The Transformation of Coal-Mining Waste Minerals in the Pozzolanic Reactions of Cements

Abstract

Abstract:The cement industry has the potential to become a major consumer of recycled waste materials that are transformed and recycled in various forms as aggregates and pozzolanic materials. These recycled waste materials would otherwise have been dumped in landfill sites, leaving hazardous elements to break down and contaminate the environment. There are several approaches for the reuse of these waste products, especially in relation to clay minerals that can induce pozzolanic reactions of special interest in the cement industry. In the present paper, scientific aspects are discussed in relation to several inert coal-mining wastes and their recycling as alternative sources of future eco-efficient pozzolans, based on activated phyllosilicates. The presence of kaolinite in this waste indicates that thermal treatment at 600˝C for 2 h transformed these minerals into a highly reactive metakaolinite over the first seven days of the pozzolanic reaction. Moreover, high contents of metakaolinite, together with silica and alumina sheet structures, assisted the appearance of layered double hydroxides through metastable phases, forming stratlingite throughout the main phase of the pozzolanic reaction after 28 days (as recommended by the European Standard) as the reaction proceeded.

Vitrified Walls in the Iron Age of Western Iberia: New Research from an Archaeometric Perspective

“…These differences indicate that the brown surface was affected by a lower temperature, since the illite disappears at a temperature of over 900 or 1000°C. Amphibole and Kfeldspars change around 1000°C, while the presence of pyroxene in the black core sample indicates a temperature higher that 1100°C (García-Giménez et al, 2016). We conclude that the whole rock was vitrified, reaching a temperature of 850°C, and, although temperatures were more regular than those at Pozos de los Moros, they can also be related to an irregular fire, accidental or deliberate, with an oxidizing atmosphere.…”

Advances in Methods for Recovery of Ferrous, Alumina, and Silica Nanoparticles from Fly Ash Waste

“…The major fractions of iron in coal are present either as sulfur-bearing or non-sulphur-bearing minerals [98]. The sulphur-containing iron minerals in coal are pyrite (FeS 2 ) [99], jarosite [KFe 3 (SO 4 ) 2 (OH) 6 ] [100], troilite [101] and pyrrhotite [102] (both FeS) [103,104], while the non sulphur-bearing iron minerals [105] are ankerite (CaFe(CO 3 ) 2 ) [106][107][108], illite [109] and siderite (FeCO 3 ) [110][111][112]. The generation of ferrospheres occurs in the carbon matrix, which provides a reducing medium when iron-containing minerals from coal interact with other elements of coal in the molten form and transform into ferrous oxides.…”

Carbonation-Induced Mineralogical Changes in Coal Mining Waste Blended Cement Pastes and Their Influence on Mechanical and Microporosity Properties

“…This study forms part of a broader research project on the development of blended cements made with activated material from coal mining waste with a view to obtaining innovative eco-efficient cements. Earlier studies [24][25][26][27][28][29][30] showed that it is scientifically and technically feasible to convert this inert pollutant waste into a supplementary cementitious material. Their findings have charted a promising alternative route for obtaining recycled metakaolinite, a pozzolan listed in the existing legislation on cement [31].…”