Microwave-assisted carbothermic reduction of red mud using palm kernel shell charcoal: A circular economy approach for sustainable iron recovery Abdul Hapid, Adji Kawigraha, Nur Vita Permatasari, Nur Ikhwani, Yeni Novitasari, Siti Zullaikah, Sri Harjanto, Agung Setiawan Biomass and Bioenergy, 2026 Red mud, a byproduct of bauxite processing, presents a significant environmental challenge with 4.6 billion tons currently stored globally and 4.3 million tons generated annually in Indonesia. Simultaneously, palm kernel shells from crude palm oil (CPO) processing represent an underutilized biomass resource of 13.2–14.3 million tons annually. This work presents a microwave-assisted reduction (MAR) process for the simultaneous valorization of both waste streams by recovering iron from red mud using palm kernel shell charcoal (PKSC) as a renewable reductant. Microwave carbothermic reduction at 2.45 GHz was employed using briquettes of red mud and PKSC, with systematic investigation of microwave power (500–900 W), reduction time (2.5–30 min), and carbon-to-oxygen (C/O) molar ratio (0.8–2.2). Characterization was conducted via X-ray diffraction (XRD), scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX), and metallization analysis. Maximum iron metallization of 94.3% was achieved under optimized conditions (800 W, 30 min, C/O = 1.4) with a peak temperature of 1214 °C, without the need for chemical additives. This result represents a 50% reduction in processing time compared to conventional electric furnace methods (60 min at 1400 °C achieving 97.2% metallization) at a 186 °C lower temperature. Thermodynamic analysis identified critical temperature thresholds for sequential oxide reduction pathways (Fe 2 O 3 → Fe 3 O 4 → FeO → Fe). The microwave-selective heating of iron oxides provides a competitive alternative to conventional external heating methods, particularly due to its volumetric and rapid heating characteristics. This process demonstrates the technical and economic viability of integrating two major Indonesian industrial waste streams into a value-added product through energy-efficient pyrometallurgical processing, with implications for establishing domestic iron raw materials supply and advancing circular economy objectives.
Response Surface Methodological (RSM) Approach for Optimizing Free Cyanide Destruction from Gold Cyanidation Waste in Artisanal and Small-Scale Gold Mining using Sulfur Dioxide and Air Process Dadan Mohamad Nurjaman, Harmin Sulistiyaning Titah, Adji Kawigraha, Ipung Fitri Purwanti, Nur Vita Permatasari Polish Journal of Environmental Studies, 2025 Artisanal and small-scale gold mining (ASGM) in Indonesia has transitioned from using mercury to cyanidation, but the treatment of cyanide waste remains unaddressed, posing environmental and health risks. This research aimed to optimize the destruction of free cyanide in gold processing waste using the sulfur dioxide and air processes catalyzed by copper, employing a response surface methodology (RSM). The cyanide waste destruction process was conducted in laboratory-scale aeration system reactors with fixed variables: an initial pH of 9.48±0.065, maintained at pH 8, dissolved oxygen levels of 4.21±0.73 mg/L, and a temperature of 28.82±0.89°C. Independent variables of the process were determined to be an SO<sub>2</sub>/CN<sup>-</sup> weight ratio of 10, a copper (II) catalyst concentration of 50 mg/L, and a processing time of 4 hours. These parameters effectively reduced free cyanide from 200 mg/L to less than 0.5 mg/L, meeting the strict environmental standards set by the Indonesian Government. This method utilizes readily available materials and equipment, aligning with the knowledge level of ASGM operators and supported by local resources. The findings contribute to addressing the environmental and health risks associated with cyanide waste in the ASGM sector in Indonesia.
Formation and growth of metallic iron microparticle during carbothermic reduction of red mud with palm kernel shell charcoal Agung Setiawan, Adji Kawigraha, Boy Attaurrazaq, Sebastian Nahar, Nur Vita Permatasari, Irwan Haryanto, Nur Ikhwani, Sri Harjanto, M. Akbar Rhamdhani Case Studies in Chemical and Environmental Engineering, 2024 The present study investigated the formation and growth behavior of metallic iron microparticles during the carbothermic reduction of red mud using palm kernel shell charcoal (PKSC) as a reducing agent. The experiments involved both thermodynamic simulations and experimental reduction work. The thermodynamic calculations predicted that liquid and solid metal, slag, mullite, corundum, and spinel would form as the main phases through the reduction process at 600–1500 °C. The experimental result revealed that the identified phases were metallic iron, spinel, and corundum when the reduced pellets reacted up to 1400 °C for 60 min. The total weight loss of a mixture of red mud and PKSC was estimated at 22.12 % based on thermogravimetric analysis. The metallization degree of iron in the reduced pellets increased with increasing the reduction temperature and the reaction time. The maximum metallization degree and mean size of iron metallic microparticles were obtained at 97.2 ± 0.7 % and 36.79 μm, respectively, when the reduced pellet was heated at 1400 °C for 60 min. The microstructure observations showed that when the temperature and reaction time increased, the metallic iron microparticles formed, sintered together, and progressively grew.
Evaluation of a recycling process for discarded integrated circuits using physical separation methods Angella Natalia Ghea Puspita, Rahmadhani Triastomo, Yurian Ariandi Andrameda, Rininta Triaswinanti, Kurniawan Kurniawan, et al. Aip Conference Proceedings, 2024 Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Twitter Facebook Reddit LinkedIn Tools Icon Tools Reprints and Permissions Cite Icon Cite Search Site Citation Angella Natalia Ghea Puspita, Rahmadhani Triastomo, Yurian Ariandi Andrameda, Rininta Triaswinanti, Kurniawan Kurniawan, Muhammad Dzikri Ahira Soefihara, Farrel Alvian Purnama, Muhammad Dzikra Ulya Soefihara, Nur Vita Permatasari, Ridha Cindra Oktian, Mujianto; Evaluation of a recycling process for discarded integrated circuits using physical separation methods. AIP Conf. Proc. 28 February 2024; 3003 (1): 020070. https://doi.org/10.1063/5.0186578 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAIP Publishing PortfolioAIP Conference Proceedings Search Advanced Search |Citation Search
Laterite Nickel Hydrometallurgical Residues Characterization and Potential Utilization of Valuable Elements Nur Ikhwani, Sri Harjanto, Adji Kawigraha, Yurian Ariandi Andrameda, Nur Vita Permatasari Aip Conference Proceedings, 2023 Approximately 80% of the hydrometallurgical process of low-grade laterite nickel ore is converted into residue. The handling of residues from processing is a significant challenge in this process According to the characterization test, each type of extraction process produces a different type of residue. The characteristics of the compound in the extraction process using High Pressure Acid Leaching (HPAL) and Sulfation-Roasting-Leaching (SRL) methods are similar to the dominance of Hematite (Fe2O3) and Fe content > 40%. Atmospheric leaching (AL) residues are dominated by compounds in the form of the mineral Fayalite with a high Si content (Si > 50%). Furthermore, Jarosite is a residue of the precipitation process of Fe impurities dissolved in Pregnant Leach Solution (PLS). Depending on the properties of the elements and compounds, each type of residue has divergent utilization potential. With a variety of recycle methods, SRL, HPAL, and jarosite waste can be converted into hematite as a raw material for the iron-steel industry. Roasting or alkaline leaching procedures can reduce the sulfur concentration in the residue to less than 1%. Furthermore, sponge iron (Fe metal) can be extracted using the direct reduction method from SRL and HPAL residue. The AL residue can be processed into the intermediate product sodium silicate. Sodium silicate can be utilized as a chemical absorbent, geopolymer, and adhesive product with the addition of additives and certain production process.
Iron Recovery from Residue of Lateritic Nickel Leaching Industry Nur V. Permatasari, Hadiyanto, Budi Warsito, Adji Kawigraha, Nur Ikhwani E3s Web of Conferences, 2021 HPAL (High-Pressure Acid Leaching) is one of the important technologies for extracting nickel and cobalt from nickel laterite ore. In the next few years, some plants using this technology will be operated in Indonesia. The production will be estimated to be 543,000 tons per year by 2025. On the other hand, HPAL will produce more than 26 million tonnes of residue, and it requires good management. The residue utilization for certain industrial raw materials is one of the solutions. To determine the potential utilization residue, the characteristic of the residue must be elaborated through some methods. The characterization is carried out based on mineralogical and chemical properties. The feed used in the HPAL process dominates with magnetite and goethite with 41,15 % Fe and 1,35 % Ni content. The residue of HPAL contains Fe and significant Sulphur content, silica, aluminium and calcium. The quantity of Sulphur must be decreased by the desulfurization method then followed by the reduction process. The analysis shows that HPAL residue is still required additional processing for reducing the Sulphur content. The residue utilization trial still needs to be done to determine the quality of the iron-making products produced produced.
