Significantly more efficient copper extraction with hydrogen peroxide

A new, environmentally friendly Evonik technology could increase yields by 10%, the company reports. The investment cost is low and these findings have been corroborated in Australian copper and gold mines. The use of hydrogen peroxide can solve an old mining problem while significantly increasing the amount of copper extracted from the ore. Certain impurities such as iron sulphides (which include pyrite) have been difficult to remove until now. A new technology based on hydrogen peroxide now offers a solution.

Using a small copper and gold mine in Australia as an example, Evonik’s development team has demonstrated that the technology works on an industrial scale and can increase the copper yield by roughly 10%.

“Up to now, mine operators have primarily been familiar with hydrogen peroxide as a wastewater treatment agent. Now we’re showing them that this material can also make metal extraction itself notably more efficient,” says Dr Ingo Hamann, who heads Production & Engineering within the Active Oxygen Business Line. As Hamann goes on to say, “Our process adds significant value for the mine operator—and it does that with very little investment and in an environmentally friendly way.”

Hydrogen peroxide is effective when added at a specific concentration and at a specific point in the flotation process. A very small amount of this highly effective oxidant is all that is required to increase the yield by approximately another 10% and to reduce the problematic pyrite content in the concentrate. Critical steps in the development process were determining the appropriate process window and adapting the process to various ore compositions.

Evonik, a creative industrial group from Germany, is one of the world leaders in specialty chemicals. One of its key areas of activity is in resource efficiency.

Evonik says that hydrogen peroxide isn’t just one of its oldest products—“it’s also one of the most innovative. Evonik is the second largest producer of hydrogen peroxide in the world.”

Hydrogen peroxide is often used as an oxidant in such metallurgical process steps as ore leaching, concentrate preparation or eluent treatment. Production of gold and uranium exemplifies some important hydrogen peroxide applications. Depending on the ore composition as well as the leaching conditions, using hydrogen peroxide can result in savings of eluents and acids, simplify management of chemicals or waste and improve overall process control.

In nature uranium occurs in the form of tetravalent or hexavalent oxide minerals (uraninite or pitchblende). Tetravalent uranium has, however, a very low solubility in both acidic or alkaline media. Thus, to achieve an economic uranium recovery, oxidation to the much more soluble hexavalent state is of great importance. Trivalent iron compounds are commonly used to increase uranium’s oxidation state. Hydrogen peroxide is applied for regeneration of the active Fe(III) ions in the eluent.

For gold production the most common method used nowadays is the cyanidation process. Depending on the leaching conditions, overall concentration of suspended ore as well as concentration of the oxygen consumers in the ore, hydrogen peroxide can be added to increase the total oxygen concentration in the system and to promote deeper leaching by direct oxidation. On the downstream side hydrogen peroxide is often used for removal of the cyanides from waste water. The cyanide oxidation takes place in a single step, without the formation of toxic intermediates.

For mining applications Evonik recommends the use of HYPROX® standard grade hydrogen peroxide.

To ensure optimal supply of hydrogen peroxide to the world market, Evonik operates production facilities at 12 locations in North and South America, Europe, Africa, and Asia.

The 12th location has just recently been added: In July 2014, Evonik Industries formally commenced operations at a new hydrogen peroxide plant in Jilin (China). The new production plant has an annual capacity of 230,000 t and is therefore not only the newest but the biggest hydrogen peroxide plant of the Group. Evonik is thereby raising its current global capacity for hydrogen peroxide production to more than 900,000 t/y.

“The Jilin plant is also proof of Evonik’s innovative strength: Evonik supplies H2O2 from Jilin via a pipeline straight to the neighbouring propylene oxide plant run by Jishen Chemical Industry, which has likewise been newly built. Jishen uses hydrogen peroxide and propylene to manufacture propylene oxide via direct synthesis on the basis of the HPPO process. Evonik developed the HPPO process together with ThyssenKrupp Industrial Solutions.

Evonik says “Hydrogen peroxide is one of the cleanest and most versatile chemicals available. Because of its beneficial properties, it is used in a variety of applications. Due to the unique chemical properties and environmental compatibility of hydrogen peroxide, Evonik in cooperation with its customers constantly develops new applications for this classic.”