SEPARATION OF NICKEL AND COBALT FROM RE-LEACH SOLUTIONS OF MIXED HYDROXIDE PRECIPITATE BY SELECTIVE OXIDATION USING OZONE AS AN OXIDANT

• Main Author: MAGNALITA OCTAVIANI (NIM : 12513032), ANGGIA
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/21095
• Institution: Institut Teknologi Bandung

Hydrometallurgical process has an advantage for treating low-grade laterite ore <br /> <br /> <br /> <br /> because of its ability to recover cobalt as a by product. One of the methods that has <br /> <br /> <br /> <br /> been used to recover nickel and cobalt from pregnant leach solution is as an <br /> <br /> <br /> <br /> intermediate product such as Mixed Hydroxide Precipitate (MHP). Furthermore, <br /> <br /> <br /> <br /> refining of MHP can be done by ammonia or sulfuric acid re-leaching followed by <br /> <br /> <br /> <br /> solvent extraction. The separation of nickel and cobalt is a difficult task due to their <br /> <br /> <br /> <br /> similar chemical properties. The difference between these two elements is the <br /> <br /> <br /> <br /> stability of Co in the form of trivalent that can be easily precipitated. Strong oxidant <br /> <br /> <br /> <br /> is required to increase interface potensial of cobalt to its trivalent ions tability. Ozone <br /> <br /> <br /> <br /> is a strong oxidant with standard reduction potential 2.07 V. In the present study, <br /> <br /> <br /> <br /> dissolution behaviour of nickel and cobalt from MHP was studied and the <br /> <br /> <br /> <br /> efectiveness of ozone as an oxidant for separation of nickel and cobalt in releach <br /> <br /> <br /> <br /> solution of MHP was investigated. <br /> <br /> <br /> <br /> This study was divided into two stages, namely re-leach of MHP and oxidationprecipitation <br /> <br /> <br /> <br /> using ozone. Initial characterization of MHP was done by X-Ray <br /> <br /> <br /> <br /> Diffraction (XRD), X-Ray Fluorosence, Atomic Absorption Spectroscopy (AAS), <br /> <br /> <br /> <br /> and moisture analysis. Variations of acid concentration, temperature, and solid-liquid <br /> <br /> <br /> <br /> ratio were conducted to study the dissolution of nickel and cobalt. The effects of pH, <br /> <br /> <br /> <br /> precipitation time, injection rate of oxygen, and temperature were studied in <br /> <br /> <br /> <br /> oxidation-precipitation experiment. Characterization of oxidation-precipitation <br /> <br /> <br /> <br /> residue from the best condition were carried out by XRD analysis. The study of <br /> <br /> <br /> <br /> cobalt precipitation kinetics was carried out by applying an-n order homogenous <br /> <br /> <br /> <br /> chemical reaction kinetic models at temperature of 25oC, 50oC, and 60oC. <br /> <br /> <br /> <br /> The investigation results showed that the increased of acid concentration and <br /> <br /> <br /> <br /> temperature enhance the percentages of Ni and Co dissolution, while the increased of <br /> <br /> <br /> <br /> solid-liquid ratio decrease the percentages of Ni and Co dissolution. The best <br /> <br /> <br /> <br /> condition of re-leach experiment was achieved in a condition of acid concentration of <br /> <br /> <br /> <br /> 2 M, solid-liquid ratio of 100 g/L at temperature 95oC, in which the percentages of <br /> <br /> <br /> <br /> nickel and cobalt dissolution were 99,97% and 95,47% respectively. In oxidationprecipitation <br /> <br /> <br /> <br /> experiment, the increased of pH and precipitation time increase the <br /> <br /> <br /> <br /> percentages of cobalt precipitation. While, the increased of feed gas oxygen injection <br /> <br /> <br /> <br /> rate and temperature decrease the percentages of cobalt precipitation. The best <br /> <br /> <br /> <br /> condition of oxidation-precipitation was obtained at pH 5, feed gas injection rate of 1 <br /> <br /> <br /> <br /> lpm, precipitation time of 2 hours at room temperature, in which the percentages of <br /> <br /> <br /> <br /> cobalt precipitation was 99,94%. The kinetics of precipitation of cobalt followed zero <br /> <br /> <br /> <br /> order kinetics of chemical reaction with activation energy of -5.401 kJ/mol. The <br /> <br /> <br /> <br /> results of XRD analysis showed that CoOOH and MnO2 were formed from oxidationprecipitation <br /> <br /> <br /> <br /> of Co and Mn in re-leach solution of MHP using ozone.