Retention Of Heavy Metals Research Articles

Rice Husk as a Sustainable Amendment for Heavy Metal Immobilization in Contaminated Soils: A Pathway to Environmental Remediation

Rice husk is a waste byproduct of rice production. This material has a moderate cost and is readily available, representing 20–22% of the biomass produced by rice cultivation. This study focused on the properties of rice husk in the remediation of soils contaminated by heavy metals. The effect of particle size, pH, and the presence of organic ligands on sorption efficiency was evaluated for Cd, Cu, and Mn. The continuous flow method was used to select suitable operative conditions and maximize the retention of heavy metals. Subsequently, pot experiments were carried out by growing two broadleaf plants, Lactuca sativa and Spinacia oleracea, in aliquots of soil collected in a Piedmont (Northwest Italy) site heavily contaminated by Cu, Cr, and Ni. Rice husk was added to the contaminated soil to evaluate its effectiveness in immobilizing heavy metals. The availability of Cr, Mn, Ni, Cu, Zn, Cd, and Pb in soil was studied using Tessier’s sequential extraction protocol. The content of the elements was also analyzed in plants and the uptake of heavy metals was evaluated in relation to the addition of rice husk. The growth of both plants was more efficient in the presence of rice husk due to its ability to reduce the mobility of heavy metals in the soil. The simplicity, cost-effectiveness, and scalability of its employment make the use of rice husk suitable for practical applications in soil remediation.

Agricultural waste-based biochars for sustainable removal of heavy metals from stabilized landfill leachate.

In this work, biochars were used as adsorbents to remove Cu, Cd, and Zn ions in a real stabilized leachate from a controlled landfill. Oak fruit shells biochar (OFSBC) and date palm fibers biochar (DPFBC) were obtained by pyrolysis of oak fruit shells and date palm fibers at 700°C and 400°C, respectively. OFSBC and DPFBC showed well-developed structures and high specific surface areas (520.16 m2/g and 470.46 m2/g, respectively). Equilibrium adsorption of heavy metal ions on DPFBC and OFSBC occurred after 4h and 2h of stirring. The removal efficiencies of Cu, Cd, and Zn ions were 97.01%, 94.40%, and 80.59% with DPFBC and 90.10%, 88.33%, and 76.16% using OFSBC, respectively. The Avrami fractional order model was appropriate for describing kinetic adsorption. Increasing the dose of adsorbent improves heavy metal ion retention. Thermodynamic tests have proven the spontaneous and endothermic adsorption of these heavy metals. The electrostatic attraction, ion exchange, complexation, metal-π bending, and surface precipitation and pore filling were regarded as the most predominant heavy metal retention mechanisms from the landfill leachate onto the biochar surface. Separately, the DPFBC showed the best performance than OFSBC regarding the improvement of leachate quality. Chemical oxygen demand (COD), biological oxygen demand (BOD5), ammoniacal nitrogen (NH3-N), and phosphorus (P) were respectively removed at an efficiency of 53.57%, 29.17%, 36.07%, and 37.5%, respectively. Thus, the results allow highlighting that the adsorption on DPFBC and OFSBC can be an effective alternative in the practice of landfill leachate treatment.

Chemical speciation and environmental risk assessment of heavy metals in ash from smouldering combustion of oily sludge

Smouldering combustion of oily sludge (OS) was carried out to learn the characteristics of heavy metals (HMs) in ash products. Ash collected from four different height layers of the column reactor was analysed for the chemical speciation and environmental risk of six HMs, including Cr, Ni, Cu, Zn, As, and Pb. The results showed that after smouldering combustion, only 21.3–32.2 % of the total HMs was remained in the ash products. The retention of HMs in ash was closely relevant to the carbonaceous destruction efficiency of OS. Smouldering combustion led to the decrease of HMs in acid-soluble/exchangeable fraction from 21.5–49.3 to 0.8–19.8% and oxidizable fraction from 22.6–49.6 to 5.3–21.3, and the increase of reducible fraction from 13.6–38.0 to 30.5–89.1% and residue fraction from 7.8–27.3 to 24.1–63.6%. Upward migration of HMs during smouldering was evidenced by their occurrence in the top clean sand layer, which was dominated in acid-soluble/exchangeable and reducible fractions, accounting for 89.7–99.1% in total. Toxicity extraction and environmental risk studies indicated that smouldering combustion would effectively reduce the toxicity and pollution risk of HMs; however, attention should be paid to the disposal of the top sand layer after smouldering operation due to its high pollution risk of HMs according to the evaluation of Risk assessment code.

Adsorption of Pb (II) ions on variable charge oxidic calcined substrates with chemically modified surface.

The paper describes lead ion adsorption on variable charge oxidic calcined substrates with chemically modified surfaces. Amphoteric oxides of iron, aluminum, titanium, and manganese, change their surface electric charge after acid or alkaline treatment, letting cationic or anionic adsorption reactions from aqueous solutions. This property allows using them as adsorbing substrate for heavy metals retention in water treatment systems. Substrate was prepared by extruding cylindrical strips from a saturate paste of the oxidic lithological material-OLM; dries it up and thermally treated by calcination. The study was performed by triplicated trial, on batch mode, using 2 grams samples of treated with NaOH 0.1N and non-treated substrate. Lead analysis was performed by AAS-GF. Freundlich and Langmuir models were used to fit results. Comparing differential behavior between treated and non-treated substrates showed the variable charge nature of the OLM. Results show L-type isotherms for the adsorption of Pb(II) ions on the activated substrate, suggesting good affinity between Pb(II) ions and OLM's surface. Average value of adsorption capacity ( K) for activated substrate (1791.73±13.06), is around four times greater than the non-activated substrate (491.54±31.97), during the adsorption reaction, 0.35 and 0.26 mmolH + of proton are produced on the activated and non-activated substrate respectively using a 1 mM Pb(II) solution and 72.2 and 15.6 mmolH + using a 10 mM Pb(II) solution. This acidification agrees with the theoretic model of transitional metals chemisorption on amphoteric oxides, present in lithological material used for the preparation of adsorbent substrates, confirming the information given by the L-type isotherms. Results suggest that these variable charge oxidic adsorbent substrate show great potential as an alternative technique for water treatment at small and medium scale using granular filtration system. The easiness and low price make them suitable to apply in rural media where no treating water systems is available.

Stabilization of heavy metals in solid waste and sludge pyrolysis by intercalation-exfoliation modified vermiculite

Increasing amounts of solid waste and sludge have created many environmental management problems. Pyrolysis can effectively reduce the volume of solid waste and sludge, but there is still the problem of heavy metal contamination, which limits the application of pyrolysis in environmental management. The intercalated-exfoliated modified vermiculite (IEMV) by intercalators of sodium dodecylbenzene sulfonate, hexadecyltrimethylammonium bromide and octadecyltrimethylammonium bromide were used to control the release of Cd, Cr, Cu, Zn and Pb during pyrolysis process of sludge or solid waste. The retention of heavy metals in sludge was generally better than that in solid waste. The IEMV by octadecyltrimethylammonium bromide as the intercalator calcined 800 °C (STAB-800) was the best additive for heavy metal retention, and the retention of Cr, Cu and Zn was significantly better than that of Pb and Cd. Cr, Cu, Zn and Pb were at low risk, while Cd had considerable risk under certain circumstances. New models were proposed to comprehensively evaluate the results of the risk and forms of heavy metals, and the increasing temperature was beneficial in reducing the hazards of heavy metals by the addition of STAB-800. The reaction mechanism of heavy metals with vermiculite was revealed by simulation of reaction sites, Fukui Function and Frontier Molecular Orbital. Thermal activation-intercalated-exfoliated modified vermiculite (T-IEMV) is more reactive and had more active sites for heavy metals. Mg atoms and outermost O atoms are the main atoms for T-IEMV to react with heavy metals. The Cr, Cu and Zn have better adsorption capacity by T-IEMV than Pb and Cd. This study provides a new insight into managing solid waste and sludge and controlling heavy metal environmental pollution.

Synergistic regulation of nanocomposite interlayered forward osmosis membranes with 1D/2D nanostructures for enhanced heavy metal retention

The treatment of heavy metal wastewater poses a significant challenge due to its adverse environmental consequences and potential hazards to human well-being, necessitating effective and sustainable solutions. Forward osmosis (FO) is an efficient and low-energy separation technology that serves as an effective strategy to address this issue. However, it still faces the trade-off between water permeability and selectivity, which directly impacts the solute separation efficiency and retention characteristics. In this study, a covalent organic framework (COF) interlayer was introduced via in-situ growth, and the surface properties of polyamide (PA) were synergistically regulated by amine-functionalized multi-wall carbon nanotubes (MWCNT-NH2), resulting in a 1D/2D nanocomposite interlayered FO membrane with a high crosslinking density, improved hydrophilicity, excellent stability, and antifouling properties. The synergistic effect of COF and MWCNT-NH2 led to an increase in the concentration of MPD participating in interfacial polymerization (IP) and a decrease in MPD diffusion rate. These improvements led to enhanced water permeability and selectivity, as well as outstanding retention efficiencies for heavy metal ions (Cr3+, Ni2+), exceeding 99.2 %. Therefore, this study holds significant implications for targeted application development of high-efficiency FO membranes in the future, demonstrating practical value in the treatment of heavy metal wastewater and environmental pollution control.

Effective stabilization of heavy metals in solid waste and sludge pyrolysis using intercalated-exfoliated modified vermiculite: Experiment and simulation study

Pyrolysis is effective in reducing the volume of solid waste and sludge, and produces less pollutants than incineration and landfill, but the process still suffers from heavy metal pollution. Four types of intercalated-exfoliated modified vermiculite (UIV, DIV, TIV and 3IV) were prepared using urea, dimethylsulfoxide, tributyl phosphate and 3-aminopropyltriethoxysilane as intercalators for the control of Cd, Cr, Cu, Pb and Zn in municipal sewage sludge (MSL), paper mill sludge (PML), municipal domestic waste (MWA) and aged refuse (AFE). The larger the interlayer spacing of the vermiculite, the more favorable the retention of heavy metals. 3IV was the most effective additive, with an average retention of more than 75 % of all heavy metals at 450 ℃ for the four raw materials. Cr, Cu, Pb and Zn were all at low potential ecological risk (Pr), while Cd was moderate or considerable Pr, and the addition of 3IV reduced the Pr. Distribution of intercalators between vermiculite interlayers was haphazard, and interlayer spacing results were close to those of the experiment (except for tributyl phosphate). The reactive electrons mainly flowed from the Highest Occupied Molecular Orbital (HOMO) of vermiculite flakes to the Lower Unoccupied Molecular Orbital (LUMO) of heavy metal chlorides. In contrast, the reactive electrons mostly flowed from the HOMO of heavy metal oxides to the LUMO of vermiculite flakes. Heavy metal oxides were more readily adsorbed on vermiculite flakes than heavy metal chlorides, and the adsorption capacity of Cr and Zn was stronger than that of Cd, Pb and Cu.

Chitosan-Based Beads Incorporating Inorganic-Organic Composites for Copper Ion Retention in Aqueous Solutions.

In recent years, there has been a challenging interest in developing low-cost biopolymeric materials for wastewater treatment. In the present work, new adsorbents, based on different types of chitosan (commercial, commercial chitin-derived chitosan and chitosan synthesized from shrimp shell waste) and inorganic-organic composites have been evaluated for copper ions removal. The efficacy of the synthesis of chitosan-based composite beads has been determined by studying various characteristics using several techniques, including FTIR spectroscopy, X-ray diffraction, porosimetry (N2 adsorption), and scanning electron microscopy (SEM). Adsorption kinetics was performed using different adsorption models to determine the adsorption behavior of the materials in the aqueous media. For all composite beads, regardless of the type of chitosan used, good capacity to remove copper ions from simulated waters was observed (up to 17 mg/g), which proves that the new materials hold potential for heavy metal retention. However, the adsorption efficiency was influenced by the type of chitosan used. Thus, for the series where commercial chitosan (CC) was used, the removal efficiency was approximately 29%; for the series with chitosan obtained from commercial chitin (SC), the removal efficiency was approximately 34%; for the series with chitosan enriched with CaCO3 (SH), the removal efficiency was approximately 52%.

Assessment of heavy metals retention in sediments and mangroves along the Saurashtra coast, Gujarat

This study aimed to investigate the impact of heavy metal pollution on the mangrove ecosystem on the Gujarat coast, which is facing pressure due to rapid industrialization. The concentrations of 5 heavy metals, including Pb+2, Cd+2, Zn+2, Cu+2, Fe+2 and Mn+2, were measured in the sediments and tissues of 4 mangrove species, Avicennia marina (Family: Acanthaceae), Rhizophora mucronata (Family: Rhizophoraceae), Ceriops tagal (Family: Rhizophoraceae) and Aegiceras corniculatum (Family: Primulaceae), in 8 habitats along the coast of Gujarat, India. The results indicated that the sediments in the study sites had relatively high heavy metal accretion (Pb+2 > Cu+2 > Fe+2 > Zn+2 > Mn+2 > Cd+2), but A. marina selectively accumulated only Cu (3.59 ppm) and Zn (0.63 ppm), while avoiding other heavy metals. The morphology of the plants did not show any visible impact from heavy metals stress. These findings highlight the significance of comprehending how industrial pollution affects mangrove ecosystems and the potential processes by which these plants can adapt to survive in such settings. Another advantage of mangroves is their capacity to absorb pollutants from many environments. Mangrove stems play a major role in absorbing pollutants.

Effects of Using Softwood Pellet Biochar Prepared at Different Temperatures with Grass Chippings on Retention of Heavy Metals in Contaminated Soils

Effects of Using Softwood Pellet Biochar Prepared at Different Temperatures with Grass Chippings on Retention of Heavy Metals in Contaminated Soils

Interaction of Heavy Metals with Plastic Contaminated Soil

Microplastic (MP) contamination is a threat to soil and groundwater system. Disintegration of used plastic products under exposure to solar radiations, application of sewage sludge to the soil, plastic mulching in agricultural activities leads to the formation of microplastics in significant amounts in soil. Hence there is a need from the geo environment engineering perspective on microplastic contamination in soils. Landfills and industrial areas have microplastic pollution in abundance. The presence of microplastic may alter the behaviour of liner material and surface soil in terms of heavy metal retention capacity, shrinkage, permeability and various other properties. In the present study, the soil is artificially polluted with shredded polypropylene (Pp) fragments from single use facial mask which is extensively being used in post COVID-19 situation. Heavy metals such as Lead, Nickel, Copper and Zinc at different concentrations similar to an industrially polluted soil is applied to the plastic contaminated (Pc) and normal soil. The filtrates from the test batches are studied for Total Dissolved Solids (TDS) and concentration of heavy metals using Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES). The obtained results concluded that plastic pollution significantly varied leached out heavy metals concentration to a maximum of 4.9 times that of normal soil. The TDS of the filtrate collected from plastic polluted soil varied by 31.29%.

Evaluation of Municipal Waste Compost in Relation to the Environmental Retention of Heavy Metals

This study investigates the performance of municipal compost as a heavy metal adsorbent for environmental protection systems. The performed assays test the effects of the pH (2–9) and contact time (5–250 min) on metal retention. To simulate leaching in natural systems, the soluble organic fraction was removed, leading to variations in the surface properties, including a 10% increase in the cation exchange capacity (CEC) and a 242% increase in the BET-specific surface area, accompanied by a small decrease in the surface charge (characterized by a less negative zeta potential values) of the washed municipal compost (WMC). Notably, these variations, which have not been found in previous research, yielded improved retention of Cu(II) and Zn(II) compared to raw municipal compost (RMC), attaining 96% retention for Cu(II) and 97% retention for Zn(II) at a pH of approximately 6.8–7.2 for a contact time of 120 min. The vast availability, cost-effectiveness, and resistance to desorption make municipal compost a viable option in a circular economy context for mitigating metal pollution across various environmental conditions. It is worth noting that this study can serve as a proxy for the expected outcomes in long-term exposure to environmental protection systems, enhancing the practical relevance of using compost for metal retention purposes.

Emission of nitrogen/sulfur pollutants and migration of heavy metals during combustion of oily sludge from the oil refining process in fluidized bed

Oily sludge is a kind of hazardous waste due to the enrichment of nitrogen, sulfur, and heavy metals. In this work, the combustion of oily sludge from an oil refining factory in a fluidized bed reactor at 850–1050 °C and 0.8–1.2 excess air ratios were studied, with a focus on emission of nitrogen and sulfur pollutants and migration of Cr, Ni, Cu, Zn, Cd, Pb. The emission characteristics of nitrogen and sulfur pollutants were exhibited through monitoring the flue gas. The migration characteristics of heavy metals were clarified by analyzing their retention in bottom and fly ash. Moreover, the BCR (European Community Bureau of Reference) sequential extraction of the heavy metals in bottom ash was also carried out to obtain the migration of heavy metals in different forms. The contents of NOx and SO2 in the flue gas increased with temperature and excess air ratio increasing. High temperature led to less heavy metal retention in the bottom ash. The strong oxidizing atmosphere can weaken the volatilization of heavy metals. The stabilities of the heavy metal in different forms were in the following order: F4 (residual fraction) > F3 (oxidizable fraction) > F2 (reducible fraction) > F1 (exchangeable and acid soluble fraction). F4 was the dominant fraction of heavy metals in the bottom ash. The >60 % content of F3 and F4 led to the high stability of Cu and Ni while the >57 % content of F1 and F2 led to the high volatility of Cd and Pb in bottom ash. The differences in the component map of F1-F4 for the six heavy metals gave rise to their different migration characteristics during combustion.

Experimental and theoretical study to control the heavy metals in solid waste and sludge during pyrolysis using modified expanded vermiculite

Na+/K+/Mg2+/Ca2+ expansion–modified vermiculite and calcination expansion (700 °C, 800 °C and 900 °C)–modified vermiculite (700-Mg-V, 800-Mg-V and 900-Mg-V) were prepared as additives to control the emission of five heavy metals (Zn, Cr, Cu, Pb, and Cd) during the pyrolysis of municipal sewage sludge, paper mill sludge, municipal domestic waste, and aged refuse. Mg2+-Modified vermiculite obtained via thermally activated calcination at 800 °C retained 65% of heavy metals from all raw materials at 450 °C. Zn, Cr, and Cu retained nearly 90%. Although modified vermiculite could reduce the ecological risk, Cd had an ecological risk level higher than Zn, Cr, Cu, and Pb. The fine textural properties, laminated morphology, and expansion capacity of modified vermiculite were positively correlated with its retention of heavy metals. Heavy metals interacted with the (002) surface of vermiculite, and the reactions were mainly concentrated near the 17-O and surrounding atoms. The heavy-metal monomers were less capable of binding to the (002) surface of vermiculite than the oxides and chlorides of heavy metals. The effect of heavy-metal oxides and chlorides binding to the (002) surface of vermiculite was related to heavy metals.

Synergistic retention of heavy metals and in-situ reduction of NO and SO2 by co-combustion of sewage sludge and coal gangue: A promising approach for contaminant management and emission reduction

This study aims to evaluate the influence of co-firing municipal sewage sludge with coal gangue at 800–1000 °C on the emissions of pollutants such as NO, SO2 and heavy metals (HMs). The results revealed that co-combustion resulted in smoother combustion (e.g., lower ignition and burnout temperatures, and a higher comprehensive combustion index) as well as a reduction in activation energy by approximately 30 kJ/mol when the sewage sludge ratio was above 60%. Moreover, the retention of HMs in the ashes during co-combustion was significantly improved through reactions between the dominant minerals (especially quartz (SiO2), berlinite (AlPO4), hedenbergite (CaFeSi2O6), magnetite (Fe3O4) and gehlenite (Ca2Al2SiO7) with HMs species presented in the wastes, leading to an increase in HMs content by 1 to 3 times. Additionally, in-situ desulfurization and denitration were observed during co-combustion at above 900 °C and below 850 °C, respectively. It is likely that berlinite has a direct impact on NO emissions, while gehlenite, whitlockite (Ca2.86Mg0.14(PO4)2) and diopside (CaMgSi2O8) present in the ashes are associated with the evolution of SO2 during co-combustion. These findings suggest that co-combustion of multiple wastes is a feasible approach for their resource utilization while reducing the environmental impacts associated with solid waste disposal.

Application of modified olivine to a two-stage gasification process to evaluate the effects on hydrogen generation and retention of heavy metals

An environmentally-friendly and efficient waste-to-energy and heavy metal retention system was successfully developed in this study. The natural resource-olivine was applied to be the bed material of second-stage gasifier, and the effects of second-stage gasifier temperature, and steam/biomass ratio on the hydrogen (H2) production ratio of syngas and heavy metal retention were discussed in detail. The optimal hydrogen production ratio (30.3%) was achieved when second-stage temperature, steam/biomass ratio (S/B ratio) were respectively controlled at 900 °C, and 0.25. The characterization analysis results evidenced that the Fe and Mg from pristine olivine and calcined olivine can facilitate the waste-to-hydrogen during the gasification reaction. Moreover, the NiO and Ni loaded on the surface of the calcine olivine could not only facilitate the water–gas shift reaction for H2 production, but also provide strong binding sites for the linkage of ether and cleavage of the C–O bond, leading to formation of CH4. The formed CH4 would be further dissociated over the metallic Ni/olivine, resulting in a significantly improved H2 production efficiency. In general, the order based on the H2 ratio of the syngas at the second-stage was calcined Ni-loaded olivine > calcined olivine > olivine; the heavy metal retention efficiency of three bed materials was in the order of Cu > Pb > Zn.

Experimental and theoretical-based study of heavy metal capture by modified silica-alumina-based materials during thermal conversion of coal at high temperature combustion

Heavy metals emitted from coal combustion can easily pose many threats. In this study, five modified additives based on kaolin were prepared for reducing the emission of heavy metals from high temperature coal combustion and characterized by XRD, FT-IR, XRF, BET, SEM and zeta potential. The heavy metal retention characteristics of the additives under high temperature (900–1300 °C) coal combustion were investigated by static and dynamic experiments, and the results showed that pseudo-boehmite-metakaolin (BMK) was the most effective additive, and the ability of heavy metal capture was Cr > Zn > Pb > Cd, and the dynamic experiments were better than the static experiments. The quantum chemical models of heavy metals (monomers, oxides and chlorides), kaolin and adsorbent-active substances were developed and optimized, and the adsorption energy was calculated. The morphological changes of the active substances were taken into account in the simulation, and new mathematical models for adsorption energy calculation were proposed, which effectively solved the extreme results of adsorption energy calculation and made a comprehensive evaluation of heavy metal adsorption for the whole studied temperature range system. The mechanism of heavy metal adsorption on the active substance was further investigated by the simulations. Heavy metal atoms can form covalent or ionic bonds with O atoms of the active substance, Cl atoms of heavy metal chlorides can be covalently bonded or non-bonded with Al atoms of the active substance, and O atoms of heavy metal oxides can combine with Al atoms of the active substance to form ionic bonds. This study sheds new light on the control of heavy metals in high-temperature coal combustion, the methods for the optimization of simulation and the adsorption mechanism of heavy metals on relevant reactive substances. The method has a promising potential for large-scale application due to its simple preparation, low cost and significant effect.

Sodium oxalate activation of basic oxygen furnace slag for building materials

Basic oxygen furnace (BOF) slag is a waste from the steel-making process characterised by its low hydraulic behaviour and heavy metals content. This study investigates activation of BOF slag with disodium oxalate to enhance the early hydration kinetics, microstructure development and heavy metals retention to develop it as a 100% replacement alternative for ordinary Portland cement. The results reveal that the activator boosts the reactivity not only of brownmillerite and calcium silicate but also Mg-wuestite. The main products formed are hydrogarnets and calcium-silicate-hydrate (C-S-H) gel. The maximum dosage added of 3 wt.% reached sufficient strength of 32.8 MPa at 28 days, being the most promising mixture. Leaching results of heavy metals are below the Dutch Soil Quality Decree limits. In summary, the BOF slag-oxalate cement offers an attractive approach for the future of steel-making and the building materials industry.

Chelated heavy metals removal by in-situ formed Fe(II) and Fe(III) iron (oxy)hydroxides: Mechanism and performance

For more than a century, coagulation-precipitation using Fe(II) and Fe(III) are ubiquitous in wastewater treatment, however, a systematic understanding of the underlying mechanism and their performance toward chelated heavy metals (e.g. CuII-EDTA) is still lacking. In this study, we therefore investigate the efficiency of Fe(II) and Fe(III) salts coagulation-precipitation, the properties (coagulation and crystallization behavior) of in-situ formed iron (oxy)hydroxides and explore the reaction mechanism using a suite of characterization techniques. Our results reveal that no matter Fe(II) and Fe(III) exhibited an exceptional removal performance for Cu(II) in terms of kinetics and iron dosage along with pH. Impressively, under optimal condition, over 95 % of chelated Cu(II) was removed within 10 min from Fe(II) while about 85 % from Fe(III) dosing. The highly reductive structural Fe(II) existing on mixed-valent iron bearing mineral results in reductive decomplexation of CuII-EDTA in the Fe(II) coagulation-precipitation process in compare with replacement decomplexation in the Fe(III) coagulation-precipitation process, and then released free metal ions (Cu(I) and Cu(II)) can be removed by adsorption and coprecipitation. In addition, the in-situ formed Fe(III) (oxy)hydroxides were amorphous 2-line ferrihydrite with stable flocs and better sedimentation behavior than crystalline lepidocrocite from Fe(II) dosing, and these factors are crucial to the subsequent retention of heavy metals. The elucidation of this study has highlighted the great potential of using in-situ formed iron (oxy)hydroxides for cost-effective treatment of chelated heavy metal-bearing industrial wastewaters.

The interaction of different chlorine-based additives with swine manure during pyrolysis: Effects on biochar properties and heavy metal volatilization

Poor properties and high concentrations of heavy metals are still major concerns of successful application of animal manure-derived biochar into the environment. This work thus proposed to add chlorine-based additives (Cl-additives, i.e., CaCl2, MgCl2, KCl, NaCl, and PVC, 50 g Cl/ kg) to improve biochar properties and enhance heavy metal volatilization during swine manure pyrolysis. The results showed that the addition of CaCl2 could improve the retention of carbon (C) by up to 13.1% during pyrolysis, whereas other Cl-additives had little effect on it. Moreover, CaCl2 could enhance the aromaticity of biochar, as indicated by lower H/C ratio than raw biochar. Pretreatment with CaCl2, MgCl2 and PVC reduced phosphorus (P) solubility but increased its bioavailability via the formation of chlorapatite (Ca5(PO4)3Cl). The CaCl2 was more effective for enhancing the volatilization efficiency of heavy metals than other Cl-additives, except for Pb that tended to react with the generated Ca5(PO4)3Cl to form more stable and less volatile Pb5(PO4)3Cl. However, high pyrolysis temperature (900℃) was essential for CaCl2 to simultaneously decrease the bioavailability of heavy metals. Our results indicated that co-pyrolysis of swine manure with CaCl2 is a promising strategy to increase C retention, P bioavailability, and volatilization of heavy metals, and, at higher temperature, reduce the bioavailability of biochar-born heavy metals.