ASX-listed American Tungsten and Antimony (AT4) plans to initiate the restart of the Del Sol antimony refinery, in Nevada, before the end of the September quarter.

The restart will be done in phases with initial batches focused on establishing circuit performance before throughput is progressively increased. The restart of the Del Sol antimony flake circuit will be done using feedstock from the White Spar antimony mine, which AT4 recently entered into an acquisition agreement for.

The phased approach to the Del Sol restart is expected to derisk the ramp-up of the plant, identify bottlenecks in the existing configuration and identify equipment additions that may be required to lift capacity within the existing building footprint.

The restart programme is designed to generate data across batch cycle time, throughput, antimony recovery, reagent and consumable consumption, power draw, cathode quality and product purity, labour requirements and maintenance intervals. This data set is intended to inform the engineering and design work for any expanded facility, including the scope and specification of additional caustic leach tanks, filter presses and electrowinning cells.

Antimony flake produced from the restart is intended to allow AT4 to provide product samples to prospective customers and progress product qualification for potential offtake discussions.

Additionally, the operating data set gathered from the plant is expected to form a technical base for US government funding applications.

The company has issued requests for proposal to international engineering firms covering antimony flake capacity expansion and the addition of Regulus II antimony metal, antimony trisulphide, sodium antimonate and ammonium paratungstate (APT) circuits at Del Sol.

AT4 has also had a pre-application meeting with the Nevada Division of Environmental Protection to confirm the requirements for a formal application to expand permitted capacity at Del Sol form 18 500 short tons of feed a year to about 100 000 short tons of feed a year and to add APT production.

For context, the Del Sol refinery and White Spar mine are the subject of a share sale and purchase agreement announced on July 28, which has not yet been finalised. AT4 says all work programmes are conditional on completion of the acquisition.