Heavy Metals In Aqueous Solutions Research Articles

Chalcogen-based aerogels as a multifunctional platform for remediation of radioactive iodine

Aerogels employing chalcogen-based (i.e., S, Se, and/or Te) structural units and interlinking metals are termed chalcogels and have many emerging applications. Here, chalcogels are discussed in the context of nuclear fuel reprocessing and radioactive waste remediation. Motivated by previous work on removal of heavy metals in aqueous solution, we explored the application of germanium sulfide chalcogels as a sorbent for gas-phase I2 based on Pearson's Hard/Soft Acid–Base (HSAB) principle. This work was driven by a significant need for high-efficiency sorbents for 129I, a long-lived isotope evolved during irradiated UO2 nuclear fuel reprocessing. These chalcogel compositions are shown to possess an affinity for iodine gas, I2(g), at various concentrations in air. This affinity is attributed to a strong chemical attraction between the chalcogen and I2(g), according to the HSAB principle. The high sorption efficiency is facilitated by the high porosity as well as the exceptionally large surface area of the chalcogels. This paper briefly discusses the current and alternative waste forms for 129I, elaborates on preliminary work to evaluate a Pt-Ge-S chalcogel as a I2(g) sorbent, and discusses the unknown chalcogel properties related to these materials in waste form.

Simultaneous detection of cyanide and heavy metals for environmental analysis by means of µISEs

AbstractIn environmental analysis, cyanide and heavy metals play an important role, because these substances are highly toxic for biological systems. They can lead to chronic and acute diseases. Due to the chemical properties of cyanide it is frequently used for industrial processes such as extraction of silver and gold. Heavy metals can be found as trace elements in nature and are often applied in industries e.g., galvanization processes. Up to now, cyanide and heavy metals can be detected by several sensors separately and their detection is often limited to laboratory investigations. In this publication, with regard to an in situ analysis, a new miniaturized silicon‐based sensor system for the simultaneous detection of cyanide and heavy metals in aqueous solutions is presented that is based on chalcogenide glass‐based micro ion‐selective electrodes (µISEs). The µISEs are incorporated into a specially designed measuring system for the simultaneous detection of heavy metals and cyanide in solutions and validated by simultaneous measurements of Cu2+‐ and CN−‐ions, Cd2+‐ and CN−‐ ions and Pb2+‐ and CN−‐ions. The particular sensor system has shown good sensor properties in the µ‐molar ion‐concentration range. For simultaneous measurements in complex heavy metal and cyanide solutions an intelligent software using fuzzy logic is discussed.

Sensitive detection of metals in water using laser-induced breakdown spectroscopy on wood sample substrates

Water contaminated with toxic heavy metals can be a great risk to humans. Laser-induced breakdown spectroscopy (LIBS) is a promising candidate to monitor heavy metals in aqueous solutions on site, but the sensitivity is still a major problem. To perform sensitive analysis of analyte metals in aqueous solutions with LIBS, a thin wood sample substrate was used as a liquid absorber to transform the liquid sample analysis to a solid sample analysis. We focus on investigating the performance of this technique using different laser wavelengths (266, 532, and 1064 nm) with a low pulse energy (<5 mJ) and a different number of shots (from 10 to 1000). We demonstrate that a limit of detection of 30 ppb can be achieved using low energy pulses with a 1000 shot accumulation. This technique provides a potentially simple approach for a portable micro LIBS system to monitor water samples.

Facilitated transport of cobalt through bulk liquid membranes containing D2EHPA as carrier. Kinetic study of the influence of some operational variables

The presence of heavy metals in aqueous solutions beyond certain limits creates serious threat to the environment due to their non-degradability and toxicity. So the search for techniques to remove those pollutants is of increasing interest. Liquid membranes have shown great potential in this way, especially in cases where pollutant concentrations are relatively low and other techniques cannot be applied efficiently. A kinetic study of the influence of some operational variables (organic phase volume, emulsifier concentration in the membrane phase and stirring rate) on the transport of cobalt (II) through bulk liquid membrane containing di(2-ethylhexyl) phosphoric acid (D2EHPA), as mobile carrier, in kerosene and protons, as counter ions, in the product phase (H2SO4), is carried out is this paper. The transport kinetic was analysed by means of a kinetic model involving two consecutive irreversible first order reactions. The rate constants of the extraction and stripping reactions were determined for all the experimental conditions studied. Maximum transport fluxes of cobalt (II) through the bulk liquid membrane were also calculated.

Determination of Trace Metals by Differential Pulse Voltammetry at Chitosan Modified Electrodes

Surface modification by chitosan (CT) on a glassy carbon electrode (GCE) was employed in the present study to determine metal traces (Cu, Pb, Cd, Co, As and Pt). Previous report about the chitosan film affinity toward positive or negative species demonstrated and allowed the application of these polymeric films for detecting heavy metals in aqueous solutions. The modified surface exhibited an affinity to chelating metal ions in solution, forming complexes. Differential pulse voltammetry combined with a pre-concentrating process and standard addition method were employed for trace analysis, obtaining the detection ranges (Cu (II) from 3.99×10 -6 to 3.91×10 -5 mol L -1 , Pb(II) from 1.99×10 -6 to 1.58×10 -5 mol L -1 , Cd(II) from 1.59×10 -5 to 6.23×10 -5 mol L -1 , As(IV) from 7.99×10 -6 to 5.04×10 -5 mol L -1 , Pt(IV) from 8.19×10 -6 to 3.59×10 -5 mol L -1 , Co(II) from 6.11×10 -4 to 2.78×10 -3 mol L -1 ), calibrations plots and relevant equations for each metal. Finally, cyclic voltammetry technique was used to characterize the polymeric surface behavior in presence of different metals and during the differential pulse voltammetric analysis. The results are described and discussed in the light of the existing literature.

Stripping voltammetric behavior of nitrogen-doped tetrahedral amorphous carbon thin film electrodes in NaCl solutions

Conductive nitrogen-doped tetrahedral amorphous carbon (ta-C:N) thin films fabricated with a filtered cathodic vacuum arc technique were investigated for their ability to detect multiple trace heavy metals such as mercury, copper and lead by linear sweep anodic stripping voltammetry in sodium chloride aqueous solutions. The ta-C:N film electrodes exhibited a significant stripping response for determination of individual elements (Pb 2+ and Hg 2+) and multiple elements (Pb 2+ + Hg 2+ and Cu 2+ + Hg 2+), indicating that these electrodes have a great potential for simultaneously tracing multiple heavy metals in aqueous solutions.

Contribution of agro‐waste material main components (hemicelluloses, cellulose, and lignin) to the removal of chromium (III) from aqueous solution

AbstractBACKGROUND: Agro‐waste materials can be used as biosorbents of heavy metals in aqueous solution. However, it is necessary to further study the contribution of agro‐waste materials components (i.e. hemicelluloses, cellulose, and lignin) to the heavy metal ions removal from aqueous solution to better understand the biosorption mechanism, and also based on the biosorbents main components, to predict their potential to remove heavy metals.RESULTS: Cellulose is contained in major proportion (greater than 46%) in the agro‐waste materials reported herein compared with hemicelluloses (from 12% to 26%), lignin (varying from 3% to 10%), and other compounds (22% to 30%) that were removed after the neutral detergent fiber procedure. The identified functional groups in agro‐waste materials and their fractions included hydroxyl, carboxyl, and nitrogen‐containing compounds. Lignin contributed in higher proportion than hemicelluloses to Cr (III) adsorption capacity in both sorghum straw and oats straw. On the other hand lignin was the main fraction responsible for Cr (III) adsorption in agave bagasse.CONCLUSION: Hemicelluloses and lignin were the main contributors to Cr (III) removal from aqueous solution, and cellulose contained in the agro‐waste adsorbents studied did not seem to participate. Copyright © 2009 Society of Chemical Industry

Effect of various oxidants in a photocatalysis/filtration system for the treatment of contaminants

This study was conducted to investigate the effect of a photocatalysis/oxidant system for the treatment of humic acid and hazardous heavy metals in aqueous solutions. Hydrogen peroxide, ozone, and potassium peroxodisulfate were tested as oxidants. The effect of oxidant concentration was conducted with a pH of 7, a UV intensity of 64 W, and a TiO2 dosage of 0.3 g L−1. The oxidant addition in the UV/TiO2 system enhanced the degradation efficiency of humic acid and hazardous heavy metals compared to no addition of an oxidant. The addition of oxidants over the amounts of H2O2 50 mg L−1, O3 20 g m−3, and K2S2O8 50 mg L−1 inhibits the system efficiency. The negative effect of higher oxidant concentrations likely results from OH radical quenching caused by the excess oxidant. Therefore, the optimal dosages of oxidants such as a hydrogen peroxide, ozone, and potassium peroxodisulfate were found to be 50 mg L−1, 20 g m−3, and 50 mg L−1, respectively. The degradation efficiency of UV/TiO2/oxidant systems for the removal of humic acid and hazardous heavy metals was much greater in the UV/TiO2/H2O2 system using H2O2 as an oxidant.

Sorption potentials of waste tyre for some heavy metals in aqueous solution

An investigation into the adsorption potential of activated and unactivated waste tyre powders for some heavy metals (Pb 2+ and Cd 2+ ) in their aqueous solution has been studied. The result indicated that unactivated waste tyre is a good non-conventional adsorbent for the removal of Cd2+ from aqueous solution. A total of 93.3% of cadmium, contents was removed. The unactivated waste type proved a good absorbent for the removal of Cd 2+ 5g of 500µm activated tyre removed over 86.66% of Pb 2+ from solution.

The removal of heavy metals in aqueous solution by hydroxyapatite/cellulose composite

Hydroxyapatite has an excellent ion-exchangeability and is expected to be used as an agent for the removal of heavy metal ions in wastewater. However, the pure hydroxyapatite is very difficult to use because it exists in the form of white powder. Thus, the pure hydroxyapatite was mixed with cellulose to utilize its ion-exchangeability. In this research, a method for dispersion of hydroxyapatite in cellulose matrix is described and its dispersion is observed with scanning electron microscopy. The removal ratios of some heavy metal ions with hydroxyapatite composite are examined with regard to reaction time and amount of hydroxyapatite composite. The ion-exchangeability of hydroxyapatite composite did not seem to be interfered by cellulose matrix during removing heavy metal ions.

Performance of Photocatalysis/Chemical Oxidants in Aqueous TiO&lt;sub&gt;2&lt;/sub&gt; Suspensions

This study was conducted to evaluate the effect of a photocatalysis/oxidant system for the treatment of humic acid and heavy metals in aqueous solutions. Hydrogen peroxide, ozone and potassium peroxodisulfate were tested as oxidants. The effect of the oxidant concentration was conducted with a pH of 7, a UV intensity of 64 W and a TiO2 dosage of 0.3 g/L. The addition of oxidants over the amounts of H2O2 50 mg/L, O3 20 g/m3 and K2S2O8 50 mg/L inhibits the system efficiency. The negative effect of the high concentration of oxidants likely results from OH radical quenching caused by the excess oxidant. Therefore, the optimal dosages for the oxidants such as a hydrogen peroxide, ozone and potassium peroxodisulfate were found to be 50 mg/L, 20 g/m3 and 50 mg/L, respectively. The addition of an oxidant in the UV/TiO2 system enhanced the degradation efficiency of humic acid and heavy metals compared to no addition of an oxidant. The degradation efficiency of humic acid and heavy metals was much greater for the UV/TiO2/H2O2 system.

Equilibrium isotherm studies for the uptake of cadmium and lead ions onto sugar beet pulp

The adsorption of Cd 2+ and Pb 2+ on sugar beet pulp (SBP), a low-cost material, has been studied. In the present work, the abilities of native (SBP) to remove cadmium (Cd 2+) and lead (Pb 2+) ions from aqueous solutions were compared. The (SBP) an industrial by product and solid waste of sugar industry were used for the removal of Cd 2+ and Pb 2+ ions from aqueous water. Batch adsorption studies were carried out to examine the influence of various parameters such as initial pH, adsorbent dose, initial metal ion concentration, and time on uptake. The sorption process was relatively fast and equilibrium was reached after about 70 min of contact. As much as 70–75% removal of Cd 2+ and Pb 2+ ions for (SBP) are possible in about 70 min, respectively, under the batch test conditions. Uptake of Cd 2+ and Pb 2+ ions on (SBP) showed a pH-dependent profile. The overall uptake for the (SBP) is at a maximum at pH 5.3 and gives up to 46.1 mg g −1 for Cd 2+ and at pH 5.0 and gives 43.5 mg g −1 for Pb 2+ for (SBP), which seems to be removed exclusively by ion exchange, physical sorption and chelation. A dose of 8 g L −1 was sufficient for the optimum removal of both the metal ions. The Freundlich represented the sorption data for (SBP). In the presence of 0.1 M NaNO 3 the level of metal ion uptake was found to reach its maximum value very rapidly with the speed increasing both with the (SPB) concentration and with increasing initial pH of the suspension. The reversibility of the process was investigated. The desorption of Cd 2+ and Pb 2+ ions which were previously deposited on the (SBP) back into the deionised water was observed only in acidic pH values during one day study period and was generally rather low. The extent of adsorption for both metals increased along with an increase of the (SBP) dosage. (SBP), which is cheap and highly selective, therefore seems to be a promising substrate to entrap heavy metals in aqueous solutions.

Humic acid complexation to Zn and Cd determined with the new electroanalytical technique AGNES

Environmental context. Humic substances are complex mixtures that play an important role in trace metal bioavailability in soils and aquatic environments. The bioavailability of a metal depends on what chemical forms, or species, it is in. We need to know how much of the metal is present as a free metal ion in solution, and how much is bound up in complexes with humic acids, for example. This work reports the complexation of Cd and Zn to humic acids by means of a simple and robust technique, AGNES (absence of gradients and Nernstian equilibrium stripping). Abstract. AGNES (absence of gradients and Nernstian equilibrium stripping), an emerging electroanalytical technique specifically designed for the determination of the free concentration of heavy metals in aqueous solutions, is here implemented to characterise the binding of CdII and ZnII to a soil humic acid. A set of metal titration experiments were performed by adding Cd or Zn to a purified humic acid (Aldrich) at pH 4, 5, 6 and 7 and measuring the free metal concentration by AGNES. The application of a program with two potential steps along the deposition stage allows for the reduction of the deposition time in the humic titration. The polyelectrolytic effects of the macromolecular ligand were taken into account through the Donnan model. Data free of electrostatic effects were reasonably described by the NICA isotherm, which accounts for heterogeneity, considering just a monomodal distribution (because of the range of pH covered). The obtained affinity parameters indicate a similar strength for Zn and Cd binding to the purified humic acid.

Application of Photocatalytic Metal Membrane System for Water Purification

This study was conducted to evaluate the applicability of photocatalytic metal membrane system for the treatment of humic acid and heavy metals in aqueous solution. The catalysts, TiO2 powder P25 Degussa and metal membrane with 0.5 μm nominal pore size were used for experiments. Removal efficiency of humic acid and heavy metals increased with the increase of TiO2 dosage, however decreased over 0.3 g/L of TiO2 dosage. The addition of H2O2 as an oxidation reagent had a positive effect for the removal rate of humic acid and heavy metals. Metal membrane with stainless steel seemed to be quite stable to UV light with oxidation reagent in long-term operational periods over 6 months. Moreover, TiO2 particles can be effectively separated from the treated water by membrane rejection and the permeation flux was also enhanced by the combination of photocatalytic reaction.

An electroanalytical application of 2-aminothiazole-modified silica gel after adsorption and separation of Hg(II) from heavy metals in aqueous solution

2-Aminothiazole covalently attached to a silica gel surface was prepared in order to obtain an adsorbent for Hg(II) ions having the following characteristics: good sorption capacity, chemical stability under conditions of use, and, especially, high selectivity. The accumulation voltammetry of mercury(II) was investigated at a carbon paste electrode chemically modified with silica gel functionalized with 2-aminothiazole (SIAMT–CPE). The repetitive cyclic voltammogram of mercury(II) solution in the potential range −0.2 to +0.6 V versus Ag/AgCl (0.02 mol L −1 KNO 3; v = 20 mV s − 1 ) show two peaks one at about 0.1 V and other at 0.205 V. The anodic wave peak at 0.205 V is well defined and does not change during the cycles and it was therefore further investigated for analytical purposes using differential pulse anodic stripping voltammetry in differents supporting electrolytes. The mercury response was evaluated with respect to pH, electrode composition, preconcentration time, mercury concentration, “cleaning” solution, possible interferences and other variables. The precision for six determinations ( n = 6) of 0.02 and 0.20 mg L −1 Hg(II) was 4.1 and 3.5% (relative standard deviation), respectively. The detection limit was estimated as 0.10 μg L −1 mercury(II) by means of 3:1 current-to-noise ratio in connection with the optimization of the various parameters involved and using the highest-possible analyser sensitivity.

Heavy Metals Uptake by Sardinian Natural Zeolites: Experiment and Modeling

Sardinian natural clinoptilolites are examined to evaluate their performance for heavy metals, i.e., lead, cadmium, copper, and zinc, removal. The natural material is either used as received or once converted into the sodium homoionic form. Equilibrium data for heavy metals in aqueous solutions and the natural material are obtained. The corresponding behavior is quantitatively correlated using classical adsorption isotherms as well as the ion-exchange equilibria model developed by Melis et al. (Ind. Eng. Chem. Res. 1995, 34, 3916), whose parameters are estimated by fitting the equilibrium data. To evaluate removal performance under dynamic conditions, breakthrough experiments are also conducted. The latter ones are compared with different ion-exchange rate laws (namely, equilibrium model, linear driving force (LDF), and film model rate approximations, along with Nernst−Planck model) with the aim of pointing out the importance of the hindrance effect of intra- and interphase mass transport when using the n...

A study on removal characteristics of heavy metals from aqueous solution by fly ash

The purpose of this study was to investigate the possibility of the utilization of coal fly ash as a low cost adsorbent. Batch experiments were conducted to evaluate the removal of heavy metals from aqueous solutions by fly ash under various conditions of metal concentration, pH and fly ash dosage. The heavy metals used in this study were zinc, lead, cadmium and copper. Adsorption studies were done at various pH values (3–10) at 25 °C and at heavy metal concentrations of 10–400 mg/L using fly ash concentrations of 10, 20 and 40 g/L, respectively. Experiments were also conducted without fly ash to determine the extent of heavy metal removal by precipitation. Kinetic experiments were also performed and the zeta-potentials of the fly ash particles were measured at various pH's. The adsorption data was described by the Freundlich adsorption model. The test results using real wastewater indicated that fly ash could be used as a cheap adsorbent for the removal of heavy metals in aqueous solutions if not strongly acidic.

Synthesis of a New Cellulose Ion Exchanger and Use for the Separation of Heavy Metals in Aqueous Solutions

Ion exchange resin based on cellulose has been synthesized to separate the heavy metals, such as Pb, Cd, Co, Cu, Fe, Ni, Zn, and Cr in aqueous solutions. The total ion exchange capacity (IEC) of resin synthesized was determined 3.3 meq · g−1 as wet and 4.1 meq · g−1 as dry and average swelling percentage as 19.8. Sodium trimetaphosphate was used as an elution agent for the removal of heavy metals. Distribution coefficients of these elements have been determined regarding five different concentrations of sodium trimetaphosphate (3 · 10−3 M; 5 · 10−3 M; 0.01 M; 0.05 M; 0.1 M) on the this resin. By considering these distribution coefficients, the separation of heavy metals has been performed with 5 · 10−3 M sodium trimetaphosphate at room temperature. Qualitative and quantitative determinations were realized by ICP. This study has been indicated that the resin synthesized has preferable properties.

Cellulose/chitin beads for adsorption of heavy metals in aqueous solution

We successfully prepared the biodegradable cellulose/chitin beads by coagulating a blend of cellulose and chitin in 6 wt% NaOH/5 wt% thiourea aqueous solution with 5 % H 2SO 4 as coagulant, and investigated the adsorption of heavy metals (Pb 2+, Cd 2+, Cu 2+) from an aqueous solution on the beads by atomic absorption spectrophotometer. Batch adsorption experiments were carried out as a function of ion concentrations, initial pH, ionic strength, temperature, adsorption time and desorption time. The results revealed that the cellulose/chitin beads could adsorb effectively Pb 2+, Cd 2+ and Cu 2+ ions, and the uptakes of Pb 2+, Cd 2+ and Cu 2+ ions on cellulose/chitin beads were 0.33 mmol/g at pH 0 4, 0.32 mmol/g at pH 0 5 and 0.30 mmol/g at pH 0 4, respectively. Experimental results also showed that the adsorption of these heavy metals was selective to be in the order of Pb 2+>Cd 2+>Cu 2+ in a low ion concentration solution. The adsorption equilibrium time of these heavy metals on beads was 4–5 h, but the desorption time was 5–15 min.Moreover, these beads could be regenerated up to about 98% by treating with 1 mol/L HCl aqueous solution. The mechanisms for the removal of free heavy metal ions by cellulose/chitin beads was based on mainly complexation adsorption model, as well as a affinity of hydroxyl groups of the materials on metals. Therefore, we developed new environment-friendly beads prepared by a simple produce process for removal and recovery of heavy metals.

수용액 중의 중금속 (Cd2+,Pd2+,Zn2+,Cu2+)이온 분리를 위한 티오펜 및 퓨란기를 포함하는 리간드들의 합성과 착화합물의 안정도상수 결정

In this paper, the discussion is concentrated on the properties of the polluted sediments and the combination of clean-up and disposal process for the upper layer heavily polluted sediments with good flowability. Based on the systematic analyses of various clean-up processes, a suitable engineering process has been evaluated and recommended. The process has been applied to the river reclamation in Yangpu District of Shanghai City, China. An improved centrifuge is used for dewatering the dredged sludge, which plays an important role in the combination of clean-up and disposal process. The assessment of the engineering process shows its environmental and technical economy feasibility, which is much better than that of traditional dredging-disposal processes.