Integral recycling of municipal solid waste incineration (MSWI) bottom ash fines (0-2mm) and industrial powder wastes by cold-bonding pelletization

The leaching behavior of hazardous element under different leaching procedure utilizing slag-fly ash-based agent: Chromium, antimony, and lead

Low-carbon cementitious materials based on blast furnace slag (BFS) and municipal solid waste incineration (MSWI) fly ash play a pivotal role in the construction industry by substituting cement clinker. This innovation significantly reduces CO2 emissions and enables the extensive utilization of both industrial solid waste and hazardous urban waste on a large scale. However, the application of MSWI fly ash as a precursor for alkali-activated cementitious materials presents a significant leaching risk of heavy metal during the extended reaction process, posing a critical barrier to the efficient and widespread utilization of these solid waste. Three static leaching methods [horizontal vibration (HV), sulphuric acid & nitric acid (SN), and acetic acid buffer solution (AAB)], along with acid neutralization capacity (ANC) leaching tests, were applied in BFS-fly ash-based cementitious materials (BFCM) to assess the leaching behavior of high-risk elements-Cr, Sb, and Pb-within MSWI fly ash. The A4 matrix (BFS: MSWI fly ash:FGDG = 70:20:10) exhibits a compressive strength of 72.51 MPa at 180 day, with the leaching concentrations of target elements remaining below the standard limit under chemical attack (H+ and OH-). The critical pH determined is 9.2 from the ANC leaching test results. Visual MINTEQ simulation illustrates the occurrence states of Cr, Sb, and Pb as (CrO4)2-, [Sb(OH)6]-, and Pb(OH)3- within the BFCM system, respectively. The "double salt effect", intended to enhance the dissociation degree of BFS, acts as the driving force behind the long-term hydration reaction. It also serves as an assurance in controlling the long-term leaching risk of object elements. The dissociation degree of BFS within A4 matrix increased by 38.71 %, with the relative content of the typical low-solubility double salt "Ettringite" reaching 29 % at 180 d. This study provides novel theoretical and data-driven evidence to investigate the leaching behavior associated with MSWI fly ash and the accomplishment of replacing cement clinker with low-carbon BFCM.

Risk control of heavy metal in waste incinerator ash by available solidification scenarios in cement production based on waste flow analysis

Incineration is a common method in municipal solid waste management, which has several advantages such as reducing the volume of waste, but with concerns about exhaust gas and ash management. In this study, heavy metals in bottom ash, secondary furnace ash and fly ash of two waste incinerators in Tehran and Nowshahr were analyzed and its control in cement production was investigated. For this purpose, twelve monthly samples of three types of incinerator ash were analyzed. By combining the studied ashes in the raw materials, the quantity of metals in the cement was analyzed. Finally, by investigating four scenarios based on quantitative variations in the routes of municipal solid waste, ash quantity and the related risk caused by its heavy metals were studied. The results showed that the concentration of heavy metals in the three ash samples of the studied incinerators was 19,513-23,972 µg/g and the composition of the metals included Hg (less than 0.01%), Pb (2.93%), Cd (0.59%), Cu (21.51%), Zn (58.7%), As (less than 0.01%), Cr (15.88%), and Ni (0.91%). The best quality of produced cement included 20% ash and 10% zeolite, which was the basis of the next calculations. It was estimated that the reduction of the release of metals into the environment includes 37 gr/day in best scenario equal to 10.6 tons/year. Ash solidification can be considered as a complementary solution in waste incinerator management.

Influence of Carbonated Bottom Slag Granules in 3D Concrete Printing

This study investigates the possibility of utilising bottom slag (BS) waste from landfills, and a carbonation process advantageous for the use of artificial aggregates (AAs) in printed three-dimensional (3D) concrete composites. In general, the main idea of granulated aggregates is to reduce the amount of CO₂ emissions of printed 3D concrete objects (wall). AAs are made from construction materials, both granulated and carbonated. Granules are made from a combination of binder (ordinary Portland cement (OPC), hydrated lime, burnt shale ash (BSA)) and waste material (BS). BS is a waste material left over after the municipal waste burning process in cogeneration power plants. Whole printed 3D concrete composite manufacturing consists of: granulating artificial aggregate, aggregate hardening and sieving (adaptive granulometer), carbonation of AA, mixing 3D concrete, and 3D printing. The granulating and printing processes were analysed for hardening processes, strength results, workability parameters, and physical and mechanical properties. Printings with no granules (reference 3D printed concrete) were compared to 3D printed concretes with 25% and 50% of their natural aggregate replaced with carbonated AA. The results showed that, theoretically, the carbonation process could help to react approximately 126 kg/m³ CO₂ from 1 m³ of granules.

Exploring the carbon capture and sequestration performance of biochar-artificial aggregate using a new method

To achieve the ambitious goal of carbon neutrality, more carbon sequestration channels need to be developed. In this study, we tried to combine biochar with cold-bonded artificial lightweight coarse aggregate (ALCA) which is made from municipal solid household waste incineration bottom ash (MSWIBA).The strong carbon capture ability of biochar was used to attract external CO₂ into the interior of ALCAs, which combined with CaO in MSWIBA to form CaCO₃ to achieve the effect of chemical carbon sequestration. The total carbon sequestration and carbon sequestration rate of biochar-ALCAs were quantified by a self-designed CO₂ concentration change test box, the physical and mechanical properties of biochar-ALCAs were investigated, as well as the changes before and after carbonization. The results showed that biochar and ALCAs had good synergistic carbon sequestration ability. The total carbon sequestration of biochar-ALCAs could reach 30.58-33.06 kg/ton. The carbon sequestration efficiency could reach 70.2 % and 84.9 % at 28 d/56 d in a low CO₂ concentration environment (0.05 % VOL). In addition, the water absorption of biochar-ALCAs decreased by 4.3 %-13.9 %, the apparent density increased by 0.9 %-2.8 %, and the strength increased by 4.3 %-7.0 % after carbon sequestration, and the physical and mechanical properties were significantly improved. The purpose of this paper is to investigate the synergistic carbon sequestration of biochar in combination with ALCAs and to quantitatively assess its ability to solidify low concentrations of CO₂ in the natural environment. A new test apparatus and test method were designed for this purpose. This paper may contribute for an important advance on the preparation of recyclable cement-type composites able to capture and solidify CO₂ from the natural environment.

Valorization of municipal solid waste incineration bottom ash (MSWIBA) into cold-bonded aggregates (CBAs): Feasibility and influence of curing methods

The municipal solid waste incineration bottom ash (MSWIBA) contains amounts of hazardous elements or composition, and its disposal to landfills may pose a serious threat to the ground water and soil. To reduce the environmental impact of MSWIBA, a novelty application into the utilization of MSWIBA for the manufacture of cold-bonded aggregates (CBAs) was investigated in this study. This study explored the impacts of curing systems on the comprehensive properties of CBAs. Furthermore, the hydrating phases of the designed CBAs were studied by X-ray diffractometer, and the micro characteristics of CBAs was analyzed by Scanning Electron Microscopy. The results show that CBAs produced from the MSWIBA had good properties with density of 1.75-1.98 g/cm³, moisture content of 0.78-16.48 %, water absorption of 3.99-14.02 % and compressive behavior of 1.6-4.8 MPa. Moreover, the heating water curing environment can significantly improve the comprehensive properties of CBAs. Specifically, the compressive strength of the CBAs under the 80 °C curing condition was increased by 74 %-113 %, and the water absorption rate was reduced by 3.4 %-8 %, compared with other curing regimes. Additionally, the XRD analysis showed that there are spinel phases in the CBAs compounds, which is beneficial to solidify the hazardous metals. Also, low-carbon CBAs also greatly reduce the amount of Cu and Pb leaching, which meets the limit requirements in the Chinese standards. Overall, application of MSWIBA as admixture in CBAs is an effective approach to recycle waste and replace natural aggregates. Meanwhile, this work can provide an insight for the production of eco-friendly LWAs.

Review of alternative ash aggregates in concrete-solution towards waste management and environmental protection

Owing to the depletion of natural resources, new alternative materials are emerging in construction industry. Especially, development of alternative binders and aggregates using industrial by-products paves way for the development of eco-friendly concrete. As aggregates occupy about 60-70% of the volume of concrete, new alternative materials developed as a substitute for aggregates are considered as need of the day for achieving sustainability in concrete industry. In the past few decades, many industrial by-products are researched as an alternative for natural aggregates. Ash being the largely produced by-products from different industries, it has huge potential in the development of artificial aggregates. Nevertheless, ashes produced from different sources such as coal, municipal solid waste and biomass have different characteristics and affect the properties of aggregates made out of them. The volume of research works reported on development of ash aggregates all over the globe shows that there is a faster growth rate in the development of alternative aggregates and its utilization in concrete. In this context, the current study aims to review the literature reported on mortar/concrete made of ash aggregates from various sources such as thermal power stations, biomass and municipal solid waste incinerator. The characteristics of different types of ash, development of aggregate and its properties in mortar/concrete are reviewed. Based on the review, future recommendations and directions are provided to utilize more of ash aggregates in the place of natural aggregates to prevent depletion of natural resources.

The Effect of Pelletized Lime Kiln Dust Combined with Biomass Combustion Ash on Soil Properties and Plant Yield in a Three-Year Field Study

Extensive application of mineral fertilizers resulted in high soil acidity, which is one of the major problems for crop production and soil degradation. Industrial solid waste, such as lime kiln dust and wood ash, can be used as alternative liming materials to benefit sustainable agricultural development. In this work, pelletized lime kiln dust with and without wood ash was utilized as liming material and the results of the three-year field study were compared with conventional mineral-based liming materials. It was determined that pelletized lime kiln dust satisfies the requirements posed by the recent European Union regulations to qualify as liming materials. The application of 2000 kg/ha Ca equivalent pelletized lime kiln dust increased soil pHKCl by ~0.55 pH units. Moreover, pelletized lime kiln dust significantly increased spring wheat grain yields ranging from 33.6% to 40.4%, depending on the pellet size. The usage of these liming materials not only increased crop yield but also decreased heavy metal concentration in soil. Due to high alkalinity, carbonate content, easy handling, and the transportation of pelletized lime kiln dust with and without wood ash, the materials have the potential to be used in agriculture as liming materials to reduce soil acidification and increase crop productivity or be used as soil amendments.

Preparation and Characterization of the Functional Properties of Synthetic Aggregates from Silico-Manganese Slag

A large number of natural aggregates are used in the field of construction materials, resulting in the exhaustion of natural aggregates. Therefore, looking for an alternative will slow down the consumption of natural aggregates. The sintering method not only consumes a lot of energy to prepare aggregates but also produces a lot of pollutants. In this study, silico-manganese (SM) slag was dried, ground into powder, and used as raw material. Solid and liquid alkaline activator methods were used to prepare SM slag non-burning aggregate (SMNA) by the cold bonding method. The effects of grinding time, amounts of solid and liquid alkaline activators, curing temperature, and the amount of added fly ash on aggregate properties were investigated. The aggregate microstructure was characterized by XRD, SEM, and FTIR methods, and the toxic leaching analysis of aggregate was performed. The results showed that with a fixed amount of liquid activator (16.2% wt.) and solid activator (15% wt.) and fly ash (20% wt.), respectively, and curing was performed at room temperature, the aggregate properties were optimal: the bulk density of 1236.6-1476.9 kg/m³ and the water absorption lower than 4.9-5.5%. The apparent density was 1973.1-2281.6 kg/m³, and the bulk crushing strength was 24.7-27.9 MPa. The XRD, SEM, and FTIR results indicated that amorphous gel could be formed from SM under an alkaline activator, improving the aggregate strength. The results of toxic leaching showed that the aggregate prepared from SM exhibited environmentally friendly characteristics. The SMNA was obtained via the simple and low-energy consumption production process, paving the new way toward large-scale utilization of SM.

Synthesis of sodium silicate using industrial by-products glauber's salt and microsilica: Effective reuse of the waste

Large amounts of by-products, including glauber's salt (GS) and microsilica (MS), are accumulated from chlor-alkali industry and ferrosilicon industry development, which not only wastes precious resources, but also causes serious environmental problems. In order to recycle and reuse these industrial by-products, solid sodium silicate was synthesized using GS and MS as the main raw materials, and semi-coke (SC) as the reducing agent. The effects of melting parameters including GS/SC and MS/GS molar ratio, heating rate, temperature, reaction time, and SC particle size on the conversion efficiency and modulus of solid sodium silicate were investigated and optimized. Under optimal conditions, the maximum conversion efficiency of 94.91% was obtained with modulus of 2.5. Characterization analysis of the products indicated that the amorphous silicate sodium was successfully synthesized. Moreover, the reaction mechanism was investigated, which focused on the thermal behavior and phase transformation using thermo-gravimetric and differential scanning calorimetric (TG-DSC) and in-situ X-ray diffraction. Additionally, the causes and suppression measures of "glauber's salt water" (GSW) during the experiment were summarized. This work not only creates resource utilization of GS and MS, but also provides the foundation for the synthesis of sodium silicate with GS.

The Durability of Mortar Containing Alkali Activated Fly Ash-Based Lightweight Aggregate

Beneficiating fly ash as valuable construction material such as artificial lightweight aggregate (LWA) could be an alternative solution to increase the utilization of the industrial by-product. However, generally, LWA is characterized by high porosity and a related high water absorption, which on the one hand allows production of lightweight mortar, but on the other hand can affect its performance. Thus, in this research, the durability performance of mortar composed with alkali-activated fly ash-based LWA, and commercial expanded clay (EC) LWA was investigated. The fly ash LWA was prepared in a pan granulator, with a 6-molar solution of NaOH mixed with Na₂SiO₃ in a Na₂SiO₃/NaOH weight ratio of 1.5 being used as activator (FA 6M LWA). The results revealed that mortar containing FA 6M LWA had equivalent mechanical strength with mortar containing EC LWA. The mortar containing FA 6M LWA had comparable capillary water uptake and chloride migration resistance with the reference and EC LWA mortar. Furthermore, the addition of FA 6M LWA was proven to enhance the carbonation resistance in the resulting mortar, due to the denser interfacial transition zone (ITZ) of mortar with LWA.

Properties of Alkali Activated Lightweight Aggregate Generated from Sidoarjo Volcanic Mud (Lusi), Fly Ash, and Municipal Solid Waste Incineration Bottom Ash

Production of artificial lightweight aggregate (LWA) from industrial by-products or abundant volcanic mud is a promising solution to prevent damaging the environment due to the mining of natural aggregate. However, improvements are still needed in order to control the high water absorption of LWA and strength reduction in resulting concrete or mortar. Hence in this research, fly ash, municipal solid waste incineration bottom ash (MSWI BA), and Sidoarjo volcanic mud (Lusi) were employed as a precursor and activated using NaOH 6 M and Na₂SiO₃ in producing LWA. The influence of the type of the precursors on the physical properties of resulting LWA was investigated. The effect of replacing natural fine aggregate with the resulting LWA on the compressive strength and volume density of mortar was also determined. Finer particles, a high amount of amorphous phase, and low loss on ignition (LOI) of the raw material improved the properties of resulting LWA. Mortar compressive strength was decreased by 6% when replacing 16% by volume of natural fine aggregate with fly ash based LWA. Compared to the expanded clay LWA, the properties of alternative LWAs in this study were slightly, but not significantly, inferior. Alternative LWA becomes attractive when considering that expanded clay LWA requires more energy during the sintering process.

Recycling municipal solid waste incineration slag and fly ash as precursors in low-range alkaline cements

Application of municipal solid waste incineration (MSWI) products - fly ash (MSW-FA) and bottom ash (MSW-BA), is increasingly popular, mostly due to the need to reintroduce it in the industrial chain, but also because its technical performance is constantly enhanced by a growing research effort. This paper deals with the less popular application of these wastes without the addition of a more competent precursor. Several pastes based on MSW-FA, MSW-BA or MSW-FA+MSW-BA were prepared, using sodium silicate or sodium hydroxide. Their overall performance was then assessed through mechanical (uniaxial compressive strength - UCS and seismic wave velocity), environmental (leaching) and durability tests (freeze-thaw and wetting-drying). Cement stabilised MSW-BA pastes were also tested, for reference. Results showed that a preliminary mechanical activation, achieved by milling, is fundamental; the activation with silicate is more effective than with hydroxide, especially in the case of the MSW-BA pastes, when the UCS values are more than triplicated (3-10 MPa); the MSW-BA is a more competent precursor than the MSW-FA and the durability and leachability of the alkali activated pastes is similar to that obtained with cement. The most performing paste, in terms of UCS, was obtained with BA activated exclusively with sodium silicate, with an activator/precursor weight ratio of 0.5. In general, the low-cost solidification/stabilisation proposed in this study showed competitive with the alternative use of up to 30% cement and should be regarded as a valid alternative for simple storage or low-range applications, in substitution of Portland cement.

Accelerated carbonation technology granulation of industrial waste: Effects of mixture composition on product properties

The use of accelerated carbonation technology in combination with a granulation process was employed to produce aggregates from a variety of industrial wastes, which included municipal solid waste incineration fly ash and air pollution control residue, oil shale ash, cement kiln dust, and quarry fines that have been produced in Estonia. Focusing mainly on the effects produced by the content of municipal solid waste incineration ash in the admixtures, the granule compositions were varied in order to tailor granule properties on the basis of CO₂ uptake, strength development, leaching behaviour, microstructure, and morphology. All the steps involved in the accelerated carbonation technology granulation process, from mixing with additives to granulation and carbonation treatment, were carried out in the same apparatus - an Eirich EL1 intensive mixer/granulator. The amount of CO₂ that was bound ranged from 23 to 108 kg per tonne of waste. The granules that included the optimised mixture of municipal solid waste incineration air pollution control residue, oil shale ash, cement kiln dust, and ordinary Portland cement were characterised by the highest compressive strength (4.03 MPa) and water durability for the size range of 4-10 mm. In addition, the process was found to be effective in reducing alkalinity (pH < 11.5) and immobilising heavy metals (especially zinc) and chloride. The composition and properties of the respective waste materials and mechanisms associated with the characteristics of the resulting granules were also addressed.

Use of CO2 curing to enhance the properties of cold bonded lightweight aggregates (CBLAs) produced with concrete slurry waste (CSW) and fine incineration bottom ash (IBA)

In this study, concrete slurry waste (CSW) obtained from ready-mixed concrete plants was recycled as a fresh cementitious binder and used together with municipal solid waste incineration (MSWI) fine bottom ash (IBA) from waste-to-energy plants to produce cold bonded lightweight aggregates (CBLAs) by using a pelletizing technique. The influence of different curing methods on the properties of the produced CBLAs were experimentally investigated, including moist curing, steam curing, and accelerated CO₂ curing at 0.1 bar and flow-through CO₂ curing under ambient pressure. The results showed that CBLAs obtained by steam curing at 60 °C had the highest pellet strength, and the CO₂ cured samples had the lowest water absorption values. CO₂ curing with a pressure of 0.1 bar promoted a better pellet strength. The CO₂ curing method can sequestrate 3.5-4.1% (by mass of pellets) of CO₂, which can serve as a sustainable CO₂ sequestration process to produce CBLAs.

Valorization of concrete slurry waste (CSW) and fine incineration bottom ash (IBA) into cold bonded lightweight aggregates (CBLAs): Feasibility and influence of binder types

In this study, concrete slurry waste (CSW) and fine incineration bottom ash (IBA) (<2.36 mm) were innovatively valorized to produce cold bonded lightweight aggregates (CBLAs) through a pelletizing method. The contribution of CSW to CBLAs as a fresh recycled cementitious paste was investigated and the influences of adding various binders (OPC, GGBS, lime, silica fume) on the properties of CBLAs were explored. Meanwhile, the leaching behaviours of the produced CBLAs were further assessed. The experimental results showed that CSW and IBA had a good compatibility to produce CBLAs by the pelletizing method. The use of fresh and workable CSW collected from ready-mixed concrete plants as a recycled cementitious paste could effectively bond the IBA particles. Due to the residual hydration behaviour of CSW, the produced CBLAs, even without additional binders, had good mechanical properties. The use of small percentages of cement and GGBS as additional binders could significantly increase the strength of CBLAs, while the use of lime and silica fume only showed slight improvement due to the high porosity induced. Moreover, it was found that using GGBS which could react with Ca(OH)₂ in CSW to lower the pH benefited the immobilization of heavy metals in CBLAs.

Binders alternative to Portland cement and waste management for sustainable construction - Part 2

The paper represents the "state of the art" on sustainability in construction materials. In Part 1 of the paper, issues related to production, microstructures, chemical nature, engineering properties, and durability of mixtures based on binders alternative to Portland cement were presented. This second part of the paper concerns the use of traditional and innovative Portland-free lime-based mortars in the conservation of cultural heritage, and the recycling and management of wastes to reduce consumption of natural resources in the production of construction materials. The latter is one of the main concerns in terms of sustainability since nowadays more than 75% of wastes are disposed of in landfills.

Influence of the grade on the variability of the mechanical properties of polypropylene waste

The prior properties of recycled polypropylene depend on the origin of waste deposits and its chemical constituents. To obtain specific properties with a predefine melt flow index of polypropylene, the suppliers of polymer introduce additives and fillers. However, the addition of additives and/or fillers can modify strongly the mechanical behaviour of recycled polypropylene. To understand the impact of the additives and fillers on the quasi-static mechanical behaviour, we consider, in this study, three different recycled polypropylenes with three different melt flow index obtained from different waste deposits. The chemical constituents of the additives and filler contents of the recycled polypropylenes are determined through thermo-physico-chemical analysis. Tensile and bending tests performed at different strain rates allow identifying the mechanical properties such as the elastic modulus, the yield stress, the maximum stress, and the failure mechanisms. The results obtained are compared with non-recycled polypropylene and with few researches to explain the combined effect of additives. Finally, a post-mortem analysis of the samples was carried out to make the link between the obtained mechanical properties and microstructure.