Aqueous Pb Research Articles

Removal characteristics of Pb(II) and Cd(II) from aqueous single metal solutions by vermicompost combined with nano-CaO

ABSTRACT Vermicompost (CV) and nanomaterials have been identified as potential amendments to adsorb environmentally toxic heavy metals. This study analyzes multi-aspect properties of CV and its nanocomposite (CV-nCa) with nano calcium oxide (nCaO), which include pH, electrical conductivity (EC), cation exchange capacity (CEC), ash content and surface characteristics, aiming to compare their potential for removing aqueous Pb(II) and Cd(II). The results demonstrated that CV-nCa had a higher pH, EC, CEC, ash content, pore parameters and specific surface area than CV. Adsorption isotherm studies showed that CV-nCa had a higher adsorption capacities for Pb(II) and Cd(II), with the maximum adsorption capacities being 255.1 mg/g and 137.7 mg/g. The adsorption rates (ARs) by CV-nCa were both above 99.72% within the initial concentration of Pb(II) being 200–800 mg/L and Cd(II) being 100–200 mg/L. In addition, CV-nCa can effectively remove Pb(II) and Cd(II) within a wider pH range (3–6) and a lower mass concentration (MC) of 4 g/L. Kinetic studies showed that the Pb(II) and Cd(II) adsorption by CV-nCa were both best fitted with the pseudo-second-order model. FTIR analysis demonstrated that the interaction of CV and CV-nCa with Pb(II) and Cd(II) mainly depended on thearomatic/aliphatic acids, some primary/secondary alcohols and some silicate and carbonates. XRD analysis showed that the addition of nCaO into CV mainly increased CaCO3 content and affected the adsorption characteristics. Thus, combining nCaO with vermicompost may broaden heavy metal remediation and vermicompost utilization in the environment.

Isolation of heavy metal-immobilizing and plant growth-promoting bacteria and their potential in reducing Cd and Pb uptake in water spinach

Heavy metal-immobilizing bacteria are normally capable of stabilizing metals and affecting their absorption by plants. However, few studies have elucidated the mechanisms employed by novel heavy metal-immobilizing and plant growth-promoting bacteria to immobilize Cd and Pb and reduce their uptake by vegetables. In this study, polyamine (PA)-producing strains were isolated and their effects on biomass and metal accumulation in water spinach (Ipomoea aquatica Forssk.) and the underlying mechanisms were investigated. Two PA-producing strains, Enterobacter bugandensis XY1 and Serratia marcescens X43, were isolated. Strains XY1 and X43 reduced the aqueous Cd and Pb levels (49%–52%) under 10 mg L−1 Cd and 20 mg L−1 Pb because of metal ion chelation by bacterially produced PAs and cell adsorption. Further evidence showed that Cd and Pb were bound and precipitated on the bacterial cell surface in the form of Cd(OH)2, CdCO3 and PbO. Compared with strain-free water spinach, greens inoculated with strains XY1 and X43 showed 51%–80% lower Cd and Pb contents. The rhizosphere soil pH and PA contents were significantly higher, and lower contents of the rhizosphere soil acid-soluble fractions of Cd (18%–39%) and Pb (31%–37%) were observed compared to the noninoculated control. Moreover, inoculation with XY1 reduced the diversity of the bacterial community, but the relative abundances of plant growth-promoting and PA-producing bacteria in rhizosphere soil were enriched, which enhanced water spinach resistance to Cd and Pb toxicity. Our findings describe novel heavy metal-immobilizing bacteria that could be used to improve the habitat of vegetables and reduce their uptake of heavy metals.

Iron/titanium oxide-biochar (Fe2TiO5/BC): A versatile adsorbent/photocatalyst for aqueous Cr(VI), Pb2+, F- and methylene blue

This is the first report of the metal Fe-Ti oxide/biochar (Fe2TiO5/BC) composite for simultaneous removal of aqueous Pb2+, Cr6+, F- and methylene blue (MB). Primary Fe2TiO5 nano particles and aggregates were dispersed on a high surface area Douglas fir BC (∼700 m2/g) by a simple chemical co-precipitation method using FeCl3 and TiO(acac)2 salts treated by base and heated to 80 °C. This was followed by calcination at 500 °C. This method previously was used without BC to make the neat mixed oxide Fe2TiO5, exhibiting a lower energy band gap than TiO2. Adsorption of Cr(VI), Pb(II), fluoride, and MB on Fe2TiO5/BC was studied as a function of pH, equilibrium time, initial adsorbate concentration, and temperature. Adsorption isotherm studies were conducted at 5, 25, and 45 ℃ and kinetics for all four adsorbates followed the pseudo second order model. Maximum Langmuir adsorption capacities for Pb2+, Cr6+, F- and MB at their initial pH values were 141 (pH 2), 200 (pH 5), 36 (pH 6) and 229 (pH 6) mg/g at 45 ℃ and 114, 180, 26 and 210 mg/g at 25 ℃, respectively. MB was removed from the water on Fe2TiO5/BC by synergistic adsorption and photocatalytic degradation at pH 3 and 6 under UV (365 nm) light irradiation. Cr6+, Pb2+, F-, and MB each exhibited excellent removal capacities in the presence of eight different competitive ions in simulated water samples. The removal mechanisms on Fe2TiO5/BC and various competitive ion interactions were proposed. Some iron ion leaching at pH 3 catalyzed Photo-Fenton destruction of MB. Fe2TiO5, BC, and Fe2TiO5/BC bandgaps were studied to help understand photocatalysis of MB and to advance supported metal oxide photodegradation using smaller energy band gaps than the larger bandgap of TiO2 for water treatment. A long range goal is to photocatalytically destroy some sorbates with adsorbents to avoid the need for regeneration steps.

Examining the Effect of a Chitosan Biopolymer on Alkali-Activated Inorganic Material for Aqueous Pb(II) and Zn(II) Sorption.

Biopolymers and alkali-activated materials have attracted a great deal of attention as adsorbents for the removal of heavy metal contaminants from aqueous solutions. Both materials are sustainable and feature unique properties, but biopolymers are relatively more expensive or difficult to prepare and exhibit low mechanical and surface properties, a narrow pH range, and thermal stability. In this study, hybrid adsorbents were prepared from both types of material, by alkali activation of low-cost fly ash precursors accompanied by incorporation of 0-2%mass chitosan biopolymer. Two types of alkaline activating solutions, NaOH and Na2SiO3, were employed to generate two sets of hybrid adsorbents with varying chitosan contents. The effect of the chitosan dosage on the aqueous Pb(II) and Zn(II) sorption efficiency was also investigated. The adsorbents exhibited 98-100% removal efficiencies for both metals, but the sorption of Zn(II) was generally higher than that of Pb(II). The addition of 0.1-2.0%mass chitosan resulted in very little improvement in the overall efficiency of the adsorbents. In contrast, 0.05%mass chitosan led to a decrease in the sorption efficiency; this was linked to the decrease in the adsorbents' ζ potential. The Na2SiO3-activated materials featured larger BET surface areas and better overall sorption performance, while the NaOH-activated materials showed the worst Pb(II) sorption performance and hence more noticeable improvement upon addition of chitosan. Mechanistic investigation shows that the sorption process follows second-order kinetics and is a chemisorption-driven process.

Cellulose acetate-polyurethane film adsorbent with analyte enrichment for in-situ detection and analysis of aqueous Pb using Laser-Induced Breakdown Spectroscopy (LIBS)

In this work, we have investigated the potential application of cellulose acetate-polyurethane (CA-PU) film, as an adsorbent material as well as an enrichment medium for aqueous Pb quantification using Laser-Induced Breakdown Spectroscopy (LIBS). CA-PU was reported to be a good adsorbent for Pb removal from water medium due to its possession of O- and N-containing functional groups. The adsorption was first qualitatively investigated by observing Pb I (405.7 nm) emission line, before and after the adsorption. The study was further carried out using varied laser energies in order to optimize the produced spectra. The optimum laser energy was 54 mJ (gain = 1,500; width = 30 µs). The other aspects this work considered were contact time and pH, where the stable analysis was obtained after 12 h enrichment process and at pH 7. Normalization using C I (247.8 nm) internal standard line could compensate for the errors generated during the analysis. The non-linear regression of the calibration curve achieved correlation as high as R2 = 0.99997 and LOD = 1.02 mg/L. Based on the obtained LOD, this analytical method is suitable for the wastewater control in chemical industries in Indonesia. As an addition, LIBS is a potential technique to measure the binding energy of the adsorbent surface which requires further studies.

A Highly Efficient Adsorbent Based on Starch-Graphene Oxide Architecture for Scavenging Aqueous Pb(II): Isotherms, Kinetics, Thermodynamics and Interaction Mechanism

Heavy metal pollution stems from the modern industry is a severe environmental problem. In this work, a highly efficient adsorbent based on starch-graphene oxide architecture (SGO) was fabricated, characterized and employed to scavenge aqueous Pb(II), a major water contaminant. The scavenging performance was evaluated, and the interaction mechanism between SGO and Pb(II) was elucidated. Results indicate, the starch introduction brought performance enhancement, consequently made SGO outperform either single starch or GO regarding adsorption efficiency. Specifically, SGO adsorbs 95.83% of Pb(II) in 16 min, with adsorption capacity 383.32 mg‧g−1, manifesting some advantages over other analogous adsorbents, such as higher capacity and faster kinetics. The chemical interaction between Pb(OH)+ and C = O, C–O related groups in SGO supported the adsorption, which was a spontaneous, exothermic and entropy increasing process. The adsorption was well described by the Freundlich, pseudo-second-order model and intra-particle diffusion models, adsorption rate simultaneously controlled by intra-particle diffusion and chemical interaction. Based on its high adsorption efficiency, SGO may have promising application in heavy metal scavenging from water.

Insight into the Metabolic Profiles of Pb(II) Removing Microorganisms.

The objective of the study was to gather insight into the metabolism of lead-removing microorganisms, coupled with Pb(II) removal, biomass viability and nitrate concentrations for Pb(II) bioremoval using an industrially obtained microbial consortium. The consortium used for study has proven to be highly effective at removing aqueous Pb(II) from solution. Anaerobic batch experiments were conducted with Luria-Bertani broth as rich growth medium over a period of 33 h, comparing a lower concentration of Pb(II) with a higher concentration at two different nutrient concentrations. Metabolite profiling and quantification were conducted with the aid of both liquid chromatography coupled with tandem mass spectroscopy (UPLC-HDMS) in a “non-targeted” fashion and high-performance liquid chromatography (HPLC) in a “targeted” fashion. Four main compounds were identified, and a metabolic study was conducted on each to establish their possible significance for Pb(II) bioremoval. The study investigates the first metabolic profile to date for Pb(II) bioremoval, which in turn can result in a clarified understanding for development on an industrial and microbial level.

Optimization of hydrothermal synthesis of hydroxyapatite from chicken eggshell waste for effective adsorption of aqueous Pb(II).

Proper disposal of the millions of tons of eggshell waste generated around the world every year is a significant environmental challenge. However, eggshell waste can be converted into new materials that may be useful for a wide range of applications. In this study, four methods, including the conventional subcritical hydrothermal method (CSHM), microwave-assisted subcritical hydrothermal method (MSHM), conventional low-temperature hydrothermal method (CLHM), and ultrasonic-assisted low-temperature hydrothermal method (ULHM) were used to convert eggshell waste into hydroxyapatite (HAP). For each hydrothermal method, increasing the reaction temperature increased production efficiency and improved the degree of crystallinity of HAP. X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) surface area analysis, Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) were used to characterize the preferred eggshell-derived HAP, which was produced by the MSHM at 180 °C in a period of only 1 h. For the MSHM, the HAP yield was 75.3%, the degree of HAP crystallinity was as high as 0.78, and pure, rod-like, nano-sized HAP particles with high specific surface area were produced. For the preferred HAP produced by the MSHM, the adsorption capacity of Pb2+and pH were positively related in the range of pH 1-6. Consequently, the HAP produced by the MSHM showed relatively high maximum adsorption (qm= 505.05 mg/g) of Pb2+ in aqueous solution. The adsorption process followed a pseudo-second-order reaction model, and the equilibrium adsorption was well fit by the Langmuir model.

Magnetite Nanoparticles Decorated Graphene Oxide Composite as an Efficient and Recoverable Adsorbent for Removing Aqueous Ni(Ⅱ), Pb(Ⅱ)

Massive disposal of various heavy metals by industrial activities gives rise to serious environmental contamination. Herein, a magnetite nanoparticles decorated graphene oxide composite (MNGO) was facilely prepared via simple co-precipitation. The as fabricated MNGO was characterized and used as adsorbent to remove aqueous Ni(Π) and Pb(Π) with high efficiency. The removal performance was investigated, and the interaction mechanism between adsorbent and adsorbate was analyzed. Control experiment presents, MNGO outperforms either single Fe3O4 or graphene oxide (GO), which is owing to the mutual positive effects between the two phases. Concretely, MNGO efficiently adsorbs 391.63 mg·g–1, 373.59 mg·g–1 of Ni(Π), Pb(Π) in 5 min, respectively. In addition, Fe3O4 introduction brings magnetic separability, which make MNGO recoverable. Adsorptions are spontaneous, exothermic and randomness decreasing, which conform well to the Freundlich and pseudo second order models. The interaction mechanism is clarified as: oxygen atoms in C=O, C–O related groups chemically interact with Ni(Ⅱ), Pb(Ⅱ). The high efficiency performance of MNGO entails inspiring application in heavy metal scavenging.

Improving the stability of Pb2+ ion-selective electrodes by using 3D polyaniline nanowire arrays as the inner solid-contact transducer

Polyaniline nanowire arrays (PANI- NWA) were synthesized by electrochemical deposition, then successfully applied as the ion-to-electron transducer in ion selective electrodes (ISEs) for the detection of aqueous Pb2+ ions. When used as the solid-contact layer in Pb2+-ISEs, the PANI- NWA delivered a high capacitance and low impedance as measured by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), respectively, thus delivering efficient ion-to-electron transfer. Owing to the open structure of the nanowire arrays, Pb2+ ions can able to easily penetrate the PANI layer, further enhancing the detection efficiency. Developed GC/PANI- NWA/Pb2+-ISE showed outstanding potentiometric performance, including a low Pb2+ detection limit (2.5 × 10−8 M), a short response time (about 1 s), high stability in N2 (or O2) and no light sensitivity. Further, the water layer between the solid-contact layer and the ISM was largely eliminated when three-dimensional PANI- NWA were applied as the solid contact layer, thus enhancing the stability of the ISE.

Enhanced adsorption of aqueous Pb(II) by modified biochar produced through pyrolysis of watermelon seeds

A biochar (BC) was obtained by the pyrolysis of watermelon seeds (WM) in nitrogen environment. In addition, a modified biochar (HP-BC) was obtained by means of H2O2 treatment of BC. Later on, both kinds of biochar (BC and HP-BC) were characterized and compared as regards their potential for Pb(II) adsorption from wastewater. Characterization was performed by using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), energy dispersive spectroscopy (EDS), Zeta potential analysis, elemental mapping, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Pb(II) adsorption characteristics for HP-BC and BC as were evaluated as a function of solution pH, contact time and Pb(II) equilibrium concentration, using kinetic and thermodynamic studies, as well as adsorption isotherms. Regarding kinetics, the pseudo-second order model showed good fitting to experimental data. Based on the Langmuir model, the maximum Pb(II) adsorption capacities were calculated as 44.32 mg g−1 and 60.87 mg g−1 for BC and HP-BC, respectively. Thermodynamic study indicated that Pb(II) adsorption onto BC and HP-BC was spontaneous and primarily governed by chemisorption and surface complexation. In view of the results, the H2O2 modification of the watermelon seeds biochar can be considered as a promising and cost effective approach as regards Pb(II) removal from water/wastewater, which would not cause adverse impacts on the surrounding environments. Overall, it can be seen as a procedure promoting the effective recycling of a waste/by-product, in line of the precepts of the circular economy, aiding to protect human and environmental health.

The impact of an Amberlite XAD-16-based chelating resin for the removal of aqueous Cd(II) and Pb(II)ions

The main objective of this study is to investigate the influence of the Amberlite XAD-16-based chelating resin, 1,8-(3,6-dithiaoctyl)-4-polyvinylbenzenesulphonate (dpvbs), for the removal of the highly lethal Pb(II) and Cd(II) from aqueous solutions. The extractor`s behavior is examined, as adsorbent as well as coordinating agent showing structural changes upon the interaction with the targeted metal ions. Elemental analyses, FTIR, electronic spectra, EDS and XPS were used to provide a close image of the composition, structural and morphological changes upon the interaction with Pb(II) and Cd(II). Thermal behavior of the sorption products, compared with the coordinating resin, were also, studied and the estimated thermodynamic parameters indicated an endothermic spontaneous sorption mechanism. The BET surface area, BJH desorption volume and the pore diameters increased upon chelation with Cd(II) and Pb(II), indicating the destruction of the cross-linking of the free resin. SEM and AFM studies confirmed the surface morphological change of dpvbs, after sorption processes. The sorption effectiveness was examined utilizing batch and column methods, showing high removal efficiency with an average sorption of 99.9%. dpvbs was tested for the removal of metal ions from tap watershowing a metal uptake of almost the same after 3 cycles, with an efficiency of 98–99%.

Efficacy of treated sodium alginate and activated carbon fibre for Pb(II) adsorption

Efficacy of treated sodium alginate (TSA) and activated carbon fibre (ACF) for aqueous Pb(II) uptake was comparatively investigated. By employing FTIR, SEM, EDX, XRD, point of zero charges and surface area measurements, the available functional groups, morphology, crystallinity, surface charge and surface areas of both adsorbents were respectively elucidated. The Pb(II) uptake performance of both adsorbents was also studied via batch mode at varied process conditions. The experimental isotherm and kinetic data for both adsorbents were best fitted to nonlinear forms of Langmuir and pseudo-first-order models, respectively. Similarly, intraparticle diffusion was the sole controlling mechanism. Despite the huge variation in the surface area, TSA (7.8 m2/g) with high carboxyl content (395.6 meq-COOH/100 g of sample) performed better by all standards than the ACF (975 m2/g). This finding showed that although the surface area of a given adsorbent is a key indicator of its adsorptive performance, the inherent surface functional groups play a superior role. The experimentally derived maximum adsorption capacities of 221.25 mg/g (for TSA) and 183.34 mg/g (for ACF) were recorded at an equilibrium time of 30 min and 45 min, respectively. Therefore, TSA and ACF demonstrated effectiveness for aqueous Pb (II) sequestration.

A cross scale investigation of galena oxidation and controls on mobilization of lead in mine waste rock

Galena and Pb-bearing secondary phases are the main sources of Pb in the terrestrial environment. Oxidative dissolution of galena releases aqueous Pb and SO4 to the surficial environment and commonly causes the formation of anglesite (in acidic environments) or cerussite (in alkaline environments). However, conditions prevalent in weathering environments are diverse and different reaction mechanisms reflect this variability at various scales. Here we applied complementary techniques across a range of scales, from nanometers to 10 s of meters, to study the oxidation of galena and accumulation of secondary phases that influence the release and mobilization of Pb within a sulfide-bearing waste-rock pile. Within the neutral-pH pore-water environment, the oxidation of galena releases Pb ions resulting in the formation of secondary Pb-bearing carbonate precipitates. Cerussite is the dominant phase and shannonite is a possible minor phase. Dissolved Cu from the pore water reacts at the surface of galena, forming covellite at the interface. Nanometer scale characterization suggests that secondary covellite is intergrown with secondary Pb-bearing carbonates at the interface. A small amount of the S derived from galena is sequestered with the secondary covellite, but the majority of the S is oxidized to sulfate and released to the pore water.

Time-sequence development of metal(loid)s following the 2015 dam failure in the Doce river estuary, Brazil

In the context of the Doce river (Southeast Brazil) Fundão dam disaster in 2015, we monitored the changes in concentrations of metal(loid)s in water and sediment and their particulate and dissolved partitioning over time. Samples were collected before, during, and after the mine tailings arrival to the Doce river estuary (pre-impact: 12, 10, 3 and 1 day; acute stage: tailing day – TD and 1 day after – DA; chronic stage: 3 months and 1 year post-disaster). Our results show that metal(loid) concentrations significantly increased with time after the disaster and changed their chemical partitioning in the water. 35.2 mg Fe L−1 and 14.4 mg Al L−1 were observed in the total (unfiltered) water during the acute stage, while aqueous Al, As, Cd, Cr, Cu, Fe, Mn, Ni, Pb, Se and Zn concentrations all exceeded both Brazilian and international safe levels for water quality. The Al, Fe and Pb partitioning coefficient log (Kd) decrease in the acute stage could be related to the high colloid content in the tailings. We continued to observe high concentrations for Al, Ba, Cd, Cr, Cu, Fe, V and Zn mainly in the particulate fraction during the chronic stage. Furthermore, the Doce river estuary had been previously contaminated by As, Ba, Cr, Cu, Mn, Ni and Pb, with a further increase in sediment through the tailing release (e.g. 9-fold increase for Cr, from 3.61 ± 2.19 μg g−1 in the pre-impact to 32.16 ± 20.94 μg·g−1 in the chronic stage). Doce river sediments and original tailing samples were similar in metal(loid) composition for Al, As, Cd, Cr, Cu, Fe, V and Zn. As a result, these elements could be used as geochemical markers of the Fundão tailings and considering other key parameters to define a baseline for monitoring the impacts of this environmental disaster.

Utilization of low-cost sugarcane waste for the adsorption of aqueous Pb(II): Kinetics and isotherm studies

In this study, the sorption capacity of local sugarcane waste (SW) for aqueous Pb(II) was investigated. The SW was fully characterized using Scanning microscopy (SEM), Energy-dispersive X-ray Analysis (EDX), Fourier Transform Infrared Spectroscopy (FTIR), and Brunauer–Emmett–Teller (BET) area measurements. The uptake efficiency of SW was assessed via the batch mode. Also, the effect of several process variables on the Pb(II) uptake efficiency was elucidated. The Freundlich (R2 ​= ​0.991; ARE ​= ​0.340) and pseudo-second-order (R2 ​= ​0.999; ARE ​= ​0.056) model, respectively merged as the best fit models for equilibrium and kinetic studies. The maximum adsorption capacity was found to be 132 ​mg ​g−1 (at pH 5 and 30 ​°C) from the Langmuir model. A very short equilibrium time of 10 ​min recorded in the study distinguishes SW as fast and efficient in aqueous Pb(II) uptake.

Semifluidized Bed Adsorption Column Studies for Simultaneous Removal of Aqueous Phase Pb2+ and Cd2+ by Composite Adsorbents: an Experimental and Mass Transfer Dynamic Model–Based Approach

In this present work, the performance of a semifluidized bed adsorption column has been evaluated for the removal of Pb2+ and Cd2+ in a semi-continuous mode. The composite adsorbents have been synthesized from waste biomass–based biochar and alginate-based biopolymer. Synthesized adsorbent characterized and finally tested its effectiveness in the removal of both Pb2+ and Cd2+ metal ions by batch and semifluidized bed column adsorption studies. The adsorptive removal efficiencies were found to be dependent on solution pH, initial metal ion concentration, adsorbent dose or initial bed height, static bed height, system temperature and inlet flow rate of semifluidized bed operation. Pseudo-second-order kinetic model was fitted to the batch adsorption experimental data by non-linear and linear regression method and it was found that the non-linear method gives a better way of obtaining the various kinetic parameters and its applicability. A solute phase mass transfer–based dynamic model has been developed to explain the adsorptive behaviour of metal ions onto adsorbents during the semi-continuous mode of operation of a semifluidized bed system. Various mass transfer parameters and degree of dispersion coefficients for the individual packed and fluidized section were obtained from the developed model.

Nanoanalytical Identification of Siderite Dissolution-Coupled Pb Removal Mechanisms from Oxic and Anoxic Aqueous Solutions

Lead(II) is a toxic pollutant often found in metal-contaminated soils and wastewaters. In acidic aqueous environments, Pb(II) is highly mobile. Chemical treatment strategies of such systems therefore often include neutralization agents and metal sorbents. Since metal solubility and the retention potential of sorbents depend on the redox state of the aqueous system, we tested the efficiency of the naturally occurring redox-sensitive ferrous iron carbonate mineral siderite to remove Pb(II) from acidic aqueous solutions in batch experiments under oxic and anoxic conditions over a total of 1008 h. Siderite dissolution led to an increase in reactive solution pH from 3 to 5.3 and 6.9, while 90 and 100% of the initial aqueous Pb(II) (0.48 × 10–3 mol kg–1) were removed from the oxic and anoxic systems, respectively. Scanning and transmission electron microscopy, combined with X-ray absorption and photoelectron spectroscopy, indicated that under oxic conditions, Pb(II) was consumed by cerussite precipitation and inner-sphere surface complexation to secondary goethite. Under anoxic conditions, Pb(II) was removed by the rapid precipitation of cerussite. This efficient siderite dissolution-coupled sequestration of Pb(II) into more stable solid phases demonstrates this potential method for contaminated water treatment regardless of the redox environment.

Adsorption of Pb(II) from aqueous solutions using crosslinked carboxylated chitosan/carboxylated nanocellulose hydrogel beads

Chitosan modification is an important method for the development of adsorbents that has attracted considerable interest in recent years. In this regard, a new type of efficient Pb(II) adsorbent was prepared in a simple and cost-effective way. In this study, carboxylated chitosan (CYCS) and carboxylated nanocellulose (CNC) were used to chelate and synthesize hydrogel spheres with effective adsorption sites, in calcium chloride solution. The prepared carboxylated chitosan/carboxylated nanocellulose (CYCS/CNC) hydrogel beads were used as Pb(II) adsorbents, and using scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy, the structure and adsorption properties of the prepared beads were investigated. The CYCS/CNC adsorbents exhibited an excellent aqueous Pb(II) adsorption capacity (qm = 334.92 mg g−1), and the experimental results further revealed that the adsorption data fitted well with the Langmuir model, and the adsorption kinetics accorded with the pseudo-second-order model. Additionally, the adsorption mechanism was identified as monolayer chemisorption.

The dynamic uptake of lead and its radionuclides by natural and synthetic aluminium-phosphate-sulfates

The ability of aluminium-phosphate-sulfate (APS) phases to preferentially sorb lead and its radionuclides, particularly 210Pb, from metallurgical processing streams has been recently recognised empirically. This suggests that APS minerals may be suitable for the removal of lead from environmental and anthropogenic processes. We investigated the Pb sorption capabilities of APS with different Ca:Sr and SO4:PO4 ratios over a range of aqueous Pb concentrations (10–1000 ppm) and pH (1.5–5.5) typical of metallurgical processes and acid drainage conditions. Through a combination of characterization techniques including electron probe microanalysis, (laser ablation-) inductively coupled plasma mass spectrometry and X-ray absorption spectroscopy, we confirm the rapid (< 8 h) incorporation of Pb into the crystal lattice of APS phases. We also provide a mechanistic pathway for the sorption mechanism, with Pb sorption favoured at pH 3.5–5.5 via the direct replacement of lattice-bound Ca by Pb within the APS crystal structure. The observed Pb-incorporation dynamics of APS minerals, along with their insolubility and high thermodynamic stabilities, support the use of APS minerals as a novel agent for the uptake of Pb, radiogenic and nonradiogenic, from process-, surface-, and groundwaters. Since Pb quickly enters the crystal structure of environmentally stable APS minerals, these phases have much potential for long-term storage of Pb waste, and in particular for sequestration of the highly radioactive 210Pb isotope enriched in U-bearing geological materials.