Stabilization study of a contaminated soil with metal(loid)s adding different low-grade MgO degrees

Low-grade magnesium oxide (LG-MgO) was proposed as ordinary Portland cement (OPC) or lime substitute (CaO) for metal(loid)s remediation in contaminated soils. Some metal(loid)s precipitate at pH ≈ 9 in insoluble hydroxide form thus avoiding their leaching. LG-MgO avoids the re-dissolution of certain metal(loid)s at 9.0 < pH < 11.0 (pH-dependents), whose solubility depends on the pH. A highly contaminated soil with heavy metal(loid)s was stabilized using different LG-MgO by-products sources as stabilizing agents. Two of the three studied LG-MgOs were selected for the stabilization, by mixing 5, 10, and 15 wt.%. The effect of using LG-MgO not only depends on the size of the particles, but also on those impurities that are present in the LG-MgO samples. Particle size distribution, X-ray fluorescence (XRF), X-ray diffraction (XRD), thermogravimetric analysis, citric acid test, specific surface, bulk density, acid neutralization capacity, batch leaching tests (BLTs), and percolation column tests (PCTs) were techniques used to deeply characterize the different LG-MgO and the contaminated and remediated soils. The remediation's results efficacy indicated that when the medium pH was between 9.0 and 11.0, the concentration of pH-dependent metal(loid)s decreases significantly. Although around 15 wt.% of a stabilizing agent was appropriate for the soil remediation to ensure an alkali reservoir that maintains optimal stabilization conditions for a long period, 5 wt.% of LG-MgO was enough to remedy the contaminated soil. When evaluating a polluted and decontaminated soil, both BLTs and PCTs should be complementary procedures

Granular material development applied in an experimental section for civil engineering purposes

In this study, a granular material (GM) derived from wastes generated in waste-to-energy plants was developed. Weathered bottom ash (WBA) and air pollution control (APC) ashes obtained from municipal solid waste incineration (MSWI) were used as raw materials. A mortar (M) with 50 wt. % of APC and 50 wt. % of Ordinary Portland Cement (OPC) CEM-I was prepared. The GM formulation was 20 wt. % M and 80 wt. % WBA. At the laboratory scale, WBA, APC, M, and crushed GM were evaluated by means of dynamic leaching (EN 12457-4) tests, and WBA, M, and crushed GM by percolation column (CEN/TS 16637) tests. The metal(loid)s analyzed were below the non-hazardous limits, regarding the requirement of the metal(loid)s released for waste revalorization. In order to simulate a road subbase real scenario, the crushed GM was tested in an experimental section (10 × 20 × 0.2 m). During a 600-day period, the leachates generated by the percolation of rainwater were collected. This research shows outstanding results regarding the metal(loid)s released for both the 'accumulated' and 'punctual' leachates collected. An accomplishment in the immobilization of metal(loid)s from APC residues was achieved because of the encapsulation effect of the cement. The GM formulation from both MSWI wastes can be considered an environmentally safe procedure for revalorizing APC residues

APC fly ash recycling: development of a granular material from laboratory to a pilot scale

The aim of this article is to present the research carried out over a 10 year period to develop an environmentally safe method for recycling Air Pollution Control (APC) residues. The initial studies aimed to formulate a mixture of Weathered Bottom Ash (WBA), APC residues and Portland Cement (PC) to be used as a sub-base in road constructions. Mechanical performance was subsequently enhanced by preparing a mortar prior to mixing it with WBA in order to obtain a granular material. After testing different formulations, the optimum mortar consisted of 50% APC residues and 50% PC. The evaluation was carried out based on the concentration release of the heavy metals and metalloids included in the Catalan legislation for revalorization of residues. After the applicability of the granular material was successfully demonstrated at laboratory scale from an environmental and mechanical point of view, a pilot scale plant was designed in order to assess its performance in a real scenario during four month. Thus, three roads were built: two containing 100% granular material and a third containing 100% WBA. The results showed that the immobilisation of all toxic species from APC residues is accomplished by the pozzolanic effect of the cement. The WBA, APC, and PC proportions show to be the most appropriate for compliance with regard to environmental and mechanics requirements

Preparation and exhaustive characterization of paraffin or palmitic acid microcapsules as novel phase change material

In this study, two different types of Phase Change Materials (PCM) suitable for Thermal Energy Storage (TES) applications were used as a core material in a microencapsulation process. The wall material for these microencapsulated PCM (MPCM) was Poly(styrene-co-ethylacrylate) (PScEA). Microcapsules were prepared using an emulsion co-polymerization technique. The prepared MPCM were characterized as follows: morphology, shape and size were analyzed by Scanning Electron Microscopy (SEM) and Particle Size Distribution (PSD). Besides, Fourier Transformed Infrared spectroscopy (FT-IR) was used to perform the chemical characterization of the shell microcapsules. Moreover, thermophysical properties were analyzed by Differential Scanning Calorimetry (DSC) for the two PCM in usage (paraffin 42-44 and palmitic acid) meanwhile the thermal stability was evaluated by Thermogravimetrical Analysis (TGA). Mechanical characterization of the prepared microcapsules was performed by using the Atomic Force Microscopy (AFM) as indentor. Experiments were performed at two different temperatures 25 °C and 70 °C, and two parameters were evaluated: the Young's modulus on a punctual area and the vertical force required to plastically deform the MPCM. At the light of the results, it can be considered that these synthesized MPCM were successfully prepared being able to be used in a TES system

Municipal solid waste incineration bottom ash as alkali-activated cement precursor depending on particle size

Bottom Ash (BA) is the main by-product of municipal solid waste incineration (MSWI). It is stabilised outdoors to obtain weathered bottom ash (WBA) whose main application is in the construction sector as a secondary aggregate for road sub-base. Here, the aim of this work is to advance the study of the potential use of WBA as a precursor in the synthesis of new alkali-activated cements (AACs). An exhaustive physicochemical characterisation (X-ray fluorescence, X-ray diffraction, Fourier-transform infrared spectroscopy, inductively coupled plasma - optical emission spectroscopy, and Inductively coupled plasma - mass spectroscopy) of WBA was provided depending on its particle size (<30, 30-16, 16-8, 8-4, 4-2 and 2-0 mm). The study reveals that WBA is composed mainly of the essential reactive phases to form AACs, which are SiO2, Al2O3, and CaO. It is demonstrated the larger the particle size, the higher the content of SiO2; and the smaller the particle size, the higher the heavy metal(loid) content. The availability of reactive phases was analysed through chemical attacks with HF and NaOH solutions of different concentrations (2M, 4M, and 8M). The results demonstrate the availability of reactive phases (including 150-250 g kg−1 of SiO2 and 50-65 g kg−1 of Al2O3) in all the particle size fractions studied. WBA potential will be of considerable use to formulate AACs, depending on the particle size fraction and the Si/Al ratio, both as the sole precursor and mixed with others

Municipal solid waste incineration bottom ash as sole precursor in the alkali-activated binder formulation

The concern about the large amount of weathered bottom ash (WBA) produced in waste-to-energy plants (WtE) has caused an increased search for alternatives to reduce their environmental impact. The present study aims to provide an added value through the WBA valorization from municipal solid waste incineration (MSWI) for its use as a sole precursor for developing alkali-activated binders (AABs). Alkali-activated weathered bottom ash binders (AA-WBA) were formulated with a liquid-to-solid ratio of 1.0 and using sodium silicate (80 wt.%) and NaOH (20 wt.%) at different concentrations (2, 4, 6, and 8M) as alkali-activator solutions. AA-WBA were cured at room temperature to extend their applicability. The effect of the alkali-activator solution molarity on the final properties of the AA-WBA was evaluated. The physicochemical characterization by XRD, FTIR, and SEM evidenced the presence of the typical phases (calcium silicate hydrate and gehlenite) of C-(A)-S-H gel. Leaching concentrations of As, Cu, and Mo exceed the acceptance in landfills for inert waste, while the leaching concentration of Sb exceeds the one for non-hazardous waste. The structure of the binders depends on the alkalinity of the activator, obtaining better results using NaOH 6M in terms of microstructure and compressive strength (6.7 MPa). The present study revealed that AA-WBA for non-structural purposes can be obtained. The AA-WBA formulation contributes to the WBA valorization and development of low-carbon cements; therefore, it is an encouraged alternative to ordinary Portland cement (OPC). Considering the amounts and costs of the WBA, sodium silicate, NaOH, and wat

Alkali-activated binders using bottom ash from waste-to-energy plants and aluminium recycling waste

Alkali-activated binders (AABs) stand out as a promising alternative to replace ordinary Portland cement (OPC) due to the possibility of using by-products and wastes in their manufacturing. This paper assessed the potential of weathered bottom ash (WBA) from waste-to-energy plants and PAVAL® (PV), a secondary aluminium recycling process by-product, as precursors of AABs. WBA and PV were mixed at weight ratios of 98/2, 95/5, and 90/10. A mixture of waterglass (WG) and NaOH at different concentrations (4 and 6 M) was used as the alkaline activator solution. The effects of increasing NaOH concentration and PV content were evaluated. Alkali-activated WBA/PV (AA-WBA/PV) binders were obtained. Selective chemical extractions and physicochemical characterization revealed the formation of C-S-H, C-A-S-H, and (N,C)-A-S-H gels. Increasing the NaOH concentration and PV content increased porosity and reduced compressive strength (25.63 to 12.07 MPa). The leaching potential of As and Sb from AA-WBA/PV exceeded the threshold for acceptance in landfills for non-hazardous waste

Alkali-activated binders based on the coarse fraction of municipal solid waste incineration bottom ash

The potential of the least polluted fraction (from 8 to 30mm) of municipal solid waste incineration (MSWI) weathered bottom ash (WBA) as an alkali-activated cement precursor was evaluated. Alkali-activated WBA binders (AA-WBA) formulations were prepared through alkali-activation of WBA as sole precursor. Sodium silicate (Na2SiO3) and sodium hydroxide (NaOH) mixtures with different pH's were used as alkali-activator solution. The effect of alkali-activator solution pH on the final properties was assessed. Results showed the hydrolytic stability of allformulations. The selective chemical extractions and physicochemical characterisation revealed the formation of the C-S-H, C-A-S-H, and (N,C)-A-S-H gels. The promising compressive strength results demonstrated the potential of AA-WBA binders. The increase of pH in the alkali-activated solution promotes the formation of gel reaction products and enhance mechanical properties. This investigation promotes the green cements manufacturing and the use of secondary resources to reduce the impact of natural resources extraction used for the ordinary Portland cement (OPC) production

Rapid sintering of weathered municipal solid waste incinerator bottom ash and rice husk for lightweight aggregate manufacturing and product properties

This study assessed the technical feasibility of formulating lightweight aggregates (LWA) from municipal solid waste incinerator bottom ash (IBA) and residual biomass. Weathered IBA (WIBA) particles larger than 8 mm contain a mixture of calcium-rich compounds and other silicates mainly composed of glass and synthetic and natural ceramics, with low contents of heavy metals and soluble salts. Unfired LWA were formulated with the particle size fraction of WIBA larger than 8mm and rice husk (RH) used as the bloating agent. Rapid sintering of the unfired spherical pellets at 1,100°C for 5min produced some cohesive sintered LWA, whose porosity, apparent particle density, water absorption, and compressive strength directly correlated with the percentage of RH added. The fired LWA formulated with 5wt% of RH showed the highest bloating index (115%) and porosity (53%) and the lowest apparent particle density (0.61Mgm−3) and compressive strength (1.4MPa). The addition of more than 5wt% of RH increased the internal temperature of the sintered aggregates and decreased the viscosity of the molten glassy materials, resulting in the collapse of the inner structure. Consequently the porosity decreased and the apparent density of the particles increased, thereby shrinking the volume of the fired LWA. According to the standard leaching test (EN 12457-4), both the unfired precursor and the sintered aggregates showed concentrations of heavy metals and metalloids in the leachates that were well below the safety limits established for their reuse as secondary material

Can tundish deskulling waste be used as a magnesium oxide source to develop magnesium phosphate cement?

Ordinary Portland cement (OPC) has a significant environmental impact since approximately 0.81 kg of CO2 is generated for every kilogram produced. Thus, it is mandatory to look for sustainable alternative cements. One of the most promising materials in this sense is magnesium phosphate cement (MPC). This study evaluates the possibility of revaluing a waste obtained from the tundish deskulling (TUN) as a raw material for formulating alternative MPC. This approach aims to promote the circular economy and minimizing the environmental impact of MPC. The tundish working lining is a crucial refractory material used in continuous steel casting. An optimal cement formulation was achieved by maximizing the compressive strength (CS) at 7 days, resulting in the combination of 60 wt% of TUN and 40 wt% of KH2PO4, with a water/cement (W/C) ratio of 0.27. The physical and mechanical properties were evaluated at three different stages: after 1, 7, and 28 days of curing. Furthermore, an exhaustive physicochemical characterization was conducted to investigate the feasibility of using it as an alternative cement. This study confirms the feasibility of formulating MPC using TUN as raw material due to the main product obtained, which is K-struvite. The use of TUN implies important economic savings and enhances sustainability criteria avoiding its management in landfills