Mineral processing with molten salts

The University of South Australia (UniSA), the South Australian and Western Australian governments and Centrex Metals are funding technology that will significantly reduce the cost of mineral processing using molten salts. The research, based around Centrex’s Oxley Potassium Project (Oxley), will expand current molten salt research for solar energy applications into minerals processing.

The project will be the basis of research targeting potassium from potassium feldspar, an alkali metal silicate mineral (KAISi₃O₈). Centrex has already developed a process route for its Oxley potassium deposit that is a mix of molten salt processing for conversion of potassium to a leachable form, followed by extraction and purification in a low-temperature aqueous circuit. The process route is focused on the production of high-value specialty fertilisers such as potassium nitrate or potassium sulfate.

Undertaken at UniSA’s School of Engineering and Future Industries Institute, the program will develop a minerals processing circuit to leach, extract and purify metals from silicate minerals in a solely molten salt environment, without the need for subsequent aqueous processing. If the research provides the ability for all processing steps to be undertaken in a molten salt environment, it will lower energy and water use and the associated costs, allowing consideration of and expansion of the project into lower-value bulk potassium chloride fertiliser to be manufactured by Centrex.

The research is proposed in three stages over approximately three years. Stage 1 will provide proof of concept for the behaviour of ore to be processed in a molten salt environment; Stage 2 will seek to design, build and test the required processing equipment components for the molten salt circuit; and Stage 3 will seek to construct a continuous pilot plant to demonstrate the technology. $464,000 of external funding has already been committed for the first two stages of research.

UniSA Associate Research Professor Frank Bruno, who is leading the project, said the challenges to providing proof of concept for the molten salt separation technology include mechanical and materials engineering issues involved with transferring and separating solids from highly reactive molten salts at high temperatures.

“Currently, molten salts are being used commercially in the solar and nuclear industries at temperatures up to 600°C and while molten salts are used commercially at higher temperatures for batch style minerals roasting processes, this project will develop novel technology for reaction, separation and purification processes in molten salts above 850°C,” Associate Professor Bruno said.

“The knowledge developed in relation to the mechanical and materials engineering issues involved with transferring and separating solids from highly reactive molten salts at high temperatures can be adopted in other applications such as solar power plants, high-temperature thermal energy storage, molten salt reactors, glass optical property modification and refining for other minerals.”

Contracts for the program are now being prepared and the research is due to commence in the second half of the year.