Thermal characteristics of ferronickel slag on roasting process with addition of sodium carbonate (Na₂CO₃)

Thermal characterization of ferronickel slag waste has been studied using TG / DTA, XRD, and SEM-EDX. The characterization of the initial samples of ferronickel slag was carried out TG / DTA to 1200°C. The result obtained is at a temperature of 800°C, there is an increasing mass and up to 4.68% at a temperature of 1200°C. At temperature of 807.4°C to 845.8°C, an exothermic reaction occurs. The increasing mass is due to the ferronickel slag which is originally in the form of metal, and then it was roasted to undergo an oxidation reaction so that the metal that has been formed, it returned into oxides. So that the weight of the sample mass increase. Samples of ferronickel slag added with sodium carbonate were also analyzed using TG / DTA. The results obtained are 2 endothermic peaks at temperatures of 90.6°C and 858.9°C with a total mass reduction of 49.3%. At a temperature of 90.6°C, there is a heavy loss caused by 2.38% loss of surface water. The XRD result of ferronickel slag is composed of enstatite (MgSiO₃), forsterite (Mg₂SiO₄), fayalite (Fe₂SiO₄), and quartz (SiO₂) structures. From the XRD analysis, the composition of silica oxide associates with magnesium and iron in the form of enstatite, forsterite, and fayalites is a very dominant composition. The roasting process of a mixture of ferronickel slag with sodium carbonate was carried out by heating at a temperature of 800-1000°C for 1 hour, and the sample result of roasting were analyzed using XRD. The result of roasting shows that the roasting process takes place more perfectly at higher temperature; it is indicated by the increasing phase intensity of SiO₂ and the formation of sodium silicate (Na₂SiO₃). The result of SEM shows that the higher the temperature, the distribution of Na, Si, and O elements tend to cluster in the same place or spot, while the elements of Mg, Si, and O are less bonded.