Desorption Of Zn Research Articles

Integrating HYDRUS-2D and Bayesian Networks for simulating long-term sludge land application: Uncovering heavy metal mobility and pollution risk in the soil-groundwater environment

The release of sludge-derived heavy metals (HMs) to soil and their subsequent migration into groundwater poses a significant challenge for safe and low-carbon sludge land application. This study developed a predictive framework to simulate 60-year sludge land application, evaluating the risk of HMs pollution in the soil-groundwater environment and assessing the influence of soil and water properties. HYDRUS-2D simulations revealed that highly mobile Cu, Ni, and Zn penetrated a 10 m soil layer over a 60-year period, contributing to groundwater pollution. In contrast, Cr was easily sequestered within the topsoil layer after 5-years continuous operation. The non-equilibrium parameter α could serve as an indicator for assessing their potential risk. Furthermore, the limited soil adsorption sites for Pb (f = 0.02772) led to short-term (1-year) groundwater pollution at a 0.5 m-depth. Bayesian Networks model outcomes indicated that humic-like organics crucially influenced HMs transformation, enhancing the desorption of Cd, Cu, Ni, Pb, and Zn, while inhibiting the desorption for Cr. Additionally, electrical conductivity promoted the release of most HMs, in contrast to the Mn mineralogy in soil. This study bridges the gap between the macro-level HMs migration trends and the micro-level adsorption-desorption characteristics, providing guidance for the safe land application of sewage sludge. Environmental ImplicationThis study introduces a framework integrating HYDRUS-2D simulations with Bayesian Networks to assess the risks of groundwater pollution by heavy metals (HMs) over a 60-year sludge application. Sludge-derived Cu, Ni, and Zn are found to penetrate soil up to 10 m and exceed safety limits, with the non-equilibrium parameter α serving as an indicator for pollution risk. The importance of nutrients from sludge-amended soil for the transformation of HMs in the subsurface environment highlights the need for enhanced sludge management, specifically through more detailed regulation of nutrient composition. These findings contribute to developing precise strategies for the long-term sludge land application.

Effect of long-term dry-wet circulations on the Solidification/stabilization of Municipal solid waste incineration fly ash using a novel cementitious material.

Solidification/stabilization (S/S) is a typical technique to immobilize toxic heavy metals in Municipal solid waste incineration fly ash (MSWI FA). This study utilized blast furnace slag, steel slag, desulfurization gypsum, and phosphoric acid sludge to develop a novel metallurgical slag based cementing material (MSCM). Its S/S effects of MSWI FA and long-term S/S effectiveness under dry-wet circulations (DWC) were evaluated and compared with ordinary Portland cement (OPC). The MSCM-FA block with 25 wt.% MSCM content achieved 28-day compressive strength of 9.38MPa, indicating its high hydration reactivity. The leaching concentrations of Pb, Zn and Cd were just 51.4, 1895.8 and 36.1 μg/L, respectively, well below the limit standard of Municipal solid wastes in China (GB 16889-2008). After 30 times' DWC, leaching concentrations of Pb, Zn and Cd for MSCM-FA blocks increased up to 130.7, 9107.4 and 156.8 μg/L, respectively, but considerably lower than those for OPC-FA blocks (689, 11,870.6 and 185.2 μg/L, respectively). The XRD and chemical speciation analysis revealed the desorption of Pb, Zn and Cd attached to surface of C-S-H crystalline structure during the DWC. The XPS and SEM-EDS analysis confirmed the formation of Pb-O-Si and Zn-O-Si bonds via isomorphous replacement of C-A-S-H in binder-FA blocks. Ettringite crystalline structure in OPC-FA block was severely destructed during the DWC, resulting in the reduced contents of PbSO4 and CaZn2Si2O7·H2O and the higher leachability of Pb2+ and Zn2+.

Desorption kinetic and sequential extraction of Pb and Zn in a contaminated soil amended with phosphate, lime, biochar, and biosolids.

The mining and metallurgical industry sector activities often release potential toxic elements (PTE) surrounding exploitation area. We evaluated the addition of phosphate and lime using the dosage of 0.5:1, 1:1, and 2:1 molar ratio of PO43- and CO32- to the sum of PTE, respectively, and also, biochar and biosolids using the dosage of 2.5, 5, and 10% (m:m) to immobilize PTE in contaminated forest soil (Pb (270mgkg-1) and Zn (858mgkg-1)) near an abandoned mine site in Brazil. The desorption by stirred flow kinetics revealed that 15% of the total Zn and 12% Pb contents are mobile before any amendment application. Phosphate amendment decreased Pb desorption but increased Zn desorption. Biochar and biosolids immobilize high amounts of Zn and Pb because of their high cation exchange capacities and alkaline properties; however, 20% biosolid dose increased Pb desorption. X-ray absorption spectroscopy suggested Zn-kerolite as the major species in the contaminated soil, likely from mine dust. The change in Zn speciation after soil amendment addition indicated that biochar and lime kept a high proportion of Zn-Al species, whereas phosphate and biosolids led to more Zn-Fe species. Our results pointed out that lime might reduce both Pb and Zn mobilities; however, field trials are crucial to confirm the immobilization efficiency of lime and other amendments over long term.

The Effect of Temperature and Calcium Cloride Extract on Zinc Desorption in Changed Calcareous Soils

Zinc desorption studied for ten soils was variance in calcium carbonate, clay percent, and organic matter from Duhok province in the north of Iraq involved (Bamarny, Zawita Assih, Semeel, Kanimasi-1& 2, Khanke, Zakho, Batofa, and Faydi, locations). Soil testers after air dried up ground and filtered through a 2-mm sieve was taken to know the properties of the soils, zinc forms and desorption. Results showed the soluble, available, exchangeable and zinc total alternated among (0.29 - 0.94), (0.88 - 1.64), (1.71 - 2.05), and (12.25 - 56.15) mg.kg−1 one-to-one, Zn desorption raise with the raising of Zn added to research soils, extraction concentration CaCl2 from 0.1 to 1 molarity and temperature. Higher quantity of Zn release at 298K, was found in the soil of Kanimassi-1 (31.40 - 264.81) μg. g−1 at 0.1M, 1M CaCl2 extraction respectively, it may be owing to the high value of available phosphorus, CEC and organic matter and lower quantity of available-Zn and CaCO3. But the lowest amount observed in Faydi soil (14.10-118.69) μg. g−1. The high desorption of Zn at 321K, noted in Faydi soil between (50.50 - 421.00) μg. g−1 and low amount in Semeel soil between (26.35 - 222.10) μg.g−1 at 0.1 to 1M CaCl2 extraction respectively, designated Zn released more with increasing temperature. In general low quantity of Zn releases as of all researched soils causes to the great amount of CaCO3, quality and amount of clay minerals dominant that cause raise Zn bonding also low desorption from all studied soils. The effect of CaCl2 extraction concentration to increase Zn desorption was more than the effect of temperature in all soils.

Environmental risks of organic fertilizer with increased heavy metals (Cu and Zn) to aquatic ecosystems adjacent to farmland in the northern biosphere of Japan

In Abashiri, Hokkaido, northern Japan, composted sewage sludge (CSS) containing a large amount of zinc (Zn) and copper (Cu) is used as fertilizer in agriculture. The local environmental risks of Cu and Zn from such organic fertilizers were studied. The study area, especially the brackish lakes located near the farmlands, is important for inland fisheries. The risks posed by heavy metals to the brackish-water bivalve, Corbicula japonica, was therefore investigated as an example. First, the long-term effect of CSS application in agricultural fields was monitored. Second, using pot cultivation, factors influencing Cu and Zn availability in the presence of organic fertilizers were evaluated under different scenarios of SOM content. In addition, the mobility and availability of Cu and Zn in organic fertilizers were evaluated in a field experiment. In the pot cultivation, both organic and chemical fertilizers increased the availability of Cu and Zn with a decrease in pH, possibly caused by nitrification. However, this decrease in pH was inhibited by higher SOM content, i.e. SOM mitigated the heavy metal risk from organic fertilizer. In the field experiment, potato (Solanum tuberosum L.) was cultivated using CSS and pig manure (PM). As observed in the pot cultivation, the applied chemical and organic fertilizers increased the soil-soluble and 0.1 N HCl-extractable Zn with increased nitrate. Considering the habitat and the LC50 values of C. japonica that were lower than the concentration of Cu and Zn in the soil solution phase, there is no significant risk from heavy metals in the organic fertilizers. However, the Kd values for Zn were significantly lower for CSS or the PM-applied plot in the field experiment soil, indicating a higher Zn desorption rate from organically fertilized soil particles. The potential risk of heavy metals from agricultural lands under changing climate conditions must therefore be monitored carefully.

Zinc speciation and desorption kinetics in a mining waste impacted tropical soil amended with phosphate

Mining is an important component of the Brazilian economy. However, it may also contribute to environmental problems such as the pollution of soils with zinc and other potentially toxic metals. Our objective was to evaluate changes in the chemical speciation and mobility of Zn in a soil amended with phosphate. Soil samples were collected from a deactivated mining area in the state of Minas Gerais, Brazil, and amended with NH4H2PO4 saturated with deionized water to 70 % of maximum water retention and incubated at 25 ± 2 °C in open containers for 60 days. The soil was chemically and mineralogically characterized, and sequential extraction, desorption kinetics, and speciation were carried out using synchrotron bulk-sample and micro–X-ray Absorption Near-Edge Structure (XANES/μ-XANES) spectroscopy at the Zn K-edge, and X-ray fluorescence microprobe analysis (μ-XRF). The combination of μ-XRF and μ-XANES techniques made it possible to identify Zn hotspots in the main species formed after phosphate remediation. The best fit combination for bulk XANES and μ-XANES was observed in Zn-montmorillonite, Zn-kerolite, Zn-ferrihydrite, and gahnite. In the course of phosphate treatment, gahnite, Zn layered double hydroxides (Zn-LDH), Zn3(PO4), and ZnO were identified by bulk XANES, while Zn-ferrihydrite, Zn-montmorillonite, and scholzite were identified by μ-XANES. Zinc in the phosphate-amended soil had the strongest partial correlations (r′ > 0.05) with Ni, Co, Fe, Cr, Mn, Si, P, Cd, Pb, and Cd, while the unamended soil showed the strongest correlation with Cu, Pb, Fe, and Si. The application of NH4H2PO4 altered Zn speciation and favored an increase in Zn desorption. The most available Zn contents after phosphate amendment were correlated with the release of exchangeable Zn fractions, associated with carbonate and organic matter.

Assessing the impact of different salinities on the desorption of Cd, Cu and Zn in soils with combined pollution.

Exploring the relationships between heavy metal release and salinity can help address the problems of combination of toxic heavy metals and salinization in contaminated soils. Therefore, in this study, the release characteristics of heavy metals (Cd, Cu and Zn) under different salt types and mass concentrations were investigated through batch desorption experiments. Spearman's correlation analysis was performed to assess the effects of typical physicochemical properties on metal release under salt stress. The results indicated that the types and concentration gradients of salt had notably different impacts on the release of different metals; specifically, there were significant impacts for Cd but slight impacts for Cu and Zn. MgCl2 and CaCl2 had more obvious promoting effects on Cd release, followed by a salt mixture and NaCl, and this pattern was similar for Zn release. Most salts could slightly restrain the release of Cu, except for MgCl2 and Na2SO4, which had slight promoting effects. Moreover, low levels of CaCl2 could effectively restrain the release of Cu. The results showed that the release capacities of metals followed the order of Cd > Cu > Zn, possibly attributed to the competitive adsorption among cations. Ferromanganese oxides in the soil favored the release of Cd and Zn under salt treatments, and redox potential was an important factor affecting Cu release. The results also suggested that the background values of metals could affect metal release, but the effects were varied under different salt treatments for Zn. The reason for this may be that the addition of different salts changed the effects of certain soil properties on the metal release. Overall, this study can serve as an important reference for controlling heavy metal pollution in soils in salinization and coastal areas.

Biochar-graphene oxide composite is efficient to adsorb and deliver copper and zinc in tropical soil

Highly weathered soils have low micronutrient availability and very low efficiency for most soluble fertilizers . In this article the effect of poultry litter biochar-graphene oxide composite (PLB-GO) as a novel adsorbent for copper (Cu) and zinc (Zn) was evaluated, as well as its fertilizing effects on plant growth, nutrient use efficiency and soil fertility . In order to do so, poultry litter biochar (PLB) and PLB-GO were produced, characterized and evaluated by isotherm adsorption and kinetics studies regarding their Cu and Zn sorption and desorption properties. Cu and Zn loaded on PLB and PLB-GO as biochar-based fertilizers (BBF) were also evaluated. PLB-GO showed 16.2% and 17.7% higher Cu and Zn adsorption capacity , respectively, than pristine PLB, and in both cases <0.5% of the sorbed metal content was released in water. Plant effects on growth and nutrient uptake were, in general, higher or similar to the results obtained for sulfates . The application of PLB increased Cu availability while PLB-GO increased Zn availability after cultivation, even after increasing nutrient uptake and being little soluble in water. Addition of small amounts (≤0.5%) of GO in biochar has potential to increase its properties to retain micronutrients and enhance the fertilizer use effectiveness in highly weathered soils. • Biochar enrichment with graphene oxide increased metals adsorption from 16.2% to 17.7%. • Copper and zinc adsorbed by graphene oxide-biochar showed low water solubility (<0.5%). • Biochar-based micronutrient fertilizer increased grain production from 8% to 17%. • Biochar-based micronutrient fertilizer showed enhanced efficiency in highly weathered soil.

Citric and Tartaric Acids Effect on Zn&lt;sup&gt;2+&lt;/sup&gt; Desorption in the Soil around Textile Industry Area-Yogyakarta

Study of physico-chemical properties, adsorption and desorption of Zn using citric acid and tartaric acid on the textile industrial area has been carried out. This study aims to analyze the physico-chemical character of the soil and the content of heavy metals around the textile industry which is suspected of being contaminated by waste, the adsorption isotherm and capacity of Zn, the desorption kinetics of Zn using citric acid and tartaric acid solutions. Soil samples were divided into three sample points based on the location where they were taken, namely sample points I, II and III. The physical and chemical properties of soil were measured, included pH, ash content, electrical conductivity, total organic carbon, cation exchange capacity and content of heavy metals The adsorption capacity was studied by the adsorption of Zn on the soil. Meanwhile, the desorption was studied by using both citric and tartaric acid solution. The results showed that sample I had the highest total organic carbon content of 692.3 mg g-1, and a cation exchange capacity of 42.0 cmol+ kg-1 with a metal content of 735.0 mg kg-1. The maximum adsorption capacity of Zn is 708.7 mg kg-1. The optimum desorption using citric acid occurs at a concentration of 0.6 mol L-1, pH 3 and a time of 7 h, while tartaric acid occurs at a concentration of 0.8 mol L-1, pH 3 and a time of 7 h. Keywords: citric acid, tartaric acid, physico-chemical properties, zinc

Adsorption and desorption of Cu, Zn, Pb, and Cd on surface sediments from a shallow lake, North China

The processes of adsorption and desorption of heavy metal ions on sediments is of great significance for water quality conservation. To investigate the adsorption and release characteristics of heavy metals on sediments from shallow lakes, an isothermal adsorption and desorption experiment of Cu2+, Zn2+, Pb2+, and Cd2+ on sediments from Baiyun Lake was carried out. Our results showed that sediments demonstrated a strong capacity of absorbing these heavy metal ions in a sorption system. The maximum sorption capacity for heavy metals on sediments followed the order Pb2+> Cd2+> Cu2+> Zn2+. The followed order of the maximum buffer capacities for heavy metals was Pb2+ > Cu2+ > Zn2+ > Cd2+. The Langmuir isotherms model can better fit the adsorption of Cu2+, whereas the Freundlich isotherm model for the adsorption of Zn2+, Pb2+, and Cd2+. In the maximum initial concentration treatment, Pb exhibited the highest desorption amount, followed by Cu and Zn, whereas the lowest amount of Cd was observed. The exponential and quadratic functions could describe the relationships of adsorption and desorption. In the maximum initial concentration treatment, the adsorption rates of these four heavy metals followed the order Pb2+ > Cd2+> Cu2+> Zn2+, whereas the desorption rates followed an opposite order. The hysteresis index (HI) values for Zn was smaller than 1, whereas the HI values for Cu and Cd were slightly larger than 1, suggesting slightly negative hysteresis processes. However, the HI value of Pb was larger than 1, indicating that Pb2+ was easily desorbed from sediments.

Enhanced desorption of cationic and anionic metals/metalloids from co-contaminated soil by tetrapolyphosphate washing and followed by ferrous sulfide treatment

In this study, a novel approach was employed for the remediation of cationic and anionic metals/metalloids co-contaminated soil by tetrapolyphosphate enhanced soil washing coupled with ferrous sulfide treatment. Tetrapolyphosphate could simultaneously enhance the desorption of cationic metals (Pb and Zn) and anionic metal/metalloid (Cr and As) from the contaminated soil in the whole tested pH range of 2–10. With addition of 0.15 mol/L tetrapolyphosphate at pH 7.0, the removal ratio of Pb, Zn, As and Cr could achieve 83.1%, 70.4%, 75.7% and 66.4% respectively. The fractionation analysis of heavy metals/metalloids demonstrated the release of exchangeable and Fe/Mn bound forms contributed to most desorption of Pb and Zn. The decreases of non-specifically sorbed form and amorphous and poorly-crystalline hydrous oxides of Fe and Al bound form were responsible for most removal of As. The comparison with other common washing agents (EDTA, oxalate and phosphate) under their respective optimal dosage could confirm that tetrapolyphosphate was superior to simultaneously desorb the cationic and anionic metals/metalloids with higher efficiency. After 12 h, applying 150 mg/L FeS at pH 3.5 could totally remove Pb, Zn, As and Cr from the washing effluent by sulfide precipitation, reduction and adsorption processes. Higher pH would inhibit the removal of As and Cr by FeS. Meanwhile, the residual of tetrapolyphosphate could be totally recovered from the washing effluent by employing anion exchange resin. This study suggests tetrapolyphosphate enhanced soil washing coupled with ferrous sulfide treatment is a promising approach for remediation of cationic and anionic metals/metalloids co-contaminated soil in view of its high efficiency and simple operation.

Lignocellulose-Based Superabsorbent Polymer Gel Crosslinked with Magnesium Aluminum Silicate for Highly Removal of Zn (II) from Aqueous Solution.

Lignocellulose (LCE) was ultrasonically treated and intercalated into magnesium aluminum silicate (MOT) clay to prepare a nano-lignocellulose magnesium aluminum silicate polymer gel (nano-LCE-MOT) for the removal of Zn (II) from aqueous solution. The product was characterised using nitrogen adsorption/desorption isotherm measurements, Fourier-transform infrared spectroscopy, scanning electron microscopy and energy-dispersive X-ray spectroscopy. The conditions for the adsorption of Zn (II) on nano-LCE-MOT were screened, and adsorption kinetics and isotherm model analysis were carried out to explore the adsorption mechanism and achieve the optimal adsorption of Zn (II). Optimal adsorption was achieved at an initial Zn (II) concentration of 800 mg/L at 60 °C in 160 min at a pH of 4.52. The adsorption kinetics were explored using a pseudo-second-order model, with the isotherm adsorption equilibrium found to conform to the Langmuir model. The maximum adsorption capacity of the nano-LCE-MOT polymer gel toward Zn (II) is 513.48 mg/g. The materials with adsorbed Zn (II) were desorbed using different media, with HCl found to be the most ideal medium to desorb Zn (II). The optimal desorption of Zn (II) was achieved in 0.08 mol/L HCl solution at 65 °C in 60 min. Under these conditions, Zn (II) was almost completely desorbed from the adsorbents, with the adsorption effect after cycling being slightly different from that of the initial adsorption.

An In Situ and Real-Time Plasmonic Approach of Seed/Adhesion Layers: Chromium Buffer Effect at the Zinc/Alumina Interface

The effect of additives on metal/oxide interfaces is explored in situ and in real time on evaporated films by a combination of surface science techniques, among which a very flexible optical method shows a unique ability to scrutinize the growth and wetting properties of supported clusters that involve several elements. The study focuses on Cr at the Zn/α-Al2O3(0001) interface at 300 K. A particular interest of the present interface is that Zn does not stick at all on bare alumina. The sticking and morphology of both Cr and Zn films during their growth are analyzed from sub-monolayer to multilayer thicknesses. After an initial oxidation reaction with residual OH groups, shown to be detrimental to Zn adhesion, Cr growth proceeds through the formation of high aspect ratio particles that percolate around an average thickness of 10 Å. With regard to Zn growth on a Cr deposit, two very distinct stages can be distinguished. In the sub-monolayer thickness range, Cr forms a seed layer that drastically increases the Zn sticking coefficient from 0 to nearly 1 due to a diffusion length of physisorbed Zn adatoms before desorption larger than Cr island separation; Zn clusters are anchored on the Cr seeds that they encapsulate, but their wetting behavior is dictated by the interaction with alumina. In a second stage, as soon as the Cr film percolates, it forms an adhesion layer on which Zn grows in a nearly two-dimensional mode. In all cases, Cr films are stable upon annealing. On Cr-covered alumina, the Zn desorption energy is enhanced as compared to bare surfaces, which, in line with atomistic simulations, is assigned to the formation of more favorable Cr–Al2O3 and Cr–Zn than Zn–Al2O3 bonds. Generally speaking, the ability demonstrated herein of small amounts of additives to dramatically increase the adhesion of films is of great practical interest. It shows that noncontinuous and partially oxidized films of additives, closer to realistic cases of application, can strongly enhance the sticking of films. Also, anchoring a functional film by discrete predeposited seeds can keep its properties intact.

Modeling the kinetics of competitive sorption and desorption of Zn(II), Ni(II), and Pb(II) in an acidic soil: Stirred‐flow experiments

AbstractThe mobility and fate of heavy metals in soils is of environmental concern. Stirred‐flow experiments were conducted to study the competitive sorption and desorption of Zn, Ni, and Pb in binary systems in acidic Olivier loam soil. For all three binary systems, consecutive pulse applications demonstrated that the metal of highest affinity displaced sorbed amounts of metals of low affinity, whereas sorbed concentrations of the ion of highest affinity were unaffected by the addition of the metal of lower affinity. The displacement of Ni by Zn appeared irreversible, whereas the displacement of Zn by Pb and Ni by Pb was reversible. A two‐site competitive kinetic model consisting of common and ion‐specific sites successfully described the experimental data. Specifically, the model was able to accurately predict lower sorbed concentrations in concurrent pulse studies, as well as the displacement of Ni by Zn and Zn by Pb in the consecutive pulse studies. The presented model provided significant improvement over single‐ion models that have been previously used to describe competitive interactions between species in stirred flow experiments.

Hydrogen absorption, desorption and embrittlement of Zn and ZnNi-electrodeposited bolts

The H contents and H embrittlement (HE) of Zn- and ZnNi-electrodeposited SCM435 bolts were quantitatively evaluated before and after baking. The Zn-coated bolt possessed higher H contents than the ZnNi-coated bolt in as-electrodeposited and baked states. H atoms were strongly trapped inside the coating layers. The Zn-coated bolt underwent flaking of coating layer during baking at temperatures above 200 °C due to H effusion through the brittle δ phase. The Zn-coated bolt exhibited no HE regardless of baking despite of its high H content due to no permeation of H into the steel substrate during electrodeposition and tensile deformation.

Plant Available Zinc Is Influenced by Landscape Position in the Amhara Region, Ethiopia

Zinc (Zn) is an important element determining the grain quality of staple food crops and deficient in many Ethiopian soils. However, farming systems are highly variable in Ethiopia due to different soil types and landscape cropping positions. Zinc availability and uptake by plants from soil and fertilizer sources are governed by the retention and release potential of the soil, usually termed as adsorption and desorption, respectively. The aim of this study was to characterize the amount of plant available Zn at different landscape positions. During the 2018/19 cropping season, adsorption-desorption studies were carried out on soil samples collected from on-farm trials conducted at Aba Gerima, Debre Mewi and Markuma in the Amhara Region. In all locations and landscape positions, adsorption and desorption increased with increasing Zn additions. The amount of adsorption and desorption was highly associated with the soil pH, the soil organic carbon concentration and cation exchange capacity, and these factors are linked to landscape positions. The Freundlich isotherm fitted very well to Zn adsorption (r2 0.87–0.99) and desorption (r2 0.92–0.99), while the Langmuir isotherm only fitted to Zn desorption (r2 0.70–0.93). Multiple regression models developed by determining the most influential soil parameters for Zn availability could be used to inform Zn fertilizer management strategies for different locations and landscape positions in this region, and thereby improve plant Zn use efficiency.

Effects of substrate temperature on thermal stability of Al-doped ZnO thin films capped by AlOx

Effects of substrate temperature on the thermal stability of Al-doped ZnO (AZO) films have been studied. Degradation of electrical properties of AZO films by annealing under flowing N2 gas depends on their crystallinity controlled by the substrate temperature. A thin AlOx capping layer was employed to passivate the thermal degradation of the AZO layer. A strong correlation between Zn desorption and reduction in carrier concentration was observed. Thermal desorption of Zn was prevented by the AlOx layer, retaining carrier concentration. With the AlOx capping layer, the reduction in Hall mobility was prevented in samples with good c-axis orientation, while the reduction in Hall mobility was still observed in poor c-axis oriented films. However, the reduction was smaller than that in bare AZO films. The dependence of Hall mobility evolution on the substrate temperature, and therefore, on crystallinity, strongly suggests the impact of grain boundary scattering on thermal degradation. An increase in optical mobility, which was evaluated from optical spectra using the Drude model, with annealing temperatures, supports the conclusion that an increase in grain boundary scattering by annealing caused the degradation of Hall mobility. The increase in grain boundary scattering induced by Zn desorption was prevented by the capping layer, while contributions of domain alignment and other segregation of defects to the grain boundary scattering, which depend on the substrate temperature retained, leading to different evolutions of Hall mobility.

Effect of contamination sources on the rate of zinc, copper and nickel release from various soil ecosystems

Background and objectiveSoil is a substantive component in biosphere habitually endangered to superfluity contaminants particularly potential toxic elements (PTEs). The source of soil contaminants is very critical in controlling both their release and expected hazards in the different soil ecosystems. This study aims to investigate the effect of low-quality irrigation water (LQW) on the extent of soil pollution through desorption of zinc (Zn), nickel (Ni) and copper (Cu) from different polluted soils, collected from LQW irrigated farms for more than 40–80 years at Giza and Kafr-Elsheikh Governorates, Egypt.ResultsModels incorporated modified Freundlich (MFE), Elovich, first order and parabolic diffusion (PDE) showed significant results in describing the kinetic data under Egyptian conditions. Results entailed that according to the coefficient of determination (R2) and standard error, all used models well described the desorption of Cu, Ni and Zn, the most prevalent contaminants in the trailed soil ecosystems; for example, the R2 values were higher than 0.96** for zinc desorption using MFE model. As far as the PTEs levels are considered, the highest contaminant desorption rates were recorded at Kafr-Elsheikh site, followed by Kombora, and the lowest ones were in Abo Rawash soil ecosystem. The succession of more than one model to describe the kinetic perspective confirmed that the different mechanisms take place in PTEs sorption, distribution and subsequently release from different soil ecosystems.ConclusionsThe numerical values indicated that the soil ecosystems contaminated with industrial effluents were higher than those irrigated with sewage effluents regardless of the type of land use. More attention should be paid to low-quality water application in agriculture irrigation and its environmental risks.

Study of the Adsorption and Desorption of Zn(II) and Pb(II) on CaF2 Nanoparticles

This paper explores the adsorptive properties of CaF2 nanoparticles for the removal of Pb(II) and Zn(II) from aqueous solutions and their selective recovery. CaF2 nanoparticles were synthesized by a facile one-step reaction and characterized by N2 physisorption at 77 K, XRD, and TEM. The adsorption of Zn(II) and Pb(II) fits well with Elovich and Langmuir isotherm models, respectively. Kinetic data are well described by the pseudo-second-order model. Our results show that Zn(II) and Pb(II) could be totally and selectively desorbed with HCl solution (0.01 M). The results of the competitive adsorption and desorption of Pb(II) and Zn(II) show that Zn(II) is desorbed before Pb(II) leading to a good separation. The desorption yield reaches 89% for Zn(II) and 95% for Pb(II), which opens the route to regenerate the adsorbent for other cycles.

Distribution of copper and zinc fractions in a Regosol profile under centenary vineyard

Phytosanitary treatments using Bordeaux mixture or zinc (Zn) fungicides are often used in vineyards, which increase soil copper (Cu) and Zn contents. In this study, the accumulation and distribution of Cu and Zn fractions (water soluble, exchangeable, oxidic, organic and residual fractions) was evaluated along a Regosol profile cultivated with vine since 1890 and treated with Bordeaux mixture. Copper and Zn contents of the superficial layer were around 2000 mg kg−1 and 170 mg kg−1, respectively, and decreased through depth profile. However, accumulation of these metals was also observed in deeper layers of the soil, until 50 cm depth. Most of the total Cu was bound to the mineral fraction, whereas Zn was predominantly in the residual one. In the superficial layer, the desorption potential was 25% for Cu and 46% for Zn of these metals total content. Although the dominance of chemical forms with low geochemical mobility, desorption of Cu and Zn occurs easily, representing a high risk of transference in the environment.