Recovery Of Hg Research Articles

Solid Phase Extraction Using a Sulfoxide Adsorbent for Preconcentration and Separation of Hg(II) in Natural Water Followed by ICP-MS Measurements

A separation and preconcentration method based on solid-phase extraction using sulfoxide adsorbent was developed for the determination of Hg(II) in natural water samples by inductively coupled plasma mass spectrometry (ICP-MS). The sulfoxide adsorbent was packed into a commercially available syringe-driven column (with a bed volume of 1.0 mL), which permitted off-line sample loading and on-line elution/measurement. The optimized operating conditions were as follows: sample condition for Hg(II) adsorption, 0.5% HCl; sample-loading flow rate, 10 mL min(-1); eluent for recovering Hg(II), 1% cysteine water solution. A test using multi-element mixed solution showed that most trace elements in natural water, except for Bi, could be completely separated from Hg(II). The recoveries of Hg(II) were 99.0 ± 3.2 and 100.7 ± 4.3%, respectively, when 0.64 and 0.16 ng mL(-1) of Hg(II) were added into the test sample. The detection limit of Hg(II) using a quadrupole ICP-MS after 10-fold preconcentration was 1.5 pg mL(-1). The blank value was 2.8 ± 0.5 pg mL(-1).

Development of a multi-component chemically reactive detection conjugate for the determination of Hg(II) in water samples

Mercury ions (Hg(II)) are considered highly toxic and hazardous element even at low levels. The contamination of Hg(II) is a global problem. To develop selective and sensitive technique for the detection of Hg(II) has attracted considerable attention. In this study, a multi-component chemically reactive detection conjugate for determination of Hg(II) has been synthesized and a competitive format assay was proposed. In the technique, the chemically reactive capture conjugate was coated on the plate. The reactive detection conjugate was then captured by the capture conjugate. TMB solution was added and catalyzed by HRP molecules immobilized on AuNPs. Finally, the developed enzymatic signal was measured at 450nm. The linear range of the assay was 0.35–350ppb with a detection limit of 0.1ppb. The average recoveries of Hg(II) from mineral water, tap water and lake water were 100.03%, 103.13% and 102.03%, respectively. All coefficients of variation (CVs) were less than 10%. The results are closely correlated with those from inductively coupled plasma mass spectrometry (ICP-MS), which indicated that the developed technique is a reliable method for and sensitive detection of Hg(II) in water samples.

Transport and interactions of kaolinite and mercury in saturated sand media

To evaluate the potential of Hg release and co-transport by colloids, it is important to understand how Hg, colloids and Hg-loaded colloids migrate in soils. Hg sorption by kaolinite and sand were nonlinear and fit the Langmuir model, with the maximum Hg sorption capacity being 1.2mg/g kaolinite and 0.11mg/g sand. Co-transport of Hg and kaolinite was evaluated using: (1) 1 or 100mg/L Hg or 100mg/L kaolinite, (2) 1 or 100mg/L Hg mixed with 100mg/L kaolinite, (3) 1 or 100mg/L Hg presorbed onto kaolinite, and (4) 250mg/L kaolinite in Hg-loaded sand columns. The presence of kaolinite (100mg/L) reduced Hg's mobility through sand column by increasing deposition rate of Hg-loaded kaolinite. At 100mg/L Hg, soluble Hg dominated Hg transport; but at 1mg/L Hg, colloidal Hg (Hg sorbed on kaolinite) affected Hg transport. Preloading 100mg/L Hg onto kaolinite (0.43mg/g) reduced kaolinite's mobility with low recovery rate (78%), with Hg retardation (R=1) in Hg-loaded kaolinite being lower than Hg retardation at 100mg/L Hg (R=1.287). The Hg recovery rate (93%) from Hg-loaded kaolinite at 1mg/L Hg was higher compared to 22% from 1mg/L Hg. Kaolinite can serve as a carrier to enhance Hg transport in porous media, with 250mg/L kaolinite mobilizing ∼2.4% Hg presorbed onto sand media. Correlation analysis revealed that desorbed Hg was significantly correlated with kaolinite (r=0.81, P<0.0001). Hence kaolinite enhanced Hg transport in the sand media serving both as a carrier (Hg was loaded before transport) and as mobile colloids stripping Hg off the sand media (Hg was loaded during transport).

Improving data quality on low level mercury wastewater analysis

In order to compare treatability test results evaluating low-level mercury (Hg) removal from oil refinery wastewater, improvements in Hg analytical methods were conducted at two US EPA certified analytical labs. The revisions in the analytical protocols improved Hg recoveries and hence enabled more reliable data interpretation and comparison for the specific wastewater tested. Nevertheless, significant differences between results from the two laboratories were identified in a split-sample experiment.

Mercury speciation in South African coal

Total mercury (HgT) and mercury speciation in coal samples from power stations was analysed using the automatic mercury analyser (AMA-254) and capillary electrophoresis (CE) coupled with photodiode array (PDA) detector. For mercury (Hg) speciation analysis, the samples were first extracted by acid leaching, followed by complexation with cysteine before analysis.Total Hg analysis of reference materials show good agreement with the respective certified values provided for reference materials. However, total Hg analysis in acid extracts showed that 80% of Hg was extracted with the respective certified values provided for reference materials. The same trend was observed in coal samples from various power stations. This is due to the fact that Hg in South African coal is associated with pyrite, followed by organic fraction and carbonate. Pyrite is linked to the content of sulphur in the coal. Pyrite is soluble in HCl and HNO3 hence 80% recovery of Hg was obtained. The 20% not recovered can be associated with insoluble forms, either organic matter and silicates which are insoluble in HCl and HNO3.Mercury speciation using CE in acid extracts showed that only Hg2+ species was detected from the extracts and that 96% of total Hg in acid extracts is in the Hg2+ species form. From results and discussions on acid extraction in coal, it can be assumed that the 4% which was not detected by the CE is organic mercury and that its concentration is below the detection limit (1ppm for methylHg+ and ethylHg+). Based on results obtained in this study, it can be concluded that although the coal samples contain mainly inorganic mercury, small amounts of organic mercury is also present.

Preparation and characterization of immobilized [A336][MTBA] in PVA–alginate gel beads as novel solid-phase extractants for an efficient recovery of Hg (II) from aqueous solutions

The coarse PVA–alginate matrix gel beads entrapping the micro-droplets of the ionic liquid tricaprylylmethylammonium 2-(methylthio) benzoate ([A336][MTBA]) as novel solid-phase extractants were prepared for the removal of mercury (II) from aqueous media. The ionic liquid [A336][MTBA] immobilized PVA–alginate beads (PVA/IL) have been characterized by FTIR, SEM and TGA. The influence of the uptake conditions was investigated including aqueous pH, PVA/IL dosage, the content of [A336][MTBA] and initial Hg (II) concentration; maximum Hg (II) ion adsorption capacity obtained was 49.89 (±0.11) mg g −1 at pH 5.8 with adsorptive removal of approximately 99.98%. The selectivity of the PVA/IL beads towards Hg (II), Pb (II) and Cu (II) ions tested was Hg > Pb > Cu. The rate kinetic study was found to follow second-order and the applicability of Langmuir, Freundlich and Tempkin adsorption isotherm model were tested as well. The results of the study showed that PVA/IL beads could be efficiently used as novel extractants for the removal of divalent mercury from aqueous solutions under comparatively easy operation conditions.

Rapid methods to detect organic mercury and total selenium in biological samples.

BackgroundOrganic mercury (Hg) is a global pollutant of concern and selenium is believed to afford protection against mercury risk though few approaches exist to rapidly assess both chemicals in biological samples. Here, micro-scale and rapid methods to detect organic mercury (< 1.5 ml total sample volume, < 1.5 hour) and total selenium (Se; < 3.0 ml total volume, < 3 hour) from a range of biological samples (10-50 mg) are described.ResultsFor organic Hg, samples are digested using Tris-HCl buffer (with sequential additions of protease, NaOH, cysteine, CuSO4, acidic NaBr) followed by extraction with toluene and Na2S2O3. The final product is analyzed via commercially available direct/total mercury analyzers. For Se, a fluorometric assay has been developed for microplate readers that involves digestion (HNO3-HClO4 and HCl), conjugation (2,3-diaminonaphthalene), and cyclohexane extraction. Recovery of organic Hg (86-107%) and Se (85-121%) were determined through use of Standard Reference Materials and lemon shark kidney tissues.ConclusionsThe approaches outlined provide an easy, rapid, reproducible, and cost-effective platform for monitoring organic Hg and total Se in biological samples. Owing to the importance of organic Hg and Se in the pathophysiology of Hg, integration of such methods into established research monitoring efforts (that largely focus on screening total Hg only) will help increase understanding of Hg's true risks.

Measurement of Mercury in Flue Gas Based on an Aluminum Matrix Sorbent

The measurement of total mercury in flue gas based on an economical aluminum matrix sorbent was developed in this paper. A sorbent trap consisted of three tubes was employed to capture Hg from flue gas. Hg trapped on sorbent was transferred into solution by acid leaching and then detected by CVAAS. Hg adsorbed on sorbent was recovered completely by leaching process. The 87.7% recovery of Hg in flue gas by tube 1 and tube 2 was obtained on the equipment of coal combustion and sampling in lab. In order to evaluate the ability to recover and accurately quantify Hg0 on the sorbent media, the analytical bias test on tube 3 spiked with Hg0 was also performed and got the average recovery of 97.1%. Mercury measurements based on this method were conducted for three coal-fired power plants in China. The mercury in coal is distributed into bottom ash, electrostatic precipitator (ESP) ash, wet flue gas desulfurization (WFGD) reactant, and flue gas, and the relative distribution varied depending on factors such as the coal type and the operation conditions of plants. The mercury mass balances of three plants were also calculated which were 91.6%, 77.1%, and 118%, respectively. The reliability of this method was verified by the Ontario Hydro (OH) method either in lab or in field.

Stabilization of quercetin-functionalized silica gel against hydrolysis by blocking silanol groups with TiO2 or ZrO2 and its application for the removal of Hg(II)

Free silanol groups of silica-gel functionalized with quercetin (QSG) were blocked with TiO2 or ZrO2 to produce TiO2-QSG and ZrO2-QSG, respectively. The silica materials were characterized by infrared, Raman spectra, thermogravimetric, elemental analyses, magic angle spinning 13C-nuclear magnetic resonance, BET specific surface area measurements and inductively coupled plasma—optical emission spectrometry-monitored silica hydrolysis. Siloxane groups are reinforced in the blocked QSG samples without affecting the hydrophilic nature or the porosity of silica. Quercetin is unaffected by the titania layer in contrary to zirconia. Also, the stability of silica against hydrolysis in TiO2-QSG and ZrO2-QSG was remarkably improved in the range of pH 3.5–9.1, attributed to the interruption of the intramolecular interaction of silanol groups with the amino groups. The hydrolyzed silica of TiO2-QSG and ZrO2-QSG decreased to 46.6 and 18.5%, of that of QSG and to 7.6 and 3.1%, of that of 3-aminopropylsilica gel at pH 9.1, respectively. TiO2-QSG was applied for the extraction of Hg(II) with separation efficiency of 99.0 ± 0.6% at pH 8.5. The capacity loss of TiO2-QSG per recovery cycle of Hg(II) was lowered in comparison with the uncovered material. It was successfully applied for the recovery of Hg(II) from spiked water and referenced samples.

Solid phase extraction of trace Hg(II) on silica gel modified with 2-(2-oxoethyl)hydrazine carbothioamide and determination by ICP-AES

In this work, a new 2-(2-oxoethyl)hydrazine carbothioamide modified silica gel (SG-OHC) sorbent was prepared and applied for preconcentration of trace mercury(II) prior to the measurement by inductively coupled plasma atomic emission spectrometry (ICP-AES). The optimization of some analytical parameters affecting the adsorption of the analyte such as acidity, shaking time, sample flow rate and volume, eluent condition, and interfering substances were investigated. At pH 3, the maximum static adsorption capacity of Hg(II) onto the SG-OHC was 37.5 mg g −1. The quantitative recovery (>95%) of Hg(II) could be obtained using 2 mL of 0.5 mol L −1 HCl and 1% CS(NH 2) 2 solution as eluent. Common coexisting substances did not interfere with the separation of mercury(II) under optimal conditions. The detection limit of present method was 0.10 ng mL −1, and the relative standard deviation (RSD) was lower than 4.0% ( n = 8). The prepared sorbent was successfully applied for the preconcentration of trace Hg(II) in certified and water samples with satisfactory results.

Synthesis and characterization of Hg(II)-ion-imprinted polymer: Kinetic and isotherm studies

Hg(II)-ion-imprinted polymer (IIP) was prepared by the formation of a binary complex of mercury (imprint ion) with 4-(2-thiazolylazo) resorcinol (TAR) and thermally copolymerizing with methacrylic acid (monomer) and ethylene glycol dimethadrylate (crosslinker), and 2, 2’-azobisisobutyronitrile as initiator in cyclohexanol as porogen. Mercury(II) was leached with 0.5 M HCl–1 M thiourea. Control polymer (CP) was also prepared without using imprint ion. The prepared IIP and CP were characterized with FT-IR, microanalysis, SEM analysis and surface area measurement. The effect of pH, adsorption kinetic and adsorption isotherm of imprinted polymer and control polymer were studied. The mechanism for adsorption of mercury was found to follow Freundlich isotherm and pseudo first order model. The adsorption capacity of Hg(II) on IIP and CP is 125 and 57.6 µmol g -1, respectively. The relative selectivity factor ( α r) values of Hg(II)/Zn(II), Hg(II)/Cu(II), Hg(II)/Ni(II) and Hg(II)/Co(II) are 62.5, 65.3, 64.6 and 70.6, respectively. The detection limit corresponding to three times the standard deviation of the blank was found to be 2.875 µg L -1. The IIP has been successfully applied for the recovery of trace Hg(II) in real water samples and those spiked with standards.

Analysis of total dissolved mercury in waters after on-line preconcentration on an active gold column

A reagent-free fully automated flow injection analysis (FIA) system coupled to atomic fluorescence spectrometry (AFS) for mercury (Hg) quantification is reported, using active nano-structured gold collectors for direct preconcentration of dissolved mercury species from natural waters. Recently we had shown the potential of such an approach for Hg analysis in seawater. This paper now describes the optimisation and validation of the proposed method including the investigation of possible limitations arising with matrix constituents, such as dissolved organic carbon (DOC). A broad variety of water matrices (seawater, river water, moorland water, effluent from wastewater treatment plant) were investigated in order to check the feasibility of the proposed method for total dissolved Hg determination in natural waters. All FIA parameters were optimised by checking Hg recovery in real water samples. Figures of merit of the proposed method - working range, carry over effects, detection limit, reproducibility, etc. - were determined. The method provides a high sensitivity (detection limit: 0.2pgHg) and very good reproducibility (RSD 1.1%, [Hg]=5ngL(-1), n=10). It offers several advantages because no reagents are needed for species conversion, preconcentration, or desorption and therefore the risk of contamination and blank values are lowered, reagent and time consumption are minimized. The system was successfully validated by measurement of a series of recoveries in real waters (all >96%) and in the certified standard reference material BCR 579 (mercury in coastal sea water, recovery 100.5%). Furthermore, the proposed method was applied to 15 real water samples for Hg ultra trace analysis.

Experimental study of mass-independence of Hg isotope fractionation during photodecomposition of dissolved methylmercury

Experiments modelling photolytic decomposition of methylmercury chloride in aqueous solutions of different chemical composition have been performed. Ion-exchange chromatographic separation using Chelex® 100 resin was used in order to separate methylmercury from inorganic mercury prior to the isotope ratio measurements by solution nebulization multicollector inductively coupled plasma mass spectrometry (MC-ICPMS). The performance of the chromatographic separation has been evaluated in terms of recovery of both methylmercury and inorganic Hg using synthetic solutions. Both mass-dependent and mass-independent fractionation of Hg isotopes concomitant with the decomposition process have been observed. Mass-independent Hg isotope fractionation (MIF) resulted in selective enrichment of 199Hg and 201Hg relative to the other isotopes in the methylmercury molecules and has been attributed to the magnetic isotope effect. The highest extent of MIF of Hg isotopes, expressed as Δ199Hg and Δ201Hg values, has been observed in acidified solution with low concentration of total dissolved solids (TDS). Progressive decrease in Δ199Hg and Δ201Hg values in acidified solution with higher concentration of TDS, alkaline solutions of both low and high concentration of TDS, and in a solution of ascorbic acid has been attributed to suppression of the radical pair reaction mechanism, responsible for the occurrence of the magnetic isotope effect, by substances acting as radical scavengers, such as OH− or ascorbic acid. The data obtained in this study demonstrate the significance of spin chemistry effects in the isotope fractionation of mercury.

Chromatographic pre-concentration of Hg from dilute aqueous solutions for isotopic measurement by MC-ICP-MS

Previous studies have demonstrated both mass-dependent fractionation (MDF) and mass-independent fractionation (MIF) of Hg isotopes in the environment and the potential for their application in biochemistry and geochemistry. However, little has been reported for Hg isotope geochemistry in natural aqueous environment due to the very low concentration (1–20 ng/L). We report here, for the first time, a new protocol for directly pre-concentrating Hg using AG 1 × 4 ion-exchange resin, which allows the measurement of Hg isotope composition in freshwater samples. The protocol is validated by testing both synthetic and natural solutions of varying concentrations, and by assessing the effect of Hg recovery and organic complexants on the reproducibility and the accuracy of measured isotopic ratios. The method results in acceptable procedural blanks and quantitative yields (101% ± 6%) in the final Hg eluates. The instrumental mass bias was corrected using modified empirical external normalization (MEEN) with Tl as internal dopant. The sensitivity of the method to the solution matrix (Hg/Tl ratio, organic matter concentration) was also evaluated. The pre-concentration and isotopic measurement protocol was applied to 16 natural water samples with Hg concentrations ranging from 0.9 ng/L to 15600 ng/L. The result showed a total variation of 2.4‰ for δ202Hg and evident MDF and MIF of Hg isotopes. Our study demonstrates that more research is required to fully understand the behavior of Hg isotopes in the aqueous environment.

Studies on Selective Uptake Behavior of Hg(II) and Pb(II) by Functionalized Poly(Ethylene Terephthalate) Fiber with 4-Vinyl Pyridine/2-Hydroxyethylmethacrylate

The adsorption behavior of 4-vinyl pyridine and 2-hydroxyethylmethacrylate grafted poly(ethylene terephthalate) fiber toward the Hg(II) and Pb(II) ions in aqueous solutions was studied by a batch equilibration technique. The influence of the treatment time was considered as well as the pH of the solution, the initial metal ions concentration, the graft yield, and the temperature. Such parameters as the adsorption kinetics, the adsorption isotherm, and the desorption time were further studied. Maximum adsorption occurred at pH 3 and pH 6 for Hg(II) and Pb(II), respectively. The adsorption kinetics followed the mechanism of the pseudo-second-order equation for heavy metal ions. The adsorption data is a good fit with Freundlich isotherm. Desorption studies indicated that the maximum percent recovery of Hg(II) and Pb(II) was 93.4% and 76.3%, respectively with 1 M HNO3.

Cold-vapour atomic absorption spectrometry underestimates total mercury in blood and urine compared to inductively-coupled plasma mass spectrometry: an important factor for determining mercury reference intervals

In recent years, the application of inductively-coupled plasma mass spectrometry (ICP-MS) has been used increasingly in clinical laboratories for the measurement of various trace elements and heavy metals. However, full evaluation of this technique has not been conducted to ensure the transfer of comparable results from conventional cold-vapour atomic absorption spectrophotometry (CVAAS) for blood and urine total mercury (Hg) analysis. A total of 131 blood and 223 urine samples from both patients and normal healthy subjects were collected from a university-based trace element laboratory and a population survey of healthy school adolescents. Correlation study was conducted for total Hg concentration measured by the traditional on-line digestion with flow injection CVAAS and the newly installed ICP-MS. Reference materials were used for method validation and quality control. Standard addition of fixed amounts of inorganic and methyl Hg standards into blood and urine were performed for recovery study. Bias in total Hg measurement was investigated by re-calibrating both instruments using methyl Hg standards. The intra- and inter-assay coefficients of variation in the ICP-MS were <6% in the range of 14-259 nmol/L for Hg in blood and urine samples assayed. The detection limit was 1.1 nmol/L and linearity was up to 186 nmol/L. The results from analyses of a range of whole blood and urine reference materials agreed well with the certified values. The correlation study showed a significant correlation between ICP-MS and CVAAS with: [ICP-MS] = 7.36 + 1.69*[CVAAS] in blood samples (r = 0.84, p < 0.0001) and [ICP-MS] = 1.90 + 1.14*[CVAAS] in urine samples (r = 0.93, p < 0.0001) for total Hg. Recovery study showed that the % recovery of inorganic Hg in blood for ICP-MS and CVAAS ranged from 83 to 95% and 77 to 84%, respectively, while that of inorganic Hg in urine for ICP-MS and CVAAS ranged from 92 to 126% and 43 to 93%, respectively. For methyl Hg, the % recovery in blood for ICP-MS and CVAAS ranged from 72 to 89% and 37 to 75%, respectively, while that in urine for ICP-MS and CVAAS ranged from 65 to 85% and 29 to 42%, respectively. When both instruments were re-calibrated using methyl Hg standards, the blood and urinary total Hg results in ICP-MS were corrected at 24% and -11% of CVAAS, respectively. Analysis of total Hg was underestimated at about 69% in blood and 14% in urine using the traditional CVAAS method compared to ICP-MS, plausibly due to incomplete oxidation and reduction of methyl Hg species in CVAAS method. The normal limit of blood total Hg concentration has been targeted at <50 nmol/L based on the traditional CVAAS method, and the in vivo proportion of methyl Hg of individuals mainly depends on the dietary intake of seafood. Therefore, for clinical laboratories preparing to change over to ICP-MS method for total Hg analysis, the local reference interval for blood total Hg should be re-determined using a non-occupationally exposed population. Otherwise, over-diagnosis of Hg intoxication can result. We have found that by using ICP-MS for total Hg analysis, the local reference range in blood was <77 nmol/L while in spot urine was <15 nmol/L or 1.2 nmol/mmol of creatinine.

Removal and recovery of Hg(II) from aqueous solution using chitosan-coated cotton fibers

Two types of chitosan-coated cotton fibers (SCCH and RCCH) were applied to remove and recover Hg(II) ions in aqueous solution. The adsorption kinetics and isotherms of the two fibers for Hg(II) were investigated at different temperatures. The results revealed that the adsorption kinetic processes of SCCH and RCCH fibers for Hg(II) followed the pseudo second-order model at lower temperatures and the pseudo first-order model at higher temperatures. Both the Langmuir and Freundlich models well described the adsorption isotherms of SCCH and RCCH fibers for Hg(II) in the temperature range studied. SCCH and RCCH fibers selectively adsorbed Hg(II) from binary ion systems in the presence of Pb(II), Cu(II), Ni(II), Cd(II), Zn(II), Co(II), Mn(II) and Ag(I). Increased temperature was beneficial to adsorption. The recovery of Hg(II) from aqueous solutions was also studied as a function of sample flow rate and volume, concentration and volume of eluent, elution rate, quantity of adsorbents added and concomitant ions. The results showed that the two fibers efficiently enriched and recovered Hg(II) in the presence of alkali and alkaline earth metals and some heavy metals under optimum conditions. The RCCH fiber exhibited better stability than the SCCH fiber following repeated use.

Stir bar sorptive extraction with in situ derivatization and thermal desorption–gas chromatography–mass spectrometry for trace analysis of methylmercury and mercury(II) in water sample

A method for the trace analysis of methylmercury (MeHg) and Hg(II) in water sample was developed, which involved stir bar sorptive extraction (SBSE) with in situ alkylation with sodium tetraethylborate and thermal desorption (TD)–gas chromatography–mass spectrometry (GC–MS). The limits of quantification of MeHg and Hg(II) are 20 and 10 ng L −1 (Hg), respectively. The method shows good linearity and the correlation coefficients are higher than 0.999. The average recoveries of MeHg and Hg(II) in tap or river water sample are 102.1–104.3% (R.S.D.: 7.0–8.9%) and 105.3–106.2% (R.S.D.: 7.4–8.5%), respectively. This simple, accurate, sensitive, and selective analytical method may be used in the determination of trace amounts of MeHg and Hg(II) in tap and river water samples.

CYPHOS IL 101 (Tetradecyl(Trihexyl)Phosphonium Chloride) Immobilized in Biopolymer Capsules for Hg(II) Recovery from HCl Solutions

A composite polymer (made of gelatin and alginate) was used for the synthesis of Cyphos IL 101-immobilized resins. These resins (with varying size and different ionic liquid (IL) content) have been tested for the recovery of mercury from concentrated HCl solutions (0.1–5 M HCl concentrations). Prior to the study of sorption performance on resins, the reactivity of Cyphos IL 101 versus mercury was tested using solvent extraction methodology. These results showed that the extraction was hardly affected by the concentration of HCl and that an ion exchange mechanism was probably involved in metal recovery (binding of HgCl4 2-). The performance of these resins for Hg(II) recovery was tested through sorption isotherms and uptake kinetics, investigating the effect of resin size, ionic liquid content, metal concentration, agitation speed, and resin state (dry state versus wet state). Sorption capacity (which was proportional to the IL content) can reached up to 150 mg Hg g−1 in 1 M HCl; this sorption capacity was decreased by increasing chloride concentration. The kinetics were described well by the pseudo-second order equation and by the intraparticle diffusion equation (the so-called Crank's equation). The intraparticle diffusion coefficient was in the range of 10−11–1.2 × 10−10 m2 min−1. The kinetic profiles were controlled by the IL content, sorbent dosage, and the sorbent particle size. Drying of the resins significantly decreased diffusion rates in the resins. The presence of competitor metals did not affect sorption capacity except when stable chloro-anionic species such as in the case of Zn(II) were formed. Mercury can be desorbed using 6 M nitric acid solutions; and the sorbent can be recycled for at least six sorption/desorption cycles without significant decrease in the sorption performance.

Sorption of Hg(II) onto Carica papaya: Experimental studies and design of batch sorber

A novel sorbent, Carica papaya, was evaluated for sorption of Hg(II) from aqueous solution under the varying conditions of contact time, metal ion concentration, sorbent dose and pH. The results indicate that sorption equilibrium was established in about 120 min. The Hg(II) sorption was strictly pH dependent, and maximum removal was observed at pH 6.5. The sorption interaction of Hg(II) onto C. papaya obeyed the pseudo-second order rate equation. The batch biosorption rate for the system based on an intraparticle diffusion rate parameter derived from the plots of Hg(II) sorbed versus the square root of time indicated that the adsorption mechanism was predominantly intraparticle diffusion but there was also a dependence on pore size as the Hg(II) diffuses through macro-, meson-, and microspores. The sorption isotherm data provided a very good fit to the Langmuir isotherm equation with a monolayer sorption capacity of 155.6 mg g−1 and the regression coefficient (R2) 0.9959 with low S.E. and SSE values. A design procedure was proposed using the Langmuir isotherm to design a two stage sorption system to minimize the amount of biomass required for the treatment of Hg(II) solution using C. papaya. Desorption studies indicated that the maximum percent recovery of Hg(II) was 96.7 ± 0.80 with 0.1 N HCl and 99.0 ± 0.49 with 1% KI.