Leaching Of Heavy Metals Research Articles

The effect of copper slag as a precursor on the mechanical properties, shrinkage and pore structure of alkali-activated slag-copper slag mortar

Copper slag, an industrial by-product produced in large quantities during copper smelting and refining, has the potential to be used as an alternative precursor for alkali-activated materials. This approach not only reduces the environmental impact of copper slag but also addresses the growing scarcity of conventional precursors, such as ground granulated blast furnace slag. In this research, copper slag was used as an alternative precursor for alkali-activated slag-copper slag mortars. Sodium hydroxide and water glass served as the activators. The workability, mechanical properties, autogenous shrinkage and drying shrinkage were investigated to evaluate the influence of copper slag content. Furthermore, the reaction products and pore structure of hardened mortar were analysed to gain deeper insights into its performance. The results show that the incorporation of copper slag effectively prolongs the setting time and increases the fluidity. Copper slag reduces the autogenous shrinkage, but it also results in an undesirable increase in drying shrinkage. While copper slag delays strength development and reduces the strength, incorporating copper slag at a 50 % ratio still results in strength comparable to that of mortars utilizing 100 % ground granulated blast furnace slag as the precursor. The incorporation of copper slag alters the composition of calcium aluminosilicate hydrate and promotes the formation of ferro-silicate. Although it reduces the proportion of macropores in the total pore volume, it simultaneously increases the amount of capillary pores. Copper slag alters pore solution, and although heavy metal leaching remains minimal, risks in complex environments require further study.

The Basic Properties of Lightweight Artificial Aggregates Made with Recycled Concrete Fines

The production of lightweight aggregate based on waste is an important step towards sustainable and ecological construction. It contributes to reducing the negative impact of the construction sector on the environment by reducing the consumption of natural raw materials and reducing waste of various origins, including rubble concrete. The physical and mechanical properties, including grain shape index, water absorption, bulk density, resistance to crushing, frost resistance, leachability of heavy metals, and porosity of lightweight artificial aggregate made from rubble concrete waste (KRC) were presented in the paper. The obtained test results prove that the proposed artificial aggregate has similar water absorption and bulk density and even better frost and crushing resistance than artificial aggregates available on the market. Due to its properties, it can be used for lightweight concrete, gardening, or as a separating layer in home sewage treatment plants.

Insights into the environmental risk variation of heavy metals from MSWI fly ash after thermal plasma vitrification

Thermal plasma vitrification of municipal solid waste incineration fly ash (MSWI FA) shows potential for effective dioxin degradation and heavy metal immobilization. However, the environmental risks posed by heavy metals released after vitrification remain understudied. This work investigates two types of MSWI FA—circulated fluidized bed fly ash (CFA) and mechanical grate furnace fly ash (GFA)—blended with waste glass and vitrified via thermal plasma treatment. The physical and chemical properties of the original FA and vitrified glasses (CFA-glass and GFA-glass) were analyzed. Environmental risks were assessed using the risk assessment code (RAC) and the overall pollution toxicity index (OPTI). Results showed that CFA, with higher Si and Al content, exhibited better vitrification than GFA. Plasma vitrification reduced chlorine content from 5.79 % and 10.59 % to 0.22 % and 0.16% due to Cl volatilization. Heavy metals with low boiling points, such as Cd and Pb, were significantly reduced, while high-boiling-point Cr, Ni remained and the acid resistance of vitrificated FA significantly deteriorated, which increased the potential leaching of heavy metals. In alkaline conditions, the OPTI value of CFA-glass dropped to 2, indicating a strong immobilization effect. This study provides critical insights for managing heavy metals in fly ash through thermal plasma vitrification.

Preparation of printing and dyeing sludge biochar/macromolecule polymer microsphere as a non-sacrificial persulfate activator with excellent reusability and reduced heavy metals leaching

Biochar-based environmental functional materials offer a promising approach for the resourceful utilization of printing and dyeing sludge (PADS). However, pollutant desorption and heavy metal leaching pose potential environmental risks. In this study, we developed a novel PADS biochar (PADSBC) macromolecule polymer microsphere with outstanding reusability and stability. This microsphere effectively activated peroxymonosulfate (PMS) for the degradation of sulfadiazine (SDZ) while significantly reducing heavy metal leaching compared with PADSBC. The SDZ removal efficiency was not influenced by the type of macromolecule polymers (calcium alginate (CA), cellulose nanofibers (CNF), and polyvinyl alcohol (PVA)) incorporated into PADSBC. In the CA-PADSBC800 microsphere/PMS system, 97 % of SDZ was removed within 40 min, primarily through 1O2-induced oxidative degradation (62 %) and adsorption by CA-PADSBC800 (29 %). Additionally, CA-PADSBC800 prevented SDZ desorption for over five consecutive cycles, while PADSBC800 exhibited 25 % desorption. The presence of HCO3- and humic acids slightly delayed SDZ removal, while Cl- slightly accelerated it. Doping CA, CNF, and CA + CNF into PADSBC800 reduced the leaching of Cu and Cr by over 90 %, and Ni by over 80 %, under both experimental conditions and simulated surface water and landfill leachate situations. The excellent performance of the PADSBC-macromolecule polymer microspheres was attributed to the presence of carboxyl, hydroxyl, and C = O functional groups.

Synergistic effect of rhamnolipid and Bacillus mucilaginosus on detoxification and activation of municipal solid waste incineration fly ash

In recent years, the substantial increase in municipal solid waste incineration fly ash (MSWIFA) production has made its treatment a critical issue. However, the high toxicity of MSWIFA makes its utilization still in the exploratory stage. In this study, the heavy metal leaching rate, particle size distribution and activity index of MSWIFA were tested to investigate the detoxification and activation effects of Bacillus mucilaginosus on MSWIFA by introducing rhamnolipid. The results show that the microbial treatment can greatly increase the leaching rate of heavy metals in MSWIFA and its 28-day and 90-day activity indexes, especially by the synergistic treatment. For the Bacillus mucilaginosus and rhamnolipid treated MSWIFA (BR-MSWIFA), the maximum leaching rates follow the order from high to low of 85.57% Cr, 78% Cu, 76.38% Zn, 62.78% Pb and 37.65% Mn, while having a low mass loss of less than 5%, which is important for its reuse. Moreover, compared with the untreated MSWIFA (U-MSWIFA), the average particle sizes of Bacillus mucilaginosus treated MSWIFA (B-MSWIFA) and BR-MSWIFA decrease from 8.39 μm to 7.80 μm and 4.31 μm, and the 28-day activity indexes increase from 80.19% to 101.59% and 110.61%. The effect mechanism is that rhamnolipid not only can promote the growth, reproduction, and metabolic acid production of Bacillus mucilaginosus, but also disperse the extracellular polymeric substance (EPS) and MSWIFA particles, thus increase their contact area and the bioleaching. This study provided a theoretical foundation for the harmless treatment and resource utilization of solid wastes containing heavy metals.

Utilization of calcium carbide residue based soil stabilizer in road construction: Strength, environmental impact, and field application

This research paper delves into the utilization of calcium carbide residue (CCR)based stabilizer (designated as CSC) in road subgrade soil stabilization, with a comprehensive evaluation of its mechanical strength, environmental safety, and efficacy in field applications. Amid growing environmental concerns and the push for sustainable construction materials, this study presents an innovative approach by repurposing CCR, a by-product of the acetylene production process, in enhancing the structural integrity of road foundations. Through a series of laboratory tests, the investigation reveals significant improvements in the unconfined compressive strength (UCS) and California bearing ratio (CBR) of CSC-stabilized soils, compared to traditional lime stabilization methods. The field test DCPI results indicate that the CBR value of the field test CSC stabilised soil is 50.19% after three days, whereas the CBR value of the field test lime stabilised soil is only 29.51% after the same period. The CBR value of the CSC stabilised soil is significantly higher than that of the lime stabilised soil. This study also tested the leachate of the stabilised soil, analysing the concentration of heavy metals. The results indicated that the leachate from the stabilised soil complies with heavy metal leaching standards, demonstrating the ecological benefits of CSC utilisation. Furthermore, field experiments conducted on the G312 National Highway in Jiangsu Province, China, further validated the laboratory test results. The findings from the field trials indicated that sections stabilised with CSC exhibited superior performance in terms of reduced soil deformation and enhanced load-bearing capacity. Additionally, a life cycle carbon emission analysis was conducted for the field trial section, comparing the carbon emissions of the CSC binder with those of the lime binder throughout the entire life cycle of road construction. The results from the trial section demonstrated that the use of the CSC binder significantly reduced carbon emissions. The study underscores the potential of CSC as a cost-effective, environmentally friendly stabilizing agent, offering a pragmatic solution to the dual challenges of industrial waste management and soil stabilization in road construction.

Assessment of mechanical and heavy metal leaching behavior of engineered cementitious composites incorporating ultra-high-volume municipal waste incineration bottom ash

This study aimed to explore the feasibility of incorporating 100% municipal solid waste incineration bottom ash (MSWIBA) as a replacement for fine aggregates in engineered cementitious composites (ECCs). To improve mechanical properties, three types of polymer fibers (PVA, PP, and PE) were used at dosages of 0-2% by volume. The impact of fiber content on compressive strength, elastic modulus, and other key performance indicators such as peak strain, ultimate strain, damage modulus, and toughness index was systematically investigated. Results showed that while the elastic modulus and peak stress slightly decreased with increasing fiber content due to fiber agglomeration and increased macro-porosity, fibers significantly enhanced the deformation capacity and toughness. For instance, the MSWIBA-ECCs with 2% PP fibers exhibited the highest compressive damage energy of 205.47 J, a 79.48% increase over the control group, demonstrating superior toughness. Additionally, the study developed a new constitutive model that accurately predicted stress-strain behavior considering fiber characteristics. Environmental assessment revealed that MSWIBA-ECCs effectively immobilized hazardous heavy metals (Cu, Ni, Pb, Zn), with a solidification efficiency of 97%, ensuring compliance with Chinese environmental standards. These findings suggest that MSWIBA-ECCs, combined with optimized fiber content, offer a sustainable and high-performance alternative for construction applications.

Molybdenum doping leads to faster photo-dissolution of commercial molybdate red pigment than chrome yellow pigment under sunlight irradiation

The photo-dissolution of lead chromate pigments poses specific environmental hazards. In this study, we report that doping molybdenum in lead chromate pigments, resulting in commonly known molybdate red pigment, increases the risk of heavy metal leaching when exposed to light. Commercial molybdate red pigments undergo photo-dissolution when exposed to simulated sunlight and exhibit lower photostability compared to lead chromate pigments such as chrome yellow. After 24 h of irradiation, the leaching rates of toxic lead and chromium from molybdate red pigments were 2.98 and 3.70 times higher, respectively, than those from chrome yellow pigments. The primary factor leading to decreased pigment photostability is the activation of pigment semiconductors facilitated by molybdenum doping. Molybdate red pigments exhibit a broader light absorption spectrum and more efficient separation and transfer of photogenerated charge carriers than chrome yellow pigments, boosting the photochemical activity. To the best of our knowledge, this is the first study to illustrate the doping effect on the photostability of commercial inorganic pigments and the consequent heavy metal leaching. Our results suggest that Mo doping reduces the photostability of lead chromate pigments, highlighting the potential elevated environmental risks associated with complex inorganic pigments.

Dynamic leaching behaviors of heavy metals from recycled coal gangue aggregate under loading conditions during solid backfill mining

In solid backfill coal mining, recycled coal gangue aggregate (RCGA) is subject to the combined effects of overlying strata stress and leaching by mine water in the goaf. This process causes heavy metals to be leached and released from RCGA, which can lead to groundwater contamination. In this study, the release patterns of heavy metals in RCGA under the coupled effects of stress, solution pH, and solution flow rate were investigated, and the interactions between RCGA and the surrounding environment were explored. The findings indicate that: (1) The combined action of effective stress and mine water promotes the leaching of heavy metals. Specifically, the leaching of Pb, Zn, and Mn of RCGA is primarily influenced by the pH value of the leaching solution, while the leaching of Cu and Cr of RCGA is more closely related to the stress level; (2) Acidic environments accelerate the release of carbonate-bound fraction (CAR) in elements, facilitating the transformation of Fe/Mn oxide-bound fraction (XXI) into soluble forms; (3) The leaching ratios (Lr) of heavy metals follow the order: LrZn > LrPb > LrMn > LrCu > LrCr. This research provides guidance for the safe application of RCGA in solid backfill coal mining.

Enhancing dewaterability and reducing heavy metal leaching in industrial landfill sludge: The role of extracellular polymeric substances

Enhancing dewaterability and reducing heavy metal leaching in industrial landfill sludge: The role of extracellular polymeric substances

Utilization of Municipal Solid Waste Incineration (MSWIFA) in Geopolymer Concrete: A Study on Compressive Strength and Leaching Characteristics.

This study explores the utilization of municipal solid waste incineration fly ash (MSWIFA) in geopolymer concrete, focusing on compressive strength and heavy metal leachability. MSWIFA was sourced from a Shenzhen waste incineration plant and pretreated by washing to remove soluble salts. Geopolymer concrete was prepared incorporate with washed or unwashed MSWIFA and tested under different pH conditions (2.88, 4.20, and 10.0). Optimal compressive strength was achieved with a Si/Al ratio of 1.5, water/Na ratio of 10, and sand-binder ratio of 0.6. The washing pretreatment significantly enhanced compressive strength, particularly under alkaline conditions, with GP-WFA (washed MSWIFA) exhibiting a 49.6% increase in compressive strength, compared to a 21.3% increase in GP-FA (unwashed MSWIFA). Additionally, GP-WFA's compressive strength reached 41.7 MPa, comparable to that of the control (GP-control) at 43.7 MPa. Leaching tests showed that acidic conditions (pH 2.88) promoted heavy metal leaching, which increased over the leaching time, while an alkaline environment significantly reduced the leachability of heavy metals. These findings highlight the potential of using washed MSWIFA in geopolymer concrete, promoting sustainable construction practices, particularly in alkaline conditions.

An Overview of the Soil Acidity Causes in Ethiopia, Consequences, and Mitigation Strategies

Soil acidity is a serious land degradation problem and worldwide danger, impacting approximately 50% of the world's arable soils and limiting agricultural yield. Soil acidification is a complicated series of events that lead to the production of acidic soil. In its widest sense, it can be defined as the total of natural and human processes that reduce the pH of soil solutions. Soil acidity affects around 43% of agricultural land in Ethiopia's humid and sub humid highlands. The main objective of this seminar is to highlight different literatures on the concepts of soil acidity and to give a wealth of knowledge on the causes of soil acidity, the effects it has on agricultural production, and management strategies for reducing soil acidity and raising crop yield. Acid soils in western Ethiopia are mostly caused by topsoil erosion caused by heavy rains and high temperatures. This results in the loss of organic matter and the leaching of exchangeable basic cations (Ca<sup>2+</sup>, Mg<sup>2+</sup>, Na<sup>+</sup>, and K<sup>+</sup>). Because ammonium-based fertilizers are easily converted to nitrate and hydrogen ions in the soil, they play a significant role in acidification. One of the reasons of soil acidity is inefficient nitrogen usage, which is followed by alkalinity exports in crops. Soil acidity in Ethiopian highlands is mostly caused by the clearance of crop residues, continuous crop harvest without sufficient fertilization, cation removal, and usage of acid-forming inorganic fertilizers. Acid soil reduces nutrient availability and produces Al and Mn toxicity. In addition to these effects, soil acidity may rapidly degrade soil physicochemical qualities such as organic carbon (OC), cation exchange capacity (CEC), soil structure, porosity, and texture. Liming, the use of organic materials as ISFM, and the adoption of crop types that are resistant to Al toxicity are all alternatives for correcting acid soils. Liming can minimize toxicity by lowering concentrations, improving the availability of plant nutrients like P, Ca, Mg, and K in the soil, and reducing heavy metal solubility and leaching. Application of organic matter has a liming impact because of its abundance in alkaline cations (such Ca, Mg, and K) that were released from OM during mineralization. The pH of the soil is raised by soil organic matter, which helps with soil acidity supplements.

Fly ash admixture originating from lignite combustion in construction mortars – Time evolution of technical parameters and heavy metals leachability

The production of cement, the predominant construction binder, is associated with high energy consumption, enormous raw material depletion, and a large volume of CO2 emissions, making cement one of the most polluting materials. This study aims to contribute to the sustainability of the construction industry by significantly reducing the proportion of Portland cement (PC) in the composition of mortars. The binder content reduction was achieved by the addition of large amounts of fly ash admixture (FA) from lignite combustion while studying the effectiveness of the immobilization of heavy metals (HMs), which are present in FA, in the PC/FA matrix. Along with the analysis of the FA admixture amount on the properties of the prepared mortars, emphasis was put on the study of the influence of prolonged curing on the development of the physical parameters of the mortars and the immobilization efficiency of the HMs. It was revealed that FA can be added to PC by up to 20 wt%, enabling the production of construction mortars with high strength and low porosity, while confining hazardous substances such as HMs in the matrix. Prolonged curing at elevated relative humidity led to the continuous evolution and solidification of the mortar structure, improving its engineering properties and HMs immobilization efficiency.

Effects of accelerated carbonation on fine incineration bottom ash: CO2 uptake, strength improvement, densification, and heavy metal immobilization

Incinerating municipal solid waste (MSW) can effectively reduce its mass and volume while producing electricity. However, this process generates incineration bottom ash (IBA), which is an aggregate-like waste containing heavy metals. Due to the higher heavy metal contents, fine IBA can be removed from total IBA and treated separately to promote the use of IBA. Furthermore, MSW incineration generates carbon dioxide (CO2), which is another concern. In this context, it is beneficial to use accelerated carbonation to treat fine IBA, because it can not only contribute to carbon capture but also provide carbonated IBA that may be utilized as aggregates in civil engineering. The accelerated carbonation process of fine IBA is affected by many parameters. Therefore, this study investigated the effects of CO2 pressure (PCO2), initial water content (wi), and carbonation time on the properties of carbonated IBA, including CO2 uptake, unconfined compressive strength (UCS), density, and leaching of heavy metals. The evolution of mineralogy and microstructure of carbonated IBA was also analyzed. The results showed that IBA with wi of 15% and PCO2 of 200 kPa could achieve a CO2 uptake of 6% of IBA mass. The carbonation time significantly affected UCS and dry density of carbonated IBA. As the carbonation time increased from 0 h to 120 h, the UCS increased from 67 kPa to 691 kPa while the dry density increased from 1.38 g/cm3 to 1.51 g/cm3. Compared with untreated IBA, the leaching concentrations of Cu, Cr, Zn, and Pb from carbonated IBA were reduced significantly. As the carbonation time increased, the microstructure of carbonated IBA became denser. This densified structure was one of the reasons for the strength improvement and dry density increment of carbonated IBA.

Hazardous waste alternative fuels to novel ecological energy: Combustion characteristics and effects on clinker's environmental safety

Due to their detrimental and persistent impacts on the environment, it is imperative to manage and dispose of hazardous wastes (HW) in a secure manner. This study investigates the combustion characteristics and environmental impacts of using HW as alternative fuels in clinker production. The HW categories analyzed include industrial hazardous waste (IHW), medical hazardous waste (MHW), and household hazardous waste (HHW). Specifically, IHW consists mainly of waste mineral oils, waste organic solvents, organic resin wastes, waste residues, and waste coatings. MHW primarily consists of medical plastic products. HHW mainly includes packaging from waste pharmaceuticals, waste pesticides, disinfectants, and waste paints. Compared to traditional pulverized coal, hazardous waste alternative fuel (HWAF) exhibits a lower fixed carbon content, with its heat generation primarily dependent on volatile substances, and a higher ash content, chemically similar to coal ash. The combustion process of HWAF involves three stages: moisture evaporation (0 °C–150 °C), volatile matter combustion (150°C–400 °C), and fixed carbon combustion (400 °C–550 °C). The primary emissions from this process include CO2, CO, trace amounts of SO2, NO2, H2O, and various complex organic compounds such as carboxylic acids, alcohols, ketones, and aldehydes. While HWAF ignites more readily than pulverized coal, it burns more slowly and less completely. The incorporation of combustion by-products into the cement clinker formulation does not interfere with the clinker's hydration processes or reactions. HWAF ensures a reduced heavy metal input rate in the firing system without significantly impacting the heavy metal content in the clinker. Mortar samples produced with this clinker meet the heavy metal leaching standards, affirming the environmental safety of the cement product. Increasing the proportion of HWAF results in a reduction in standard coal consumption and an increase in CO2 reduction, achieving a maximum coal saving of 3.67 kgce/t.cl and a CO2 emission reduction of 10.11 kg/t.cl. This study presents a clean production model for the co-processing of HWAF, effectively transforming waste into valuable resources by using hazardous waste materials as alternative fuels.

Interactions between microplastics and heavy metals in leachate: Implications for landfill stabilization process

The emission of microplastics and heavy metals in landfills has attracted widespread attention for its stabilization process. Microplastics have become carriers of heavy metals due to their adsorption properties, affecting their environmental behavior. However, the effects of landfill stabilization on the interaction between microplastics and heavy metals in leachate are ambiguous. This work explored the abundance characteristics of microplastics and heavy metals in leachate from 10 landfills in Beijing. Overall, the average abundance of microplastics was 196.3 items/L, dominated by small particle size (20–50 µm) and film microplastics. The levels of Cr and As were much higher than other heavy metals. The average abundance of microplastics and polymer types tended to decrease as the landfill stabilization proceeded, and the surface composition of microplastics became more complex. Statistical analysis revealed that the correlations between microplastics and heavy metals in the leachate of landfill stabilization presented significant parabolic characteristics, and Cr and As were more susceptible to landfill stabilization with significant positive correlation with a wide range of microplastics such as 20–30 µm. These results were intended to provide a scientific basis for the treatment and disposal of waste leachate and the synergistic prevention and control of new and traditional pollutants.

The promoting effect of Fe on the immobilization of heavy metals in MSWI FA–lead–zinc tailings-based backfill materials under field application: Dynamic simulation leaching and immobilization mechanisms

Currently, research on solid waste-based backfill materials containing municipal solid waste incineration fly ash (MSWI FA) was primarily concentrated at the laboratory stage, with insufficient studies on their leaching safety and heavy metal immobilization mechanisms under field application. This study demonstrated that MLBM (Binder weight ratio: MSWI FA: steel slag (SS): blast furnace slag (BFS): flue gas desulfurized gypsum (FGDG): coal fly ash (CFA) = 10 %:33.6 %:33.6 %:12.8 %:20 %; binder-to-lead–zinc tailings (LZT) ratio was 1:8; mass concentration was 60 %) exhibited excellent leaching safety in actual backfilling. The study found that MLBM posed no risk of heavy metal and anion leaching under various leaching standards. Furthermore, MLBM showed no risk of harmful element leaching within a simulated percolation period of 100 years. The release mechanisms of Pb, As, Zn, and Cr in MLBM were diffusion, diffusion, flushing, and dissolution, respectively. The immobilization efficiency of Pb, Zn, Cr, As, Cl−, and SO42− positively correlated with the pH value (pH>7.5). The immobilization mechanism included: 1) Formation of insoluble heavy metal compounds. In the MLBM system (The pH ranged from 7.89 to 8.87), Fe(III) (Fe(OH)3(aq) and Fe(OH)4−) contributed to the immobilization of Pb2+ and SO42− and oxidized As(III) (H2AsO3−) and Cr(III) (Cr(OH)3(aq)), forming As(V) (HAsO42−) and Cr(VI) (CrO42−), respectively. 2) Adsorption. The negatively charged surface of C–(A)–S–H gel could immobilize Zn2+ and Pb2+ through adsorption, and the ionic forms of Pb(II) and Zn(II) were PbOH+ and ZnOH+, respectively. This study provided theoretical support for the leaching safety and immobilization mechanisms of solid waste-based backfill materials containing MSWI FA in field applications.

Nitrogen Forms and Heavy Metals Leachability Following Biosolids Application to Sandy Soil.

Nitrogen Forms and Heavy Metals Leachability Following Biosolids Application to Sandy Soil.

Oil-based drilling cutting pyrolysis residues-recycled fine powder sintered ceramsite: Basic properties, microsintering mechanism, lightweight concrete application and heavy metals solidification

Oil-based Drilling Cutting Pyrolysis Residue (ODPR) is a waste produced during oilfield drilling using oil-based mud. Recycled Fine Powder (RFP) consists of particles less than 0.16 mm, crushed and sieved from waste concrete. China's solid waste is characterized by high production, low utilization rates, and high pollution levels. This study explores the feasibility of preparing ceramsite from ODPR and RFP. By examining the effects of varying temperatures and proportions on the macroscopic and microscopic properties of ODPR-RFP ceramsite (ORC), the optimal process was determined: ODPR: RFP = 7:3, 2 % borax flux, 10 minutes ball milling, 1200℃ sintering temperature, and 30 minutes insulation. The resulting ORC, with a bulk density of 1120 kg/m³, cylinder compression strength of 10.50 MPa, and water absorption rate of 7.8 %, meets the "Lightweight aggregates and its test methods (GT/B17431.2)" standard. Batch production of ORC products of various sizes was conducted to evaluate their practical application in LC30 lightweight aggregate concrete. Replacing the aggregate in lightweight concrete with ORC yielded a concrete with excellent mixing performance, reaching a maximum strength of 31.2 MPa after 7d and 44.8 MPa after 28d. The damage pattern of ORC lightweight concrete is characterized by longitudinal splitting, with varied crack initiation and expansion paths. In the interfacial transition zone of ORC concrete, the ORC form a strong bond with the cement mortar, enhancing the strength of the lightweight concrete. Additionally, the leaching of heavy metals (HMs) from the ORC was examined to assess potential environmental pollution. The results indicated that preparing ORC from these two types of solid waste can effectively immobilize HMs, with a solidification rate of up to 92.10 %. Pb with high content is mainly solidified in the form of solid solution to form (Ba, Pb) SO4. The ecological risk assessment method for HMs shows that using this solid waste and process to prepare ORC does not pose HMs risks and is an environmentally friendly building material.

Study on hydration and heavy metal leaching of washed MSWI FA as a green cementitious material

Despite municipal solid waste incineration fly ash (MSWI FA) being classified as hazardous waste, there is a consensus on its significant potential for resource utilization. The high content of soluble chlorides in MSWI FA not only limits its co-disposal in cement kilns but also hinders its application in the field of construction materials. The research aimed to investigate the viability of MSWI FA as a binding material in the construction engineering field. Through examining the impact of liquid/solid ratio and pH levels on the chemical composition of MSWI FA during the washing procedure, the study delved into the mechanisms affecting hydration and the characteristics of heavy metal contamination before and after washing pretreatment. The results indicate the feasibility of developing MSWI FA into construction engineering materials. The liquid/solid ratio is a significant factor affecting the removal of chlorides, with an optimal ratio of 30. pH plays a crucial role in the mineral composition during the water-washing process of MSWI FA. An acidic environment can remove a higher proportion of chlorides, while an alkaline environment can form more calcium salts. The compressive strength of pure MSWI FA at 28 days is 3.92 MPa, which can be increased by 0.99 MPa after washing. The washed MSWI FA not only exhibits heightened reactivity but also demonstrates reduced leaching concentrations of heavy metals, and its leaching toxicity was much lower than the safe landfill threshold. Therefore, MSWI FA, after washing, is a very promising alternative material for construction engineering.