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Biosorption from aqueous solutions by eggshellmembranes and Rhizopus oryzae: equilibriumand kinetic studiesBogdana Koumanova,1 P Peeva,1 Stephen J Allen,2* KA Gallagher2 and MG Healy21Department of Chemical Engineering, University of Chemical Technology and Metallurgy, Sofia 1756, Bulgaria2School of Chemical Engineering, Queens University of Belfast, David Keir Building, Stranmillis Road, Belfast, UK

Abstract: This study assesses the use of eggshell membranes and Rhizopus oryzae as media for the

biosorption of p-chlorophenol (p-CP), 2,4-dichlorophenol (2,4-DCP), 3,5-dichlorophenol (3,5-DCP),

reactive dye and cadmium from aqueous solutions. The performance of the adsorbents was quantied

by measuring the equilibrium uptake and the batch rate kinetics from solutions. The constants in the

Freundlich, Langmuir and RedlichPeterson isotherm models were calculated through the lineariza-

tion of the equations and linear regression. The kinetics of the adsorption systems for cadmium and a

reactive dye have been assessed in a batch stirred adsorber. The effect of the process parameters such

as pH, adsorbate concentration, adsorbent dosage, adsorbent particle size, temperature and agitationspeed are reported. The external mass transfer coefcients are reported for some different system

conditions. Both materials are determined to be effective adsorbents and could nd application in the

treatment of contaminated wastestreams.

# 2002 Society of Chemical Industry

Keywords: Eggshell membrane; Rhizopus oryzae; biosorption; isotherms

NOTATION

aL Langmuir isotherm constant (dm3

mg1

)

aR RedlichPeterson isotherm constant

(dm3mg1)

b RedlichPeterson isotherm constant(dimensionless)

Ce Equilibrium liquid phase solute

concentration (mgdm3)

C0 Initial solute concentration (mgdm3)

Ct Solute concentration at time t (mgdm3

)

kf External mass transfer coefcient (cm s1)

Kf Freundlich isotherm constant (dm3g1)

KL

Langmuir isotherm constant (dm3g1)

KR

RedlichPeterson isotherm constant

(dm3g1)

ms Concentration of particles in liquid (gdm3)

M Mass (g)

n Exponent in Freundlich equation

(dimensionless)

qe Equilibrium solid phase concentration

(mgg1)

Ss Specic surface (cm2

cm3

)

t Time (s)

INTRODUCTION

Biosorption is talked of frequently in relation to the

removal of metal ions.1,2 In addition, this study aimed

to asses the suitability of biosorption for the removal of

organics from water. In biosorption it is accepted that

the cell wall and its associated functional groups are

responsible for the metal biosorbent property of deadcells. However, the mechanism of binding is relatively

poorly understood.3 This may be due to the many

possible binding sites on the variety of biomolecules

present in microbial cell walls. It is also strongly

believed that biosorbents show preferences for heavy

metals, reecting the size of their ionic radii.4

Biomass materials by their nature are cheap and

abundant. They may be generated as a waste by-

product from large-scale fermentation, as is the case

with Sacchromyces cerevisiae,5,6 or produced in large

quantities by nature as is the case with Ascophyllum

nodosum.2

It is currently believed that biomass-based technol-

ogies can either enhance the performance of, or

replace altogether, certain conventional methods for

the removal of constituents from water. It is believed

that some of these technologies are actually competi-

tive with existing non-biomass-based treatments.7

This is true particularly if the biomass is produced as

a waste product from another industrial process, eg

enzyme fermentation8 or brewing, as mentioned

above. Biomass from fungal/bacterial sources is also

a renewable material which can be replaced, which is a

(Received 21 November 2001; accepted 30 November 2001)

* Correspondence to: Stephen J Allen, School of Chemical Engineering, Queens University of Belfast, David Keir Building, Stranmillis Road,Belfast, UK

Contract/grant sponsor: Ministry of Education, Science and Technologies, Sofia, Bulgaria; contract/grant number: X-604

# 2002 Society of Chemical Industry. J Chem Technol Biotechnol 02682575/2002/$30.00 539

Journal of Chemical Technology and Biotechnology J Chem Technol Biotechnol 77:539545 (online: 2002)DOI: 10.1002/jctb.601


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distinct advantage over other non-renewable adsor-

bents. The ability to regenerate the adsorbent as

distinct from renewing or growing new material is not

under investigation. However, it is accepted that the

regeneration of an adsorbent is of importance in many

applications.

Despite this stiff opposition numerous examples

exist where biosorbents can out-perform non-biomass-based alternatives. For example Rhizopus oryzae

removes 2.5 and 3.3 times more uranium than ion-

exchange resin or activated carbon respectively.9

Two

commercial biosorbents are also available. They are

made from consortia of biomass types and processed

in various ways to create Algasorb2

and Bio-Fix2

.10

Within the class of fungi known as the Zygomycetes

the order of Mucorales is very abundant Mucorales are

saprophytes (ie they obtain organic matter in solution

from dead or decaying tissues of plants or animals),

Rhizopus oryzae is a member of this order. This fungus

contains chitosan as a major component. Chitosan is

the polymer of n-glucosamine which has undergone

little or no acetylation and is found as a cell wall

component of R oryzae and other Mucorales fungi.11

Chitin is the acetylated form of the glucosamine

polymer. These biopolymers are signicant constitu-

ents of R oryzae, therefore it stands to reason that the

adsorption performance of this biomass is likely to be

very signicantly dictated by these bioploymers.

In addition, by harvesting R oryzae during the late

exponential growth phase it is possible to maximise

production of chitosan in the cellular structure,12

thereby facilitating improved adsorptive performance.

Initial investigations in the context of dye biosorp-tion have been based upon extrapolation of data and

information obtained from studies into heavy metal

and humic/fulvic acid biosorption. The work by Zhou

and Banks13

has shown Rhizopus species to be capable

of humic/fulvic biosorption via adsorption to the

chitin/chitosan cell wall component. The same authors

have however noticed differences in process kinetics,

thus suggesting the existence of different biosorption

mechanisms.

Chlorophenols are one of the more hazardous

pollutants found in industrial wastewaters and require

careful treatment before discharge into a receivingbody of waters. Activated carbon adsorption is one of

the most widely used methods for removal of organic

compounds from efuents. In granular or powdered

form it has a good capacity for the adsorption of

organic molecules such as chlorinated phenols. How-

ever, the high cost of activated carbon and the inherent

expensive regeneration of spent carbon are two of the

reasons that have stimulated interest in examining the

feasibility of using cheaper adsorbent materials. Fly

ash, peat, soil, rice husk and wood are some

adsorbents which have been used for organic pollu-

tants.1419 Live and dead biomasses are available as

abundant and cheap biosorbents.2023 A full evalua-tion of the economic viability of the utilisation of these

adsorbents is essential.

MATERIALS AND METHODS

Eggshell membrane (ESM) is located on the inner

surface of the shell of a hen's egg. Eggshell membrane

is a dual membrane whose structure can be described

as an intricate lattice meshwork of large and small

bres which interlock with each other to form a

tenacious sheath.24 By mechanical dissection, the two

membranes can be separated, as a clear plane cleavageexists between these two layers. Apart from collagen,

eggshell membrane is considered to contain poly-

saccharides.25

The ESM used for the study of the adsorption of the

phenols was obtained from a local farm in Co Down.

For the preparation of the ESM a 25% (w/v) aqueous

acetic acid solution was rst used to dissolve the

eggshell. The membrane was then taken out of the

beaker and twice cleaned with fresh distilled water and

dried overnight at a temperature of 40 C. The dried

membrane was ground and sieved to the required

particle size range of 355500mm. The materials used

as adsorbents for the experiments were eggshell

membrane and R oryzae (autoclaved), 300500mm.

Rhizopus oryzae was purchased from the Interna-

tional Mycological Institute, Surrey, UK, as IMI

Strain 266680 and was isolated from soil in Sri Lanka.

The freeze-dried spores were re-activated and then

cultured in malt extract broth (MEB; 17g dm3 malt

extract and 3 g dm3

mycological peptone dissolved in

distilled water and adjusted to pH 5.40.2). TheMEB was inoculated using a standard sterile tech-

nique and incubated at 32 C for 3 days in an orbital

shaker set at 175rpm. Three ceramic beads were

inserted into each batch of broth to break up thelamentous growth as much as possible. The biomass

was harvested and washed thoroughly in tap water

followed by distilled water and oven-dried at 50C to

constant mass. The dried biomass was ground in a

hammer mill. The ground biomass was then sieved

and the various fractions retained. Only the 300

500mm size fraction was used in the investigations.

Pure p-CP, 2,4-DCP and 3,5-DCP (>97%),

obtained from Fluka, were used as adsorbates in this

study. The solutions were prepared by dissolving

quantities of the adsorbates in distilled water. Initial

concentrations were varied between 2 and 50mgdm3. For the dye and cadmium systems, initial

concentrations up to 1000mgdm3 were employed.

Samples containing only water and biosorbent were

treated in the same procedure to avoid a possible

interference during the UV-measurements. The dye

used in these studies, Levax Brilliant Red E-4BA, is

produced by the company Dystar, the dyestuff

company of Bayer and Hoechst in Frankfurt, Ger-

many. The structure and the molecular weight of any

dye are kept secret by Dystar.10 Experimental equili-

brium adsorption data were obtained as follows. A

known amount of adsorbent (ranging between 0.1 and

0.5g dry weight) was weighed into each of severalErlenmeyer asks and shaken with 50cm

3of aqueous

solutions of pollutant of varied concentration at a

540 J Chem Technol Biotechnol 77:539545 (online: 2002)

B Koumanova et al


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constant temperature of 20C for either 6 days (the

time required for equilibrium to be reached for the

cadmium and phenols), or 21 days (for the dye

system). Blanks containing no adsorbate and replicates

of each adsorption point were used for each series of

experiments. The pH of the solution, before and after

the adsorption process, was measured with a LPH

430T pH-meter, TACUSSEL electronique. Afterltering through a Whatman1 GF/A lter paper the

solutions were analysed using a Perkin-Elmer 323

UV-Vis NIR Spectrophotometer to determine the

residual concentration of the studied compound.p-CP

was analysed by UV absorbance at 280nm (eggshells

as adsorbent) and 226nm (R oryzae as adsorbent),

2,4-DCP at 285 nm and 3,5-DCP at 278 nm. The dye

concentration of the bulk phase was measured with a

Perkin-Elmer Lambda 12 UV-Vis Spectrophotometer

at the maximum wavelength. Metal ion concentrations

were determined using a Perkin-Elmer 400 Series

ICP-OES (Inductively Coupled Plasma-Optical Emis-

sion Spectrometer).

The batch study was set up according to previous

studies.2628 After the adsorbent was added to the dye

or metal ion solution, samples were taken at least every

10min during the rst hour, every 30min afterwards

until the end of the second day and every hour during

the third day.

ADSORPTION MODELS AND DATA ANALYSIS

The adsorption process is a mass transfer operation

which can be described mathematically by an equili-

brium process and a rate process. The equilibrium isestablished between the concentration of the material

dissolved in the water and that bound to the adsorbent.

To facilitate the description of an adsorption process

in terms of a batch equilibrium process a nite amount

of adsorbent is brought into contact with various

concentrations of the adsorbate. Batch equilibrium

studies yield information as to the total capacity of an

adsorbent for a particular material in single compo-

nent systems. Additionally, isotherm constants, neces-

sary in the mathematical modelling of sorption

systems, may be obtained from representation of the

equilibrium data as isotherm plots. The results arepresented as plots of solid-phase equilibrium metal

concentration; expressed perhaps as milligram adsor-

bate per gram adsorbent (y-axis), versus the liquid-

phase equilibrium adsorbate concentration; expressed

as milligram adsorbate per dm3 of solution (x-axis).

These data will then be represented mathematically by

isotherm relationships such as the Langmuir, Freund-

lich and RedlichPeterson adsorption isotherms.

These relationships are described elsewhere.29,30

A

summary of the isotherm relationships is presented as:

Langmuir : qe KLCe

1 aLCe1

or qe QmCe

Ce Kd2

Freundlich : qe KfCne 3

Redlich--Peterson : qe KRCe

1 aRCbe4

The assumptions associated with the Langmuir

model are well known.31 The Freundlich model

assumes a heterogeneous adsorption surface with sites

that have different energies of adsorption and are not

equally available. The Freundlich isotherm is more

widely used but provides no information on the

monolayer adsorption capacity in contrast to the

Langmuir model. The RedlichPeterson model is

described as combining elements of both of the other

models and is often used to describe equilibrium over a

wide concentration range. KR approximates to KL, the

Langmuir constant.

The slope and intercept of the transformed data

plots were used to estimate the two parameters in the

Freundlich and Langmuir equations and the aR and bvalues in the RedlichPeterson model (Table 1).

Adsorption isotherms are a useful quantitative tool

when representing the adsorption capacity of an

adsorbent for a given solute. However isotherms are

obtained under equilibrium conditions, whereas in

most adsorption treatment applications the retention

time is too short for equilibrium to be attained. For

this reason we must obtain information on the time

dependence of adsorption processes by carrying out

process-orientated kinetic studies.

In adsorption, the rate of uptake will be affected by

various system variables or parameters. During theadsorption mechanism there exists a series of resis-

tances to mass transfer. These may be either `external

resistances' in the case of the resistance encountered

Table 1. Isotherm constants for R oryzaeand ESM adsorption systems

Adsorbate K L aL R2 Kf n R

2 KR b aR R2

p-Chlorophenol on R oryzae 0.581 0.052 0.985 0.635 0.756 0.989 0.581 1.135 0.035 0.976

2,4-Dichlorophenol on ESM 0.344 0.143 0.996 0.448 0.484 0.989 0.344 1.023 0.134 0.996

3,5-Dichlorophenol on ESM 0.319 0.100 0.994 0.309 0.695 0.987 0.319 0.878 0.133 0.991

Cadmium on R oryzae 0.361 0.019 0.860 1.090 0.518 0.777 0.361 0.890 0.071 0.850

Cadmium on ESM 24.27 0.33 0.760 32.49 0.19 0.85 0.33 1.41 0.77 0.721Reactive dye on R oryzae 8.143 0.042 0.947 43.62 0.248 0.898 8.143 0.762 0.129 0.895

Reactive Dye on ESM 2.10 0.006 0.61 6.450 0.650 0.671 2.10 0.16 21.82 0.911

J Chem Technol Biotechnol 77:539545 (online: 2002) 541

Biosorption by eggshell membranes and R oryzae


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by solute molecules as they diffuse as a solute `lm'

onto the adsorbent particle surface, or `internal

resistances' in the case of that encountered by solute

molecules as they diffuse through the liquid lling the

pores on its way to the adsorption site. The former is

characterised by the external mass transfer coefcient

and the latter by pore and solid diffusivities.

Kinetic models which consider one type of resis-tance alone are termed single resistance models. These

determine the relative effect of lm diffusion (external

mass transfer) on the adsorption rate in isolation.2628

By plotting a concentration decay curve we can see

how the rate of adsorption changes with time. If we

assume that the resistances to mass transfer posed by

the bulk aqueous phase and uptake at the adsorption

site to be negligible,32

then we can concentrate on the

internal and external mass transfer resistances caused

by diffusion and the boundary layer as being respon-

sible for controlling the rate of mass transfer. Models

which concentrate on one type of resistance in

isolation are called single resistance models. A

straightforward, but also less accurate, method of

obtaining a measure of resistance to external mass

transfer is by obtaining kf (external mass transfer

coefcient) by the initial slope method of Spahn and

Schlunder.33 This entails a graphical differentiation of

concentration decay at time zero, since at t= 0 Cs0

and CtC0. The expression is shown below in eqn

(5). The initial slope of this plot of Ct/C0 v t plot will

give a slope from which kf can be extracted:

dCt

C0

dt

2664 3775t0

kfSs 5

RESULTS AND DISCUSSION

It is well known that the most critical parameter in the

adsorption of chlorinated phenols that affects biosorp-

tion capacity is the pH of the sorption medium. A

series of experiments demonstrated that the pH of the

initial model solutions was 6.0 and after addition of the

biosorbent it initially remained the same. Measure-ment of the pH at the end of the sorption process

demonstrated that it had changed to pH 7. The results

indicate that for chlorophenol adsorption, pH change

is only signicant in the acidic region, pH 1.06.0. The

nature of the biosorbent inuences the pH of the

medium.

It was established that the uptake of dichlorophenols

by eggshell membrane was higher than that of p-CP.

The highest values of uptake in the case of 2,4-DCP

(C0 2.5mgdm3) were 48.2% (0.1g sorbent) and

71.2% (0.3 g sorbent), respectively. The values for

3,5-DCP (C0

4.3mgdm3) were 37.2% and 74.4%,

respectively. The uptake of p-CP from the solutionswith initial concentrations ranging from 2 to 30mg

dm3 was very low (no more than 5%).

The adsorption isotherms determined for 2,4-DCP

and 3,5-DCP on eggshell membranes have the general

shape of a Type I isotherm in the Brunauer classica-

tion.34 Sample isotherms according to Langmuir,

Freundlich and RedlichPeterson in linear form are

given in Fig 1. The isotherm constants for both com-

pounds are useful parameters for predicting adsorp-

tion capacities. These have been calculated and their

values are presented in Table 1. Figures 14 compare

plots of the equilibrium isotherm and the model ts.

Figure 2 shows the model ts for 3,5-DCP and for

example the data obtained are correlated better by the

Langmuir and RedlichPeterson isotherms than the

Freundlich isotherm.

The adsorption is affected by the substituents of the

aromatic ring which modify the electron density of the

aromatic ring.35 Chlorine decreases the electrondensity of the aromatic ring and as a result the

interaction of the system with the biosorbent will

increase with increasing basicity. The higher chlorine

content in the phenol molecule strongly inuences the

adsorption uptake. The adsorption capacity deter-

mined for both dichlorophenols is very similar. The

lower adsorption capacity for p-CP compared with

those for 2,4-DCP and for 3,5-DCP conrms this

statement.

The adsorption isotherm for p-CP has the general

shape of a Type I isotherm of the Brunauer classica-

tion. In the case of this biosorbent the adsorption

Figure 1. 2,4-DCP adsorption isotherms and model fits on eggshell

membranes.

Figure 2. 3,5-DCP adsorption isotherms and model fits on eggshell

membranes.


B Koumanova et al


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isotherm is described better with the Freundlich

model.

Compared with eggshell membranes R oryzae has a

greater adsorption capacity for p-CP. The relative

uptake of p-CP was higher at lower concentrations. It

was 77.8% at a C0

of 4.5mgdm3 (0.5g sorbent) and

decreased to 48.1% at a C0 of 48.5mgdm3

. When the

sorbent quantity was 0.3g the uptake was 55.5% and

when the initial concentration ofp-CP was increased it

decreased to 32.1%.

Apart from the equilibrium studies, batch studies

were undertaken to determine external mass transfer

coefcients for the sorption processes. It can be seen

that agitation rate affects the uptake with time. The

mass transfer coefcients shown in Table 2 demon-

strate how increasing agitation shears the boundary

layer, reducing resistance to mass transfer and

increasing the effective rate of mass transfer for all

three adsorbate systems.

The effective rate of adsorption falls as initial

concentration is increased. In theory a concentrationgradient between the bulk solution and the external

surface should help drive adsorption, therefore as the

initial concentration increases we would expect to see

an increased rate of adsorption due to the correspond-

ing reduction in concentration gradient. The smaller

relative decrease in kf

for the R oryzaedye as opposedto the Cd uptake system is not entirely unexpected

since McKay and colleagues27,28 showed kf

to be

independent of initial dye concentration during the

uptake of dyes by chitin which is a signicant

component of the biomass used. The reason given

was that all parameters in the system which affect

mixing power number and energy dissipation rate are

constant.

Adsorbent particle size has a minimal effect on the

rate of uptake of the adsorbates by the R oryzae.

Adsorption as a surface phenomenon would be

inuenced by surface area, therefore we would expect

the rate to decrease as the particle size increased due to

the subsequent reduction in surface area of the largeradsorbent. The results shown can be justied by saying

that R oryzae is predominately microporous. There-

fore, external surface area contributes very little to

overall surface area. Hence any increase in adsorption

rate is purely dependent upon the decrease in

diffusional resistance and not on additional available

surface area.

The rate of cadmium uptake is minimally increased

by increased adsorbent dosage. Dye uptake rates

appear to be independent of this parameter. Mathe-

matical analysis assumes spherical adsorbent particles,

consequently varying adsorbent dosage and hence

surface area available for adsorption, Ss, caused

minimal variation in kf, supporting this approximation.

Decreasing solution pH increases the rate of dye

uptake. The rate of metal ion uptake shows the

opposite trend with effective rate increasing with

increasing solution pH. This is in agreement with the

strong pH dependence shown in equilibrium studies.

Table 2 shows the adsorption rate of dye to be

slightly increased by temperature with cadmium

adsorption uptake showing a decreased rate. There is

no obvious trend in these results. Therefore it may be

possible that no Arrhenius dependence is in effect and

that no activation energy threshold must be encoun-tered during adsorption in these systems. Adsorption

systems which encountered more signicant chemi-

sorption may have a more obvious Arrhenius depen-

dence.

By comparing experimental decay curves with data

predicted by single resistance mass transfer models it is

possible to evaluate the usefulness of that model. This

generates the theoretical, or predicted, concentration

decay curves which can then be correlated with

experimental data to give an indication of the goodness

of t. An example of this is shown in Fig 5 which shows

experimental and theoretical data for the uptake ofcadmium by R oryzae under different conditions. With

very few exceptions adsorption of dye and cadmium

under the inuence of all process parameters is

favourably predicted by the model as t0. However

it appears that as time increases past the initial few

minutes this favourable prediction breaks down. Since

this model is concerned with resistance to mass

transfer by external surface boundary layers which

will be overcome as t0, then the results are proof of

the models' limited usefulness. Deviation between

experimental and theoretical data at longer contact

time may be attributed to the effect which intraparticle

diffusion has on the overall rate of adsorption.

Figure 4. Equilibrium isotherm for R oryzaeand reactive dye.

Figure 3. p-CP adsorption isotherms and model fits on RO, 300500mm.




6/7

CONCLUSIONS

Of the three isotherms considered, the Langmuir

and RedlichPeterson sorption models adequately

describe the equilibrium processes for chlorophenol

adsorption. The equilibrium uptake appears to be

inuenced by the presence of chlorine in the com-

pounds. The biosorption data in this study show that

eggshell membranes are a suitable material for reduc-

tion of the concentrations of some chlorinated phenols

in water. R oryzae has a higher sorption capacity for

p-CP. Here, the Freundlich isotherm appears to

describe the sorption process more favourably.

Dye and cadmium equilibrium adsorption can besuccessfully modelled using either the Langmuir,

Freundlich or RedlichPeterson isotherms. The

description by the Langmuir model conrms chemi-

sorption as the rate-controlling step, since the reactive

dye is supposed to react with reactive groups on the

surface of the ESM. The single resistance model

allowed the resistance to mass transfer posed by the

external boundary layer to be described. It was found

that agitation rate, initial adsorbate concentration, and

temperature all affected the external mass transfer

coefcient which was used as an effective adsorption

rate parameter. In general the model was able to

predict adsorption decay in the very early stages of

adsorption. Dye uptake was very sensitive to pH

changes in the adsorption system. Maximum dye

uptake was observed at pH 2 but decreased sharply as

the pH value increased.

ACKNOWLEDGEMENTS

The present work has been supported by the Ministry

of Education, Science and Technologies (project No

X-604), Soa, Bulgaria.

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Table 2. External mass transfer co-efficients for dye and cadmium uptake

System variable

Reactive dye on

R oryzae,

kf (104)cms1

Cadmium on

R oryzae,

kf (104)cms1

Agitation rate(rpm)

100 1.540 5.128

200 2.051 4.103

300 1.542 5.128400 2.561 9.450

500 3.080 11.077

Initial conc (mgdm3)

100 4.103 10.256

200 4.103 9.143

300 2.564 5.103

400 2.051 4.103

500 2.062 2.051

Particle size (mm)

50180 1.059 1.325

180300 1.934 2.762

300500 1.382 4.608

500710 2.098 3.986Adsorbent dosage (gdm3)

0.25 2.564 2.564

0.5 2.564 3.057

1.0 3.077 3.111

1.5 2.564 3.859

2.0 2.064 2.051

Solution pH

1.5 5.411 4.103

3.0 3.077 5.128

4.5 3.464 4.103

6.0 2.564 4.223

Temperature (C)

5 2.668 4.103

20 3.077 5.12830 3.103 3.077

40 3.103 2.751


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