Heavy Metal Cations Research Articles

Effect of heavy metal co-contaminants on the sorption of thirteen anionic per- and poly-fluoroalkyl substances (PFAS) in soils

Understanding the sorption behavior of per- and poly-fluoroalkyl substances (PFAS) in soils are essential for assessing their mobility and risk in the environment. Heavy metals often coexist with PFAS depending on the source and history of contamination. In this study, we investigated the effect of heavy metal co-contaminants (Pb2+, Cu2+ and Zn2+) on the sorption of 13 anionic PFAS with different perfluorocarbon chain length (C3-C9) in two soils with different properties. Results revealed that Pb2+, Cu2+ and Zn2+ had little effect on the sorption of most short-chain compounds, while the presence of these heavy metals enhanced the sorption of long-chain PFAS in two soils. The distribution coefficients (Kd) of several long-chain PFAS linearly increased with increasing concentrations of heavy metal, especially in the presence of Pb2+ (ΔKd/Δ [Pb2+] > 3 for PFOS and PFNA vs <1 for PFPeS and PFHxS). While several mechanisms may have contributed to the enhancement of sorption of PFAS, the heavy metals most likely contributed through enhanced hydrophobic interactions of PFAS by neutralizing the negative charge of adsorption surfaces in soils and thus making it more favorable for their partitioning onto the solid phase. Moreover, the increase in the concentrations of heavy metals led to a decrease in the pH of the system and promoted sorption of long-chain compounds, especially in soil with lower organic carbon content. Overall, this study provides evidence that the presence of co-existing heavy metal cations in soils can significantly enhance the sorption of long-chain PFAS onto soil, thereby potentially limiting their mobility in the environment.

Fluorescence Naphthalene Cationic Schiff Base Reusable Paper as a Sensitive and Selective for Heavy Metals Cations Sensor: RSM, Optimization, and DFT Modelling.

Heavy metals are particularly damaging contaminants in the environment, and even trace concentrations represent a risk to human health due to their toxicity. To detect the heavy metals of Mn2+ and Co2+ ions, a novel selective reusable paper-based Fluorescence naked-eye sensor based on naphthalene cationic Schiff base (NCSB) was synthesized and confirmed using FT-IR, 1H-NMR, and MS tools. Based on a blue to colorless color change in the aqueous solution, the NCSB sensor is utilized to Mn2+ and Co2+ cations selectively among other metal ions (Fe2+, Cu2+, Mg2+, Ni2+, Zn2+, Cd2+, Hg2+, Pb2+, Sn2+ and Cr3+). In the aqueous medium, the NCSB sensor displayed high sensitivity, with limits of detection (LOD) values of 0.014 µM (14.08 nM) and 0.041 µM (41.47 nM) for Mn2+ and Co2+ cations, respectively. The paper-based sensor naked-eye detected Mn2+ and Co2+ cations in water at concentrations as low as 0.65 µM (65 nM) and 0.086 µM (86 nM), respectively. It was discovered that 5min of incubation time and a pH range of 7 to 11 were optimal for the complexation reaction between the Mn2+ and Co2+ ions and the NCSB sensor. Through a static quenching process, the interaction of the different metal ions with the Schiff base group in the NCSB molecule results in the development of a ground-state non-fluorescent complex. NCSB sensor was also successfully applied in analysis of Mn2+ and Co2+ in environmental water with good recoveries of 94.8-105.9%. The theoretical calculations based on density functional theory (DFT) studies are in support of experimental interpretations. The links between the input factors and the anticipated response were evaluated using the quadratic model of the response surface methodology (RSM) modeling.

Microbial siderophores as molecular shuttles for metal cations: sources, sinks and application perspectives.

Iron is one of the highly abundant elements on the earth's crust, an essential micronutrient for a majority of life forms, and exists in two frequent oxidation states such as ferrous (Fe2+) and ferric (Fe3+). These two oxidation states are interconvertible by redox reactions and form complexes with a wide range of siderophores. At neutral pH in soil, Fe2+ is highly soluble upto 100mM but have less biological value, whereas Fe3+ is less soluble upto 10-9M. This reduced bioavailability of Fe3+ induces competition among microorganisms. As many microorganisms need at least 10-6M of Fe3+ form of iron for their growth, siderophores from these microbes readily withdraw Fe3+ iron from a variety of habitats for their survival. In this review, we bring into light the several recent investigations related to diverse chemistry of microbial siderophores, mechanisms of siderophore uptake, biosynthetic gene clusters in microbial genomes, various sources of heavy metal cations in soil, siderophore-binding protein receptors and commercialisation perspectives of siderophores. Besides, this review unearths the recent advancements in the characterisation of novel siderophores and its heavy metal complexes alongside the interaction kinetics with receptors.

Sulfide-occluded zeolites: Cooperative adsorption-precipitation system for near perfect decontamination of aqueous Hg species

Sulfide-occluded zeolites could allow both adsorption reaction of zeolites and precipitation reaction of sulfides to operate within one system, which leads to synergic effects on removal of toxic cationic heavy metals from aqueous systems. Here we proved that near complete decontamination of aqueous Hg cations bellow WHO guideline level of 1 ppb could be accomplished with sulfide-occluded zeolites. Interestingly, adsorption of cationic Hg species resulted in the formation of discrete HgS crusts on the surfaces of the zeolite crystals. TEM and Hg removal isotherms strongly indicated that the HgS crust played a crucial role not only in preventing the back-release of adsorbed Hg species but also in scavenging residual aqueous Hg species. Therefore, in-situ cooperation of adsorption and precipitation reactions performed by sulfide-occluded zeolites could be applied to reliable and safe Hg decontamination of aqueous systems.

Laser-induced porous graphene electrodes from polyketimine membranes for paracetamol sensing.

The development of cost-effective materials for fabricating electrodes is crucial for drug, pharmaceutical and environmental applications. This paper presents the synthesis and characterization of a novel polyketimine (PKI) membrane obtained by condensing partially of different weight percentages of oxidized polyvinyl alcohol and aminated polyether sulfone. Using the PKI membrane as a scaffold, we introduced laser-induced graphene electrodes (LIGEs) for the efficient electrochemical sensing of paracetamol (PCM), which serves as a model drug. Electrochemical measurements were conducted to assess the physico-chemical properties, including laser-induced porous graphene features, such as the heterogeneous electron transfer (HET) rate and electrochemically active surface area (ECSA). The obtained results demonstrate that the LIGEs exhibit excellent performance in PCM sensing, showing a linear detection range of 50-600 µM with a detection limit (LOD) as low as 14.3 µM and a good selectivity toward uric acid. Furthermore, the functionalization of the electrode surface with AuNPs improved the electrode physico-chemical properties (HET and ECSA) and lowered the detection limit down to 1.1 µM. Consequently, these affordable electrodes hold great potential for analysing other drugs and detecting heavy metal cations in various applications.

Biosorption of Fe (II) and Pb (II) on unmodified Senna tora: Isotherm and kinetic modeling

Contamination of environment by heavy metals has become a major concern worldwide. The role of conventional methods in remediating heavy metals has become ineffective and costly. Therefore, it becomes imperative to explore bioremediation using a cost effective, efficient and environmentally friendly alternative method of removing heavy metals. In this study, the adsorption behaviour of Senna tora, a low-cost adsorbents, with respect to Fe(II) and Pb(II) ions, has been studied in order to consider its application to the treatment of wastewater. The physicochemical properties of the unmodified Senna tora were predetermined. The batch experimental method was employed: parameters such as pH, contact time, dosage and initial metal concentration were studied. The influence of the pH of the metal ion solutions on the uptake levels of the metal ions by the adsorbent used was carried out between pH 4 and 10. The optimum pH for both Fe (II) and Pb(II) removals by Senna tora was 7. An equilibrium contact time of 60 min was required for the adsorption of Pb(II) ions onto Senna tora. Percentage sorption of Fe(II) increased from 94 to 99% and that of Pb (II) from 94.4 to 96% as adsorbent dose was increased from 2 to 10 g. The isotherms data provide information on the capacity of the adsorbent or the amount required to remove a unit mass of pollutant under the operating conditions. The equilibrium data of Fe(II) and Pb(II) adsorbed onto Senna tora pods were fitted by the Langmuir, Freundlich, and Temkin isotherms. On the basis of correlation coefficients R2, it is concluded that the Fe(II) and Pb(II) biosorption is better fitted to the Freundlich model. This suggests that the biosorption of Fe(II) and Pb(II) on the surface of Senna tora pods occurs on heterogeneous binding sites with equivalent adsorption energies and multilayer coverage. The results demonstrated that Senna tora pod holds potential to remove cationic heavy metal species from industrial wastewater.

The opposite influences of Cu and Cd cation bridges on sulfamethoxazole sorption on humic acids in wetting-drying cycles

Wetting-drying cycles in the environment could change the inner- or outer-sphere complexation of heavy metal cations on natural organic matter (NOM) and then influence ternary interactions with organic contaminants - a rarely-discussed essential geochemical process. In this work, the sorption of sulfamethoxazole (SMX) on humic acids (HAs) mediated by cations (Cu2+ and Cd2+) was investigated. Considering that outer-sphere complexation could be transformed into inner-sphere complexation during vacuum freeze-drying, the role of inner- or outer-sphere complexation on SMX sorption was explored. The experimental sorption results and density functional theory (DFT) calculations suggested that Cu2+ and Cd2+ sorption on HAs was mainly outer- and inner-sphere complexation, respectively. Cd2+ consistently promoted SMX sorption on HAs, while Cu2+ promoted and inhibited SMX sorption before and after freeze-drying. The structure of HA-Cu complexes with inner-sphere complexation was more compact than those with outer-sphere complexation, which reduced the accessibility of sorption sites for SMX on HA-Cu and inhibited SMX sorption. However, the greater number of coordination sites of Cd2+ may provide more sorption sites and the structure of HA-Cd was looser. These findings provide a groundbreaking understanding of the sorption of organics on natural adsorbents in the presence of cations.

Application of electro-spun nano-fibers based on agriculture cellulosic biomaterial wastes for removal of dye and heavy metal from polluted water

This work aims to extraction of valuable cellulosic biomaterials namely; carboxymethyl cellulose (CMC) and carbon quantum dots (CQDs) from agriculture cellulosic waste (agro wastes) via economically and ecofriendly single-step method. CMC and CQDs were then mixed with nylon-6 to get suitable composite solutions that electro-spun into nano-fibers (NFs) by using nozzle-less electrospinneret. The obtained functional NFs were applied in adsorption and capturing of dye molecules and heavy metal cation from the contaminated water. The morphological structure of the obtained NFs was investigated by SEM. Chemical and thermal properties of the obtained NFs were studied by FT IR, T GA, and DSC. Depending on their composition, the capacities of the prepared NFs to capture Cr+6 as well as to adsorb cationic dye were examined. Results of this study show the higher efficiency of the prepared cellulosic biomaterial/nylon-6 NFs to adsorb and capture dye molecules and Cr+6 reached to about 86% and 93%; respectively.

Synthesis of a three-dimensional reduced graphene oxide aerogel decorated with (Fe3O4@SiO2–NH2)–COC2H4COOH for adsorption of heavy metal cations

Hereunder, a new method for the synthesis of a three-dimensional (3D) reduced graphene oxide (r-GO) nanohybrid is presented by the use of a synthetic novel crosslinker ((Fe3O4@SiO2–NH2)–COC2H4COOH) designed for multifunctional purposes. This crosslinker not only provide a three-dimensional structure for the adsorbent (increasing adsorption capacity), but also it enables the magnetically separation of the 3D r-GO nanohybrid. According to high-resolution transmission electron microscopy (HRTEM), the r-GO sheets were well decorated with nearly spherical (Fe3O4@SiO2–NH2)–COC2H4COOH nanoparticles with an average size of 60 nm. More importantly, the X-ray photoelectron spectroscopy (XPS) showed that the 3D r-GO nanohybrid contains several oxygenous and nitrogenous functional groups that makes it an ideal heavy metallic cations adsorbent. In addition, the synthesized 3D r-GO nanohybrid showed a maximum adsorption capacity of ∼455, 448 and 232 mg/g for lead, cadmium, and copper, respectively; besides, the exothermic adsorption of these cations followed a pseudo-second-order model. It was also found that an effective metal desorption step can be achieved by using a mixture of nitric acid and acetonitrile. The adsorption percentage of the 3D r-GO nanohybrid remained unchanged after five cycles of adsorption–desorption step. At last, the experimentally observed adsorption/desorption behaviors were justified using the density functional theory (DFT).

Hindered diffusion of heavy metal cations in the adsorption rate on activated carbon fiber

Water resource pollution caused by heavy metals represents a risk to the environment because of their toxicity. Adsorption on activated carbon materials can be applied to remove heavy metals in aqueous solutions. Activated carbon fiber (ACF) is a microporous material successfully used for adsorbing heavy metals from water solutions; however, the adsorption rate on ACF has yet to be investigated in detail. The adsorption equilibrium and rate of Cd(II), Ni(II) and Zn(II) on ACF were analyzed in this study, and the experimental data were procured in a differential packed bed batch adsorber. The Radke-Prausnitz isotherm successfully interpreted the experimental adsorption equilibrium data. The adsorption rate was analyzed employing a diffusional model, supposing that the external mass transfer along with intraparticle or intrafiber diffusion affect the overall adsorption rate. Besides, the metal intrafiber diffusion was attributed exclusively to diffusion in the pores volume, excluding surface diffusion. The results revealed that intrafiber diffusion is significantly affected by hindered diffusion caused by frictional effects on pore walls (Kr), steric exclusion (Kp), and blocking provoked by metal cations adsorbed onto pore walls (Ka). The hindrance factors Kr and Kp were estimated using literature correlations, and Ka was related to the mass of metal adsorbed.

Reduced graphene oxide‒MoO3 composites via microwave-assisted synthesis for dual-functional photocatalysis of organic dyes and heavy metal cation under simulated sunlight irradiation

BackgroundWhen organic dyes or heavy metal cations are present in wastewaters, it is often necessary to add sacrificial molecules so that catalysts can effectively remove these pollutants. However, when organic dyes and heavy metal cations coexist, the composite removal rate of both contaminants by a few specific catalysts is higher, and no sacrificial molecules are needed. MethodsHerein, molybdenum trioxide (MoO3)‒reduced graphene oxide (rGO) composites were synthesized using a two-step microwave hydrothermal method. The samples were characterized with X-ray diffraction, scanning electron microscopy (SEM), Raman spectroscopy, ultraviolet-visible spectroscopy, X-ray photoelectron spectroscopy, and energy-dispersive X-ray microanalysis. The photocatalytic degradation/reduction ability of the catalysts was evaluated under irradiation from a 300-W Xe lamp. Significant findingsIn the presence of H2O2, MoO3-rGO exhibited good degradation efficiency for rhodamine B (RhB) dye. Cr(VI) reduction over MoO3‒rGO occurred more favorably in an acidic environment (pH = 2). Moreover, when RhB and Cr(VI) coexisted, the composite removal rate of both contaminants was higher, and no sacrificial molecules were needed. The dual synergistic removal of RhB and Cr(VI) occurred through the combination of the photosensitized and photocatalysis mechanisms accompanied by rGO-mediated charge transfer.

Bacterial Cellulose‐Based Material from Coconut Water as Efficient Green Adsorbent for Heavy Metal Cations

AbstractNata de coco produced via coconut water fermentation using Acetobacter xylinum was directly applied to remove metal cations in aqueous solutions without any further chemical modification. Bacterial cellulose, contributing just 0.8 wt % to nata de coco, were randomly distributed and interconnected, yielding a three‐dimensional framework with high crystallinity and porosity. Due to these characteristics and the abundant presence of electron‐rich hydroxyl groups, unmodified bacterial cellulose in nata de coco exhibited a strong affinity to metal cations in water. The adsorption efficiency of nata de coco can be significantly improved to ∼30 and ∼45 mg g−1 for Pb2+ and Fe3+, respectively, by decreasing its size by grinding to decrease its size. Notably, nata de coco can adsorb multiple cations and the uptakes were almost similar for a 100‐fold scaled‐up adsorption volume.

Porphyrin-based ligand interaction with G-quadruplex: Metal cation effects.

The G-quadruplex planar-ligand complex is used to detect heavy metal cations such as Ag+ , Cu2+ , Pb2+ , Hg2+ , organic molecules, nucleic acids, and proteins. The interaction of the three planar porphyrins (L1), 5,10,15,20-tetrakis (1-ethyl-1-λ4 -pyridine-4-yl) porphyrin (L2), and 5,10,15,20-tetrakis (1-methyl-1-λ4 -pyridine-4-yl) porphyrin (L3), coming from the porphyrin family, with G-quadruplex obtained from human DNA telomeres in the presence of lithium, sodium, potassium, rubidium, cesium, magnesium, and calcium ions was studied by molecular dynamics simulation. When G-quadruplex containing divalent ions of magnesium and calcium interacts with L1, L2, and L3 ligands, the hydrogen bonds of the lower G-quadruplex sheet are more affected by ligands and the distance between guanines in the lower tetrad increases. In the case of G-quadruplex interactions containing monovalent ions with ligands, the hydrogen bond between the sheets does not follow a specific trend. For example, in the presence of lithium ions, the upper and middle sheets are more affected by ligands, while they are less affected by ligands in the presence of sodium. The binding pocket and the binding energy of the three ligands to the G-quadruplex were also obtained in the various systems. The results show that ligands make the G-quadruplex more stable through the penetration between the sheets and the interaction with the loops. Among the ligands mentioned, the interaction level of the ligand L2 is greater than the others. Our calculations are consistent with the previous experimental observations so that it can help to understand the molecular mechanism of porphyrin interaction and its derivatives with the G-quadruplex.

A Water-Stable 3D Eu(III)-Organic Framework as a Bi-Functional Ratiometric Luminescent Sensor for Fast, Sensitive and Selective Detection of ODZ and Hg2+ in Aqueous Media

The fast, sensitive and selective detection of some antibiotics and heavy metal cations in water is highly desirable for environmental protection and human health, but it is still currently challenging. In this work, a new luminescent Eu(III)-based metal-organic framework (MOF), {[(CH3)2NH2][Eu(L)2(H2O)2]·xDMF}n (1) [H2L = 4,4’-((naphthalene-1,4-dicarbonyl)bis(azanediyl))dibenzoic acid], was solvothermally synthesized. Complex 1 exhibits good water stability and luminescent property and could serve as a bifunctional ratiometric luminescent sensor for fast, sensitive and selective detection of ornidazole (ODZ) and Hg2+ in aqueous solution. The corresponding luminescent mechanism has also been discussed. This work indicates that 1 as a promising luminescent material exhibits luminescent quenching behavior for ODZ and luminescent enhancement behavior for Hg2+ in H2O, which will promote the practical application of Ln-MOF-based ratiometric luminescent sensors in monitoring antibiotics and metal ions pollutants in the environmental water matrices.

Zeolite performance in removal of multicomponent heavy metal contamination from wastewater

Efficient removal of heavy metal pollutants from wastewater by ion-exchange sorbents requires knowledge and understanding of the interplay between the adsorption patterns of the different components. The present study elucidates the simultaneous adsorption characteristics of six toxic heavy metal cations (Cd2+, Cr3+, Cu2+, Ni2+, Pb2+, and Zn2+) by two synthetic (13X and 4 A) and one natural (clinoptilolite) zeolite from solutions containing equimolar mixtures of the six metals. Equilibrium adsorption isotherms and equilibration dynamics were obtained by ICP-OES and complemented by EDXRF. An order of magnitude lower adsorption efficiency was exhibited by clinoptilolite (maximum of 0.12 mmol ions/g zeolite), relative to that obtained by the synthetic zeolites 13X and 4 A (a maximum of 2.9 and 1.65 mmol ions/g zeolite respectively). The strongest affinities to both zeolites were demonstrated by Pb2+ and Cr3+ (1.5 and 0.85 mmol/g zeolite respectively for 13X, and 0.8 and 0.4 mmol/g zeolite respectively for 4 A adsorbed from the highest solution concentration). The weakest affinities were observed by Cd2+ (0.1 mmol/g for both zeolites), Ni2+ (0.2 and 0.1 mmol/g for 13X and 4 A respectively), and Zn2+ (0.1 mmol/g for both zeolites). Large differences were observed between the two synthetic zeolites in terms of their equilibration dynamics and adsorption isotherms. Pronounced maxima were displayed in the adsorption isotherms for zeolites 13X and 4 A. The decline in adsorption of the weaker adsorbing ions with the increase in total solution concentration was attributed to the thermodynamic equilibrium between the ions adsorbed on the zeolite surface and those in the solution. Regeneration by 3 M KCL eluting solution resulted in considerable reduction in adsorption capacities following each desorption cycle.

Spectroscopic studies of heavy metal cations influence on the structure of synthetic hydrated calcium aluminosilicates.

Calcium aluminosilicate hydrates (C-(A)-S-H) with two different C/S molar ratios of 1.0 and 1.7 were synthesized by precipitation with the use of the alkali-activation method. The samples were synthesized with solutions of heavy metals nitrates such as nickel (Ni), chromium (Cr), cobalt (Co), lead (Pb), and zinc (Zn). Metal cations were added in the amount of Ca:Me equal to 9:1, while Al/Si was 0.05. The influence of the addition of heavy metal cations on the structure of the C-(A-)S-H phase was investigated. For this purpose, XRD was used to examine the phase composition of the samples, FT-IR and Raman spectroscopy were used to determine the effect of heavy metal cations on the structure of the obtained C-(A)-S-H phase and their degree of polymerization. Using SEM and TEM, changes in the morphology of the obtained materials were determined. Possible mechanisms of immobilization of heavy metal cations have been determined. It was found that some heavy metals (Ni, Zn, and Cr) could be immobilized by precipitation of insoluble compounds. On the other hand, they could remove Ca2+ ions from the structure of aluminosilicate and take their place, as evidenced by the crystallization of Ca(OH)2 in samples with the addition of Cd, but also Ni and Zn in small amounts. A third possibility is the incorporation of heavy metal cations at the silicon and/or aluminum tetrahedral sites, as is the case with Zn.

Removal of Heavy Metal Ions Using Pristine and Functionalized Natural Zeolites

Heavy metal ions have attracted significant concern regarding their toxicity in living organisms. Concurrently, the removal of heavy metals by the adsorption method is also under the spotlight because it is effective, less cost-demanding, and easy to operate. To date, natural zeolites become one of the most used adsorbents for it is low cost, abundant in reserve, and has high selectivity towards heavy metal. Zeolites possess negatively charged three-dimensional frameworks built by SiO4 and AlO4 tetrahedra, which are balanced by counter-cations. The cations within zeolite frameworks can be exchanged with the heavy metal cations in an aqueous environment. This review comprehensively reports the adsorption capacity of heavy metal ions using pristine and modified natural zeolite. The important aspects, including the physicochemical properties of pristine and modified natural zeolites, heavy metal ion adsorption isotherms, kinetics, and thermodynamics, are discussed in detail. It is imperative to note that the physicochemical properties of natural zeolites greatly determine the adsorption capability. Furthermore, natural zeolites could be modified with various molecules such as surfactants and polymers to improve the adsorption capacity and adsorb heavy metal anions. Ultimately, this review is concluded with prospects for future improvement.

Self‐Assembled Artificial Light‐Harvesting System Constructed Using Electrostatic Interactions in Aqueous Solution for the Sensing of Heavy Metal Cations

AbstractA supramolecular artificial light‐harvesting system (LHS) is successfully constructed in an aqueous environment using carbon dots (CDs) andα,β,γ,δ‐Tetrakis(1‐methylpyridinium‐4‐yl) porphyrin p‐Toluenesulfonate (TMPyP) via electrostatic interactions. Specifically, the CDs act as a donor, and TMPyP, which is loaded to the surface of the CDs, acts as an acceptor for the LHS. Energy transfer occurs from the CDs to the TMPyP in the assembled CDs‐TMPyP upon UV excitation. To demonstrate the applicability, the CDs‐TMPyP system is used as a sensor for Hg(II) in an aqueous solution. Subsequently, a functional material suitable for the detection and removal of Hg(II) is fabricated by integrating the CDs‐TMPyP into a polymer network.

A pH-mediated field amplification sample stacking technique based on portable microchip electrophoresis heavy metal ion detection system.

We built a portable microchip electrophoresis heavy metal ion detection system and proposed a pH-mediated field amplified sample stacking (pH-mediated FASS) online preconcentration method. The pH-mediated FASS focuses and stacks heavy metal cations by controlling electrophoretic mobilities with a pH change between the analyte and the background electrolyte (BGE) in solution to improve the detection sensitivity of the system. We optimized and adjusted sample matrix solution (SMS) ratios and pH to create concentration and pH gradients for SMS and BGE. Furthermore, we optimize the microchannel width to improve the preconcentration effect further. The system and method analyzed soil leachates polluted with heavy metals and separated Pb2+ and Cd2+ within 90s, obtaining their levels at 58.01mg/L and 4.91mg/L with sensitivity enhancement factors (SEF) of 26.40 and 43.73. Compared with inductively coupled plasma atomic emission spectrometry (ICP-AES), the detection error of the system was less than 8.80%.

Recycling of phosphate tailings for an efficient hydroxyapatite-based adsorbent to immobilize heavy metal cations.

Hydroxyapatite (HAP) is a promising adsorbent for immobilizing heavy metals in soil and water. However, the preparation and modification of HAP from pure chemicals increases its cost and limits its large-scale practical application. In this study, a hydroxyapatite-based adsorbent (HAPPT) was prepared from phosphate tailing produced in the phosphorus industry to sequester Pb, Cd and Zn from solution. The results showed that HAPPT was composed of HAP and MgO, with a surface area of 27.74 m2/g. The kinetics studies showed that most Pb and Cd were removed from the initial solution in 4h and the adsorption of Zn increased with increasing contact time. Metals presented higher adsorption capacities at 35°C than that at 25°C. The adsorption isotherms showed that HAPPT presented high adsorption capacities for Pb, Cd and Zn in mono-metal solutions. The adsorption capacity of Cd at pH 6 was higher than that at pH 3, but the adsorption for Pb and Zn was similar at both pHs. HAPPT has selectivity for Pb in Pb-Cd-Zn multi-metals solution, and competitive adsorption reduced the adsorption quantity by 53%, 93% and 79% for Pb, Cd and Zn, respectively. The combined results of TEM-EDS, XRD and XPS showed that Pb was immobilized by forming phosphates due to the dissolution of HAP, whereas Cd and Zn were immobilized by forming hydroxide precipitates resulting from the function of MgO in HAPPT. The results of this study provided an efficient adsorbent for the removal of heavy metals in solution and provided a new perspective on the recycling of phosphate tailings in the phosphorus industry.