Formation Of Metal Hydroxides Research Articles

Electrocoagulation process for phosphate recovery of agricultural wastewater: effect of calcium adding, voltage, and time.

Recovery of valuable resources, such as phosphate recovery from wastewater, can help close the nutrient cycle and is interesting to investigate. This study aims to evaluate phosphate recovery and set aside TOC, OC, and IC in agricultural wastewater using electrocoagulation with a helix electrode configuration. This study employed the Response Surface Methodology (RSM) for statistical analysis and modeling, utilizing a central composite design (CCD). Variation of calcium concentration (2-7mg/L), voltage (15-45V), and electrocoagulation time (5-15min) was applied in an electrocoagulation reactor with a helix-shaped stainless steel cathode and a solid cylindrical Mg anode. Based on RSM analysis, electrocoagulation with a helical electrode configuration significantly affects phosphate recovery and the removal of TOC, OC, and IC when treating agricultural wastewater. Under operating conditions of 15V, 15min time, and 2mg/L calcium concentration, we achieved the lowest phosphate concentration of 0.003mg/L (99.74% reduction). The highest TOC allowance is > 100% of the initial concentration, the TC allowance is 55.79%, and the IC allowance is 30.91%. The formation of metal hydroxides affects the efficiency of TOC removal in the electrocoagulation process, and higher electrolysis times lead to higher TOC removal efficiency. Higher voltages also improve the coagulation and flotation processes in the reactor. Calcium concentration plays a role in enhancing the flocculation process and binding phosphonates from wastewater.

Study on the efficacy and mechanism of treatment of manganese-containing wastewater by pulse-alternating current coagulation

ABSTRACT To assess the effectiveness and underlying mechanism of pulse-alternating current coagulation (PACC) for treating manganese-laden wastewater, we examined the influence of various parameters. Specifically, we investigated the impact of current density, initial pH, initial Mn2+ concentration, electrolyte concentration, and alternating current frequency on the removal efficacy. The removal mechanism was meticulously examined using an adsorption kinetics analysis, Scanning Electron Microscope (SEM), Energy Dispersive Spectroscopy (EDS), Fourier Transform Infrared Spectrum (FTIR), and X-ray Photoelectron Spectroscopy (XPS). The findings indicated that the concentration of Re (Mn2+) was 99.09% under the specified conditions: j = 2.5 A·m−2, pH0 = 7, c 0(Mn2+) = 50 mg·dm−3, f = 500 Hz, c 0(NaCl) = 500 mg·dm−3 and t = 40 min. When Re (Mn2+) = 98%, the energy consumption (EEC) was significantly lower for PACC at 1.23 kWh·m−3, compared to 1.52 kWh·m−3 for direct current condensation (DCC). This indicated a reduction in EEC by 19.1% when using PACC over DCC. The adsorption process of Mn2+ by the iron sol adheres to the principles of pseudo-second order kinetics. The primary component of flocs generated in the PACC process is α-FeOOH. The mechanism of Mn2+ removal in the PACC process involved the synthesis of Mn oxides, the formation of metal hydroxide precipitates and adsorption by nano-iron sol. This study provides a theoretical basis and technical support for the application of PACC technology in the field of manganese-containing wastewater treatment.

Efficient Radiolabeling of Block Copolymer Micelles through Radiometal Salt Precipitation for Theranostic Applications

AbstractA variety of polymer micelles are designed for the delivery of chemotherapeutic drugs to tumors. Although the promise of these nanocarriers is very high, in the clinic the effectivity is rather limited. Determining the in vivo fate of the micelles can greatly help to improve this treatment. Here, a simple and fast chelator‐free method for radiolabeling of polymer micelles composed of different block copolymers is presented, which can allow evaluating the behavior of the nanocarriers in vivo using noninvasive nuclear imaging techniques (e.g., single photon computed tomography, SPECT). The radiolabeling method consists of adding the radioisotope ions, i.e., 111In(III), resulting in a high radiolabeling efficiencies up to 90%. The results suggest that the radiolabeling efficiency depends on two important factors: the properties of the hydrophobic block in the block copolymer composing the micelle core, and the speciation of the radiometal salts. The formation of metal hydroxides and their precipitation in the core of the micelles appears to be a key factor for high stability. Moreover, the method can be applied to radiolabel the micelles in the presence of chemotherapeutic drugs. Finally, a SPECT study shows that the radiolabeled samples are stable in vivo without any evident loss of 111In(III).

Transparent exopolymer particles-associated membrane fouling analyses of systems containing sodium alginate, calcium, iron, alum and their combination during dead-end ultrafiltration

In this work, a serious of filtration experiments were designed and implemented to compare the effects of different metal cations (Ca2+, Fe3+, and Al3+) on fouling by sodium alginate. As indicated by the experimental results, these three types of cations all induced biphasic filtration behavior by 50 mg/L sodium alginate, that addition of these cations initially aggravated the fouling but then mitigated it upon further addition. The maximum specific filtration resistance (αav) increased in the following order: Al (34.5 ± 1.2 1014 mg/kg) < Ca (52.4 ± 2.5 1014 mg/kg) ≈Fe (54.1 ± 1.2 1014 mg/kg), but the corresponding critical concentration of the cation was in the order: Al3+ (0.02 mM) = Fe3+ (0.02 mM) < Ca2+ (0.05 mM). Increasing the metal cation concentration induced a higher transparent exopolymer particle concentration with the size being initially decreased but then gradually increased via the cation bridging effect, until the cation concentration reached up to 2 mM with the formation of metal hydroxides. So the fouling resistance mainly resulted from the dynamic equilibrium between concentrations and properties of transparent exopolymer particles with different sizes (0.05–0.1 μm, 0.1–0.2 μm, 0.2–0.4 μm and >0.4 μm). Similar biphasic fouling behavior also observed in the co-existence of Ca2+ and Fe3+/Al3+, but the comparable maximum αav values were obtained at much lower ion concentrations. Besides changes in the transparent exopolymer particle concentration, the hindered back transport of different sodium alginate molecules and steric effect also contributed to the synergistic fouling. Furthermore, there was little competition between the binding sites for divalent and trivalent ions, but the coiling behavior could be limited by changing the cation dosing sequence, leading to a weakened synergistic effect. This study links cation types, transparent exopolymer particle formations and fouling layer structures, with practical relevance for the hydraulic performance of low-pressure membranes, hopefully leading to their wider application in water treatment.

Nanocrystalline structure and microhardness of cobalt-chromium alloys electrochemically synthesized using a metal hydroxide coprecipitation technique

The effect of glycine as a complexing agent on metal hydroxide formation, such as Co(OH)2 and Cr(OH)3, was investigated based on potential-pH diagrams and titration curves for Co2+-H2O and Cr3+−H2O systems. Using a potentiostatic electrodeposition technique, Co–Cr alloy-based composite films containing Cr2O3 were synthesized from a non-suspended aqueous solution within an optimized pH range. Chromium content in the composite films was controlled up to 38.9% by adjusting the cathode potential during the alloy electrodeposition. Based on the XRD profiles and electron diffraction patterns, an amorphous-like nanocrystalline structure was observed in the composite films with high chromium content. The average crystal grain size declined due to Cr2O3 particles and hydrogen evolution during the electrodeposition process. Saturation magnetization of the composite films decreased with an increase in the chromium content. Synergistic contribution of increasing dislocation density and refining crystal grain size improved the microhardness of the composite films. The microhardness reached 624.2 kgf mm−2 and greatly exceeded that of pure cobalt (ca. 250–300 kgf mm−2).

Inhibition characteristics of the electrokinetic removal of inorganic contaminants from soil due to evolution of the acidic and alkaline fronts

This study comprehensively investigates the inhibition characteristics of the electrokinetic removal (EKR) of inorganic pollutants from soil due to evolution of the acidic and alkaline fronts (EAAF). The effects of EAAF on the ion strength of the soil pore fluid, potential distribution, soil colloids, clay minerals, and soil microstructure are systematically examined, in addition to the control effects of non-target charged species on the removal of target pollutants. The results show that the transport of target species near the anode region is mainly inhibited by potential flattening, soil colloid aggregation, and the closure of soil pores. Migration near the cathode region is mainly inhibited by the immobile chemical states of metals, potential flattening, soil dehydration, and a high soil adsorption ability owing to the relatively developed pores. This results also show that H+, OH-, and soluble Al have a significantly control effect on the macroscopic dynamics of EKR of the target contaminants. The injection of acidic solution near the cathode alleviates the potential jump and prevents the formation of metal hydroxides to some extent. The average removal rates of nitrate, Pb, and Cd after EKR improved from 85.5%, 11.1%, and 21.8–98.5%, 35.8% and 47.7%, respectively.

Controlled Lattice Thermal Conductivity of Transparent Conductive Oxide Thin Film via Localized Vibration of Doping Atoms.

Amorphization using impurity doping is a promising approach to improve the thermoelectric properties of tin-doped indium oxide (ITO) thin films. However, an abnormal phenomenon has been observed where an excessive concentration of doped atoms increases the lattice thermal conductivity (κl). To elucidate this paradox, we propose two hypotheses: (1) metal hydroxide formation due to the low bond enthalpy energy of O and metal atoms and (2) localized vibration due to excessive impurity doping. To verify these hypotheses, we doped ZnO and CeO2, which have low and high bond enthalpies with oxygen, respectively, into the ITO thin film. Regardless of the bond enthalpy energy, the κl values of the two thin films increased due to excessive doping. Fourier transform infrared spectroscopy was conducted to determine the metal hydroxide formation. There was no significant difference in wave absorbance originating from the OH stretching vibration. Therefore, the increase in κl due to the excessive doping was due to the formation of localized regions in the thin film. These results could be valuable for various applications using other transparent conductive oxides and guide the control of the properties of thin films.

Enhancement of electrokinetic remediation of lead and copper contaminated soil by combination of multiple modified electrolyte conditioning techniques

Electrokinetic soil remediation is often impeded by the aggregation of small particles, within soil, during the procedure. The soil porous network is subsequently clogged which results in immediate process termination. In order to overcome this limitation, the feasibility of electrokinetic remediation coupled simultaneously with two enhancing techniques was investigated: modified periodic polarity reversal and catholyte pH control. The objective is to keep the soil pores unclogged in order to remove Pb and Cu from soil. Citric acid was used as anolyte, and 1 DCV.cm-1 was applied through the processing cell. This strategy showed 9.0 times better remediation results than that of unenhanced electroremediation. It was mainly owed to: (i) The pH adjustment that kept the catholyte ideally acid, thus avoiding the formation of metal hydroxide precipitates that could clog the soil pores. (ii) An increase of electro osmotic flow due to the modified polarity reversal technique. Approximately 96% of Pb and Cu were removed from soil. Duplicate results were obtained on soil with 10-fold the initial heavy metals concentration. This combined configuration ensured an unclogged path within soil and enhanced electrokinetic mechanisms efficiency against pollutants remediation.

Surfactant effects on structural, optical and morphological characteristics of microwave irradiated CdO nanostructures

Surfactant based microwave irradiated and alkaline medium involving wet chemical method was adopted to prepare CdO nanostructures. The phase evaluation of prepared and annealed CdO nanostrucutures has been analyzed by XRD and FTIR. The average size of the crystallite was estimated to be 54 nm for the NH4OH reagent and 60 nm for the NaOH reagent in the assisted synthesis. Specific surface area, lattice parameter, X-ray density, dislocation density, microstrain, texture coefficient and Williamson Hall have been calculated from the XRD profile. UV transmittance and the K-M plot of DRS and PL spectra were used to examine the optical properties of CdO nanostructures. The spherical and rod-like structures of CdO prepared with strong and weak alkaline medium have been recorded through SEM and TEM micrographs. The four-step process of hydration, intermediate formation, metal hydroxide formation, and metal oxide formation confirms that the experiment in the presence of 0.1 M sodium hydroxide results in rod-shaped nanostructures.

Etching oxide overlayers of NiFe phosphide to facilitate surface reconstruction for oxygen evolution reaction

Transition-metal phosphides have been of concern as efficient electrocatalysts for oxygen evolution reaction (OER) due to its high conductivity and earth-abundance reserves. However, oxide overlayers formed on their surface by spontaneously atmospheric oxidation are usually neglected, thus confusing the establishment of structure–performance relationship. Herein, we successfully etched the oxide overlayers of NiFe phosphide (NiFeP) by a dielectric barrier discharge (DBD) plasma technique, aiming to reveal the influence of the oxide overlayers on its electrocatalytic performance for OER. It is found that etching the oxide overlayers can accelerate the surface reconstruction process of NiFeP and facilitate the formation of metal hydroxides, which are key intermediate phases for OER. Consequently, the etched NiFeP-DBD material shows remarkably enhanced OER activity with an overpotential of 265 mV at a current density of 10 mA cm−2. The finding of this work probably brings a significant impact to understand the structure–performance relationship of metal phosphide in electrooxidation reaction.

Selenic Acid Etching Assisted Vacancy Engineering for Designing Highly Active Electrocatalysts toward the Oxygen Evolution Reaction.

Oxygen evolution electrocatalysts are central to overall water splitting, and they should meet the requirements of low cost, high activity, high conductivity, and stable performance. Herein, a general, selenic-acid-assisted etching strategy is designed from a metal-organic framework as a precursor to realize carbon-coated 3d metal selenides Mm Sen (Co0.85 Se1- x , NiSe2- x , FeSe2- x ) with rich Se vacancies as high-performance precious metal-free oxygen evolution reaction (OER) electrocatalysts. Specifically, the as-prepared Co0.85 Se1- x @C nanocages deliver an overpotential of only 231mV at a current density of 10mA cm-2 for the OER and the corresponding full water-splitting electrolyzer requires only a cell voltage of 1.49V at 10mA cm-2 in alkaline media. Density functional theory calculation reveals the important role of abundant Se vacancies for improving the catalytic activity through improving the conductivity and reducing reaction barriers for the formation of intermediates. Although phase change after long-term operation is observed with the formation of metal hydroxides, catalytic activity is not obviously affected, which strengthens the important role of the carbon network in the operating stability. This study provides a new opportunity to realize high-performance OER electrocatalysts by a general strategy on selenic acid etching assisted vacancy engineering.

Removal of fluoride, nitrates and phosphor from drinking water using electrocoagulation: A Review

This paper is intended to provide a review of the published literature on the topic of electrocoagulation technology. Water treatment processes containing inorganic anions (fluoride, nitrates and phosphorous) are discussed, including electrocoagulation technology. Electrocoagulation technology is a simple and environmentally friendly electrochemical technique that produces less sludge compared to other treatments. Coagulant production from dissolution of the sacrificial anode and formation of metal hydroxides. The efficiency of the process depends on the type and arrangement of the electrodes, the distance between the electrodes, the operating time, the pH, and the temperature.

Using Stable Isotopes to Disentangle Marine Sedimentary Signals in Reactive Silicon Pools

AbstractMany studies use sedimentary biogenic silica (bSiO2) stable isotopes (e.g., δ30Si) as paleoproxies but neglect signals from other sedimentary reactive SiO2 phases. We quantified δ30Si for multiple reactive Si pools in coastal river‐plume sediments, revealing up to −5‰ difference between acid‐leachable and alkaline‐digestible amorphous SiO2. Thus, previous studies have missed valuable information on early diagenetic products and, in cases where sediments were not cleaned, potentially biased bSiO2 δ30Si values. Acid‐leachable δ30Si, that is, from authigenic products, are the result of either multistep fractionation from a bSiO2 source or an ~2‰ fractionation (consistent with metal hydroxide formation) from slowly dissolving lithogenic SiO2. This analysis also suggests that sedimentary diatom bSiO2, which has increased regionally in the last half‐century, is the critical substrate of early authigenic Si precipitates. Regional eutrophication, which has stimulated sedimentary bSiO2 accumulation, may have facilitated additional sequestration of both sedimentary Si and cations from early diagenetic products.

Enhanced Electrokinetic Removal of Heavy Metals from a Contaminated Lake Sediment for Ecological Risk Reduction

ABSTRACT In this study, electrokinetic remediation (EKR) was performed to reduce the risk of heavy metal contaminants viz., Cd, Cu, Ni, Pb and Zn associated with different fractions of lake sediments. Firstly, batch experiments were performed to estimate the optimal concentration of enhancing agents such as EDTA, nitric acid and acetic acid for effective dissolution of heavy metals from sediments and to minimize the dissolution of earth metals (Fe and Al) to maintain good soil health. In addition to that, the effect of pH on dissolution of these heavy metals with optimized concentration was studied separately. The results from batch experiments showed that EDTA with the concentration of 0.01 M enhanced the heavy metal dissolution as 38–88% in the pH range 2–12. Nitric acid and acetic acid with the concentration of 0.05 M enhanced the heavy metal dissolution as 18–85% and 15–80%, respectively in the pH range 2–6. For enhancing agents like nitric acid and acetic acid, the increase of pH (above 6) led to the formation of metal hydroxides and carbonates, which reduced the efficiency of heavy metal dissolution. Secondly, EKR experiments were conducted in a reactor with optimal concentration of EDTA (0.01 M), nitric acid and acetic acid (0.05 M) as electrolyte and sediment saturation solution for 7–21 days of treatment time. After 21 days of EKR with 0.01 M of EDTA as enhancing agent, the average removal of heavy metals achieved about 46.4–78.8 % and associated risk with metals viz., Cd, Pb, Zn and Cu reduced from high to low risk and Ni reduced from high to medium risk, according to risk assessment category. Alternatively, the EKR treatment using nitric acid and acetic acid showed the average removal of heavy metals of about 17.2–43.60% and 24.9–57.2 %, respectively, and all heavy metals pose medium risk, except for Cd, which showed low risk to the environment.

A facile approach of developing Al/SnO2 xerogels via epoxide assisted gelation: A highly versatile route for formaldehyde gas sensors

A robust synthesis approach to Al/SnO2 based formaldehyde gas sensing xerogels using epoxide assisted sol-gel chemistry is reported. The route utilizes simple tin and aluminum salt precursors in alcohol/water mixture, thus eliminating the need for organometallic precursors. Propylene oxide acts as a proton scavenger and drives metal hydroxide formation and subsequent polycondensation reactions. Al/SnO2 xerogels (with Al doping 1–4 mol%) were aged for 24 h to strengthen the gel network, followed by sintering and screen printed thick films formation. Prior to gas sensing investigations, the physico-chemical properties of the material were analysed using TG-DTA, XRD, FE-SEM, TEM, SAED, EDAX, UV–Visible and FTIR spectroscopic techniques. The developed material showcase tetragonal rutile structure of SnO2 with porous morphology required for effective gas diffusion. Al/SnO2 with 3 mol% doping level exhibited excellent gas sensing ability (Ra/Rg = 15 @ 300 °C operating temperature) towards barely 100 ppm formaldehyde concentration. Not only sensor response was got improved (from Ra/Rg value 5 to 15), but also the operating temperature got reduced from 325 °C to 300 °C). An effect of formaldehyde concentration, the sensor response got increased rapidly up to 100 ppm concentration, thereafter the increase in response was observed almost stagnant. By keeping the measurement parameters as is, the sensor performance was checked six times after the initial measurement with the interval of 10 days, which showed ~89% of its initial sensitivity. The developed material showcase the potentiality of being formaldehyde gas sensor.

Alkali acetate-assisted enhanced electronic coupling in CsPbI3 perovskite quantum dot solids for improved photovoltaics

Fully inorganic CsPbI3 perovskite quantum dots (CsPbI3-PQDs) are known as the best-performing photovoltaic absorber in colloidal quantum dot solar cells. This is achieved by improving the cubic-phase-stabilization and electronic-coupling in CsPbI3-PQD solids. In conventional approaches, the hydrolysis of methyl acetate (MeOAc) resulting in acetic acid and methanol as intermediate substances plays a key role in replacing long-chain hydrocarbons with short-chain ligands, which improves charge transport in the CsPbI3-PQD solids. However, CsPbI3-PQDs suffer from lattice distortion and instability under acidic conditions including protons and polar media, leading to CsPbI3-PQD fusion and poor photovoltaic performance. Herein, we report that electronic coupling and photovoltaic performance of CsPbI3-PQD solids are improved by efficient removal of long-chain oleate ligands using a solution of sodium acetate (NaOAc) in MeOAc, which results in the direct generation of OAc ions without forming protons and methanol. NaOAc-based ligand exchange of CsPbI3-PQDs enables preservation of their nanocrystal size without fusion and minimization of surface trap states originating from metal hydroxide formation on their surfaces. Consequently, the best solar cell comprising NaOAc-treated CsPbI3-PQDs shows an improved device performance with a power conversion efficiency (PCE) of 13.3%, as compared with a lead nitrate-treated control device (12.4% PCE).

Borohydride-Assisted Surface Activation of Co3O4/CoFe2O4 Composite and Its Catalytic Activity for 4-Nitrophenol Reduction.

Surface activation of catalysts is known to be an efficient process to enhance their activity in catalytic processes. The activation process includes the generation of oxygen vacancies, changing the nature of the catalyst surface from acidic to basic and vice versa, and the reduction of catalyst surface by H2. On the other hand, magnetically separable catalysts are highly beneficial for their utilization in water or biological fluid-based catalytic processes, as they can be easily guided to the target site and recovered. Here, we present the fabrication of CoFe2O4 and composites of Co3O4/CoFe2O4/α-Fe2O3 and Co/CoFe2O4/α-Fe2O3 through solution combustion process to utilize them as catalysts for 4-nitrophenol (4-NP) reduction. Although none of the as-prepared CoFe2O4 and Co3O4/CoFe2O4 was seen to be active in 4-NP reduction reaction, the surface of the composite gets activated by borohydride (NaBH4) treatment to act as a highly active catalyst for 4-NP reduction. X-ray photoelectron spectroscopy of the composite revealed the formation of metal-hydroxide (M–O–H) species of both Co and Fe at its surface due to borohydride treatment. The mechanism of the surface activation and the dynamics of 4-NP reduction of the surface-activated composite have been studied, proposing a possible pathway for the reduction of 4-NP.

Combined Fenton process and sulfide precipitation for removal of heavy metals from industrial wastewater: Bench and pilot scale studies focusing on in-depth thallium removal

Thallium (Tl) in industrial wastewater is a public health concern due to its extremely high toxicity. However, there has been limited research regarding Tl removal techniques and engineering practices to date. In this investigation, bench and pilot studies on advanced treatment of industrial wastewater to remove Tl to a trace level were conducted. The treatment process involved a combination of hydroxide precipitation, Fenton oxidation, and sulfide precipitation. While hydroxide precipitation was ineffective for Tl+ removal, it enabled the recovery of approximately 70%–80% of Zn as Zn hydroxide in alkaline conditions. The Fenton process provided good Tl removal (>95%) through oxidation and precipitation. Tl was then removed to trace levels (< 1.0 µg/L) via sulfide precipitation. Effective removal of other heavy metals was also achieved, with Cd< 13.4 µg/L, Cu< 39.6 µg/L, Pb< 5.32 µg/L, and Zn< 357 µg/L detected in the effluent. X-ray photoelectron spectroscopy indicated that Tl2S precipitate formed due to sulfide precipitation. Other heavy metals were removed via the formation of metal hydroxides during hydroxide precipitation and Fenton treatment, as well as via the formation of metal sulfides during sulfide precipitation. This combined process provides a scalable approach for the in-depth removal of Tl and other heavy metals from industrial wastewater.

New insights into the interaction between heavy metals and struvite: Struvite as platform for heterogeneous nucleation of heavy metal hydroxide

During the struvite (MgNH4PO4·6H2O) recovery from agricultural or industrial wastewater, the extensive existence of heavy metals would pose great threats to the planting and environment. This work revealed the association of kinds of heavy metals, as possible substances in the wastewater, with the struvite. The struvite has been synthesized in situ and employed to contact with both high and low concentration heavy metal (including Cu, Ni, Pb, Zn, Mn, Cr(III)) wastewater. The heavy metal precipitation rates under different pH values from 6.0 to 10.0, and under a series of struvite addition amount have been investigated. The precipitation of heavy metals without addition of struvite is functioned as control experiments. The struvite’s presence can enhance the heavy metal precipitation rate under all pH values. The Ni and Mn have relatively lower precipitation rate compared with other metals. For extremely low heavy metal concentration the precipitation rate is 99.1%, 97.9%, 99.9%, 98.9%, 96.9%, and 98.3%, which is much higher than that of control group (10.5%, 8.7%, 13.2%, 14.1%, 6.7%, and 10.5%). Through XPS and TEM & EDS analysis, the heavy metal hydroxides is found to be precipitated on the struvite surface. Based on TEM observations, it has been found the copper hydroxides had nucleation and growth on the struvite’s surface. The heterogeneous nucleation mechanism has been proposed, which provides relationship model of sorption, nucleation, and precipitation of heavy metals in the form of hydroxides on struvite surfaces. It has been calculated that the △Gi value that thermodynamic activation energy barrier constraints on the metal hydroxide formation can be intensively abated through heterogeneous nucleation on struvite.

Application of sequential extraction analysis to Pb(II) recovery by zerovalent iron-based particles

Zerovalent iron (ZVI) is an environmental-friendly reactive reagent for recovering heavy metals. However, the detailed recovery mechanism remains unclear due to a lack of quantitative analysis of recovery products. Herein, microscale ZVI, nanoscale ZVI and Ni/Fe nanoparticles were used to recover Pb(II) in aqueous solution and a sequential extraction procedure (SEP) was applied to determine the formed lead species quantitatively. At high initial Pb(II) concentration (500 mg L−1), more than 99.5% of Pb(II) was immobilized by Ni/Fe and n-ZVI, whereas m-ZVI caused inferior recovery efficiency (<25%). XRD and XPS results revealed that Pb(II) was reduced to Pb0 prior to the formation of metal hydroxides as the external shell of ZVI. SEP results showed that the fraction bound to carbonates (PbO), fraction bound to iron oxides and exchangeable fraction were the main lead species conducted by Ni/Fe, n-ZVI and m-ZVI, respectively. Consequently, (co-)precipitation and specific adsorption dominated Pb(II) recovery by Ni/Fe and n-ZVI, whereas m-ZVI conducted Pb(II) recovery mainly via weak adsorption. The reactivity of ZVI toward Pb(II) followed the increasing order of m-ZVI << n-ZVI ≤ Ni/Fe. The detailed mechanisms of Pb(II) recovery conducted by different ZVI were proposed.