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Reaping high-value metals from slags and drosses

Non-ferrous metals producers are being offered an alternative way to process the thousands of tonnes of slags and drosses produced annually by the sector, and whose high-metal content makes them a valuable resource.

Newly available equipment called the Alchemizer (pictured) has been designed to enable producers achieve very high-metal recovery rates from aluminium, copper, copper alloy, tin and zinc drosses, and profitably recover metal from secondary aluminium process salt slags.

Alchemizer is a low-energy mechanical reduction system that is said to offer a number of advantages over the usual ball mill designs. Compared with batch processes, the continuous system is said to achieve cleaner recovered metal, free from oxide contamination. This ensures the metal yield is not reduced as commonly occurs in the ball mill process.

TTC of Newhaven, East Sussex, has been appointed the exclusive agent for Alchemizer by its developer Glynn Astbury. Commenting on the unit, TTC managing director Clive Hall says: The Alchemizer is without doubt the most reliable, efficient technology at a competitive price and cannot be matched by other dross processing equipment.

According to TTC, the action of the Alchemizer rapidly separates oxides and light dust from the metal, leaving clean, concentrated metallic pieces which, when melted, produce a very high-recovery yield. Other fractions are recovered for sale or safe disposal along with process dust. After leaving the unit, aluminium can be recovered from pulverised slag by a simple screening process and can be remelted with very low additions of new salt to achieve high-metal yields.

With a continuous throughput and a power rating of 50kW, TTC says that the Alchemizer is suited to a wide range of metal processors and that even low-grade salt slag can be treated profitably.

A complete system is supplied with the front-end feed and back-end recovery components needed for fully automatic mechanical handling and is said to be fully compliant with environmental regulations. Ancillaries include feed hopper, conveyors, screens and dust recovery systems.

With rising disposal costs and stricter environmental requirements, the economic recovery of metals from slag is a significant issue. To this end, Goudsmit Magnetic Systems recently entered into a partnership with Twence Waste Processing and Feniks Recycling in order to increase the metal yield in slag separation plants.



Recovery

The new non-ferrous separator is designed to be able to catch small metal particles of only 510mm in size. In addition 95% of all metal components in slag can now be removed. This means that the slag no longer qualifies as chemical waste and can be used in road construction. The non-ferrous separators can also be used for recovering other materials, including wood and glass.

The magnetic system works on the eddy current principle: if a magnet is moved in a conductor then an eddy current is created which itself generates a magnetic field. This works in the opposite direction to the generator so that the conductor, which is metal, is repelled. This enables separation of the conductors (metal) from the non-conductors (product) to take place. Using the Goudsmit principle, materials that can be magnetised, such as iron and tin, are removed magnetically in advance. This improves non-ferrous separation, where the application areas include: vehicle scrap, cable waste, glass, domestic waste, wood, plastic and construction and demolition rubble.

The non-ferrous separator is equipped with a conveyor belt with a width of between 0.4 and 1.5m and can be adjusted from 0.2 to 2.5m/second. A rapidly rotating magnet roller is fitted at the end of the belt and it is this that creates the eddy currents. The revolutions per minute of the roller can be accelerated from 0 to 3,600. The eddy currents generate an opposed magnetic field so that the non-ferrous metals are repelled from the roller. u

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