Adsorptive separation of Pb(II) and Cu(II) from aqueous solutions using as-prepared carboxymethylated waste Lyocell fiber

Adsorptive separation of Pb(II) and Cu(II) using modified waste Lyocell fiber adsorbent was investigated in this research. The waste Lyocell fiber was functionalized through carboxymethylation of the hydroxyl moieties using sodium chloroacetate as modifying agent and was crosslinked with epichlorohydrin to provide water stability. The maximum equilibrium batch uptake in single metal system was 353.45 mg/g for Pb(II) and 98.33 mg/g for Cu(II), according to the Langmuir isotherm model. The adsorption rates were very fast and reached equilibrium within 3 and 5?10 min for Cu(II) and Pb(II), respectively. In competitive binary metal system, the uptake of Cu(II) largely decreased to 38.40 mg/g, and Pb(II) selectivity was observed. Elemental and functional characterization suggested that the adsorption proceeded by ion exchange between the adsorbent and metal ions. In a flow-through column system, adsorption followed by desorption aided in effectively eluting ~260 mg of Pb(II) (out of ~300 mg total adsorbed) from the Pb(II)–Cu(II) binary solution. Finally, the adsorbent was very effective in four successive adsorption–desorption cycles with over 99 % uptake and 94 % desorption efficiencies. The present study may provide an alternative option for waste fiber recycling and could be useful in recovering heavy metal ions from aqueous sources to complement their depleting reserves.     

Modeling the adsorption of Cd (II), Cu (II), Ni (II), Pb (II) and Zn (II) onto montmorillonite

The adsorption of five toxic metallic cations, Cd(II), Cu(II), Ni(II), Pb(II) and Zn(II), onto montmorillonite was investigated as a function of pH and ionic strength and a two-site surface complexation model was used to predict the adsorption data. The results showed that in the lower pH range, 3∼6 for Cd, Cu, Ni and Zn, and 3∼4.5 for Pb, the adsorption was greatly affected by ionic strength, while in the higher pH range, the adsorption was not. In the lower pH range, the metallic cations were mainly bound through the formation of outer-sphere surface on the permanently charged basal surface sites (≡X⁻), while in the higher pH range the adsorption occurred mainly on the variably charged edge sites (≡SOH) through the formation of inner-sphere surface complexes. Acid-base surface constants and metal binding constants for the two sites were optimized using FITEQL. The adsorption affinity of the five metallic cations to the permanently charged sites of montmorillonite was Pb > Cu > Ni ≈ Zn ≈ Cd, while that to the variable charged sites was Pb ? Cu > Zn > Cd > Ni.     

Surface complexation modelling of Cd(II), Cu(II), Ni(II), Pb(II) and Zn(II) adsorption onto kaolinite

Proton binding constants for the edge and basal surface sites of kaolinite were determined by batch titration experiments at 25 °C in the presence of 0.1 M, 0.01 M and 0.001 M solutions of NaNO₃ and in the pH range 3-9. By optimizing the results of the titration experiments, the ratio of the edge sites to the basal surface sites was found to be 6:1. The adsorption of Cd(II), Cu(II), Ni(II), Zn(II) and Pb(II) onto kaolinite suspensions was investigated using batch adsorption experiments and results suggested that in the lower pH range the metallic cations were bound through non-specific ion exchange reactions on the permanently charged basal surface sites (X⁻). Adsorption on these sites was greatly affected by ionic strength. With increasing pH, the variable charged edge sites (SOH) became the major adsorption sites and inner-sphere specifically adsorbed monodentate complexes were believed to be formed. The effect of ionic strength on the extent of adsorption of the metals on the variable charged edge sites was much less than those on the permanently charged sites. Two binding constants, log K_(X2Me) and log K_(SOMe), were calculated by optimizing these constants in the computer program FITEQL. A model combining non-specific ion exchange reactions and inner-sphere specific surface complexations was developed to predict the adsorption of heavy metals onto kaolinite in the studied pH range. Linear free energy relationships were found between the edge site binding constants and the first hydrolysis constants of the metals.     

Effects of long-term irrigation with treated wastewater. Part II: Role of organic carbon on Cu,Pb and Cr behaviour

The long-term impact of irrigation on a Mediterranean sandy soil irrigated with treated wastewater (TWW) since 1980 was evaluated. The main soil properties (CEC, pH, size distribution, exchangeable cations and chloride, hydraulic conductivity) as well as the organic matter and Cu, Cr and Pb speciation in an irrigated soil and a non-irrigated control soil at various soil depths were monitored and compared during a 2 year experiment. In this second part, we focused on Cu, Cr and Pb behaviour in relation with soil organic carbon (SOC). Soil samples were collected every 3 months during 2 years at the depths 0–20, 20–40 and 40–60 cm and were analysed for exchangeable and total metals, organic carbon content, metal sequential extraction and humic substances – Humic Acids (HA), Fulvic Acids (FA) and Non-Humified Fraction (NHF). Long-term irrigation with a domestic treated wastewater (TWW) may be considered safe with regard to trace metal accumulation in soil. Irrigation lowered the HA and NHF fractions of SOC and made the FA fraction more mobile. Cu bound preferentially to the SOC fraction, Cr was found mainly in the reducible fraction and Pb was bound to all fractions indiscriminately. Cu exhibited a high affinity for the HA fraction, while Pb and Cr had a high affinity for the FA fraction, which indicates a greater mobility of the organically-bound Pb and Cr than of the organically-bound Cu. Evaluation of the potential metal mobility has to take into account not only the usual speciation between labile, reducible and oxidisable fractions, but also the nature of the SOC responsible for the oxidisable fraction.     

Utilization of ochre as an adsorbent to remove Pb(II) and Cu(II) from contaminated aqueous media

The ability of ochre to remove Pb(II) and Cu(II) from aqueous media has been studied by batch sorption studies varying the contact time, initial metal concentration, initial solution pH and temperature to understand the adsorption behaviour of these metals through adsorption kinetics and isotherms. The pH of the solution and the temperature controlled the adsorption of metal ions by ochre and rapid uptake occurred in the first 30 min of reaction. The kinetics of adsorption followed a pseudo-second-order rate equation (R ² > 0.99) and the isotherms are well described by the Freundlich model. Adsorption of metals onto ochre is endothermic in nature. Between the two metals, Pb(II) showed more preference towards the exchangeable sites on ochre than Cu(II). This study indicates that ochre is a very effective adsorbent in removing Pb(II) and Cu(II) from the aqueous environment with an adsorptive capacity of 0.996 and 0.628 mg g^?1 and removal efficiency of 99.68 and 62.80 %, respectively.     

Preparation of a novel two-dimensional carbon material and enhancing Cu(II) ions removal by phytic acid

A novel two-dimensional carbon material using phytic acid-functionalized graphene oxide was successfully synthesized by a simple hydrothermal method. Properties of the material were characterized by SEM, FT-IR, FITR-Rama and BET. Some factors like contact time, pH, and temperature were studied to investigate the adsorption characteristics on Cu(II) ions of the material. Experiment results showed that the material can reach equilibrium adsorption in 20 min and get maximum adsorption capacity (316.586 mg g) under the condition of pH 4.0, 304 K. The adsorption of Cu(II) ions was an exothermic and spontaneous process, and could be better simulated by the pseudo-second-order kinetics and Freundlich isotherm model.     

Influence of operating conditions on the removal of Cu, Zn, Cd and Pb ions from wastewater by adsorption

Nile Rose Plant was used to study adsorption of several cations (Cu²+, Zn²+, Cd²+ and Pb²+) from wastewater within various experimental conditions. The dried leaves of Nile Rose Plant were used at different adsorbent/ metal ion ratios. The influence of pH, contact time, metal concentration, and adsorbent loading weight on the removal process was investigated. Batch adsorption studies were carried out at room temperature. The adsorption efficiencies were found to be pH dependent, increasing by increasing the pH in the range from 2.5 to 8.5 exept for Pb. The equilibrium time was attained within 60 to 90 min. and the maximum removal percentage was achieved at an adsorbent loading weight of 1.5 g/50 mL mixed ions solution. Isothermal studies showed that the data were best fitted to the Temkin isotherm model. The removal order was found to be Pb²⁺> Zn²⁺> Cu²⁺> Cd²⁺. The surface IR-characterization of Nile rose plant showed the presence of many functional groups capable of binding to the metal cations.     

Adsorption kinetic models for the removal of Cu(II) from aqueous solution by clay liners in landfills

Liners are commonly used in engineered waste disposal landfill to minimize the potential contamination of the aquatic environment. The adsorption behavior of Cu(II) from aqueous solution onto clay admixed with various mix ratios of quarry fines was investigated. The amount of Cu(II) adsorption increases with increase in contact time. The copper removal efficiencies of the composite mixture gradually decrease from 94.53 % (raw clay) to 85.59 % (20 % of quarry fines with clay), and appreciable decrease in percent removal 75.61 % was found with 25 % of quarry fines with clay. The kinetic adsorption data were analyzed by pseudo-first-order, pseudo-second-order, Bhattacharya–Venkobachar and Natarajan–Khalaf kinetic models to classify adsorption process mechanisms. Kinetic experimental data were good agreement with pseudo-second-order kinetic model with the degree of fitness of the data (R ²) 0.9999 for the adsorption of Cu(II). The results revealed that quarry fines can be used with optimum of 20 % replacement of natural clay for removal of Cu(II) as a liner material in landfills.     

Lead removal from wastewater using fluted pumpkin seed shell activated carbon: Adsorption modeling and kinetics

Activated carbon produced from fluted pumpkin (Telfairia occidentalis) seed shell was utilized for the removal of lead (II) ion from simulated wastewater. Adsorption tests were carried out in series of batch adsorption experiments. Several kinetic models (Bhattacharya-Venkobacher, Elovich, pseudo first and second order, intra-particle and film diffusion) were tasted for conformity to the experimental data obtained. The Langmuir and Freundlich adsorption models were also used to test the data. The amount of lead (II) ion adsorbed at equilibrium from a 200 mg/L solute concentration was 14.286 mg/g. The experimental data conform very well to the pseudo-second order equation where equilibrium adsorption capacities increased with increasing initial lead (II) concentration. The rate of the adsorption process was controlled by the film (boundary layer) diffusion as the film diffusion co-efficient values obtained from data analysis were of the order of 10 ⁶cm²/s. From the plots, the linear regression coefficient (R²) of the Langmuir model was higher than that of the Freundlich: the adsorption isotherm obeyed the Langmuir model better than the Freundlich model.     

Adsorption of Cu(II) to Bacillus subtilis: A pH-dependent EXAFS and thermodynamic modelling study

Bacteria are very efficient sorbents of trace metals, and their abundance in a wide variety of natural aqueous systems means biosorption plays an important role in the biogeochemical cycling of many elements. We measured the adsorption of Cu(II) to Bacillus subtilis as a function of pH and surface loading. Adsorption edge and XAS experiments were performed at high bacteria-to-metal ratio, analogous to Cu uptake in natural geologic and aqueous environments. We report significant Cu adsorption to B. subtilis across the entire pH range studied (pH ∼2-7), with adsorption increasing with pH to a maximum at pH ∼6. We determine directly for the first time that Cu adsorbs to B. subtilis as a (CuO₅H_n)ⁿ⁻⁸ monodentate, inner-sphere surface complex involving carboxyl surface functional groups. This Cu-carboxyl complex is able to account for the observed Cu adsorption across the entire pH range studied. Having determined the molecular adsorption mechanism of Cu to B. subtilis, we have developed a new thermodynamic surface complexation model for Cu adsorption that is informed by and consistent with EXAFS results. We model the surface electrostatics using the 1pK basic Stern approximation. We fit our adsorption data to the formation of a monodentate, inner-sphere RCOOCu⁺ surface complex. In agreement with previous studies, this work indicates that in order to accurately predict the fate and mobility of Cu in complex biogeochemical systems, we must incorporate the formation of Cu-bacteria surface complexes in reactive transport models. To this end, this work recommends log K RCOOCu⁺ = 7.13 for geologic and aqueous systems with generally high B. subtilis-to-metal ratio.     

The concentration of Cu(II), Pb(II) and Zn(II) from aqueous solutions by particulate algal matter

Experimental studies of the reactions of Cu(II), Pb(II), and Zn(II) in aqueous solutions with organic matter derived from fresh samples of the green filamentous algae Ulothrix spp. and the green unicellular algae Chlamydomonas spp. and Chlorella vulgaris show that, under suitable conditions, a significant proportion of the metals is removed from solution by sorption onto the particulate organic matter of the algal suspension.The metal sorption is strongly suppressed by H⁺ but is only marginally influenced by the proportion of whole cells in the suspension and by complexing of metals in solution by the soluble organic matter. The presence of relatively small amounts of the cations Na⁺ and Mg²⁺ in solution reduces the sorption of Zn(II) to near zero, but Pb(II) and Cu(II) sorption occurs to an appreciable extent even in strong brines. This may be a means for the selective precipitation of Pb(II) from brines rich in Pb(II) and Zn(II).Metal “saturation” values indicate that particulate algal matter of the type used in these experiments could sorb sufficient quantities of metal to form an ore deposit if a weight of organic matter of similar order of magnitude to that of the inorganic sediments in the deposits was available. However, the metal sorption is an equilibrium reaction, and the experimentally determined “enrichment factors” suggest that the “saturation” values could be approached only in solutions whose metal contents were initially at least two orders of magnitude above those of normal seawater.     

Biosorption of Cu(II) and Pb(II) from aqueous solutions by chemically modified spent coffee grains

In this research, spent coffee grains were modified with citric acid solutions (0.1 and 0.6 M) to increase the quantity of carboxylic groups improving its metal adsorption capacity. Added functional groups on modified and non-modified spent coffee grains were identified and quantified by attenuated total reflection Fourier transform infrared analyses and potentiometric titrations, respectively. These adsorbents were used for the removal of lead (II) and copper (II) from aqueous solutions at 30 °C and different pH in batch systems. In addition, adsorption–desorption experiments were conducted to evaluate the possibility of re-using the modified adsorbent. Potentiometric titrations data reveal that the quantity of carboxylic groups was increased from 0.47 to 2.2 mmol/g when spent coffee grains were modified with 0.1 and 0.6 M citric acid. Spent coffee grains treated with 0.6 M citric acid, achieved a maximum adsorption capacity of 0.77 and 1.53 mmol/g for lead (II) and copper (II), respectively, whereas non-modified spent coffee grains only reached 0.24 and 0.19 mmol/g for lead (II) and copper (II), respectively. Desorption of lead (II) and copper (II) achieved around 70 % using 0.1 N HCl for non-modified and modified spent coffee grains with 0.6 M citric acid. It is suggested that lead (II) and copper (II) species were adsorbed mainly on the carboxylic groups of modified spent coffee grains and these metals may be exchanged for hydrogen and calcium (II) ions during adsorption on non-modified spent coffee grains. Finally, the adsorption equilibrium was reached after 400 min for modified spent coffee grains with 0.6 M citric acid. Modified spent coffee grains are a promising option for removing metal cations from aqueous solutions due to its low cost and high adsorption capacity (about 10 times higher than the activated carbons).     

An easy and fast IC-CL procedure for the monitoring of Cu(II) and Co(II) in environmental samples

A luminol chemiluminescence (CL) detection/flow injection analysis technique coupled with ion chromatography (IC) has been employed for the determination of low levels of Cu(II) and Co(II) in drinking water samples. The detection system was the CL of luminol/perborate or luminol/percarbonate in alkaline medium catalyzed by these transition metals. Oxalic acid in a solution of KOH and N(CH₃)₄OH was used as an eluent in the IC to improve the column selectivity (Dionex CS5A). Concentration and pH of the eluent affected simultaneously the CL intensity and the retention times (t _R). Under the elution conditions used here, the retention times of both metal ions were much greater when the concentration of oxalic acid was decreased. Thus, R _t(_Cu) = 2.15 min and t _R(_Co) = 4.50 min were measured at 80 mM oxalic acid concentration, while t _R raised to 4.12 and 18 min for Cu(II) and Co(II), respectively, using a 10-mM concentration, but on the other hand, the CL signals showed substantially higher values when the concentration of oxalic acid was lesser in the eluent. An optimum oxalic acid concentration of 20 mM and an eluent pH = 4.7 were selected in order to have reproducible signals with a total analysis time of 10 min. The optimum flow rate for the mobile phase was 1.5 mL min^?1. The concentration and pH of the postcolumn reagents also affected the CL signal, obtaining optimum concentrations of 5 mM for both oxidants (perborate or percarbonate) and luminol, this last dissolved in a 0.1-M borate buffer at pH 12. The optimum flow rate for the postcolumn reagents was 1 mL min^?1. Linear calibrations for both transition metal ions were established, with calculated detection limits of 0.15 ng mL^?1 for Co(II) and 0.20 μg mL^?1 for Cu(II). Others ions commonly present in natural waters showed little or no interference. The method was successfully applied to water samples spiked with Cu(II) and Co(II), obtaining recoveries in the range of 85–128%, depending on the metal concentrations.     

Comparison of three procedures (single,sequential and kinetic extractions) for mobility assessment of Cu,Pb and Zn in harbour sediments

The mobility of Cu, Pb and Zn in harbour sediments was investigated using single, sequential and kinetic extraction techniques. Each type of extraction provides different information on the mobility of these elements in the environment. The single HCl extraction assesses general mobility, the sequential extraction assesses geochemical partitioning and kinetic extraction allows quickly and slowly mobilized elements to be identified. Kinetic extraction also allows the influence of extraction duration to be assessed. The results presented in this paper highlight the complementary information provided by different types of mobility studies. The lack of correlation between element mobility and total metal concentration emphasises the inadequacy of using total metal concentrations in risk assessment.     

Adsorption of aqueous Pb(II), Cu(II), Zn(II) ions by amorphous tin(VI) hydrogen phosphate: an excellent inorganic adsorbent

Amorphous tin(VI) hydrogen phosphate (ATHP) was synthesized using the liquid phase precipitation method and served as an adsorbent to remove Pb(II), Cu(II), and Zn(II) from aqueous solutions. The ATHP was characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and nitrogen adsorption–desorption techniques. Adsorption properties were evaluated as a function of pH, reaction time, concentration of reactants, and salinity. Their equilibrium adsorption data were modeled using Freundlich, Langmuir, and Dubinin–Kaganer–Radushkevich isotherms, respectively. The results revealed that adsorption equilibrium reached within 180 min. ATHP indicated good adsorption even below the pH_ZPC, and best adsorption at pH 5 for Pb(II) and Cu(II) and at pH 5.5 for Zn(II) was observed. Equilibrium data fitted better to the Langmuir model for Pb(II) and Cu(II) and fitted better to the Freundlich model for Zn(II). The saturated adsorption capacities deduced from the Langmuir model were 2.425, 1.801, and 0.600 mmol/g for Cu(II), Pb(II), and Zn(II), respectively, indicating an adsorption affinity order of Cu > Pb > Zn. There is a negative correlation between the concentration of NaCl and adsorption capacity of ATHP, yet ATHP still exhibited excellent adsorption having an adsorption capacity of 19.35, 15.16, 6.425 mg/g when the concentration of NaCl was 0.6 mol/L. The free energy (E) was 12.33, 10.70, and 14.74 kJ/mol for Pb(II), Cu(II), and Zn(II), respectively. An adsorption mechanism based on ion exchange between heavy metal ions and H⁺ in the ATHP is proposed. Furthermore, the used ATHP was regenerated by HCl solution and the adsorbent was used repeatedly.     

Goethite adsorption of Cu(II), Pb(II), Cd(II), and Zn(II) in the presence of sulfate: Properties of the ternary complex

Adsorption of Cu²⁺, Zn²⁺, Cd²⁺, and Pb²⁺ onto goethite is enhanced in the presence of sulfate. This effect, which has also been observed on ferrihydrite, is not predicted by the diffuse layer model (DLM) using adsorption constants derived from single sorbate systems. However, by including ternary surface complexes with the stoichiometry FeOHMSO₄, where FeOH is a surface adsorption site and M²⁺ is a cation, the effect of SO₄²⁻ on cation adsorption was accurately predicted for the range of cation, goethite and SO₄²⁻ concentrations studied. While the DLM does not provide direct molecular scale insights into adsorption reactions there are several properties of ternary complexes that are evident from examining trends in their formation constants. There is a linear relationship between ternary complex formation constants and cation adsorption constants, which is consistent with previous spectroscopic evidence indicating ternary complexes involve cation binding to the oxide surface. Comparing the data from this work to previous studies on ferrihydrite suggests that ternary complex formation on ferrihydrite involves complexes with the same or similar structure as those observed on goethite. In addition, it is evident that ternary complex formation constants are larger where there is a stronger metal-ligand interaction. This is also consistent with spectroscopic studies of goethite-M²⁺-SO₄²⁻ and phthalate systems showing surface species with metal-ligand bonding. Recommended values of ternary complex formation constants for use in SO₄-rich environments, such as acid mine drainage, are presented.