Energy Use: Metal Casting - Copper

All aspects of primary copper production use energy. In general, mining uses about 20% of the total energy requirement, mineral processing (grinding, concentration, floatation) another 40%, and smelting, converting, and refining the remaining 40%.

Energy use will vary by type of production process (pyrometallurgical or hydrometallurgical). However, for the more prevalent pyrometallurgical approach, the smelting, converting and refining (electrolytic or fire) processes will collectively consume 30 to 40 million Btu per ton of copper produced. Flash smelters can reduce the overall energy demand to about 20 million Btu per ton.

The table on the following page illustrates the fuel and electrical energy portion of the overall energy requirements for the differing pyrometallurgical processes. Then the total million Btu / ton requirement is provided.

Other notes on pyrometallurgical energy use: Waste heat is generally recovered from both flash and reverberatory furnaces and used to preheat combustion air and / or to generate electrical power (cogeneration) in the acid plant. Waste heat can also be used to dry the furnace charge before smelting, as moisture can carry off heat from the furnace (and increase overall fuel requirements). Drying usually uses natural gas and will typically consume between 1 to 3 Mcf per ton of cathode copper. Using waste heat can reduce the overall drying requirement by up to 0.7 Mcf per ton. Oxygen enrichment is utilized in reverberatory and reactor methods to attain greater oxidation and lower energy use.

Additionally, energy (primarily electricity) is consumed to produce copper in a hydrometallurgical process. In the most common hydrometallurgical process, the ore is leached with ammonia or sulfuric acid to extract the copper. After the copper is released into solution, the copper is removed from the solution by electrowinning (a process similar to electrolytic refining). Pumping is a major energy expense for these processes. Electricity for pumps is estimated at around 13.5 million Btu / ton of cathode copper produced (nearly 4,000 kW per ton) and represents a major expense for copper producers. These costs could be addressed with Engine Drive pumps (see ED module). The main variables in pumping costs are the concentration of copper in the leachate (how much leachate is available) and the distance from the leachate production area to the solvent extraction facility.