The company said the project had reached mechanical completion and was ready to start receiving ore and wet commissioning.
"The additional electricity supply for the expansion is expected to come on stream during Q3 2019," it said. "The company believes the start-up of the expanded plant will reach its nameplate capacity of 15Mtpa by December 2019."
New flotation and concentrate handling areas are already up to speed.
Atalaya has maintained copper production guidance for 2019 at 45,000-46,500t after producing 21,108t in the first half from a mill that handled 5.01Mt for the period.
"This expansion … will increase copper production, improve operational efficiencies, reduce maintenance requirements and lower operating cash costs for the company," said CEO Alberto Lavandeira.
Proyecto Riotinto continues to face opposition from the local Junta de Andalucia and Ecologistas en Acion requests to stop mining pending broadening of its environmental plan. So far rulings by the Tribunal Superior de Justicia de Andalucía reinforcing the validity of Atalaya's operating licence have overridden any objections.
"The company continues operating the mine normally and remains confident that the ongoing process carried out by the JdA will not impact its operations at Proyecto Riotinto," Atalaya said.