# Mechanical Behavior of a Mine Tailing Stabilized with a Sustainable Binder
## 2 Materials  
### Mine Tailing  
The tailings of this study, as shown in Figure 1, came from the Neves Corvo mine located in the south of Portugal, provided by the Somincor company. After drying in an oven at a temperature of 110 \({}^{\circ}\)C, the tailings were broken down manually before testing. The following tests were conducted to characterize the tailings: (a) the value of the liquidity limit (\(\omega_{1}\)) through the Casagrande test was obtained equal to 23%; (b) the plasticity limit (\(\omega_{\rm P}\)) was obtained equal to 12%, and the plasticity index (\(\rm I_{P}\)) was equal to 11%; (c) the density of solid particles was obtained using the IGPAI standard (1965) equal to 3.51; (d) the granulometric curve of the tailing under study was determined based on the LNEC (National Laboratory for Civil Engineering) specification (1966a). The grain size curve of the specimen is shown in Figure 2. The results obtained indicated the proportions of sand (12%), silt (74.2%), and clay (13.8%) in the MT, showing that a large part of the tailing particles is the size of silt. The tailing classification was performed according to the ASTM unified classification (2006). As the percentage that passed through the #200 sieve was greater than 50% (P\({}_{\rm\#200}\) = 92.6%), the liquidity limit (\(\omega_{\rm U}\)) is equal to 23%, the plasticity index (I\({}_{\rm p}\)) is equal to 11%, and considering the tailing as an inorganic material, with a percentage retained on the #200 sieve less than 15%, the tailing was designated as CL--lean clay. The Proctor test was carried out according to the LNEC specification (1966b). The modified Proctor test determined the optimal water content (\(\omega_{\rm opt}\)) of 11.0% and the maximum dry density mass (\(\rho_{\rm d,\ max}\)) of 2.29 g/cm\({}^{3}\). The standard Proctor test determined the optimal water content (\(\omega_{\rm opt}\)) and maximum dry density (\(\rho_{\rm d,\ max}\)) of 14.9% and 2.14 g/cm\({}^{3}\), respectively. The CBR test was performed based on the LNEC specification (1967) to quantify the mechanical resistance of the tailing before and after saturation. The CBR values of 19% and  
Figure 1: Mine tailing used in this study. Figure 2: Grading curve of the mine tailing. 5% were obtained before and after the saturation of the specimen, respectively. It was found that the saturation of the tailings significantly affected its mechanical strength, resulting in very low CBR values. The permeability test was carried out based on the BS 1377-5 (1990) standard. The specimen was built based on the optimal condition resulting from the standard proctor test. The obtained permeability coefficient was 10\({}^{-7}\)cm/s. This value is typically associated with clayey soils [25; 26]. The chemical, mineralogical and microstructural composition of the tailing were evaluated using XRD, XRF and SEM analysis. The XRD analysis was carried out at the electron microscopy unit of the University of Tras-os-Montes and Alto Douro. The XRF analysis was conducted at the Instituto de Ciencias de la Construccion Eduardo Torroja in Madrid. Based on XRD analysis (Figure 3), the predominant characteristic minerals in the tailings, namely, pyrite (p = FeS\({}_{2}\)), quartz (q = SiO\({}_{2}\)), siderite (s = FeCO\({}_{3}\)) and franklinite (f = ZnFe\({}_{3}\) + 2O\({}_{4}\)), were observed. Two other elements are also highlighted, but their determination was not considered relevant due to the low percentages of the two minerals. The XRF analysis evaluated the tailing composition (Table 1). It was verified that the predominant oxides in the tailings are sulfur (23.52%), silica (22.95%), iron (21.62%), carbon (19.30%) and aluminum (7.76%). Mine tailing contains some heavy metals in its composition, including arsenic (As), chromium (Cr), copper (Cu), manganese (Mn), lead (Pb) and zinc (Zn). These results confirm the strong reactivity of the tailing when exposed to oxidizing agents and the consequent high predisposition for the generation of acid mine drainage (AMD).