New salt cake recycling technology

Processing of recycled aluminium generates by-products such as dross and salt cake. Typically, the salt cake steam contains metallic aluminium, salts (mainly potassium chloride (KCl) and sodium chloride (NaCl)), and aluminium oxides. These are some of its recoverable components that are non-toxic.

The EU-funded project ALUSALT (Efficient aluminium salt cake recycling technology) aimed to develop a recycling system that is smaller than existing technologies, making salt cake recycling more accessible and cost effective.

To achieve its goal, ALUSALT set out to develop a flue gas transfer system that takes the heat and pressure of the flue gas from the rotary furnace. The flue gas is then used as a source of heat for the evaporator. The new process reuses all available energy that is lost during the aluminium recycling process, eliminating the need for additional energy for the salt cake recycling. Proper nozzles will inject the hot flue gas from the rotary furnace.

One of the main tasks over the first project period was to characterise the flue gases of the aluminium processing. Project partners collected the flue gas particles through magnetic metal separation units and used chemical analysis methods and spectroscopy techniques to determine their composition.

Validating multiphysics models for flue gas injection in the evaporator and gas combustion in the combined heat and power system were also an important part of project work. Significant effort was devoted to determining and testing the suitability of the evaporation technology for the drying brine solution consisting of NaCl and KCl.

Other tasks were to determine the composition and volume of different salt cake gases stemming from the evaporation tanks and to design can combustors to minimise emissions.

The ALUSALT system should allow in situ recycling of salt cakes at the aluminium recycling plant, avoiding their transportation to salt cake recyclers. This minimises costs and increases the competitiveness of the European aluminium recycling industry.