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A study on the valorization of a metallic ore mining tailing and its combination with polymeric wastes for lightweight aggregates production

Moreno-Maroto, José Manuel, González-Corrochano, Beatriz, Alonso-Azcárate, Jacinto, Martínez García, Carmen
Journal of cleaner production 2019 v.212 pp. 997-1007
X-ray diffraction, additives, air, carbon fibers, civil engineering, color, concrete, cortex, energy-dispersive X-ray analysis, glass, human food chain, metals, mine tailings, mining, pellets, plasticity, porosity, scanning electron microscopy, sepiolite, soil, strength (mechanics), toxicity, water uptake, Spain
Mining activity can release important amounts of toxic metals which are able to move through the soil, water and air, or even to reach the human food chain. Consequently, the environmental and health issue related to ore extraction has led to an increased awareness of the importance of recovering mining sites. In this study, samples taken from tailings located in the abandoned metallic mine named La Unión (Mazarambroz, Spain) have been studied to sinter lightweight aggregates (LWAs). The fraction <63 μm was selected and mixed with 10 wt% of a sepiolite residue to gain plasticity. Likewise, 2.5 wt% of thermoplastic (P) and 2.5 wt% of carbon fiber (FC) wastes were added in powder form to check the effect of these two additives. The mixtures were blended with water, extruded, shaped into pellets, oven-dried and finally fired at 1175 °C for 4 min in a rotary kiln. The main technological properties of the aggregates related to bloating, density, porosity, loss on ignition, water absorption and mechanical strength were determined. Quantitative changes in mineralogy and glass formation were studied using the Rietveld refined XRD technique. Microstructural and textural characteristics were studied by microscopy. Dark color LWAs of high porosity, low density and good mechanical strength were obtained. The addition of P ad FC allowed the development of a well-distributed-porous core surrounded by a very thin shell, in contrast to the thick cortex formed when these components were not used. While the addition of FC did not mean real advantages in the technological properties, P promoted greater bloating and lower density. A high volume of glass was evolved in all the aggregates (≥60%) and augite was the main neo-formed mineral. Pyrrotite was also neo-formed, but its proportion was negligible to be detected by XRD, so that it could be only observed by SEM-EDX microscopy. These results are encouraging to continue investigating these wastes and the aggregates manufactured from them in order to determine their capacity to immobilize hazardous metals and their potential application in lightweight concrete, agriculture or civil engineering.