Production of sponge iron from the ok tedi pyrite concentrates

The Ok Tedi Copper Mine in Papua New Guinea has accumulated large quantities of pyrite concentrates over time at Bige dam where they are disposed and buried below the water table. These pyrite concentrates contained substantial amount of iron which are of economic value. Therefore this study was done to investigate the possibility of extracting iron from the pyrite concentrates in the form of sponge iron for commercial purposes. The pyrite concentrates were analyzed by Scanning Electron Microscopy (SEM) – Electron Dispersive Analysis X-ray (EDAX) and the results showed; 29.6 % Fe, 11.8 % C, 23.5 % O, 0.1 % Mg, 1.2 % Al, 4.1 % Si, 28.1 % S, 0.6 % K, and 0.7 % Ca by mass. Oxidizing roasting tests were conducted on the pyrite concentrates to increase the grades of iron oxides prior to reduction tests by use of coconut charcoal carbon. The particle sizes of pyrite concentrate range in size from 150 µm to 106µm. Several reduction tests were conducted on the various roasted pyrite concentrates in a fusion furnace at varying temperatures and times. Sample masses were noted before and after the roasting processes. The pyrite concentrates were oxidized at temperatures and times ranging from 700 °C to 1000 °C and from 5 minutes to 40 minutes, respectively. SEM-EDAX analysis of the oxidized pyrite concentrates at 1000 °C and in roasting time of 40 minutes showed; 52.3 % Fe, 20.7 % S, 12.3 % O, 5.2 % C, 5.7 % Si, 3.4 % Ca, 0.3 % Cu by mass. Loss of mass during roasting were observed and recorded. Hence, the gravimetric results indicated that the roasting kinetics were marginally faster at 850 °C. Sulfur was not completely removed however iron content was appreciably upgraded. Products of the roasted pyrite concentrates at a temperature of 1000 °C and roasting time of 60 minutes were used in the isothermal carbothermic reduction process. About 30 g of roasted products were mixed with 30 % by mass of carbon and reduced at temperatures ranging from 900 °C to 1000 °C and reduction times ranging from 30 minutes to 120 minutes. Analysis of the reduced product sat 1000 °C in 120 minutes by SEM EDAX showed; 52.7% Fe, 4.7% C, 33.6% O, 0.7% Mg, 0.7% Al, 4.4% Si, 4.5% S, and 0.7% Ca by mass.  Oxygen was not completely removed, but the iron content increased appreciably due to removal of sulphur. The results suggest that the pre-roasting of the pyrite concentrate needs to be carried out at temperatures between 850 – 900 oC with prolong time to completely remove sulfur. It also suggests that the final reduction temperature needs to be below 1000oC because CO2 is unstable above this temperature. Therefore, it is necessary to adjust the temperature and time of reduction to prevent re-oxidation of the sponge iron produced. Reduction of iron oxide will occur more efficiently if the initial sulphur in the charge is low. Hence magnetic separation of the iron oxides may be tried to increase grade.