Air tank sparging

[ajohnston]

Does anyone have any good references on how much air to put into a cyanidation leach tank, and/or an Air/SO2 detox tanks or bioleaching tanks?

The values I've got vary wildly. (0.1 to 7 vessel volumes per hour)

Please let me know plant data, published work or unsubtantiated rules of thumb.

There are several books, papers and private studies that show how much SO2 is required, how much oxygen should be consumed etc., but very little that discusses how many Nm³/h or scfm should be sparged.

Agitation power is clearly important for oxygen take up - maybe someone knows a relationship between agitation power, gas flowrates, tank head pressure and dissolved oxygen/oxygen uptake rates?

Thanks,

Adam

[jheath]

Hi Adam,

The amount of air required for sparging in a cyanide leach tank depends on the concentration of dissolved oxygen required, which is dependant on the amount of free cyanide available, and the physical oxygen solubility limits of the system (e.g. adding air vs oxygen vs LOX).

The optimum ratio of oxygen:cyanide utilises both reagents efficiently without wasting either reagent. If an excess of either reagent is present then the gold dissolution rate wont increase as the leach rate is diffusion rate controlled. This is why most plants try to maximise their oxygen concentration - as it is easy to increase the cyanide concentration but the oxygen concentration usually has a maximum concentration achieveable.

Additionally, there will be reagent consuming components in the ore that will reduce the available amount of cyanide and oxygen for gold leaching. You will often see high sulfide content plants having gold leach rates controlled by oxygen diffusion, where as an ore containing high concentrations of copper may be cyanide diffusion controlled.

For more info try look at a paper written by J.A. Rumball in Minerals Engineering vol 11, no 11, 1998.