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The widespread use of ZnO nanoparticles (ZnO-NPs) will inevitably enhance their discharge into soils, leading to serious concerns about their effects on soil microbial functions essential for sustaining environmental health. This study was designed to determine the impacts of different ZnO-NPs concentrations (100 − 1000 mg kg− 1 soil) on soil carbon (C) mineralization kinetics of soil amended with alfalfa hay and wheat straw. The microbial biomass C (MBC), basal respiration (BR), and metabolic quotient (qCO2) were also compared in the contaminated and control soil samples. The results showed that ZnO-NPs influenced the measured C mineralization criteria of the residue-amended soils, such as the total mineralized C and the C mineralization rates. The results of kinetic analysis using the double first-order model revealed that the addition ZnO-NPs increased the amount of C mineralized during the initial fast phase, while it reduced the C mineralization in the subsequent slow phase. The rate constants associated with the fast and the slow C mineralization phases were also differently affected by ZnO-NPs. Furthermore, the soil contaminated with ZnO-NPs had lower MBC and BR values compared to the uncontaminated soil, indicating that the size and activity of the soil microbial community were suppressed by ZnO-NPs. The qCO2 value increased in the ZnO-NPs contaminated soils, suggesting that the soil microbial community was subjected to toxicity stress by ZnO-NPs. In conclusion, ZnO-NPs can drastically influence the microbial abundance, maintenance energy demand, and C mineralization process in plant residue-amended calcareous soils.

Phosphate fixation is a main factor limiting phosphate availability and reducing crop production in acidic soils. Although biochar addition has been suggested as a means of ameliorating acidic soil...

Enzymes adsorbed on clay minerals and soil colloids may exhibit lower activities compared to those of free enzymes. A particular toxic metal may affect the activity of the adsorbed enzyme less critically than that of the free form, however. This information is necessary for predicting catalytic performances of clay-immobilized enzymes in natural soils as well as in food, pharmaceutical, and chemical systems. The objective of the present study was to find out how adsorption on palygorskite and sepiolite minerals modifies the catalytic activity and the Michaelis–Menten kinetics of alkaline phosphatase (ALP). Inhibition kinetics of adsorbed ALP by Cd was also compared to that of the free enzyme. The results revealed that the affinity to the substrate and the maximum reaction velocity of ALP decreased upon adsorption on the fibrous clay minerals. The ALP adsorbed maintained a reasonably high activity recovery (AR) compared to the free enzyme. The AR of the adsorbed ALP ranged from 76.9 to 92.5% for palygorskite and from 71.2 to 90.2% for sepiolite, depending on the substrate concentration applied. The presence of Cd decreased the affinity to the substrate of both the free and the adsorbed ALP, while the maximum reaction velocity remained nearly unchanged, indicating that the inhibitory effects of Cd on both the free and adsorbed ALP activities were competitive in nature. The adsorbed enzyme, however, was inhibited less severely by Cd compared to the free enzyme. The adsorption of ALP on the fibrous clay minerals, therefore, maintains the ALP activity to a great extent and provides more resistance for the enzyme against the inhibitory effects of Cd.

Chelant-assisted phytoextraction has widely been exploited as a feasible option for removing heavy metals from the contaminated soils. Some synthetic chelants have shown promising performances for this option, but they have also revealed several negative environmental consequences. This study has sought to investigate the feasibility of two biodegradable eco-friendly chelants, namely methylglycinediacetic acid (MGDA) and N,N-Bis(carboxymethyl)-L-glutamic acid (GLDA), as compared to the resistant ethylenediaminetetraacetic acid (EDTA), in enhancing phytoextraction of Zn and Pb from a contaminated calcareous soil. For this purpose, a greenhouse experiment was carried out comparing the growth and metal absorption of maize (Zea mays L.) grown on soils treated with EDTA, MGDA, and GLDA chelants at 2, 4 and 8 mmol kg(− 1) levels. Results showed that the heavy metal uptakes by the plant shoots generally increased with increasing the chelant application level. Pb uptake by maize shoots increased from 10.6 mg plant(− 1) in control to 416, 398, and 416 mg plant(− 1) in the soils treated with 8 mmol kg(− 1) MGDA, GLDA, and EDTA, respectively. The corresponding increases in Zn uptake were from 100.9 mg plant(− 1) to 798.9, 718.9, and 530.4 mg plant(− 1) in the MGDA-, GLDA-, and EDTA-amended soils, respectively. Moreover, the amounts of water-extractable, and thereby potentially leachable, Pb and Zn in the post-harvest soil were considerably greater in the soil treated with EDTA than those treated with MGDA and GLDA. Therefore, MGDA and GLDA would be potential alternatives to environmentally-persistent EDTA for enhanced metal phytoextraction from contaminated soils.

Application of alkaline biochar has been proposed as an alternative to lime for remediation of acidic soils. However, questions remain as to how the reactions and fate of metals in acidic soils can...

Study of Pb desorption processes from clay minerals by chelating ligands is crucial to better understand the fate and transport of Pb in soil and sediment environments. In this study, Pb desorption from a Pb-loaded montmorillonite (MMT) was studied as affected by ethylenediaminetetraacetic acid (EDTA) and its two alternative eco-friendly chelating agents, i.e., methylglycine diacetic acid (MGDA) and glutamic-N,N-diacetic acid (GLDA) at two concentrations of 0.25 and 1.0 mM. The impacts of a 30-day residence time on the rate and quantity of Pb desorption were also evaluated. The result showed that Pb desorption kinetics was biphasic with an initial rapid phase, lasting for about 3 h, followed by a slow phase, lasting to 12 h. The degree of Pb desorption from Ca-MMT was proven to be governed by the nature and concentration of the chelating ligands presented in the systems. The capacity of the ligands to desorb Pb from Ca-MMT was in the order EDTA > > MGDA > GLDA, according to the decreasing order in the stability constants of their complexes with Pb ions. The aging of the MMT systems caused a significant reduction in both Pb desorption quantity and rate parameters. The results suggest that EDTA would have a more serious Pb-mobilizing impact than GLDA and MGDA in contaminated soil and sediments which contain Ca-MMT as a major clay constituent.

In this study, the removal of 17 selected PCBi congeners was assessed in a transformer oil-contaminated soil amended with bentonite clay powder applied at the three levels of 0, 2, and 4% a...

The present study was conducted to screen bacterial strains most effective in increasing alfalfa growth and metal accumulation in the presence of toxic levels of lead (Pb) and zinc (Zn). Results show that, compared to root and shoot growth, alfalfa seed germination is less sensitive to high levels of Pb and Zn. Pb and Zn concentrations of 4.4 and 7.9 mM, respectively, were required to give rise to a 50% reduction in in vitro seed germination. Root growth in alfalfa seedlings is, however, completely suppressed at a Pb concentration of 4 mM or a Zn concentration of 6 mM in the agar plate medium. Inoculation of the bacterial strains capable of producing indole-acetic acid and siderophore positively affected the plant growth parameter in the metal contaminated mediums. Root and/or shoot growths of alfalfa seedlings are significantly stimulated by the seven inoculated bacterial strains investigated, among which Bacillus filamentosus YSP110 is found to be the most effective. Inoculation of alfalfa plants with B. filamentosus strain YSP110 grown in a vermiculate medium is also seen to increase Pb accumulation in plant root and shoot by 18.0 and 72.4%, respectively. Bacillus cereus YSP4 is the bacterial strain most effective in stimulating root and shoot growth in alfalfa seedlings cultured in a Zn-contaminated medium. Compared to the non-inoculated plants, alfalfa seeds inoculated with B. cereus YSP4 also exhibit increased Zn accumulation in their roots and shoots by 43.2 and 48.7%, respectively. Results suggest that B. filamentosus YSP110 and B. cereus YSP4 offer a great potential for promoting plant growth and metal accumulation, which makes them good candidates for microbe-assisted phytoextraction of metal-contaminated soils.

Long-term use of treated wastewaters for irrigation adds compounds and/or ions to soils which might alter the soil physical, hydraulic and mechanical properties. Soil mechanical properties are closely linked with the plant growth. This study was conducted to investigate the effect of short-, mid- and long-term applications of the treated wastewater of Mobarake Steel Company in Isfahan on the soil penetration resistance and shear strength in the company green space. Soil penetration resistance and shear strength were measured using a pocket penetrometer and in situ shear box, respectively. The results showed that soil penetration resistance (i.e. soil hardness) at both dry and wet conditions significantly was increased upon short-, mid- and long-term applications of wastewater; 19 years of the application of wastewater resulted in the highest soil penetration resistance at wet condition, but the well water did not significantly affect it. Surface crust in the non-irrigated locations increased the soil penetration resistance, but the irrigated sealed soils were not significantly different from the virgin soil in terms of dry and wet penetration resistances. For the soil shear strength parameters, wastewater, well water and surface crust did not significantly affect soil cohesion (c), they but significantly affected the angle of internal friction (φ). Overall, soil shear strength parameters were not greatly affected by the irrigation water treatments because of the dominant effect of the soil fractions (texture and gravel content) and the microstructure.

Recently, the life span of electric and electronic products is becoming shorter and shorter because of the rapid technology innovation and the rising standard of consuming. This also leads to a stable annual increase of waste electric and electronic equipment (WEEE). Waste printed circuit boards, the base of almost all WEEE, are always the core of WEEE recycling. However, few studies are focused on the recovery of WPCBs electronic components. Here, in this study, CPU sockets were chosen as a representative electronic component to explore if slurry electrolysis can directly and simultaneously recycle copper and gold. Four factors, HCl concentration, pulp density, current density and reaction time, were discussed in detail. The results show that copper recovery rate first increases and decreases with the rise of HCl concentration, pulp density and reaction time, and it increases with the increase current density. Copper recovery rate and purity is up to 96.67% and 98.16% respectively at the optimum conditions (4 mol/L HCl, 75 g/L pulp density, 80 mA/cm2 and 4 h). One third of copper can be electrodeposited to the cathode plate, and be collected directly. 67% copper still exit in the electrolyte, which needs to be further recycled, and less than 1% copper are in the anode residue. Gold recovery rate first increases and then decreases with the rise of the four factors, reaching to the highest value of 95.73% (4 mol/L HCl, 100 g/L pulp density, 70 mA/cm2 current density and 4 h). Gold mainly exits in the electrolyte, and little gold can be electrodeposited. Besides, the results of XRD and SEM show that the obtained metal powder is mainly copper and copper powder particles are mainly dendritic. On the basis of these results, slurry electrolysis could be applied to the recovery of copper and gold from electronic component.

The aim of this study was to isolate and characterize lead (Pb)-solubilizing bacteria from heavy metal-contaminated mine soils and to evaluate their inoculation effects on the growth and Pb absorption of Brassica juncea. The isolates were also evaluated for their plant growth-promoting characteristics as well as heavy metal and salt tolerance. A total of 171 Pb-tolerant isolates were identified, of which only 15 bacterial strains were able to produce clear haloes in solid medium containing PbO or PbCO3, indicating Pb solubilization. All of these 15 strains were also able to dissolve the Pb minerals in a liquid medium, which was accompanied by significant decreases in pH values of the medium. Based on 16S rRNA gene sequence analysis, the Pb-solubilizing strains belonged to genera Bacillus, Paenibacillus, Brevibacterium, and Staphylococcus. A majority of the Pb-solubilizing strains were able to produce indole acetic acid and siderophores to different extents. Two of the Pb-solubilizing isolates were able to solubilize inorganic phosphate as well. Some of the strains displayed tolerance to different heavy metals and to salt stress and were able to grow in a wide pH range. Inoculation with two selected Pb-solubilizing and plant growth-promoting strains, (i.e., Brevibacterium frigoritolerans YSP40 and Bacillus paralicheniformis YSP151) and their consortium enhanced the growth and Pb uptake of B. juncea plants grown in a metal-contaminated soil. The bacterial strains isolated in this study are promising candidates to develop novel microbe-assisted phytoremediation strategies for metal-contaminated soils.

Plant-based methods such as rhizodegradation are very promising for the remediation of petroleum-contaminated soils. Associations of plants with endophytes can further enhance their phytoremediation potential. In this study, a rhizobox experiment was conducted to investigate whether inoculation with the root-colonizing fungus Piriformospora indica could further enhance the degradation of petroleum hydrocarbons in the root zone of maize (Zea mays L.). The rhizoboxes were subdivided into compartments in accordance with distance from the plants. After filling the boxes with soil from a petroleum-contaminated site, seedlings that had either been inoculated with P. indica or not were grown in the middle compartments of the rhizoboxes and grown for 64 days. A plant-free treatment was included for control. The presence of roots strongly increased the counts of total and petroleum-degrading soil bacteria, respiration, dehydrogenase activity, water-soluble phenols and petroleum degradation. All these effec...

We explore changes in magnetic susceptibility (χlf), and various forms of Fe and ferrimagnetic minerals after incubation by crude oil in four different textural soils. Four soil classes: clay, sandy, silt loam and sandy loam, were collected in central Iran and incubated with 0, 2.5, 5.0, 7.5 and 10% w/w of crude oil at 80% moisture of field capacity for 1, 3 and 6 months. After each period of incubation, various forms of Fe using extraction techniques, χlf and total petroleum hydrocarbon (TPH) were measured. In addition selected samples from the four soil types were analyzed by XRD for characterization of ferrimagnetic minerals. The results showed that all forms of iron and magnetic susceptibility increased significantly with increasing concentration of crude oil and incubation time. The highest dithionite extractable iron (Fed), χlf, as well as the ratio of Fed to oxalate extractable iron (Feo) were obtained for 10% w/w crude oil after 6 months incubation due to formation of ferrimagnetic minerals. The increase in the concertation of ferrimagnetic minerals (magnetite/maghemite) was verified by XRD. Significant positive correlations were obtained among χlf, Fed and TPH after 6 months of incubation. The results from this study confirm that magnetic methods can be used as a quick and cost-effective means for evaluation of TPH in polluted soils during the remediation, as compared to the chemical analyses.

Adhesion of bacteria to clay minerals is of great importance in both natural soil environments and technological applications. In the present study, equilibrium experiments along with Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and energy-dispersive X-ray analysis (EDX) were used to investigate the adhesion of Pseudomonas putida to the palygorskite and sepiolite clay minerals. The results showed that bacterial adhesion was rapid and reached equilibrium within 30 min. Equilibrium data showed that sepiolite has higher capacity and affinity than palygorskite for P. putida retention. Mixed FT-IR peak features of the clay minerals and P. putida were observed in the clay–bacteria complex spectra, indicating significant adhesion of P. putida to the minerals. However, some differences in the position of the individual bands were observed between infrared spectra obtained for pure bacteria or clay minerals and their corresponding clay–bacteria complexes, which are b...

The extensive use of silver nanoparticles (AgNPs) in consumer and medical products leads inevitably to release of such particles into environment and soil resources. This study was conducted to provide evidences for biological effects of AgNPs in two calcareous soils with different textures and salinity levels. Basal respiration (BR) and substrate-induced respiration (SIR), as indicators of soil microbial activity and biomass, respectively, were determined in the calcareous soils spiked with a dilution series of AgNPs and AgNO3. Urease and alkaline phosphatase activities were also measured in the spiked and control soils. Finally, dose–response approach was used to model the sensitivity of the soil biological properties to AgNPs and AgNO3 contamination. The results revealed that the effects of AgNPs and AgNO3 on the soil respiration and enzyme activities depended on Ag dose and soil type. For instance, soil respiration was not affected or even stimulated by low doses of AgNPs and AgNO3, but negatively affected by high doses (> 20 mg Ag kg− 1). Soil urease and phosphatase activities were generally inhibited in the presence of AgNPs and AgNO3, though in low Ag concentrations there was no inhibition or even stimulation. Generally, the ecological dose (ED) values of AgNPs were smaller than those of AgNO3, suggesting that AgNPs have more negative effects than AgNO3 on the soil microbial and enzyme activities, at the same level of Ag dose. The results also revealed that suppression of microbial and enzyme activities by AgNPs and Ag ions are greater in the soil with lower clay content and ionic strength.

In this study, the effects of the new biodegradable chelating ligands, i.e., methylglycinediacetic acid (MGDA) and L-glutamic acid-N,N-diacetic acid (GLDA), were compared with that of ethylenediaminetetraacetic acid (EDTA) on lead (Pb) sorption by montmorillonite (MMT) at equimolar Pb:ligand ratios. The results of PHREEQC simulations indicated that Pb was predominantly present in the form of negatively-charged chelates with significantly different sorption behaviors compared to that of the Pb2+ cations. The time-dependent sorption of the Pb species on MMT was biphasic, with an initial fast phase occurring within 3 h followed by a slower one reaching equilibrium after approximately 12 h. The analysis of equilibrium data revealed that both capacity and affinity of MMT for Pb sorption were decreased in the presence of the chelating ligands. The moderating potential of ligands on Pb sorption decreased in the order of EDTA ≫ MGDA > GLDA in accordance with complex stability constants. The FE-SEM/EDX, ATR-FTIR, and XRD evidence indicated that Pb and Pb complexes were adsorbed, most likely through physical forces, on both external planar and edge surfaces of the MMT. In conclusion, GLDA and MGDA represented lower ability than EDTA to depress Pb2+ adsorption on MMT, and hence, lower potential to mobilize Pb in soils and sediments where MMT is an important mineral sorbent.

Nowadays through the world as well as in Iran, petroleum hydrocarbons have majority contribution in environmental ricks for human and other organisms. Therefore, this study evaluates hydrocarbon pollution effects on soil chemical properties, as well as soil magnetic susceptibility on a petroleum refinery compound in Isfahan province, Iran. It also examines the efficacy of using magnetic signatures to predict hydrocarbon pollution of soils. Two sites (polluted and unpolluted) with similar intrinsic soil properties and environmental attributes were selected. A total of 120 soil samples were collected at two depths of 0–10 and 10–30 cm. Laboratory analysis included measurement of electrical conductivity (EC), pH, aqua regial extractable Fe (FeA), dithionite extractable Fe (Fed), magnetic susceptibility at low frequency (χlf), total petroleum hydrocarbon (TPH), as well as powdery X-ray characterization. Polluted soils by petroleum hydrocarbons had significantly higher EC, χlf, FeA and Fed and lower pH values compared to the unpolluted soils. Positive significance (r = 0.88, p

Growing production of manufactured nanomaterials has increased the possibility of contamination of groundwater resources and soils by nanoparticles (NPs). It is crucial to study the fate of NPs in subsurface porous media in order to evaluate and control their risks to ecosystems and human health. Hence, this study was conducted to investigate the transport and retention of polyvinylpyrrolidone (PVP) stabilized silver nanoparticles (AgNPs, a diameter of 40 nm) under saturated and unsaturated conditions in intact columns of two calcareous sandy loam (TR) and loam (ZR) soils. Furthermore, similar experiments were conducted using sand quartz as a reference medium. A pulse of the AgNP suspension with an input concentration (C0) of 50 mg L−1 was injected into the columns for 3 pore volumes. The transport of bromide (Br), as a non-reactive inert tracer, was also examined. High mobility of AgNPs was observed through the sand columns due to unfavorable conditions for AgNP deposition on the quartz sand surfaces. Nearly all AgNPs introduced into the columns of both soils were retained in the soil. Percentages of AgNPs leached out of the columns were

The aim of this study was to isolate and characterize lead (Pb)-solubilizing bacteria from heavy metal-contaminated mine soils and to evaluate their inoculation effects on the growth and Pb absorption of

This study was carried out to assess the dissipation of 17 selected polychlorinated biphenyl (PCBi) congeners in a transformer oil-contaminated soil using bioaugmentation with 2 PCB-degrading bacterial strains, i.e., Pseudomonas spp. S5 and Alcaligenes faecalis, assisted or not by the maize (Zea mays L.) plantation. After 5 and 10 weeks of treatment, the remaining concentrations of the target PCBi congeners in the soil were extracted and measured using GC-MS. Results showed that the bacterial augmentation treatments with Pseudomonas spp. S5 and A. faecalis led to 21.4% and 20.4% reduction in the total concentration of the target PCBs (ΣPCBi), respectively, compared to non-bioaugmented unplanted control soil. The ΣPCBi decreased by 35.8% in the non-bioaugmented planted soil compared with the control. The greatest degradation of the PCB congeners was observed over a 10-week period in the soil inoculated with Pseudomonas spp. S5 and cultivated with maize. Under this treatment, the ΣPCBi decreased fro...

A rhizobox experiment was conducted to study the effects of alfalfa green manure (GM) and the culture system on the dry matter yield and metal uptake in corn (Zea mays) and canola (Brassica napus) grown in rhizobox systems containing a metal-rich agricultural soil. The results showed that GM application increased soil organic matter (SOM), dissolved organic carbon (DOC), and electrical conductivity (EC) by 41%, 82%, and 35%, respectively, while the soil pH decreased by ~0.3 units. These changes were associated with enhanced soil bioavailability of Zn (14%), Cu (26%), and Ni (20%) and improved shoot dry matter yield of the plants. Soil metal bioavailability was also found to be enhanced due to the presence of plant roots. Canola intercropped with corn produced greater individual plant dry weights (IPDWs) of 96% and 59% in the untreated and GM-amended rhizoboxes, respectively. The intercropped corn, however, recorded 25% and 6.4% lower IPDW values in unamended and GM-amended soils, respectively, as ...

The environmental mobility and bioavailability of heavy metals in soil are greatly influenced by sorption reactions on soil minerals, which are, in turn, controlled by the presence of various organic ligands, such as amino acids, in soil solution. In this study, the effects of l -cysteine (Cys) and l -histidine (His) amino acids on lead (Pb) sorption by palygorskite and sepiolite, as the specific silicate clay minerals of arid and semiarid soils, were studied using the batch method. Experimental Pb sorption data were subsequently analyzed by various isothermal and kinetic models. The equilibrium data revealed that both Langmuir and Freundlich models can describe the Pb sorption on palygorskite and sepiolite minerals. The sorption capacities of the minerals for Pb were decreased in the presence of Cys, probably because of the formation of neutral stable complexes of Pb and Cys as [ML] in the solution. The His effects, however, were different for the two minerals. Histidine reduced the Pb sorption capacity of sepiolite, but its diminishing effect was much lower than that of Cys. This result may be because of the formation of cationic soluble His–Pb complexes as [ML 2 H] + , which can be slightly adsorbed by the clay surfaces via electrostatic attraction. l -Histidine increased the sorption of Pb by palygorskite, probably due to formation of highly charged complexes with Pb, in the form of [ML 2 H 2 ] 2+ and [ML 2 H 3 ] 3+ , or ternary surface complexation processes. The kinetics of Pb sorption by the minerals were satisfactorily described by the power, pseudo-first order, pseudo-second order and parabolic diffusion equations, among which the power function provided the best fit. The kinetics of Pb sorption by the palygorskite was rapid, approaching equilibrium within 10 h. Lead sorption on the sepiolite, however, was much slower and equilibrium condition was attained after 10 h. The Pb sorption rate indices, such as the initial sorption rate and diffusion rate constant, were also considerably affected by the presence of amino acids. These findings emphasize the importance of amino acids in evaluating the fate of Pb in arid soils in which fibrous silicate clay minerals are dominated in the clay fraction.

In this work, the effect of raw and modified bentonite and zeolite with trivalent iron on the stabilization of watersoluble and adsorbed arsenic in a calcareous soil was studied. Raw and modified bentonite and zeolite were added to the soil in different weights in a completely randomized block design with three replications and kept to field capacity soil moisture content of 80% for 8 weeks. The concentrations of water-soluble and adsorbed arsenic, water-soluble and absorbed phosphorus in soil and soil pH were measured. Treatments significantly affected the mobility of arsenic and phosphorus in soil. Raw zeolite and bentonite in different levels increased arsenic mobility (about 107 to 325 % and 259 to 350% respectively). Despite the change in surface properties of zeolites modified with iron, this treatment at different levels increased arsenic mobility in soils by about 124 to 246%. Bentonite modified with iron had the greatest effect on reducing arsenic mobility in soil (about 91%). Phosphate mobility was similar to arsenic in different treatments. Keyword: Mobility, Arsenic, Zeolite, Bentonite, Iron. 1. Dept. of Soil Sci. Isf. Univ. of Technol., Isfahan, Iran. *:Corresponding Author, Email: shahmoradi6836@yahoo.com

Knowing thermodynamic features of sorption/desorption of metals to/from soil minerals is a very efficient tool to assess and control the fate of these chemicals in the environment. In this batch experiment, we assessed the sorption of nickel (Ni) onto palygorskite and sepiolite at temperatures of 25, 35 and 45 °C. Nickel sorption onto both minerals at the three temperatures was adequately described by the Langmuir sorption model (R 2 > 0.97 for palygorskite and R 2 > 0.84 for sepiolite). Increasing the temperature from 25 to 45 °C caused an increase in both the maximum adsorption capacity of the solid phase ( q m ) and the Langmuir sorption coefficient ( K L ), indicating the enhanced sorption potential and stronger bonding of Ni to the minerals. Positive values of enthalpy (Δ H ) revealed the endothermic nature of Ni sorption and negative free energy Δ G ° indicated that sorption of Ni to palygorskite and sepiolite under standard conditions (25 °C) is spontaneous. Time-dependent sorption data at the three temperatures were adequately described by the first order kinetic model (R 2 > 0.93 for both minerals). The rate constant of the reaction and the quantity of Ni sorbed on both minerals at equilibrium increased with increasing temperature. However, the lower activation energy ( E a ) for sepiolite compared with palygorskite indicated that Ni was more readily sorbed onto sepiolite.

Sorption using natural materials such as clay minerals is generally regarded as a suitable method for wastewater treatment. Equilibrium nickel (Ni) sorption on Ca-bentonite was determined in solutions with initial Ni concentrations ranging from 0–100 mg L−1. The effect of contact time and temperature on Ni sorption was also investigated. The equilibrium capacity of the bentonite for Ni removal was 2.93, 3.91, and 6.00 mg g−1 at 278, 298, and 318 K, respectively, showing sorption enhancement with rising temperature. The results obtained from the kinetic tests indicated that major Ni removal occurred within the first 2 h, but the equilibrium condition was not attained before 24 h. Negative changes in Gibbs free energy (ΔG°) of sorption indicated that Ni sorption on Ca-bentonite was a spontaneous reaction. The positive values of both ΔH° and ΔS° suggest the endothermic nature of the Ni sorption and increased randomness at the solid–solution interface during the Ni chemisorption on the Ca-bentonite, r...

To investigate the effects of single and mixed cultures of maize and canola, green manure addition, and distance from the rhizosphere on chemical forms of soil lead (Pb) and its uptake by plants, a greenhouse experiment was conducted using rhizobox systems. After plant harvest, the soils from different parts of the rhizoboxes were sampled and analyzed for dissolved organic carbon (DOC) concentrations and pH values. A sequential extraction procedure was also carried out to differentiate the chemical forms of Pb in the soil samples. Results showed that root activity significantly affected soil DOC concentration, pH and Pb chemical forms, while the effects generally ceased from the rhizosphere through the bulk soil. The pH value increased and DOC concentration decreased with distance from the roots. Green manure addition enhanced DOC concentration and exchangeable, carbonate-associated, and organic matter-bound Pb fractions. Green manure addition reduced the Pb concentration and uptake of maize but increased...

In this study, a novel N-cetylpyridinium (NCP)-modified sepiolite with the potential for the removal of organic contaminants from aqueous media was synthesized and the adsorptive removal of 2,4-D (2,4-Dichlorophenoxy acetic acid) herbicide by the natural and NCP-modified sepiolites was investigated. Maximum adsorption capacity of sepiolite for NCP surfactant was 240 mmol/kg, that is so much higher than the clay CEC. Fourier transformed infrared (FT-IR) spectroscopic studies revealed changes of sepiolite surface properties when this mineral was loaded with NCP, equal to the maximum adsorption capacity of the clay; however, X-ray diffraction (XRD) analysis and Scanning Electron Microscopy (SEM) showed almost no structural or morphological changes after NCP adsorption. The clay surface modification significantly improved 2,4-D removal from water. Sepiolite adsorption capacity for 2,4-D was increased with enhancing the surfactant loading, which was exceeded to the clay CEC. Therefore, the NCP-sepiolite could be efficiently applied for eliminating 2,4-D from polluted waters.

Clay minerals have obtained considerable attention for slow-release formulation of herbicides to increase weed control efficacy and reduce leaching potential and environmental pollution. This study deals with preparing, characterizing and examining the potentials of modified bentonite and zeoilite in adsorption and release of 2,4-dichlorophenoxyacetic acid (2,4-D) herbicide. 2,4-D sorption of the N-cetylpyridinium (NCP)-modified bentonites and zeolites were much higher than those of unmodified substrates. The 2,4-D adsorption capacity of the organo-minerals increased with increasing surfactant loading. Desorption isotherms of 2,4-D did not coincide their corresponding sorption isotherms showing hysteresis. The proportion of 2,4-D released from the organo-minerals after seven desorption cycles varied between 29% and 50% of the total retained herbicide. The sorbed 2,4-D on the adsorbents showed gradual release pattern with time. The release pattern of 2,4-D from NCP-modified bentonite and zeolite, make these synthetic organo-minerals suitable candidate for slow release formulation of 2,4-D.

The fate of heavy metals in the environment is largely controlled by sorption reactions. In the current study, sorption of Ni, Cd, Zn and Cu to distinctive silicate clay minerals that occur primarily in arid and semiarid regions, namely palygorskite and sepiolite, was assessed in multi-metal batch experiments. The results confirmed that competitive sorption pattern of Ni, Cd, Zn and Cu on the minerals varies with mineral type and the metal concentrations of the solution. Sorption of all four metals on palygorskite increased with increasing of metal concentrations in solution from 0 to 100 mg L − 1 . The sequence of sorption maxima on palygorskite was Cu > Zn > Cd > Ni. In the case of sepiolite, sorption isotherms of Zn, Cd and Ni showed an initial increase, up to metal concentrations of about 10 mg L − 1 , but declined significantly afterward in the presence of increasing Cu concentration. Overall, Cu and Ni were the most and the least preferentially retained metals, respectively, by both palygorskite and sepiolite minerals.

The rapid production and application of silver nanoparticles (AgNPs) have led to significant release of AgNPs into the terrestrial environments. Once released into the soil, AgNPs could enter into different interactions with soil particles which play key roles in controlling the fate and transport of these nanoparticles. In spite of that, experimental studies on the retention of AgNPs in soils are very scarce. Hence, the key objective of this research was to find out the retention behavior of AgNPs and Ag(I) ions in a range of calcareous soils. A second objective was to determine the extent to which the physico-chemical properties of the soils influence the Ag retention parameters. To this end, isothermal batch experiments were used to determine the retention of Poly(vinylpyrrolidinone)-capped AgNPs (PVP-AgNPs) and Ag(I) ions by nine calcareous soils with a diversity of physico-chemical properties. The results revealed that the retention data for both PVP-AgNPs and Ag(I) ions were well described by the classical Freundlich and Langmuir isothermal equations. The retention of PVP-AgNPs and Ag(I) ions was positively correlated to clay and organic carbon (OC) contents as well as electrical conductivity (EC), pH, and cation exchange capacity (CEC) of the soils. Due to multicolinearity among the soil properties, principal component analysis (PCA) was used to group the soil properties which affect the retention of PVP-AgNPs and Ag(I) ions. Accordingly, we identified two groups of soil properties controlling retention of PVP-AgNPs and Ag(I) ions in the calcareous soils. The first group comprised soil solid phase parameters like clay, OC, and CEC, which generally control hetero-aggregation and adsorption reactions and the second group included soil solution variables such as EC and pH as well as Cl- and Ca2+ concentrations, which are supposed to mainly affect homo-aggregation and precipitation reactions.

We synthesized a novel poly acrylic acid–organobentonite (PAA–Bent) nanocomposite by successive intercalation of cetyltrimethylammonium (CTA) surfactant and polyacrylic acid (PAA) into the bentonite (Bent) interlayer spaces. The surfactant-modified clay (CTA–Bent) and PAA–Bent nanocomposite were characterized by XRD and FT-IR techniques and used for removal of Pb(II) from aqueous solution. The XRD results confirmed the intercalation of CTA and PAA into the interlayer spaces of the bentonite increasing the d 001 spacing of the clay from 12.2 up to 38.9 A. FT-IR analysis of the modified clay samples revealed the functional groups of CTA and PAA constituents alighted on the bentonite surfaces. Maximum Pb sorption capacity of the Bent and PAA–Bent predicted by Langmuir model were 52.3 and 93.0 mg g−1, respectively, showing that the synthesized nanocomposite superiorly adsorbed Pb from the solution as compared to the Bent. The maximum Pb removal efficiency of 99.6 % was achieved by the nanocomposite at 25 °C with