Erection of slag recovery in Italy
Secondary aluminum salt slag recovery
During the re-melting process, the Secondary (recycled) Aluminum industry produces dross which typically contains metallic Aluminum (about10%wt), Aluminum Oxide (about 50%wt) and a mixture of Potassium Chloride and Sodium Chloride (about 40%wt). Metallic Aluminum is recovered by mechanical means. For environmental reasons, the remaining part of the dross cannot be disposed easily.
In GEA-Messo PT systems, the salts are separated from the insoluble Aluminum Oxide (this is eventually filtered out) in a hot leach step. Ammonia generated in the recovery process can be neutralized with Sulfuric acid, and fertilizer-grade Ammonium Sulphate can be produced. The Potassium Chloride and Sodium Chloride contained in the leachate can be crystallized separately or as a mixed salt solid. The salts can be recycled to the Aluminum Recovery section or sold for industrial uses. Evaporative Crystallization units utilizing Thermal Vapor Recompression or multiple effect evaporation are used for this task. These recovery systems can be designed to operate as Zero Liquid Discharge plants.
Zinc oxide wastewater treatment plants
When leaching Waelz oxide (zinc) from recycling of steel plant dust the resulting solutions are containing sodium and potassium chloride, as well as sulphate compounds. Heavy metals, like Zn, are precipitated with soda ash and separated by filtration.
With GEA Messo PT evaporation and crystallization experiences a processing concept has been established in the respective recycling market, which is operated under zero liquid discharge conditions. Heating is realized by MVR or Thermocompression. The crystallization of Glaserite, which is one of the compounds crystallizing as well as the material resistance, had been the challenging development targets. The obtained condensate is internally recycled.