Alumina & Bauxite: Session I
Sponsored by: TMS Light Metals Division, TMS: Aluminum Committee
Program Organizers: Errol Jaeger, The Business Consultants FZ-LLC; Stephan Broek, Kensington Technology Inc
Monday 2:00 PM
March 20, 2023
Room: 31B
Location: SDCC
Session Chair: Errol Jaeger, The Business Consultants FZ-LLC
2:00 PM
Process Simulation with Tertiary Cyclone for Kaolinite Removal from Amazonian Bauxite Reduction in Mineral Processing: Allan Reis1; Geraldo Magela Duarte1; Eslyn Neves1; Geovan Oliveira1; Thiago Jatobá2; 1Hydro Mineração Paragominas; 2Mineral Processing Solutions
Bauxite is the main ore for metallic aluminum production, consisting of aluminum and iron oxides and kaolinite, a clay mineral commonly found in Amazonian bauxites, as the main carrier of reactive silica. In the process, due to the small particle size, kaolinite is usually removed by attrition and washing of coarse material followed by desliming using hydrocyclones. In the Bayer process, kaolinite reacts with sodium hydroxide, increasing reagent consumption in the process. Beneficiation process at Mineração Paragominas is based on the separation of coarser fractions with higher gibbsite content from the clay minerals, where kaolinite is more concentrated. The separation takes place in hydrocyclones, equipment that inherently presents a by-pass of fine particles for the underflow, consequently, contaminating the concentrate with kaolinite, increasing the operating cost in the Bayer process. Additional desliming stages were evaluated for a potential increase in kaolinite removal. Industrial surveying campaigns were carried out and mass balances obtained after laboratory characterization and statistical analysis of operational databases. Nageswararao model for hydrocyclones was calibrated and used in tertiary stages simulation. A black-box model was developed for predicting the benefits on bauxite chemical composition. Five routes for bauxite silica reduction were analyzed considering the inclusion of tertiary stages of desliming in cyclones. Process simulations pointed to a potential solution for the reduction of reactive silica in Paragominas’ bauxite, setting tertiary cyclone in fine classification circuit (26” cyclones) as the most attractive solution, with a potential silica reduction of 4.9%, with 0.4% loss in metallurgical recovery of alumina.
2:25 PM
Granulometry Impact on Digestion Efficiency and Cost-economics in Alumina Refinery for East Coast Bauxite (INDIA): Suchita Rai1; M.J. Chaddha1; Prachiprava Pradhan1; K. J. Kulkarni1; M. Panchal1; A. Agnihotri1; 1Jawaharlal Nehru Aluminium Research Development and Design Centre
Due to the fast depletion of bauxite resources, beneficiation is a crucial step mainly to reduce silica and iron content. Crushing, grinding, and sieving the bauxite in various size fractions are essential to determining suitable feed size during alumina production. East Coast bauxite was grounded and crushed into different granulometry ranging from +2.8 mm to -0.045 mm. Al2O3 enriched in the coarser fractions, while SiO2, Fe2O3, and TiO2 content increased in finer fractions. There is a decrease in digestion efficiency from coarser to finer size, increasing the specific bauxite and caustic soda consumption. Consequently, up-gradation can be accomplished by discarding a few finer sizes. With an improvement in bauxite quality, for a 1-million-tonnes alumina/annum plant capacity, caustic soda consumption can be reduced by approximately 2160 tonnes of NaOH with a savings of 18000 tonnes of process bauxite.
2:50 PM
Effect of Thermal Activation Temperature on Pre-desilication of Low-grade Bauxite: Chaojun Fang1; Tianrui Cai1; Bo Lv1; Xiaowei Deng1; Jinming Zhang1; Zeya Zhao1; Bobing Dong1; 1Henan Polytechnic University
With the increase of requirements for environmental protection, the Sintering process with high carbon dioxide emission was gradually reduced in application. However, for low-grade bauxite, it was difficult to be directly economically utilized by the Bayer process, and a pre-desiliconization process was often required. This paper researched the influence of different thermal activation temperature on the pre-desiliconization process of low-grade bauxite. The results showed that the phase transformation of low-grade bauxite was not much different at different thermal activation temperatures, but the pre-desiliconization behavior was different. Compared with 650°C and 700°C, the pre-desiliconization results of low-grade bauxite after thermal activation at 600°C had a significant improvement. Only after 30 minutes of leaching, the ratio of alumina to silica of low-grade bauxite can be increased from 2.39 to 6.78. This study may have a certain significance for selecting a suitable thermal activation temperature to promote the high-efficiency pre-desiliconization of low-grade bauxite.
3:15 PM
Study of Repeatability and Reproducibility in Analyzes of Available Alumina and Reactive Silica in Bauxites: Paula Lima1; Danielle Matos1; Walter Santana1; Jaqueline Pinho1; Janyne Ramos1; 1Hydro
Bauxite is a rock composed of minerals and impurities. The main components in bauxite are kaolinite, gibbsite, hematite and anatase. Gibbsite is one of the minerals important for aluminum production. In the mining industry, quantification of minerals and impurities is needed, with gibbsite being reported as available alumina, and kaolinite, one of the major impurities, as reactive silica. The precision of these analysis results influences figuring out the KPIs needed to define the productivity of the Bayer process, aiding the decision making process. So, it is necessary to apply a robust methodology to ensure the quality of a quantitative analysis, such as repeatability and reproducibility analysis (R&R). The R&R analysis of these measurements was performed at Hydro Alunorte (Barcarena/PA/Brazil) with 3 different bauxite samples and applying an ANOVA statistical analysis. P- and T values of 6.5% and 10% were achieved for the analysis of available alumina and reactive silica, respectively. With the data it was possible to find opportunities for improvement, reduce deviations, and guarantee quality and reliability in the Bayer process.
3:40 PM Break
3:55 PM
Zero Waste Alumina Production: Casper Van Der Eijk1; Camilla Sommerseth1; 1SINTEF
The Pedersen Process is an alternative process for the production of alumina. Initially, bauxite ores, or other aluminous materials, are smelted with lime to produce pig iron and a slag of mainly calcium aluminate composition. The latter is subsequently leached in Na2CO3 solutions to extract alumina. The Pedersen Process can handle a wide range of bauxite qualities and the by-products can be used in other industries, thereby eliminating the need for land deposit. An EU financed project, called EnsureAl, has investigated the possibility of the commercialization of the Pedersen Process. The presentation will summarize the main findings of this project concerning the quality of the produced alumina and the by-products. It will also present a comparison with the Bayer process concerning the environmental impact and costs of the process.
4:20 PM
Statistical Modelling of Operating Parameters on Bauxite Slurry Hyperbaric Filtration: Clara Souza1; Eduardo Moreira1; Enio Laubyer1; Fabricia Ferreira1; Antonio Silva1; Raimundo Neto1; 1Hydro Alunorte
The Hydro Alunorte refinery receives bauxite slurry used in the alumina production from Mineração Paragominas, both sites located in Pará – Brazil. This bauxite slurry is transported via pipeline and dewatered in hyperbaric filters located in Alunorte. To improve the overall equipment effectiveness of the dewatering plant, this work evaluated the influence of the rotation speed, basin level, and slurry density on the filters' productivity by applying a factorial design. The experiment, which was carried out on the industrial filters, complemented the outcome of a previous investigation executed on a laboratory scale using slurry density, top size, and pH as control factors to assess the solids throughput through Box Behnken Design. Results indicated that a top size reduction decreases productivity by up to 20%. However, an increase in density, rotation, and basin level proved to offset this loss.
4:45 PM
Reduction of GHG Emissions and Increase Operational Reliability using Immersed Electrode Boiler in an Alumina Refinery: Rodrigo Neves1; Fernando Melo1; Everton Mendonça1; Erinaldo Filho1; Jeferson Carneiro1; 1Norsk Hydro
The Hydro Alunorte refinery, located in Pará – Brazil, uses heavy oil, mineral coal and electrical energy boilers in its energy matrix to meet the steam demand of the Bayer process. Aligned with Hydro's environmental strategy to reduce greenhouse gas (GHG) emissions, Hydro Alunorte started operating the first electric boiler with immersed electrode technology as one of the initiatives to increase the share of electricity in the steam generation energy matrix. The new immersed electrode boiler has higher operational reliability with an availability of approximately 99.5% and with load control by adjusting the level of the electrode chamber, thus loads variation can be done in minutes to control the consumption demand of the refinery. Therefore, it is expected to reduce fuel oil consumption consequently reducing CO2 emissions by approximately 150,000 tons per year.
5:10 PM
Steam Grid Stability using Advanced Process Control and Real Time Optimization in an Alumina Refinery: Rodrigo Neves1; Fernando Melo1; Danilo Arcodaci1; Daniella Costa1; João Freitas1; Ediciano Junior1; Juvenal Sousa1; 1Norsk Hydro
The Hydro Alunorte refinery has a complex steam system composed by boilers and generation turbines that use three types of fuel (heavy oil, coal and electrical energy) to produce steam for the Bayer process. Due to the complex nature of the refinery and the variable price of fuels, two programs integrated directly with the plant Distributed Control System (DCS), aims to improve energy efficiency and steam system stability, reduce greenhouse gas (GHG) emission and avoid cascade plant shutdowns. Advanced Process Control (APC) controls boilers load, steam headers pressure and minimize relief valves opening. Real Time Optimization (RTO) is above APC and is responsible for give the best configuration to steam matrix based on fuels price. This paper will describe how both programs can help steam grid to be stable and financially better to the refinery.