Adsorption of heavy metal ions using zeolite materials of municipal solid waste incineration fly ash modified by microwave-assisted hydrothermal treatment

Accumulation and translocation of lead in vegetables through intensive use of organic manure and mineral fertilizers with wastewater

In many countries with wastewater irrigation and intensive use of fertilizers (minerals and organics), heavy metal deposition by crops is regarded as a major environmental concern. A study was conducted to determine the impact of mineral fertilizers, cow manure, poultry manure, leaf litter, and sugarcane bagasse on soil's trace Pb content and edible parts of vegetables. It also evaluated the risk of lead (Pb) contamination in water, soil, and food crops. Six vegetables (Daucus carota, Brassica oleracea, Pisum sativum, Solanum tuberosum, Raphanus sativus, and Spinacia oleracea) were grown in the field under twelve treatments with different nutrient and water inputs. The lead concentrations in soil, vegetables for all treatments and water samples ranged from 1.038-10.478, 0.09346-9.0639 mg/kg and 0.036-0.26448 mg/L, The concentration of lead in soil treated with wastewater in treatment (T6) and vegetable samples was significantly higher, exceeding the WHO's permitted limit. Mineral and organic fertilizers combined with wastewater treatment reduced lead (Pb) concentrations in vegetables compared to wastewater application without organic fertilizers. Health risk indexes for all treatments except wastewater treatment (T6) were less than one. Pb concentrations in mineral fertilizers, cow manure, poultry manure, leaf litter, and sugarcane bagasse treated were determined to pose no possible risk to consumers.

Aluminosilicates-based nanosorbents for heavy metal removal - A review

Contamination of water bodies with heavy metals poses a significant threat to human health and the environment, requiring the development of effective treatment techniques. In this context, aluminosilicates emerge as promising sorbents due to their cost-effectiveness and natural abundance. This review provides a clear, in-depth, and comprehensive description of the structure, properties, and characteristics of aluminosilicates, supporting their application as adsorbents and highlighting their diversity and adaptability to different matrices and analytes. Furthermore, the functionalization of these materials is thoroughly addressed, detailing the techniques currently used, exposing the advantages and disadvantages of each approach, and establishing comparisons and evaluations of the performances of various functionalized aluminosilicates in the extraction of heavy metals in aqueous matrices. This work aims not only to comprehensively review numerous studies from recent years but also to identify trends in the study of such materials and inspire future research and applications in the field of contaminant removal using aluminosilicates.

Resource utilization of MSWI fly ash supporting TiO2/BiOCl nanocomposite for enhanced photocatalytic degradation of sodium isopropyl xanthate: Mechanism and performance evaluation

The removal of organic pollutants in water environments and the resource utilization of solid waste are two pressing issues around the world. Facing the increasing pollution induced by discharge of mining effluents containing sodium isopropyl xanthate (SIPX), in this work, municipal solid waste incineration fly ash (MSWI FA) was pretreated by hydrothermal method to produce stabilized FA, which was then innovatively used as support for the construction of FA/TiO2/BiOCl nanocomposite (FTB) with promoted photocatalytic activity under visible light and natural sunlight. When the content of FA was 20 wt% and the mass ratio of TiO2 to BiOCl was 4:6, a remarkable performance for the optimal FTB (20-FTB-2) was achieved. Characterizations demonstrated that TiO2 and BiOCl uniformly dispersed on FA contributing to high surface area and broad light adsorption of FTB, which exhibits excellent adsorption capacity and light response ability. Build in electric field formed in the interface of TiO2/BiOCl heterojunction revealed by density functional theory calculations accelerated the separation of photoinduced e- and h+, leading to high efficiency for SIPX degradation. The synergetic effect combined with adsorption and photocatalytic degradation endowed 20-FTB-2 superior SIPX removal efficiency over 99% within 30 min under visible light and natural sunlight irradiation. The photocatalytic degradation pathways of SIPX were determined through theoretical calculations and characterizations, and the toxic byproduct CS2 was effectively eliminated through oxidation of •O2-. For 20-FTB-2, reusability of photocatalyst was showed by cycle tests, also the concentrations of main heavy metals (Pb, Zn, Cu, Cr, and Cd) in the liquid phases released during photocatalyst preparation process (< 1 mg/L) and photodegradation process (< 8.5 μg/L) proved the satisfactory stability with low toxicity. This work proposed a novel strategy to develop efficient and stable support-based photocatalysts by utilizing MSWI FA and realize its resource utilization.

Remediation through the coordinated use of local rice husk residues for the selective adsorption of iron and nickel in real landfill leachate

Herein, we demonstrate the prospects of tackling several environmental problems by transforming a local rice husk residue into an effective adsorbent, which was then applied for the treatment of real landfill leachate (LL). The study focused on establishing (i) the effect of simple washing on morphological aspects, (ii) evaluating target adsorption capacity for total iron (Fe) and nickel (Ni), (iii) determining regeneration and reuse potential of the adsorbent and (iv) complying to the requirements of worldwide legislations for reuse of treated LL wastewater. The adsorbent was prepared by employing a simple yet effective purification process that can be performed in situ. The LL was collected post-membrane treatment, and the characterizations revealed high concentrations of Fe, Ni, and organic matter content. The simple washing affected the crystallinity, resulting in structural alterations of the adsorbents, also increasing the porosity and specific surface. The adsorption process for Ni occurred naturally at pH 6, but adjusting the pH to 3 significantly improved removal efficiency and adsorption capacity for total Fe. The kinetics were accurately described by the pseudo-second-order model, while the Langmuir model provided a better fit for the isotherms. The adsorbent was stable for 5 reuses, and the metals adsorbed were recovered through basic leaching. The removal capacities achieved underscore the remarkable effectiveness of the process, ensuring the treated LL wastewater meets rigorous global environmental legislations for safe use in irrigation. Thus, by employing the compelling methods herein optimized it is possible to refer to the of solving three environmental problems at once.

Analysis of composition characteristics and treatment techniques of municipal solid waste incineration fly ash in China

The rapid development of the economy and society is causing an increase in the amount of municipal solid waste (MSW) produced by people's daily lives. With the strong support of the Chinese government, incineration power generation has steadily become the primary method of treating MSW, accounting for 79.86%. However, burning produces a significant amount of municipal solid waste incineration fly ash (MSWI-FA), which contains heavy metals, soluble chlorine salts, and dioxins. China's MSWI-FA yield increased by 8.23% annually to 7.80 million tons in 2022. Besides, the eastern region, especially the southeastern coastal region, has the highest yield of MSWI-FA. There are certain similarities in the chemical characteristics of MSWI-FA samples from Northeast, North, East, and South China. Zn and CaO have the largest amounts of metals and oxides, respectively. The Cl content is about 20 wt%. This study provides an overview of the techniques used in the thermal treatment method, solidification and stabilization, and separation and extraction of MSWI-FA and compares their benefits and drawbacks. In addition, the industrial applications and standard requirements of landfill treatment and resource utilization of MSWI-FA in China are analyzed. It is discovered that China's resource utilization of MSWI-FA is insufficient through the study on the fly ash disposal procedures at a few MSW incineration facilities located in the economically developed Guangdong Province and the traditional industrial city of Tianjin. Finally, the prospects for the disposal of MSWI-FA were discussed.

The sulfidation behavior of zinc during microwave hydrothermal sulfidation of heavy metal-containing sludge

The heavy metals present in the sludge can undergo a reaction with sulfur, leading to their conversion into metal sulfides through hydrothermal sulfidation. Sulfur ions, possessing a strong sulfidation capability, can operate within a wider pH range at elevated temperatures. The high temperature environment promotes the sulfidation process of zinc within heavy metal-laden sludge. Increasing the temperature of microwave hydrothermal sulfidation and extending the sulfidation duration for heavy metal-containing sludge can enhance the growth of crystal size in the artificially synthesized zinc sulfide. Zinc sulfide predominantly takes the form of ZnS, which facilitates the subsequent flotation recovery of zinc.

Highly efficient carbonation and dechlorination using flue gas micro-nano bubble for municipal solid waste incineration fly ash pretreatment and its applicability to sulfoaluminate cementitious materials

Cement production is a primary source of global carbon emissions. As a hazardous waste, municipal solid waste incineration fly ash (MSWI-FA) can be pretreated as a cementitious and effective carbon capture material. This study proposes an efficient carbonation dechlorination pretreatment and resource recovery strategy using flue gas micro-nano bubble (MNB) to wash MSWI-FA. The results showed that the flue gas MNB water washing reaction solution inhibited CaCO3 boundary layer blocking and adsorption on NaCl and KCl leaching. Under low water-to-solid ratio and CO2 concentration conditions, two-step washing reduced the MSWI-FA chlorine content to <1%, improving the dechlorination effect by 19.72% compared to conventional carbonation. The flue gas MNB water accelerated the precipitation of Ca2+ and Ca(ClO)2 in the form of calcite. The higher the CO2 concentration in the flue gas MNB, the better the fragmentation and purification of the MSWI-FA shell, leading to improved dechlorination and CO2 fixation. Under optimized conditions, the mean particle size of MSWI-FA decreased by 47.82%, and the CO2 fixation rate reached 73.80%, with a 58.35% increase in the washing carbonation rate. MSWI-FA pretreated by flue gas MNB washing was used as both the raw material and supplementary cementitious material for sulfoaluminate cementitious (SAC) material, exhibiting excellent compressive strength and heavy metal stabilization. The maximum compressive strength of the MSWI-FA-based SAC material cured for 28 d reached 130 MPa. Cr leaching was inhibited with increased hydration time, and the leaching concentration was far below the standard limit.

Exploring Optimization of Zeolites as Adsorbents for Rare Earth Elements in Continuous Flow by Machine Learning Techniques

Unsupervised machine learning (ML) techniques are applied to the characterization of the adsorption of rare earth elements (REEs) by zeolites in continuous flow. The successful application of principal component analysis (PCA) and K-Means algorithms from ML allowed for a wide range assessment of the adsorption results. This global approach permits the evaluation of the different stages of the sorption cycles and their optimization and improvement. The results from ML are also used for the definition of a regression model to estimate other REEs' recoveries based on the known values of the tested REEs. Overall, it was possible to remove more than 70% of all REEs from aqueous solutions during the adsorption assays and to recover over 80% of the REEs entrapped on the zeolites using an optimized desorption cycle.

The current status and future of solid waste recycled building bricks

Solid waste (SW) has become a problem hindering the economic and social development. Achieving the full green cycle from raw material to production of recycled building bricks (RBB) using SW is the focus of future research. In this paper, the research results of RBB manufacturing using SW in recent years are reviewed. According to the consolidation principle of RBB, the effects of different types of SW on the physicochemical properties and microstructure of RBB are summarized based on the recycled unsintered brick (RUSB) and recycled sintered brick (RSB). By comparing and evaluating the two consolidation methods, it is proposed that RSB has good practicality due to its higher SW utilization rate, higher strength, and faster consolidation speed. Furthermore, the difference between MWS and conventional sintering (CS) is analyzed, and the research on the application of MWS in SW-RBB manufacturing in recent years is reviewed in detail. It is pointed out that microwave sintering (MWS) technology can solve many drawbacks in traditional sintering technology and has great prospects in manufacturing SW-RBB due to the low energy consumption, low pollution, and high efficiency. Finally, the shortcomings and possible challenges in the current research on manufacturing SW-RBB using MWS technology are discussed, which provides guidance for the future development of SW-RBB manufacturing.

Modeling, optimization and efficient use of MMT K10 nanoclay for Pb (II) removal using RSM, ANN and GA

Regarding the long-term toxic effects of Pb (II) ions on human health and its bioaccumulation property, taking measures for its reduction in the environment is necessary. The MMT-K₁₀ (montmorillonite-k₁₀) nanoclay was characterized by XRD, XRF, BET, FESEM, and FTIR. The effects of pH, initial concentrations, reaction time, and adsorbent dosage were studied. The experimental design study was carried out with RSM-BBD method. Results prediction and optimization were investigated with RSM and artificial neural network (ANN)-genetic algorithm (GA) respectively. The RSM results showed that the experimental data followed the quadratic model with the highest regression coefficient value (R² = 0.9903) and insignificant lack of fit (0.2426) showing the validity of the Quadratic model. The optimal adsorption conditions were obtained at pH 5.44, adsorbent = 0.98 g/l, concentration of Pb (II) ions = 25 mg/L, and reaction time = 68 min. Similar optimization results were observed by RSM and artificial neural network-genetic algorithm methods. The experimental data revealed that the process followed the Langmuir isotherm and the maximum adsorption capacity was 40.86 mg/g. Besides, the kinetic data indicated that the results fitted with the pseudo-second-order model. Hence, the MMT-K₁₀ nanoclay can be a suitable adsorbent due to having a natural source, simple and inexpensive preparation, and high adsorption capacity.

Study on the reduction of chlorine and heavy metals in municipal solid waste incineration fly ash by organic acid and microwave treatment and the variation of environmental risk of heavy metals

Municipal solid waste incineration (MSWI) fly ash usually needs to undergo dechlorination or heavy metal stabilization pretreatment for further treatment, recycling or disposal. In this paper, the removal effect of chlorine in fly ash by water washing, lactic acid, citric acid and microwave treatment was studied, and XANES was used to analyze chlorine chemical form in fly ash. In addition, the heavy metals in fly ash were also checked. The results indicated that double washing and triple washing could remove 88.0 % and 95.5 % of chlorine from fly ash respectively. The "double water washing + microwave/organic acid" could remove about 96.6 % of chlorine, and 42.9 % and 47.2 % of insoluble chloride respectively. The microwave treatment could maximize the stabilization of heavy metals with a BI value of 39.1 %, 0.11 %, 1.65 %, 15.4 % and 3.98 % for Cd, Cr, Cu, Pb and Zn. The elution of heavy metals by citric acid was obvious. "Double water washing + citric acid" removed 87.0 % of Cd, 17.2 % of Cr, 11.9 % of Cu, 39.6 % of Pb and 43.6 % of Zn, but the environmental risk of Cu and Cr increased about 2-3 % after the treatment. The results of this study provide guidance for the pretreatment of fly ash before resource utilization.

Hexavalent chromium (Cr(VI)) removal by ball-milled iron-sulfur @biochar based on P-recovery: Enhancement effect and synergy mechanism

After the biochar recovery of phosphorus (P), its role in eliminating Cr(VI) is uncertain. In this study, the iron-sulfur biochar (Fe/S@BC) was made by grinding Fe⁰, S⁰, and biochar with a ball mill. P-loaded iron-sulfur biochar (P-Fe/S@BC) was produced after recovering P from simulated wastewater and then used to remove Cr(VI) contamination in waterbodies. P-Fe/S@BC got a rich pore structure and more reactive sites through P-recovery. The experiments revealed that P-Fe/S@BC had an enhancement effect on Cr(VI) pollution with removal efficiencies of 76.9 % ∼ 99.4 %, all greater than Fe/S@BC (58.2 %). In particular, 25P-Fe/S@BC (with 6.55 mg P/g) had the most significant advantage. The combination of physical adsorption, electrostatic attraction, and precipitation contributed to Cr(VI) removal. This is an efficient strategy for reusing Fe/S@BC followed by P-recovery, intending to improve the Cr(VI) removal effect and achieve the sustainable use of P resources and wastes.

Synthesis of zeolite A from fly ash and its application in the slow release of urea

The study focused on the transformation of coal fly ash to zeolite A (ZA) as a potential carrier for the slow release of urea. After being treated with HCl aqueous solution and NaOH successively, SiO₂ and Al₂O₃ were converted into sodium silicoaluminate. The obtained silicoaluminate was then heated with NaAlO₂ in an aqueous NaOH solution at 70-110 °C for 3-18 h and zeolite A was successfully prepared according to the X-ray diffraction measurements. By changing the hydrothermal temperature and time, ZA could reach 237.3 mmol/100 g in maximum cation exchange capacity. ZA impregnated with urea (ZA-U) at a mass ratio of more than 5:1 exhibited slow release of urea and the kinetics release mechanism of ZA-U was proposed. The plant growth test proved that the slow release of urea from ZA-U can promote the growth of maize seedling.

Phosphorus recovery and reuse in water bodies with simple ball-milled Ca-loaded biochar

The demand to control eutrophication in water bodies and the risk of phosphorus scarcity have prompted the search for treatment technologies for phosphorus recovery. In this study, ball-milled Ca-loaded biochar (BMCa@BC) composites were prepared with CaO and corn stover biochar as raw materials by a new ball-milling method to recover phosphorus from water bodies. Experimental results demonstrated that BMCa@BC could efficiently adsorb phosphorus in water bodies with an excellent sorption capacity of 329 mg P/g. Hydrogen bonding, electrostatic attraction, complexation, and surface precipitation were involved in adsorption process. In addition, phosphorus recovered by BMCa@BC had high bioavailability (86.7 % of TP) and low loss (3.3 % of TP) and was a potential slow-release fertilizer. P-laden BMCa@BC significantly enhanced seed germination and growth in planting experiments, proving that it could be used as a substitute for P-based fertilizer. After five cycles of regeneration, BMCa@BC still showed good adsorption recovery and the P-enriched desorption solution could be recovered as Ca-P products with the fertilizer value. Overall, BMCa@BC has good cost-effectiveness and practical applicability in phosphorus recovery. This provides a new way to recover and reuse phosphorus effectively.

Zeolite NaP1 synthesized from municipal solid waste incineration fly ash for photocatalytic degradation of methylene blue

The disposal of hazardous municipal solid waste incineration (MSWI) fly ash is a challenge nowadays. Recently, the re-utilization of MSWI fly ash by converting it to useful zeolite-containing materials has attracted attention. However, the zeolitic products fabricated from MSWI fly ash are usually of low quality and rarely reported to be applied for photocatalysis. In this study, valuable zeolites (e.g., NaP1) are synthesized from MSWI fly ash via a modified microwave-assisted hydrothermal method. The key parameters for the hydrothermal method including temperature, duration, the amount of additive, and water volume, are investigated and optimized. Specifically, increasing the hydrothermal temperature can promote the synthesis of zeolitic materials; a relatively long hydrothermal duration is essential to accomplish the assembly of zeolites; the addition of Na₂SiO₃ can increase the precursor for the fabrication of zeolites; the water volume makes little influence on the crystal style of products. Eventually, the hydrothermal condition of 180 °C, 1 h, 0.5 g Na₂SiO₃, and 10 mL water is suggested based on the energy consumption and the quality of zeolites. The product containing zeolite NaP1 from such a condition is further applied to degrade methylene blue by photocatalysis. The removal rate has reached 96% within 12 h, which dramatically surpasses that of the raw fly ash (38%). Such excellent photocatalytic performance is attributed to the 10-fold increased surface area (24.864 m² g^-1) and active metal elements embedding in the zeolite structures.

Zeolite greenly synthesized from fly ash and its resource utilization: A review

Fly ash is an incineration byproduct of thermal power plants. Due to the complex composition of fly ash, improper disposal will seriously harm the ecological environment. Therefore, how to effectively use fly ash to safely and environmentally replace landfills is a worldwide concern. Considering the high silicon and aluminum contents in fly ash, it has the potential to synthesize zeolite, which has a wide range of applications in sewage treatment, gas adsorption, etc. Therefore, the synthesis of zeolites from fly ash is consistent with the theme of sustainable development. The synthesis mechanism of zeolite, various synthetic methods of zeolite from fly ash and their advantages and disadvantages was introduced in detail. In addition, combined with the current research hotspots, the application of synthetic zeolite from fly ash in the fields of sewage treatment and gas adsorption was introduced. Finally, the future development prospects and research directions of synthetic zeolite from fly ash to improve the utilization rate of fly ash were considered.

Adsorption of Heavy Metals in Contaminated Water Using Zeolite Derived from Agro-Wastes and Clays: A Review

Due to climate change and anthropogenic activities such as agriculture, mining, and urbanization, water contamination has become a very real modern problem. Modern solutions such as activated carbon, reverse osmosis, and ultrafiltration, among others, have been employed in the decontamination of water. These methods are, however, expensive to set up and maintain and therefore have proved a challenge to implement in developing countries. Zeolite materials exhibit excellent structural properties, such as high ion exchange capacity, porosity, and relative surface area, which make them attractive to water decontamination processes. However, conventional zeolites are expensive, and recent research has focused on utilizing low-cost materials such as agro-wastes and clays as raw materials for the synthesis of zeolites. This review aims to discuss the role of low-cost zeolites in their removal of heavy metals and the feasibility of agro-wastes and natural clays in the synthesis of zeolites. Recent research studies based on the synthesis of zeolites from clays and agro-wastes and their application in heavy metal removal have been reviewed and discussed. Agro-wastes such as rice husk ash and sugarcane bagasse ash and layered silicate clays such as kaolinite and smectites are particularly of interest to zeolite synthesis due to their high silica to alumina ratio. Zeolites synthesized through various methods such as hydrothermal, molten salt, and microwave irradiation synthesis have been discussed with their effect on the adsorption of various heavy metals.

Removal of Zn2+ from Aqueous Solution Using Biomass Ash and Its Modified Product as Biosorbent

To study the removal effect of bottom ash of biomass power plants and its modified products on zinc (Zn²⁺) in aqueous solution, a series of indoor experiments is carried out. The aim of this work is to explore a method to improve the ability of biomass ash to remove Zn²⁺ from aqueous solution and obtain its adsorption characteristics of Zn²⁺ in aqueous solution; on this basis, the feasibility of its application in the treatment of Zn²⁺-contaminated wastewater is analyzed. The mesoporous siliceous material is used to modify the biomass, and the modified material is functionalized with 3-aminopropyltriethoxysilane. The results show that the specific surface area of modified biomass ash is nine times that of the material before modification. The adsorption capacity of Zn²⁺ on the material increases with the increase of pH, and pH 6 is the optimum pH to remove Zn²⁺ from the aqueous solution. The Langmuir model and Freundlich model can show better fits for biomass ash and the modified material, respectively. Thermodynamic analysis results show that the adsorption of Zn²⁺ is spontaneous and endothermic in nature. The adsorption of Zn²⁺ onto biomass and modified biomass ash follow pseudo-first-order and pseudo-second-order kinetics, respectively.

Sustainable Recovery of Valuable Nanoporous Materials from High-Chlorine MSWI Fly Ash by Ultrasound with Organic Acids

The new technology development for municipal solid waste incineration fly ash treatment and reuse is urgent due to landfill shortage and environmental effect of leached hazardous substances. Chlorine (Cl) is worth considering due to its high levels in fly ash. In this study, a treatment process of ultrasound combined with organic acid was used to eliminate Cl from fly ash to enhance its properties for reuse. Taguchi methodology was implemented to design the experiments by controlling four impact factors and the contribution of each factor was evaluated by the ANOVA analysis of variance. Following two treatment steps within 5 min with a solid/liquid ratio of 1:10 at 165 kHz, 98.8% of Cl was eliminated. Solid/liquid ratio was the most prominent factor that contributed to the Cl removal with more than 90%, according to the ANOVA analysis of variance. Tert-butyl alcohol (tBuOH), an •OH radical scavenger, was utilized to examine different effects of ultrasonic cavitation on Cl removal efficiency. A 20 kHz ultrasound was used to explore the influence of multi-frequency ultrasound with different mechanical and sonochemical effects on the fly ash dechlorination. This ultrasonic-assisted organic acid treatment was found to be a time and cost-effective pathway for fly ash Cl removal.

Engineered macroalgal and microalgal adsorbents: Synthesis routes and adsorptive performance on hazardous water contaminants

Colourants, micropollutants and heavy metals are regarded as the most notorious hazardous contaminants found in rivers, oceans and sewage treatment plants, with detrimental impacts on human health and environment. In recent development, algal biomass showed great potential for the synthesis of engineered algal adsorbents suitable for the adsorptive management of various pollutants. This review presents comprehensive investigations on the engineered synthesis routes focusing mainly on mechanical, thermochemical and activation processes to produce algal adsorbents. The adsorptive performances of engineered algal adsorbents are assessed in accordance with different categories of hazardous pollutants as well as in terms of their experimental and modelled adsorption capacities. Due to the unique physicochemical properties of macroalgae and microalgae in their adsorbent forms, the adsorption of hazardous pollutants was found to be highly effective, which involved different mechanisms such as physisorption, chemisorption, ion-exchange, complexation and others depending on the types of pollutants. Overall, both macroalgae and microalgae not only can be tailored into different forms of adsorbents based on the applications, their adsorption capacities are also far more superior compared to the conventional adsorbents.

Natural, low-cost adsorbents for toxic Pb(II) ion sequestration from (waste)water: A state-of-the-art review

Pb(II) ions is an inorganic pollutant that is present in the environment. Its presence affects both human health and ecosystem. Economically, amongst many wastewater treatment approaches, adsorption is both cheap and environmentally friendly for removing Pb(II) ion from contaminated water. In this state of the art review, about 227 research and review based publications on adsorption-based studies between 1989 and 2021, which have used various materials as adsorbents of Pb (II) ions, were selected and reviewed for more evaluation. A number of adsorbents which have been reported in these literatures for the adsorption of Pb(II) ion are agrobased, modified agrobased, clay minerals, modified/nanocomposite clay minerals, silica-based, zeolite-based and chitosan-based adsorbents, respectively. The adsorption potential of the adsorbents is exhibited under optimum experimental conditions. The unmodified and modified agro based adsorbents were shown to exhibit the greatest Pb(II) adsorption capacity, with great potential for further exploration, compared to the others afore-listed. The effects of operating parameters such as pH, initial metal ion concentration, adsorbent dose and reaction time are discussed. Furthermore, in order to comprehend the nature of adsorption process between the adsorbent and contaminant (Pb(II)), thermodynamic analyses of adsorption systems are intensively described. All these discussions revealed the applicability of adsorption process for toxic Pb(II) ions removal with respect to wastewater treatment techniques. The review concludes by commenting on the various adsorbents' adsorption capacity and proposes some studies that should also be considered in future works.

A 3-year field study on lead immobilisation in paddy soil by a novel active silicate amendment

Lead (Pb) is a toxic metal in industrial production, which can seriously threat to human health and food safety. Thus, it is particularly crucial to reduce the content of Pb in the environment. In this study, raw fly ash (FA) was used to synthesise a new active silicate materials (IM) employing the low-temperature-assisted alkali (NaOH) roasting approach. The IM was further synthesised to form zeolite-A (ZA) using the hydrothermal method. The physicochemical characteristics of IM and ZA amendments before and after Pb²⁺ adsorption were analysed using the Scanning electron microscope-Energy Dispersive Spectrometer (SEM-EDS), Fourier Transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) apparatuses. The results revealed the considerably change in the microstructure and functional groups of IM and ZA amendments, conducive to Pb²⁺ removal. Moreover, a 3-year field experiment revealed that the IM and ZA significantly improved the growth of rice and reduced available Pb by 21%-26.8% and 9.7%-16.9%, respectively. After 3 years of remediation, the Pb concentration of the rice grain reached the national edible standard (≤0.2 mg kg^-1) of 0.171 mg kg^-1 and 0.179 mg kg^-1, respectively. Meanwhile, the concentration of acid-exchangeable Pb reduced, while those of reducible and residual fractions of Pb increased. There was no significant difference between the IM and ZA treatments. The potential mechanisms of remediation by the amendments were ion-exchange, complexation, precipitation, and electrostatic attraction. Overall, the results indicate that IM is suitable for the remediation of contaminated soil and promotes safe food production, and develops an environmentally friendly and cost-effective amendment for the remediation of polluted soil.

Performance and mechanisms of fly ash for graphene oxide removal from aqueous solution

The potential wide use of graphene oxide in various fields results in the possibility of its dispersion throughout natural water systems, with a negative impact on organisms and ecosystems. This study evaluated the removal of graphene oxide (GO) from water by fly ash (FA). The effects of various conditions (including the initial concentration of graphene oxide, the pH of the initial solution, the amount of absorbent, and temperature) on the removal rate of GO were investigated in detail. The results show that the maximum removal rate of graphene oxide by fly ash is 93%; the isotherm adsorption process conforms to a Langmuir model; the adsorption reaction is a spontaneous exothermic process. Under optimal conditions, the pH of the solution was adjusted to 6, the amount of fly ash was 5 mg, the initial concentration of GO was 60 mg·L^-1, and the temperature was 303 K. Using X-ray diffraction (XRD), Raman spectroscopy (Raman), Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), transmission electron microscopy (TEM), Zeta potential and X-ray electron spectroscopy (XPS), the adsorption mechanism was characterized. The experimental results demonstrate that fly ash is a good material for GO removal from aqueous solution.

Experimental Treatment of Hazardous Ash Waste by Microbial Consortium Aspergillus niger and Chlorella sp.: Decrease of the Ni Content and Identification of Adsorption Sites by Fourier-Transform Infrared Spectroscopy

Despite the negative impact on the environment, incineration is one of the most commonly used methods for dealing with waste. Besides emissions, the production of ash, which usually shows several negative properties, such as a higher content of hazardous elements or strongly alkaline pH, is problematic from an environmental viewpoint as well. The subject of our paper was the assessment of biosorption of Ni from ash material by a microbial consortium of Chlorella sp. and Aspergillus niger. The solid substrate represented a fraction of particles of size <0.63 mm with a Ni content of 417 mg kg-1. We used a biomass consisting of two different organisms as the sorbent: a non-living algae culture of Chlorella sp. (an autotrophic organism) and the microscopic filamentous fungus A. niger (a heterotrophic organism) in the form of pellets. The experiments were conducted under static conditions as well as with the use of shaker (170 rpm) with different modifications: solid substrate, Chlorella sp. and pellets of A. niger; solid substrate and pellets of A. niger. The humidity-temperature conditions were also changed. Sorption took place under dry and also wet conditions (with distilled water in a volume of 30-50 ml), partially under laboratory conditions at a temperature of 25°C as well as in the exterior. The determination of the Ni content was done using inductively coupled plasma optical emission spectrometry (ICP-OES). The removal of Ni ranged from 13.61% efficiency (Chlorella sp., A. niger with the addition of 30 ml of distilled water, outdoors under static conditions after 48 h of the experiment) to 46.28% (Chlorella sp., A. niger with the addition of 30 ml of distilled water, on a shaker under laboratory conditions after 48 h of the experiment). For the purpose of analyzing the representation of functional groups in the microbial biomass and studying their interaction with the ash material, we used Fourier-transform infrared (FTIR) spectroscopy. We observed that the amount of Ni adsorbed positively correlates with absorbance in the spectral bands where we detect the vibrations of several organic functional groups. These groups include hydroxyl, aliphatic, carbonyl, carboxyl and amide structural units. The observed correlations indicate that, aside from polar and negatively charged groups, aliphatic or aromatic structures may also be involved in sorption processes due to electrostatic attraction. The correlation between absorbance and the Ni content reached a maximum in amide II band (r = 0.9; P < 0.001), where vibrations of the C=O, C-N, and N-H groups are detected. The presented results suggest that the simultaneous use of both microorganisms in biosorption represents an effective method for reducing Ni content in a solid substrate, which may be useful as a partial process for waste disposal.

Adsorption and Release Characteristics of Purified and Non-Purified Clinoptilolite Tuffs towards Health-Relevant Heavy Metals

The occurrence of health-relevant contaminants in water has become a severe global problem. For treating heavy-metal-polluted water, the use of zeolite materials has been extended over the last decades, due to their excellent features of high ion exchange capacity and absorbency. The aim of this study was to assess the effect of heavy metal uptake of one purified (PCT) and two non-purified clinoptilolite tuffs (NPCT1 and NPCT2) in aqueous solutions on monovalent ions Ni+, Cd+, Cs+, Ba+, Tl+, and Pb+. Experiments were furthermore carried out in artificial gastric and intestinal fluids to mimic human digestion and compare removal efficiencies of the adsorbent materials as well as release characteristics in synthetic gastric (SGF) and intestinal fluids (SIF). Batch experiments show low sorption capacities for Ni+ and Cd+ for all studied materials; highest affinities were found for Ba+ (99–100%), Pb+ (98–100%), Cs+ (97–98%), and Tl+ (96%), depending on the experimental setup for the PCT. For the adsorption experiments with SGF, highest adsorption was observed for the PCT for Pb+, with an uptake of 99% of the lead content. During artificial digestion, it was proven that the PCT did not release Ba+ cations into solution, whereas 13,574 ng·g−1 and 4839 ng·g−1 of Ba+ were measured in the solutions with NPCT1 and NPCT2, respectively. It was demonstrated that the purified clinoptilolite tuff is most effective in remediating heavy-metal-polluted water, particularly during artificial digestion (99% of Pb+, 95% of Tl+, 93% of Ba+). In addition, it was shown that the released amount of bound heavy metal ions (e.g., barium) from the non-purified clinoptilolite tuffs into the intestinal fluids was significantly higher compared to the purified product.

Municipal Solid Waste Incineration Ash-Incorporated Concrete: One Step towards Environmental Justice

Municipal solid waste and cement manufacture are two sources of environmental justice issues in urban and suburban areas. Waste utilization is an attractive alternative to disposal for eliminating environmental injustice, reducing potential hazards, and improving urban sustainability. The re-use and recycling of municipal solid waste incineration (MSWI) ash in the construction industry has drawn significant attention. Incorporating MSWI ash in cement and concrete production is a potential path that mitigates the environmental justice issues in waste management and the construction industry. This paper presents a critical overview of the pretreatment methods that optimize MSWI ash utilization in cement/concrete and the influences of MSWI ash on the performance of cement/concrete. This review aims to elucidate the potential advantages and limitations associated with the use of MSWI ash for producing cement clinker, alternative binder (e.g., alkali-activated material), cement substitutes, and aggregates. A brief overview of the generation and characteristics of MSWI ash is reported, accompanied by identifying opportunities for the use of MSWI ash-incorporated products in industrial-scale applications and recognizing associated environmental justice implications.

Steel Slag and Autoclaved Aerated Concrete Grains as Low-Cost Adsorbents to Remove Cd2+ and Pb2+ in Wastewater: Effects of Mixing Proportions of Grains and Liquid-to-Solid Ratio

This study investigated the applicability of industrial by-products such as steel slag (SS) and autoclaved aerated concrete (AAC) grains (<0.105, 0.105–2, 2–4.75 mm) as low-cost adsorbents for simultaneous removal of Cd2+ and Pb2+ in wastewater. A series of batch adsorption experiments was carried out in single and binary-metal solutions of Cd2+ and Pb2+ by changing the mixing proportions of SS and AAC grains. In addition, the effect of the liquid-to-solid ratio (L/S) on the removal of Cd2+ and Pb2+ in multi-metal solution was examined. Results showed that SS grains had a high affinity with Cd2+ in the single solution, while AAC grains had an affinity with Pb2+. In the binary solution, the mixtures of SS and AAC grains removed both Cd2+ and Pb2+ well; especially, the tested adsorbents of SS+AAC [1:1] and SS+AAC [1:4] mixtures achieved approximately 100% removal of both metals. Based on the results in the multi-metal solutions, the metal removal % and selectivity sequence varied depending on the mixed proportions of SS and AAC grains and L/S values. It was found that the SS+AAC [1:1] mixture of SS and AAC grains showed 100% removals of Cd2+, Pb2+, Cu2+, Ni2+, and Zn2+ simultaneously at L/S = 10 and 60.

Potential of using a new aluminosilicate amendment for the remediation of paddy soil co-contaminated with Cd and Pb

Cadmium (Cd) and lead (Pb) are toxic heavy metals that impact human health and biodiversity. Removal of Cd/Pb from contaminated soils is a means for maintaining environmental sustainability and biodiversity. In this study, we applied a newly modified material fly ash (NA), zeolite (ZE), and fly ash (FA) to the paddy soils and evaluated the effects of Cd/Pb accumulation in rice via a one-year field experiment. The results showed that the application of NA and ZE enhanced the soil pH and nutrients to a large extent and reduced the availability of Cd/Pb in soil. The Cd and Pb concentrations in rice grains decreased by 32.8% and 62.9%, respectively, with the NA treatments. Similarly, the application of ZE reduced the Cd and Pb concentrations in rice grains by a factor of 27.9% and 63.5%, respectively, which indicates that the amendments can promote the transfer of Cd and Pb from acid-exchangeable fraction to oxidizable and residual fractions. The Cd/Pb showed a significant positive correlation to other metal ions and a negative correlation to the nutrients. Generally, the application of NA and ZE was effective in reducing Cd/Pb accumulation and improving rice yield. Moreover, the NA was more cost-effective than ZE. Hence, this study proves that NA may be a better amendment for remediation of Cd/Pb contaminated soils.

Selective Recovery of Copper(II) from Incineration Ash Produced from a Municipal Waste Incineration Facility Using a Flow-through Type Electrolysis Method

Recovery of copper was attempted from municipal waste incineration ashes using acid extraction and electrodeposition by a flow-through type electrolysis cell (FE). Efficient extraction of copper from the incineration ash was obtained using 0.5 mol L^-1 sulfuric acid, i.e., copper extraction rate: 78% from bottom ash and 88% from fly ash. The copper in the 10-fold diluted extractant injected into the FE was quantitatively adsorbed by applying -0.4 V and was quantitatively desorbed by eluting with nitric acid.

Effective removal of Cd(II) from aqueous solution based on multifunctional nanoporous silicon derived from solar kerf loss waste

Recycling of kerf-loss slurry waste has become a meaningful and urgent issue in recent years. In this study, a novel hybrid material was prepared by Ag-assisted chemical etching kerf loss silicon waste and subsequently functionalized by a facile three-step graft process of 3-aminopropyltrimethoxy-silane, maleic anhydride, and ethylenediamine, named as EDA-MAH-APTES-NPSi, which could work as an effective adsorbent for removal of Cd(Ⅱ) from aqueous solution. The effect of initial pH, absorption duration, and metal ion concentrations on absorption performance were investigated. The adsorption equilibrium achieved after 120 min, the maximum adsorption capacity reached up to 210.01 mg/g and pH was at 5.5. The adsorption kinetic was fitted in the pseudo-second-order model and the Freundlich equation provided an accurate description for adsorption behavior. The XPS and FT-IR analysis manifested that Cd(Ⅱ) removal might be ascribed to the adsorption on the surface organic functional group by chemical chelating reaction and the ion exchange reaction. The EDA-MAH-APTES-NPSi maintained excellent adsorption capacity which decreased approximately 15.3 % (from 40.5-34.3 mg/g) after five successive regenerated cycles. The work confirms the potential of Cd(Ⅱ) removal from aqueous solution based on the modified NPSi and opens up a new way for recycling silicon cutting waste.

Emerging trends in municipal solid waste incineration ashes research: a bibliometric analysis from 1994 to 2018

The rapidly increasing generation of municipal solid waste (MSW) threatens the environmental integrity and well-being of humans at a global level. Incineration is regarded as a technically sound technology for the management of MSW. However, the effective management of the municipal solid waste incineration (MSWI) ashes remains a challenge. This article presents the global dynamics of MSWI ashes research from 1994 to 2018 based on a bibliometric analysis of 1810 publications (research articles and conference proceedings) extracted from the Web of Science database, followed by a comprehensive summary on the research developments in the field. The results indicate the rapid growth of annual publications on MSWI ashes research, with China observed as the most productive country within the study period. Waste Management, Journal of Hazardous Materials, Chemosphere and Waste Management & Research, which accounted for 35.42% of documents on MSWI research, are the most prominent journals in the field. The most critical thematic areas on this topic are MSWI ashes characterisation, dioxin emissions from fly ash, valorisation of bottom ash and heavy metal removal. The evolution of MSWI ashes treatment technologies is also discussed, together with the challenges and future research directions. This is the first bibliometric analysis on global MSWI ashes research based on a sufficiently large dataset, which could provide new insights for researchers to initiate further research with leading institutions/authors and ultimately advance this research field.

Possibility of removing cadmium pollution from the environment using a newly synthesized material coal fly ash

Coal fly ash (FA) is a solid waste produced in coal combustion. This study focused on the removal of Cd²⁺ from wastewater by a newly synthesized adsorbent material, the low-temperature and sodium hydroxide-modified fly ash (SHM-FA). The SEM and BET analyses of SHM-FA demonstrated that the adsorbent was porous and had a huge specific surface area. The XRF, XRD, FTIR and TGA characterization showed that SHM-FA has an amorphous structure and the Si-O and Al-O in the fly ash dissolved into the solution, which improved the adsorption capacity of Cd. The results indicated that SHM-FA has desired adsorption performance. The adsorption performance was significantly affected by the dosage, starting pH, Cd²⁺ initial concentrations, and temperature, as well as adsorption time. In the optimal conditions, the removal efficiency and adsorption capacity of Cd²⁺ by SHM-FA were 95.76% and 31.79 mg g^-1, respectively. The experiment provided clearly explained adsorption kinetics and isotherms. And the results confirmed that the adsorption behavior was well described by the pseudo-second-order kinetic and Langmuir isotherm model, which means that the adsorption of Cd²⁺ was controlled by SHM-FA through surface reaction and external diffusion process. In addition, the recycling of SHM-FA for reuse after Cd²⁺ adsorption showed high removal efficiency up to six times of use. Therefore, it can be concluded that SHM-FA is a low-cost adsorbent for Cd²⁺ removal from wastewater.

Lightweight aggregate obtained from municipal solid waste incineration bottom ash sludge (MSWI-BAS) and its characteristics affected by single factor of sintering mechanism

To solve the disposal problem of municipal solid waste incineration bottom ash sludge (MSWI-BAS), using it as the main raw material to prepare lightweight aggregates (LWA) for resource utilization. Sintering is an important process to achieve the desired microstructure and material properties. This paper investigates the characteristics of LWA affected by single factor of sintering mechanism (sintering temperature, heating rate and soaking time). Results show that sintering temperature increased from 1130°C to 1160°C caused high-density microstructure materials gradually formed in LWA, leading to particle strength increased from 0.1 MPa to 3.64 MPa, particle density showed an overall upward trend, reaching a maximum of 916 Kg/m³ at 1160°C, and 1 h water absorption reduced from 68% to 25%. The heating rate of 15 K/min was beneficial to the formation of dense phase structure which could increase the particle strength, and the water absorption rate reached the lowest at this time, while the particle density was less affected by heating rate. When soaking time extended from 5 min to 20 min, particle strength and compressive density were gradually increased, and 1 h water absorption showed an overall downward trend, indicating that a longer soaking time was not conducive to the retention of pores. This study demonstrates that the utilization of MSWI-BAS to make high-performance LWA is feasible, along with the preferable environmental and economic benefits.Implications: MSWI-BAS were selected to produce lightweight aggregate (LWA), so that the sludge disposal problem is reduced. The effects of sintering temperature, heating rate and soaking time on the characteristics of LWA were investigated. Compact glass structures are formed at 1150°C and 1160°C which greatly improve the strength. The heating rate has little influence on the physical properties of LWA products. The particle density of LWA increases after the sintering soaking time reaches 15 minutes.

Sustainable valorization of mesoporous aluminosilicate composite from display panel glasses waste for adsorption of heavy metal ions

The recycling of the huge amount of thin film transistor liquid crystal display (TFT-LCD) glass wastes has become one of the worldwide environmental issues. Herein, a novel and cost-effective synthesis method for the fabrication of mesoporous aluminosilicate composite (M-ANC) from the TFT-LCD waste has been developed to serve as the environmentally benign adsorbent for the removal of metal ions including Cu²⁺, Zn²⁺ and Ni²⁺. After melting at 1000 °C in the presence of Na₂CO₃ for phase separation, nanoparticles with average particle size of 12 nm appear on the surface of M-ANC, and subsequently results in the production of mesoporous structure with a surface area of 175 m² g^-1. The tailored M-ANC shows negatively charged and functional groups, which exhibits an excellent adsorption capacity toward metal ion removal in the pH range of 1.5-7.0. The maximum Langmuir adsorption capacity of Cu²⁺, Zn²⁺ and Ni²⁺ are determined to be 64.5, 34.0 and 23.1 mg g^-1, respectively, at pH 3.5. Moreover, the environmental applicability of M-ANC is evaluated by column experiment in the presence of real electroplating wastewater. M-ANC can effectively remove Ni²⁺ in the electroplating wastewater with the adsorption capacity of 18.7 mg g^-1. Results obtained in this study clearly indicate that M-ANC recycled from TFT-LCD is a novel environmentally friendly adsorbent toward metal ion removal, which can open a gateway to fabricate mesoporous aluminosilicate materials through the recycling of other electronic wastes for real environmental application to remove metal ions and other emerging pollutants in the contaminated water and wastewater.

Modified oil shale ash and oil shale ash zeolite for the removal of Cd2+ ion from aqueous solutions

The present study attempted to prepare modified oil shale ash and oil shale ash zeolite from oil shale ash, which were characterized by X-ray diffraction, scanning electron microscopy, and N₂ adsorption-desorption. Detailed kinetics and isotherm studies of Cd²⁺ adsorption onto modified oil shale ash and oil shale ash zeolite were examined. The adsorption capacity was determined as a function for the adsorption system. The results showed that the adsorption capacity of oil shale ash zeolite was higher compared to modified oil shale ash and that the time required to reach equilibrium was shorter. The kinetics studies showed that Cd²⁺ adsorption was well fit by the pseudo-second-order kinetics model. Both the Langmuir and the Freundlich isotherms described the adsorption data well. And the maximum monolayer adsorption capacity determined by the Langmuir adsorption isotherm was found to be 108.70 and 169.49 mg/g for Cd²⁺ adsorption onto modified oil shale ash and oil shale ash zeolite, respectively. It was concluded that Cd²⁺ in aqueous solutions was more efficiently removed by oil shale ash zeolite, which could be employed as a low-cost and effective alternative adsorbent for wastewater treatment than modified oil shale ash.