Search Results (8)

Iron-rich bauxite residue (red mud) is a hazardous alkaline solid waste produced during the production of alumina from high-iron bauxite, which poses severe environmental challenges due to its massive stockpiling and limited utilization. In this study, metallic iron was recovered from high-iron red mud using the smelting reduction process. Thermodynamic analysis results show that an increase in temperature and sodium oxide content, along with an appropriate mass ratio of Al₂O₃ to SiO₂ (A/S) and mass ratio of CaO to SiO₂ (C/S), contribute to the enhancement of the liquid phase mass fraction of the slag. During the smelting reduction process of high-iron red mud, iron recoveries for low-alkali high-iron red mud and high-alkali high-iron red mud under optimal conditions were 98.14% and 98.36%, respectively. The metal obtained through reduction meets the industrial standard for steel-making pig iron, which is also confirmed in the pilot-scale experiment. The smelting reduction process of high-iron red mud can be divided into two stages, where the reaction is predominantly governed by interfacial chemical reaction and diffusion control, respectively. The apparent activation energy of high-alkali high-iron red mud is lower than that observed for low-alkali high-iron red mud. The reduced slag can be used as a roadside stone material or cement clinker. This proposed method represents a sustainable process for the comprehensive utilization of high-iron red mud, which also promotes the minimization of red mud. Full article

This paper presents a systematic review of the progress of the research on limestone-calcined clay cement (LC3), focusing on its low-carbon characteristics, sustainable applications, and performance. LC3 can be used to address the high carbon emission problem in the cement industry, as its use significantly reduces carbon dioxide emissions (by 30%–40%) due to clinker being partially replaced with calcined clay and limestone in its fabrication. Studies have shown that the hydration reaction of LC3 generates calcium-aluminum-silicate hydrate (C-A-S-H), carbon-aluminate, and calcium alumina, which optimize its microstructure and endow it with comparable mechanical properties (28 day compressive strength close to or exceeding that of OPC) and better durability (outstanding resistance to sulfate erosion and carbonation) compared to ordinary Portland cement (OPC). LC3 has been used in 3D printing, ocean engineering, geotechnical reinforcement, and other applications, all of which have verified its engineering feasibility. Despite the significant environmental and economic advantages of LC3, its high-temperature performance, freeze–thaw resistance, and long-term durability still need to be further investigated. This paper provides theoretical support and practical references for the development and promotion of low-carbon cement materials. Full article

In order to impart the properties of cementitious material to the Tibetan Agar soil, two high-temperature activation mechanisms (HTMA, HTMB) were designed in this study, and the products and hydration-hardening properties of Tibetan Agar soil high-temperature activation mechanism were analyzed by means of SEM, XRD, and XRF. The results show that the main components of Tibetan Aga soil are calcite and quartz; Aga soil is activated by HTMA high-temperature activation, forming the main products of CaO, C₂S, CaSiO₃, and CaAl₂Si₂O₈, and its products have both air-hardening and water-hardening characteristics; Aga soil is activated by HTMB high-temperature activation, and when the temperature reaches 1250 °C when the clinker is not found in the CaO, the generation of C₂S, C₃S, C₃A, C₄AF, and Mg₂SiO₄ minerals with good water-hardening cementitious properties occurs when the temperature rises to 1350 °C, although the formation of some inert minerals that do not have the cementitious properties, but this temperature activation products of the thermodynamic properties of the best; Enhancing the value of lime saturation degree (KH) and silicon rate (SM) can promote the formation of the products of the C₂S and C₃S, increase the reactivity of the Aga soil activation products, and increase the hydration heat as well as compressive and flexural strength, combined with the results of the hydration heat and mechanical test, KH is recommended to be 0.9~0.94, SM is recommended to be 1.8~2.4, and alumina ratio (IM) is recommended to be 1.8~2.4 when Aga soil is used with raw materials. Full article

Lead–zinc tailings are the typical solid wastes in mines with high yield and low utilization rates in some countries at present. They are mainly stockpiled in tailings reservoirs, occupying massive land resources and threatening the health of the environment. One of the advantages of building material production in sustainability is the ability to utilize large amounts of industrial solid wastes, and the use of lead–zinc tailings in building materials is an effective way to meet the dual needs of environmental protection and economic development. This paper reviews the progress of utilizing lead–zinc tailings as building materials and mainly summarizes the status of lead–zinc tailings in cement, geopolymer, concrete, building brick, and foam ceramic. According to previous research, lead–zinc tailings contain large amounts of silica–alumina oxide, which can be used in the production of cement clinker. The addition of lead–zinc tailings to the sintered material can reduce the sintering temperature. The active components contained in lead–zinc tailings can be used in concrete instead of cement or in the preparation of geopolymers. Meanwhile, lead–zinc tailings can also be used as a fine aggregate. However, there are few studies on the durability of building materials with lead–zinc tailings. Additionally, most of the research results of building materials are in the laboratory stage, which are difficult to be promoted. In view of these problems, corresponding suggestions and prospects are given in the end in order to provide a reference for the research on the utilization of lead–zinc tailings. Full article

This paper is the continuation of our previous paper. In this work, we optimized the synthesis of aluminum borides by the SHS method. The purpose of the research was to develop the foundations of waste-free technology. The initial components were powders of boric anhydride (B₂O₃), aluminum (Al), the oxide-heating additive (KNO₃), various fluxing additives, including mixed ones. The optimal ratios of the initial components for increasing the yield of aluminum boride with a high boron content and obtaining slag suitable for the production of high-alumina clinkers were determined. Studies have shown that the development of a waste-free technology for producing aluminum borides by the method of self-propagating high-temperature synthesis (SHS) is possible and yields target (alloy) and by-product (slag) products that meet the requirements for chemical and phase composition. Full article

Early age cracking in concrete is caused by a combination of the chemical and autogenous shrinkage caused by the exhaustion of the water in the pores during the hydration of cement phases. Generally, this process takes place in the first 72 h of concrete casting. The use of supplementary cementitious materials (SCMs) can mitigate cracking due to several factors, among them: dilution effect, provision of extra nucleation sites due to the high specific surface of the SCMs, and the increased water retention associated with the presence of fine SCMs. This paper compares the impact of two SCMs systems on early age cracking of the following concretes: (i) pozzolanic cement with natural pozzolan (zeolite) and (ii) a ternary binder limestone-calcined clay cement (LC3). The study was Carried out on cement paste and concrete. The addition of calcined clay and limestone decreases early age cracking better than in any other system, including the Portland-pozzolan system. It is related to a lower clinker factor and improved hydration of the system, and a better-developed microstructure at early ages due to the energetic reaction of the alumina phase C₃A, enhanced by the extra alumina (Al₂O₃) provided by the calcined clay. Full article

Aluminium dross is a hazardous industrial waste generated during aluminium production. It contains metallic oxides of aluminium and magnesium, other phases (aluminum nitride), and residues of fluxes and salts from the melting process of aluminium. Discarding this by-product is considered an environmental and economic challenge due to the high reactivity of dross with water or even air humidity. After removing the hazardous components from the as-received dross, one of the optional approaches is to incorporate the treated dross into construction materials. Dross is applied in several types of research as a secondary raw material source for alumina, clinker, cement or glass-ceramic production, but only a few papers focus on the usage of dross as a foaming agent for foams. Even fewer research are reported where dross was applied as a basic component of foam glasses. In this work, foam glasses were produced completely from waste materials: Aluminium dross, container (SLS) glass, and cathode ray tube (CRT) glass. The research holds several specificities, i.e., combining two industrial waste materials (CRT glass and dross), and adding an increased amount from the wastes. The physical and mechanical characteristics were examined with a special focus on the effect of the foam glass components on the microstructure, density, thermal conductivity, and compressive strength. Full article

In order to avoid potential environmental pollution from geopolymer-based material wastes, this work investigated the feasibility of using these materials as alternative raw materials in the preparation of cement clinker. The geopolymer binders and mortars were used as substitutes for natural mineral clays since they are rich in silica and alumina. Simulated geopolymer wastes were prepared by the activation of metakaolin or fly ash by an alkaline silicate solution. The cement-clinkers fired at 1450 °C for 1h were characterized by XRD, XRF, SEM-EDS, and a free lime (CaO_f) content test. The anhydrous clinker mineral phases C₃S (Ca₃SiO₅), C₂S (Ca₂SiO₄), C₃A (Ca₃Al₂O₆), and C₄AF (Ca₄Al₂Fe₂O₁₀) were well-crystallized in all investigated formulations. The free lime was lower than 1.3 wt% in all elaborated clinkers, which indicates a high degree of clinkerization. The results demonstrate that geopolymer binder and mortar materials are suitable substitutes for natural mineral clay incement clinker preparation. Full article