Fly ash dan bottom ash (FABA) merupakan limbah hasil sisa pembakaran batubara dari pembangkit listrik tenaga uap (PLTU). FABA yang dihasilkan akan terus meningkat seiring dengan meningkatnya kebutuhan energi listrik yang harus dipenuhi. Komposisi FABA secara umum berupa silika, alumina, oksida besi, dan senyawa oksida lainnya. Abu yang dihasilkan dari pembakaran batubara berpotensi secara ekonomis karena mengandung beberapa unsur berharga antara lain Ge, Ga, unsur tanah jarang (REY), Nb, Zr, V, Re, Au, Ag, dan logam dasar seperti Al. Karakteristik fisik dan kimia FABA merupakan aspek penting yang dapat memengaruhi, baik potensi penggunaan maupun metode pembuangan atau penyimpanan limbah yang akan dilakukan. Potensi pemanfaatan FABA telah banyak digunakan pada bidang geoteknik, salah satunya diaplikasikan sebagai material geopolimer. Selain itu, FABA juga mengandung cenosphere yang merupakan salah satu material bernilai ekonomis tinggi dan telah banyak diaplikasikan pada berbagai bidang industri. Berbagai teknik pemisahan material untuk meningkatkan potensi nilai guna FABA telah berhasil dikembangkan, antara lain metode ektraksi cenosphere, logam berharga serta unsur jejak seperti REY, juga unburned carbon.
The escalating demand of REY in various industrial applications becomes an important issue nowadays. REY has prominent evidence to improve material properties such as high electropositive and good conductivity. In addition REY can be classified as one of renewable and clean energy resources. Due to the increasing demand of REY, exploration of alternative sources such as red mud, spent catalyst, and coal fly ash has been conducted. Coal fly ash is one of the promising alternative sources of REY in regarding to the low radioactive material concentration. The conventional method to recover REY from coal fly ash using inorganic acids produces harmful by-product to the environment. In this research, two steps experimental methods were conducted. The first step was silicate digestion which was performed using sodium hydroxide 8 M in which REY is concentrated, with solid to liquid ratio of 1:4 and temperature of 90°C for 120 minutes. The second step was leaching the REY using citric acid. The variables studied were pH, temperature and solid to liquid ratio. The optimum condition was at the temperature of 90°C, pH 1.7 and solid to liquid ratio (15%) for each element. The maximum recovery for each elements are 77.33% Lanthanum (La), 83.47 % Cerium (Ce), 88.78% Dysprosium (Dy) and 55% Neodymium(Nd). In addition, temperature does not have any significant efect at pH 3.8.
Spent catalyst is listed as one of the hazardous wastes. Based on the toxicity characteristic shows that spent catalyst contains some heavy metals at concentration above the regulations limits. This situattion becomes an important issue in nowadays. In this research, fungus Aspergillus niger was investigated to produce weak organic acid (citric acid). Batch experiments were performed to compare the leaching efficiency from spent catalyst of pulp density (2% and 4%) and particle size (212 µm, 150 µm and 75 µm). Result showed that after direct bioleaching process, maximum recovery of valuable metal 24.94%, 7.42%, 1.09%, 3.51%, 4.87% and 1.66% were achieved for aluminum, calcium, iron, copper, silver and platinum respectively at 2% pulp density. Overall data shows that metal recovery at pulp density 2% are higher than 4% pulp density. The maximum recovery based on particle size shows that the smaller particle (75 µm) the higher metal recovery (Al, Ag and Pt) and for some metals was different such as Fe, Cu and Ca.
In five years, from 2015 to 2020, the need of coal in Indonesia is doubled to 166.2 million tonnes and increasing up to 2050 as stated in the Indonesian Energy Mix policy. Generally, coal is used in the coal-fired power plan. After the combustion, there are some residual materials such as mineral matter, fly ash and bottom ash (FABA) listed as hazardous materials due to the toxicity and metal contents. Referring to the amount of coal consumption in 2020, the fly ash and bottom ash will be of about 19.92 million tonnes. The utilization of FABA is then become a must thing to do. One of the alternatives is rare earth element (REE) extraction. Indonesian coal contains sufficient amount of REE to extract that is concentrated in the FABA to the value of more than 400 ppm. Regarding to the REE mode of occurrence that is mostly concentrated in the glass form or amorphous silicate, this study was conducted in order to observe the effect of sodium hydroxide to breakage the amorphous silicate structure. In order to obtain the amorphous silicate, magnetic separator was applied. Based on the XRF analysis, the non-magnetic fly ash (amorphous silicate of glass form) contained major elements of SiO2, Al2O3, Fe2O3, CaO, MgO and the rest were minor and trace elements such as Na2O, K2O, Cr2O3, MnO, SrO and P2O5. The particle size of the amorphous silicate is less than < 38 μm (- 400 mesh). To run the experiments, sodium hydroxide was used as the reagent with varied concentrations of 6 M, 8 M and 10 M. Other variables were temperature of 28 0C (room temperature), 60 0C and 90 0C and residence time of 2, 4, and 6 hour. Based on the results analysis, the amorphous silicate was decomposed to the most of about 22 % at 90 0C of temperature, 10 M of sodium hydroxide concentration, and 6 hour of residence time.
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