Study of quenching treatment after limonite ore reduction to decrease silica content

Limonite is one of the nickel lateritic ores presents in Indonesia. It contains many compounds such as hematite (Fe2O3) and silica (SiO2) besides its nickel main content. As one of the the most dominant compounds in the limonite ore, silica complicates the process of increasing nickel content from the ores. In the previous study, addition of sodium additives such as Sodium Hydroxide or (NaOH) and Sodium Sulfate (Na2SO4) helps to bind Si content from nickel ores and liberate iron to increase nickel content, which possibly occurs by phase transformation into silica or iron-contained phase such as Na2MgSiO4 and FeO. In this study, Na2CO3 is used to bind silica from the ores, so the nickel recovery is estimated easier and higher than before. In addition, quenching post-reduction treatment is conducted to transform the solid silica-based phase into aqueous phase, then separating it from its residue. In this research, the samples are divided into roasting without quenching and roasting-quenching treatments. The roasting is done at 825°C operating temperature held for an hour, and ratios between Na2CO3 and limonite are 0:4, 1:2, 3:4, and 1:1. The quenching is done for roasting-quenching samples right after the reduction, followed by drying of the samples. Simulated Thermal Analysis (STA), X-Ray Fluorescence (XRF), X-Ray Diffraction (XRD), and Inductively Coupled Plasma (ICP) analysis are the methods used to determine reduction temperature, chemical contents in the limonite samples, phase transformation after reduction, and silica contents at the filtrate, respectively. Based on this study, the silica contents in roasting-quenching samples are higher than without quenching process, showing that the binding reaction in the samples is stopped forcefully by the rapid-cooling of water, when the roasting without quenching samples still have more reaction time due to slow cooling rate in the furnace.