South32 and Fives join hands to limit HF emissions at its Hillside aluminium smelter

Headquartered in Perth, South32, the mining and metals company has been working on an ambitious project in the Hillside Smelter to decrease GTC stack Hydrogen Fluoride (HF) emissions to 0,5 mg/Nm³ by April 2025 to meet new environmental regulations. Following the installation of the first Alumina Cascade Feeding System on one Gas Treatment Centre (GTC) earlier this year, fives has reaffirmed its plan to deploy the solution on four other GTCs, as well as to convert its VIBRAIR pocket filters into Extended Surface Bags.

Incorporating the now-famous technology of the "Extended Surface Bag" into GTC has several benefits, including increased filtering surface, increased pollution treatment capacity, decreased system pressure drop, and decreased HF stack emissions. At the start of the year, fives struck a collaboration deal with SOLAFT, an Australian firm known for its innovation capabilities. SOLAFT has recently created the Primaflow™ Starbag™ and Starcage™, which de-bottleneck the original extended surface bag design.

The conventional alumina distribution system must be rearranged and modified to accommodate the Fives Alumina Cascade Feeding System. This solution entails injecting twice as much fresh alumina into the first filter of a pair of parallel filters, each processing an equivalent amount of raw gas, and then redirecting the overflow of partially fluorinated alumina from the first filter to the second in series, where it flows to the fluorinated alumina silo and then to the pots. During the warmer season or when emissions exceed typical levels, the control room operator will activate the Cascade mode automatically.

This approach reduces fluoride gas emissions from GTCs by 30 to 50 per cent during the summer, reduces scale development, and is simple to install on existing GTCs. This initiative is part of Hillside's commitment to implementing Fives recommendations from earlier audits to achieve emissions objectives, tackling the difficulties of a more virtuous sector.