Synthesis of silica precipitates from ferronickel slag using water leaching with alkali fusion treatment

Ferronickel slag is a by-product of ferronickel processing. The amount of ferronickel slag is comparatively large to ferronickel products with a ratio of 6:1. The content in ferronickel slag that can still be utilized is silica (Si) and magnesium (Mg), its two largest main compositions. With a very high content of up to 50%, Si can be extracted as silica precipitates. Silica precipitates is widely used for various industrial applications such as paints, bitumen, ceramics, glass, absorbents, fillers, and others. The manufacturing process of silica precipitate from ferronickel slag used in this research consists of several stages. The initial stage is the drying of ferronickel slag in an oven at a temperature of 110°C for 8 hours. The next step is to mix the ferronickel slag with sodium carbonate in a ratio of 1:1 (wt.%/wt.%) using a mixer for 1 hour. The roasting process is carried out at a temperature of 900°C in a muffle furnace for 2 hours. The roasting results are then dissolved in water with room temperature variations up to 100°C, a leaching time of 1 to 4 hours, solids: water weight ratio of 1:5, and stirring speed of 500 RPM. The last step is to precipitate silica by titration the sodium silicate solution using hydrochloric acid, filtering the silica precipitate formed, and finally drying the silica precipitate in an oven at a temperature of 110°C for 8 hours. The results of XRD analysis show an amorphous silica reference graph which is an indication of the silica precipitates formation. This is also supported by the results of SEM-EDS mapping which shows the distribution of silica element along with oxygen which is very dominant in a large area. Moreover, the XRF results on silica precipitates also showed that the SiO2 content analyzed is of 96.071%.