NEAR-INFRARED SPECTROSCOPY (NIRS) SORTING IN THE UPGRADING AND PROCESSING OF SKORPION NON-SULFIDE ZINC ORE

摘要

In 2008 Anglo American sponsored a research project at RWTH Aachen University to assess thernfeasibility of the use of near-infrared spectroscopy (NIRS) for ore waste discrimination at thernSkorpion zinc mine.rnThe Skorpion mine is an open pit zinc mine located in Namibia, owned by Anglo American with anrnannual production of 150 000 t/a of super high grade pure zinc. Opportunities for the implementationrnof NIRS sorting for the Skorpion process exist to upgrade currently subeconomic material, includingrnthe marginal dump (over 2000 000 tonnes, av grade of 2.5 per cent Zn).rnNIRS sorting is not yet implemented or established in the minerals industry however it is a provenrntechnology in the plastics recycling industry, where more than 2000 NIRS sorters have already beenrninstalled. NIRS sorting, a type of sensor-based sorting, is a single particle sorting technique whichrnclassifies the particles based on the absorbed/reflected radiation in the near-infrared (NIR) region. Arndisadvantage of NIRS is that it is a surface measurement technique, but NIRS sorting shows overallrngreat potential for the minerals industry.rnSkorpion ore minerals include zinc bearing phases such as sauconite, hemimorphite, smithsonite,rnand hydrozincite. These display diagnostic responses in the near-infrared. There are three majorrnabsorption features that characterise the reflectance spectra of the ore bearing minerals. These arerndue to OH and H_2O molecular bonds. The spectral response of the waste material is caused by otherrnminerals such as non-zinc-bearing clay minerals, calcite and impure quartz.rnTest work showed that it is theoretically possible to separate ore material from most waste materialrnbased on spectral response in the NIR region. In addition to upgrading material by removal of wasternit is also potentially feasible to classify the material based on zinc grade. A tentative correlationrnbetween zinc grade and spectral response seems to exist for the sample test suite in the NIR region.