First off, as hydrogen peroxide is a very strong oxidizer and thus used to destroy cyanide, I doubt if you really want to add it to your CIL circuit. By the same reasoning you probably do not want to add it to any part of your water circuit where it can get back to your leach circuit.

You probably want to add it to your tails just before disposal. Which brings up the point of material compatibility, you need to use special piping usually plastic, stainless or aluminum, but not carbon steel.

Are you trying to improve gold leaching or destroy cyanide in the tailings? If it is for leaching then the hydrogen peroxide must be diluted to below 5% or it will consume cyanide. If you want to destroy cyanide then the peroxide still has to be diluted but perhaps down to 10% at most.

The best method to add it is by pumping the strong peroxide into a double nozzle system where it is mixed with water immediately before it goes into the pulp. This avoids the need for a separate tank to hold diluted peroxide.

The peroxide is used to improve gold leaching; basically it's used when the normal oxygen injection system failed.

Concerning the injection to the double nozzle system, can you give me the name of a supplier?

I would recommend my colleagues the review of the Eh-pH diagrams of the systems Au-CN-H2O and other associated systems such as Fe-CN-Au, etc., so the physical chemistry of the leach and recovery system is understood and the plants can be operated efficiently.

I'm not sure who supplies the nozzles, but one of the companies that supplies hydrogen peroxide may be able to help. You could try Evonik Degussa Ltd.

Degussa has developed a cyanidation process using hydrogen peroxide as an oxygen supplier. This method allows the cyanidation to be run at elevated oxygen levels, even considerably surpassing the oxygen saturation limit of the pulp. The application of H2O2 to cyanidation shows no detrimental effect on the cyanide demand, if the H2O2-concentration is controlled strictly. To guarantee the economical performance of Degussa's cyanidation process, automatic dosage of H2O2 by measuring the oxygen concentration in the pulp has been developed.

The advantage of this process is that the kinetics of the gold extraction are increased significantly. The final gold extraction can be reached after 2-6 hours, while 24-48 hours are required with the conventional aeration technique. If the process is applied in existing plants, the retention time effect is avoided and the gold output is increased by 2-10 %. An economic viability analysis of Degussa's cyanidation process has using a typical South African ore has shown that an increase of only 0.5 - 1% in the gold output may compensate the extra reagent costs. This increase appears to be well within the scope of the process.

Since it is generally known that active carbon acts as a catalyst for the decomposition of H2O2, the application of Degussa's cyanidation process to the Carbon-In-Leach-process was tested. After 4 hours of cyanidation. active carbon was added and CIL continued up to 48 hours. Neither the H2O2-consumption nor the NaCN demand was increased compared to the values obtained with simple cyanidation without active carbon. The gold extraction was 98 % (in solution) after only 4 h and remained at this level till 48 h (related to the residue). This demonstrates that active carbon does not have any detrimental effect on the CIL process if Degussa's cyanidation process is applied.

If I added hydrogen peroxide to cil is that increase the recovery and decrease the time of leaching?

The effect of hydrogen peroxide on gold leaching rates in alkaline cyanide solution is a matter of controversy and debate. Early studies indicated that the reduction of hydrogen peroxide on gold surfaces is kinetically hindered, and the dissolution rate of gold in oxygen-free solutions containing hydrogen peroxide is very slow.

Other studies have indicated that hydrogen peroxide can play a direct role. One such investigation has demonstrated that for pure gold the leaching rate could be increased significantly using a concentration of 0.015 M H2O2 in a solution containing 0.01 M NaCN at pH 10.

In general, hydrogen peroxide alone is not considered to be a very effective oxidant for use in gold leaching, except under conditions where dissolved oxygen is limited (e.g., at high altitude or in the presence of significant oxygen consumers in the ore). Hydrogen peroxide is very effective for the oxidation of sulfides, although expensive for this purpose. However, it has been used successfully in some cases to accelerate low pressure (atmospheric) oxidation kinetics

Methods of increasing dissolved oxygen levels in leach slurries, for example, by using pure oxygen or hydrogen peroxide as an oxidant, may also need to be considered to maintain adequate gold dissolution rates.

Hydrogen peroxide could also be used for low-pressure oxidation, but the economics are quite unfavorable for most ores, although one notable exception is Pine Creek (Australia), where hydrogen peroxide has been used during gold leaching, principally for sulfide mineral oxidation.

When treating ores that contain oxygen-consuming minerals, pure oxygen or hydrogen peroxide have been added to increase dissolved oxygen concentrations above those attainable with simple air sparging systems.

Review http://www.saimm.co.za/Conferences/ExtractiveMetallurgyOfGold/0831-Chapter15.pdf for the word peroxide

SEE THIS PAPER PDF

The dissolution rate of precious metals in the cyanidation process is closely related to the concentration of dissolved oxygen in the pulp. This could also be confirmed in our extensive leaching tests. The gold extraction rates for a typical gold ore, as obtained with H2O2 (adjusted to O2-levels of 10 and 18 ppm) and compressed air as oxidants, are represented in Table 2. The data outline the following advantages of Degussa's cyanidation process in comparison to the standard aeration technique:

• The kinetics of the gold extraction are greatly accelerated by the use of H2O2 as an oxidant compared to compressed air. Already after 4 hours, the gold extraction is more than 10% higher if H2O2 is used.
• Using to Degussa's cyanidation process the final gold extraction yield (95-96%) is already reached after 2 to 4 hours, although the O2-level has been kept steady at only 4-5 ppm. The same level (about 96%) was reached only after 48 hours, if the standard aeration technique was used.
• Using H2O2 as an oxidant, the gold concentration in solution does not drop again, if the leaching process is continued up to 48 hours.

The data from our leaching tests show that hydrogen peroxide is not a "magic chemical" in cyanidation. Only the cyanide-accessible-gold can be extracted, but the extraction kinetics are significantly accelerated. Therefore, the advantages of Degussa's cyanidation process can be used in the fallowing way:

• New plants can be designed much smaller for a fixed throughput; this saves a lot of the investment costs.
• Plants already running can significantly increase their throughput of the gold ores.

If Degussa's cyanidation technique is applied to a conventional gold plant and the leaching time can be reduced from 24-48 hours using compressed air to 18-36 hours using H2O2, the overall gold output may be increased by 2-10 percent absolute. This also results from the faster extraction kinetics using H2O2, since the retention time of the pulp in the plant is characterized by a Gaussian-distribution and some parts of the ore always stay for too short a period in the leaching tanks to reach the final gold extraction using the standard aeration technique.