Hg Adsorption Capacity Research Articles

Tuning the adsorptive properties of drinking water treatment residue via oxygen-limited heat treatment for environmental recycle

As a by-product generated increasingly during potable water production, drinking water treatment residue (DWTR) recycling for environmental remediation can lead to a win–win situation. In this study, oxygen-limited heat treatment was applied to DWTR, attempting to tune the properties of DWTR for better recycling. The results showed that after the treatment, N2 sorption capacity of DWTR was enhanced significantly: the specific surface area (SSA) and total pore volume (TPV) increased from 72.7 to 148–184m2g−1 and from 0.0746 to 0.189–0.201cm3g−1, respectively. The treatment also relatively increased the amorphous Al/Fe contents in DWTR although Al/Fe aging and transformation from hydroxides to oxides with high stability were observed. The retained organic matter (OM) was dominant in humin, with higher aromaticity and lower aliphaticity as the treatment temperature increased. Further analysis suggested that aromaticity increase induced higher SSA, the combined effect of OM aromaticity increase, OM loss (e.g. C in COO−), and metal oxides formation resulted in larger TPV, OM inhibited Al/Fe aging, while Al/Fe oxides formation in turn enhanced OM aromaticity. Additionally, the maximum Hg adsorption capacity of DWTR treated at 200–400°C (estimated by Langmuir model) increased from 53.5 to 69.9–147mgg−1, and the lability of heavy metals (e.g. Cu) in DWTR tended to decrease after treatment. The overall results demonstrated that oxygen-limited heat treatment sequestrated C, making DWTR be a more reliable adsorbent.

Absorption of heavy metals using resorcinol formaldehyde aerogel modified with amine groups

Resorcinol–formaldehyde (RF) aerogels modified with amine groups were used to remove heavy metal ions from aqueous solutions. RF aerogel was synthetized under subcritical conditions and then was modified by 3-aminopropyl trimethoxysilane. The ability of modified RF aerogels to remove Pb(II), Hg(II), and Cd(II) ions from aqueous solution was investigated using batch-adsorption technique with respect to the changes in pH, contact time, sorbent concentration, initial metal concentration, and temperature. The maximum adsorption capacity of metal ions Pb(II), Hg(II), and Cd(II), was found to happen at pH 6, 6, and 5, respectively, after about one hour. The experimental findings showed that the ions’ adsorption on the surface of the aerogel was endothermic. Adsorption isotherms indicated that the adsorption behavior of modified aerogel could fit in both Langmuir and Freundlich models. The outcomes of this study also showed that amine-modified RF aerogels can be used as an effective sorbent for the removal of heavy metal ions Pb(II), Hg(II), and Cd(II) from aqueous solutions.

Comparative study of Hg(II) adsorption by thiol- and hydroxyl-containing bifunctional montmorillonite and vermiculite

A novel approach to prepare adsorbents for Hg(II) uptake from aqueous media based on the grafting of dimercaprol (BAL), containing thiol and hydroxyl groups, onto the natural montmorillonite and vermiculite was investigated concerning the evaluation of the adsorption capacity. The kinetic study showed that the adsorption process abided by pseudo-second-order model. The adsorption behavior of Hg(II) onto the obtained samples fitted well with Langmuir isotherm model, exhibiting an enhanced maximum adsorption capacity of 8.57 and 3.21mgg−1 for BAL-Vm and BAL-Mt, respectively. The feasibility of Hg(II) uptake onto the the samples was studied thermodynamically and the calculated coefficients such as ΔH, ΔS and ΔG indicated a physical and spontaneous process. The pH values and coexisting cations had a great influence on Hg(II) removal, confirming the optimal pH value of 4.0–5.0 and the negative correlation between the ionic strength and the adsorption capacity of Hg(II). In general, BAL-Vm possessed a higher efficiency of Hg(II) uptake than BAL-Mt, contrary to that of the pristine clays. The pristine and functionalized materials were investigated by XRD, FTIR, BET, SEM and zeta potential analysis to gain in-depth insight into the structure and surface morphology. The results showed that BAL was successful grafted on montmorillonite and vermiculite surface, providing plentiful adsorption sites as chelating ligands. The mechanisms of Hg(II) adsorption on these samples could be further explained as ion exchange and electrostatic attraction for Vm and Mt, and formation of complexes for BAL-Vm and BAL-Mt.

Highly efficient adsorption of Hg(II) and Pb(II) onto chitosan-based granular adsorbent containing thiourea groups

A series of granular hydrogels containing carboxy group and thiourea group were prepared by a facile redox-initiated polymerization in air atmosphere at room temperature, and then were used as the adsorbents for efficient adsorption of Pb(II) and Hg(II). The variables affecting the adsorption capacity were systematically investigated, including pH, initial concentration, contact time, and desorption and reusability. The results indicate that the as-prepared adsorbent has fast adsorption kinetics and high adsorption capacity, in particular for Hg(II), with the equilibrium time of about 40min and the maximum adsorption capacity of 1106.72mg/g for Hg(II). Over the pH range studied, this granular hydrogel shows insignificant changes in the adsorption capacity for Hg(II), while some noticeable differences are visible for Pb(II). The adsorption process for Pb(II) and Hg(II) can be described using the pseudo-second-order kinetic model and the equilibrium isotherm matches well with the Langmuir model. The reusability demonstrates that after five adsorption–desorption cycle, a high adsorption capacity is still observed for Pb(II) and Hg(II), though a decreasing tendency is inevitable. Consequently, the as-prepared granular hydrogel can be recognized as an effective adsorbent for the removal and recovery of heavy metal ions, especially for Hg(II) from aqueous solution.

Synthesis of Polyvinyltetrazole Resin by Combination of RAFT Polymerization and Click Chemistry for Adsorption of Hg(II)

The combination of reversible addition-fragmentation chain transfer (RAFT) polymerization and Click Chemistry was employed as a new approach to synthesize polyvinyltetrazole resin from acrylonitrile. The chemical composition and structure of the polyvinyltetrazole resin was studied by Fourier-transform infrared spectrometry and UV-Vis spectroscopies. Elemental analysis indicated the higher tetrazole content of the polyvinytetrazole resin. The polyvinyltetrazole resin exhibited excellent adsorption for metal ions and the maximum adsorption capacity for Hg(II) was 5.79 mmol/g. The resin could be reused stably in the adsorption of heavy metal ions.

DFT study of Hg adsorption on M-substituted Pd(1 1 1) and PdM/γ-Al2O3(1 1 0) (M = Au, Ag, Cu) surfaces

The adsorption of Hgn (n=1–3) on the Au-, Ag-, Cu-substituted Pd(111) surfaces as well as the PdM/γ-Al2O3(110) (M=Au, Ag, Cu) surfaces has been investigated using spin-polarized density functional theory calculations. It is found that M-substituted Pd(111) surfaces show as good Hg adsorption capacity as the perfect Pd(111) at low Hg coverage, while the Hg adsorption capacity is only slightly weakened at high Hg coverage. On the basis of stepwise adsorption energies analysis, it is concluded that M-substituted Pd(111) surfaces can contribute to the binding of Hg atom on the surfaces at high Hg coverage. The electronic properties of the second metal atoms are the main factor contributes to the Hg adsorption capacity. Gas phase Pd2 shows better Hg adsorption capacity than Pd2/γ-Al2O3, while PdM/γ-Al2O3 can adsorb Hg more efficiently than bare PdM clusters. It suggests that the γ-Al2O3 support can enhance the activity of PdM for Hg adsorption and reduces the activity of Pd2. It is also found that Pd is the main active composition responsible for the interaction of mercury with the surface for PdM/γ-Al2O3 sorbent. Taking Hg adsorption capacity and economic costs into account, Cu addition is a comparatively good candidate for Hg capture.

Hg(II) Adsorption By Alginate-guar Gum Templated Titania Spheres: Kinetic And Isotherm Studies

In present communication we report on the kinetic and isotherm studies on Hg(II) removal using our recently reported material, the millimeter sized hollow titania spheres (TSP). The mesoporous spheres with high surface area (11.75 m 2 /g) and bimodal pore size distribution were fabricated by a facile sol-gel approach using alginate-guar gum hybrid beads as the structure directing agent. In order to investigate the utility of TSP for Hg(II) adsorption, the batch adsorption experiments were conducted at various pH values (2–7), initial Hg(II) concentrations (50–300 mg/L), and TSP doses (20-100 mg) at 150 rpm, and 30 °C temperature. The spheres exhibited good capacity to adsorb Hg(II) in wide pH range (pH 3 to pH 7). It was possible to remove >95 % Hg(II) from 100 mg/L synthetic Hg(II) solution at pH 5, and 50 mg TSP dose in 10 h. The adsorption equilibrium data were better fitted to Langmuir model at low temperatures while Freundlich model become favored as the temperature was increased to 40 ºC. Langmuir adsorption isotherm study indicated that the monolayer adsorption capacity of TSP was 62.5 mg/g 62.5 mg/g 78.7 mg/g and 100 mg/g at 10, 20, 30, and 40 ºC respectively, which suggested good Hg(II) adsorption capacity of TSP. The calculated RL values evidenced the feasibility of the adsorption. Adsorption kinetic data well accorded with pseudo-second order kinetic model with the rate constant k, equal to 2.5 x 10 -4 g/mg.min 1.99 x 10 -4 g/mg.min and 0.28 x 10 -4 g/mg.min at 100, 150 and 200 mg/mL initial Hg (II) concentrations, indicating chemisorption taking place in the rate determining step. At high initial Hg(II) concentration (200 mg/mL), the adsorption was exclusively controlled by intraparticle diffusion. The study revealed the suitability of TSP for the mercury removal from wastewater.

Facile synthesis of monodisperse functional magnetic dialdehyde starch nano-composite and used for highly effective recovery of Hg(II)

By covalently linking dialdehyde starch and amine functionalized Fe3O4 nanoparticle, and modifying with aminothiourea functional group, the novel monodisperse nano-composite has been successfully synthesized without any toxic crosslinking agent. The resulting nano-composite was characterized by means of the Fourier transform infrared spectra (FT-IR), transmission electron microscope (TEM), X-ray diffraction (XRD), elemental analysis and vibrating sample magnetometer (VSM). As the new kind of low-cost and environmentally friendly adsorbent with the excellent monodispersity in aqueous phase, the obtained nano-composite has shown not only the good adsorption capacity for Hg(II) on high initial concentration, but also the strong removal ability on low concentration. Moreover, the unique selectivity for Hg(II) among the mixed metal ions solution and good regeneration performance of nano-composite has also been demonstrated by batch experiments.

Synthesis of peanut shell/polyacrylonitrile copolymer via Cu(0)-mediated RDRP and its adsorption behavior after modification

Peanut shell (PNS) was used to prepare a novel adsorbent to achieve resource recovery of the agricultural residue. The hydroxyl groups of peanut shell were turned into –C(CH3)2–Br pendant groups to initiate polymerization of acrylonitrile. Graft copolymer peanut shell/polyacrylonitrile (PNS-g-PAN) was modified by hydroxylamine hydrochloride to transform the cyano groups into amidoxime (AO) groups. The modified copolymer of AO-PNS-g-PAN was used as adsorbent. The maximum adsorption capacity for Hg(II) was 4.45 mmol g−1. The adsorption process fitted well the Freundlich isotherm model and followed pseudo-second-order model. The modified copolymer demonstrated its potential as an efficient adsorbent to solve the problem of Hg(II) contamination. The peanut shell (PNS) macroinitiator was obtained by acylation of hydroxyl groups on the cellulose backbone of the peanut shell and initiated by Cu(0)-mediated RDRP of acrylonitrile. PNS-g-PAN was modified by NH2OH·HCl and used to remove heavy metal ions. The maximum adsorption capacity of Hg(II) was 4.45 mmol g−1.

CePO4 Catalyst for Elemental Mercury Removal in Simulated Coal-Fired Flue Gas

CePO4 catalyst (termed Ce–P–O) was for the first time employed to capture elemental mercury (Hg0) under simulated coal-fired flue gas conditions. As compared with commercial SCR catalyst (i.e., V–W–Ti), the Ce–P–O catalyst showed a much better performance in Hg0 removal. The high Hg0 adsorption capacity, abundant active oxygen species, and excellent SO2 poisoning resistance account for the performance of the Ce–P–O catalyst. When the catalyst was subjected to individual flue gas component conditions, it was found that the presence of NO can significantly improve the Hg0 removal efficiency over the Ce–P–O catalyst; however, HCl did not show promotion effect. It is proposed that the former occurs because the generated NO2 (originated from NO oxidation) could react with Hg0 ad-species (e.g., Hg2O), regenerating the HgO and hence enhancing the Hg0 chemisorption. The latter was found to be due to the absence of the Deacon reaction over the catalyst.

Highly enhanced adsorption for the removal of Hg(II) from aqueous solution by Mercaptoethylamine/Mercaptopropyltrimethoxysilane functionalized vermiculites

Vermiculites modified with Mercaptoethylamine (MEA) and 3-Mercaptopropyltrimethoxysilane (MPTMS) were used as effective adsorbents for the removal of Hg(II) from aqueous solution. The physicochemical characteristics of the pristine and functionalized vermiculites were analyzed by XRD, BET, FTIR, SEM, TEM and Zeta potentials, confirming that the vermiculite was successfully functionalized by the organic ligands containing the thiol (SH) metal-chelating groups. Batch adsorption experiments demonstrated that the factors such as initial pH, contact time, temperature, coexisting cations and initial Hg(II) concentration could significantly influence the adsorption behaviors typically for VER and MEA-VER, whereas the adsorption capacity of MPTMS-VER showed negligible dependence on such factors. The maximum adsorption capacity of Hg(II) ions was greatly improved after functionalization, which was in the order of MPTMS-VER>MEA-VER>VER (286.29μgg−1, 176.33μgg−1, 99.95μgg−1, respectively). The adsorption isotherm could be well described with Langmuir model and the kinetic studies indicated that the adsorption process fitted well with the pseudo-second-order model. The calculated thermodynamic parameters suggested that the adsorption process was feasible and spontaneous. The adsorption mechanism of Hg(II) on thiol groups was studied through XPS analysis. Considering the favorable adsorption capacities, thiol-functionalized vermiculites show a promising application in the removal of Hg(II) from wastewater.

Comparative study of element mercury removal by three bio-chars from various solid wastes

Three kinds of bio-chars derived from various solid wastes, such as municipal solid wastes, agricultural wastes and medicinal residues, were modified by physical and/or chemical modification. The Hg0 adsorption capacities of the modification bio-chars in flue gas were comparatively studied. Physical modification increased the surface areas of the bio-chars, which was favorable in the physisorption of Hg0. Chemical modification resulted in the chemisorption of Hg0. Both physisorption and chemisorptions played a role in Hg0 capture, whereas chemisorption was more important. The X-ray photoelectron spectroscopy (XPS) analysis results suggested that chemisorption of Hg0 was due to the C–Cl groups generating on the surfaces of bio-chars during NH4Cl impregnation, which could transform Hg0 into HgCl2 or other Hg–Cl complexes. The bio-chars modified by combined physical and chemical modification all had an excellent performance for Hg0 removal, especially for C6WN5 exhibiting higher Hg0 adsorption than modified activated carbons or modified activated carbon fibers. It indicated that the sequence for Hg0 removal capacity decreased as: C6WN5 (from agricultural wastes, 11,400μg/g)>MW6N5 (from medicinal residues, 840μg/g)>W6WN5 (from municipal solid wastes, 160μg/g).

Surfactant-free green synthesis of Fe3O4 nanoparticles capped with 3,4-dihydroxyphenethylcarbamodithioate: stable recyclable magnetic nanoparticles for the rapid and efficient removal of Hg(II) ions from water.

Mercury is considered one of the most notorious global pollutants due to its high toxicity and widespread use in industry. Although many materials have been developed for the removal of mercury for water purification, most of these materials are difficult to reuse, which may lead to an increase in the mercury handling expense. Therefore, new sustainable materials that can be easily recycled and are highly efficient for the removal of mercury are required. Herein, we report the surfactant-free green synthesis of Fe3O4 magnetic nanoparticles (MNPs) using a watermelon (Citrullus lanatus) rind extract. The Fe3O4 MNPs were further functionalized with 3,4-dihydroxyphenethylcarbamodithioate (DHPCT) and applied to the removal of Hg(ii). Evaluation of the mercury removal efficiency and the amount adsorbed by DHPCT@Fe3O4 MNPs demonstrated a high Hg(ii) removal efficiency (98%) with a maximum Hg(ii) adsorption capacity of 52.1 mg g(-1). Systematic studies of the adsorption mechanism and selectivity suggest that the soft ligand (DHPCT) can preferentially coordinate with the soft metal ion (Hg(ii)) resulting in selective mercury removal. The developed DHPCT@Fe3O4 MNPs were readily recycled several times using an external magnet by exploiting their ferromagnetic character, without a significant decline in the Hg(ii) removal efficiency. This study provides a new insight into the preparation of a highly efficient adsorbent for Hg(ii) removal by an eco-friendly method.

Removal Hg<sup>0</sup> from Flue Gas with Modified VTSS by KBr and KI

Vanadium titanium steel slag (VTSS) containing transition metal can promote the adsorption of Hg0. The method of KBr and KI impregnation was applied to modify VTSS and the properties of the adsorbents were tested. The Hg0 removal tests were carried out with a fixed bed under different conditions. The results showed that the Hg0 adsorption capacity increase with the increasing temperature. The efficiency was highest with KI(3)/VTSS at 20。C and adsorption capacity was 163.4 ug/g after 3 h. The highest Hg0 removal efficiency were 90.6% for KI(3)/VTSS, 73.5% for KBr(10)/VTSS/ VTSS at 120。C, respectively.

Removal of Hg(II) by poly(1-vinylimidazole)-grafted Fe3O4@SiO2 magnetic nanoparticles

Fe3O4@SiO2 magnetic nanoparticles modified by grafting poly(1-vinylimidazole) oligomer (FSPV) was fabricated as a novel adsorbent to remove Hg(II) from water. Fourier transform infra-red spectroscopy confirmed the successful grafting of oligomer, and thermogravimetric analysis showed FSPV had a high grafting yield with organic content of 22.8%. Transmission electron microscopy image displayed that FSPV particles were polymer-coated spheres with size of 10–20 nm. With saturation magnetization of 44.7 emu/g, FSPV particles could be easily separated from water with a simple magnetic process in 5 min. The Hg(II) adsorption capacity of FSPV was found to be 346 mg/g at pH 7 and 25 °C in 10 mM NaCl. Moreover, the removal of Hg(II) by FSPV was not obviously affected by solution pH (from 4 to 10) or humic acid (up to 8 mg/L as TOC). The presence of seven common ions including Na+, K+, Ca2+, Mg2+, Cl−, NO3−, and SO42− (up to 100 mM ionic strength) slightly increased the adsorption of Hg(II) by FSPV. X-ray photoelectron spectroscopy analysis revealed that the N atom of the imidazole ring was responsible for the bonding with Hg(II), whereas the bonding of Hg with N did not result in cleavage of Hg–Cl bond in HgCl2 and HgClOH. The regeneration of Hg(II)-loaded FSPV could be achieved with 0.5 M HCl rapidly in 10 min, and the removal of Hg(II) maintained above 94% in five consecutive adsorption–desorption cycles. Therefore, FSPV could serve as a promising adsorbent for Hg(II) removal from water.

Selective Extraction and Detection of Hg2+ in Aqueous Solution by using Rhodamine Dye-Modified Silica Gel

Novel silica gel-immobilized rhodamine (SGR) anchored by hydrazinium hydrate was synthesized. The selectivity and adsorption ability of the SGR for metal cations were investigated with fluorophotometry and atomic absorption spectrophotometery, respectively. The SGR exhibits high selectivity and adsorption capacity for Hg2+. The maximum static adsorption capacity of the SGR for Hg2+ was 25.8 μmol g−1. The linear response range covers a concentration range of Hg2+ from 20 ppb to 2000 ppb and the detection limit is 10 ppb. The determination of Hg2+ in real water samples displays satisfactory results, and the SGR can be used repeatedly by treating with a solution of tetrabutylammonium hydroxide.

The cooperation of Fe[sbnd]Sn in a MnOx complex sorbent used for capturing elemental mercury

Manganese oxide (MnOx) was an effective sorbent for capturing elemental mercury (Hg0) from coal-fired flue gas, but its usage was markedly limited by its lower porosity, lower temperature range, and sensitivity to sulfur dioxide (SO2). Tin (Sn) and iron (Fe) were tested for their ability to enhance MnOx sorbent, and the FeSnMnOx complex exhibited excellent performance as a novel mercury sorbent. SnO2 appeared to be inert for Hg0 adsorption, but it could act as a suitable support to disperse MnOx, which helps to produce more activated sites. The BET surface areas increased by approximately 10 times, and there was an increase of 3 times the Hg0 adsorption capacity. The available temperature range of the sorbent can be extended from 100 to 300°C. Specifically, the presence of Fe can significantly improve the SO2 resistance of the sorbent. Furthermore, the mechanism of adsorption and SO2 tolerance at high temperatures was investigated by in situ Diffuse Reflectance Infrared Fourier Transform spectra (DRIFTs); Fe reacted with SO2 when O2 was present, which could protect manganese active sites from being poisoned by SO2.

A first-principles study of Hg adsorption on Pd(1 1 1) and Pd/γ-Al2O3(1 1 0) surfaces

Spin-polarized density functional theory calculations were carried out to investigate the adsorption of Hgn (n=1–3) on the perfect, step and vacancy-defective Pd(111) surfaces as well as the Pd/γ-Al2O3(110) surface. It is found that Hg atoms prefer to adsorb on the hollow sites on Pd(111) surfaces. The adsorption of Hg on the step and vacancy-defective Pd(111) surfaces is stronger than on the perfect Pd(111) surface, which indicates that the existence of vacancy and step defects can enhance the mercury adsorption activity of Pd adsorbents. As indicated by the calculated adsorption energies, the mercury adsorption on γ-Al2O3 is weak. The γ-Al2O3 supported single Pd atom shows as good Hg adsorption activity as the perfect Pd(111) surface at low Hg coverage, while more coordination unsaturated active Pd atoms is needed to achieve high Hg adsorption capacity. In addition, it was also found that the Hg adsorption on Pd/γ-Al2O3 weakens the binding of Pd to the γ-Al2O3 surface.

Mercury removal from drinking water by single iron and binary iron-manganese oxyhydroxides

In this study, single iron oxyhydroxides (FeOOH) and binary iron/manganese (FeMnOOH) oxyhydroxides were used to serve as potential mercury adsorbents. The selection of the optimum adsorbent and the corresponding conditions of the synthesis was based not only on its maximum Hg(II) adsorption capacity but also on its ability to achieve the mercury health regulation limit for drinking water in National Sanitation Foundation challenge water matrix. The experimental results revealed improved adsorption capacity for Hg by the FeMnOOH compared to FeOOH. In addition, the synthesis parameters of FeMnOOH, pH, and redox showed a significant influence on Hg removal efficiency. High redox values and mild alkaline pH improve mercury removal capacity of binary ferric manganese oxyhydroxides.

Surface chemistry modifications of rice husk toward enhancement of Hg(II) adsorption from aqueous solution

The modified rice husks were characterized in terms of morphology (scanning electron microscopy), functional groups (Fourier transform infrared spectroscopy), surface charge (pHpzc), and elemental composition which indicate the treatments that led to significant changes to its surface chemistry. Batch adsorption studies showed that the highest adsorption capacity of Hg(II) was 89 and 118 mg/g obtained by sulfur-functionalized rice husk (RH-CS) and organosilane-grafted rice husk (RH-GM), respectively. The reusability of raw rice husk (RH-Raw) and alkali-treated rice husk (RH-NaOH) was superior to RH-CS and RH-GM; even though their adsorption capacities were slightly lower. However, their selectivity was comparable to that of the RH-CS and RH-GM. In addition, the results demonstrated the potential application of rice husk-based adsorbents for treating Hg(II) containing wastewaters such as produced water from oil and gas exploration activities.