Preparation and Characterization of Novel Sulfoaluminate-Cement-Based Nonautoclaved Aerated Concrete.

The production of autoclaved aerated concrete via the autoclaving process incurs substantial energy consumption, posing a challenge to sustainable economic development. Herein, a novel nonautoclaved aerated concrete (NAAC) was prepared using sulfoaluminate cement as the primary raw material and aluminum powder as the aerating agent. The physicomechanical characteristics and pore structures of the sulfoaluminate-cement-based (SAC) NAAC (SAC-NAAC) were examined through X-ray diffraction, thermogravimetry, and scanning electron microscopy. The findings revealed that the optimal mechanical attributes of the SAC-NAAC were achieved at a water-cement ratio of 0.55, with a specific content ratio of polycarboxylate superplasticizer-borax-calcium stearate-sodium hydroxide at 0.24%:0.32%:0.36%:2.90%, along with 0.40% aluminum powder. The SAC-NAAC samples, with a bulk density range of 600-750 g/m3, exhibited a compressive strength of 3.55-4.16 MPa, porosity of 45.9-63.5%, and water absorption rate of 60.2-74.4%. The weight loss in the SAC-NAAC with different aluminum powder contents ranged between 15.23% and 16.83%. The prismatic ettringite (AFt) crystals served as the main source of strength for the SAC-NAAC, and AH3 was attached to the AFt surfaces in a microcrystalline gel phase, thereby further enhancing the strength of the SAC-NAAC. Thus, the lightweight, high-strength SAC-NAAC has great potential as a nonautoclaved aerated concrete.

High-Efficiency Iron Extraction from Low-Grade Siderite via a Conveyor Bed Magnetization Roasting-Magnetic Separation Process: Kinetics Research and Applications.

Upgrading and utilizing low-grade iron ore is of great practical importance to improve the strategic security of the iron ore resource supply. In this study, a thermal analysis-infrared (IR) analysis-in-situ IR method was used to investigate the reaction mechanism and kinetics of Daxigou siderite. Experiments were conducted using a conveyor bed magnetization roasting process (CBMRP) to investigate the magnetization of siderite. Multi-stage magnetic separation processes were adopted to extract magnetite. The results show that simultaneously the iron carbonate in siderite decomposes, and magnetite is formed between 364 °C and 590 °C under both inert and reducing atmospheres. The activation energy of the magnetization roasting reaction is 106.1 kJ/mol, consistent with a random nucleation and growth reaction mechanism. Magnetization roasting at 750-780 °C for approximately 3.5 s in the CBMRP results in a magnetic conversion rate of >0.99 of the iron minerals in the siderite. A beneficiation process of one roughing, one sweeping, and three cleaning processes was adopted. A dissociation particle size of -400 mesh accounting for 94.78%, a concentrate iron grade of 62.8 wt.%, and a recovery of 68.83% can be obtained. Overall, a theoretical and experimental basis is presented for the comprehensive utilization of low-grade siderite.

Magnetic Properties and Washability of Roasted Suspended Siderite Ores.

Steel is one of the most important industrial materials, which mainly comes from the smelting of iron ore. In view of the huge steel consumption every year, the exploitation of vast reserves of siderite ores is significant for improving the self-sufficiency rate of iron ore resources and ensuring the strategic security of the iron and steel industries. This paper investigated the influence of temperature, time, and other parameters on the magnetic properties of roasted siderite ores using the method of suspended roasting and analyzed the washability of roasted ores under weak-magnetic-field conditions using the magnetic separation tube experiment. The findings of the study explained the iron phase transformation process, i.e., FeCO3 was transformed into Fe3O4 by suspension magnetization roasting. Furthermore, the saturation magnetization of the roasted ore increased in due time at a constant temperature range of 550-750 °C and a roasting time of less than 5 s. It also increased with increasing temperature and constant time. The roasted ore achieved the best magnetic characteristics after roasting at 750 °C for 5 s. After low-intensity magnetic separation, the iron grade of the concentrate changed to 55.12%, with a recovery rate of 90.34%. The study results provide a reference for the development and application of siderite suspension magnetization roasting technology.

Kinetics of Dehydroxylation and Decarburization of Coal Series Kaolinite during Calcination: A Novel Kinetic Method Based on Gaseous Products.

The analysis of gaseous products reveals the characteristics, mechanisms, and kinetic equations describing the dehydroxylation and decarburization in coal series kaolinite. The results show that the dehydroxylation of coal series kaolinite arises from the calcination of kaolinite and boehmite within the temperature range of 350-850 °C. The activation energy for dehydroxylation is 182.71 kJ·mol-1, and the mechanism conforms to the A2/3 model. Decarburization is a two-step reaction, occurring as a result of the combustion of carbon and the decomposition of a small amount of calcite. The temperature range in the first step is 350-550 °C, and in the second is 580-830 °C. The first step decarburization reaction conforms to the A2/3 mechanism function, and the activation energy is 160.94 kJ·mol-1. The second step decarburization reaction follows the B3 mechanism function, wherein the activation energy is 215.47 kJ·mol-1. A comparison with the traditional methods proves that the kinetics method utilizing TG-FTIR-MS is feasible.