I haven't heard of that except when oxygen is required for bio oxidation, could you measure the Dissolved Oxygen in solutions exiting the leach pad if you think it may be a limitation.

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Sampling the solution exiting the leach pad have been contacted by air and do not represent the interior.

From my point of view oxygen is unstable under atmospheric conditions and tries to leave the solution. So if we try to add air to solution you will have just a little incremental amount in the few meters of the pad. If your ore accepts higher flow rates than 10 l/(hr-m2) you can add more oxygen to push the reaction and the kinetics can be improve. Due the ratio solution vs. ore tn is a KPI to improve the recovery.

The oxygen consumption for the gold reaction is low. The addition of oxygen (air) to the heap would be required if pyrite required oxidation. But the problem with pyrite oxidation in the gold heap is the consumption of cyanide and lime will increase significantly.

If you construction the heaps and operate them properly the percent extraction will approach the result for column tests. If the heap is constructed poorly (compaction due to traffic or segregation of particle size) or the irrigation management is poor quality. Then the extraction will be lower than the column.

The solubility of oxygen is dependent on temperature and atmospheric pressure (elevation). But you can assume 6-8 ppm oxygen in the leach solution.

Note the KPI of the ratio of solution to tons of ore is not correct. I have proven this in a number of gold, silver and copper heap leach operations over the last 30 years. The first heap leach I did this was in 1988. I turned a 30,000 tpd Merrill-Crowe plant into a 20,000 tpd and still produced 1 ton of silver per week. The heap should have the maximum volume under irrigation at all time. The irrigation rate should reduce with the reduction in the rate of metal extraction. 

The main problem we experienced was that the actual air distribution invariably disturbed the leach-bed so introduced channeling. The global integrity of the leach bed is paramount to maximum extraction. As mentioned, oxygen or air in leaching is not critical unless you are dealing with Biological Oxidation. By the way I also worked with Merrill- Crowe plant (telfer 87 commissioning to 91) I also re commissioned a silver Merrill-Crowe heap leach at around 100kg/day and If I can make an observation, a full Merrill-drove with vacuum tower is a large piece of hardware, you only need the Zn feeder and recovery filter press, as the solution is returned. In a plant set up however set you need absolutely barren as it otherwise ends up in the tailings dam with only limited return.

The volume of air added must have been very high to introduce channeling. One point on irrigation is that high irrigation rates tend to follow large channels between the large particles. Every heap has an optimum irrigation rate to start with.

I disagree with the removal of the Crowe tower. I visited one operation that complained about the high zinc consumption and low lifetime of graphite crucibles. When I asked the plant metallurgist what was the DO before the zinc cone he said he did not know. When I asked about the DO meter he said it was broken. When I asked how long it had been broken. He said 9 months. Maintaining operating conditions for zinc precipitation is very important. The DO must be 0.5 ppm or less. This is why the Crowe tower is used. Otherwise zinc is used to consume oxygen and maintain a low barren grade for gold. The operation with a high barren in a heap leaches places metal in inventory. Why should this be allowed for a small savings in capital cost?

What kind of ore you have? If you have a lot of fine the percolation rate will be decreased and oxygen and cyanide will in the same condition. If it is the case, you can mix coarse with fine ore to increase the percolation.

We have dump Leach, ore from the pit, and we are gold mine. I will start testing 100m2.