REPROCESSING SLIMES TAILINGS FROM A TUNGSTEN MINE

This paper describes the development of a new process route for ultrafine wolframite recovery, to enable the efficient reprocessing of historical mine tailings as well as current plant slimes tailings from the Beralt Tin and Wolfram operations at Minas da Panasqueira in Portugal. Much of the wolframite in these tailings is below 25 microns in size and is associated with a complex mixture of other minerals including zinc, copper and other sulphides, tourmaline, siderite, ferromagnetic and other strongly magnetic material. The paper reports on flotation, magnetic separation and gravity concentration testwork, undertaken at both laboratory and pilot scale on the historical mine tailings and on the current slimes tailings of the plant. Froth flotation of the Panasqueira wolframite has been investigated over a number of years with very inconsistent results. This work highlighed further inconsistencies between the current tailings (which floated) and the old dam tailings (which did not). High intensity magnetic separation (at low to moderate fields) could not recover the finest wolframite and could not achieve the differential needed between the wolframite and siderite and the other strongly magnetic minerals present. At higher fields, there was a substantial recovery of the magnetic silicates and consequently poor weight rejection. Gravity separation testwork centred on the Multi-Gravity Separator with some work also being carried out using the Kelsey jig and Duplex separators. Results indicated that a three stage process with intermediate sulphide flotation could potentially produce a wolframite concentrate of 50% to 55% WO3, at a reasonable recovery. Concentrate cleaning options were logistically very difficult to investigate, one tonne of dam material only yielding a few kilogrammes of concentrate for testwork. In order to provide a thorough investigation, the limited testwork was backed up by extensive computer simulation. Computer simulation also played an integral part in developing the overall process flowsheet and in optimising this flowsheet to maximise recoveries.