Inclusion Removal Process of Homogeneous CuCr50 Alloy In-Situ Synthesized by Al-Mg Composite Strengthening Reduction Coupling Slagging.

To overcome the problem of Cr2O3 and Al2O3 inclusions in CuCr50 alloy prepared by aluminothermic reduction method, in this paper, a novel methodology for strengthening metal-slag separation through in situ slagging is proposed. CuCr50 alloys were prepared by metallothermic reduction using Al and Al-Mg as reducing agents, and the physical properties of the slag, such as viscosity, density, and surface tension, were adjusted by controlling the proportion of CaO in the slagging agent in the raw material to achieve good separation of the slag-metal. The results show that with the ratio of CaO increased, CaO and MgO were coupled to make slag, which combined with Cr2O3 and Al2O3 to form CaCr2O4, MgCr2O4, and CaAl4O7 in the slag, thus reducing the content of impurities in the alloy. When RCaO/(CaO + Al2O3 + MgO) = 20%, the Cr content ranged from 46.61% to 47.09%, the inclusions accounted for 1.60%, the Cr particle size was refined to 20 µm, the number of Cr spherical crystals accounted for 9.88%, the conductivity reached 14.96 MS/m, and the hardness reached 100.23 HB. After heat treatment, the Cr phase was refined in the alloy, the conductivity increased from 14.96 MS/m to 18.27 MS/m, and the hardness increased from 100.23 HB to 103.1 HB. This method is expected to provide an effective method for the preparation of CuCr50 contact materials.

Co-Extraction of Aluminum and Silicon and Kinetics Analysis in Carbochlorination Process of Low-Grade Bauxite.

Addressing the issue that the Bayer process is not suitable for low-grade bauxite, carbochlorination was proposed to recover aluminum and silicon from low-grade bauxite. This study focused on the behavior of aluminum and silicon during the carbochlorination process of low-grade bauxite. The impact of various process parameters on the chlorination efficiency was investigated, and the chlorination mechanism and kinetics of aluminum and silicon chlorination in bauxite were analyzed and discussed. Under optimal experimental conditions, the chlorination efficiency of Al2O3 and SiO2 reached 94.93% and 86.32%, respectively. The carbochlorination of aluminum and silicon in bauxite adhered to a shrinking, unreacted core model governed by gas diffusion within the product layer. This process can be bifurcated into two stages. Additionally, calculations were conducted to determine the apparent activation energy and reaction order of the chlorination processes involving Al2O3 and SiO2. Examining the chlorination mechanism revealed that the bauxite carbochlorination encompasses transformations among various minerals. Notably, the aluminum component prefers to participate in the carbothermal chlorination reaction over silicon.

Summary of sulfur hazards in high­sulfur bauxite and desulfurization methods.

With the gradual depletion of high-grade bauxite, the development of the alumina industry has been seriously constrained. High­sulfur bauxite reserves are abundant and can be used as an effective supplement to bauxite resources. Therefore, the development of desulfurization and comprehensive utilization methods for high sulfur bauxite has been widely studied. Excessive sulfur content in bauxite and complex valence changes in the Bayer process have serious impacts on products and equipment. This paper will introduce pre-treatment desulfurization and post-treatment desulfurization methods such as roasting, flotation, electrochemical and biological methods. Roasting methods use oxidative roasting to convert sulfur to sulfur dioxide-containing flue gas; flotation methods enrich pyrite through flotation chemicals; biological methods use complex chemical reactions of microorganisms to remove sulfur; and electrolysis methods convert sulfur to sulfate through oxidants produced by electrolysis. Post-treatment methods add precipitants such as zinc oxide to treat small amounts of sulfur entering the Bayer process. The reaction mechanism and development of various desulfurization methods are summarized, and the problems of these desulfurization methods are analyzed. The aim is to combine their advantages to develop economical and environmentally friendly desulfurization methods, and propose suggestions for the future resource utilization of high­sulfur bauxite.

Research on the Process, Energy Consumption and Carbon Emissions of Different Magnesium Refining Processes.

Under the policy of low carbon energy saving, higher requirements are put forward for magnesium smelting. As the mainstream magnesium smelting process, the Pidgeon process has the disadvantages of a long production cycle, high energy consumption and high carbon emission, which makes it difficult to meet the requirements of green environmental protection. This paper reviews the research progress on different magnesium smelting processes and further analyzes their energy consumption and carbon emissions. It is concluded that the standard coal required for the production of tons of magnesium using the relative vacuum continuous magnesium refining process is reduced by more than 1.5 t, the carbon emission is reduced by more than 10 t and the reduction cycle is shortened by more than 9.5 h. The process has the advantages of being clean, efficient and low-carbon, which provides a new way for the development of the magnesium industry.

A comprehensive review of aluminium electrolysis and the waste generated by it.

Aluminium is produced by electrolysis using alumina (Al2O3) as raw material and cryolite (Na3AlF6) as electrolyte. In this Hall-Héroult process, the energy consumption is relatively large, and solid wastes such as spent anodes and spent pot liner, flue gas and waste heat are generated. Therefore, this article discusses from the perspective of high energy consumption and high pollution and summarizes the methods to reduce energy consumption and solve pollution problems. The functions of carbon anode, carbon cathode, refractory material and sidewall in aluminium electrolysis cells are discussed in detail. The process of aluminium electrolysis and the ways to improve the current efficiency of aluminium electrolysis cells and reduce their energy consumption are outlined. The causes and treatment methods of spent anodes, spent cathodes, spent refractories and spent spot liner are reviewed. The research progress of waste heat recovery and aluminium electrolysis flue gas purification are analysed. And the future research directions of aluminium electrolysis flue gas are provided.

Preparation of polyamidoamine dendrimer-functionalized chitosan beads for the removal of Ag(I), Cu(II), and Pb(II).

Chitosan bead grafted by third-generation dendrimers (CB-G3) with a diameter of 1.40 mm was synthesized to investigate their performance in recovering Ag(I), Cu(II), and Pb(II) ions in aqueous media. The prepared adsorbents were characterized by XRD, FT-IR, elemental analysis, TGA, and SEM, and the effects of pH, contact time, concentration, and temperature were examined. The results showed that the adsorbents were successfully fabricated. The optimum pH value was 5, and the increased generation number contributed to adsorption capacity improvement, indicating that electrostatic interactions between amine groups and metal ions are the governing mechanism of adsorption by the CB-G3. The kinetics, isotherms, and thermodynamics of Ag(I), Cu(II), and Pb(II) adsorption onto the CB-G3 were investigated. The adsorption processes can be described using pseudo-second-order kinetic and Langmuir models. The maximum monolayer adsorption capacities were 105.62, 88.82, and 97.87 mg·g-1 for Ag(I), Cu(II), and Pb(II) at 30 °C within 210 min, respectively. Electrostatic interactions and hydrogen bonds are the main mechanisms between metal ions and N atoms. Therefore, the CB-G3 is a promising candidate for Ag(I), Cu(II), and Pb(II) adsorption owing to its splendid ability in easy separation, good adsorptivity, and reusability for efficiently adsorbing Ag(I), Cu(II), and Pb(II) ions.

Summary of research progress on separation and extraction of valuable metals from Bayer red mud.

Bayer red mud is a strong alkaline solid waste discharged during alumina production. Due to large emissions and strong alkalinity, red mud is now mostly dammed or buried, which not only occupies huge land but also contaminates the surrounding ecosystem, causing the risk of collapse and landslide. In addition to its overall utilization in building materials, agriculture, the environment, and the chemical industry, red mud also contains valuable metals such as sodium, aluminum, iron, titanium, and scandium and is considered to be an important secondary resource. In this paper, the physicochemical properties and hazards of red mud are first introduced, and then, the overall utilization of red mud is summarized. Then, the latest research progress on the separation and extraction of valuable metals from red mud is reviewed in detail and a new comprehensive utilization method is recommended and evaluated. This paper also provides suggestions for the future development direction of the comprehensive utilization technology of red mud.

Removal of Cr(VI) and Ag(I) by grafted magnetic zeolite/chitosan for water purification: Synthesis and adsorption mechanism.

In this paper, a novel grafted zeolite/Fe3O4/chitosan (ZMC-MAH-TEPA) adsorbent was greenly synthesized and evaluated for the removal of Cr(VI) and Ag(I) in single and bi-component solutions. The characterization data of XRF, XRD, FT-IR, VSM, TGA, BET and SEM showed the successful fabrication of the adsorbent with abundant -NH2 and -NH- as well as great recovery properties (11.70 emu/g). The effects of experimental parameters, including pH value, initial concentration, temperature, time, and coexisting ions on single and bi-component adsorption, were investigated. The results demonstrated that the adsorption capacities increased with the enhanced shaking time and concentration until equilibrium was reached. The optimum pH value was 3 for Cr(VI) adsorption and 5 for Ag(I) adsorption. The maximum adsorption capacities for Cr(VI) and Ag(I) ions, obtained by the Langmuir model, were 50.75 and 70.12 mg·g-1 in single metal solutions and 45.45 and 58.94 mg·g-1 in bi-component metal solutions (Cr(VI)/Ag(I) = 1:1), respectively. Additionally, the adsorption mechanism of Cr(VI) and Ag(I) was explained in terms of electrostatic interaction and hydrogen bonding between metal ions and -NH2 and -NH- in ZMC-MAH-TEPA. Taken together, this study provides a clean approach to synthesizing chitosan-based adsorbents for the efficient removal of Cr(VI) and Ag(I) ions.

Desulfurization of Cu-Fe Alloy Obtained from Copper Slag and the Effect on Form of Copper in Alloy.

In order to realize the high-value utilization of copper slag, a process for preparing Cu-Fe alloy through the reduction of copper slag is proposed. The sulfur in the alloy exists in the form of matte inclusions, which is different from sulfur in molten iron. The reaction of CaO with Cu2S is difficult. It is necessary to add a reducing agent to promote desulfurization. To avoid the introduction of other elements, Fe-Mn and CaC2 additions were used as desulfurizers for the desulfurization of Cu-Fe alloy. The thermodynamics of the desulfurization reaction were calculated and the experimental process was studied. It was found that the Gibbs free energy of desulfurization reactions was negative for Fe-Mn and that CaC2 can reduce the sulfur in the alloy to 0.0013% and 0.0079%, respectively. The desulfurization process affected the shape of copper in the alloy. Part of copper in this alloy exists in the form of nano-copper spheres, and the size of the spheres is found to increase after desulfurization. Reducing agents can facilitate the desulfurization process of stable sulfides.

Research on the Dealkalization Treatment of Bauxite Residue and Deep Extraction of Alumina.

Bauxite residue is the bulk solid waste generated by the alumina industry, and the environmental treatment of bauxite residue has always been a focus of attention. In this study, in the high calcium system, the bauxite residue was intensively digestion by the calcification-carbonation method, and the mole ratio of solution, the mass ratio of CaO/SiO2 of the digestion process were changed, so that the high-efficiency dealkalization of bauxite residue was realized and the aluminum oxide in bauxite residue was deeply extracted. The experimental results showed that the calcification process could achieve the recovery of 17.83% alumina at 260°C, reaction duration of 60 min, liquid-solid ratio = 5:1, the mass ratio of CaO/SiO2 = 3.5, and 200 g/L NaOH solution. The whole process can recover 49.61% of alumina from bauxite residue, and 94.4% of alkali in bauxite residue can be removed.

Research on Bayer Red Mud Slurry Electrolysis.

The Bayer red mud is the solid waste generated during the production of alumina by the Bayer process. At present, the stock of red mud in China exceeds 1.1 billion tons, covering an area of more than 120,000 mu, and the annual production volume is increasing by 100 million tons. The comprehensive utilization of red mud is still a difficult problem. Therefore, it is of great significance to actively explore new methods for removing sodium from red mud. In this study, the traditional red mud desalination process and the slurry electrolysis process are combined, and the influence of three different leaching agents on the leaching and sodium removal of red mud slurry in the presence of an electric field is explored. In the slurry electrolysis experiment, it was found that the sodium removal rate obtained by different leaching agents was CaO > CaCl2 > HCl. The red mud leached with pure dilute hydrochloric acid has the highest Na removal rate, which is 93.11%. In view of this situation, a pre-slurry-electrolysis cycle process with HCl as leaching agent was proposed. The core of slurry electrolysis is electrolyzing NaCl solution, and HCl only participates in the process as circulating medium. The design of this process reduces cost and increases efficiency.

Research on the mechanism of sodium separation in bauxite residue synergy preparation of potassium-containing compound fertilizer raw materials by the hydrothermal method.

Bauxite residue poses an increasingly serious ecological safety problem in the alumina industry. A novel process for removing sodium in bauxite residue synergistic preparation of potassium-containing compound fertilizer raw materials was proposed to relieve pressure on the fertilizer industry. In this paper, synthetic sodalite and katoite were used to simulate the main mineral phases of bauxite residue to determine the suitable conditions for the method, and the transformation mechanism of the process was researched by analyzing the phase structure and microscopic morphology of the samples using X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and specific surface area detection. The results show that the ideal reaction condition is 320 g/L K2O with solid reactants at 200 °C for 1 h. The separation rate of Na in the sodalite-katoite mixture reached 93.60%, with potassium aluminum silicate and katoite being the primary phases of the product, with a mesoporous structure and easy to be absorbed by crops. The bauxite residue transformation residue consisted of katoite and kaliophilite. With a total effective K2O, CaO, and SiO2 content of 38.22%, the Na2O content was 0.54%, meeting the requirements of compound fertilizer content on the market. The transformation mechanism is a dissolution-precipitation controlled sodium-potassium ion replacement reaction. This study provides theoretical guidance for the preparation of mineral fertilizer from bauxite residue and has practical production potential, opening up a new perspective for bauxite residue resource usage in the agricultural field.

Study on Iron Extraction from High Iron Bauxite Residue by Pyrite Reduction.

A new method of solid-phase reduction magnetic separation with pyrite as a reducing agent was proposed in order to realize resource utilization of high iron bauxite residue while reducing environmental harm. FeS2 powder and high iron bauxite residue powder were uniformly blended and roasted in a closed environment. A magnetic separator was utilized to separate the magnetic iron concentrate at 2400 GS, and the recovery rates were calculated. Experimental results show that the best iron recovery was 91.5% at 1:6 roasted bauxite: residue at 800℃ for 2 h. The recovery of Fe can be improved by reducing high iron bauxite residue with pyrite, and iron in both pyrite and high iron bauxite residue can be recovered simultaneously, alleviating the pressure of iron ore resources and improving its utilization value.

Extraction and Utilization of Valuable Elements from Bauxite and Bauxite Residue: A Review.

Bauxite is the ideal raw material for the manufacturing of alumina. Aside from the primary constituents of aluminum and silicon, bauxite is frequently coupled with many valuable elements such as gallium (Ga), titanium (Ti), scandium (Sc), and lithium (Li). The bauxite residue and circulating spent liquor in alumina production typically include significant amounts of valuable elements, making them a potential source of polymetallic. The recovery of these essential components can greatly increase alumina manufacturing process efficiency while reducing industrial liability and environmental impact. This study gives a critical analysis of existing technology used to recover valuable elements from bauxite residue and circulating spent liquor to provide insight into the broader usage of bauxite residue as a resource rather than a waste. A comparison of existing process features demonstrates that an integrated process for valuable elements recovery and waste emission reduction is advantageous.

Calcification-Carbonation Method for Bayer Red Mud Treatment: Carbonation Performance of Hydrogarnets.

Hydrogarnets are vital intermediate products in the calcification- carbonation method, which is designed for Bayer red mud treatment. Their carbonation performance greatly depends on SiO2 substitution. In this study, different SiO2-substituted hydrogarnets were synthesized and characterized. Then, batch experiments were performed to evaluate the potential effects of important parameters such as CO2 pressure, and SiO2 substitution degree (x) on the carbonation process. The SiO2 substitution degrees of the hydrogarnets synthesized at 60, 120, 180, and 240°C were 0.27, 0.36, 0.70, and 0.73, respectively. As the SiO2 substitution degree increased, the hydrogarnet carbonation extents gradually declined. With an increase in CO2 pressure, the hydrogarnet carbonation percentages increased gradually and rose from 80.33% to 98.19% within 120 min. The phases detected in the carbonized products were strip-like aragonite as well as some calcite; the Al-rich and Si-rich phases in the carbonized products were amorphous.

Comprehensive Application Technology of Bauxite Residue Treatment in the Ecological Environment: A Review.

The emission of bauxite residue continues to grow with the increase of alumina production capacity, along with the large amounts of bauxite residue currently stored in stockpiles. The exposed problems of high yield, strong alkalinity, low comprehensive utilization rate, and threats to the ecological environment are becoming increasingly prominent. With the strict requirements of environmental protection, improving the comprehensive utilization rate of bauxite residue and bulk consumption of bauxite residue has become an urgent issue to be solved. A large number of researchers have conducted in-depth investigations into the application of bauxite residue over a wide range, and this paper summarizes its application in the environment in recent years, providing guidance for the high value and harmless application of bauxite residue, which can help reduce environmental pollution and human life and health hazards caused by bauxite residue.

Experimental Research on Vortex Melting Reduction of High-Iron Red Mud (Bauxite Residue).

In this study, the advantages of the vortex melting reduction treatment of red mud were verified. Vortex melting reduction can improve the feeding rate, promote the reaction and the directional deposition of iron, which was conducive to the separation of slag and gold. The effects of different adding methods, stirring speed and reaction time on iron recovery were investigated by using red mud, aluminum leached slag and calcified slag as raw materials. According to the experiment, the best reaction conditions were that the raw material put into the furnace by rolling pellets, stirring speed 125 RPM, and reaction time 30 min. The results provided an experimental basis for the harmless and high-value utilization of high-iron red mud treated by vortex melting reduction.

Research on the oxidation characteristics of zinc sulfite in the zinc oxide desulfurization process.

Aiming at the pollution problem of low-content SO2 in non-ferrous metal production industry, the oxidation kinetics of zinc sulfite in the zinc oxide desulfurization process was studied. The concentration change of Zn2+, variation of pH, temperature and apparent activation energy in the oxidation process of two ZnSO3 samples were investigated systematically. The results indicate that the raw material with different crystal water has little effect on the oxidation kinetic of zinc sulfite. The reaction process comprises two stages: the dissolution process and the oxidation process. The zinc ion concentration is linearly rising with the action time during the oxidation process. The pH value rises quickly in the dissolution process and goes down slowly with reaction time in the oxidation process. The process is mainly controlled by a diffusion step and less effected by the temperature. The apparent activation energy Ea obtained for the two samples are 8.662 and 9.645 kJ/mol, respectively. Integrated with the kinetic model, the oxidation rate of zinc sulfite is controlled by the diffusion of HSO3- and O2 to the gas-liquid interface.

The Development Scenarios and Environmental Impacts of China's Aluminum Industry: Implications of Import and Export Transition.

Aluminum is widely used in buildings, transportation, and home appliances. However, primary aluminum production is a resource, energy, and emission-intensive industrial process. As the world's largest aluminum producer, the aluminum industry (ALD) in China faces tremendous pressure on environmental protection. This study combines material flow analysis and scenario analysis to investigate the potential of resource conservation, energy saving, and emission reduction for China's ALD under the import and export trade transition. The results show China's per capita aluminum stock will follow a logistic curve to reach 415 kg/capita by 2030. However, unlike the continued build-up of stocks, domestic demand for aluminum will peak at 44 million tons (MT) in 2025 and fall to 36 MT in 2030. The scenario analysis reveals that China's primary aluminum output could peak in 2025 at around 52 MT if the restrictions are not implemented (Scenario A). Compared to Scenario A, demand for primary aluminum is effectively limited in Scenarios B and C where exports of aluminum products are reduced. Correspondingly, both scenarios also have obvious benefits in reducing the environmental load of China's ALD. Besides, if hydropower used in aluminum electrolysis increases to 25% by 2030, the total GHG emissions in 2030 will be reduced by 12%. Therefore, promoting import/export and energy mix transformation can become an essential means for the sustainable development of China's ALD. Supplementary Information: The online version contains supplementary material available at 10.1007/s40831-022-00582-0.

Simultaneous separation of Fe & Al and extraction of Fe from waste coal fly ash: Altering the charge sequence of ions by electrolysis.

A significant amount of coal fly ash is generated and this type of waste material causes severe environmental hazards. Metal (Al and Fe) extraction from coal fly ash is beneficial to the resource utilization of waste coal fly ash. However, the coexistence of Al and Fe in coal fly ash means that the separation of Al and Fe is required, which is a key and difficult step to prepare high value-added products from coal fly ash. This work presents a novel electrolysis method to alter the charge sequence of Al3+, Fe3+, and H2O, leading to a process different from their natural tendency for simultaneous separation of Fe3+ and Al3+, and extraction of Fe. The single iron removal efficiency was 43.48%, and the aluminum extraction efficiency was <0.30% under optimal conditions. The iron product had a purity of 98.3 wt% Fe, 0.45 wt% Al, and 0.18 wt% S. This process occurs without chemical additions and expensive membranes, avoiding impurity introduction, slag generation, and membrane limitations. Fe(s), H2(g), Al2(SO4)3(aq), and O2(g) are the main products during the electrolysis. Flake Fe is selectively produced instead of colloidal Fe(OH)3. Fe is a magnetic substance and is easier to remove from the solution by magnets than colloidal Fe(OH)3. H2 is a green fuel. Wastewater (Al2(SO4)3(aq)) can be directly used to further extract alumina. Therefore, this study provides an alternative method of zero pollution discharge for simultaneous separation of Fe3+ and Al3+, and extraction of Fe from coal fly ash leachate.