Experimental Research on Improving Activity of Calcinated Coal Gangue via Increasing Calcium Content

Abstract

In this investigation, non-spontaneous combustion coal gangue was activated by two methods: (1) low-temperature calcination and (2) calcium addition. Differences in the activity of the activated coal gangue were studied at various calcination temperatures and amounts of calcium addition. Meanwhile, the cementation activity of the activated coal gangue was evaluated according to the activity effect analysis. Furthermore, the influences of the activated coal gangue on the cementation activity of cement were investigated. The results indicated that the activities of the activated coal gangue increased at a temperature between 500 °C and 700 °C. The calcium addition method can also increase the activity of coal gangue, with the effect being better when the gangue is mixed with slag. The addition of calcium and the calcination of coal gangue can promote the production of active minerals such as metakaolin, which is the main reason for the increased cementation activity.

Thermal Activation of High-Alumina Coal Gangue Auxiliary Cementitious Admixture: Thermal Transformation, Calcining Product Formation and Mechanical Properties

“…As compared with the strength of mortar with the mixture of calcined CG and lime (CaO) as auxiliary cementitious material, the used HACG auxiliary cementitious material demonstrates an enhanced effect on the strength of mortar. Zhao et al [20] prepared calcium added to calcined CG by mixing CG calcined at temperatures of 500-700 • C with 10% lime and 5% desulfurization gypsum, and found that the 7-d and 28-d flexural and compressive strengths of mortar specimens decreased with the content of calcium added to calcined CG. The reason for this may be due to the lack of calcining CG-lime mixture, so no hydratable products are generated from the chemical reaction between CaO and metakaolin.…”

“…The second route is to increase calcium oxide content by the addition of minerals containing calcium element in CG, such as lime, limestone, gypsum and fluorite, and then to calcine CG with the minerals at a high temperature, above 1000 • C, for the formation of hydratable products such as 3CaO•SiO 2 (C 3 S), 2CaO•SiO 2 (C 2 S) and so on. The second route requires a high calcining temperature, since calcination at low temperatures of 500-900 • C was not found to have a significant effect on improving the activity of CG with the addition of minerals containing calcium [18][19][20][21].…”

The Design of a Novel Alkali-Activated Binder for Solidifying Silty Soft Clay and the Study of Its Solidification Mechanism

“…China's CG annual emissions account for about 25% of all categories of industrial solid waste [21]. In 2021 alone, 743 million tons of CG were generated, of which nearly one-third spontaneously combusted under natural conditions to form self-combusted coal gangue (SCCG) [22,23]. It has been reported that the spontaneous combustion process can stimulate the activity of silicon oxide and aluminum oxide in CG to some extent [24,25].…”