A Commonwealth Scientific and Industrial Research Organisation (CSIRO) designed gas liquid nozzle is making gold production more efficient by reducing the amount of oxygen wasted during processing.
Dr Jie Wu, who has led the research team developing the technology at CSIRO Manufacturing and Infrastructure Technology, says the nozzle technology was developed after problems were identified with ‘sparging’ gases into liquids – forcibly blowing gases such as oxygen or nitrogen into a liquid, where some of the gas dissolves.
He says sparging is a common, but not particularly efficient technique for dissolving gas into liquids within many industries, including gold production, mineral sands processing, pharmaceuticals manufacturing and brewing.
“When the gas goes through a liquid, only a small amount of the gas is dissolved. Most of the bubbles just rise to the surface and go into the air as waste,” Dr Wu says.
By enhancing the rate gas is absorbed into the liquid as bubbles pass through it, the efficiency of the process can be improved. The CSIRO nozzle makes smaller bubbles, which are absorbed easier.
“If we make them smaller, we have more surface area [compared to total volume] and therefore we can increase the rate of transfer of gas into the liquid,” Dr Wu says.
Creating smaller bubbles, however, requires the gas to be pumped through the nozzle at a high velocity, which can erode the nozzle material.
“So our nozzle has a unique design, which does not cause nozzle material erosion while operating at high velocity to produce smaller bubbles,” he says.
Trials of the nozzle started at the Stawell Gold Mine, owned by the Melbourne-based Leviathan Resources, in 2003.
Figures from the trials show the nozzle cut the amount of oxygen needed by up to 25 per cent in some types of slurry, such as those containing basalt. The average reduction was 13 per cent. The nozzles are likely to save the company more than $35,000 a year in each of the two leach tanks at the processing plant.Peter Wemyss, senior metallurgist at Stawell Gold Mine, says the nozzle had “greatly simplified” the oxygen injection system being used at the plant and would pay for itself within three months. He says the nozzle also seemed to wear “extremely well” with no wear evident on a nozzle after a year of operation.