DEVELOPMENT OF THE HARTLEY-PLATINUM LEACHING PROCESS

The flowsheet for the Base Metal Refinery of BHP-Delta Gold's new Hartley Platinum mine in Zimbabwe was developed jointly by BHP, as manager of the joint venture, and Outokumpu Research at Outokumpu's research laboratories in Pori, Finland in 1994. Leaching and solid-liquid separation testwork was carried out on matte produced from the Hartley trial mine in bench scale equipment. The objectives of the program were to prove the process flowsheet as well as to provide engineering design data for the project team. The mine will produce a matte containing about 42% nickel, 34% copper, 1% iron, 0.4% cobalt and 22% sulphur along with the platinum group metals. The base metals will be selectively leached from this matte leaving the primary product, namely a precious metals concentrate, suitable for toll refining by a third party. The by-products from the refinery will be cathodic nickel and copper, a crude cobalt sulphate crystal as well as a sodium sulphate by-product. During flowsheet development, emphasis has been put on reduction of recirculating loads of the 'soluble' precious metals as well as product and by-product quality. The plant will be commissioned by mid-1996 with full production to be realised in early 1997 when the mine builds up to the planned output of 153,000 ounces of platinum per year.