Preparation of a heterogeneous hollow-fiber affinity membrane having a mercapto chelating resin and...

Preparation of a Heterogeneous Hollow-Fiber AffinityMembrane Having a Mercapto Chelating Resinand Its Recovery of Hg21 Cations

Bing Wang, Wei Liu, Lei Huang

Key Laboratory of Hollow Fiber Membrane Material and Membrane Process (Ministry of Education),School of Materials Science and Chemical Engineering, Tianjin Polytechnic University, Tianjin 300160, China

Received 23 December 2006; accepted 11 July 2007DOI 10.1002/app.27137Published online 20 September 2007 in Wiley InterScience (www.interscience.wiley.com).

ABSTRACT: A kind of heterogeneous hollow-fiber affinityfilter membrane with a high chelating capacity for Hg21 wasprepared by phase separation with blends of a mercapto che-lating resin and polysulfone as the membrane materials, N,N-dimethylacetamide as the solvent, and water as the extractionsolvent. The adsorption isotherms of the hollow-fiber affinityfilter membrane for Hg21 were determined. The heterogene-ous hollow-fiber affinity filter membrane was used for theadsorption of Hg21 cations through the coordination of themercapto group and Hg21 cations, and the effects of the mor-phology and structure of the affinity membrane on the chelat-ing properties were investigated. The chelating conditions,including the chelating resin grain size, pH value, concentra-tion of the metallic ion solution, mobile phase conditions, and

operating parameters, had significant effects on the chelatingcapacity of the hollow-fiber affinity filter membrane. Theresults revealed that the greatest chelating capacity of the hol-low-fiber affinity filter membrane for Hg21 was 1090 lg/cm2

of membrane under appropriate conditions, and the adsorp-tion isotherms of Hg21 could be described by the Langmuirisotherm. The dynamic chelating experiments indicated thatthe hollow-fiber affinity membrane could be operated at ahigh feed flow rate and that large-scale removal of Hg21

could be realized. � 2007 Wiley Periodicals, Inc. J Appl Polym Sci107: 501–508, 2008

Key words: adsorption; blending; fibers; membranes; sep-aration techniques

INTRODUCTION

An affinity filter membrane with definite millipores hasan affinity agent on its inner and outer surfaces as a car-rier of the affinity agent, which integrates the advan-tages of both affinity chromatography and modernmembrane techniques.1–6 When the solution is filteredthrough the affinity membrane, the target materialswill quickly and efficiently combine with the relevantfunctional groups of the affinity reagent. The materialsadsorbed on the affinity membrane can be soon de-sorbed when an eluent passes through the membrane.Poisonous mercury-containing industrial effluents,which come from the plants that use or produce mer-cury and mercury compounds, are the major sources ofmercury pollution. Recently, we prepared highly quali-fied heterogeneous polysulfone (PSF) affinity plate filtermembranes with chelating groups by phase separationwith blends of a chelating resin and PSF, and the resultsrevealed that the greatest chelating capacity of an affin-ity filter membrane for Hg21 was 1050 lg/cm2 of mem-

brane under appropriate conditions.7,8 As everyoneknows, the loadability of the unit volume of a hollow-fiber membrane surface is much larger than that of aplate membrane, and the intensity of a hollow-fibermembrane is hard enough to support itself, whereas aplate membrane is not. In this study, a mercapto chelat-ing resin was used as a carrier of a chelating affinityagent and blended with PSF to prepare a new type ofheterogeneous hollow-fiber affinity filter membrane forthe removal of Hg21, and the greatest chelatingcapacity of Hg21 reached 1090 lg/cm2 of membrane.

EXPERIMENTAL

Materials and reagents

The mercapto chelating resin (D190; the structurewas styrene–divinyl benzene (DVB)–SH, and thedegree of crosslinking was 8%) used in this studywas supplied by Nankai University Chemical Plant(Tianjin, China), PSF (intrinsic viscosity 5 0.57) wasobtained from Shanghai Shuguang Chemical Plant(Shanghai, China), and N,N0-dimethylacetamide(DMAC) and poly(ethylene glycol) (PEG; molecularweight 5 1000) were obtained from Tianjin ChemicalReagent Plant (Tianjin, China). Sodium chloride wasanalytical grade and was purchased from TianjinYaohua Chemical Plant (Tianjin, China).

Correspondence to: B. Wang ([email protected]).Contract grant sponsor: Natural Science Foundation of

Tianjin; contract grant number: 05YFJMJC04200.

Journal of Applied Polymer Science, Vol. 107, 501–508 (2008)VVC 2007 Wiley Periodicals, Inc.

Main apparatus and equipment

The XL30 environmental scanning electron micro-scope was made by Philips (Holland). The HD-201electronic strand strength meter was made by Hon-gda Laboratory Apparatus, Ltd. (China). The wet-spinning equipment (see Fig. 1) was made by TianjinPolytechnic University (Tianjin, China). The retentionmeasurement apparatus for the membrane (see Fig.2) was made by Tianjin Polytechnic University.

Preparation of the heterogeneoushollow-fiber affinity membranehaving a mercapto chelating resin

Some PSF and PEG (content, 6%) were dissolved inDMAC to form a PSF solution of a certain concentra-tion. Then, the quantitative mercapto chelating resin(D190), which was ground and sifted, was put intothe PSF solution, and the solution of D190 and PSFwas rigorously stirred for 8 h. Because D190 couldnot be dissolved in DMAC, the solution of D190 andPSF was heterogeneous. A certain composition of theheterogeneous D190/PSF spin-casting solution wasobtained after vacuum deaeration. The wet-spinningmethod was adopted to prepare the heterogeneoushollow-fiber affinity membrane in the spinningequipment. The spin-casting solution was put intothe storage tank and deaerated under negative pres-sure. High-pressure nitrogen was used as the pres-sure source to push out the spin-casting solution,which was measured from the spinning head; at thesame time, the core liquid went from the central cav-ity of the spinning head into the hollow-fiber cavityas its supporter and inner coagulum medium underthe pressure of the head tank. Lastly, the spinningdope went away from the spinning head, passingthe air clearance between the spinning head andcoagulating bath tank, into the coagulating bathtank; when it had been coagulated into the moldcompletely by heat-drawing and heat-setting treat-ment, the heterogeneous hollow-fiber affinity mem-brane, modified with a mercapto chelating resin, wasprepared. The heterogeneous hollow-fiber affinity

membrane modified with a mercapto chelating resinwas preserved in a hygrometric state.

Assembly of the modules of the hollow-fiberaffinity membrane having a mercaptochelating resin

To produce the hollow-fiber affinity membrane filter,the hollow-fiber membrane was cut into 19-cm-longpieces, these pieces were put together into a bundle,and one end of the bundle was invaginated into anylon sleeve whose external diameter was 10 mmand length was 30 mm; the bundle reveal 20 mm,the ringed section of the hollow-fiber membrane ny-lon tube was cast with the epoxy resin and curingagent in a ratio of 4:1, the other end was sealed, andwe waited until it was cured. The hollow-fiber mem-brane filter was put into a stainless steel sleeve, theshell pass of which was 31.60 mL, in the experimen-tal apparatus of the hollow-fiber membrane for theremoval of Hg21.

Removal of the hollow-fiber affinitymembrane having a mercapto chelatingresin for Hg21 in the mobile phase

The experiment was adapted to the Hg21-removalexperimental apparatus for the hollow-fiber mem-brane, which was made at Tianjin Polytechnic Uni-versity. The peristaltic pump extruded the solutioninto the hollow-fiber affinity membrane. The solutionwent through the pores of the membrane in theexternal pressure mode and flowed out from the endof the hollow-fiber membrane module that was notsealed; then, the permeated liquid was collected by acollector. The properties of the membrane can bedescribed by the adsorption amount of the mem-brane for Hg21 (G), which was calculated as follows:

C ¼ ðC0 � CtÞ=S (1)

where C0 is the original concentration of Hg21, Ct isthe residual concentration of Hg21 after Hg21 isthrough the membrane, and S is the membrane area.

Figure 1 Schematic diagram of the wet-spinning appara-tus: (1) motor agitator, (2) pressure gauge, (3) feed inlet,(4) kettle, (5) heating jacket, (6) shut-off valve, (7) blanket,(8) controlled volume pump, (9) spinning head, (10) boreliquid, (11) block, (12) water bath, (13) eling roll, and (14)heater.

Figure 2 Schematic diagram of the retention measure-ment apparatus of the membrane: (1) reservoir, (2) ther-mometer, (3) water pump, (4) barometer, (5) plate mem-brane module, and (6) volumetric cylinder.

502 WANG, LIU, AND HUANG

Journal of Applied Polymer Science DOI 10.1002/app

Quantity measurements of Hg21

The concentration of Hg21 was determined with thedithizone method.9 In an acidic medium, Hg21

reacted with an overdose of dithizone to form or-ange-yellow dithizonate [Hg(HDz)2], which could bedissolved in CCl4. The free dithizone was removedwith a dilute NH3 solution. At a maximum wave-length of 485 nm, the extinction of the Hg(HDz)2 so-lution was determined with a model 7220 spectro-photometer (Beijing RuiLi Instrument Plant, Beijing,China). Furthermore, the Hg21 quantity with respectto the Hg(HDz)2 extinction could be determined.

RESULTS AND DISCUSSION

Optimal process to prepare the hollow-fiberaffinity membrane having a mercaptochelating resin

It is a necessary technical process to control the reel-ing velocity in the spinning process. After trial anderror, the results showed that the velocity controlledat 20–30 m/min was appropriate. The temperatureof the spinning dope should match other qualifica-tions in the spinning process of the membrane. Theviscosity of the spinning dope varied with changesin the contents of the additive PEG, mercapto chelat-ing resin, and PSF. To increase the mobility of thespinning dope through an increase in the pressureblindly would have caused troubles in matchingother conditions in the spinning. Therefore, the spin-ning temperature was fixed relatively for the specialcomposition of the spin-casting dope. The spinningtemperature of the blending hollow-fiber membranewas generally controlled between 25 and 358C. Thehollow-fiber membrane was easily off-center whenthe temperature of the raw solution was lower andthe pressure was higher. An environmental scanningelectron microscopy photograph is shown in Figure 3.Because of the difference in the thickness of the hol-low-fiber wall, the decentralized hollow-fiber mem-brane was breached at the thin wall point for theyield stress under the effect of the external pressurethat appeared as the bearing capacity decreased, andthe use of the membrane was affected. The core liq-uid could not only provide the internal support for asmall section of the hollow-fiber membrane structurejust off the spinning head but also control the inter-nal diameter of the hollow-fiber membrane; it alsocould change the composition of the wall of the hol-low-fiber membrane that extruded from the porousarea. When the as-formed fiber with some mobilitywent into the coagulating bath, the closer micellecould be frozen at its point for the low temperatureof the coagulating bath and prevent the further den-sification of the hollow-fiber membrane before theskin layer reached its maximum density. In this way,

the distances between micelles were relatively long,and so the resistance was little when the liquid flewthrough them. The thickness of the compact layer ofthe membrane had a close relationship with the per-meating liquid; if the compact layer was thicker, theflux was less, and if the compact layer was thinner,the flux was more. The thickness of the compactlayer had a relationship with the vaporization dis-tance. The experiment proved that the longer the va-porization distance was, the thicker the compactlayer was, and if the vaporization distance was less,the compact layer was thinner. In the spinning pro-cess of the blending hollow-fiber membrane, the va-porization distance was normally between 120 and300 mm.

Isothermal absorption equation of thehollow-fiber affinity membrane havinga mercapto chelating resin for Hg21

The absorption isotherm is the relationship betweenthe solution equilibrium concentration and the equi-librium adsorptive quantity of the membrane afterthe absorption equilibrium. In this study, thedynamic absorption isotherm of the affinity mem-brane was determined to reflect the practical processof the Hg21 absorption of the membrane truly. Themeasuring method with the external pressure was asfollows. A raw material solution of a given concen-tration was extruded into the membrane by the peri-staltic pump, and the Hg21 in solution was absorbedby the mercapto chelating groups of the membrane.When the Hg21 concentration at the outlet of thehollow-fiber affinity membrane did not vary with

Figure 3 Environmental scanning electron microscopyphotograph of a cross section of the hollow-fiber affinitymembrane having a mercapto chelating resin.

HETEROGENEOUS HOLLOW-FIBER AFFINITY MEMBRANE 503


time, the Hg21 adsorption of the affinity membranewas saturated to reach the balance, and then theHg21 absorbed was dissociated by a given concen-tration of an HCl solution. The raw material concen-tration and the quantity of Hg21 dissociated werethe equilibrium concentration of the solution and theequilibrium absorption quantity of the membrane,respectively. The dynamic absorption experimentwas carried out with a series of concentrations of theHg21 solution at room temperature, and the isother-mal absorption curve of the membrane was obtainedby the plotting of the equilibrium absorption quan-tity versus the equilibrium concentration of the solu-tion (see Fig. 4). If there are N chelating absorptionpoints on the surface of the membrane and thesepoints are distributed uniformly, every absorptionpoint may be for nothing or absorb the metal ionHg21 (that is the single-molecule absorption hypoth-esis; among them, there are NA adsorbing the metalion Hg21. If the partition function of each metal ionis q0(T), from knowledge of the quantum chemistry,the main partition function (Q) is given as follows:10

Q ¼ N!qN0 ðTÞNA!ðN �NAÞ! (2)

where Q is the main partition function.According to the Stiring equation

lnQ ¼ N lnN �NA lnNA � ðN �NAÞ lnðN �NAÞþN ln q0ðTÞ ð3Þ

Then, the chemical potential of the metal ion Hg21

on the membrane (la) is

la ¼ RTð@ lnQ

@NÞV;T ¼ RT ln

NA

ðN �NAÞqðTÞ� �

(4)

The chemical potential of the metal ion Hg21 in so-lution (lc) is

lc ¼ l0 þ RT lnC (5)

where C is the concentration and l0 is standardchemical potential.

When the absorption reaches balance

la ¼ lc

Then

u

1� u

1

q0ðTÞ ¼ expl0RT

8: 9; (6)

where u is the fraction of coverage.When q0(T) is combined with exp(l0/RT) to a tem-

perature constant of A(T) 5 q0(T)exp(l0/RT), the the-oretical maximum absorption is Gm; then, the iso-thermal absorption equation is obtained:

C ¼ CmAðTÞC1þ AðTÞC (7)

Combined with the experiment, the isothermalabsorption equation for the Hg21 absorption of themembrane can be given as follows:

C ¼ 2:8305C

1þ 0:0049C(8)

From Figure 4, it could be concluded that in relationto the experiment, the error of the adsorption quan-tity of the isothermal absorption equation associatedwith describing the Hg21 absorption of the mem-brane was less.

Effect of the chelating resin grain size on theretention of the hollow-fiber affinity membranehaving a mercapto chelating resin for Hg21

The effect of the chelating resin grain size on the reten-tion of the hollow-fiber affinity membrane for Hg21 isshown in Table I. Table I indicates that the chelatingresin grain size produced an effect on the retention ofHg21. The smaller the chelating resin grain size was,the greater the specific surface was of the chelatingresin. It also means that both the sorption speed andsaturated absorption amount of Hg21 increased withthe decrease in the chelating resin grain size.

Effects of the raw solution concentration on theretention of the hollow-fiber affinity membranehaving a mercapto chelating resin for Hg21

Figure 5 shows the effect of the Hg21 concentrationof the raw solution on the retention of the mem-brane. When the concentration of the raw material

Figure 4 Adsorption isothermal curve of the hollow-fiberaffinity membrane having a mercapto chelating resin forHg21 (additive PEG content, 6%; feed-solution Hg21 con-centration, 400 lg/mL; operation flow speed, 3.8 mL/min;and feed volume, 20 mL).



solution changed in the range of 100–600 lg/mL, thechange of the retention of the membrane for Hg21

was not too obvious. The adsorption of the hollow-fiber affinity membrane was based on the coordina-tion between the mercapto chelating groups on themembrane with Hg21, and the coordination washighly efficient. When raw material solutions withdifferent Hg21 concentrations permeated the hollow-fiber membrane, the Hg21 in solution could combinewith mercapto (��SH) on the membrane abundantly,and the affinity was stronger. The membrane hadpreferable retention ability for solutions with differ-ent Hg21 concentrations, and the effect of removingHg21 was good, but when the concentration of theraw material solution was very high, chelation of themembrane for Hg21 could easily be saturated, andthe retention would decrease distinctly.

Effect of the pH of the raw material solution onthe retention of the hollow-fiber affinity membranehaving a mercapto chelating resin for Hg21

In the exchange of the chelating ions, the pH valueof the raw material solution was the most importantparameter to control the separation of metal ions.The effect of the pH value on the retention of the

membrane for Hg21 is shown in Figure 6. In thisexperiment, Hg21 was dissolved in different buffersolutions with different pHs. With an increase in thepH value of the feed solution, the retention of themembrane for Hg21 increased accordingly. The alter-native mercapto groups of the membrane createdstable compounds with Hg21. The mercapto groupson the membrane were subacidity groups and had astrong affinity to H1. Therefore, the H1 concentra-tion had an important effect on the chelates formedby ��SH and Hg21 in the membrane. The pH wasone of the key factors that affected the chelatingcapacity of the membrane for Hg21; the stronger theacidity was, the greater the decomposition was ofR��S��Hg��S��R and the lower the chelatingcapacity was of the membrane for Hg21, and thechelating capacity could be enhanced by an increasein the pH in the mobile phase. However, under thealkaline condition, Hg21 hydrolyzed, deposited, andjammed the membrane pores. This resulted in thedecrease of the flux and the retention.

Effects of the ionic strength of a raw materialsolution on the retention of the hollow-fiberaffinity membrane having a mercapto chelatingresin for Hg21

The mercapto chelating group on the membrane wasa subacidity group, and its conjugate base formed acoordination bond with Hg21. Changes in the mobilephase such as the temperature, pH, and ionicstrength directly affected the chelating affinityadsorption of the membrane for Hg21. The removalproperty of the membrane for Hg21 can beexpressed with retention as follows:

J ¼ L1L2

(9)

TABLE IEffect of the Chelating Resin Grain Size on the

Retention of the Hollow-Fiber Affinity MembraneHaving a Mercapto Chelating Resin for Hg21

Grain diameter (lm) Degree of entrapment (%)

125–147 93.497–105 94.774–88 95.8

Additive PEG content, 6%; feed-solution Hg21 concen-tration, 400 lg/mL; operation flow speed, 3.8 mL/min;and feed volume, 20 mL.

Figure 5 Effect of the feed-solution Hg21 concentrationon the retention of the hollow-fiber affinity membrane hav-ing a mercapto chelating resin for Hg21 (additive PEGcontent, 6%; operating speed, 3.6 mL/min; feed volume,20 mL; and pH, 7.0).

Figure 6 Effect of pH on the retention of the hollow-fiberaffinity membrane having a mercapto chelating resin forHg21 (additive PEG content, 6%; feed-solution Hg21 con-centration, 400 lg/mL; operation flow speed, 3.8 mL/min;and feed volume, 20 mL).



where J is the retention, L1 is the elution amount,and L2 is the feed amount. The most effective way toincrease the ionic strength in the mobile phase is toadd a common electrolyte to it, and these commonelectrolytes should be purified, have good solubilityand low coordination ability, and not create an insol-ubility outcome. In this study, NaCl was used toadjust the ionic strength, and other parameters wereconstant when the effect of the ionic strength wasconsidered. The effect of the NaCl concentration onthe retention of the membrane is shown in Figure 7.When the NaCl concentration increased in the rawsolution, the retention of the membrane for Hg21

decreased a little. The ionic strength was one of thekey factors affecting the physical properties of theraw material solution. Adding NaCl to the raw ma-terial solution could change the ionic strength. Thechange in the ionic strength affected the hydrationlayer and charge distribution around Hg21. TheDebe-Hukele limit formula is as follows:11

� ln g� ¼ Cjzþz�jI1=2 (10)

C ¼ ð2pLq�AÞðe2=4pe0e�r kTÞ3=2

where L is Avogadro’s constant; q�A is the density ofthe pure solvent; e is the electrical voltage of an elec-tron; e0 is the vacuum permittivity; er is the relativepermittivity of the solute; k is Boltzmann’s constant;T is the thermodynamic temperature; z1 and z2 arethe charge numbers of positive and negative ions ofthe electrolyte, respectively; I is the ionic strength;and g6 is the mean activity coefficient of the ions.From the Debe-Hukele limit formula, we learn thatwhen the ionic strength increased, the ionic meanactivity coefficient decreased, that is, the activity

decreased. However, with an increase in the NaClconcentration, the ionic strength increased, and so theHg21 activity decreased, and the chelating capacity ofthe membrane for Hg21 decreased.

Effects of the operating rate on the retentionof the hollow-fiber affinity membrane havinga mercapto chelating resin for Hg21

Figure 8 shows the effect of the feeding rate on theretention of the membrane under the condition of agiven feeding amount. It can be concluded that withan increase in the feeding rate, the retention of themembrane for Hg21 decreased a little. The bondability of Hg21 in the mobile phase with a mercaptogroup on the membrane was a litter stronger, andthe bonding rate was also fast. The chelating groupmercapto (��SH) was mostly bonded on the internalsurface of the hollow-fiber membrane. When the rawsolution permeated through the membrane in a con-vection way, the chelating group mercapto (��SH)on the membrane could soon chelate with Hg21.That is why the change in the feeding rate of themobile phase had little effect on the retention of themembrane. The fast bonding kinetics of the mer-capto (��SH) chelating group on the membrane withHg21 permitted the hollow-fiber affinity membraneto be operated at a high feeding rate. At the sametime, the Hg21 adsorption of the hollow-fiber affinitymembrane fully used the highly efficient and fastbonding characteristics of the mercapto (��SH) onthe membrane with Hg21, and this could realizespeedy separation and reclamation of the hollow-fiber affinity membrane for Hg21 on a large scale.The fast feeding rate and short separation periodcould make an industrial foundation for the removalof Hg21 for the membrane.

Figure 7 Effect of the NaCl concentration on the retentionof the hollow-fiber affinity membrane having a mercaptochelating resin for Hg21 (additive PEG content, 6%; feed-solution Hg21 concentration, 400 lg/mL; operation flowspeed, 3.8 mL/min; and feed volume, 20 mL).

Figure 8 Effect of the operating speed on the retention ofthe hollow-fiber affinity membrane having a mercapto che-lating resin for Hg21 (additive PEG content, 6%; feed vol-ume, 20 mL; feed-solution Hg21 concentration, 400 lg/mL; and pH, 7.0).



Effects of a raw material solution of a givenconcentration on the retention of thehollow-fiber affinity membrane havinga mercapto chelating resin for Hg21

The chelating capacity of the hollow-fiber affinitymembrane for Hg21 was a constant at a givenHg21concentration of the raw material solution.With an increase in the raw material solution of agiven concentration, the mercapto (��SH) chelatinggroups unemployed on the affinity membranebecame fewer and fewer. When the raw material so-lution of a given concentration reached a certaindegree, the affinity membrane could not absorbHg21, and the absorption reached a balance. The sat-uration of the membrane (S) for Hg21 is expressedas follows:

S ¼ CCm

(11)

where G is the Hg21 quantity absorbed by the mem-brane and Gm is the balance absorption quantity ofthe membrane at the feeding concentration. Figure 9shows the relationship between the raw material so-lution of a given concentration and the retention ofthe hollow-fiber affinity membrane for Hg21; Figure10 shows the relationship of the raw material solu-tion of a given concentration and the absorption sat-uration of the hollow-fiber membrane. On the basisof the figures, it can be concluded that with anincrease in the relative raw material solution of agiven concentration, the retention of the hollow-fiberaffinity membrane for Hg21 decreased gradually,but the absorption saturation of the hollow-fiber af-finity membrane became higher and higher. There-fore, in the process of reclamation of Hg21, theretention and saturation of the hollow-fiber affinity

membrane should be considered comprehensively. Itshould confirm the raw material solution of a givenconcentration on the basis of the required productionrecovery and saturation of the membrane.

The affinity membrane was recycled through soak-ing in 500 mL of a 0.1M dilute HCl solution for 14 hat room temperature, and the concentration of Hg21

in HCl was 13 lg/mL. The recycled affinity mem-brane was used to remove Hg21, and the dynamicadsorption capacity was 305 lg/cm2�of membrane,which was a little lower than that of the brand newmembrane. This shows that the affinity membranecan be easily and conveniently recycled in a diluteHCl solution, and this will play an important role inthe utilization of such an affinity membrane in thetreatment of Hg21 in industrial wastewater.

CONCLUSIONS

Blends of a mercapto chelating resin and PSF can beused to prepare a high-quality, heterogeneous hol-low-fiber affinity membrane with a high chelatingcapacity for Hg21 by phase-separation technology,and the isothermal adsorption equation of the affinitymembrane is set on the basis of the physical structureand the chemical equilibrium theory also. An increasein the ionic concentration of the raw material solutionis not favorable for the removal of Hg21 of the affin-ity membrane. The pH value has a great effect on theremoval of Hg21. At a low pH value, the removal ofHg21 decreases greatly, and the pH value of the rawmaterial solution is appropriately 5–7. The concentra-tion of the raw solution has little effect on the re-moval of Hg21 at a given feeding rate of Hg21, andthe membrane can be used to remove Hg21 in alarger concentration range. The removal of Hg21

decreases a bit with an increase in the feeding rate

Figure 9 Effect of the feed volume on the retention of thehollow-fiber affinity membrane having a mercapto chelat-ing resin for Hg21 (additive PEG content, 6%; feed-solu-tion Hg21 concentration, 400 lg/mL; and operating speed,3.8 mL/min).

Figure 10 Effect of the feed volume on the saturationdegree of the hollow-fiber affinity membrane having amercapto chelating resin for Hg21 (additive PEG content,6%; feed-solution Hg21 concentration, 400 lg/mL; andoperating speed, 3.8 mL/min).



when the feeding rate of Hg21 does not vary; that is,the membrane can be operated to remove Hg21 at ahigher feeding rate on a large scale. With an increasein the feeding rate of Hg21, the recovery of Hg21

decreases a bit, and the adsorption saturation of themembrane increases gradually. In the practical pro-cess of removal of Hg21, the feeding rate of the rawmaterial solution should be confirmed on the basis ofthe required production recovery and the saturationof the hollow-fiber affinity membrane.

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