SOME LANGMUIR ADSORPTION PARAMETERS OF

&

Nig . .I. Pure Printed

Appl.

Sci.

Vol.

0794-0378/99

15 (2000)

©

in Nigeria

2000

Faculty

of Science

Univ.

$3.00 of /lorin.

+0.00 Nigeria

SOME LANGMUIR ADSORPTION PARAMETERS OF ACTIVATED CARBON PRODUCED FROM LOCAL MATERIALS *G. O. Adediran, F. O. Nwosu and F. A Adekola Department

of chemistry.

University

of Ilorin.

/lorin.

*Aulhor to whom correspondence lIIay be addressed ABSTRACT:

Some Langmuir

adsorption parameter intercept of linearized

adsorption

parameters

of activated

carbon

types made from local materials

were determined.

The Langmuir

K. \Vas found to be in the range of 6.0-7.1 flM for the carbon types with the exception of cow hoof carbon. equation of Langmuir. Xm using linear regression analysis values were calculated and found to fall within

01'62.9-285.7 ~lmol/g for the carbon types. The K values were determined from the slope of linearized help in predicting the adsorption capabilities of the carbon types and hence their applicability.

Langmuir

equation.

These

From the the range parameters

INTRODUCTION The tremendous application of activated carbon in various areas of our society has created the need to search for cheap sources for its production. Activated carbon has been useful for quality industrial products. pollution control and purification of water. Browning (1972) enumerated areas to which activated earhon have heen found very useful. They include agriculture, medicine, sugar decolourizing and be\'erage industries: reclaiming of solvent. separation of metals and so on. The adsorptive parameters of activated carbon determines the usefulness of equation is'ti'equently used to interpret adsorption data from solution as reported al (1981). They also indicated that adsorption from sol ution in general appear to Langmuir (1918) however predicted that under equi Iibrium conditions and adsorption should obey a function of the form: XmbP X = --

such carbon type. Langmuir by Waller (1962) and Rubin el form only one molecular layer. constant temperature. simple

( I)

1+ bP

Where X is the adsorption density Xm is a maximum surface coverage representing the formation of monomolecular layer on the surface of the adsorbent. P is the equilibrium gas pressure b is a constant related to the energy of adsorption Michaelis-Menten form of equation of enzyme kinetics is obtained if denominator and numerator multiplied by K. Hence equation (I) becomes:

11K

IS

substituted

for b and both

XmP X = --

(2)

K+P

Rubin el af ( 1981) states that a plot of X as a function of P passes through the origin and is nearly linear at low pressures. Adsorption approaches a limiting value of Xm as pressure increases. If the equilibrium

gas pressure is replaced with the equilibrium

adsorbate

concentration,

XmC X

= --

(3)

K+C

Linearizing

equation (3) by taking its reciprocal

gives equation (4).

\075

equation (2) becomes:

G. O. Adediran

el al

..................... (4)

I Ising sinlpic graphic technique.

evaluation

of K and Xm are possible.

Narasilllha I{ao el al (1964), Olaofe el al (1979) and Odozi el 01 (1986) successfully produced acti \'ated carbon fl't agrieullul'al wastes such as coconut shell. rice husk. and palm kernel shell. The ausorption propertics or earhon ohtailH:d by pyrolysis at 500°C, and that which is treated with zinc chloride after pyrolysis ,II 5()O"C have been ellillpared' by Kutanov el 01 (1965). The study showed no di fference in ausorption propt:r·tics or thc two prodUJ.:lS. They howcver cxhihited lower adsorption capabilities than industrial activc carbon. In another report, t\dediran and Nwosu (19l)(») prouuccd activated carbon from unripe plantain pcel. vehicle tyre and e()\\' hair', They showed that Freunulich adsorption parameters obtained by these carbon types arc in agrcement \\ ilh those reported Ill!' conventional indllstrial active carbon, Mkayula el 01 (1994) rcported thc preparation or acli\'aled earhon rrom agrowastes and studied their properties, Morris and Webber (1962) reported Xm values that rell in lhe range or I(jO-400 ~Lnlol/g and K values ranging from 0,5 to 4~LM Il)r the adsorption of alkylbenzcne sulphonate detergcnt hy activated carbon. They recorded I090~lmol/g Xm value and 9,3~lM K vallie Il)r the adsorption or phenol by activated carbon from 5-210(~lM) equilibrium eonccntration range, Gile el 01 (1974) exalllil1L:d lhe IIse of Langmuir equation to calculate Xm and K making IIse of methylene blue adsorption data alHlltHlnd thalmethylene blue is extensively adsorbed minimizing the relative error orthe calculated adsorption densities, X. They also found that adsorption densities reached a plateau of limiting values. whieh is the tyrical !.angllluir behaviour. The Langmuir adsorption parameter K of I. 10-phenanthroline on Nuchal' WV-l. powdered activated carbon at pI! 7, I have been reported by Rubin el (1981) to be equal to 12pIVI and ILl 1~tl1lol/g as Xm value for 30-90 (~lM) phenanthroline, 111 1

ill

MATERIALS AND METHODS The used lyres were obtained 1"J'()1ll vulcanizers workshtl[J along road sides \vhilc unripe plantain peel. cow hair and hoof were collected as wastcs at Ipata market. Ilorin. K\vara State of Nigeria, l'hree major processes namely carbonization, [Juri f1cation and activation were used in the production of activated carbon. The carbonization process was achieved by burning I00,7g of the tyre (3.0 x 2,Ocm) in a specially designed tin t,hat limits air supply for aDOllt 40 minutes, It was cooled for about six hours, The process was repeated three times, The cooled residue obtained weighed between 38,Og and 39,3g, About 40.2g of dried cow hair and 50,9g of cow hoof were separately charred on a hot plate using specially constructed tins. Residues obtained \vere cooled and weighed to be 18,2g and 25,2g resrectively, 71,Og sun dried unripe plantain peel was also carbonized in a srecially designed tin that limits air suprly. The carbonization was repeated three times. g,2g residue was obtained on the average for the unripe plantain peel. Purification and Activation of Carbon Types Eaeh of the carbon residues obtained was ground to reduce its particle sizes. About I OOcm2 of IIV!HCI was added to IO.Og of each carbon residue in a 250cm·1 beaker. A foul gas was given ofT. which smells rotten egg in the case of used tyre, Each mixture was gently warmed until the effervescence stopped, Distilled \vater was added to the mixture. stirred. and filtered, Eaeh of the carbon types residue was washed several times with distilled water and filtered till the t1Itrate became neutral to blue or red litmus paper. It was then dried in an O\'en at 105°C for two hours to obtain odourless carbon types. The carbon types were sized into 0.25-0, 125nrn range with the aid of a standard sieve, Each carbon type was subjected to high temperature activation using a muffle furnace for an hour with exception of the plantain peel carbon that was activated at low temperature of 500e, The used tyre carbon was activated at 800°C while cow hair and hoof carbon types were differently activated at 5200e,

Studies on Determination of Adsorption Parameters of Carbon Types Different concentrations ranging from 5-25~lM were made from freshly prepared 50~LM stock solution of Methylene blue. O.lg of 0.25-0.125mm particle sized activated carbon types produced from local sources as well as the industrial active carbon were di fferently added to I 00cm3 of each of the concentrations, Using Spectronic 20 spectrophotometer. their absorbances were n;ad at 27°± I°e after an hour at 630nm wavelength, Initial absorbanees of the solutions were read before the addition of activated carbon types. The residual concentrations, Cr. of Methylene blue were obtained using a predetermined calibration graph of Absorbance. Ao versus initial concentrations, Co,

1076

Langmuirs

adsorption

parameters

of activated

carbon

RESULTS The results of the studies on carbonization process and determination carbon types are shown in Tables I to 3 and Figures 1-5.

of Langmuir adsorption

The percentage yield of carbon types is shown in Table I. The plantain (11.6%) while cow hoof had the highest yield (49.8%) of carbon residue. Table Raw Material

I. Percentage

Mass of Raw Material

Yield of Carbon Mass of Carbon Produce

(g)

100.7 40.2 50.9 71.0

Tyre Cow (-lair Cow Hoof Plantain Peel

parameters

of the

peel had the least percentage

yield

Types Percentage

Yield

(%)

(g)

38.7 18.2 25.2

38.4 45.3 49.8

8.2

11.6

'Each recorded result is mean of three determinations.

~ .,0.190 0.340 Ar 0.220 0.265 0.\05 0.011 0.010 05.0 0.240 0.100 0.095 0.150 0.330 2.50 0.114 0.250 0.400 -10.0 -15.0 1135.0 62.5 5.0 11.50 0.087 0.007 0.015 0.140 4.50 0.222 0.080 0.180 0.392 0.040 0.667 0.029 7.50 0.285 0.385 0.019 18.25 67.5 0.055 0.270 9.50 0.220 4.00 6.50 8.75 0.154 0.171 0.013 -0.100 -0.067 0.006 0.009 141.5 110.0 769835.0 4.6 0.308 7.5 6.25 2.55 24.5 37.5 0.160 0.166 0.041 1.50 45.0 0.133 0.167 13.50 9.75 65.0 52.5 0.103 0.074 0.207 0.090 5.85 50.550 11X(llmol) IICr t/X(llmol) (111\11"1) tlCr t/X(llmot) (11M") The Langmuir Cr(IlM) t/Cr adsorption (111\11"') data of methylene (Ilmo1/g)· X (Ilmol/g)

re Carbon

Co (11M) Table 2. Langmuir

blue by 0.25-0.125mm

Adsorption

Data of Methylene

1077

carbon types are given in Table 2 (a - e).

Blue by Carbon

Types

G. O. Adediran

et

01

y = 0.0357x + 0.005 R~ = 0.9871 0.01.

r------------.

0.012

y ~ IIr))

0.0214x + 0.0035 R~ c 0.9266

001

0006

0000 fllli 0004

0007

o '--o

'" FI~. I.

0'

07

IJclt'fllIinf111nn

I11dhylrne blur

or

Lnll~mllir

0.6

adsorption

parameten

07

for tyrr carhon

~

0",

0'

~--~

0"

~--~-025

07

0.6

0.'

0"

0.4

tier

on

Fig. 2.

DelenninatloJl

of Lanl!mulr

ad~nrptlon

parameten

for plantain

cubnn.

~U)lutll)lI.

0'"

~

0

0.14 ,--------------------------,

OO~

0005 0035 0015 0" 0 0025 003 0.01

y = 0.0786x + 0.0112 R2 = 0.9671

012

Y= 0.1578x + 0.0611 R2 = 0.0061

0.1

008

006

00'

0.02

oos

0.1

0.15

o.~

0.25

0.3

0.35

0.4

for cow

hair" on

0.45

o

used tyre > cow hair>

reference

surface area available.

industrial

active carbon>

then the order of surface

area

cow hoof Least surface area

Largest surface area

The amount of K vah~e which is a constant related to the energy of adsorption indicates whether the adsorbent will be effective at low solution concentration. Thus. the small values of? .1. 7.0.6.1. and 6.0 (llM) of used tyre, cow hair. plantain peel and industrial active carbon types respectively are effective adsorbent at low solution concentrations. These values conform with the order of K values 01'0.5 to 4(~lM) reported by Morris el 01 (1962) for adsorption of alkyl benzene sulphonate detergents by activated carbon. The Xm value of 16.4~lmol/g for cow hoof carbon is too small that the adsorbent might be ineffective. This may account for the scattered plotted points for the cow hoof carbon type (and the attendant low coefficient of multiple determination of 0.0061 (Fig. 4). The variation of I/X against IICr was also subjected to statistical evaluation by determining the values of coefficient of multiple determination (R2). All the carbon types had values ranging from 0.9266 to 0.9871. They are all higher than that of the reference industrial active carbon (R2 = 0.6631) with the exception of cow hoof carbon. These values of R' . greater than 0.9, therefore support the linear variability of 1/X with IICr. The experimental results of cow hoof carbon type can therefore be regarded as been scattered with no definite pattern of variation. The negative values obtained for adsorption density in respect of cow hoof do not correspond to real situation. These values are therefore discarded and not use lor further calculation. These values are·only noted here lor information sake. There may be release of impurities from the cO'v hoof carbon medium into the solution. which could probably account for these negative \·alues. G.!. Brown (1977) reported that there are cases whereby adsorbent could be nuisance in that the adsorbent adds impurities or give false quantitative result. Further work on the cow hoof carbon type analysis will be necessary to determine precisely which component of the cow hoof carbon is responsible lor this behavior. However it is not unlikely thal the substance being released into the solution could also be adsorbing at the same wavelength as methylene blue. It is of interest to note that some of the carbon types exhibited the Langmuir behaviour in that a maximum value of adsorption density was obtained as indicated by the carbon types when their adsorption density. X is plotted against their residual concentrations: (Cr) respectively. In agreement with G. !. Brown (1977) the precise mechanism of adsorption from solution is not known but there could be a limit to the adsorption by a given mass of adsorbent. Adsorption from solution may also probably continue until a unimolecular layer is built up. However at low concentrations the isotherm form by this carbon types are assumed at certain point along the isotherm to form a monolayer coverage approaching completion. In line with Narasimha Rao el al (1964) and Fomalt el al (1963). it could be suggested that the raw material from which the carbon types were di fferently produced as well as the reference industrial active carbon determines the adsorptive capacity of the carbon types. Since the appl icability of activated carbon is dependent upon its adsorptive properties. the findings in this study may suggest that tyre. unripe plantain peel and cow hair carbon types could be alternative source of activated carbon that is needed by many industries.

REFERENCES Adediran.

G. O. and Nwosu. F. O. (1996). Some Freundlich Adsorption Pararmeter of Activated produced from Local Materials. Journal of Chemical Society of Nigeria 21 :28-32.

Brown, G. I. (1977). Introduction to physical chemistry S.I. Edition. Limited London.

1081

6th

Impression p. 495-498.

Carbon

Longman Group

G. O. Adediran

Ilrmvning.

(;, ( I')72). New Water-clean

'I.

el al

up Roles for Powdered Activated Carbon; Chem. Eng. vol. 79 Number

p ..1(I.

(iilcs, C. II, Smith, D" Huitson, A. (1974). General Treatment J ('III/Ilid In/erface Science 47:455.

and Classification

Klitanov

I, 1', and Udarov, B. E. (1965). Zinc Chloride 'I: 112-114.

l.angllluir

I. (19\ R). Adsorption