In every pyrometallurgical process, slag is produced. The slag can then be charged back into the existing process lines or in settling units that recover valuable metals. Alternatively, it is discarded and either sold to off-takers (in the cement or construction industry) or needs to be dumped in costly deposits. Dumping of the slag will become the most undesirable solution and should be avoided. SMS has developed several possibilities to convert the slag into products. These slag treatment solutions are a central part of the circular economy approach as part of our BlueTechnology philosophy.
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Electric slag settling and slag cleaning furnaces
BenefitsAs one of the leading suppliers of electric slag cleaning and matte settling furnaces, Metix – as part of SMS group – has gone a step further and developed a new generation of these furnaces. In continuous operation, the novel, rectangular furnace design boasts significant advantages compared to conventional circular furnaces. The electrodes are arranged in-line to ensure uniform power distribution and cover the whole furnace vessel. The system also has additional positive effects during the cleaning and settling process, ensuring that the copper content in the cleaned slag is reduced to a minimum. SMS group offers its customers cooling and lining concepts that increase the lifetime of the furnace significantly.
Moreover, SMS group is working on innovative concepts to boost recycling rates. Electric slag cleaning furnaces are primarily used in the nickel, copper, lead, and PGM (platinum group metals) industries, recovering metals from slags. This began in the 1950s when SMS group installed its first units. The units are so successful that more than 40 units have been supplied by SMS group / Metix to date. Depending on the slag properties and volumes, rectangular or circular solutions are possible.
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BlueSlag process – slag conditioning technology
The nonferrous metals industry produces large amounts of various slag types. The objective of many producers is to sell the slag as a premium product and avoid dumping costs. Due to tighter legislation, this is becoming more challenging for certain types of slag, because the benchmark for undesired elements and components in the slag is too high. SMS group has been working on optimizing the slag conditioning process for decades.
The BlueSlag process follows a two-step principle, the ladle treatment station and the slag settling furnace, and was primarily developed for the treatment of copper and nickel slag. In the ladle treatment station, the slag is heated and purged/stirred with gaseous reduction media. Fluxing and the addition of solids is also possible. During operation, the liquid metal droplets, which are entrapped in the slag, grow as a result of the stirring and enhanced coagulation effects in the stirred melt.
The treated slag is then charged into a rectangular settling furnace, where the enlarged droplets fall onto the furnace hearth and are tapped separately from the slag. Our goal is to reduce Cu content in discard slag to under 0.3 %. Impurities in Cu slag, such as Zn, Pb, or As, are also reduced to obtain slag as a product.
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Benefits
- Joule’s heat liberation for additional temperature increase by electrodes
- Additional chemical reduction
- Injection of reduction gases to accelerate the rate of reduction (optional)
- Forced migration of metal/matte droplets under stirring conditions
- Coalescence of metal/matte inclusions due to stirring
- Settling of the larger metal/matte inclusions under gravity
