Removal Of Zn Research Articles

Fluorinated Interface Engineering toward Controllable Zinc Deposition and Rapid Cation Migration of Aqueous Zn-Ion Batteries.

Metallic zinc (Zn) is a highly promising anode material for aqueous energy storage systems due to its low redox potential, high theoretical capacity, and low cost. However, rampant dendrites/by-products and torpid Zn2+ transfer kinetics at electrode/electrolyte interface severely threaten the cycling stability, which deteriorate the electrochemical performance of Zn-ion batteries. Herein, an interfacial engineering strategy to construct alkaline earth fluoride modified metal Zn electrodes with long lifespan and high capacity retention is reported. The compact fluoride layer is revealed to guide uniform Zn stripping/plating and accelerate the transfer/diffusion of Zn2+ via Maxwell-Wagner polarization. A series of in situ and ex situ spectroscopic studies verified that the fluoride layer can guide uniform Zn stripping/plating. Electrochemical kinetics analyses reveal that positive effect on the removal of Zn2+ solvation sheath provided by fluoride layer. Meanwhile, this fluoride coating layer can act as a barrier between the Zn electrode and electrolyte, providing a high electrode overpotential toward hydrogen evolution reaction to hold back H2 evolution. Consequently, the fluoride-modified Zn anode exhibited a capacity retention of 88.2% after 4000 cycles under10 A g-1 . This work opens up a new path to interface engineering for propelling the exploration of advanced rechargeable aqueous Zn-ion batteries.

Application of peanut shell ash in geosynthetic clay liners to reduce the Zinc contamination in leachate

Human health is seriously harmed by heavy metal contamination. Municipal solid waste disposal facilities are one of the most preferred options that contaminate the land and the groundwater. The liquid produced by the anaerobic oxidation of solid waste in landfills is known as leachate. The leachate contains organic, inorganic, and heavy metals depending upon the type of waste. The main issue in developing nations is the pollution of ground and surface water caused by the generation of leachate. Most heavy metals are carcinogenic in nature and Zinc (Zn) is one of the heavy metals present in the leachate. Kanpur (Uttar Pradesh, India) is a highly polluted city with 1500 Metric tons of waste generated per day. A leachate sample was collected for the study area and its Physico-chemical composition was analyzed. The concentration of Zn was found as 11.47 mg/l in the leachate sample which is more than two times the permissible limit of 5.0 mg/l. The objective of this study is to reduce the Zn concentration of leachate samples after passing through a modified Geosynthetic Clay Liner (GCL). The modified geosynthetic clay liner was developed by adding different proportions (0%, 5%, 10%, 15%, 20%, 25%, and 30%) of Peanut Shell Ash (PSA) with encapsulated Sodium Bentonite (Na-B) in commercial GCL. The efficiency of Zn removal from wastewater using peanut shells has been evaluated. In this study, it has attempted to find the best proportion of Na-B and PSA as encapsulated material of GCL to reduce the concentration of Zn.

Hybrid biosorbents from exopolymeric substances immobilized in Ca-alginate and their biosorption mechanisms in single and multi-metal systems

ABSTRACT This study developed a hybrid biosorbent consisting of exopolymeric substances (EPS) from Bacillus cereus immobilized in the gelling agent Ca-alginate. Metal removal tests revealed that the hybrid EPS beads showed significantly higher metal removal compared to plain alginate beads. This higher removal efficacy in hybrid biosorbents was attributed to the increased number of functional groups detected via FTIR analysis. Hybrid EPS beads bind metals via the formation of strong covalent bonds (chemisorption), rather than through weak van der Waals forces (physisorption), complying with the pseudo-second order model. This was consistent in both single and multi-metal systems. For adsorption isotherm, metal removal (pH 5, 25ºC, 120 rpm) by hybrid biosorbents in single metal systems fits the Langmuir isotherm (monolayer adsorption). In multi-metal systems, however, the removal of Zn and Cd demonstrated a better fit to the Freundlich isotherm (multilayer adsorption) compared to the typical Langmuir isotherm (for Cu, Pb and Cr). The isotherm models indicated that the maximum biosorption capacity for Cu, Pb, Zn, Cd and Cr was at 34.97, 156.24, 19.19, 11.66 and 38.61 mg g−1, respectively. The hybrid EPS beads are superior for the biosorption of Cu, Pb and Cr compared to existing biosorbents.

In-situ coupling of N-doped carbon dots with manganese hexacyanoferrate as a cathode material for aqueous zinc-ion batteries

Prussian blue analogs (PBAs) are a competitive class of aqueous Zn-ion batteries (AZIBs) cathode materials with an ideal three-dimensional open structure for rapid insertion and removal of Zn2+. Meanwhile, PBAs have the advantages of high working voltage and a simple synthesis process. However, these materials are inherently poor in electrical conductivity and are susceptible to structural collapse during cycling. These defects affect the performance of zinc storage in this type of material. Here, the integration of zero-dimensional nitrogen-doped carbon dots (NCDs) and in-situ grown manganese hexacyanoferrate (MnHCF) affords the MnHCF/NCDs cathode materials, which are applied to AZIBs. The introduction of NCDs modifies the active component of MnHCF effectively. Meanwhile, NCDs significantly enhance the overall electrical conductivity and structural stability of the composites and also provide abundant active sites for electrochemical reactions. Benefiting from these merits, the MnHCF/NCDs composite exhibits an excellent electrochemical zinc storage performance. It has a high discharge-specific capacity of 131.2 mAh g−1 at 50 mA g−1 and has outstanding cycling stability of 91% capacity retention after 1000 cycles at 1000 mA g−1. The electrochemical performance of PBAs-based cathodes for AZIBs may be improved using the straightforward and efficient method presented in this work.

Growing maize while biological remediating a multiple metal-contaminated soil: a promising solution with the hyperaccumulator plant Sedum alfredii and the earthworm Amynthas morrisi

This study was aimed to investigate the effect of earthworm Amynthas morrisi on the metal bioaccumulation by two plant species, Sedum alfredii Hance (Sedum) and maize (Zea mays L.), in a co-cropping system and possible influencing pathways, and assess the remediation potential of all combination of these organisms to identify the best option. In this study, an eight-week microcosm experiment was conducted to investigate the main and interactive effects of the earthworm Amynthas morrisi, the hyperaccumulator plant Sedum alfredii Hance (Sedum), and maize (Zea mays L.) on C and N forms, and microbial characteristics and diethylene triamine penta acetic acid (DTPA) extractable metals of a soil heavily contaminated by multiple metals (i.e., Cd, Zn, Pb, and Cu). In addition, plant growth and metal accumulation were evaluated and the possible influencing pathways of metal accumulation by the two plant species were assessed. Finally, a remediation strategy was proposed based on the amounts of metals removed by sedum and maize. The soil quality index achieved after eight weeks of experiments, was best with Sedum, and worst in the control with no plants and no earthworms. A path analysis suggests that earthworms exerted strong effects on plant metal accumulation by changing plant growth, with soil microbes playing a mediating role. The association of Sedum and Maize significantly increased the Zn concentration and decreased the Pb and Cu concentrations in the aboveground parts of Sedum compared with Sedum alone, whereas Sedum decreased the Zn, Cd, Pb, and Cu concentrations in the aboveground parts of maize compared with maize alone treatment. PCA showed that when maize was co-cropped with Sedum, metal transfer from its roots to the aboveground parts decreased. The Earthworm + Sedum + Maize treatment displayed the most effective Cd and Zn removal, indicating that the combined introduction of A. morrisi and S. alfredii can effectively remediate soils co-contaminated by Cd and Zn in maize cropping systems.

An assessment of the efficacy of sodium carbonate for semi-passive treatment of circumneutral zinc-bearing mine waters

This study reports on the novel application of sodium carbonate dosing specifically for the semi-passive precipitation of Zn from circum-neutral mine water and demonstrates the use of Na2CO3 as a readily available, safe to handle reagent which can precipitate Zn at pH within environmental quality standards. >95 % Zn removal was achieved for each mine drainage investigated, requiring differing dosages of Na2CO3 with residual Zn concentrations <1 mgL−1. Geochemical modelling and precipitate characterisation using XRD, SEM-EDS, TGA and full chemical digest suggests that the precipitate predominantly comprised of hydrozincite. Laboratory trials demonstrated that (i) adding the precipitant dropwise could reduce the sludge volume by circa 50 %, and (ii) That following a laboratory protocol for simulating type II High Density Sludge (HDS) process resulted in substantial decreases in sludge volumes compared to single pass sludge, with 5.3 mL per litre mine water treated compared to 55.3 mL per litre for conventional single pass treatment after 25 cycles. Such reductions in sludge volume are a very advantageous outcome for practical applications. Particle size distribution and zeta potential determinations on the resultant HDS sludge suggest that increased heterogenous precipitation and decrease in zeta potential are important in the formation of HDS when using sodium carbonate to treat zinc-bearing waters. This work demonstrates that sodium carbonate is an efficacious reagent for semi-passive treatment of zinc-bearing mine waters and as such could find widescale application to this pressing global problem.

3D coaxial printing of porous construct stacked with hollow filaments for heavy metal removal

Biopolymers-based hydrogels/aerogels have been widely used for removing heavy metals from water. However, the adsorption efficiency is limited by the monolithic macroscopic structure due to low exposed adsorption sites and ion diffusion rate. In this study, we report a proof-of-concept micro-extrusion-based 3D coaxial printing technology to solve the aforementioned problems in heavy metal removal. The 3D printed grid-like architectures stacked with hollow filaments prepared by alginate and cellulose nanocrystal showed excellent heavy metals (including Cu, Zn, Cr, and Cd) removal performance over other common adsorbents. The Cu(II) adsorption was greatly influenced by the initial pH and ionic strength. It followed pseudo-second order kinetics and Langmuir isotherms models. The maximum adsorption capacity of the porous construct was found to be 97.22 mg∙g−1 at room temperature. Moreover, the equilibrium adsorption capacity and adsorption rate of Cu(II) in the hierarchical porous adsorbents (~68 mg∙g−1, 2.29×10−3 g∙mg−1∙min−1) were much higher than that in its corresponding solid chunk hydrogel (~48 mg∙g−1, 7.27×10−4 g∙mg−1∙min−1). It exemplifies that the 3D coaxial printing strategy for wastewater treatment enables shape-specific applications of functional hierarchical porous adsorbents.

Removal of Zn2+ from glycolytic monomers of the polyethylene terephthalate based on electrodeposition

The usage of zinc-containing catalysts in glycolysis causes the residue of Zn2+ in the polyethylene terephthalate (PET) degradation monomer bis-hydroxyethyl (BHET), which limits the high-value utilization of BHET. This work first used electrodeposition combined with one-time recrystallization to purify BHET. Electrodeposition was suitable for dealing the Zn2+ concentrations of degradation solutions within 50–100 ppm, and decreased the content of Zn2+ in BHET from 141.30 to 2.41 ppm, which reached the standard of repolymerization into PET bottles. The removal rate of Zn2+ was 90 % for the degradation solutions, which decreased the concentration of Zn2+ in wastewater from 100 to 8.97 ppm. Meanwhile, the Zn2+ removed from the degradation solutions was deposited on cathode, which obtained metal Zn materials and realized the recycling of Zn resources from Zn(OAc)2. Therefore, electrodeposition could realize the purification of BHET, recycling of Zn(OAc)2, reducing the environmental pollution caused by the emission of Zn2+ and the protection of human health, simultaneously. Electrodeposition had less water consumption, lower loss rate of BHET (from 60 % to 10 %) and shorter processing time, compared with six-times recrystallizations. This study first proposed the formation of quadridentate between BHET and Zn2+, and put forward a new three-steps electrodeposition mechanism of Zn2+: the addition of electric field destroyed the dissociation equilibrium of quadridentate and made it shift to release free Zn2+; the free Zn2+ gathered to form ionic groups and they migrated to copper; Zn2+ reduced on copper, of which the first step was the speed limited step.

The Fate of Heavy Metals and Risk Assessment of Heavy Metal in Pyrolysis Coupling with Acid Washing Treatment for Sewage Sludge.

Pyrolysis is an emerging and effective means for sludge disposal. Biochar derived from sludge has broad application prospects, however, is limited by heavy metals. In this study, the fate of heavy metals (HMs) in pyrolysis coupling with acid washing treatment for sewage sludge was comprehensively investigated for the first time. Most of the HMs redistributed in the pyrolyzed residues (biochar) after pyrolysis, and the enrichment order of the HMs was: Zn > Cu > Ni > Cr. Compared with various washing agents, phosphoric acid presented a superior washing effect on most heavy metals (Cu, Zn, and Cr) in biochars derived at low pyrolysis temperature and Ni in biochars derived at high pyrolysis temperature. The optimal washing conditions for heavy metals (including Cu, Zn, Cr, and Ni) removal by H3PO4 were obtained by batch washing experiments and the response surface methodology (RSM). The total maximum HM removal efficiency was 95.05% under the optimal washing specifications by H3PO4 (acid concentration of 2.47 mol/L, L/S of 9.85 mL/g, and a washing temperature of 71.18 °C). Kinetic results indicated that the washing process of heavy metals in sludge and biochars was controlled by a mixture of diffusion and surface chemical reactions. After phosphoric acid washing, the leaching concentrations of HMs in the solid residue were further reduced compared with that of biochar, which were below the USEPA limit value (5 mg/L). The solid residue after pyrolysis coupling with acid washing resulted in a low environmental risk for resource utilization (the values of the potential ecological risk index were lower than 20). This work provides an environmentally friendly alternative of pyrolysis coupling with acid washing treatment for sewage sludge from the viewpoint of the utilization of solid waste.

Chlorine and heavy metals removal from municipal solid waste incineration fly ash by electric field enhanced oxalic acid washing

Electric field enhanced oxalic acid (H2C2O4) washing was conducted to examine the simultaneously removal efficiency of heavy metals (HMs) and chlorine, especially insoluble chlorine from municipal solid waste incineration fly ash (MSW FA). Results show that chlorine and HMs can be effectively removed with a total chlorine, As, Ni and Zn removal rate of 99.10%, 79.08%, 75.42% and 71.43%, when the electrode exchange frequencies is 40 Hz, current density is 50 mA/cm2, H2C2O4 adding amount is 0.5 mol/L and the reaction time is 4 h. Insoluble chlorine removal efficiency is up to 95.32%, much higher than reported studies. And the chlorine content in the residue is lower than 0.14%. Meanwhile, HMs removal efficiency is remarkable, 41.62%–67.51% higher than that of water washing. The high-efficient removal effect is caused by the constantly changing direction of electrons hitting the fly ash surface, which provides more escape channels for internal chlorine and HMs. These results proved that electric field enhanced oxalic acid washing could be a promising method for removing contaminants from MSWI fly ash.

Enhanced Phytoremediation for Trace-Metal-Polluted Farmland with Hibiscus cannabinus–Sedum plumbizincicola Rotation: A Case Study in Hunan, China

Trace metal pollution in farmland threatens the health of both crops and humans. Restoring these polluted farmlands safely and utilizing them to elevate farmers‘ incomes are extremely needed. Phytoremediation is a promising method for metal extracting but its popularization is limited by both its low efficiency and the low economic value of the plants used. Herein, a field study was conducted to investigate the potential of using a rotation with the hyperaccumulator of Sedum plumbizincicola and kenaf (Hibiscus cannabinus) for combined heavy-metal-contaminated farmland remediation. Results showed that the kenaf obtained an aerial biomass of up to 21 Mg ha−1 under combined heavy metal contaminations, which was significantly higher than that for S. plumbizincicola (&lt;8 Mg ha−1). However, the concentrations of Cd, Cu, Pb, and Zn in S. plumbizincicola were at least 100, 2, 8, and 75 fold higher than that for kenaf, respectively. The removal of Cd, Pb, and Zn for S. plumbizincicola can be more than 3800, 720, and 104,347 g ha−1, which was at least 38, 3, and 27 times higher than that for kenaf, respectively. Finally, the removal of Cd, Cu, Pb, and Zn by rotation of the two crops was increased by 7.88%, 126%, 33.5%, and 4.39%, respectively, compared with the S. plumbizincicola monoculture. Hence, the rotation with kenaf and S. plumbizincicola can not only remove more heavy metals from the contaminated soil and accelerate the phytoremediation pace, but also can supply a large number of raw materials for industrial applications.

Ability of Deep Eutectic Solvent Modified Oat Straw for Cu(II), Zn(II), and Se(IV) Ions Removal

In the proposed study, agro-waste biomass oat straw (OS) was considered a potential adsorbent for Cu(II), Zn(II), and Se(IV) removal from aqueous solutions. In order to obtain material with better adsorption abilities, the OS was modified by a deep eutectic solvent (DES). Structural changes caused by the applied modification route were considered by pHpzc, SEM, FTIR, and DSC/TG analysis. These methods discovered that lignocellulosic biomass degradation and material functionalization were achieved by DES treatment. Preliminary adsorption tests showed an over fourfold increase in capacity upon modification. The kinetic parameters implied that adsorption on modified material followed the pseudo-second-order kinetic model. Different isotherm models were applied to experimental data, while the Sips isotherm model best describes the equilibrium of the adsorption process on the tested modified material. According to this isotherm model, the maximum achieved adsorption capacities of Cu(II), Zn(II), and Se(IV) were 48.21, 55.06, and 87.85 mg/g, respectively. The summarized experimental results revealed that the adsorption process of selected cations on modified OS was predominantly caused by chemisorption, while, in addition to chemisorption, electrostatic forces were also responsible for Se(IV) removal. Desorption test showed that the prepared material could be reused for at least 3 cycles, with minimal efficiency loss. Briefly, this study reinforces that DES-modified agro-waste biomass could be used as a promising adsorbent for cations and oxyanions from wastewater.

Dust removal ash coupled with high-temperature exhaust gas to produce energy gas CO and remove the heavy metals synchronously

In order to solve the utilization problem of dry quenching coke dust removal ash (DRA) and high-temperature exhaust gas (HTEG) at the same time, this study proposes a new technology that combines DRA and high-temperature exhaust gas to produce energy gas CO and realize the removal of heavy metals in dust removal ash. The reaction properties of DRA and high-temperature exhaust gases, as well as the migration law of heavy metals, are preliminarily evaluated using thermodynamic simulation software (FactSage) and a combination of thermogravimetric mass spectrometry (TG-MS). The dropper furnace (DF) experiments are used to verify the feasibility of the new technology by simulating the high-temperature flue gas environment. The findings reveal that as pressure rises, the content of gas products namely CO2 and CH4 rises while the content of gas products CO and H2 falls. At the same time, when the temperature rises, the CO and H2 contents rise. Heavy metals such as Cd, Pb, and Zn are also more volatile, whereas heavy metals such as Ni, Cr, and Cu, require higher temperatures to volatilize. As the temperature increases from 800 to 1200 °C, the Pb removal rate climbs from 34.6% to 92.5%, the Cd removal rate increases from 46.5% to 95.6%, and the Zn removal rate increases from 13.4% to 80.5%. The new technology captures CO2 from high-temperature exhaust gases and converts them into CO energy gases, simultaneously realizing the removal of heavy metals. This provides an innovative solution for the treatment of organic solid waste.

Tailoring MOF structure via iron decoration to enhance ORR in alkaline polymer electrolyte membrane fuel cells

Fe-N-C catalysts were synthesized by combining a Zn-based zeolitic imidazolate framework (ZIF-8) structure, adopted as a nitrogen-carbon template, with an iron salt and conductive carbon support followed by a thermal treatment. The effect of three different pyrolysis temperatures (700, 900, and 1000 °C) on Zn removal from ZIF-8 was investigated to enhance the formation of Fe-based moieties in the Nx-C groups during carbonization. Electrochemical characterization using a rotating ring disk electrode in an alkaline electrolyte demonstrated that ORR activity increased as the pyrolysis temperature increased. This trend can be ascribed to a more effective Zn removal and formation of high-active iron- and nitrogen-based catalytic sites, as pointed out by the Fe-N-C materials' chemical surface analysis after the pyrolysis step. The sample Fe-N-C-1000 demonstrated a remarkable ORR activity, even higher than Pt/C taken as reference.When subjected to accelerated stress tests, the Fe-N-C-1000 sample displayed higher performance durability over a long cycling duration (30,000 cycles) compared to Pt/C taken as control. Tests in the AEMFC fed with H2 showed that the performance of the Fe-N-C-1000 catalyst was competitive (OCV = 0.98 vs. 1.05 V, 149 vs. 148 mW cm−2) compared to the state-of-the-art Pt/C electrode, using a FUMASEP® FAA-3-50 membrane. The material found an application also in alkaline direct methanol fuel cell (ADMFC) fed with methanol solutions at high concentrations (up to 10 M) due to a high methanol tolerance, as pointed out by rotating disk electrode experiments.

Experimental and Modeling Study on the Removal of Mn, Fe, and Zn from Fiberboard Industrial Wastewater Using Modified Activated Carbon

In this work, the use of agricultural waste from oil palm petioles (OPP) as a raw material for the production of activated carbon (AC) and its characterization were examined. By soaking these chars in nitric acid (HNO3) and potassium hydroxide (KOH) at a 10% concentration, AC with favorable high-porosity carbons was generated. To maximize AC synthesis, the AC was pyrolyzed at 460, 480, and 500 °C temperatures for 20 min. Based on micrographs of formed pores and surface functional groups, 480 °C carbonization temperature on both chemical HNO3 and KOH was shown to be the best. The FTIR measurements reveal that chemical activation successfully transformed the raw material into AC. Moreover, FESEM micrographs show the pores and cavities of the prepared AC achieve a high surface area. This is further supported by BET results of HNO3 OPP AC and KOH OPP AC with surface areas of 883.3 and 372.4 m2/g, respectively, compared with the surface area of raw OPP of 0.58 m2/g. Furthermore, the tests were revealed by an optimization model, namely response surface methodology (RSM), using a central composite design (CCD) technique. The findings showed that all three parameters (pH, time, and dose) had a substantial impact on the removal of Zn, Fe, and Mn. Analysis of variance (ANOVA) and analytical error indicated that the models were accurate, with a low error value and a high R2 &gt; 0.9. Remarkably, the good correlation between actual and predicted removal values showed that the modified activated carbon is a promising adsorbent for heavy metal removal from wastewater.

Potential of using jackfruit peel (Artocarpus heterophyllus) as green solution for removal of copper (II) and zinc (II) from aqueous solution: Adsorption kinetics, isotherm and thermodynamic studies

Adsorbent from agricultural waste has become a popular alternative method for heavy metal removal from aqueous solutions. The purpose of this study was to look into the feasibility of employing jackfruit peel (JP) (Artocarpus heterophyllus), a solid waste that is abundant in Malaysia, for the adsorption of Cu (II) and Zn (II) from an aqueous solution. In this work, jackfruit peels were investigated as an adsorbent with no chemical modification (JP), acidified (HJP), and base modified (NaJP) for Cu(II) and Zn(II) removal from aqueous solution by using batch-adsorption modes. Spectroscopic and electron microscopic methods were used to analyze the presence of surface functional groups such as -COOH and -OH and the morphologies of the adsorbent. Adsorption investigations were carried out by adjusting adsorbent dosage (0.10–0.50 g), solution pH (3−8), initial metal ion concentrations (20–250 mg/L), temperature (298–328 K), and contact time (0–360 min). Sorption equilibrium is quickly reached within 60 min, with a higher percentage of Cu(II) and Zn(II) removal for NaJP. Regarding the effect of initial concentration on JP, the maximum adsorption for Cu(II) and Zn(II) is at 50 mg/L and 30 mg/L, respectively. Meanwhile, for HJP, the maximum adsorption for Cu(II) and Zn(II) is at 230 mg/L and 30 mg/L, respectively. For NaJP, the maximum adsorption for Cu(II) and Zn(II) is at 20 mg/L. The pseudo-second-order model best characterized the kinetic data for both metal ions using JP, HJP, and NaJP. The experimental findings fit well with the Langmuir model in explaining the adsorption process, dominated by electrostatic interaction between the adsorbent and adsorbates, showing monolayer adsorption at the binding sites on the adsorbent's surface. It was proven that with the increase of adsorbent dosage, the percent of heavy metals removal was increased due to the increasing adsorption capability of the adsorbent. In conclusion, our findings show that jackfruit peel has the potential to remove Cu(II) and Zn(II) from an aqueous solution. The adsorption process for Cu(II) and Zn(II) was favourable in acidic conditions. Under the experimental conditions, the adsorption of Cu(II) and Zn(II) onto the surface of JP, HJP, and NaJP was exothermic and non-spontaneous. The results showed that the jackfruit peel, a waste material, has a high potential as an adsorbent for removing harmful metals such as copper and zinc from water.

Synthesis and Characterization of Biodegradable Poly(vinyl alcohol)-Chitosan/Cellulose Hydrogel Beads for Efficient Removal of Pb(II), Cd(II), Zn(II), and Co(II) from Water

Globally, water contamination by heavy metals is a serious problem that affects the environment and human health. Adsorption is the most efficient way of water treatment for eliminating heavy metals. Various hydrogels have been prepared and used as adsorbents to remove heavy metals. By taking advantage of poly(vinyl alcohol) (PVA), chitosan (CS), cellulose (CE), and the process for physical crosslinking, we propose a simple method to prepare a PVA-CS/CE composite hydrogel adsorbent for the removal of Pb(II), Cd(II), Zn(II) and Co(II) from water. Structural analyses of the adsorbent were examined by Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy-energy dispersive X-ray (SEM-EDX) analysis, and X-ray diffraction (XRD). PVA-CS/CE hydrogel beads had a good spherical shape together with a robust structure and suitable functional groups for the adsorption of heavy metals. The effects of adsorption parameters such as pH, contact time, adsorbent dose, initial concentration of metal ions, and temperature on the adsorption capacity of PVA-CS/CE adsorbent were studied. The adsorption characteristics of PVA-CS/CE for heavy metals may be completely explained by pseudo-second-order adsorption and the Langmuir adsorption model. The removal efficiency of PVA-CS/CE adsorbent for Pb(II), Cd(II), Zn(II), and Co(II) was 99, 95, 92, and 84%, respectively, within 60 min. The heavy metal's hydrated ionic radius may be crucial in determining the adsorption preference. After five consecutive adsorption-desorption cycles, the removal efficiency remained over 80%. As a result, the outstanding adsorption-desorption properties of PVA-CS/CE can potentially be extended to industrial wastewater for heavy metal ion removal.

Implementation of electrocoagulation for reduction of Zn in an outlet stream from waste incineration plant

The paper is focusing on the full-scale operation of electrocoagulation for Zn removal from wastewater with origin in a municipal incineration plant. The process was custom designed for continuous full-scale operation. Total capacity of the process varied between 1200 and 1400L/h. This was achieved by two simultaneous electrocoagulation cells operated in parallel. Residual concentrations of Zn in the treated water were consistently lower than 0.5 mg/L during the testing period. Residual concentrations of Zn and other accompanying contaminants were reduced below the desired limits (current limit for Zn in outlet water is 1.5 mg/L). The process cost was critically assessed. The electricity consumption for the operation of electrocoagulation cells is 0.75–1.1 kWh/m3 of purified water. A more significant expense is the consumption of electrode cartridges. The service life of electrode cartridges with a plate thickness of 5 mm is about 1 200 m3 of water/electrode pack, which represents a cost of around 0.6–1 EUR/m3 out of total 1.6 EUR/m3 of purified water. Waste incineration plants usually produce their own electricity therefore technologies like electrocoagulation become affordable and competitive.

The Importance of Reversible Scavenging for the Marine Zn Cycle Evidenced by the Distribution of Zinc and Its Isotopes in the Pacific Ocean

AbstractThe North Pacific has played an important role in ongoing discussions on the origin of the global correlation between oceanic dissolved Zn and Si, while data in the North Pacific have remained sparse. Here, we present dissolved Zn and δ66Zn data from the US GEOTRACES GP15 meridional transect along 152°W from Alaska to the South Pacific. In the south (&lt;20°N) Zn and Si exhibit a tight linear correlation reflecting strong Southern Ocean influence, while in the north (&gt;20°N) an excess of Zn relative to Si in upper and intermediate waters is due to regeneration of Zn together with PO4. Using a mechanistic model, we show that reversible scavenging is required as an additional process transferring Zn from the upper to the deep ocean, explaining the deep Zn maximum below the PO4 maximum. This mechanism applied for reversible scavenging also provides an explanation for the observed isotope distribution: (a) fractionation during ligand binding and subsequent removal of residual heavy Zn in the upper ocean, drives the upper ocean toward lower δ66Zn, while (b) release of heavy Zn then coincides with the PO4 maximum where carrier particles regenerate, causing a mid‐depth δ66Zn maximum. In the upper ocean, seasonal physical stratification is an additional important process influencing shallow δ66Zn signals. At the global scale, this mechanism invoking fractionation during ligand binding coupled with reversible scavenging offers a global explanation for isotopically light Zn at shallow depths and corresponding elevated mid‐depth δ66Zn signals, seen dominantly in ocean regions away from strong Southern Ocean control.

Salinity and temperature influence removal levels of heavy metals and chloride from water by wetland plants

Stormwater with low temperatures and elevated salinity, common in areas where deicing salt is used, might affect the removal of heavy metals by plants in stormwater treatment systems such as floating treatment wetlands. This short-term study evaluated the effects of combinations of temperature (5, 15, and 25 °C) and salinity (0, 100, and 1000 mg NaCl L−1) on the removal of Cd, Cu, Pb, and Zn (1.2, 68.5, 78.4, and 559 μg L−1) and Cl− (0, 60, and 600 mg Cl− L−1) by Carex pseudocyperus, C. riparia, and Phalaris arundinacea. These species had previously been identified as suitable candidates for floating treatment wetland applications. The study found high removal capacity in all treatment combinations, especially for Pb and Cu. However, low temperatures decreased the removal of all heavy metals, and increased salinity decreased the removal of Cd and Pb but had no effect on the removal of Zn or Cu. No interactions were found between the effects of salinity and of temperature. Carex pseudocyperus best removed Cu and Pb, whereas P. arundinacea best removed Cd, Zu, and Cl−. The removal efficacy for metals was generally high, with elevated salinity and low temperatures having small impacts. The findings indicate that efficient heavy metal removal can also be expected in cold saline waters if the right plant species are used.