I cannot see you avoid that even in very low quantities dissolved in cyanide. The active carbon works very well in absorbing copper. I think you are experiencing copper in your bullion? Rinse/reduce the copper off the carbon with a cold cyanide rinse before you preheat for the real elution. If you have more than 30 ppm copper in the solution you can plate it out using an in line strainer/cathode.

We have about 50 ppm de copper in solution y 30 -40 ppm of free cyanide. We have grown to 90 ppm of free cyanide without significant results so far.

I'll echo your comment - conventional wisdom is that one way of reducing the amount of copper adsorbed is through pushing the copper to the Cu (CN)4 complex, which doesn't load as well. In theory the 90 ppm of CN- should do the trick, but it is borderline - maybe push it up to around 100 ppm (which is 1.2 times stoichiometry), and see if you notice a difference? I'd give this a go in the lab using plant solution and with fresh carbon first, as you may have a really big load of copper on your carbon in the plant which will need to be gotten rid of over time.

If this doesn't work well enough for your needs, then you may well need to go with cold cyanide wash options, which unfortunately introduces a new step into the process, although you should be able to do it in your existing elution column, provided you have the capacity in your circuit. 

Agree with all the above points but copper loadings on carbon are higher at a lower pH. Several years ago when I was operating a large CIL plant which was experiencing major problems with copper adsorption to the extent a separate cold copper wash(and recovery) circuit as mentioned was considered. Our circuit pH was however very low at pH 9.5 as we wanted to maintain a low residual cyanide tenor for environmental reasons. We eventually solved the copper problem by raising the circuit pH up to approximately 11. Unfortunately if you are already operating at the more normal pH of 11 then this option isn’t open to you but maybe worth checking the pH profile across your circuit anyway.

You may find the paper by C.A. Fleming and M.J. Nicol very interesting. Especially the details that are presented in Figure 7 of the paper! They have shown that cyanide to copper ratios (Molar ratios) greater than 4 at a pH of 10 results in low copper adsorption onto activated carbon. The article can be found here:

http://is.gd/qp9umD

I tried this in recent times and found that it works very well. However; it leads to high cyanide consumptions if high amounts of copper are present. Additionally; you need to make sure that the WAD cyanide in your tails is in line with your operating license. I was just wondering if you solved your copper adsorption issues in your CIC circuit. 

With high pH adding some excess of cyanide will help, the cupper hexacyanide doesn't load that readily on carbon.

We increase to 120 ppm the free cyanide and the copper content in the loaded carbon decreased from 2000 ppm to 1100 ppm. We will follow with the optimization.

The only way to remove Cu from the leach solution is by carbon. The act of forcing the Cu loading on carbon down will increase the concentration of Cu in the solution in the future. Cu is removed by dore or slag.

Unless one wants to do cold cyanide strip first and precipitate the Cu as a sulfide or as CuCN. The SART process where the pregnant stream is treated is expensive and requires a gypsum precipitation circuit. The cold cyanide elution concentrates the Cu into a Na cation solution versus the Ca cation solution when the pregnant solution is treated. The amount of sulfuric acid required for reduction of pH is less due to concentration of the Cu in a smaller volume. If NaHS is used to precipitate the CuS, the efficiency will be higher. The filtrate would be combined with the barren solution to allow for gypsum precipitation in the heap. If the pH is dropped to 3, CuCN and other compounds will precipitate. There is additional chemistry that can be used to generate a copper product from the precipitate.

I had this problem in Ecuador and solved it by lowering the free cyanide concentration. Gold and silver are preferentially dissolved instead of copper in low free cyanide concentrations. It is, however, very important to maintain the low free cyanide concentration by staged, small additions of cyanide (we used dissolved NaCN in pH 10.5 NaOH solution with a peristaltic dosing pump).

We had significant secondary benefits by lowering our operating costs, and spent solution clean-up costs as well.

I think you are on to something here. It will however; be important not to look at the total copper in isolation. In other words it will be important to look at the actual cyanide soluble copper content of the ore. It is well known that different minerals have different solubility; thus different copper minerals will have different solubility in cyanide solutions.

I guess I am taking it one step further and say the mineralogy of the ore will play a significant role. Some more interesting information is available here:

http://is.gd/FlmR6F