Alkali-activated materials (AAMs) are one of the alternative low-CO2 binders. One-part AAMs, (that is, mixing a solid precursor with a solid alkali activator and adding water) have recently attracted ...increasing interest. The purpose of this study is to examine if fast-dissolving solid synthetic sodium metasilicate could be replaced by a combination of sodium hydroxide and slow-dissolving silica derived from rice husk ash or microsilica in the preparation of one-part alkali-activated blast furnace slag mortar. The replacement would improve the carbon footprint and the cost efficiency of the binder. The results demonstrate that silica availability significantly affects compressive strength development as a function of time or mixture composition. The highest compressive strength (107 MPa, 28 d) was obtained with fast-dissolving silica. Furthermore, setting times could be adjusted based on the mix composition, and the durability of mortar remained good after 120 freeze–thaw cycles. The results highlight the overall effect of silica availability on the fresh and hardened properties of one-part AAMs.
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•One-part alkali-activated slag mortar was prepared from different silica sources.•Aim was to improve environmental impact and cost-efficiency.•Rice husk ash and microsilica resulted approx. 30 MPa compressive strength at 28 d.•Synthetic sodium metasilicate resulted 107 MPa compressive strength at 28 d.•All mixtures indicated good freeze-thaw resistance.
Cold weather (<0 °C) is known for its detrimental impacts on concrete, and thus expensive and energy-consuming heating and insulation systems are used in cold-weather concreting to prevent frost ...damage. Supplementary cementitious materials are not recommended for use in cold-weather concreting because they slow down the setting time of concrete. In this study, one-part alkali-activated slag (AAS) was presented as an alternative environment-friendly binder for winter construction. The impacts of iron-containing submicron metallurgical residue on the reactivity, hardened properties, and durability of subzero-cured one-part AAS pastes and mortars were comprehensively studied. The incorporation of submicron particles (SMPs) enhanced the reactivity of AAS pastes by increasing the amount of precipitated hydrate phases and developing supplemental hydration products like calcium ferrosilicate hydrate. The positive effects of SMPs were highlighted via the denser microstructure, higher ultrasonic pulse velocity, increased compressive strength, and better durability properties of the AAS mortars. These improvements were attributed to the nucleation and filling behaviors of the added SMPs. On the contrary, decreased subzero curing temperature hindered the reaction progress, which adversely affected the hardened and durability properties of the mortars and limited the SMPs efficiency. With additional above-zero curing, higher compressive strength and lower water absorption and permeable porosity were measured in the AAS mortar cured initially at −5 °C compared to that cured at +20 °C.
•One-part alkali-activated slag (AAS) mortar was cured at subzero temperatures.•Reactivity was enhanced by the incorporation of submicron particles (SMPs).•The addition of SMPs results in a denser microstructure of AAS mortar.•Embedding SMPs improves the hardened properties of AAS mortar.
The mining industry produces a huge quantity of sulphidic mine tailings, which cause several short- and long-term environmental problems when disposed by landfilling in impounding lakes. The ...possibility of immobilizing several heavy metals from gold mine tailings by reactive geopolymerization technique has been investigated in the present study. The chemical stability of geopolymers synthetized by the alkali activation of metakaolin and blast furnace slag and the addition of 40–50 wt% gold mine tailings is demonstrated. The geopolymers were cured at room temperature, and the effects of different Si/Al and Na/Al molar ratios and curing times were investigated. The inertization effectiveness was evaluated by means of leaching tests carried out according to standard EN 12457 after 7 and 28 days and after 18 months. The samples were immersed into the water for 1 day, and the leachable metals in the test solution were determined by ICP-OES. The results show that various elements (Cr, Cu, Ni, Zn and Mn) from gold mine tailings are able to immobilize almost completely by alkali activation with proper co-binder material. The immobilization efficiency were highly improved with longer curing period also for the problematic elements As, V, Sb and B.
•Alkali activation of gold mine tailings with high quantity of arsenic were researched.•Cr, Cu, Ni, Zn and Mn were almost completely stabilized inside the structure.•Stabilization of arsenic increased with longer curing period.
Mine tailings account for most of the environmental incidents related to the extractive industry, with risks increasing due to steadily rising tonnage of low-grade ore and extreme weather events. ...Recycling of tailings in raw-material-intensive applications presents an interesting alternative to costly tailings management with associated restoration efforts. Chemically bonded ceramics may offer a route to upgrading mine tailings into raw materials for ceramics. In this review such chemically bonded ceramic methods that may be used to recycle mine tailings as raw materials, are reviewed while focusing in particular on two methods: 1) geopolymerization/alkali activation and 2) chemically bonded phosphate ceramics. The aim of the review is not to give exhaustive review on the wide topic, but to scope the required boundary conditions that need to be met for such utilization. According to the findings, alkali activation has been studied for 28 separate silicate minerals in the scientific literature, and presents a viable method, which is already in commercial use in calcium-rich cement-like binder applications. Phosphate bonding literature is more focused on phosphate containing minerals and waste encapsulation. Very little work has been done on low-calcium tailings utilization with either technology, and more knowledge is needed on the effect of different pre-treatment methods to increase reactivity of mine tailings in chemically bonded ceramics.
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•Phosphate bonding and alkali-activation of tailing minerals.•Ceramic-like materials vs. hydraulic cements.•Research gaps identified: potential of pre-processing.•Relatively new research field with potential.
Blast furnace slag from the steel industry is commercially utilized as a cement replacement material without major processing requirements; however, there are many unutilized steel production slags ...which differ considerably from the blast furnace slag in chemical and physical properties. In this study, calcium sulfoaluminate belite (CSAB) cement clinkers were produced using generally unutilized metallurgical industry residues: AOD (Argon Oxygen Decarburisation) slag from stainless steel production, Fe slag from zinc production, and fayalitic slag from nickel production. CSAB clinker with a target composition of ye'elimite-belite-ferrite was produced by firing raw materials at 1300 °C. The phase composition of the produced clinkers was identified using quantitative XRD analyses, and the chemical composition of the clinker phases produced was established using FESEM-EDS and mechanical properties were tested through compressive strength test. It is demonstrated that these metallurgical residues can be used successfully as alternative raw materials for the production of CSAB cement that can be used for special applications. In addition, it is shown that the available quantities of these side-streams are enough for significant replacement of virgin raw materials used in cement production.
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•CSAB clinkers were produced using metallurgical residues.•Fe and fayalitic slag are used to make CSAB with ye'elimite, belite, and ferrite.•The fluorine content in AOD slag enabled the formation of fluorellestadite.•Compressive strength of the produced CSAB mortars is comparable to commercial PC.
Concrete production is globally a major water consumer, and in general, drinking-quality water is mixed in the binder. In the present study, simulated sea water and reverse osmosis reject water were ...used as batching water for one-part (dry-mix) alkali-activated blast furnace slag mortar. Alkali-activated materials are low-CO2 alternative binders gaining world-wide acceptance in construction. However, their production requires approximately similar amount of water as regular Portland cement concrete. The results of the present study revealed that the use of saline water did not hinder strength development, increased setting time, and did not affect workability. The salts incorporated in the binder decreased the total porosity of mortar, but they did not form separate phases detectable with X-ray diffraction or scanning electron microscopy. Leaching tests for monolithic materials revealed only minimal leaching. Furthermore, results for crushed mortars (by a standard two-stage leaching test) were within the limits of non-hazardous waste. Thus, the results indicated that high-salinity waters can be used safely in one-part alkali-activated slag to prepare high-strength mortars. Moreover, alkali-activation technology could be used as a novel stabilization/solidification method for reverse osmosis reject waters, which frequently pose disposal problems.
The mining industry produces billions of tons of mine tailings annually. However, because of their lack of economic value, most of the tailings are discarded near the mining sites, typically under ...water. The primary environmental concerns of mine tailings are related to their heavy metal and sulfidic mineral content. Oxidation of sulfidic minerals can produce acid mine drainage that leaches heavy metals into the surrounding water. The management of tailing dams requires expensive construction and careful control, and there is the need for stable, sustainable, and economically viable management technologies. Alkali activation as a solidification/stabilization technology offers an attractive way to deal with mine tailings. Alkali activated materials are hardened, concrete-like structures that can be formed from raw materials that are rich in aluminum and silicon, which fortunately, are the main elements in mining residues. Furthermore, alkali activation can immobilize harmful heavy metals within the structure. This review describes the research on alkali activated mine tailings. The reactivity and chemistry of different minerals are discussed. Since many mine tailings are poorly reactive under alkaline conditions, different pretreatment methods and their effects on the mineralogy are reviewed. Possible applications for these materials are also discussed.
The mining industry generates a notable amount of mine tailings (MTs). Disposal of MTs creates environmental impacts such as air pollution and the release of heavy metals into surface and underground ...water. The European Union (EU)-funded project “Integrated mineral technologies for more sustainable raw material supply” (ITERAMS) includes an effort to produce eco-friendly backfill materials to enhance operation and mine safety and covers for surface deposits of tailings based on geopolymerization technology. This paper investigates the effects of activator concentration, curing temperature and time on alkali-activated materials based on low-alumina MTs from the Cu/Ni mine in Northern Finland. Alkaline activators containing sodium silicate solution (Na
2
SiO
3
) at different concentrations were used and two different curing temperatures, 40 °C and 60 °C, for periods of 7, 14, and 28 days were considered. Scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDS) and X-ray diffraction (XRD) were performed to investigate the structure, morphology and phase compositions of the alkali-activated products. The effect of curing temperature and alkaline solutions on mechanical strength and water absorption were investigated. The results indicate that the alkalinity and curing temperature affect the mechanical and microstructural properties of the compositions of alkali-activated MTs. The 30 wt% Na
2
SiO
3
addition enables the alkali activated MT to improve the compressive strength with a highest value of 6.44 and 15.70 MPa after 28 days of curing at 40 °C and 60 °C, respectively. The results of this study deliver useful information for recycling and utilization of MTs as sustainable material through the alkali activation.
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•Cellulose nanofibers (CNFs) take inordinate amount of time to drain water.•Modifying CNFs by sonication in the presence of lactic acid (LA) drains water rapidly.•LA modified CNFs ...drains water faster than the addition of NaCl, a common additive.•Nanopapers prepared from LA modified CNFs have enhanced mechanical properties.•LA modified CNFs can be scaled commercially to quickly prepare CNF reinforced paper.
This paper addresses the issue of high water retention by cellulose nanofibers (CNFs) that lead to exorbitant time consumption in the dewatering of CNF suspensions. This has been a bottleneck, which is restricting the commercialization of CNF derived products such as nanopapers and CNF reinforced paper sheets. As a remedy, we suggest an eco-friendly water-based approach that involves the use of sonication energy and lactic acid (LA) to modify the surface of CNFs. The suggested modification resulted in rapid water drainage, and dewatering was completed in 10 min; with unmodified CNFs, it took around 45 min. We have also compared the draining characteristics of LA modification of CNF suspensions with a common draining agent (NaCl); LA modification drains water 56% faster than the use of NaCl, and produced mechanically superior dimensionally stable nanopaper. Additionally, LA modification allows the addition of 10 wt.% CNF in paper sheets, with dewatering done in 2 min (while the unmodified CNFs took 23 min).
The mining industry produces a large quantity of sulphidic mine tailings, which cause several environmental issues during waste management. Currently, there is increasing interest in new technologies ...to recycle and utilize mine tailings more effectively in the future. In this present study, the geopolymerization of mine tailings has been studied. Sulphidic mine tailings from a gold mining site were activated with a NaOH solution and commercial ground granulated blast furnace slag (GGBFS) was used as a co-binder. Characterization of the mine tailings and the mechanical strength of the specimens produced were investigated. In addition, the effects of different NaOH concentrations and the amount of co-binder materials on a matrix were tested. The porosity of the specimens produced was evaluated using water absorption tests, the microstructure of the fractures was analyzed with field emission scanning electron microscope (FESEM), and the crystalline phases were identified by X-ray diffraction. The results show that the unconfined compressive strength (UCS) of the specimens produced from pure mine tailings was in the range of 1.3–3.5MPa. The UCS increased and water permeability decreased with 5% GGBFS content in the mixture. By optimizing the NaOH concentration and GGBFS content, the UCS of the specimens varied from 1.8MPa to 25MPa. The alkali-activation of mine tailings allows binders to be made with sufficient compressive strength, which can be used as a backfill in mining sites or raw material in the construction industry.
•Alkali-activation of sulphidic mine tailings with ground granulated blast furnace slag (GGBFS)•Geopolymers with 95% of mine tailings has mechanical strength of 4MPa in dry and underwater conditions.•Mechanical strength more than 20MPa when using 25% of GGBFS as a co-binder
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