Condensed from an OPSIS AB article by Bengt Löfstedt, first published 2025-10-30.
Aluminium production has to manage occupational health and safety as well as the effect of the potline and its emissions on the surrounding environment. Hydrogen fluoride attracts the most attention: it is highly reactive and harmful, and the potline environment — high temperature, heavy dust and strong electromagnetic fields — makes on-line measurement difficult. Aluminium is well suited to recycling and remelting, but much of the metal still comes from new capacity, extracted from bauxite in two stages. The ore is ground, mixed with sodium hydroxide and treated at high temperature and pressure to give alumina; the alumina is then electrolysed in a molten fluoride bath, where carbon anodes are consumed and the oxygen from the alumina forms CO and CO2 at the anode, together with NO2, SO2 and HF. Electrolysis is energy-intensive, so this stage is often located where electricity is cheap. HF matters because it attacks glass, forms a corrosive and toxic acid with water, burns skin, can cause blindness and leads to fluid in the lungs; at high concentrations it can be fatal. Both workplace concentrations and emissions matter, the latter through stacks and as diffuse emissions from potroom roof vents. The OPSIS LD500 laser analyser measures HF in ducts and in potroom air with the same instrument.
Chinese smelters are large and the potroom is the hard part: strong magnetic fields, dust, heat, and fluoride that attacks anything exposed. An extractive system needs a heated, corrosion-resistant sample path and frequent filter changes, while a cross-duct or open-path optical measurement keeps the electronics away from the potline — which is why we favour it for HF. Two engineering points. Choose the optical path above the crust breaker and clear of crane travel, and make sure purge air is dry and oil-free, because humid purge air forms hydrofluoric acid on the window and etches it. For stack emissions the industry standard sets the limit and the monitoring requirement, with the CEMS following HJ 75 and HJ 76 like any other stationary source. For workplace monitoring the target is an occupational exposure limit with a different averaging time, which is a different measurement: the same analyser can serve both only if the two data streams are kept separate and clearly labelled.
Environmental Monitoring in the Aluminium Industry — read the original at opsis.se ↗
Written by Bengt Löfstedt, OPSIS AB, first published 2025-10-30. The summary and the A.Johnson note above are our own text; the OPSIS article remains the authoritative version. Chinese reader? See the full Chinese article.
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