Aluminium fluoride for aluminium smelting
AlF3 is currently produced from aluminium hydroxide, an intermediate form of alumina, by reaction with anhydrous hydrogen fluoride gas (AHF) that is produced from fluorspar and sulfuric acid. Fluorspar is classed as a critical material in the USA and EU, and high-quality fluorspar is increasingly in short supply. About 10% of AlF3 production uses fluorosilicic acid (FSA) in place of AHF. FSA is a by-product from production of phosphoric acid (fertiliser).
The Alcore process produces AlF3 from low-cost raw materials, including recycled aluminium smelter wastes.
Bath: Aluminium smelting pots use molten cryolite as the electrolyte ’bath’ to dissolve the alumina feedstock and allow electrolytic smelting to produce metal. AlF3 is regularly added to maintain optimum bath chemistry and efficiency.
Over time the process generates excess bath, which is periodically removed (‘tapped’) and sold to other smelters that require bath, particularly new smelters. In the last decade, the global bath market has moved into oversupply and smelters are increasingly finding it difficult to sell tapped bath, and increasingly do so at a loss. The likelihood that China will ban bath imports will exacerbate the problem.
Dross smelter waste forms on top of the molten aluminium in casting furnaces and consists of aluminium oxide, aluminium metal and some cryolite. Aluminium metal can be recovered, but the non-metallic component is sold at a loss, e.g. as an additive for steelmaking. Many smelters have significant stockpiles of dross that are an ongoing cost, environmental and community relations issue.
Alcore recovers fluorine from tapped bath and selectively reacts metal oxides to produce metal fluorides. The selective reaction of metal oxides allows the use of aluminium-rich but slightly impure, low-cost raw materials such as dross, because impurities do not report to the AlF3 product.
AlF3 prices are quoted monthly and typically range from US$1,000/t to US$1,800/t ex China, before transport costs.
Producer costs range between US$1,000/t and US$1,700/t (Roskill) and raw materials typically represent 75% of the production cost; mainly fluorspar and aluminium hydroxide.
Alcore’s costs are in the lowest quartile and returns are high. Results are all-equity and assume no by-product revenues.
Table 1: Scenarios for first 10,000 t/y and expanded AlF3 Alcore production modules
The Alcore process will close waste loops in aluminium smelters to further enhance their environmental performance, add security of supply and increase efficiency.
: Improved aluminium value chain and environmental benefits from recycling after adoption of the Alcore process
Alcore is working closely with major aluminium producers to secure feedstock materials, assess product quality and plan Alcore’s path to market. Alcore has an MoU with the Japanese global trading company Sojitz to explore a potential business relationship.
The critical prerequisites for the recovery of fluorine from tapped bath, and the production of AlF3 from aluminium hydroxide, are routinely achieved in the laboratory.
Table 2: Latest AlF3 produced at the Alcore Research Laboratory
Commercial Plant: Alcore’s first plant is planned to be located at Bell Bay, northern Tasmania, near an existing hydro-powered aluminium smelter. This will be the first AlF3 plant in Australia.
The initial capacity is intended to be 10,000 t/y aluminium fluoride, which would supply about 35% of the demand from the Australasian aluminium smelters. The ultimate capacity is intended to be 30,000-60,000 t/y.
Initial production may commence using aluminium hydroxide as a risk-minimisation strategy (still economically attractive), but Alcore will then start using low-cost feed materials such as bauxite or dross, which provides a major cost advantage for Alcore.
Pilot Plant Stage: Engineering validation has commenced to reduce the technical risk for the 10,000 t/y plant. Evaluation of some process steps in a 10 kg/h pilot plant will finalise the first production plant design.
Alcore will continue coordination with governments on this project, which meets many prerequisites under various government stimulus packages.