Normandy Mining committed to a production-scale deaeration system on the zinc concentrate thickener feed at Golden Grove. Capital expense was justified by the revenue loss that resulted from carryover of zinc concentrate into the thickener overflow. Overflow combines with smaller amounts of copper/lead concentrate and tailings material in the process water pond. Combined material is difficult and costly to recover.
The concentrate system is comprised of a hopper that is fed by gravity from the flotation circuit and a froth pump, which then delivers the concentrate to a thickener "boil box" where it mixes with the filtrate from the zinc concentrate filters and the recycled concentrate from the clean-up sump in the flotation area. From the "boil box," the concentrate gravitates to the thickener feedwell. The deaerator was placed on the thickener bridge. So, the "boil box" has been bypassed by the main concentrate line, which now delivers directly into the feed manifold and then to the deaerators. Fitting a dilution water line to the concentrate pump hopper allows concentrate to be delivered to the deaerators at the desired pressure, of 80 to 100 kiloPascals (kPa).
Three deaerators were installed in a parallel bank, capable of handling feed at 80 m<num> [superscript] /hr each. Installation of the system was completed in January 2000. Prior to starting up the system, the froth layer (about 100-mm thick) on the thickener was partially cleared so that the effect of the deaerators could be observed. With the deaerators in operation, residual froth was quickly dispersed and showed no sign of rebuilding. The rising solution was observed to be essentially air-free.
At times since start-up, however, the feed pressure to the deaerators has dropped to 60 kPa, and at this pressure, some air entrainment still persists. This confirms the test results, which showed consistently that the deaerator performance is pressure dependent.
The other factor which introduces air bubbles into the thickener is that the sump reclaim system and filtrates still bypass the deaerators, and these streams do contain some entrained air. This could be eliminated by rerouting the bypass streams to the concentrate hopper so that all thickener feed is treated in the deaerators, and improving the pump control system ensures a constant pressure feed to the deaerators.
Overflow clarity determinations to date, with the deaerators online, 250 to 300 parts per million (ppm) was a realistic expectation. This is somewhat better than the average clarity obtained during the pilot-scale testwork, which was 850 ppm. With the deaerator offline, the pilot scale thickener produced an average overflow clarity of 5,040 ppm, an represented an 83% improvement.
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|Title Annotation:||zinc concentrate processing, Australia|
|Publication:||E&MJ - Engineering & Mining Journal|
|Article Type:||Brief Article|
|Date:||Apr 1, 2002|
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