Roles of red mud in remediation of contaminated soil in mining areas: Mechanisms, advances and perspectives.

Red mud (RM) is a kind of strong alkaline solid waste produced from the aluminum industry, which contributes significantly to environmental pollution and can cause severe health issues.Currently, RM is widely recognized as a potential material for soil remediation because of its rich metal oxide content, such as Fe/Al oxides. However, there is no comprehensive description on the roles of RM in passivation remediation of contaminated soil in mining areas. This review summarizes the mechanisms of passivation of heavy metals (HMs) in contaminated soil by RM, including precipitation, adsorption and ion exchange. Besides the effects of adding RM on soil physicochemical properties, heavy metal forms and ecological environment are further elaborated. Moreover, using the co-hydrothermal carbonization of RM and biomass for enhancing the efficiency of contaminated soil remediation is proposed as the main prospective research. This paper provides technical references for the resource utilization of RM and the treatment of heavy metal-contaminated soil.

Channel-aware low Earth orbit satellite cluster networking for space-to-Earth laser communication: reliability and bandwidth advantages.

The reliability of the space-to-Earth laser communication plays a crucial role in providing uninterrupted real-time services in satellite optical networks. In traditional satellite optical networks, the space-to-Earth laser communication is carried out using a monolithic satellite in close proximity to the target optical ground station. However, the reliability of the communication in this approach is heavily influenced by the atmospheric environment. For instance, variations in cloud thickness can cause fluctuations in the link quality of the space-to-Earth laser communication, significantly reducing its reliability. This study proposes an innovative channel-adaptive space-to-Earth laser communication (CA-S2E-LC) architecture based on satellite cluster optical networking (SCON). SCON provides space-diversity link sets, reducing the probability of space-to-Earth laser communications affected by clouds. By leveraging the perception of link quality, the CA-S2E-LC architecture can adaptively choose the better space-to-Earth laser communication links established by member satellites within a satellite cluster under different environments, and properly schedule the resource, ensuring reliable space-to-Earth laser communication. The principles of the SCON is analyzed and the implementation of the CA-S2E-LC architecture is demonstrated through the explanation of hardware and functional modules, workflows, finite state machines, and strategies. Simulation results demonstrate that the CA-S2E-LC architecture can significantly enhance communication reliability and capacity compared with the traditional monolithic satellite. Furthermore, the workflow of the architecture is demonstrated to validate the feasibility.

Catalytic degradation of antibiotic sludge to produce formic acid by acidified red mud.

As complex and difficult-to-degrade persistent organic pollutants (POPs), antibiotics have caous damage to the ecological enused serivironment. Because of the difficult degradation of antibiotics, sewage and sludge discharged by hospitals and pharmaceutical enterprises often contain a large number of antibiotic residues. Therefore, the harmless and resourceful treatment of antibiotic sludge is very meaningful. In this paper, amoxicillin was selected as a model compound for antibiotic sludge. Acidified red mud (ARM) was used to degrade antibiotic sludge and produce hydrogen energy carrier formic acid in catalytic wet peroxidation system (CWPO). Based on various characterization analyses, the reaction catalytic mechanism was demonstrated to be the result of the non-homogeneous Fanton reaction interaction between Fe3O4 on the ARM surface and H2O2 in solution. Formic acid is the product of the decarboxylation reaction of amoxicillin and its degradation of various organic acids. The formic acid was produced up to 792.38 mg L-1, under the optimal conditions of reaction temperature of 90 °C, reaction time of 30 min, H2O2 concentration of 20 mL L-1, ARM addition of 0.8 g L-1, pH = 7, and rotor speed of 500 rpm. This research aims to provide some references for promoting red mud utilization in antibiotic sludge degradation.

Enhanced sequestration of CO2 from simulated electrolytic aluminum flue gas by modified red mud.

The aluminum industry is facing severe economic and environmental problems due to increasing carbon emissions and growing stockpiles of red mud (RM). RM is a strongly alkaline, high-emission solid waste from the alumina industry with potential for CO2 sequestration. However, the effectiveness of RM carbon sequestration is poor, and the mechanism behind it is not well understood. In this study, the effect of microwave and tube furnace activation of RM on CO2 sequestration in alumina was first investigated at different temperatures. The result showed that the CO2 sequestration capacity of unmodified RM (URM) was only 14.35 mg/g at ambient temperature and pressure, and the CO2 sequestration capacity could be increased to 52.89 mg/g after high-temperature activation and modification. Besides, high-temperature activation and modification will effectively improve the carbon sequestration capacity of RM. The carbonized RM was characterized by FT-IR, SEM, XRD, laser particle size, TG-DSC, and pH measurements. In addition, the mechanism of RM capturing CO2 was also proposed, which shows that CO2 was finally sequestered in the RM as CaCO3. The change in particle size distribution and the mineral phase in the RM indicated that high-temperature activation modification positively affects the application of RM to the sequestration of CO2. This study can provide a promising technology for the low-carbon and green development of the aluminum industry, as well as achieving the waste treatment and utilization objective.

A numerical simulation method for pressure drop and normal air velocity of pleated filters during dust loading.

Pressure drop is an important indicator that affects the filtration performance of the pleated filter, and the deposition of dust particles within the pleats is crucial to the evolution of the pressure drop. In this study, the pressure drop during PM10 loading process was investigated for a series of V-shaped and U-shaped filters with a pleat height of 20 mm and different pleat ratios (the ratio of pleat height to pleat width: α = 0.71-3.57). In the numerical simulations, numerical models suitable for different pleated geometries were obtained through experimental verification on the local air velocity. Then, assuming that the dust cake thickness is proportional to the normal air velocity of the filters, the variation of the pressure drop with the dust deposition is derived by means of successive numerical simulations. This simulation method saved a significant amount of CPU time required for the growth of dust cake. It was found that the relative average deviations between experimental and simulated pressure drops were 3.12% and 1.19% for V-shaped and U-shaped filters, respectively. Furthermore, it was found that under the same pleat ratio and the mass of dust deposition per unit area, both the pressure drop and unevenness of normal air velocity of the U-shaped filter were lower than the V-shaped filter. Therefore, the U-shaped filter is recommended due to its better filtration performance.

Study on adsorption of hexavalent chromium by composite material prepared from iron-based solid wastes.

A new adsorbent with chromium removal function was synthesized by carbon thermal method using iron-containing waste Fenton sludge and carbon-containing solid waste fly ash to treat high pH scoring wastewater generated from industrial processes. The results showed that the adsorbent used T = 273.15 K, pH = 10, t = 1200 min, C0 = 100 mg/L, had a removal rate of Cr(VI) of more than 80%, and the adsorption capacity could reach 393.79 mg/g. The characterization results show that the synthesized mesoporous nitrogen-doped composite material has a large specific surface area and mesoporous structure, and the surface of the material is rich in oxygen-containing functional groups and active sites. Compared with other studies, the adsorption capacity of the material is larger, which indicates that the removal effect of Cr(VI) in this study is better. The adsorption kinetic results show that the adsorption follows a pseudo second kinetic model, and the adsorption process is a chemisorption involving electron sharing or electron exchange. This experiment designed a simple method to synthesize mesoporous nitrogen-doped composites using industrial solid waste, with raw materials from cheap and easily available industrial solid waste, and solved the dual problems of heavy metals in wastewater and solid waste, providing a new idea for the resource utilization of Fenton sludge while not producing secondary pollution.

Desulphurization mechanism and engineering practice of carbide slag.

In order to give full play to the alkaline neutralization value of carbide slag and reduce the environmental hazards of carbide slag, it is of great practical significance to study the resource utilization of carbide slag. The adsorption of sulfur compounds on carbide slag was studied in the laboratory, and the process parameters of carbide slag desulfurization were explored and optimized. The specific surface area, pore distribution, and other physicochemical parameters were analyzed by XRD and SEM, which explained the changes of products and carbide slag before and after desulfurization. The test results show that carbide slag and limestone have almost the same desulfurization effect. The kinetics of carbide slag desulfurization process conforms to pseudo-first-order kinetics, and the sulfur content of calcium carbide slag reaches to 1000 mgSO2·g-1. A project demonstration was carried out in the gold smelting Tielu Plant of Zhenyuan Huashuo Precious Metals Development Co., Ltd., in Yunnan. The results of the 2-year demonstration project showed that the desulphurization efficiency of the four-stage series desulphurization tower exceeds 95%. The concentration of sulfur dioxide in the discharged flue gas is reduced to less than 20 mg·m-3, which meets the requirements of ultra-low emission standard in China. Therefore, whether from theoretical research or engineering practice analysis, it is feasible to replace limestone with calcium carbide slag for flue gas desulfurization. The paper also discusses the problems existing in the demonstration project, and provides a new idea of "using waste to treat waste" in order to solve the problem of carbide slag disposal.

Preparation of Iron Carbon Composite Material by Extracting Iron from Bauxite Residue and Its Adsorption of Heavy Metal Cd(II).

An effective method of iron extraction from bauxite residue was explored, and iron was used to prepare iron carbon composite material, which have a good adsorption effect on the heavy metal cadmium. After acid washing, acid leaching, Fe(III) reduction and ferrous oxalate decomposition, FeSO4·H2O(RM) was successfully extracted from bauxite residue, and the iron loss was only 4.35%. FexOy-BC(RM) nanocomposite materials were prepared by loading FeSO4·H2O(RM) onto walnut shell biochar (BC) (a kind of agricultural and forestry waste) by an in situ reduction and oxidation method. The results showed that the adsorption effect of FexOy-BC(RM) on Cd(II) was better than that of commercial FexOy-BC. XPS, TEM, SEM characterization analysis showed that FexOy-BC(RM) immobilized Cd(II) by adsorption, complexation, etc.to achieve a highly efficient adsorption of heavy metal Cd(II) in wastewater.

Purification of Low-Concentration Carbonyl Sulfide by Red Mud-Based Adsorbent.

Bauxite residue, also known as red mud (RM), is a kind of industrial solid waste with high alkali content, complex composition and difficult utilization. In this study, a new type of RM-based adsorbent was prepared by using polyethylene glycol modified RM and was used to remove low concentration of COS in flue gas. The optimum preparation conditions of adsorbent and the optimum technological parameters of COS adsorption purification were investigated. Under the optimal conditions, the adsorption efficiency of the new adsorbent exceeds 95%, and the COS adsorption capacity reaches 63.56 mg/m3. The characterization results showed that the main active components of the adsorbent were active alkali, FeOOH and Fe3O4, and the main products were Na2S2O3, Na2SO4, FeS and FeS2.

Design of a High-Performance Electrocatalyst for N2 Conversion to NH3 by Trapping Single Metal Atoms on Stepped CeO2.

Single-atom catalysts (SACs) have recently been shown to have high performance in catalyzing the synthesis of NH3 from N2. Here, we systematically investigated a series of single transition metal atoms anchored on stepped CeO2 (CeO2-S) to screen the potential electrocatalysts for a N2 reduction reaction (NRR) via density functional theory computations. We first demonstrated that these SACs are stable via large calculated binding energies. Second, we evaluated the adsorption of *N2 over CeO2-S-supported single atoms. Here, those systems that can activate N2 molecules were selected as candidates. We then showed that CeO2-S-supported single Mo and Ru atoms have high catalytic activity for NRR via low limiting potentials of -0.52 and -0.35 V, respectively. Meanwhile, the competitive hydrogen evolution reaction is highly suppressed over these two SACs because the adsorption of *N2 is prior to *H. Finally, the origin of the NRR activity over these SACs was investigated. This work offers useful insights into designing high-performance CeO2-based electrocatalysts for NRR.