Removal of Lead(II) from Aqueous Solutions using Pre-boiled and Formaldehyde-Treated Onion Skins as a New Adsorbent

The adsorption characteristics of Pb²⁺ on pre-boiled treated onion skins (PTOS) and formaldehyde-treated onion skins (FTOS) were evaluated. The effects of Pb²⁺ initial concentration, agitation rate, solution pH, and temperature on Pb²⁺ adsorption were investigated in batch systems. Pb²⁺ adsorption was found to increase with increase in initial concentration. The point of zero net charge (PZC) was 6.53. The optimum pH for the maximum removal of Pb²⁺ was 6.0. The adsorption equilibrium data was best represented by the Langmuir isotherm model for FTOS and the Freundlich isotherm model for PTOS. The maximum amounts of Pb²⁺ adsorbed (qm), as evaluated by the Langmuir isotherm, was 200 mgg^?1 for FTOS. The efficiencies of PTOS and FTOS for Pb²⁺ removal were 84,8.0% and 93.5% at 0.15 g/200 mL^?1 adsorbent dose, respectively. (C ₀ = 50 mg L^?1). Study concluded that onion skins, a waste material, have good potential as an adsorbent to remove toxic metals like Pb²⁺ from water. Boehm titration analysis was conducted to determine the surface groups. It was found that the adsorption kinetics of Pb²⁺ obeyed pseudo-first-order kinetic model as based on Δq (%) values. FTIR and SEM images before and after adsorption was recorded to explore changes in adsorbent-surface morphology. Activation energy (Ea) was obtained as 25.596 kJ/mol.     

Comparative Study of Zn2+, Cd2+, and Pb2+ Removal From Water Solution Using Natural Clinoptilolitic Zeolite and Commercial Granulated Activated Carbon. Equilibrium of Adsorption

Abstract

The aim of this work is to study the effectiveness of regional, low-cost natural clinoptilolitic zeolite tuff in heavy metal ions removal from aqueous solution, through comparative study with commercial granulated activated carbon. The equilibrium of adsorption of Cd²⁺, Pb²⁺, and Zn²⁺ on both adsorbents have been determined at 25, 35, and 45°C in batch mode. The granulated activated carbon has shown around three times higher adsorption capacity for Cd²⁺ and Zn²⁺ than natural zeolite, and almost the same adsorption capacity for Pb²⁺ as the natural zeolite. The metal ion selectivity series Pb²⁺ > Cd²⁺ > Zn²⁺, on a mass basis, has been obtained on both adsorbents. The Langmuir and Freundlich model have been used to describe the adsorption equilibrium. The thermodynamic parameters were calculated from the adsorption isotherm data obtained at different temperatures. The study of the influence of the acidity of the metal ion aqueous solution has shown an increase of metal ion uptake with increase of the pH. The sorption mechanism of Cd²⁺, Pb²⁺, and Zn²⁺ on natural zeolite changes from ion-exchange to ion-exchange and adsorption of metal-hydroxide with increase of the pH from 2 to 6 (and 7 for Zn²⁺). The preliminary cost calculation, based on adsorbents maximum adsorption capacity and their price, have revealed the potential of natural zeolite as an economic alternative to the granulated activated carbon in the treatment of heavy metal polluted wastewater.     

Removal of Cupric Ions from Aqueous Solutions by Contact with Corncobs

Abstract

The separation of cupric ions from aqueous solution by adsorption onto modified corncobs (hemicellulose-free) was studied. The adsorption process was found to take ～ 15 minutes to attain equilibrium in experiments with continuous agitation at 35°C. The process was found to be pH-dependent, with increasing adsorption as pH increases up to 6.00. There is evidence that the adsorption mechanism is an ion-exchange one involving carboxylate groups, and that two binding sites may be present at the adsorbent. The adsorption was found to fit a Langmuir isotherm, and the parameters n ^s (adsorbent capacity) and b (adsorption intensity) were calculated. The results obtained show that corncobs are an interesting adsorbent because they are available in large quantities at several places in the world at little or no cost, and they retain cupric ions rapidly. The corncobs studied also contain aliphatic and phenolic hydroxyl groups that allow for the incorporation of other functional groups and thus increase the adsorbent capacity.     

The Separation of Zn and Cu Using Chelating Ion Exchangers and Temperature Variations

Abstract

This paper reports the results of a study on the ion-exchange equilibrium of Cu ²⁺ and Zn ²⁺ at different temperatures on chelating ion-exchange resins: Amberlite IRC-718 (iminodiacetic acid based functional groups), VPC-1 (picolinic acid based) and thiourea-based resins. The separation factors and the conditional equilibrium constants of the ion-exchange reaction were determined in temperature range from 15 to 75 °C. An estimation of thermodynamic functions has also been carried out. Possibility of the separation of Cu and Zn mixture by dual temperature ion-exchange method has been demonstrated.     

Cation Exchange and Sorption Properties of Aluminum Phosphate

ABSTRACT

The ion-exchange properties of amorphous aluminum phosphate have been studied in aqueous electrolyte solutions of KCl over a temperature range of 300–320 K. The data were explained by the law of mass action. Sorption of Cu²⁺, Ni²⁺, and Co²⁺ on AIPO₄ was also studied as a function of temperature and concentration, and the data were fitted to Langmuir adsorption equations. In all cases the adsorption was found to increase with increases in temperature and concentration in the selectivity order Cu²⁺ > Co²⁺ > Ni²⁺. Further, the values of Langmuir constants were used to calculate the thermodynamic parameters δS°, δH°, and δG°.     

Recovery of Zinc,Cadmium, and Lanthanum by Biopolymer Gel Particles of Alginic Acid

Abstract

Biopolymer gel particles of alginic acid were found to be a useful material for recovering zinc, cadmium, and lanthanum from aqueous solutions. The metals sorbed by the gel particles could be completely eluted by using dilute HCl solution of 0.1 kmol/m³. The distribution ratios of the individual metals between the gel and liquid phases were measured by using a batch method. The equilibrium data were consistent with predictions made assuming that sorption takes place with the ion-exchange reaction between metal ions and alginic acid. The maximum sorption capacity of the gel particles and the distribution equilibrium constants for the metals were determined by comparing the experimental data with the theoretical predictions. The observed effect of temperature on the distribution equilibrium was insignificant in the range from 15 to 35°C.     

Adsorption of heavy metal cations from aqueous solutions by wool fibers

Adsorption of metal cations by kivircik wool from aqueous NiCl₂, CuCl₂, ZnCl₂, CdCl₂, HgCl₂ and Pb(NO₃)₂ solutions at 25°C and 50°C was investigated using atomic absorption spectroscopy. A fiber diffusion controlled adsorption rate model was used to predict the effective diffusion coefficients of metal ions in wool. It has been shown that wool is a potential adsorbent for removing toxic metal ions from contaminated water.     

A Study on the Adsorption of Gold(III) with Macroporous Crosslinked Polyacrylate (MET) Resins. I. Adsorption Equilibrium

Abstract

Equilibrium data for the adsorption of gold tetrachloride from aqueous solutions of four different concentrations of hydrochloric acid (0.250, 0.500, 0.750, and 1.00 mol·dm^?3 HCl) by macroporous crosslinked polyacrylate (MET) resins which have the same functional groups and different structural characteristics have been obtained at a temperature of 25 ± 0.5°C. It was found that the mechanism of adsorption can be regarded as simple ion exchange, and that the adsorption of gold in the resin phase is a “homogeneous” adsorption. The equilibrium constants and the capacities for the adsorption of gold by MET resins were estimated, and the influence of the acidity of the solutions on the equilibrium parameters were discussed.     

Mercury Extraction By The TRUEX Process Solvent: III. Extractable Species And Stoichiometry†

ABSTRACT

Mercury extraction from acidic aqueous solutions by the TRUEX process solvent, 0.2 M n-octyl(phenyl)N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO), 1.4 M tributylphosphate (TBP) in n-dodecane, has not been extensively examined, Research is currently in progress at the Idaho Chemical Processing Plant to evaluate the TRUEX process for actinide removal from several acidic waste streams, including liquid sodium-bearing waste (SBW), which contains significant quantities of mercury. Reactions for two mercury species, HgCl₂ and HgCl₄ ^?2, are reported. Classical slope analysis techniques were utilized to evaluate the stoichiometric coefficients of each Hg species independently for both CMPO and TBP. The slope analysis results indicate that even the HgCl₄ ^?2 species extracts as HgCl₂. The results also indicate that 1.9 to 2.2 moles of CMPO and 1.5 to 1.81 moles of TBP are required per mole of HgCl₂ extracted. A generic equation for mercury extraction into CMPO or TBP has been shown to be:

where x = 2 or 4, y = 0 or ?2, E = CMPO or TBP, a = the experimentally determined CMPO or TBP stoichiometry, and over lines indicate organic species. Equilibrium constants for HgCl₂ species were determined to be 295 when extracted by CMPO and 18.2 when extracted by TBP. Equilibrium constants for the HgCl₄ ^?2 species were found to range between 5.8 and 12.0 for the CMPO reaction and 0.13 to 0.27 with TBP.     

Removal of Chlorophenols from Aqueous Solution by Anion-Exchange Resins

Abstract

The effects of pH value and chloride ion concentration on the removal of chlorophenols from aqueous solutions by Purolite A-510 resin [macroreticular polystyrene-divinylbenzene resin with R(CH₃)₂(C₂H₄OH)N⁺ group] are discussed by the species distributions of chlorophenols. Those chlorophenols include phenol, 2-chlorophenol, 2,4-dichlorophenol, and 2,4,6-trichlorophenol. The investigations showed that the chlorophenols could be removed effectively at alkaline conditions where the ion-exchange reaction was dominant. Also, the removal of chlorophenols increased with the number of chlorine atoms on the chlorophenols. The removal of chlorophenols via the ion-exchange reaction was hindered by the presence of chloride ions. The effect of chloride ions, however, was diminished in acidic solutions where the adsorption reaction was dominant. The proposed equilibrium model, which considers both adsorption and ion-exchange reactions, adequately describes the sorption behavior of chlorophenols. The partition constants of the protonated chlorophenols can be estimated from the octanol/water partition coefficients of the phenolic compounds.     

Adsorptive removal of cationic dye from aqueous solutions by ZnO/ZnMn2O4 nanocomposite

The ZnO/ZnMn₂O₄ nanocomposite (ZnMn) was used as adsorbent for the removal of cationic dye Basic Yellow 28 (BY28) from aqueous solutions. The adsorbent was characterized by X-ray diffraction, scanning electron microscope, TEM, Fourier transform infrared ray, BET, particle size distribution and zeta potential measurements. The adsorption parameters, such as temperature, pH and initial dye concentration, were studied. Kinetic adsorption data were analyzed using the pseudo-first-order, pseudo-second-order and intraparticle diffusion kinetic models. The Langmuir and Freundlich isotherm models were applied to fit the equilibrium data. The maximum adsorption capacity of BY28 was 48.8 mg g^?1. Various thermodynamic parameters, such as ΔG°, ΔH° and ΔS°, were calculated.     

REACTION KINETICS OF POLYSTYRENE-BASED PHOSPHINIC ACID ION EXCHANGE/REDOX RESINS WITH METAL IONS

ABSTRACT

The ion exchange/redox kinetics displayed by the phosphinic acid polymer with aqueous solutions of silver and mercury is presented as a function of reaction temperature (6° to 45° C) and solution pH (0 to 5). The network variables studied include the crosslink level and macroporosity. At each pH, increasing the temperature leads to a more rapid approach to equilibrium. The amount complexed at equilibrium is lowest at pH Q relative to the higher pH solutions due to increased H⁺ competition for ligating sites. Metal ion reduction, rather than ion exchange, is the dominant component at equilibrium. Matrix rigidity and macroporosity do not affect Ag(I) kinetics. The rate of Hg(II) sorption is much faster than for Ag(I). Macroporosity is an important variable with mercury: macroporous resins complex more than twice the amount found with gels at 15 minutes contact. It is proposed that Ag kinetics are limited by a slow redox reaction while the Hg kinetics are diffusion-limited due to a fast redox reaction. Differences in reactivity arise from the reaction stoichiometry     

Microwave assisted hydrothermal synthesis of MnO2·0.5H2O ion-sieve for lithium ion selective adsorption

Li_1.6Mn_1.6O₄ (LMO) synthesized by microwave assisted hydrothermal method were used to obtain MnO₂·0.5H₂O ion sieves (HMO) after acid treatment. The HMO-1 prepared with a Li/Mn molar ratio of 4, at 100ºC for 1 h under microwave irradiation, exhibits an effective Li⁺ adsorption capacity of 5.6 mmol·g^?1 and a high selectivity to Li⁺ with an equilibrium distribution coefficient of 12366.44 mL·g^?1. Moreover, it shows almost saturated ion-exchange capacity (> 95%) for Li⁺ extracted/inserted process. Thus HMO ion-sieves with high adsorption capacity and selectivity to Li⁺ are expected to be a promising application for Li⁺ selective adsorption from brine, seawater, and aqueous lithium generated in industries.     

Reactor Analysis of Metal Ion Extraction in Liquid Dispersions

Abstract

A comprehensive research program is undertaken to predict the effects of mixing on the extraction efficiency for Co(NO₃)₂-Di-2-ethylhexyl phosphoric acid in toluene system in mechanically agitated dispersed phase reactors. The experimental and theoretical studies on this complex hydrometallurgical extraction system have yielded the following results.

a) A two phase organic and aqueous equilibrium model, which accounts for the aqueous phase equilibria, is developed to predict the distribution of cobalt. The equilibrium model is based on cobalt ion complexation with the DEPHA dimer as suggested by Komasawa et al. 151. The aqueous phase activities are represented by the Davies Model.

b) Physical mass transfer and chemical extraction experiments conducted in a stirred transfer reactor show that the reaction occurs in the aqueous film. A two film diffusionreaction model is developed to accurately predict the observed fluxes over the experimental range.

The composition and temperature ranges for the equilibrium and kinetic experiments are, respectively: a) pH, 3–5; [CO±_T, 0.001 to 0.1 M; [DEHPA±₂, 0.1 to 1.0 M; T, 25–50°C, and b) pH, 3–5; [Co±_T, 0.001 to 0.1 M; [DEHPA±₂, 0.01 to 0.5 M; T = 25°C

c) A previously developed Monte Carlo Simulation procedures is employed with the above equilibrium and kinetic models to predict the effect of droplet mixing on extraction efficiency for various process variables.     

THERMODYNAMIC EQUILIBRIA OF THE EXTRACTION OF CHROMIUM(VI) WITH TRI-N-OCTYLPHOSPHINE OXIDE FROM AQUEOUS SOLUTIONS

ABSTRACT

The distribution of chromium( VI ) between aqueous solutions and the kerosene solutions of tri-n-octyl-phosphine oxide (TOPO) have been studied at 25 °C and pH 2-4, in which range the predominant forms of Cr(VI) are HCrO₄ and Cr₂O₇ ^2?. The extraction equilibrium is influenced by the total chromium(VI) concentration, aqueous pH value, and total extractant concentration. The thermodynamic equilibria among all species in the aqueous phase were used for the analysis of distribution data, and the activity coefficients of ionic species were estimated according to Debye-Hiickel or Bromley equation. By numerical method, the complexes of Cr(VI ) with TOPO formed in the organic phase were found to be H₂CrO₄ (TOPO) and H₂Cr₂O₇ (TOPO) ₃. The corresponding extraction constants were 2019 and 3.69× 10⁸, respectively.     

Elemental mercury removal from syngas at high-temperature using activated char pyrolyzed from biomass and lignite

Activated char obtained by the co-pyrolysis of a mixture of lignite and biomass impregnated with ZnCl₂ solution was found to be effective for the high-temperature capture of mercury from syngas. The prepared samples were characterized by X-ray photoelectron spectroscopy, Hg-thermal programmed desorption as well as Brunauer- Emmett-Teller analysis. The results show that activated char exhibits a large surface area as well as abundant micropores and C-Cl, C=O, and COOH functional groups. During the chemisorption of mercury, gaseous Hg⁰ is first oxidized by C-Cl to HgCl₂; HgCl₂ which acts as the intermediate product then reacts with the C=O and COOH functional groups on the surface of activated char to generate Hg-OM. At high adsorption temperatures, Hg-OM on the adsorbent surface can further decompose and generate HgO. The C-Cl group is important for the first oxidation step of gaseous Hg⁰, and the formation of HgCl₂ is the rate-determining step for the entire process of adsorption.     

Fractionation of Lithium Isotopes in Cation-Exchange Chromatography

Abstract

Cation-exchange chromatography of lithium was carried out to investigate the lithium isotope effect in aqueous ion-exchange systems. The heavier isotope, ⁷Li, was preferentially fractionated into the resin phase in every experiment conducted, and this result is consistent with the results of previous work. The value of the separation factor was 1.00089–1.00171 at 25°C. A comparison of lithium isotope effect with those of potassium and rubidium indicated that the isotope effect originating from hydration is larger than the effect due to phase change for lithium, while the opposite is the case with potassium and rubidium.     

Elimination of inorganic mercury from waste waters using crandallite‐type compounds

The removal of inorganic mercury from waste water streams arising from mines, using an artificial amorphous compound of the crandallite type synthesized in our laboratory, Ca_0.5Sr_0.5Al₃(OH)₆(HPO₄) (PO₄), has been investigated. This compound exhibits an extremely wide range of ionic substitutions: Ca²⁺ and Sr²⁺ were interchanged with Hg²⁺, so the mercury content of the waste water, ranging from 70 to 90 ppm, was reduced to less than 0.1 ppm. The process has been studied under batch conditions. The crandallite showed a high capacity for the exchange of mercury from mercuric nitrate solutions, 1.555 meq g^?1. The ion‐exchange equilibrium isotherms for Hg²⁺ were correlated by the Langmuir equation. The recovery of mercury from Hg‐crandallite using HCl solutions and thermal treatment was also studied. Optimum recuperation of mercury is achieved by chemical reaction with HCl solution (pH 2.25). At these conditions, 75% of the mercury is recovered as the HgCl₄^2? complex in a simple batch process, and the crandallite (in the protonic form) can be reused. © 2003 Society of Chemical Industry     

Synthesis and adsorptive properties of sulfonated nanocomposites based on carbon-encapsulated iron nanoparticles and styrene-p-divinylbenzene copolymer

ABSTRACT

A method of the synthesis of novel magnetic nanocomposite adsorbent of Fe(III) from aqueous solutions is presented. The nanocomposites consisted of carbon-encapsulated iron nanoparticles and styrene-p-divinylbenzene copolymer. The adsorptive active sites were introduced via the post-synthesis sulfonation. The presented sulfonated magnetic nanocomposite adsorbents can be easily separated using permanent magnets and their adsorption performance was comparable to the commercially available ion-exchange resins. The determined maximum adsorption capacities were between 10.9 and 49.5 mg?g^?1, whilst the equilibrium was reached for the contact time lower than 60 minutes.     

A novel carbon aerogel prepared for adsorption of copper(II) ion in water

A novel carbon aerogel with network pore and surface group of hydroxyl was prepared from cellulose colloid, through sol-gel reaction, freeze-drying and carbonization. Surfactant like isooctyl alcohol ether phosphate was taken as structure inducer in sol-gel reaction, for construction of porous network in the prepared samples. Characteristic of a specific area about 725.12 m²/g and total pore volume about 0.64 cm³/g, the prepared cellulose-based carbon aerogel of CCA₂, has a maximum capacity about 55.25 mg/g for Cu²⁺ in neutral aqueous solution. Its adsorption equilibrium can be reached within 10 min in an aqueous solution of pH7.0 at 25?°C, while desorption of Cu²⁺ need about 1 h eluted by HCl or HNO₃ solution of 0.01 M. And regeneration of the carbon aerogel in adsorption of Cu²⁺ can be repeated for five times, remaining 96% adsorption capacity. It is also found in adsorption process the kinetics nicely follows pseudo-second-order rate expression, and the isotherm fits Langmuir model.