IMPROVING THE EFFECTIVENESS OF SCANDIUM SOLVENT EXTRACTION IN SULPHATE SOLUTION BY OPTIMIZING SCRUBBING AND STRIPPING PROCESSES

• Main Author: Puspa Wardhani, Dhita
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/71823
• Institution: Institut Teknologi Bandung

Scandium is a rare earth element (REE) with the highest value compared to other REEs. Examples of end products of the scandium extraction and refining processes are Sc2O3 and ScF3 compounds with a purity of 99%. The prices of these scandium extraction and refining products are pretty high due to the lack of scandium sources with high grade and volume as well as a challenging extraction and refining proces route. One of the metal ores that has the potential to become the raw material for scandium extraction is lateritic nickel ore. In previous studies, experiments were carried out on leaching of nickel laterite ore from Halmahera Island along with two-stage precipitation, re-leaching of scandium-bearing precipitate, and solvent extraction (SX) of the re-leached solution. Selective separation between scandium and impurities such as iron and aluminum can be carried out during solvent extraction stage. However, the results of solvent extraction experiments from the previous investigation showed that scandium extraction selectivity was not optimal. Therefore, this research was conducted to increase the effectiveness of scandium solvent extraction by optimizing the scrubbing and stripping processes in sulfate solutions that simulate the re-leach solution of scandium precipitate from limonite nickel ore processing obtained from Sangaji, Halmahera Island. The SX feed solution was prepared by conducting high pressure acid leaching of the ore sample at a temperature of 240°C and a pressure of 32 bar with sulfuric acid addition of 300 g/kg-ore followed by a two-step precipitation process to obtain scandium-bearing precipitate, which then re-leached again with sulfuric acid. After knowing the chemical composition of the second stage of the leaching solution of the iron precipitate, then an artificial sulfate solution is prepared with a dissolved metal concentration that simulates the second stage of the solution of the second stage of iron precipitate leaching. A series of SX experiments using D2EHPA as extractant was carried out in the extraction stage to study the effect of the sulfuric acid concentration of the feed solution on the extraction percentage of scandium, iron, nickel, cobalt, and aluminum as well as the separation factor of scandium and these metals. After extraction, scrubbing was carried out to study the effect of the type and concentration of reagents and volume ratio of organic solution to aqueous solution (O/A) on the scrubbing percentage of iron and aluminum. In the stripping stage, the effect of stripping agent concentration (NH4F), O/A ratio, and temperature on the stripping percentage of scandium, iron, nickel, cobalt, and aluminum was studied. Metal concentrations in aqueous solutions were measured using Inductively Coupled Plasma – Mass Spectroscopy (ICP-MS) and Atomic Absorption Spectroscopy (AAS). The experimental results showed that the best conditions for extraction stage was obtained at a sulfuric acid concentration in feed solution of 2M, D2EHPA concentration of 5% (v/v), O/A ratio 1/1, and process time 10 minutes with Sc, Fe, Ni, Co, dan Al extraction percentage of 99.87%, 4.71%, 10.96%, 6.98% and 16.74%, respectively. When the acid concentration of the feed solution is increased, the percentage of scandium extraction tends not to change, while the percentage of extraction of iron, nickel, cobalt, and aluminum tends to decrease. After the extraction stage, the scrubbing stage was carried out where the best conditions were obtained at 5M HCl concentration and 1/1 O/A ratio with yields of iron and aluminum scrubbing percentages of 72.92% and 4.16%, respectively. The scrubbing process is more effective using HCl than H2SO4, where the percentage of iron and aluminum scrubbing tends to increase with increasing concentrations of these two acids. The percentage of iron scrubbing tends to decrease with increasing O/A ratio, while the percentage of aluminum scrubbing tends to increase with increasing O/A ratio. For the stripping experiment, the best conditions were obtained at a concentration of 2M NH4F, an O/A ratio of 3/1, and a temperature of 40 oC with the percent stripping of Sc, Fe, Ni, Co, and Al respectively 96.35%, 21.50%, 1.30%, 0.64%, and 2.41%. The percentage of scandium stripping tends to increase as the NH4F concentration increases with the highest value at 2M NH4F concentration and then decreases again. Percent stripping of scandium, iron, and aluminum increases with increasing process temperature while their values decrease with increasing O/A ratio.