Nexa Resources — then Votorantim Metais

Double filtration and gas treatment in the Waelz process

During implementation of the Waelz kiln for zinc recovery from recycled materials, the filtration system needed to combine product collection with treatment of contaminants in the process gases.

The challenge

With a total flow rate of 463,000 m³/h, the operation required a large-scale solution capable of recovering Waelz oxide and treating a gas stream containing contaminants such as dioxins and furans, heavy metals, and acidic compounds. The challenge was to integrate product recovery and environmental control without mixing the valuable material with residues from the treatment stage.

The solution

The project, carried out by Tersel, whose technological assets and customer portfolio were incorporated into Kleema in 2020, adopted two baghouses and an intermediate reaction tower, separating product recovery from gas treatment.

In the first stage, the baghouse collects Waelz oxide, a zinc-rich material recovered from the process. The gas stream then passes to the reaction tower, where hydrated lime and activated carbon are introduced.

Hydrated lime neutralizes acidic components, while activated carbon adsorbs dioxins, furans, and metallic contaminants susceptible to this mechanism. The second baghouse then retains the reagents, reaction products, and contaminants associated with the solids.

This configuration allows the product recovered in the first filtration stage to be collected separately from the material generated by environmental treatment in the second.

The results

The system passed the environmental tests performed and became an essential stage in zinc recovery, combining Waelz oxide collection with process gas treatment.