Kinetic study for copper adsorption onto soil minerals in the absence and presence of humic acid

Potassium adsorption capacity and desorption kinetics in soils of Qenberenaweti sub-watershed, central highlands of Ethiopia

Determining the supply and uptake of K nutrient and the dynamic equilibrium (adsorption-desorption) reactions among the K forms in the soils are not commonly addressed in the highlands of Ethiopia. A study was therefore initiated to determine the adsorption capacity of the exchangeable K and the release kinetics of the non-exchangeable K in the soils of the Qenberenaweti Sub-watershed. Twelve disturbed surface (0-20 cm) soil sub-samples were collected from every farmland which was representative of each pre-identified soil type (Vertic Cambisols, Pellic Vertisols, Pisoplinthic Luvisols, Relictistagnic Cambisols, Pisoplinthic Cambisols, and Plinthofractic Cambisols). A composite sample was made in duplicate for the determination of K adsorption capacity and desorption kinetics per soil type. The mean maximum (69.47 ± 4.31 %) and minimum (56.16 ± 6.04 %) K adsorption rates were obtained from the Plinthofractic Cambisols and Vertic Cambisols, respectively. Among the tested isotherm models, the goodness of the Freundlich was better fit the data of all experimental soils; hence, a modified equation of this model (qe = aCeb/a) could be used to describe the theoretical doses of K fertilizers required to develop K levels in soil solutions. The highest constant K releases from the Plinthofractic Cambisols (47 mg kg-1), Pisiopllintic Cambisols (46 mg kg-1), and Pisoplinthic Luvisols (44 mg kg-1) were attained at the 9th extraction. In comparison, it was noticed at the 7th and 11th extractions of the Relictistagnic Cambisols (45 mg kg-1) and both Pellic Vertisols (48 mg kg-1) and Vertic Cambisols (42 mg kg-1), respectively. The equation of power function was the best to successfully describe the released K+ from all the experimental soils. Eventually, determining the adsorption capacity and release kinetics of K at a site-specific level helps to know the relative potential of the soils to supply K and also plan for an effective K fertilization strategy.

Effects of biochar-based materials on nickel adsorption and bioavailability in soil

The potential for toxic elements to contaminate soil has been extensively studied. Therefore, the development of cost-effective methods and materials to prevent toxic element residues in the soil from entering the food chain is of great significance. Industrial and agricultural wastes such as wood vinegar (WV), sodium humate (NaHA) and biochar (BC) were used as raw materials in this study. HA was obtained by acidizing NaHA with WV and then loaded onto BC, which successfully prepared a highly efficient modification agent for nickel-contaminated soil, namely biochar-humic acid material (BC-HA). The characteristics and parameters of BC-HA were obtained by FTIR, SEM, EDS, BET and XPS. The chemisorption of Ni(II) ions by BC-HA conforms to the quasi-second-order kinetic model. Ni(II) ions are distributed on the heterogeneous surface of BC-HA by multimolecular layer adsorption, which accords with the Freundlich isotherm model. WV promotes better binding of HA and BC by introducing more active sites, thus increasing the adsorption capacity of Ni(II) ions on BC-HA. Ni(II) ions in soil are anchored to BC-HA by physical and chemical adsorption, electrostatic interaction, ion exchange and synergy.

Bentonite binding with mercury(II) ion through promotion of reactive oxygen species derived from manure-based dissolved organic matter

This study reports the mercury binding by bentonite clay influenced by cattle manure-derived dissolved organic matter (DOM). The DOM (as total organic carbon; TOC) was reacted with bentonite at 5.2 pH to monitor the subsequent uptake of Hg²⁺ for 5 days. The binding kinetics of Hg²⁺ to the resulting composite was studied (metal = 350 µM/L, pH 5.2). Bentonite-DOM bound much more Hg²⁺ than original bentonite and accredited to the establishment of further binding sites. On the other hand, the presence of DOM was found to decrease the Hg²⁺ binding on the clay surface, specifically, the percent decrease of metal with increasing DOM concentration. Post to binding of DOM with bentonite resulted in increased particle size diameter (~ 33.37- ~ 87.67 nm) by inducing the mineral modification of the pore size distribution, thus increasing the binding sites. The XPS and FTIR results confirm the pronounced physico-chemical features of bentonite-DOM more than that of bentonite. Hydroxyl and oxygen vacancies on the surface were found actively involved in Hg²⁺ uptake by bentonite-DOM composite. Furthermore, DOM increased the content of Hg²⁺ binding by ~ 10% (pseudo-second-order q_e = 90.9-100.0) through boosting up Fe³⁺ reduction with the DOM. The quenching experiment revealed that more oxygen functionalities were generated in bentonite-DOM, where hydroxyl was found to be dominant specie for Hg²⁺ binding. The findings of this study can be used as theoretical reference for mineral metal interaction under inhibitory or facilitating role of DOM, risk assessment, management, and mobilization/immobilization of mercury in organic matter-containing environment.

Overlooked mechanism of Pb immobilization on montmorillonite mediated by dissolved organic matter in manure compost

In this study, three kinds of dissolved organic matter (DOM) derived from fresh chicken manure (FDOM), immature compost (IDOM) and mature compost (MDOM) were employed to compare their effects on Pb adsorption onto montmorillonite (MMT). The potential mechanism was revealed by characterization of mineral structure and calculation of interface force. The results demonstrated that the adsorption capacity (q_max) of Pb onto MMT was decreased by 14.3% and 29.8% in the presence of FDOM and IDOM, respectively, while increased by 44.4% in the presence of MDOM, resulting from the release or co-adsorption of DOM-Pb complexes. Parallel factor (PARAFAC) further indicated that Pb mainly bound to protein-like substances in FDOM and IDOM, and fulvic-like in MDOM. The X-ray diffraction (XRD) analysis proved that MDOM-Pb complex had a stronger ability to enter into the interlayer of MMT. The van der Waals force dominated the adsorption of FDOM-Pb and IDOM-Pb, while ligand exchange was involved in the case of MDOM-Pb. This study provided a comprehensive insight into the geochemical behavior of livestock manure and its compost as well as their interactions with heavy metal and soil mineral.

Copper (Cu) speciation in organic-waste (OW) amended soil: Instability of OW-borne Cu(I) sulfide and role of clay and iron oxide minerals

The geochemistry of copper (Cu) is generally assumed to be controlled by organic matter in soils. However, the role of clay and iron oxide minerals may be understated. Soil density fractionation, X-ray diffraction (XRD), and X-ray absorption spectroscopy (XAS) were combined to assess the long-term behavior of Cu in an agricultural soil subject to organic waste application. Two unprecedented molecular environments of natural Cu (i.e. Cu inherited from the parent rock) in soils are reported: Cu dimer in the interlayer of vermiculite and Cu structurally incorporated within hematite. Moreover, the soil naturally containing Cu-vermiculite, Cu-hematite, but also Cu-kaolinite (Cu_total = 122 mg·kg^-1) was amended over 11 years with Cu-rich pig slurry in which Cu was 100 % Cu(I) sulfide. Natural Cu associated with clay and iron oxide minerals persisted in the amended soil, but the exogenous Cu(I) sulfide was unstable. The increase in Cu concentration in the amended soil to 174 mg·kg^-1 was accounted for the increase of Cu sorbed to kaolinite and Cu bound to organic matter. These results are important for better understanding the natural occurrence of Cu in soils and for assessing the environmental impacts of organic waste recycling in agricultural fields.

Speciation of heavy metals in soils and their immobilization at micro-scale interfaces among diverse soil components

Heavy metal (HM) pollution of soils is a globally important ecological and environmental problem. Previous studies have focused on i) tracking pollution sources in HM-contaminated soils, ii) exploring the adsorption capacity and distribution of HMs, and iii) assessing phyto-uptake of HMs and their ecotoxicity. However, few reviews have systematically summarized HM pollution in soil-plant systems over the past decade. Understanding the mechanisms of interaction between HMs and solid soil components is consequently key to effectively controlling and remediating HM pollution. However, the compositions of solid soil phases are diverse, their structures are complex, and their spatial arrangements are heterogeneous, all leading to the formation of soil micro-domains that exhibit different particle sizes and surface properties. The various soil components and their interactions ultimately control the speciation, transformation, and bioavailability of HMs in soils. Over the past few decades, the extensive application of advanced instrumental techniques and methods has greatly expanded our understanding of the behavior of HMs in organic mineral assemblages. In this review, studies investigating the immobilization of HMs by minerals, organic compounds, microorganisms, and their associated complexes are summarized, with a particular emphasis on the interfacial adsorption and immobilization of HMs. In addition, methods for analyzing the speciation and distribution of HMs in aggregates of natural soils with different particle sizes are also discussed. Moreover, we also review the methods for speciating HMs at mineral-organic micro-scale interfaces. Lastly, developmental prospects for HM research at inorganic-organic interfaces are outlined. In future research, the most advanced methods should be used to characterize the interfaces and in situ characteristics of metals and metal complexes. In particular, the roles and contributions of microorganisms in the immobilization of HMs at complex mineral-organic interfaces require significant further investigation.

Sonoelectrochemical activation of peroxymonosulfate: Influencing factors and mechanism of FA degradation, and application on landfill leachate treatment

In this work, sonoelectrochemically activated peroxymonosulfate (US-EC/PMS) was used to degrade fulvic acid (FA) in water. Compared with other technologies, the US-EC/PMS system can achieve higher FA decolorization in a short time. Moreover, the benefits of synergy are more prominent in the US-EC/PMS system. The effects of operating parameters on the sonoelectrochemical degradation of FA were investigated, including initial pH, initial FA concentration, current density, ultrasonic power, PMS dosage. The results showed the initial FA concentration and current density were critical to the degradation of FA. Under optimized parameters: initial pH of 2, 50 mg L^-1 initial FA concentration, 30 mA cm^-2 current density, 50 W ultrasonic power, 1 mM PMS dosage, the US-EC/PMS system can achieve 93% FA decolorization. The calculation results of current efficiency and energy consumption indicate that the introduction of PMS into the US-EC system has economic applicability. Scavenger experiments and electron paramagnetic resonance suggest that hydroxyl radicals, sulfate radicals, and singlet oxygen were the main ROS produced in the US-EC/PMS system. Accordingly, the possible mechanism of FA degradation by sonoelectrochemical activation PMS was proposed. Finally, the US-EC/PMS system was used to treat the aged landfill leachate. Three-dimensional fluorescence analysis showed that most of the humic substances (Hss) were effectively removed, and the biodegradability of the leachate was considerably improved. In addition, the effective removal of COD, chroma, and ammonia nitrogen were observed, proving that this technology is a powerful means to treat organic wastewater contaminated by Hss.

Estimation of Pb Content Using Reflectance Spectroscopy in Farmland Soil near Metal Mines, Central China

The contamination of farmlands with hazardous metals from mining puts the safety of agricultural commodities at risk. For remediation, it is crucial to map the spatial distribution of contaminated soil. Typical sampling-based procedures are time-consuming and labor-intensive. The use of visible, near-infrared, and short-wave infrared reflectance (VNIR-SWIR) spectroscopy to detect soil heavy metal pollution is an alternative. With the aim of investigating a methodology of detecting the most sensitive bands using VNIR-SWIR spectra to find lead (Pb) anomalies in agriculture soil near mining activities, the area in Xiaoqinling Mountain, downstream from a series of active gold mines, was selected to test the feasibility of utilizing VNIR-SWIR spectroscopy to map soil Pb. A total of 115 soil samples were collected for laboratory Pb analysis and spectral measurement. Partial least squares regression (PLSR) was adopted to estimate the soil Pb content by building the prediction model, and the model was optimized by finding the optimal number of bands involved. The spatial distribution of Pb concentration was mapped using the ordinary kriging (OK) interpolation method. This study found that five spectral bands (522 nm, 1668 nm, 2207 nm, 2296 nm, and 2345 nm) were sensitive to soil Pb content. The optimized prediction model’s coefficient of determination (R2), residual prediction deviation (RPD), and root mean square error (RMSE) were 0.711, 1.860, and 0.711 ln(mg/kg), respectively. Additionally, the result of OK interpolation was convincing and accurate (R2 = 0.775, RMSE = 0.328 ln(mg/kg)), comparing maps from estimated and ground truth data. This study proves that it is feasible to use VNIR-SWIR spectral data for in situ estimation of the soil Pb content.

Flocculation with heterogeneous composition in water environments: A review

Flocculation is a key process for controlling the fate and transport of suspended particulate matter (SPM) in water environments and has received considerable attention in the field of water science (e.g., oceanography, limnology, and hydrology), remaining an active area of research. The research on flocculation has been conducted to elucidate the SPM dynamics and to diagnose various environmental issues. The flocculation, sedimentation, and transportation of SPM are closely linked to the compositional and structural properties of flocs. In fact, flocs are highly heterogeneous in terms of composition. However, the lack of comprehensive research on floc composition and structure has led to misconceptions regarding the temporal and spatial dynamics of SPM. This review summarizes the current understanding of the heterogeneous composition of flocs (e.g., minerals, organic matter, metals, microplastic, engineered nanoparticles) and its effect on their structure and on their fate and transport within aquatic environments. Furthermore, the effects of human activities (e.g., pollutant discharge, construction) on floc composition are discussed.

Magnetic aminated lignin/CeO2/Fe3O4 composites with tailored interfacial chemistry and affinity for selective phosphate removal

Phosphorus (P) has brought a series of environmental problems while benefiting mankind. To reclaim phosphorus from wastewater efficiently and conveniently, a novel magnetic adsorbent with aminated lignin/CeO₂/Fe₃O₄ composites (AL-NH₂@Fe₃O₄-Ce) possessing a high affinity to phosphate and easily separated from aqueous solutions was developed in this work. The characterization results revealed that Fe and Ce elements have been doped into the aminated lignin successfully. Batch experiment results convinced that the maximum phosphate adsorption capacity of AL-NH₂@Fe₃O₄-Ce was 183.72 mg P/g at pH = 3, which was roughly 4.5 times greater than aminated lignin and 8.5 times greater than cerium oxide, respectively. The adsorption isotherm was fitted well by the Langmuir model, and the adsorption kinetics was in line with the pseudo-second-order model. The adsorption thermodynamics indicated the adsorption process was spontaneous and naturally exothermic. Additionally, AL-NH₂@Fe₃O₄-Ce exhibited high selectivity towards phosphate over common coexisting anions (Cl^-, NO₃^-, HCO₃^-, SO₄^2- and F^-). After five consecutive cycles, the adsorption performance of AL-NH₂@Fe₃O₄-Ce decreased by only 16% compared with the fresh adsorbent, indicating that AL-NH₂@Fe₃O₄-Ce exhibited excellent recycling ability. The results of XPS analysis and batch experiments showed that the possible mechanisms were electrostatic attraction and inner-sphere complexation. The tailored interfacial chemistry affinity to phosphate as well as endowed magnetic property reveled AL-NH₂@Fe₃O₄-Ce could be adopted as an up and coming adsorbent in phosphate removal process.

Glyphosate adsorption onto kaolinite and kaolinite-humic acid composites: Experimental and molecular dynamics studies

Glyphosate (PMG) has been the most widely used herbicide in the world, and its environmental mobility and fate are mainly controlled by interactions with mineral surfaces. In soil systems, kaolinite is typically associated with humic acids (HAs) in the form of mineral-HA complexes, and hence it is crucial to characterize the molecular-scale interactions that occur between PMG and kaolinite and kaolinite-HA complexes. Batch experiments, Fourier transform infrared spectrum (FTIR) and X-ray photoelectron spectroscopy (XPS), isothermal titration calorimetry (ITC), and molecular dynamics (MD) simulations were performed to decipher the molecular interactions between PMG and kaolinite and kaolinite-HA composites. Our results reveal that kaolinite-HA composites adsorb higher concentrations of PMG than does kaolinite alone, likely due to more adsorption sites existed on kaolinite-HA than on kaolinite. FTIR and XPS analysis reveal that the carboxyl, phosphonyl and amino groups of PMG interacted with kaolinite and kaolinite-humic acid via Hydrogen bonds. The ITC results and interaction energy calculations indicate that the adsorption of PMG onto the kaolinite-HA is more energetically favorable relative to that onto kaolinite. MD simulations suggest that the PMG molecule adsorbs parallel to the surface of kaolinite and the composites through hydrogen bonding. Humic acid increases the adsorption of PMG through the creation of H-bond networks between PMG, the kaolinite surface, and humic acid. The results from this study improve our molecular-level understanding of the interactions between PMG and two important components of soil systems, and hence yield valuable information for characterizing the fate and behavior of PMG in soil environments.

Copper and Zn distribution in humic substances of soil after 10 years of pig manure application in south of Santa Catarina, Brazil

This study aims to evaluate available Cu and Zn levels in soil and related in soil organic matter (SOM) fractions (fulvic acids-FA, humic acids-HA, and humins-HU) after 10 years of application of pig slurry (PS) and pig deep litter (PL). Soil samples were collected from an experiment with black oat/corn succession under no-tillage in southern Brazil. The treatments consisted of fertilization of 90 and 180 kg N ha^-1 applied as PS and PL from 2002 to 2012 and a control treatment without any fertilization. SOM chemical fractionation was performed in air-dried samples. Copper and Zn concentrations were analyzed in soil (total, EDTA- and CaCl₂-extracted) and in SOM fractions. The amount of Cu and Zn (in mol) related to each fraction of SOM (Cu/C and Zn/C molar ratios) was established. The applications of PS and PL promoted the accumulation of total and available Cu and Zn, especially in the PL180 treatment. The highest amount of Zn was found with HU, while for Cu both HA and HU were important retention compartments. The highest Cu/C_FA, Cu/C_HA and Cu/C_HU ratios were found with the addition of PL. Increases in Zn/C ratio were found mainly in FA fraction. The high levels of Cu and Zn obtained in the HCl-extracted SOM fraction suggest that a considerable part is bound to SOM and clay minerals with low energy. However, the SOM is an important source of metal adsorption in soils with swine manure application.

Removal of Cadmium from Contaminated Water Using Coated Chicken Bones with Double-Layer Hydroxide (Mg/Fe-LDH)

Occurrence of heavy metals in freshwater sources is a grave concern due to their severe impacts on public health and aquatic life. Cadmium (Cd2+) is one of the most dangerous heavy metals, and can cause serious diseases even at low concentrations. Hence, a wide range of treatment technologies exist, such as nanofiltration and biological reactors. In this context, the present investigation aims at the development of a new adsorption medium, made from chicken bones coated with iron (Fe) and magnesium (Mg) hydroxides, to remove cadmium from water. This novel chicken bone functional substance was manufactured by applying layered double hydroxides (LDH) into the chicken bones. Initially, the new adsorption medium was characterized using Fourier-transform infrared spectroscopy (FTIR technology), then it was applied to remove cadmium from water under different conditions, including pH of water (3–7.5), agitation speed (50–200 rpm), adsorbent dose (1–20 g per 100 mL), and contact time (30–120 min). Additionally, the reaction kinetics were studied using a pseudo-first order kinetic model. The results obtained from the present study proved that the new adsorption medium removed 97% of cadmium after 120 min at an agitation speed of 150 rpm, pH of 5, and adsorption dose of 10 g per 100 mL. The results also showed that the new adsorption medium contains a significant number of functional groups, including hydroxyl groups. According to the outcomes of the kinetic study, the mechanism of removing metal is attributed to surface precipitation, ion exchange, complexation, hydrogen binding between pollutants, and the LDH-chicken bone substance.

Molecular dynamics simulation of the interaction of water and humic acid in the adsorption of polycyclic aromatic hydrocarbons

Humic acid (HA) and water play an important role in polycyclic aromatic hydrocarbons (PAHs) adsorption and biodegradation in soil. In this work, molecular dynamics (MD) and electrostatic potential surfaces (EPSs) simulations are conducted to research the contribution of quartz surface, leonardite humic acid (LHA), and water to PAH adsorption. The adsorption energies between PAHs and LHA are much higher than that between PAHs and quartz. Simulation shows that the hydroxyl and carboxyl groups' attraction by LHA is the main adsorption force between PAHs and LHA. The π-π interaction between PAHs and LHA also contributes to the adsorption process. In addition, the mobility of water on quartz surface is much higher than that of LHA. Water should be regarded as an adsorbate in the system as well as PAHs. However, the presence of water has a remarkable negative effect on the adsorption of PAHs on LHA and quartz. The bridging effect of water could only enhance the stability of the aggregation system. The adsorption contribution of quartz and LHA to PAHs in the soil model tends to 0 if the water layer reaches 2.0 nm. Graphical abstract.

Influence of colloidal Fe(OH)3 on the adsorption characteristics of strontium in porous media from a candidate high-level radioactive waste geological disposal site

Colloids in groundwater or geological barriers generally play a key role in the migration of special nuclides. Adsorption characteristics of strontium were investigated on porous media in the presence of colloidal Fe(OH)₃ from the Beishan Site, the only high-level radioactive waste disposal site candidate in China. The effects of colloid amounts, solid contents, and pH were determined and studied by batch texts. The results revealed that the presence of colloidal Fe(OH)₃ in porous media contributed to promotion of the sorption effect, and the influencing factors had a significant impact on the adsorption process. The sorption ability increased with increasing colloid amount when the equilibrium time was approximately 10 h under an optimal solid-liquid ratio of 20 g L^-1. The sorption effect in alkaline conditions was better than that under acidic conditions. The sorption kinetics indicated that the strong chemical interaction and/or surface complexation contributed primarily to strontium sorption. The sorption isotherms and model fitting revealed that the sorption of strontium onto porous media in the presence of colloidal Fe(OH)₃ was a monolayer adsorption, and the presence of colloidal Fe(OH)₃ is an important factor that greatly influences the removal of strontium from aqueous solutions. These findings provide useful information for the treatment of strontium in radioactive waste disposal sites.

Adsorption-desorption and co-migration of vanadium on colloidal kaolinite

Vanadium (V) pollution in soil has been widely noted, while knowledge about the effect of soil colloid on migration of V is scarce. Batch adsorption-desorption and transportation of the colloid-adsorbed V in columns packed with quartz sand under various environment conditions were carried out to explore the retention and transportation of V by colloidal kaolinite. Batch adsorption-desorption studies show that the adsorption of V by the colloidal kaolinite was mainly specific adsorption and redox played a limited role in the adsorption process. The maximum adsorption capacity of the colloidal kaolinite was 712.4 mg g^-1, and about 5.9-8.7% of the adsorbed V could be desorbed. Both the adsorption-desorption and migration of V with colloidal kaolinite were highly ambient condition dependent. The column studies show that V was highly mobile in the saturated porous media. An easier transfer of V with an increase in pH, IS, and velocity of flow was noted. However, the increase of IS lead to the blockage of the colloidal kaolinite transportation. The recovery rate of the colloidal kaolinite at pH 7 and 9 was 2.0 and 2.1 times that at pH 5, respectively. The migration of colloidal-adsorbed V in sand column preceded that of V ion, but more colloidal-bound V than V ion remained in the column. Lack of consideration of the combination and co-transportation of V and colloidal kaolinite will lead to an overestimation of the risk of V to deeper soil profiles and groundwater. Graphical abstract.

Immobilization and sorption of Cd and Pb in contaminated stagnic anthrosols as amended with biochar and manure combined with inorganic additives

The present study evaluated the efficiency of pre-selected composite amendments (CA-1: biochar-lime-sepiolite-zeolite and CA-2: manure-lime-sepiolite) for immobilization and sorption of Cd and Pb in field and batch sorption experiments. The field experiment was performed in a co-contaminated clay purple soil (stagnic anthrosols). Along with a control experiment (T1), CA-1 and CA-2 were tested at different rates including 750, 1500, 3000 and 6000 kg ha^-1 by growing wheat as the test crop. The obtained results revealed that the highest dose of both composites (T5: 6000 kg ha^-1 and T9: 6000 kg ha^-1) increased the soil pH to 6.85 and 6.81, respectively as compared to the control (5.63). DTPA-extractable Cd and Pb contents decreased with composite treatments (T7 and T4) at harvest stage samples. Metal fractionation depicted that application of amendments decreased the exchangeable fraction at harvesting stage. Application of CA-2 and CA-1 (3000 kg ha^-1) significantly increased the plant biomass (by 28% and 24%, respectively) and grain yield (by 26% and 22%, respectively) of wheat. Furthermore, batch sorption experiment results revealed that Langmuir adsorption model better fitted the sorption results with R² values ranging between 0.99 and 0.91 for Cd and Pb, respectively. CA-1 and CA-2 exhibited the maximum adsorption capacity for Cd with no significant difference among treatments but Pb adsorption capacity was highest in CA-1 followed by CA-2 and control. The results of our experiments revealed that the application of organics combined with inorganic materials enhanced Cd and Pb immobilization and sorption, consequently reducing metals availability in laboratory and field conditions. Moreover, for field trials, application of the composite amendments at 3000 kg ha^-1 emerged as the suitable treatment for tested wheat-grown area.

Surface modifications at the oxide/water interface: Implications for Cu binding, solution chemistry and chemical stability of iron oxide nanoparticles

The oxidation of magnetite into maghemite and its coating by natural organic constituents are common changes that affect the reactivity of iron oxide nanoparticles (IONP) in aqueous environments. Certain ubiquitous compounds such as humic acids (HA) and phosphatidylcholine (PC), displaying a high affinity for both copper (Cu) and IONP, could play a critical role in the interactions involved between both compounds. The adsorption of Cu onto four different IONP was studied: magnetite nanoparticles (magnNP), maghemite NP (maghNP), HA- and PC-coated magnetite NP (HA-magnNP and PC-magnNP, respectively). According to the results, the percentage of adsorbed Cu increases with increasing pH, irrespective of the IONP. Thus, protonation/deprotonation reactions are likely involved within Cu adsorption mechanism. Contrary to the other studied IONP, HA-magnNP favor Cu adsorption at most of the pH tested including acidic pH (pH = 3), suggesting that part of the active surface sites for Cu²⁺ were not grabbed by protons. The Freundlich adsorption isotherm of HA-magnNP provides the highest sorption constant K_F (bonding energy) and n value which supports a heterogeneous sorption process. The heterogeneous adsorption between HA-magnNP and Cu²⁺ can be explained by both the diversity of the binding sites HA procured and the formation of multidendate complexes between Cu²⁺ and some of the HA functional groups. Such favorable adsorption process was neither observed on PC-coated-magnNP nor on maghNP, whose behaviors were comparable to that of magnNP. On another hand, HA and PC coatings considerably reduced iron (Fe) dissolution from magnNP as compared with magnNP. It was suggested that HA and PC coatings either provided efficient shield against Fe leaching or fostered dissolved Fe re-adsorption onto the functional groups at the coated magnNP surfaces. Thus, this study can help to better understand the complex interfacial reactions between cations-organic matter-colloidal surfaces which are relevant in environmental and agricultural contexts. This work showed that magnetite NP properties can be affected by surface modifications, which drive NP chemical stability and Cu adsorption, thereby affecting the global water chemistry.

Heavy metal behaviour at mineral-organo interfaces: Mechanisms, modelling and influence factors

The mineral-organo composites control the speciation, mobility and bioavailability of heavy metals in soils and sediments by surface adsorption and precipitation. The dynamic changes of soil mineral, organic matter and their associations under redox, aging and microbial activities further complicate the fate of heavy metals. Over the past decades, the wide application of advanced instrumental techniques and modelling has largely extended our understanding on heavy metal behavior within mineral-organo assemblages. In this review, we provide a comprehensive summary of recent progress on heavy metal immobilization by mineral-humic and mineral-microbial composites, with a special focus on the interfacial reaction mechanisms of heavy metal adsorption. The impacts of redox and aging conditions on heavy metal speciations and associations with mineral-organo complexes are discussed. The modelling of heavy metals adsorption and desorption onto synthetic mineral-organo composites and natural soils and sediments are also critically reviewed. Future challenges and prospects in the mineral-organo interface are outlined. More in-depth investigations are warranted, especially on the function and contribution of microorganisms in the immobilization of heavy metals at the complex mineral-organo interface. It has become imperative to use the state-of-the-art methodologies to characterize the interface and develop in situ analytical techniques in future studies.

Effect of Colloidal Silicate on the Migration Behaviour of Strontium in Groundwater Environment of Geological Disposal Candidate Site

Various colloids are present in the natural groundwater environment, and colloids act on the processes involved when radionuclides leak from a repository in a high-level waste disposal site. This paper investigates the effect of colloidal silicate in natural groundwater environments on the migration behaviour of Sr(II). Three different experimental cases have been designed: (1) effect in the presence of colloidal silicate, (2) effect in the presence of a porous medium, and (3) effect in the presence of both colloidal silicate and porous medium (referred to as CS, PM, and PC, respectively). Batch experiments were used to study the effect of influencing factors on Sr(II) migration behaviour, such as the amount of CS, solid-to-liquid ratio, pH, contact time, and initial concentration of Sr(II). The experiments showed that the effect of PC on the migration behaviour of Sr(II) was greatest, and the presence of CS enhanced the sorption. The colloid amount, pH, and solid-to-liquid ratio significantly affected the migration behaviour. The more the colloids were added, the better the adsorption effect. The optimal pH and solid-to-liquid ratio were 6 and 20 : 1, respectively. The alkaline environment is more conductive to colloid sorption. When the solid-to-liquid ratio was 20 : 1, the sorption percentage of PC is 0.5 times larger than PM. Although the PC has a longer adsorption equilibrium time, the percentage of adsorption can be larger than that in the other two cases. The kinetics and isotherms of Sr(II) were best described by the pseudo-second-order and Langmuir models. It was inferred that strong chemical interactions and/or surface complexation contributed primarily to Sr(II) sorption, and the process was on the monolayer adsorption of the outer surface. These findings provide valuable information for the migration behaviour of strontium in groundwater environments of geological disposal site. At the same time, it provides information for the implementation of permeable reactive barrier technology to control the transport of radioactive Sr(II) and its species in natural surface and groundwater.

Effects of pH Conditions and Application Rates of Commercial Humic Substances on Cu and Zn Mobility in Anthropogenic Mine Soils

We studied the effects of commercial humic substances derived from leonardite at different rates (0, 0.25, 2, 10 g kg−1) and pH (4.5, 6.0, 8.0) on Cu and Zn mobility, to evaluate their use for remediation of metal contaminated mine soils and to optimize their application conditions. We conducted a single-step extraction experiment and analyzed extracts for metal concentrations, soluble organic carbon and their E4/E6 ratio (ratio of absorption at 465 to 665 nm). Metal speciation in a soil solution was simulated by the non-ideal competitive adsorption-Donnan (NICA-Donnan) model. Increasing the amount of humic substances and the pH caused higher release rates of soluble organic carbon with a lower humic/fulvic acids ratio. This led to a higher mobility of metals (up to 110 times Cu concentration in control and 12 times for Zn) due to the formation of soluble metal-humic complexes. Speciation modeling predicted that increasing rates of humic substances would result in a higher proportion of Cu and Zn associated with fulvic acids, more mobile than the humic acids fraction. Application of commercial leonardite humic substances at 2–10 g kg−1 and with pH levels similar to or below natural soil could be useful for assisted-phytoextraction of contaminated anthropogenic soils. High rates of humic substances in more alkaline conditions could entail a considerable risk of metal leaching to groundwater, toxicity and transfer to the trophic chain.

Sorption of copper and norfloxacin onto humic acid: effects of pH, ionic strength, and foreign ions

Copper (Cu) and norfloxacin (Nor) are frequently used as feed additives for animal growth promotion, which results in a great probability of Cu²⁺ and Nor coexisting in animal excretion and in soils. Sorption of Cu²⁺ and Nor on soil organic matter (SOM) can markedly affect their environmental fate. Thus, humic acid (HA), a major fraction of SOM, was chosen to investigate the cosorption behaviors of Cu²⁺ and Nor on HA under different solution chemistry conditions (pHs, ionic strengths, and foreign ions). The addition of Nor decreased the maximum adsorption capacity (Q_m) of Cu²⁺ and an increasing effect was observed with increasing Nor concentration. Meanwhile, the addition of Cu²⁺ also markedly inhibited the sorption of Nor on HA. The Q_m of Cu²⁺ increased with increasing pH from 3.0 to 5.0 whether Nor was present or not, but more addition of Nor led to less increment in Q_m of Cu²⁺ at the same pH. The Q_m of Nor was observed at pH 4.0 without Cu²⁺, but that was found at pH 5.0 and 3.0 with the addition of 20 and 100 mg L^-1 Cu²⁺, respectively. The sorption of Cu²⁺ on HA decreased with increasing ionic strength and followed an order of NaH₂PO₄ > Na₂SO₄ ≈ NaNO₃ at pH 5.0 whether Nor was present or not. Additionally, the higher valence cation had a stronger inhibition effect on Cu²⁺ sorption. The competition between Cu²⁺ and Nor for sorption on HA under the same conditions indicated that the coexistence of Cu²⁺ and Nor may enhance the feasibility of their mobility and environmental risk.

Potentiality of white-rot fungi in biosorption of nickel and cadmium: Modeling optimization and kinetics study

The present study aimed to analyze simultaneous biosorption of Cd⁺² and Ni⁺² by living Phanerochaete chrysosporium as low-cost and eco-friendly biosorbent following optimization by applying a central composite design. The effect of operating parameters such as solution pH (4.0-8.0), temperature (20-40 °C), contact time (3-15 h), initial Cd⁺² and Ni⁺² concentrations (15-35, 5-25 mg L^-1, respectively) was evaluated by response surface methodology (RSM) for optimizing biosorption process. The Cd⁺² and Ni⁺² ions at 25 and 16 mg L^-1 were accumulated in P. chrysosporium with the efficiency of 96.23% and 89.48%, respectively, at pH of 6 and 36 °C after around 9 h under well mixing. The equilibrium data were fitted well with Langmuir isotherm model with maximum biosorption capacity of 71.43 and 46.50 mg g^-1 for Cd⁺² and Ni⁺², respectively. In addition, the pseudo-second order kinetic model could describe the kinetic data adequately. Further, possible interaction pathway among metals and P. chrysosporium functional groups were studied by Fourier transform infrared (FT-IR) spectroscopy. Furthermore, scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) techniques were applied for morphology investigation and semi elemental analysis.

Speciation of Phosphorus Zinc and Copper in Soil and Water-Dispersible Colloid Affected by a Long-Term Application of Swine Manure Compost

The objective of this study was to investigate the concentration and chemical species of Zn, Cu, and P in the bulk soil and water-dispersible colloid (WDC) fraction collected from a field where swine manure (SM) compost has been continually applied for 23 years. A filtration and ultracentrifugation process was used to separate and collect WDC (20-1000 nm) from the soil. The continual application of SM increased soil P from 1.6 to 4.5 g kg^-1, Zn from 109 to 224 mg kg^-1, and Cu from 87 to 95 mg kg^-1 for 23 years. The continual SM compost application also enhanced the formation of soil WDC in which Zn (215 mg kg^-1) and Cu (62 mg kg^-1) were highly accumulated and P (25 g kg^-1) was greater than in the bulk soil. According to the result of X-ray absorption spectroscopy (XAS), the continual application of SM compost increased P associated with Fe hydroxides in the soil and WDC fraction. Iron K-edge XAS revealed the dominance of goethite and ferrihydrite in the WDC fraction, suggesting that P was bound to these (oxy)hydroxides. Copper K-edge XAS determined the dominance of Cu(II) associated with humus in the soil and WDC fraction. For Zn species in the SM-compost-applied soil, hopeite and Zn associated with humus were accumulated in the bulk soil, whereas Zn associated with humus was the primary species in the WDC fraction. Our study suggests that the formation of organic complexes in the WDC fraction could enhance the mobility of Zn and Cu as the repeated application of SM compost continues.

Dissolved organic matter binding with Pb(II) as characterized by differential spectra and 2D UV-FTIR heterospectral correlation analysis

Dissolved organic matter (DOM) in aquatic environment significantly influences the behavior and fate of heavy metals via binding, complexation and thus changes the metal speciation; however detailed interfacial processes and mechanisms are still unclear. Here, differential absorbance and fluorescence spectra and two dimensional UV-FTIR heterospectral correlation analysis were applied to probe into the Pb(II)-DOM interaction at a wide range of pH and ionic strength (IS). The absorbance of DOM molecules under all conditions increased with metal addition, while the different extents of absorbance variations along the wavelength range in the differential zero-order and log-transformed absorbance spectra indicated the site heterogeneity within the DOM pool for metal binding. Spectral parameters, namely differential fluorescent components 1 and 2 (DFC1 and DFC2) and differential slopes of log-transformed absorbance in the range of wavelength 350-400 nm (DSlope_350-400) were found to be highly correlated with the total amounts of DOM-bound Pb(II) predicted by the NICA-Donnan model, while the differential absorbance spectra at 235 nm (DA₂₃₅) was related to the extent of Pb(II) bound by carboxylic groups. Thus, these parameters are an indicator or proxy for the in situ Pb(II)-DOM interaction extent. Aryl C-H gave the fastest response to Pb(II) binding at lower pH and IS (e.g., pH 4.7 and IS = 0.01 M), followed by carboxyl C=O and polysaccharide C-OH and then chromophoric groups at 265 nm (CDOM₂₆₅). However, the CDOM₂₆₅ bound to Pb(II) prior to aryl C-H and polysaccharide C-OH groups at higher pH and IS (6.0 and 0.1 M, respectively), showing that the binding sequences were highly dependent on solution chemistry. Differential spectra combined with two dimensional UV-FTIR heterospectral correlation analysis can be used as a promising approach to elucidate metal-DOM interaction processes, including site heterogeneity, binding sensitivity and sequence at the functional group level.

Synthesis of mesoporous bismuth-impregnated aluminum oxide for arsenic removal: Adsorption mechanism study and application to a lab-scale column

High mobility and toxicity of arsenic [As (III)] limit its removal from an aquatic environment and pose a threat to human health. In this work, batch adsorption experiments were conducted to investigate the adsorption capacity of bismuth-impregnated aluminum oxide (BiAl). Continuous application of As (III) removal was achieved via a lab-scale column reactor. Bismuth impregnation decreased the specific surface area of aluminum oxide and affected its pore size distribution. However, because of its abundant and well-proportioned mesoporous character, it also enhanced its adsorption capacity through the surface complexation of As (III). Batch adsorption experiments demonstrated a suitable Freundlich model and a fitted pseudo-second-kinetic model for As (III) adsorption. The main mechanism was chemisorption with both bismuth and aluminum atoms; however, physisorption also contributed to arsenic adsorption at the initial stage of the reaction. The Adams-Bohart model better described the breakthrough curves than the Thomas model. BiAl exhibited efficient As (III) adsorption over a wide pH range and could be applied to As (III) removal from wastewater. A high As (III) removal efficiency (91.6%) was obtained at an initial As (III) concentration of 5 mg L^-1 at a flow rate of 1 mL min^-1. This study indicates the potential for the practical application of BiAl in As (III) removal.

Nano-cerium oxide functionalized biochar for phosphate retention: preparation, optimization and rice paddy application

In this study, nano-cerium oxide functionalized maize straw biochar (Ce-MSB) was prepared and utilized to remove P from agricultural wastewater. Response Surface Model was applied to optimize the operating conditions. Moreover, Ce-MSB was applied to actual rice paddy column for the first time. Response Surface Model (RSM) showed higher materials ratio had positive effect on PO₄^3- adsorption capacity, while higher pyrolysis temperature had negative effect. The maximum adsorption capacity of Ce-MSB for PO₄^3- was 78 mg g^-1, implying that Ce-MSB was an effective functionalized adsorbent for P removal. Paddy soil column experiment showed that application of Ce-MSB decreased total phosphorus concentration of surface water by 27.33% and increased total phosphors (TP) content of top soil by 7.22%. Further, Ce-MSB tends to increase rice plant height and leaf area. Therefore, Ce-MSB can be used as a promising functionalized biochar to reduce the risk of phosphorus loss from paddy field surface running water.

Reducement of cadmium adsorption on clay minerals by the presence of dissolved organic matter from animal manure

Clay minerals are the most popular adsorbents/amendments for immobilizing heavy metals in contaminated soils, but the dissolved organic matter (DOM) in soil environment would potentially affect the adsorption/immobilization capacity of clay minerals for heavy metals. In this study, the effects of DOM derived from chicken manure (CM) on the adsorption of cadmium (Cd²⁺) on two clay minerals, bentonite and zeolite, were investigated. The equilibrium data for Cd²⁺ sorption in the absence or presence of CM-DOM could be well-fitted to the Langmuir equation (R² > 0.97). The presence of CM-DOM in the aqueous solution was found to greatly reduce the adsorption capacity of both minerals for Cd²⁺, in particular zeolite, and the percentage decreases for Cd²⁺ sorption increased with increasing concentrations of Cd²⁺ as well as CM-DOM in aqueous solutions. The adsorption of CM-DOM on zeolite was greater than that on bentonite in the absence of Cd²⁺, however, a sharp increase was observed for CM-DOM sorption on bentonite with increasing Cd²⁺ concentrations but little change for that on zeolite, which can be attributed to the different ternary structures on mineral surface. The CM-DOM modified clay minerals were utilized to investigate the effect of mineral-adsorbed CM-DOM on Cd²⁺ sorption. The adsorbed form was found to inhibit Cd²⁺ sorption, and further calculation suggested it primarily responsible for the overall decrease in Cd²⁺ sorption on clay minerals in the presence of CM-DOM in aqueous solutions. An investigation for the mineral surface morphology suggested that the mineral-adsorbed CM-DOM decreased Cd²⁺ sorption on bentonite mainly through barrier effect, while in the case of zeolite, it was the combination of active sites occupation and barrier effect. These results can serve as a guide for evaluating the performance of clay minerals in immobilizing heavy metals when animal manure is present in contaminated soils.

Preferable uptake of phosphate by hydrous zirconium oxide nanoparticles embedded in quaternary-ammonium Chinese reed

Phosphate capture from aqueous was conducted using hydrous zirconium oxide (HZO) embedded in quaternary-ammonium Chinese reed (CR-N⁺-HZO), and the characteristics of adsorbent was determined. HZO was dispersed as nanoparticles or nano-clusters on the external or inside the networking pores of CR-N⁺-HZO. The surface of CR-N⁺-HZO was heterogeneous with multiple adsorption sites, HZO nanocomposite and N⁺(CH₂CH₃)₃Cl^-, which both contributed to the adsorption process. The phosphate uptake by CR-N⁺-HZO was optimal at pH 3.0 and phosphate uptake by HZO nanocomposite was greatly inhibited at alkaline pH. Kinetics studies suggested that both the intra-particle mass-transfer and external resistances were likely to be the rate controlling steps. The Q_max (maximum adsorption capacity) of phosphate uptake by CR-N⁺-HZO and CR-N⁺ (30°C) calculated based on Langmuir model was about 59.2mg(P)/g(CR-N⁺-HZO) and 30.4mg(P)/g(CR-N⁺). A high usage efficiency of Zr in CR-N⁺-HZO was observed with calculated molar ratio of P/Zr to be 3.07.

Sorption of vanadium (V) onto natural soil colloids under various solution pH and ionic strength conditions

Batch sorption kinetics and isothermal characteristics of V(V) were investigated on three natural soil colloids (manual loessial soil colloid (MSC), aeolian sandy soil colloid (ASC), and cultivated loessial soil colloid (CSC)) under various solution pH and ionic strength (IS) conditions. Colloids were characterized by atomic force microscopy (AFM), X-ray diffraction (XRD), and fourier transform infrared spectroscopy (FTIR). AFM micrographs showed CSC with an aggregated shape with larger particle diameter as compared with ASC and MSC. XRD spectra revealed the presence of different minerals in natural soil colloids including biotite, kaolinite, calcite and quartz, which might contribute to sorption process. The sorption ability decreased with increase of colloidal particle size. The sorption was mainly attributed to complexation by active carboxylate and alcohol groups of colloidal components. Sorption kinetics and isotherms of V(V) onto natural soil colloids were best fitted with Pseudo-second-order and Freundlich models. Langmuir model indicated that sorption capacity of MSC and ASC was comparable (285.7 and 238.1 mg g^-1); however, CSC exhibited the lowest sorption capacity (41.5 mg g^-1) due to its larger particle diameter and aggregated shape. The maximum V(V) sorption capacity reached plateau values at a solution pH ranged between 5.0 and 9.0 for MSC and ASC, and 6.0-8.0 for CSC. Sorption capacity of V(V) onto natural soil colloids decreased with increasing IS. Based on result of this study we can conclude that sorption of V(V) onto natural soil colloids is pH- and IS-dependent. These findings provide insights on the remediation of vanadium-contaminated soils.

Removal of Ni(II) and Cu(II) from aqueous solutions using 'green' zero-valent iron nanoparticles produced by oak and mulberry leaf extracts

The production of zero-valent iron nanoparticles, using extracts from natural products, represents a green and environmentally friendly method. Synthesis of 'green' zero-valent nanoparticles (nZVI) using oak and mulberry leaf extracts (OL-nZVI and ML-nZVI) proved to be a promising approach for Ni(II) and Cu(II) removal from aqueous solutions. Characterization of the produced green nZVI materials had been conducted previously and confirmed the formation of nanosize zero-valent iron particles within the size range of 10-30 nm, spherical with minimum agglomeration observed by transmission electron microscopy and scanning electron microscope morphology measurements. Batch experiments revealed that the adsorption kinetics followed a pseudo-second-order rate equation. The obtained adsorption isotherm data could be well described by the Freundlich model and OL-nZVI showed higher adsorption capacity for Ni(II) removal than ML-nZVI, while ML-nZVI adsorption capacity was higher for Cu(II). In addition, investigation of the pH effect showed that varying the initial pH value had a great effect on Ni(II) and Cu(II) removal. Adsorbed amounts of Ni(II) and Cu(II) increased with pH increase to pH 7.0 and 8.0. This study indicated that nZVI produced by a low-cost and non-toxic method with oak and mulberry leaf extracts could be used as a new material for remediation of water matrices contaminated with Ni(II) and Cu(II).

Arsenic(V) adsorption-desorption in agricultural and mine soils: Effects of organic matter addition and phosphate competition

High total and bioavailable concentrations of As in soils represent a potential risk for groundwater contamination and entry in the food chain. The use of organic amendments in the remediation of As-contaminated soils has been found to produce distinct effects on the solubility of As in the soil. Therefore, knowledge about As adsorption-desorption processes that govern its solubility in soil is of relevance in order to predict the behaviour of this element during these processes. In this paper, the objective was to determine As adsorption and desorption in four different soils, with and without compost addition, and also in competition with phosphate, through the determination of sorption isotherms. Batch experiments were carried out using three soils affected differently by previous mining activity of the Sierra Minera of La Unión-Cartagena (SE Spain) and an agricultural soil from Segovia province (central Spain). Adsorption was higher in the mining soils (and highest in the acidic one) than in the agricultural soils, although the latter were not affected negatively by organic matter or phosphate competition for sorption sites. The results show that As adsorption in most soils, both with and without compost, fitted better a multimolecular layer model (Freundlich), whereas As adsorption in competition with P fitted a monolayer model (Langmuir). Moreover, the use of compost and phosphate reduced the adsorption of As in the mining soils, while in the agricultural soils compost increased their low adsorption capacity. Therefore, the use of compost can be a good option to favour As immobilisation in soils of low adsorption, but knowledge of the soil composition will be crucial to predict the effects of organic amendments on As solubility in soils and its associated environmental risk.

Effect of pectin on adsorption of Cu(II) by two variable-charge soils from southern China

The influence of pectin on Cu(II) adsorption by two variable-charge soils (an Oxisol and an Ultisol) was investigated. Pectin increased the adsorption, and the extent of adsorption increased linearly with the dose of pectin, being greater in the Oxisol than that in the Ultisol because the adsorption of pectin by the Oxisol was greater. Both Langmuir and Freundlich equations fitted the adsorption isotherms of Cu(II) for both soils well. The fitting parameters of both equations indicated that pectin increased not only the adsorption capacity of the soils for Cu(II) but also the adsorption strength of Cu(II). The effect of pectin decreased with rising pH in the pH range 3.5-6.0, although the extent of electrostatic adsorption of Cu(II) by both soils was markedly greater over the pH range. Fourier-transformed infrared spectroscopy analysis and zeta potential measurement of soil colloids indicated that adsorption of pectin by the soils made the negative charge on both soils more negative, which was responsible for the increase in the electrostatic adsorption of Cu(II) induced by the addition of pectin. In conclusion, pectin-enhanced adsorption of Cu(II) especially at low pH would be beneficial to the soils as it would decrease the activity and mobility of Cu(II) in acidic variable-charge soils.

Extractive and oxidative removal of copper bound to humic acid in soil

Copper (Cu) is often found strongly bound to natural organic matter (NOM) in soil through the formation of strong Cu-NOM complexes. Therefore, in order to successfully remediate Cu-contaminated soils, effective removal of Cu bound to soil organic matter should be considered. In this study, we investigated soil washing methods for Cu removal from a synthetic Cu-contaminated model silica soil coated with humic acid (HA) and from field contaminated soil. Various reagents were studied to extract Cu bound to NOM, which included oxidant (H2O2), base (NaOH), and chelating agents (citric acid and ethylenediaminetetraacetic acid (EDTA)). Among the wash reagents, EDTA extracted Cu most effectively since EDTA formed very strong complexes with Cu, and Cu-HA complexes were transformed into Cu-EDTA complexes. NaOH extracted slightly less Cu compared to EDTA. HA was effectively extracted from the model soil under strongly alkaline conditions with NaOH, which seemed to concurrently release Cu bound to HA. However, chemical oxidation with H2O2 was not effective at destroying Cu-HA complexes. Fourier transform infrared spectroscopy and elemental analysis revealed that chelating agents such as citrate and EDTA were adsorbed onto the model soil via possible complexation between HA and extraction agents. The extraction of Cu from a field contaminated soil sample was effective with chelating agents, while oxidative removal with H2O2 and extractive removal with NaOH separated negligible amounts of Cu from the soil. Based on these results, Cu bound to organic matter in soil could be effectively removed by chelating agents, although remnant agents may remain in the soil.