BIOLEACHING OF RARE EARTH ELEMENTS FROM RED MUD WASTE OF THE BAUXITE ORE PROCESSING INDUSTRY IN TAYAN, WEST KALIMANTAN, USING THE BACTERIUM SERRATIA RUBIDAEA STRAIN SKC-11 WITH IRON-SELECTIVE BIOFLOCCULATION PRE- TREATMENT

• Main Author: Angelina Ayu Widayati, Lisna
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/77327
• Institution: Institut Teknologi Bandung

Red mud is the residue of processing bauxite ore into alumina. Red mud is alkaline and toxic but contains precious metals such as Fe, Si, Al, Ti, and rare earth elements (REEs) such as Ce, Sc, Y, Nd, and Gd. As an alternative energy metal extraction especially REEs from red mud was developed using the environmentally friendly biohydrometallurgical processes. In general, the low percent extraction of REEs from the bioleaching process is due to the high iron content in the red mud. In this study, pre-treatment of iron selective bioflocculation for red mud from the bauxite ore processing industry in Tayan, West Kalimantan using the bacterium Bacillus nitraiireducens strain SKC/L-2 as a bioflocculant before leaching with bioleaching process using the bacterium Serratia rubidaea strain SKC-11 to increase the percentage of REEs extraction. A series of experiments were carried out to optimize REEs bioleaching from red mud by studying the influence of feed, pulp density, and bioleaching time on the percentage of REEs extraction. After sample preparation, pre-treatment of selective iron bioflocculation is carried out on red mud (200# 74 ????m). The bioflocculation process was carried out for 5-8 minutes using a 100 mL graduated cylinder with a volume ratio of red mud slurry (10 g/L) pH 7 and bioflocculant of 8:2. Futhermore, the bioleaching process was carried out at room temperature (±25°C), medium pH 1, 10% (v/v) bacterial inoculum, and rotary shaker speed 183 rpm for 14-21 days. Bioleaching experiments were carried out at variations of feed (red mud, bioflocculated precipitate, and supernatant precipitate), variations of 2% and 5% pulp density, and variations of 14 and 21 days of bioleaching. Percentage of REEs extraction as a function of time under various bioleaching was periodically determined by ICP-MS (Inductively Coupled Plasma-Mass Spectrometry) analysis. Iron-selective bioflocculation pre-treatment of red mud before bioleaching results in a higher percent extraction of REE than without bioflocculation. The total percentage of extracted REE was 71,514%. The complexity of the mineral composition and the presence of inhibitory compounds in red mud can lead to a reduced percentage of REE extraction. At a higher pulp density, the concentration of metals will increase, and the environment will become more toxic for bacteria, decreasing the percent extraction of REE. The longer the bioleaching time, the higher the percentage of REE extraction, but if it is too long, the bacteria will enter the deadly phase, thus inhibiting the extraction process. Based on the experimental results, the best bioleaching process parameter is the variation of 2% pulp density with bioflocculated precipitate feed carried for 14 days, with a percent REE extraction value of 93,7% Eu; 93,3% Y; 91,7% Ce; 89% Gd; 88,7% Tb; 88,7% Dy; 88,3% Pr; 86,3% Nd; 73,7% La; 66,9% Er; 62,1% Sm; 60,6% Ho; 57,4% Yb; 43,8% Tm; 35,5% Lu; and 29,7% Sc.