Selective Scandium (Sc) Extraction from Bauxite Residue (Red Mud) Obtained by Alkali Fusion-Leaching Method

Bauxite residue, known as “red mud,” is a potential raw material for extracting rare-earth elements (REEs). The main REEs (Sc, Y, La, Ce, Nd, Nb, and Sm) from the raw bauxite are concentrated in RM after the Bayer leaching process. The earlier worldwide studies were focused on the scandium (Sc) extraction from RM by concentrated acids to enhance the extraction degree. This leads to the dissolution of major oxides (Fe2O3 and Al2O3) from RM. This article studies the possibility of selective Sc extraction from alkali fusion red mud (RMF) by diluted nitric acid (HNO3) leaching at pH ≥ 2 to prevent co-dissolution of Fe2O3. RMF samples were analyzed by X-ray fluorescence spectrometry (XRF), X-ray diffraction (XRD), electron probe microanalysis (EPMA), and inductively coupled plasma mass spectrometry (ICP-MS). It was revealed that Sc concentration in RMF can reach up to 140–150 mg kg−1. Sc extraction was 71.2% at RMF leaching by HNO3 at pH 2 and 80 °C during 90 min. The leaching solution contained 8 mg L−1 Sc and a high amount of other REEs in the presence of relatively low concentrations of impurity elements such as Fe, Al, Ti, Ca, etc. The kinetic analysis of experimental data by the shrinking core model showed that Sc leaching process is limited by the interfacial diffusion and the diffusion through the product layer. The apparent activation energy (Ea) was 19.5 kJ/mol. The linear dependence of Sc extraction on magnesium (Mg) extraction was revealed. According to EPMA of RMF, Sc is associated with iron minerals rather than Mg. This allows us to conclude that Mg acts as a leaching agent for the extraction of Sc presented in the RMF in an ion-exchangeable phase.

Selective Scandium (Sc) Extraction from Bauxite Residue (Red Mud) Obtained by Alkali Fusion-Leaching Method

One of the potential sources of rare-earth elements (REEs) is the solid waste from alumina industry - bauxite residue, known as “red mud” (RM). The main REEs from the raw bauxite are concentrated in RM after the Bayer leaching process. The earlier worldwide studies were focused on the scandium (Sc) extraction from RM by concentrated acids to enhance the extraction degree. This leads to the dissolution of major oxides (Fe2O3 and Al2O3) from RM. This article studies the possibility of selective Sc extraction from alkali fusion red mud (RMF) by diluted nitric acid (HNO3) leaching at pH ≥ 2 to prevent co-dissolution of Fe2O3. RMF samples have been analyzed by X-ray fluorescence spectrometry (XRF), X-ray diffraction (XRD), electron probe microanalysis (EPMA), and inductively coupled plasma mass spectrometry (ICP-MS). Sc extraction has been found to be 71.2 % at RMF leaching by HNO3 at pH=2 and at 80 °C during 90 min. The kinetic analysis of experimental data by the shrinking core model has shown that Sc leaching process is limited by the interfacial diffusion and the diffusion through the product layer. The apparent activation energy (Ea) was 19.5 kJ/mol. We have established that according to EPMA of RMF, Sc is associated with iron minerals; it could act as the product layer. The linear dependence of Sc extraction of magnesium (Mg) extraction has been revealed. This fact indicates that Mg can act as a leaching agent of Sc presented in RMF by ion-exchangeable phase.

Advances in the Safe Disposal and Comprehensive Utilization of Spent Carbon Anode From Aluminum Electrolysis: Prospects for Extraction and Application of Carbon Resources From Hazardous Waste

Spent carbon anode (SCA) is a dangerous solid waste that is continuously discharged from the aluminum electrolysis industry and has a large number of valuable resources and a high risk of environmental pollution. Its safe disposal and resource utilization have become a resource and environmental problem that must be solved urgently. Current methods for SCA disposal include flotation, vacuum metallurgy, physical activation, roasting, bubbling fluidized bed combustion, alkali fusion, alkali leaching, and chemical leaching combined with high temperature graphitization. In this paper, the material composition, resource properties, and environmental risks of SCA are discussed. Working principle, treatment process, advantages and disadvantages of the above methods are also briefly described and compared. Results showed that flotation is the safest disposal and comprehensive utilization technology that is suitable for characteristics of SCA raw materials and has the most large-scale application potential. In addition, characteristics of SCA recovery products are correlated to the recycling of aluminum reduction cells. This technology can alleviate the shortage of high-quality petroleum coke resources in China’s carbon material industry and the high cost of raw materials in aluminum electrolysis industry.

Preparation and Characterization of Chabazite from Construction Waste and Application as an Adsorbent for Methylene Blue

Construction waste, produced from building projects, was utilized to prepare chabazite by alkali fusion hydrothermal synthesis method. The synthesized chabazite was used as an adsorbent for the removal of methylene blue (MB). XRD, FTIR, and N2 adsorption/desorption curves were adopted to describe the physical and chemical properties of the samples. The results show that the synthesized chabazite possesses crystalline structure, typical functional groups, and large specific surface area of 421.34 m2 g-1. Adsorption isotherms and kinetic curves show that the adsorption process follows the Langmuir model and pseudo-second-order kinetics model. The maximum adsorption capacity of MB on the synthesized chabazite reaches up to 129.18 mg g-1 at 298 K, which is about 16 times that of construction waste. The removal rate of MB reaches more than 90%, and the adsorbed amount is about 35 mg g-1 after 1 h at 298 K. Thermodynamic parameters, namely Δ H , Δ S , and Δ G of -12.83 kJ mol-1, -27.37 J mol-1 K-1, and -4.68 kJ mol-1 at 298 K, respectively, indicate that the adsorption of MB on the chabazite is physical, orderliness-tended, and spontaneous process. Moreover, the synthesized chabazite has a good property of regeneration and reuse. The results indicate that using construction waste to prepare chabazite in application as an adsorbent is feasible, which provides a novel and environment-friendly way for recycling construction waste.

THE EFFECT OF PH AND CALCINATION TEMPERATURE ON THE ZrO2 PHASE FORMATION FROM NATURAL ZIRCON SAND OF KERENG PANGI

In this research ZrO2 has been synthesized from Kereng Pangi zircon sand in Central Kalimantan through alkali fusion-coprecipitation method. Firstly, zircon sand (ZrSiO4) was purified to reduce impurities by magnetic separation, cleaned using an ultrasonic cleaner, soaked/leached with HCl 2 M for 12 hours and leached with HCl at 60 ºC for 3 hours. Secondly, alkali fusion was done with KOH as an alkali. This product was then washed by water and dried before leached with HCl 30% at 90 ºC for 30 minutes to precipitate and seperate Silica from Zircon. ZrO2 filtrate (ZrOCl2) precipitated with NH4OH at pH 4, pH 7, and pH 10 forms Zr(OH)4 gel. Zr(OH)4 gel was dried and characterized by DTA-TGA, which was then followed by calcination based on DTA TGA results at temperature ranges of 550 ºC - 700 ºC to produce ZrO2. XRD results show that single tetragonal phase of ZrO2 is formed in all variations of pH precipitation and calcination temperature. An analysis using MAUD software show that crystal size reduces as the increase in precipitation of pH. The crystal size results are 110 nm, 66 nm and 48 nm at pH 4, pH 7 dan pH 10 at 700 ºC, respectively. Moreover, XRF results show that ZrO2 with purity is at around 95.8 % at pH 4 and 96.3 % at pH 7 and pH 10.

Efficiency of acid digestion procedures for geochemical analysis of tungsten mining wastes

Tungsten is a critical element used in the industry with increasing global demand. There are millions of tons of current and legacy mineral processing tungsten tailings worldwide that can potentially contaminate the environment and pose human health risks. These tailings could also potentially turn into valuable resources if we thoroughly characterise their geochemical composition. In this study, an innovative method was developed to achieve the complete digestion of tungsten tailings. We tested three different digestion methods (hotplate digestion, bomb digestion, and ColdBlockTM digestion) and compared the results. Additionally, an alkali fusion for major element analysis was also applied and tested. The results showed that alkali fusion is the best method for major elements analysis, while bomb digestion is the best method for tungsten and trace element analysis, but volatile chlorite loss was also observed. The hot plate digestion method for tungsten mine tailings was not recommended, because of poor recoveries of trace elements compared to the bomb digestion method. The quick and safer ColdBlockTM digestion method could be used for Bismuth (Bi), Molybdenum (Mo), and several rare earth element analyses indicated by their recoveries being close to the bomb digestion method.

Decomposition of ferronickel slag through alkali fusion in the roasting process

Ferronickel slag is a by-product of the nickel smelting process. Recycling of ferronickel slag is required since it contains valuable elements besides its potency to pollute the environment. In order to take advantage of the valuable materials and reducing the potential hazard, beneficiation of ferronickel slag is essential. Alkali fusion of ferronickel slag using Na2CO3 in the roasting process was carried out. This study aims to determine the decomposition of the mixture of ferronickel slag-Na2CO3 in the roasting process. Roasting temperature and time were 800–1,000 °C and 60‒240 minutes, respectively. Characterizations of the ferronickel slag were conducted by XRF, ICP-OES, XRD and SEM-EDS. Meanwhile, roasted products were characterized using ICP-OES, XRD and SEM-EDS. Characterization of the ferronickel slag indicates that Mg and Si are the main elements followed by Fe, Al and Cr. Moreover, olivine is detected as the main phase. The roasting process caused percent weight loss of the roasted products, which indicates decomposition occurred and affected the elements content, phases and morphology. The roasting process at about 900 °C for 60 minutes is a preferable decomposition base on the process conditions applied and the change of elements content. Aluminum (Al) and chromium (Cr) content in the roasted products upgraded significantly compared to iron (Fe) and magnesium (Mg) content. Olivine phase transforms to some phases, which were bounded with the sodium compound such as Na2MgSiO4, Na4SiO4 and Na2CrO4. The rough layer is observed on the surface of the roasted product as a result of the decomposition process. It indicates that liquid-solid mass transfer is initiated from the surface