Search Results (5)

Magnesium slag (MS) is a solid by-product during magnesium production using the Pidgeon process. Around 5–6 million tons of magnesium slag was produced in China in 2023, which accounted for 83% of the total disposal of magnesium slag worldwide. To explore the innovative and high-end application of MS in building materials, this study investigated the preparation of calcium carbonate cementitious composites produced by high-volume (80%) MS and 20% of traditional ordinary Portland cement (OPC), low-carbon cement–calcium sulfoaluminate cement (CSA), or green cement–alkali-activated materials after CO₂ curing. The effects of OPC, CSA, and AAM on the performance evolution of MS blends before and after carbonation curing were analyzed. The results indicated that AAM contributed to a superior initial strength (7.38 MPa) of MS composites after standard curing compared to OPC (1.18 MPa) and CSA (2.72 MPa). However, the lack of large pores (around 1000 nm) in the AAM-MS binder caused the slowest CO₂ penetration during the carbonation curing period compared to the OPC- and CSA-blended samples. Less than 3 days were required for the full carbonation of the CSA- and OPC-blended MS mortar, while 7 days were required for the AAM blends. After carbonation, the OPC-blended MS exhibited the highest strength performance of 51.58 MPa, while 21.38 MPa and 9.3 MPa were reached by the AAM- and CSA-blended MS mortars, respectively. OPC-blended MS composites exhibited the highest CO₂ uptake of 13.82% compared to the CSA (10.85%) and AAM (9.41%) samples. The leaching of Hg was slightly higher than the limit (<50 µg/L) in all MS mortars, which should be noticed in practical application. Full article

In the scientific literature, the terms sustainable, green, ecofriendly and environment(ally) friendly are used regarding magnesium alloys applied in cars. When sustainability is defined as remaining within safe planetary boundaries for mankind or as conserving natural capital for transfer to future generations, current alloys based on primary magnesium applied in cars are not sustainable. Current alloys based on primary magnesium are not green, ecofriendly or environmentally friendly when these terms mean that there is no burden to the environment or a minimal burden to the environment. Available environmental data do not support claims that current alloys based on magnesium originating from the Pidgeon process, which replace primary mild conventional steel in automotive applications, can be characterized as green, ecofriendly or environmentally friendly. There are options for substantially reducing contributions to the life cycle environmental burden of magnesium alloys. Minimizing the life cycle environmental burden of magnesium alloys may enable them to be characterized as environmentally friendly, ecofriendly or green in the sense of a minimal burden to the environment. Full article

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. Full article

Spent Pot Lining First Cut (shortened to SPL-1cut) is a solid waste discharged from a primary aluminum electrolytic production process. SPL-1cut is classified as hazardous waste in China because it contains large amounts of soluble sodium fluoride and a tiny amount of cyanide. Most of SPL-1cut is carbon—about 65%—and its calorific value is 22.587 MJ∙kg⁻¹. There is a high level of sodium fluoride in SPL-1cut—about 15%—and sodium fluoride is randomly distributed in the carbon granule. The recycling of SPL-1cut using dolomite as a reactant, based on the characteristics of the two-step decomposition of dolomite at a high temperature, is discussed. The recycling of SPL-1cut was performed under the following heating conditions: the heating temperature was 850 °C, the holding time was 120 min, and 40% of the dolomite was added to the SPL-1cut. It was found that the cyanides are completely oxidized and decomposed, and dolomite is decomposed into MgO and active CaCO₃. At the same time, NaF reacts with active CaCO₃ and converts into CaF₂. The results provide references for using SPL-1cut as an alternative fuel in the dolomite calcination process of the Pidgeon Process. Full article

In this paper, the theoretical and industrial definitions of metallic calcium production by the metallothermic process in a vacuum atmosphere were investigated. In the experiments, Al is the only reductant used for metallothermic calcium production. The effects of Al stoichiometry, time variances, and temperature changes were investigated. The experiments were carried out at 1200 °C, 1250 °C, and 1300 °C, and with 100% Al, 125% Al, and 150% Al stoichiometry to produce metallic calcium from the residue of metallic magnesium production. Both the raw materials and the residue phases were characterized by atomic absorption spectrometry (AAS), X-ray diffraction (XRD) spectrometry, and chemical analysis techniques. Experimental results were investigated to determine the highest efficiency of reduction conditions. From the results of the experiments, reaction kinetics and activation energy were calculated. According to the experimental results, the highest recovery rate parameters for the reduction of calcium are 150% stoichiometric Al for 480 min at 1300 °C, with 72% recovery. Full article