For his massive contribution to the large-scale commercialisation of solvent extraction of copper, in Zambia and worldwide, Jack Anthony Holmes, formerly Technical Director of Anglo American Corp (AAC), has been nominated by Ken Severs (formerly Group Metallurgical Executive, Rio Tinto) and Les Stewart (formerly Technical Director, Anglo American Corp, South America).
In 1970, Holmes, after a year of private study and calculation, persuaded the understandably apprehensive Board of Anglo American Central Africa Ltd to abandon convention and rather invest upwards of $150 million in some innovative technology to recover 100,000 t/y of residual acid-soluble copper from current and accumulated flotation tailings at Nchanga mine: that technology was solvent extraction (coupled with electro-winning). This bold proposal was made at a time when SX of copper was in its mere infancy, having been installed in only Arizona at very small scale, in specifically Ranchers Bluebird (5,000 t/y copper) and Bagdad (7,000 t/y copper). The recommended venture represented considerable (albeit much-investigated, by JAH himself) technical and financial risk to Nchanga mine; and it was a major vote of confidence in Jack’s capabilities, for a positive decision to have been taken by the Board, at that time. The Zambian project accordingly went ahead and the plant was commissioned in 1973. The operation’s early and obvious success generated universal confidence in the technology and heralded the subsequent worldwide acceptance of SX-EW as a reliable and preferred technology for recovery of leached copper (and later zinc and cobalt). Although a succession of other plants of substantial size soon emulated the Nchanga project, the latter remained the biggest in the world for a decade or more.
Recovery of the material from the tailings dams was done by hydraulic monitoring, as used at English China Clays; and this too was probably a first for the metals mining industry. Leached tailings were dewatered in the biggest horizontal-belt-filter installation in the world; and indeed, the filters were developed and modified, especially for the project.
It was an inspired decision of Jack’s, before final plant design, to seek permission from Bagdad Copper Company, to ‘borrow’ sections of its 7,000 t/y commercial plant, for his metallurgists to use as a pilot plant, in which newer technologies and optimising techniques could be researched and developed. One piece of Anglo knowledge that was disclosed gratuitously to Bagdad and allowed to become public, was the use of dissolved cobalt (in electrolyte) to stabilize lead anodes when operating at increased levels of acidity and current density. This modus operandi is now standard practice, throughout the industry.