Recycling and Application of Mine Tailings in Alkali-Activated Cements and Mortars—Strength Development and Environmental Assessment

Abstract

Mine tailings (MT) could represent a step forward in terms of the quality of the aggregates usually used in civil engineering applications, mostly due to its high density. The Portuguese Neves Corvo copper mine, owned by the Lundin Mining Corporation, produces approximately 3 million tonnes per year. Nevertheless, it cannot be used in its original state, due to its high levels of sulphur and other metals (As, Cr, Cu, Pb, Zn). This paper focuses on the stabilisation/solidification of high-sulphur MT, without any previous thermal treatment, using alkali-activated fly ash (FA). The variables considered were the MT/FA ratio and the activator type and concentration. A fine aggregate was then added to the pastes to assess the quality of the resulting mortar. Maximum compressive strengths of 14 MPa and 24 MPa were obtained for the pastes and mortars, respectively, after curing for 24 h at 85 • C. Thermogravimetric analysis, scanning electron microscopy, X-ray energy dispersive spectroscopy, X-ray diffraction, and infrared spectroscopy were used to characterize the reaction products, and two types of leaching tests were performed to assess the environmental performance. The results showed that the strength increase is related with the formation of a N-A-S-H gel, although sodium sulphate carbonate was also developed, suggesting that the total sodium intake could be optimized without strength loss. The solubility of the analysed metals in the paste with 78% MT and 22% FA was below the threshold for non-hazardous waste. potential use of MT as a replacement for natural aggregates, which are usually obtained through an extraction process that severely affects the environment, would not only reduce the consumption of natural resources but also decrease the volume of landfilled MT. However, this waste generates acid mine drainage when exposed to oxygen and water [5], which makes it impractical as an aggregate in common applications, like embankments or roads, if not previously stabilised.Another possible use is inclusion in alkali-activated mortar and concrete, a recent research topic, with promising results in terms of mechanical and environmental performance [5,6]. Some studies focused on the use of MT as a precursor, albeit requiring a previous thermal treatment [7][8][9][10][11], while others used a different approach by considering the MT as a filler and/or coarse aggregate in composite materials, cemented by aluminosilicate gel formed from the alkali activation of fly ash, metakaolin, waste glass, or slags [11][12][13][14][15][16][17][18][19]. Although many of the above-mentioned studies were dealing with tailings resulting from tungsten and gold mines, several studies have also been produced targeting copper mine tailings [16,[19][20][21][22][23]. From an environmental perspective, it is important to highlight that alkaline activation has already proved to be very effective for containing and neutralising different types of wastes [24][25][26][27][28][29][30][31][32][33][34][35] and, specifically, wastes resulting from m...

Characterization of Slag Reprocessing Tailings-Based Geopolymers in Marine Environment

“…For example, Ahmari et al used sodium hydroxide as an alkaline activator to prepare copper mine tailings-based geopolymers, which were suitable for application of road base material at a room temperature [5]. Cristelo et al applied fly ash as additive, and sodium hydroxide and sodium silicate as alkaline activators to prepare high-sulfur copper mine tailings-based geopolymer, which had a maximum compressive strength of 23.5 MPa [6]. Generally, mine tailings contain a substantial amount of crystal minerals and exhibit inert in geopolymeric reaction, so that the calcination of the tailings or addition of calcined materials (e.g., metakaolin and slag) is usually necessary; the reasons are: (1) the calcined materials (e.g., metakaolin and slag) have a large amount of silicon, aluminum and calcium, which are vital elements required for geopolymerization, (2) the calcined raw materials usually have a fast dissolution and gelation rate that makes geopolymers show high early compressive strength.…”

Treatment of Mining and Thermoelectric Waste Through the Geopolymerization Process

“…The TCLP analysis demonstrates a significant reduction in the levels of the contaminants Mr. Ca, Fe, Pb, Ba, Be, and Cu present in the raw materials after treatment by geopolymerization, demonstrates the chemical encapsulation of the contaminants, as well as the evidence of Cristelo et al Elements such as Mo, Na, Ni, P, K, Li, Se and V, present difficulty to fix this kind of ions in the geopolymer matrix due to their high solubility in alkaline environments. This increases their presence in the formed geopolymer, as [27] show in their results, so these elements are scattered in the geopolymer matrix as [28], this predominant mechanism depends on the level of solubility of the heavy metal ions, i.e. the highly soluble elements are more spread throughout the matrix, while the less soluble elements form larger volume nuclei that are then involved by the gel matrix, which makes this geopolymer present a chemical and physical encapsulation for elements such as Sr, Ca, Fe, Pb, Ba, Be, and Cu and a physical encapsulation for the other elements Mo, Na, Ni, P, K, Li, Se and V, taking into account that the geopolymer formed is an aggregate with great mechanical properties, This marks an absolute difference between other treatments due to the properties obtained in this research work, which was treated under natural environmental conditions in the Tacna Peru region, which shows that it is possible to reduce the contaminating elements without the need to calcine the mixture of raw materials, however the curing time is 35 days to achieve optimal properties in the geopolymer formed, it is recommended to carry out more studies related to the encapsulation of heavy contaminating elements, in addition to studies of future applications of these materials for use in structures or roads.…”

Exploring the Potential for Utilization of Medium and Highly Sulfidic Mine Tailings in Construction Materials: A Review

“…Those massive amounts are of great concern in the world as well as in Europe. Some examples of huge volumes of sulfidic mine tailings produced by individual mines are (a) the Neves Corvo Cu-Zn mine (Portugal) produces 2.9 million tonnes of tailings per year [31], (b) the Mamut Cu-Au-Ag mine (Indonesia) produced 250 Mt of overburden and 150 Mt tailings during its operation [32], (c) the Lavrion Ag-Pb mine (Greece) has produced nearly 800,000 m 3 of sulfidic flotation tailings, occupying a 94,000 m 2 area [33], (d) the Navodari mine (Romania) has generated nearly 1,000,000 m 3 of pyritic cinders [34], (e) the Laver Cu-Au-Ag mine and Stekenjokk Cu-Zn-Cu mines (Sweden) respectively stored 1.2 million tonnes and 4.4 million tonnes of tailings in containments [35], (f) it is estimated that Alberta, Canada needed at least 130 km 2 for tailings slurry impoundment [36], (g) the O'Kiep Cu-Pb-Zn ores in South Africa has nearly 5.8 Mt metalliferous tailings [37].…”

“…Examples of the PSD of medium and highly sulfidic tailings obtained utilizing laser diffraction granulometry [25,31,[42][43][44][45][46][47] were redrawn from the literature and are presented in Figure 1. Table 3 shows the diameter ranges observed for d 10 , d 50 , and d 90 , specific surface area (SSA), and specific gravity (SG).…”