cell.