Leaching Characteristics Of Heavy Metals Research Articles

Long term environmental safety evaluation of incineration fly ash and its use as admixture after freeze-thaw

Extensive research has been conducted on the short-term performance of incineration fly ash resource utilization. However, research on the long-term leaching characteristics of heavy metals under external environmental conditions is limited. Therefore, the frost resistance of cement prepared with incineration fly ash as an admixture focused on the leaching characteristics of heavy metals from incineration fly ash and mortar after freeze-thaw were studied by XRD, MIP, SEM, and ICP-MS. The results showed that after 100 freeze-thaw cycles, Cd (HJ 299–2007) in incineration fly ash leached heavy metals exceeding 42.07 % of the GB 18598-2019 limit value. 5 % incineration fly ash enhanced the compressive strength of cement, but exceeding 5 % led to a decrease in compressive strength. After freeze-thaw, incineration fly ash increased the mortar mass loss, strength loss, and porosity. The leaching concentration of heavy metals from incineration fly ash increased under three environment, with the leaching concentration of Ni (HJ 300–2007) after 200 freeze-thaw and the leaching concentration of Cd exceeding 2323.87 % of the limit of GB 16889-2008. Although the concentration of heavy metals in mortar increased with the number of freeze-thaw, the leaching concentration was only 1.73 % of the standard limit, posing no risk of exceeding the limit. Therefore, resource utilization could effectively mitigate the leaching of heavy metals from incineration fly ash under external environmental conditions.

Comparison and mechanism analysis of MgO, CaO, and Portland cement for immobilization of heavy metals in MSWI fly ash

The significant production of municipal solid waste incineration fly ash (MSWI FA) underscores the importance of developing efficient solidification materials. This study employed MgO and CaO for immobilizing MSWI FA (with a 70% fly ash incorporation), and the immobilization effect was compared with that of Portland cement (PC). Experimental findings revealed that MgO exhibited the most effective stabilization for heavy metals (Cd, Cu, Pb, and Zn) compared to CaO and PC. XRD, FTIR, TG, and SEM analysis indicated that the principal hydration products in MSWI FA binders solidified with MgO, CaO, and PC were Mg(OH)2, CaCO3, and C-S-H gel, respectively. Mg(OH)2 efficiently immobilized heavy metals through chemical complexation and surface adsorption mechanisms. The MgO-treated MSWI FA demonstrated the highest residual fractions and the lowest easily leachable fractions. Moreover, the leaching characteristics of heavy metals were significantly influenced by the pH level, so MgO-treated MSWI FA with a leachate pH of 9.18 achieved the precipitation and stabilization of most heavy metals. In summary, this study provided an effective material selection for MSWI FA immobilization and presented a novel strategy for MSWI FA management.

Environmental performance of unfired bricks produced from co-disposal of mine tailings and municipal solid waste incineration fly ash based on comprehensive leaching tests

The potential leaching of heavy metals is a crucial concern for construction materials produced from solidification/stabilization (S/S) treatment of wastes. This study comprehensively evaluated the leaching characteristics of heavy metals from the unfired bricks produced from co-disposal of Pb–Zn mine tailings and municipal solid waste incineration fly ash using batch, sequential, and semi-dynamic leaching tests. The results show that S/S treatment drastically reduced the leachability of heavy metals from the unfired bricks through lowering their distribution in the acid-soluble fraction. The effective diffusion coefficients of heavy metals within unfired bricks were all below 1.55 × 10−13 cm2/s, which is indicative of low mobility in the environment. The release of heavy metals from the unfired bricks was primarily governed by diffusion and dissolution. Slaking treatment of fly ash significantly reduced the leaching of heavy metals from the unfired bricks due to their improved structural integrity and compactness, which minimizes the surface area in the solid matrix accessible by the leaching medium. The leachability indices of heavy metals within the unfired bricks ranged from 13.12 to 18.10, suggesting that they are suitable for “controlled utilization” in specific scenarios. Compared to untreated mine tailings, converting them into unfired bricks could reduce the releases of heavy metals by several to hundreds of folds. These findings demonstrate that S/S can be an effective and sustainable strategy for co-disposal of mining tailings and incineration fly ash to produce construction materials with sound long-term environmental performance.

Preparation of geopolymer based on municipal solid waste incineration fly ash-phosphorus slag and its function for solidification of heavy metals

Municipal solid waste incineration fly ash (MSWIFA) contains potential contaminants and needs to be efficiently solidified/stablized and so should be managed properly. To achieve this goal, alkali-activated MSWIFA and phosphorus slag (PS) based geopolymer solidified bodies were investigated. Therefore, the mechanical properties of the solidified body, heavy metal leaching characteristics, heavy metal chemical forms, and heavy metal solidification/stabilization mechanisms were also analyzed. The results show that: The addition of an appropriate amount of PS can promote the strength development of a solidified body. When the mass ratio of MSWIFA to PS is 7:3, the strength of the solidified body reaches 22.8 MPa at 90d curing age, which is 5.3 times higher than that of the unmodified material. The MSWIFA/PS immobilized Zn 99.9 %, Pb 99.4 % and Cd 99.8 % in 60 day leaching tests. Meanwhile, PS can significantly increase the proportion of chemically stabilized forms of heavy metals in the solidified body. PS affects on the hydration process of the solidified body. When the mass fraction of PS doping was 30 %, the main hydration products of the solidified body were calcium silicate hydrate (C-S-H) and calcium alumina (AFt). When the mass fraction of PS is 50 %, the main hydration products are calcium aluminosilicate hydrate (C-A-S-H), sodium aluminosilicate hydrate (N-A-S-H), and AFt. These hydration products have good solidification effects on heavy metals. Therefore, it can be concluded that the MSWIFA/PS solidified body is an environmentally friendly and efficient binder.

Leaching Characteristics of Heavy Metals from Asphalt Mixture with Basic Oxygen Furnace Slag as Aggregate

Abstract Basic oxygen furnace (BOF) slag, which has good mechanical properties, can be recycled as pavement materials. However, BOF slag contains several kinds of heavy metals. Batch leaching tests are usually conducted to investigate the leaching characteristics of asphalt mixture with BOF slag, which has a few limitations. In this article, the leaching characteristics of heavy metals were investigated through the column leaching test device self-designed in the laboratory. The factors that influence the leaching of heavy metals were evaluated. The experimental results indicate that high-basicity BOF slag that has high content of free calcium oxide (f-CaO) can effectively inhibit the leaching of heavy metals from asphalt mixture. Copper and nickel have no leaching risk in neutral and weakly acidic conditions. However, zinc and lead in asphalt mixture with medium-basicity BOF slag have a risk of causing environmental implication in long-term leaching process. Moreover, covering of asphalt inhibits the leaching of f-CaO and hinders the contact between heavy metals and the leachant at the same time. The conclusions of this article provide a theoretical basis for the green application of BOF slag as an asphalt pavement material.

Research progress of geopolymer solidification / stabilization of heavy metal contaminated soil

As a new type of green and environmentally friendly aluminosilicate gel material, geopolymer has attracted much attention from scholars for its good ability to immobilize heavy metals compared with traditional cement-based curing agents. Based on the research progress of geopolymer solidification of heavy metal contaminated soil at home and abroad in recent years, this paper introduces the process of geological polymerization reaction. The solidification mechanism of geopolymer on heavy metal contaminated soil and the influence of different factors on the solidification effect of geopolymer on heavy metal contaminated soil are described in detail. The leaching characteristics of heavy metals in geopolymer solidified heavy metal contaminated soil under freeze-thaw cycle, dry-wet cycle and carbonization were further discussed. Finally, the problems existing in the solidification of heavy metal contaminated soil by geopolymer are analyzed and the future research and development direction is prospected.

Long-term leaching characteristics of heavy metals from bauxite tailing slurry-based geopolymer backfill: experimental and numerical simulation studies

ABSTRACT This study aimed to evaluate the potential of replacing fly ash (FA) with bauxite tailing (BT) slurry for geopolymer synthesis and investigate the long-term leaching behaviour of BT slurry/FA geopolymers (BFGs) for heavy metal immobilisation. The mechanical properties and heavy metal immobilisation efficiency of BFGs were tested, and numerical simulations were conducted to assess their environmental impact as a backfill material. The results showed that the incorporation of 5 Wt.% BT increased the early compressive strength of the geopolymer without any additional treatment. A small quantity of Cu2+ improved the mechanical strength, while excess heavy metals harmed the geopolymer. Heavy metal immobilisation efficiency decreased with increased heavy metal addition and exceeded 99.9% for Pb2+ and Cu2+ when simulating acid rain leachate. The modified Elovich equation described the leaching kinetics of Cu2+ well, and the leaching rate decreased with time. Numerical analysis indicated that Cu2+ leaching from landfill leachate occurred in three phases, with an initial increase followed by a gradual decrease, stabilisation, and diffusion into the surrounding soil layer. This study provides insight into the material’s long-term stability and environmental performance, offering a scientific basis for relevant engineering applications. Highlights Direct utilisation of unprocessed tailing slurry to synthesise geopolymer. The leaching pattern of Pb2+ and Cu2+ under acidic conditions was explored. The modified Elovich equation effectively describes the leaching kinetics of Cu2+. The environmental impact of bauxite tailings slurry-based geopolymers was evaluated.

Research on leakage environmental risk assessment and risk prevention and control measures in the long-term landfill process of ultra-alkaline fly ash

In this study, we simulated the actual landfill disposal process using accelerated carbonization experiments, based on the leaching characteristics of heavy metals from “alkaline” fly ash, and used the LandSim–HELP coupling model to assess the environmental risk of the leaching. The results showed that the leaching data of “alkaline” fly ash before carbonization showed the illusion of admission to landfill with only a small amount of chemical addition or even without curing/stabilization. The leached concentrations of Zn and Cd from “alkaline” fly ash after carbonation were significantly higher. The risk assessment of the leakage of heavy metals in the case of a single artificial composite liner system showed that the exposure concentrations of Pb, Zn, and Cd in samples exceeded Standard for groundwater quality (GB/T 14848–2017) the Class III permissible limits after carbonation; exposure risk for Cd was exceeded in all samples. However, although the use of a double-layer artificial composite liner to improve the level of impermeability effectively reduced the risk of Cd leaching, so that none of the non-carcinogenic risks exceeded the standard, the carcinogenic risk of Cd in the carbonized samples exceeded the factor of 1.1–4.5 of the acceptable hazard quotient, and the contamination characteristics of the alkaline fly ash still need to be kept in view.

Agro-Waste Biochar to Reduce the Leaching of Heavy Metals from Coal Fly Ash Amended Soil

The soils added with coal fly ash may contain heavy metals potentially up to the levels of toxicity. Biochars have been successfully used in the past to reduce the bioavailability and leaching of heavy metals in contaminated soils. Therefore, the co-application of biochar together with coal fly ash could positively change the bioavailability and leaching characteristics of heavy metals in sandy soils through various fixing mechanisms. In the present study, the authors investigated the effect of agro-waste biochar in modifying the leaching loss of heavy metals from coal fly ash contaminated soils. Column leaching tests with simulated rainfall conditions were conducted for sandy Ultisol soils mixed with coal fly ash and avocado branch cut biomass biochar at 5 tons/ha rate. The results showed the presence of heavy metals in the leachate of fly ash added soil. Application of biochar significantly reduced the leachability of all the tested heavy metals in the study. The reduction rates were up to 55% compared to non-amended samples. Therefore, the agro-waste biochar can effective be used in stabilizing the heavy metals in coal fly ash contaminated soils, to minimize the risk of environmental contamination.

A novel method for solidification/stabilization of MSWI fly ash by graphene nanoplatelets synergistic alkali-activated technology

Municipal solid waste incineration (MSWI) fly ash with considerable heavy metals needs to be safely disposed of before landfill. In this study, graphene nanoplatelets (GNPs)/MSWI fly ash solidified body was prepared by alkali-activated technology, in order to improve the solidification ability of heavy metals and maximize the utilization of MSWI fly ash to cope with the scarcity of landfill. This paper studied the effect and mechanism of GNPs on heavy metal leaching characteristics. Results showed that solidified body with adding 0.05 wt% GNPs exhibited the highest compressive strength and the lowest heavy metals leaching concentration. Adding GNPs promoted heavy metals in solidified body to be converted into the residual state. Meanwhile, the microstructure and morphology characteristic analysis results indicated that GNPs promoted C-(A)-S-H gels formation. There were various kinds of solidification/stabilization (S/S) mechanisms including physical adsorption, physical encapsulation and chemical bonding in GNPs/MSWI fly ash solidified bodies. This study paves a potential new way for the application of nanomaterials in S/S MSWI fly ash through alkali-activated technology, and graphene is a more promising additive.

Immobilization of chromium ore processing residue by alkali-activated composite binders and leaching characteristics.

Chromium ore processing residue (COPR) is classified as hazardous solid waste because of the leachable Cr(VI). Cementitious materials are often used to solidify and stabilize heavy metals. However, most of them focus on the leaching concentration of particles after solidification and stabilization and lack research on leaching characteristics. This study investigated the leaching characteristics of heavy metals in three simulated environments (HJ557-2010, HJ/T299-2007, TCLP) after immobilizing COPR with composite binders. Industrial solid waste coal fly ash and lead-zinc smelting slag are used to prepare composite binders through alkali activation technology. Compressive strength, particle leaching toxicity, acid neutralization capability, and semi-dynamic leaching test are used to evaluate the performance of the solidified body. The solidified body can be applied to building materials or treated as general industrial waste. Heavy metals are mainly released from the matrix by surface washing at a low rate. The analysis results, including XRD, FTIR, and SEM-EDS, show that chemical binding and physical encapsulation are the main immobilizing mechanisms to realize the coordinated disposal of Zn and Cr(VI).

Leachability of lead, cadmium, and antimony in cement solidified waste in a silo-type radioactive waste disposal facility environment

The waste acceptance criteria for heavy metals in mixed waste should be developed by reflecting the leaching behaviors that could highly depend on the repository design and environment surrounding the waste. The current standards widely used to evaluate the leaching characteristics of heavy metals would not be appropriate for the silo-type repository since they are developed for landfills, which are more common than a silo-type repository. This research aimed to explore the leaching behaviors of cementitious waste with Pb, Cd, and Sb metallic and oxide powders in an environment simulating a silo-type radioactive waste repository. The Toxicity Characteristic Leaching Procedure (TCLP) and the ANS 16.1 standard were employed with standard and two modified solutions: concrete-saturated deionized and underground water. The compositions and elemental distribution of leachates and specimens were analyzed using an inductively coupled plasma optical emission spectrometer (ICP-OES) and energy-dispersive X-ray spectroscopy combined with scanning electron microscopy (SEM-EDS). Lead and antimony demonstrated high leaching levels in the modified leaching solutions, while cadmium exhibited minimal leaching behavior and remained mainly within the cement matrix. The results emphasize the significance of understanding heavy metals' leaching behavior in the repository's geochemical environment, which could accelerate or mitigate the reaction.

Comparative Study on the Leaching Characteristics of Cd Passivated in Soils under Continuous Simulated Acid Rain

The in situ passivation is considered a feasible and effective remediation for moderately and lowly heavy-metal-polluted soil. Under natural precipitation, the continuous leaching characteristics of heavy metals with the immobilizers are unclear and require more study for practical applications. In this work, calcium superphosphate (CS) and activated carbon (AC) were added as stabilizers to passivate Cd in hydromorphic paddy (HP) and gray fluvo-aqvic (GF) soils. Simulated acid precipitation at different pH and salt concentrations were used as eluents. The leachate and soil were collected to analyze the stability and fraction changes of Cd. The results showed that with the eluents from 120–200 mL to 200–250 mL, the leached Cd increased and reached the highest concentration and then gradually decreased. Comparative analysis showed that the two passivators in GF soil had higher application values than those in HP soil, while AC showed 3–77 times the capacity of CS in multiple conditions. The addition of AC conversed the exchangeable and oxidized states of Cd to the residual and reduced states, while the addition of CS conversed the exchangeable and reduced states of Cd to the residual and oxidized states. The above results can provide important references for the immobilization of heavy metal cations in soil and the sustainable utilization of soil.

Leaching Characteristics of Heavy Metals in the Baghouse Filter Dust from Direct-Fired Thermal Desorption of Contaminated Soil.

After thermal desorption, the total amount of heavy metals (HMs) is enriched in baghouse filter dust. To further understand the related environmental impact, the leaching characteristics under various conditions must be explored. Therefore, this study aimed to examine the leaching characteristics of seven HMs in the dust generated in the direct-fired thermal desorption process and to compare the differences in heavy metal leaching characteristics in the soil before and after thermal desorption. The leaching characteristics and bioaccessibility of seven HMs-arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), lead (Pb), nickel (Ni), and zinc (Zn)-were analyzed in dust and in soil before and after thermal desorption. The activity of HMs in dust was strong. Therefore, environmental effects and effects on human health should be considered in the treatment of soil and dust after thermal desorption.

Speciation and leaching characteristics of heavy metals from municipal solid waste incineration fly ash

• Characteristics of heavy metals in MSWI fly ash were investigated. • Coarse and fine particles MSWI fly ash can enrich more heavy metals. • Long-term environmental risk was low for As and Cr, but high for Pb and Hg. • CaO can effectively inhibit the leaching of As and Pb from MSWI fly ash. Fly ash from municipal solid waste incineration (MSWI) is classified as hazardous waste because it is rich in heavy metals (HMs), dioxins and other hazardous substances. In this paper, four kinds of MSWI fly ash were selected and tested to understand their physical and chemical properties, HM enrichment pattern, HM fugacity pattern and leaching toxicity. The results show that the main mineral components of MSWI fly ash are chlorine minerals and calcium minerals (NaCl, NaSO 4 , KCl, CaClOH, CaCO 3 , CaSO 4 , etc.), while only NaSO 4 and NaCl exist in MSWI fly ash without CaO injection. The HM contents in MSWI fly ash were As (25.8–922.0 μg/g), Cr (26.9–173.3 μg/g), Pb (988.8–1259.4 μg/g) and Hg (7.29–8.47 μg/g) and showed a trend of an initial decrease and later increase as the MSWI fly ash particle size decreased. The major species of As and Cr in the four MSWI fly ash samples were As(V) and Cr(III); Pb mainly existed as PbCl 2 and PbSO 4 . The injection of CaO could make the fly ash alkaline and promote the formation of Ca 3 (AsO 4 ) 2 , CaCrO 4 and PbCl 2 , which reduced the leaching rate of As and Pb to<10 % and 15 %, respectively. Hg exists mainly in the species of Hg 0 , Hg-OM, HgCl 2 , HgO and HgSO 4 , and its distribution is mainly influenced by the flue gas components. These results can provide a basis for studying the escape mode and leaching toxicity of HMs in MSWI fly ash.

Influence of CaO on Physical and Environmental Properties of Granulated Copper Slag: Melting Behavior, Grindability and Leaching Behavior.

Due to its potential pozzolanic activity, granulated copper slag (GCS) has been proven to act as a supplementary cementitious material (SCM) after thermochemical modification with CaO. This modification method reduces cement consumption and CO2 emissions; however, the additional energy consumption and environmental properties are also not negligible. This paper aims to evaluate the economics and environmental properties of thermochemically modified GCS with CaO through the melting temperature, grindability, and heavy metal leaching characteristics. The X-ray fluorescence spectroscopy (XRF) results indicated that the composition of the modified GCS shifted to the field close to that of class C fly ash (FA-C) in the CaO-SiO2-Al2O3 ternary phase diagram, demonstrating higher pozzolanic activity. The test results on melting behavior and grindability revealed that adding CaO in amounts ranging from 5 wt% to 20 wt% decreased the melting temperature while increasing the BET surface area, thus significantly improving the thermochemical modification’s economics. The unconfined compressive strength (UCS) of the cement paste blended with 20 wt% CaO added to the modified GCS after curing reached 17.3, 33.6, and 42.9 MPa after curing for 7, 28, and 90 d, respectively. It even exceeded that of Portland cement paste at 28 d and 90 d curings. The leaching results of blended cement proved that the heavy metal elements showed different trends with increased CaO content in modified GCS, but none exceeded the limit values. This paper provides a valuable reference for evaluating thermochemically modified GCS’s economics and environmental properties for use as SCM.

Study on leaching characteristics of MSWIFA in different pH environment

The change of leaching solution of waste incineration fly ash (MSWIFA) after shaking under different initial extractant pH was studied, and the change trend was compared with that of fly ash under different extractant concentrations. In addition, the leaching characteristics of heavy metals were analyzed under the two methods. The results showed that the pH change of the initial extractant can not truly simulate the environment of fly ash landfill, and the former can not reflect the pH of the final leaching solution. Changing the initial extractant concentration within a certain range can gradually change the final leaching solution from alkaline to acidic, which can truly reflect the environmental changes experienced by fly ash in the landfill (such as rainstorm scouring, drought and other environment). The leaching concentration of heavy metals in the leaching solution obtained by shaking fly ash under different acetic acid concentrations reflects the actual leaching characteristics of heavy metals under different pH conditions, in which Pb and Zn are amphoteric leaching, and the other metals are cationic leaching.

Study on leaching characteristics of MSWIFA in different pH environment

The change of leaching solution of waste incineration fly ash (MSWIFA) after shaking under different initial extractant pH was studied, and the change trend was compared with that of fly ash under different extractant concentrations. In addition, the leaching characteristics of heavy metals were analyzed under the two methods. The results showed that the pH change of the initial extractant can not truly simulate the environment of fly ash landfill, and the former can not reflect the pH of the final leaching solution. Changing the initial extractant concentration within a certain range can gradually change the final leaching solution from alkaline to acidic, which can truly reflect the environmental changes experienced by fly ash in the landfill (such as rainstorm scouring, drought and other environment). The leaching concentration of heavy metals in the leaching solution obtained by shaking fly ash under different acetic acid concentrations reflects the actual leaching characteristics of heavy metals under different pH conditions, in which Pb and Zn are amphoteric leaching, and the other metals are cationic leaching.

Physiochemical properties, heavy metal leaching characteristics and reutilization evaluations of solid ashes from municipal solid waste incinerator plants.

A clear understanding of the physicochemical, compositional, morphological properties and heavy metal leaching behaviours of municipal solid waste (MSW) incinerated fly ash (FA) and bottom ash (BA) are essential to guide their respective re-utilizations. In this study, FA and BA collected from three MSW incinerator plants located in Xiamen were systematically exploited. Results indicated that FA in the three plants exhibited more porous structures than BA, and the particle sizes of FA and BA were 45-295μm and >3000μm, respectively. However, both ashes showed similar main mineralogical crystalline phases of Ca(OH)2, CaCO3 and SiO2, indicative of high feasibilities in manufacturing cement, bricks or construction materials. Additionally, the heavy metal migration of MSW into leachate, flue gas, FA and BA were all specifically measured in this study to provide full data analyses and in-depth understandings of heavy metal migrations, manifesting that the heavy metals of MSW majorly migrated into the FA and BA with clearly discrepant metal ratios and only a very small fraction migrated into the leachate and flue gas. To maximumly reuse both FA and BA, importantly, the green degree and cost-benefit analysis methods were integrated into this study to evaluate their re-utilization alternatives on environmental impacts and economic benefits, and results implied that FA was beneficial for re-utilizing as aggregates in bricks while BA was optimum as paving materials. This study provides overall systematic perspectives on guiding the re-utilization of FA/BA from the MSW incinerators and also considers their environmental and economic benefits for future long-term management.

Properties and heavy metal leaching characteristics of leachate sludge-derived biochar.

Heavy metals and metalloids, in sludge and sediments, are environmental pollutants of concern with long-term negative effects on human and ecological health. In this study, sludge from biological treatment of municipal waste leachate was pyrolyzed into leachate sludge-derived biochar (LSDB) at 300°C to 900°C, comprising complex organic and inorganic (particularly heavy metals) species formed from heterogeneous chemical reactions. Based on different advanced material analyses, that is, Thermogravimetric Analysis (TGA), Fourier transform infrared (FTIR), scanning electron microscopy (SEM), and X-ray diffraction (XRD) analysis, this study revealed that mass loss and microstructural changes of LSDBs occurred primarily due to decomposition of volatiles, aromatic rings, carbonates, and hydroxides. The leaching behaviors of heavy metals from LSDBs were evaluated using the Synthetic Precipitation Leaching Procedure (SPLP). The final pH in SPLP increased from 7.5 to 12.5 with pyrolysis temperature. The pH increase favored the retention of heavy metals in the LSDBs due to the formation of low soluble precipitates at alkaline pH. The heavy metals and metalloids in the LSDBs were present as surface precipitates due to precipitation and cation exchange rather than surface complexation. The leaching contents of metals and metalloids, such as Cr, Cd, Ni, Pb, and As, were all below their respective maximum discharge standards for the first priority pollutants in China.