Separation and Purification Technology (v.50, #1)

Full Title Page (pp. iii).

Isotherms, kinetics and thermodynamics of dye biosorption by anaerobic sludge by Yi Wang; Yang Mu; Quan-Bao Zhao; Han-Qing Yu (pp. 1-7).

Experiments were conducted to investigate the adsorption characteristics of dyes by anaerobic sludge in this study. Influence of dye type, sorption time, initial dye concentration, sludge concentration and temperature on dye biosorption was evaluated. Furthermore, the isotherms, kinetics and thermodynamic of biosorption were also explored. Experimental results show that anaerobic sludge had a much higher equilibrium adsorption density on Rhodamine B than on Eosin Y. The adsorption density of Rhodamine B onto sludge decreased with enhancing sludge concentration. At a lower Rhodamine B concentration, adsorption could reach saturation in a lower sludge concentration. Results also indicate that both Langmuir and Freundlich adsorption models were able to adequately describe the biosorption equilibrium of Rhodamine B onto anaerobic sludge. The biosorption followed the pseudo second-order adsorption kinetics.

Keywords: Anaerobic sludge; Biosorption; Dye; Eosin Y; Freundlich model; Kinetics; Langmuir model; Rhodamine B; Thermodynamics

Temperature swing adsorption of heavy metals on novel phosphate-type adsorbents using thermosensitive gels and/or polymers by Hideaki Tokuyama; Kiyomi Yanagawa; Shuji Sakohara (pp. 8-14).

A novel thermosensitive adsorbent was developed, which adsorbs and/or desorbs heavy metals through temperature swing process. The gel-type and polymer-type adsorbents, composed of N-isopropylacrylamide (NIPA) as a thermosensitive component and 2-methacryloyloxyethyl phosphate (MEP) as an interactive component, were prepared by free radical copolymerization. For each type of poly(NIPA- co-MEP), phase transitions and temperature dependences for the amount of Cu, a model metal ion, adsorbed was examined. The proposed mechanism associated with the temperature swing adsorption (TSA) of Cu to poly(NIPA- co-MEP) is as follows. In the case of the shrinking gel at higher temperatures, two MEP groups are positioned so as to interact with one Cu ion, while in the swelling gel at lower temperatures, Cu is desorbed from isolated MEP groups. In the case of copolymers, at temperatures lower than the lower critical solution temperature (LCST), two MEP groups interact with one Cu ion as well as those in shrunken gels, and at temperatures higher than the LCST, an aggregate of the copolymer, which is strongly hydrophobic, ejects free water along with Cu ion in the shrinking process. The temperature dependences for adsorption to the copolymer are opposite to gels, even in the gel with a low density of crosslinking points.

Keywords: Thermosensitive gel; Temperature swing adsorption; N; -Isopropylacrylamide; Heavy metal; Copolymer

Adsorptions of heavy metal ions by a magnetic chelating resin containing hydroxy and iminodiacetate groups by Chuh-Yean Chen; Chen-Li Chiang; Po-Chen Huang (pp. 15-21).

A magnetic Fe₃O₄–glycidyl methacrylate–iminodiacetic acid–styrene–divinyl benzene resin (MPGI) was synthesized by the polymerization of glycidyl methacrylate–iminodiacetic acid (GMA–IDA), divinyl benzene and styrene in the presence of magnetic Fe₃O₄ for the removal of Cu(II), Cd(II) and Pb(II) from aqueous solutions. The weight fractions of Fe₃O₄ and GMA–IDA within MPGI were analyzed by potentiometric titration of carboxylic acids and thermogravimetric analyzer. The equilibrium adsorption capacities of MPGI from their single-metal ion solutions were 0.88mmol/g for Cu(II), 0.81mmol/g for Pb(II) and 0.78mmol/g for Cd(II). Increasing the concentration (0–0.3M) of KCl, NaCl, MgCl₂ and CaCl₂ in Cu(II) or Pb(II) solution affected the adsorption behavior slightly. As the salt concentrations in Cd(II) solution increased, the adsorption capacities of Cd(II) decreased in the order: Mg²⁺>Ca²⁺>Na⁺>K⁺. Within the pH range of 2–5, decreasing the pH of the Cu(II) solution did not produce remarkable changes in the equilibrium adsorption capacities. However, significant decrements occurred for the adsorptions of Pb(II) or Cd(II) when the pH values of the solutions were less than 3. The competitive adsorption tests verified that this resin had good adsorption selectivity for Cu(II) with the coexistence of Pb(II) and Cd(II).

Keywords: Resin; Adsorption; Competitive adsorption; Selectivity; Iminodiacetic acid

Microwave-enhanced roasting of copper sulfide concentrate in the presence of CaCO₃ by Yixin Hua; Chaojun Cai; Yan Cui (pp. 22-29).

The microwave irradiation is used to the oxidative roasting of copper sulfide concentrate in the presence of CaCO₃ with the aim of eliminating sulfur dioxide emissions and accelerating roasting process. The calcine obtained is leached with NH₃–(NH₄)₂CO₃ solution for the recovery of copper. It is shown that the copper extractions from the calcine roasted with microwave heating are as high as 90–96.6%, while those with conventional heating are only 71–77.4%. The sulfur retention is greater than 96% for both the microwave and conventional heating. The reaction rates of the roasting process increased 3.97–17.15 times when using microwaves instead of conventional heating. The phase changes and reaction mechanism of the roasting process are also investigated with X-ray diffraction and thermal analysis.

Keywords: Microwave irradiation; Copper sulfide concentrate; CaCO; ₃; Roasting; Leaching

Synergistic extraction of rare earths by mixture of bis(2,4,4-trimethylpentyl)phosphinic acid and Sec-nonylphenoxy acetic acid by Xiaobo Sun; Jinping Wang; Deqian Li; Hongfei Li (pp. 30-34).

Synergistic extraction of trivalent rare earths (RE=Sc, Y, La, Gd, Yb) from hydrochloride medium using mixture of bis(2,4,4-trimethylpentyl)phosphinic acid (HL, Cyanex272) and Sec-nonylphenoxy acetic acid (HA, CA-100) in n-heptane has been studied. The synergistic enhancement coefficients were observed for La (1.30), Gd (1.97), Y (3.59), Yb (8.21) and Sc (14.41). The results indicated yttrium was extracted into n-heptane as YH₅A₄L₄ mixed species instead of Y(HL₂)₃, Y(OH)₂A(HA)₃ which were extracted by Cyanex272 and CA-100, respectively. A cation exchange mechanism was proposed and further clarified by IR spectra. The equilibrium constants, formation constants and thermodynamic functions such as Δ G, Δ H and Δ S were determined. The Cyanex272+CA-100 system not only enhanced the extraction efficiency of RE but also improved the selectivities significantly. The mutual separation factors of these ions suggested the mixture system would be of practical value in extraction and separation of rare earths.

Keywords: Synergistic extraction; Rare earths (RE); Cyanex272; CA-100; Separation factors

Removal of Pd(II), Zr(IV), Sr(II), Fe(III), and Mo(VI) from simulated high level liquid waste by extraction chromatography utilizing the macroporous silica-based polymeric materials by Anyun Zhang; Etsushu Kuraoka; Mikio Kumagai (pp. 35-44).

To eliminate a few specific elements from highly active liquid waste (HLW), two macroporous silica-based N, N, N′, N′-tetraoctyl-3-oxapentane-1,5-diamide (TODGA) and octyl(phenyl)- N, N-diisobutylcarbamoylmethylphosphine oxide (CMPO) impregnated polymeric composites, TODGA/SiO₂-P and CMPO/SiO₂-P, were synthesized. It was done by an advanced vacuum sucking technique through impregnation of the chelating agents into the pores of SiO₂-P particles support. The partitioning of Sr(II), Pd(II), Zr(IV), Mo(VI), and Cs(I) from a 3.0M HNO₃ solution containing some typically simulated fission and non-fission products Ru(III), Rb(I), Fe(III), Na(I), K(I), and Ba(II) was performed at 298 and 323K, respectively. In the first column packed with TODGA/SiO₂-P, Sr(II), Pd(II), and Zr(IV) were adsorbed and eluted effectively by 0.01M HNO₃, 0.05M DTPA-pH 2.5, and 0.5M oxalic acid, respectively, while others showed very weak or almost no adsorption and flowed into effluent along with 3.0M HNO₃. Cs(I), Fe(III), and Mo(VI) containing effluent was then applied to the second column packed with CMPO/SiO₂-P. Fe(III) and Mo(VI) were found to be adsorbed together and eluted utilizing 0.05M DTPA-pH 2 at 323K. The effective partitioning of Fe(III) was of great benefit to the evaporation, concentration, and finally geological disposal of HLW. The separation of Sr(II) and Mo(VI) was useful for the vitrification of HLW due to the Sr heat generator property and low solubility of Mo oxides in molten glass materials. Cs(I) can be separated by a novel silica-based 1,3-[(2,4-diethyl-heptylethoxy)oxy]-2,4-crown-6-calix[4]arene (Calix[4]arene-R14) impregnated polymeric composite (Calix[4]arene-R14/SiO₂-P). In terms of the results obtained, a highly specific partitioning process of Fe(III) and some specific fission products Sr(II), Pd(II), Zr(IV), Cs(I), and Mo(VI) from a simulated HLW by extraction chromatography was proposed.

Keywords: Extraction chromatography; Separation; Silica-based polymeric composite; Highly active liquid waste; Chelating agent

Pervaporation of benzene/cyclohexane mixtures through supramolecule containing poly(vinyl acetal) membranes by Vinita Dubey; Lokesh Kumar Pandey; Chhaya Saxena (pp. 45-50).

Poly(vinyl acetal) PVAc was synthesized by the acid-catalyzed acetalisation of poly(vinyl alcohol). Three different morphologically modified variants of the polymer were prepared by the addition of supramolecules; namely α and β cyclodextrins (CD) and butyl calixerene (calix) to the PVAc sol. 20% (w/v) of the solution of the polymers in tetrahydrofuran (THF) was used to cast the membranes. These membranes were characterized using spectroscopic and thermoanalytical techniques, and also tested for their chemical resistance and mechanical strength. The pervaporative behaviour of modified membranes vis-à-vis PVAc for the separation of a wide composition of benzene (Bz)/cyclohexane (Chx) mixtures was evaluated. Addition of αCD or calix to PVAc reduced the overall flux while dispersion of βCD favoured an enhanced flux especially in the Bz-lean and azeotropic region.

Keywords: Pervaporation; Benzene; Cyclohexane; Poly(vinyl acetal); Supramolecules

Mass transport of aliphatic alcohols and esters through hydrophobic pervaporation membranes by Olivera Trifunović; Gun Trägårdh (pp. 51-61).

Mass transport in pervaporation of multi-component mixtures of homologous series of alcohols and esters through composite pervaporation membranes has been investigated. Pervaporation experiments were performed in a concentration range relevant for aroma recovery, using a membrane with an active layer of poly(octyl)methylsiloxane (POMS) caste on a porous polyetherimide (PEI) support. The fluxes, selectivities and average diffusion coefficients were determined for each compound studied and were related to the properties of the permeating molecule. The reduction in the selectivity of the higher homologues of the alcohol series with increase in feed concentration was explained by a decrease in diffusion coefficient with respect to feed concentration. There was evidence of a tendency towards aggregation of water molecules, lower homologues of alcohol series and the first two homologues of the ester series, which resulted in a decrease in diffusivity for the polar, lower homologues in both series.

Keywords: Hydrophobic pervaporation; Mass transport; Diffusion; Support layer

Determination of kinetics and equilibrium of Pb/Na exchange on clinoptilolite by Ayşe Engin Kurtoğlu; Gülten Atun (pp. 62-70).

Ion exchange kinetics and equilibria of lead on Na-pretreated clynoptilolite have been studied using batch method by means of electrometric and polarographic techniques. Equivalent fraction of lead ions exchanged with sodium has been determined by measuring time dependent Na⁺ ion concentration with sodium ion selective electrode (SISE). Electrode readings could be taken for a time interval of 15s at early time of exchange. Time dependence of pH during exchange process has been followed simultaneously. Time dependent exchange curves showed a sharp increase at the beginning followed by a slower one for longer times until reaching equilibrium. The McKay equation for isotopic exchange kinetics has been applied to describe experimental results both in terms of out- and in-going ions. The film and particle diffusion coefficients evaluated from the McKay constants are not significantly affected by initial solution concentrations studied in the range of 1×10⁻⁴ to 1×10⁻⁴M. Kinetic curves have been successfully modeled using the diffusion coefficients. An increase in the pH values at low concentrations below 10⁻³M Pb can be attributed to contribution of H⁺/Na⁺ exchange whereas the decrease of pH is indicative of the uptake of hydroxyl ions to form lead hydroxide clusters into clinoptilolite at higher concentrations. Total amount of Pb adsorbed and exchanged at equilibrium condition has been determined from polarographic measurements and compared with those found for exchanged Pb. Equilibrium data have been analyzed and modeled in terms of Freundlich and Langmuir adsorption isotherms. Thermodynamic parameters for transition state have been evaluated from temperature dependent kinetic results.

Keywords: Ion exchange kinetics; Lead; Clinoptilolite; Ion selective electrodes; Polarographic measurement

Desorption of lanthanum, europium and ytterbium from Sargassum by Vivian Diniz; Bohumil Volesky (pp. 71-76).

The desorption of La, Eu and Yb was studied in this work. The purpose of this work was to verify the reversibility of the sorption reaction, and thus the possibility of the desorption process for simultaneous metal recovery and regeneration of the biomass. The desorption of calcium ions at different levels of pH using mineral acid was also verified and the Ca release increased with decreasing pH, achieving 2.5mequiv.g⁻¹ at pH 2 and 2.8mequiv.g⁻¹ using 0.1molL⁻¹ HNO₃. Several eluting agents at different concentrations were tested to desorb the lanthanides including nitric and hydrochloric acids, calcium nitrate and chloride salts, EDTA, oxalic and diglycolic acids. 95–100% desorption for all metals was obtained with 0.3molL⁻¹ HCl. La desorption with the other eluting agents was 70% with 2molL⁻¹ CaCl₂, 83.7%, with 0.5molL⁻¹ EDTA and 88.4% with 0.023molL⁻¹ diglycolic acid. A plateau was reached when a liquid to solid ratio (L/S) of 2Lg⁻¹ was used with 0.1molL⁻¹ HNO₃. Desorption levels ranged between 85 and 95%. At the same (L/S) ratio, 0.2molL⁻¹ HCl was able to elute all the metals from the individual metal loaded biomass, although it could not remove the metals completely from the mixed-metal loaded biomass. The desorption levels decreased with increasing metal sorption affinity as follows, 94.0, 86.3 and 75.2% for Yb, La and Eu, respectively when the eluting agent was 0.1NHCl. There was no difference between not washing the biomass at all and washing it either once or twice after the sorption process.

Keywords: Desorption; Lanthanum; Europium; Ytterbium; Sargassum

Selective uphill Zn²⁺ transport via a bulk liquid membrane using an azacrown ether carrier by Ali Reza Fakhari; Afshin Rajabi Khorrami; Mojtaba Shamsipur (pp. 77-81).

5,6,14,15-Dibenzo-1,4-dioxa-8,12-diazacyclopentadeca-5,14-diene (DBDA15C4) as a mobile carrier and histidine as a stripping agent were used for the selective uphill and proton driven transport of Zn²⁺ ions through a bulk liquid membrane. A study of different parameters on zinc transport has been carried out. This include the pH of the feed phase, amount of DBDA15C4 in the liquid membrane, type and concentration of acid and amino acid in the strip phase and transport. In the optimum procedure conditions, the maximum transport of Zn²⁺ ions at 3h was observed (96.2±1.2%). With this system, Zn²⁺ as Zn-histidine complex could be separated from Cu²⁺, Cd²⁺, Pb²⁺, Mn²⁺, Cr³⁺, Al³⁺, Co²⁺, Ni²⁺, Ca²⁺, Mg²⁺ and Fe³⁺. The transport mechanism of this system has been described.

Keywords: Zinc; Uphill transport; Bulk liquid membrane; 5,6,14,15-Dibenzo-1,4-dioxa-8,12-diazacyclopentadeca-5,14-diene; Histidine

Characterization of Pd–Cu–Ni ternary alloy membrane prepared by magnetron sputtering and Cu-reflow on porous nickel support for hydrogen separation by Shin-Kun Ryi; Jong-Soo Park; Sung-Hyun Kim; Sung-Ho Cho; Dong-Won Kim; Ki-Youn Um (pp. 82-91).

Pd–Cu–Ni alloy membrane was successfully deposited 4μm in thickness on porous nickel support by multitarget sputtering and Cu-reflow technique. The surface of porous nickel support needed not to be modified because it has very uniform and small pore distribution as 33nm. From the XRD and SEM analysis, it was clarified that the fabricated Pd–Cu–Ni ternary alloy film had Pd–Cu–Ni alloy character and no defects on the surface of thin membrane. The weight composition of Pd:Cu:Ni was 89:4.5:6.5 from EDS analysis. As a result of single gas permeation test using H₂ and N₂, hydrogen permeance increased with an increase of operating temperature and transmembrane pressure difference. Furthermore, hydrogen separation factor with single gas test was infinity indicating pinhole-free palladium-based alloy membrane. In additions, it was so stable that the morphology of the surface was not changed and there were no indications of metal interdiffusion during time-on-stream test for 10 days with the cycling of operating temperature and transmembrane pressure difference.

Keywords: Porous nickel support; Sputtering method; Cu-reflow; Pd–Cu–Ni ternary alloy membrane; Hydrogen separation

Effect of pH on microfiltration of Chinese herb aqueous extract by zirconia membrane by Weixing Li; Weihong Xing; Wanqin Jin; Nanping Xu (pp. 92-96).

At present, microfiltration is used to purify the Chinese herb decoction as a new advanced technology, but the fouling leads to the dramatic decline of the permeate flux of membrane. Adsorption is generally considered to be of great effect on the fouling. In order to understand the adsorption phenomena on the surface of ceramic membranes, the adsorption behavior of macromolecules in Chinese herb aqueous extract on ZrO₂ particles was studied in this work. The equilibrium isotherm of adsorption obtained at pH 5.0 had good correspondence to the Langmuir model. The adsorption kinetics experiments showed that the rate and mass of adsorption were the largest at pH value of ZrO₂ particle's isoelectric point (IEP). A ZrO₂ ceramic membrane with the mean pore size of 150nm was used in the microfiltration of the aqueous extract of a kind of Chinese herb (Radix Rehmannia) at various pH values. The fouling at pH value of ZrO₂ particle's IEP was most serious, which resulted in the minimum steady flux and the highest rejection of total solids. This was in agreement with the adsorption behavior of the macromolecules in the aqueous extract onto the ZrO₂ particles.

Keywords: Adsorption; Chinese herb; Zirconia; Kinetics; Microfiltration

Guidelines for the application of a stationary model in the prediction of the overall mass transfer coefficient in a hollow fiber membrane contactor by Dominique Trébouet; Michel Burgard; José Miguel Loureiro (pp. 97-106).

A dynamic model describing the behavior of a hollow fiber membrane extractor, working as a closed system, is developed. Plug flow of both the aqueous and organic phases inside the fiber module is supposed while the reservoirs are considered to be perfectly mixed. The resistances to mass transfer between the phases, inside the module, are lumped in an overall mass transfer coefficient. This dynamic model shows that the system behavior is controlled by five dimensionless parameters: one equilibrium, one mass transfer, two volume ratios and one ratio of space times. A parametric study is conducted and the influence of each parameter on the system behavior is assessed independently. When a pseudo-steady state approximation is made, considering the module in steady state, the currently used stationary model is obtained [N.A. D’Elia, L. Dahuron, E.L. Cussler, Liquid–liquid extraction with microporous hollow fibers, J. Membr. Sci. 29 (1986) 309–319]. The operating region for the determination of the global mass transfer coefficient between the aqueous and organic phases using this simplified model is identified by the comparison of the histories of solute concentrations inside the respective reservoirs, obtained by the solutions of both the dynamic and the stationary models. Based on this comparison, guidelines for the application of the simplified model are given both in terms of the dimensionless parameters and of the operating variables.

Keywords: Hollow fiber membrane contactor; Liquid–liquid extraction; Extraction modeling; Overall mass transfer coefficient

Kinetics of aqueous photocatalytic oxidation of fulvic acids in a photocatalysis–ultrafiltration reactor (PUR) by Jianfeng Fu; Min Ji; Yaqian Zhao; Lizhang Wang (pp. 107-113).

The photocatalysis of natural organic matter, fulvic acid (FA), by P25 TiO₂ in terms of UV₂₅₄ and TOC concentrations was investigated in this study. The experiments were conducted in a lab-scale photocatalysis–ultrafiltration reactor (PUR) with TiO₂ suspension. Groups of experiments were designed to examine the effects of pH of bulk solution, TiO₂ concentration and additives strength as well as light intensity on the degradation of FA. Results from this study revealed that the degradable behaviour of FA can be reasonably described by first-order kinetics. In addition, it was demonstrated that low pH value, increased additives concentration and relative high light intensity were all beneficial parameters for TOC removal. By inspecting the relationship between rate constant ( k) and influencing factors, an overall FA oxidation rate kinetic model was established. The utility of the model was demonstrated by the agreement of predictive and experimental results.

Keywords: Fulvic acid; Kinetic model; Photocatalytic; Ultrafiltration membrane; Reactor

Cloud point extraction of phenol and benzyl alcohol from aqueous stream by B. Haddou; J.P. Canselier; C. Gourdon (pp. 114-121).

Two-aqueous phase extraction of phenol and benzyl alcohol as a solute from their aqueous solutions was investigated using polyethoxylated alcohols (CiEj) as a biodegradable non-ionic surfactant. First, the phase diagrams of the binary systems, water–surfactant (Oxo-C₁₀E₃ and Oxo-C₁₃E₉), and the pseudo-binary systems, water–surfactant with a constant concentration of solute was determined. The effect of sodium chloride and sodium sulphate on water–surfactant systems were studied. According to the given surfactants concentrations and temperatures, the extraction results were expressed by the following four parameters, percentage of extracted solute, E, which reached 95 and 90% for phenol and benzyl alcohol, respectively, residual concentrations of solute, X_s,w, and the surfactant, X_t,w, in the dilute phase and volume fraction of the coacervate at the equilibrium condition, ϕ_c. The values of these parameters were determined by an analyzing central composite designs. After the first extraction process, phenol and benzyl alcohol concentrations in the effluent were reduced about ten times for the first and four times for the second, correspondingly.

Keywords: Cloud point; Phenol; Benzyl alcohol; Non-ionic surfactant; Extraction

Effect of solute geometry and orientation on the rejection of uncharged compounds by nanofiltration by José L.C. Santos; Philip de Beukelaar; Ivo F.J. Vankelecom; Svetlozar Velizarov; João G. Crespo (pp. 122-131).

This work discusses a new approach to model the rejection of uncharged solutes by nanofiltration membranes. A mathematical description of the solute is developed – Geometric radius – in which the molecular geometry is represented by a prolate revolution ellipsoid and a possible preferential orientation (orientation angle) of the molecule during permeation through the membrane is considered in the calculations. The model simulations suggest that the target solute rejection depends strongly on its preferential orientation, especially for elongated molecules due to the higher difference in their Geometric radii. In order to evaluate the model, the rejection of defined solutes ( n-alcohols and di-alcohols) with different chain length, polarity, symmetry and functional group position was studied experimentally. It was found that the common approach to model the solute rejection, using the molecular Stokes radius, failed to predict the experimental results for the n-alcohols studied, but was applicable for some of the di-alcohols. On the other hand, the Geometric model proposed allowed in all cases for a better description of the experimental rejection data due to its extra degree of freedom – the molecular orientation angle during membrane permeation. Based on these calculated orientation angles, which were dependent of the transmembrane pressure applied, the model could be used as an interpretative tool, allowing for a better understanding of the dominant factors that determine the rejection of uncharged solutes with different molecular geometry.

Keywords: Nanofiltration; Membrane rejection; Molecular geometry; Stokes radius; Desal DK

Sorption of Pb(II), Ni(II), Cu(II) and Cd(II) from aqueous solution by olive stone waste by Núria Fiol; Isabel Villaescusa; María Martínez; Núria Miralles; Jordi Poch; Joan Serarols (pp. 132-140).

Olive stone waste generated in the olive oil production process has been investigated as metal biosorbent for Pb(II), Ni(II), Cu(II) and Cd(II) from aqueous solutions for its wide availability as agricultural waste and also for its cellulosic matrix rich of potential metal binding active sites. The effect of contact time, solution pH, ionic medium and initial metal concentration were studied in batch experiments at room temperature. Maximum metal sorption was found to occur at initial pH around 5.5–6.0. Kinetic studies revealed that the initial uptake was rapid and equilibrium was established in 1h for all the studied metals and that the data followed the pseudo-second order reaction. The equilibrium sorption data for single metal systems at initial pH 5.5 were described by the Langmuir and Freundlich isotherm models; however, the non-competitive Freundlich model has been found to provide the best correlation. The highest value of Langmuir maximum uptake, ( q_max), was found for cadmium (6.88×10⁻⁵molg⁻¹) followed by lead (4.47×10⁻⁵molg⁻¹), nickel (3.63×10⁻⁵molg⁻¹) and copper (3.19×10⁻⁵molg⁻¹). Similar Freundlich empirical constants, k, were obtained for all metals (2.4×10⁻⁵ to 2.8×10⁻⁵). Adsorption-complexation, in addition to ion-exchange, must be involved in the sorption process of copper, lead and cadmium while ion-exchange is the most important mechanism for Ni sorption. An increase of ionic strength concentration caused a decrease in metal removal. Sorption experiments with equimolar concentration of each metal in binary mixtures were also performed and then the extended Langmuir isotherm model fits adequately the experimental data. Desorption experiments put into evidence that after three contacts neither HCl nor EDTA solutions were able to desorb metals from the olive stones completely. The results obtained show that olive stone waste, which has a very low economical value, may be used for the treatment of wastewaters contaminated with heavy metals.

Keywords: Metal removal; Low cost sorbent; Biosorption; Sorption isotherms; Binary mixtures

Synthesis of new ‘biomimetic’ dye-ligands and their application in the purification of alkaline phosphatase by Jingyun Wang; Xiaojun Peng; Dan Liu; Yongming Bao; Lijia An (pp. 141-146).

A series of new ‘biomimetic’ dye-ligands were synthesized for the enzyme alkaline phosphatase. The biomimetic dye-ligands were immobilized on Sepharose CL-6B and the affinity adsorbents, together with the non-biomimetic adsorbent bearing Cibacron Blue 3F-GA, were studied for their ability to purify alkaline phosphatase from calf intestine. The results showed that all synthesized dye-ligands have certain affinity to alkaline phosphatase, but the affinity is varying with different molecular structures (such as functional groups or their positions) of the dye-ligands. In particular, the dye V has the higher affinity to alkaline phosphatase. Detailed investigation on the elution conditions of alkaline phosphatase on synthesized dye V-immobilized Sepharose CL-6B showed that pulse elution by 0.1M NaCl and 30mM Na₂HPO₄ in turn could lead to 65-fold purification in a single step with high enzyme recovery (84%) of alkaline phosphatase. Kinetic inhibition studies showed that dye V inhibits alkaline phosphatase in a competitive manner with a K_I of 1mM.

Keywords: Alkaline phosphatase; Affinity chromatography; Dyes; Enzyme; Specific activity

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Separation and Purification Technology (v.50, #1)