THE COPPER PRODUCTION PROCESS
KAZ Minerals operates 6 producing mines. The 3 mines in East Region are underground while the Bozshakol, Aktogay and Bozymchak mines are open pit. The mines generally contain sulphide ores and by-products that vary in quantities and proportions between mines. The main by-products are zinc, silver, gold and molybdenum. Each step in the copper process focuses on removing increasing amounts of unwanted materials, turning ore into concentrate and then finished metals.
Our major growth project at Aktogay commenced production of copper cathode from oxide ore via SX/EW in December 2015 and the main sulphide concentrator at Aktogay commenced commissioning in December 2016. Bozshakol commenced production of copper concentrate from sulphide ore in February 2016.
Since completion of the Group restructuring on 31 October 2014 KAZ Minerals no longer carries out smelting and refining activities internally, instead sending copper concentrate directly to export markets or to external providers of smelting and refining services in Kazakhstan.
- Sulphide ores are taken from underground or open-pit mines by drilling and blasting with explosives.
- Large power shovels collect the ore and load it into haul trucks, The trucks transport the ore to the primary crushers. Primary crushing may take place in the mine to simplify transportation.
- The ore is processed through a series of crushers and mixed with water. This produces finely ground ore in the form of a paste or slurry.
- The slurry is mixed with various chemical reagents that can identify and coat the specific mineral particles.
- A liquid ‘frother’ is added to aid the separation process.
- This slurry is processed though the several flotation stages. The process recovers all valuable components of the ore, such as zinc, copper and precious metals.
- In the first stage of the flotation process (bulk flotation), the slurry (with reagents) is pumped into flotation tanks and injected with air to create bubbles. All the sulphide particles cling to the surface of the bubbles, which are skimmed off into troughs.
- In the second flotation stage (selective flotation) valuable minerals of different metals are separated from each other by adding special chemical compounds. These compounds force one mineral to cling to the surface of the bubbles and other minerals to stay inactive.
- As the bubbles condense, the water is drained off. This creates separated copper and zinc concentrates. Copper concentrate contains approximately 20% copper, plus various sulphides of copper and iron, and small concentrations of other materials, including gold and silver. Zinc concentrate contains approximately 40-45% zinc with other associated elements.
- Since completion of the Group restructuring on 31 October 2014 KAZ Minerals no longer carries out smelting and refining activities internally, instead sending copper concentrate directly to export markets or to external providers of smelting and refining services in Kazakhstan.
- When sent for smelting, the copper concentrate and a silica material known as a flux are fed into a Vanyukov furnace.
- The concentrate and flux melt and make the matte, comprising copper, iron and sulphur that settles at the bottom of the furnace. The rest of the iron chemically combines with the flux to form a slag, which can be separated off.
- Part of the sulphur in the concentrate combines with oxygen and forms the off-gas. This comprises sulphur dioxide, oxygen, water and nitrogen. Most of the sulphur dioxide is captured in the form of sulphuric acid. Sulphuric acid can be neutralised or sold for a wide range of applications. KAZ Minerals utilises sulphuric acid from Balkhash in the oxide ore heap leaching operations at Aktogay.
- The remaining material, called matte, contains 40-60% copper by weight.
- The molten matte is transferred into a smelting vessel called a converter. Here, additional silica flux and blast air are added to remove the iron and sulphur.
- The resulting molten material is called 'blister copper' and contains around 99% copper by weight.
- The blister copper is transferred into a refining furnace. Air is blown into the molten copper to oxidise part of the copper and most of the impurities. A sodium carbonate flux is added to remove traces of arsenic and antimony.
- The operator tests samples to determine when the impurities have reached the acceptable level.
- Oxidised copper is reduced using fuel oil to produce 99.5% pure copper. This is poured into moulds to form large plates of copper called 'anodes'.
- The anodes are loaded in a polymer-concrete tank. Next to each anode is a thin sheet of copper, known as a cathode. An electrical current is passed through the plates – the anode being the positive electrode and the cathode acting as a negative electrode.
- The tanks are filled with an acidic copper sulphate solution, which acts as an electrical conductor between the anode and cathode. The copper is dissolved from the anode and deposited to the cathode. Over approximately two weeks, the pure copper is formed on the cathodes from the anodes.
- As the copper is plated, the remaining impurities (slimes) fall to the bottom of the tank. These slimes contain the gold and silver.
- The cathodes are removed from the tank, and will be around 99.95-99.99% copper. The slimes are taken to a precious metals refinery, where they are refined into finished metal.
- KAZ Minerals receives by-product credits from the smelting and refining provider in return for the precious metals and other by-products contained within the copper concentrate we deliver.