Outotec’s technology for the Kolwezi project involves 42-m, high-rate preleach thickeners. In what the company describes as a world first, its new Directional Autodil feed dilution system will be combined with a new-generation vane feedwell system. Outotec claims the patented Directional Autodil system has demonstrated outstanding advances in flocculant dispersion and effective feed dilution.

“The technology is a significant advance because, other than some minor design changes, feedwells in high-rate thickeners have changed little in the past 15 years,” said Richard Triglavcanin, global manager-thickening technology.

“Modern high-rate thickeners generally incorporate some form of internal dilution into the feedwell to dilute the feed and improve flocculation,” said Triglavcanin. “Directional Autodil advances this process by delivering dilution water into the feedwell in a controlled manner based on feed density so that it complements the flow of the slurry feed. There is, therefore, a strong flow pattern within the top half of the feedwell, ensuring optimized mixing of high density slurry feed and dilution water, together with flocculant.

“The shelf and vanes of this design produce both upper and lower zones in the feedwell. Vanes on the angle act as baffles to enhance mixing and dissipate the energy of the incoming flows. The bottom half of the feedwell is less turbulent and ideal for aggregate growth prior to exiting the feedwell,” said Triglavcanin.

The resource that underpins the Kolwezi project consists of stockpiled tailings from a mineral concentrator that processed high-grade ore from surrounding mines from the 1950s. Because of the poor recoveries obtained from conventional concentrating techniques, valuable amounts of copper and cobalt were discharged into two tailings dams that will be “mined” using high-pressure monitors.

In its first-half 2008 financial report, First Quantum noted that progress has continued on detailed design for the project and by the end of the second quarter the engineering design was approximately 76% complete, with detailed drafting 61% complete. Acid plant design progressed substantially and the majority of long lead equipment items have been ordered. Substantial design completion for the project is estimated for late 2008. Approximately $213 million of the project budget has been committed to date.

According to the company, construction work on the process plant has begun and by the end of the second quarter plant earthworks were progressing, the first major concrete pours had occurred, onsite tankage fabrication had started and first deliveries of structural steel had been dispatched from the fabricator and were en route to the site. Project construction completion and commencement of precommissioning is estimated for the fourth quarter of 2009.

Commercial start-up is expected to take place during the first quarter of 2010. The plant, which will begin producing at a rate of 35,000 mt/y copper and 7,000 mt/y of cobalt hydroxide, is being designed and built to allow doubling of its capacity for an incremental capital cost of $40 million. According to the company, future development of a cobalt metal facility and expansion of copper and cobalt capacity will depend on actual experience onsite and on commodity market conditions.