The company said the pilot plant was designed to produce up to 3 tonnes per month of battery-grade lithium carbonate.
"Despite COVID-19 restrictions and minor delays, the Millennial team has advanced the lithium concentration ponds and the pilot plant to the production stage," president and CEO Farhad Abasov said.
The development comes as lithium remains in a low-price environment due to oversupply and ramifications of COVID-19.
"While Benchmark expects the lithium market to remain in a surplus moving into 2021, we forecast a structural deficit from 2022 onwards as insufficient supply is due to come online to meet the battery industry's growing needs," Benchmark Mineral Intelligence said last week.
Millennial Lithium had received an environmental permit for Pastos Grandes in June.