adsorption of dodecylbenzenesulfonates by soil colloids and influence of soil colloids on their...

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This article was downloaded by: [Flinders University of South Australia] On: 06 October 2014, At: 23:57 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK Soil Science and Plant Nutrition Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/tssp20 Adsorption of dodecylbenzenesulfonates by soil colloids and influence of soil colloids on their degradation Katsuhiro Inoue a , Kazum Kaneko a & Minoru Yoshida a a Faculty of Agriculture , Iwate University , Morioka , Japan Published online: 29 Mar 2012. To cite this article: Katsuhiro Inoue , Kazum Kaneko & Minoru Yoshida (1978) Adsorption of dodecylbenzenesulfonates by soil colloids and influence of soil colloids on their degradation, Soil Science and Plant Nutrition, 24:1, 91-102, DOI: 10.1080/00380768.1978.10433082 To link to this article: http://dx.doi.org/10.1080/00380768.1978.10433082 PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://www.tandfonline.com/ page/terms-and-conditions

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Page 1: Adsorption of dodecylbenzenesulfonates by soil colloids and influence of soil colloids on their degradation

This article was downloaded by: [Flinders University of South Australia]On: 06 October 2014, At: 23:57Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK

Soil Science and Plant NutritionPublication details, including instructions for authors andsubscription information:http://www.tandfonline.com/loi/tssp20

Adsorption ofdodecylbenzenesulfonates bysoil colloids and influence of soilcolloids on their degradationKatsuhiro Inoue a , Kazum Kaneko a & Minoru Yoshida aa Faculty of Agriculture , Iwate University , Morioka , JapanPublished online: 29 Mar 2012.

To cite this article: Katsuhiro Inoue , Kazum Kaneko & Minoru Yoshida (1978) Adsorption ofdodecylbenzenesulfonates by soil colloids and influence of soil colloids on their degradation,Soil Science and Plant Nutrition, 24:1, 91-102, DOI: 10.1080/00380768.1978.10433082

To link to this article: http://dx.doi.org/10.1080/00380768.1978.10433082

PLEASE SCROLL DOWN FOR ARTICLE

Taylor & Francis makes every effort to ensure the accuracy of all the information(the “Content”) contained in the publications on our platform. However, Taylor& Francis, our agents, and our licensors make no representations or warrantieswhatsoever as to the accuracy, completeness, or suitability for any purpose of theContent. Any opinions and views expressed in this publication are the opinions andviews of the authors, and are not the views of or endorsed by Taylor & Francis. Theaccuracy of the Content should not be relied upon and should be independentlyverified with primary sources of information. Taylor and Francis shall not be liablefor any losses, actions, claims, proceedings, demands, costs, expenses, damages,and other liabilities whatsoever or howsoever caused arising directly or indirectly inconnection with, in relation to or arising out of the use of the Content.

This article may be used for research, teaching, and private study purposes. Anysubstantial or systematic reproduction, redistribution, reselling, loan, sub-licensing,systematic supply, or distribution in any form to anyone is expressly forbidden.Terms & Conditions of access and use can be found at http://www.tandfonline.com/page/terms-and-conditions

Page 2: Adsorption of dodecylbenzenesulfonates by soil colloids and influence of soil colloids on their degradation

Soil Sci. Plant Nutr., 24 (1), 91-102, 1978

ADSORPTION OF DODECYLBENZENESULFONATES BY SOIL COLLOIDS AND INFLUENCE OF SOIL

COLLOIDS ON THEIR DEGRADATION

Katsuhiro INOUE, Kazumi KANEKO,· and Minoru YOSHIDA

Faculty of Agriculture. Iwate University. Morioka. Japan

Received July 12, 1977

In order to elucidate the behavior of surfactants in soil ecosystems, the mechanism involved in the reaction of dodecylbenzenesulfonates (ABS and LAS) with soil colloids was studied in 19 soils. Soil colloids, especially sesquioxides, were capable of adsorbing considerable quanti­ties of dodecylbenzenesulfonates. ABS adsorption on soils was strongly affected by pH, and was scarecely affected by Cl- but appreciably by SO,I- and H,PO,-. ABS was adsorbed by the ligand exchange on soil colloids. ABS adsorption on clay surfaces follows the Langmuir isotherm. However, "intermolecular associations" occurred with increasing ABS concentra­tion. Within certain levels of adsorption, ABS-c1ay complex became hydrophobic and floated to the liquid surface. The degradation of ABS was depressed by the addition of soil, while a difference among soils was slight. On the o~her hand, LAS degradation rate differed from one another depending upon the soil. LAS adsorbed on soils containing large amounts of aIlo­phane and/or sesquioxides was partially protected from microbial degradation. Additional Index Words: dodecylbenzenesulfonate, Langmuir adsorption isotherm, flotation etrect, ligand exchange.

In addition to the variety of environmental pollutions caused by organic pesticides and heavy metals, the deterioration of river- and sea-water caused a social problem in Japan owing to drainages which originated in the mining industry and the city sewage.

Surfactants have been utilized in a wide variety as synthetic detergents, emulsifiers, and spreading agents in the past one and a half decades. Nowadays more than 600,000 tons of surfactants are produced every year in Japan and anionic detergents account to about 70% of all surfactants. Especially, synthetic detergents usually contain significant amounts of tripolyphosphate as a builder. The pollution and the eutro­phication of irrigation water, lakes, and marshes attributed to detergents resulted. Dodecylbenzenesulfonates, anionic surfactants common in detergents, enter soils and water systems through waste disposal. Underground- and service-water were also contaminated with dodecylbenzenesulfonates (6).

It has become apparent that ABS severely inhibits root elongation in the rice plant at the level of 5 to 20 ppm and deteriorates the quality of rice (11). From radioauto­graphs using 35S-LAS, YOSHINO (14) indicated the incorporation of organic 3SS-com-

• Present address: Institute for Technical Research, Fujita Kogyo Co., Ltd., Yokohama, Japan. Ql

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92 K. INOUE, K. KANEKO, and M. YOSHIDA

pounds into Cucumis sativus L., Brassica campestris L., Triticum aestivum L., Oryza sativa L., and Zea Mays L., especially into their roots.

LAW and KUNZE (9) reported that cationic surfactants were greatly adsorbed on the surfaces of montmorillonite and kaolinite through ionic bonding, and nonionic surfactants were adsorbed by hydrogen bonding of polar active groups to oxygen rich clay surfaces, but anionics were only slightly adsorbed. The importance of the soil clay, especially montmorillonite, sesquioxide, and organic matter contents in LAS adsorption was suggested by KRISHNA et al. (8). The effect of salt impurities on ABS adsorption on montmorillonite was investigated by CLEMENTZ and ROBBINS (1). Further RENEAU and PETIRY (12) studied the movement of methylene blue active substances from septic tank effluent through the coastal plain soils and concluded that soils were capable of adsorbing large quantities of LAS.

However, limited information is available on the behavior of surfactants in soil ecosystems. The purpose of the present study is to investigate the mechanism involved in the reaction of dodecylbenzenesulfonates with soil colloids and to clarify the influence of soil colloids on the degradation of dodecylbenzenesulfonates.

MATERIALS AND METHODS

Soils. Nineteen soil samples various in content of organic matter and in kind of clay minerals were used in the present study. Tables 1 and 2 give a brief description of soils. They were air-dried and passed through a 20-mesh sieve.

Clays. The montmorillonitic, kaolinic, and allophanic clays less than 2 Jl in effective diameter were prepared from soils, W-116, MK-2, K-l, and 510, respectively. A part of the clays were treated with Na-citrate-bicarbonate-dithionite (10). The clays were made into homonioic Na-clays.

Goethite. Goethite was prepared by hydrolyzing ferric sulfate solution at 80°C for 7 hr (7). Electron micrographs of an artificial goethite showed that most crytals were acicular.

Clays and an artificial goethite were washed successively with water, ethanol, and acetone, air-dried and passed through a ISO-mesh sieve.

Dodecylbenzenesu/fonates. Sodium dodecylbenzenesu!fonates used were obtained in two forms from Tokyo Kasei Co. One is the branched-chain alkylbenzenesulfonate (Na-ABS, 100%), and the other is the linear alkylbenzenesulfonate (Na-LAS, 60% in water). Fresh aqueous standard solutions of these surfactants were prepared with distilled water.

Determination of dodecylbenzenesulJonates. Dodecylbenzenesulfonates were deter. mined colorimetrically by using the methylene blue method with a minor modification (3). The method employed is based on the formation of dodecylbenzenesulfonate salts of the cationic dye, methylene blue.

Adsorption experiment. Prior to adsorption experiments, the rate of ABS adsorp. tion on soils was investigated as a preliminary experiment. Soils (2.0 g) were shaken

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Page 4: Adsorption of dodecylbenzenesulfonates by soil colloids and influence of soil colloids on their degradation

Abbreviation

K-l 905 510 KR SJ MK-2 W-116 KA S-l S-2 S-3 S-4 s-s S-6 S-7 S-8 S-9 S-10 S-11

Adsorption of Dodecylbenzenesulfonates by Soil Colloids

Table 1. Description of soil samples.

Source

Andosol, A, Koiwai, Iwate Weathered volcanic ash, B, Uemura, Kumamoto Andosol, B, Choyo, Kumamoto Andosol, A, Kuroishibaru, Kumamoto Aged paddy soil, A, Saijyo, Hiroshima Weathered granite, B, Mikawa, Aichi Weathered shale, B, Nakajyo, Nagano Tertiary, Kashii, Fukuoka Andosol, A, Minamiippongi, Iwate Weathered volcanic ash, BC, Choyo, Kumamoto Weathered volcanic ash, A, Kanda, Tottori Weathered volcanic ash, Minamiippongi, Iwate Weathered volcanic ash, A, Kaisawano, Iwate Aged paddy soil, A, Nyuzen, Toyama Weathered granite, A, Mikawa, Aichi Alluvium, A, Morioka, Iwate Alluvium, A, Higashitokuta, Iwate Allubium, A, Saga, Saga Tertiary, B, Kato, Fukuoka

Major cIayl) mineral

Imog, Allo Allo,lmog Allo Allo, Ver Kn,I1I Kn, III Mt,I1I Mt Allo,lmog Allo Intg Intg Intg Kn, ChI Kn, III Kn, Ver, III Mt,Kn Mt Mt

93

11 Allo, allophanej Imog, imogolitej Intg, intergradesj Kn, kaolinej III, illite; Ver, vermiculite; Mt, montmorillonite; ChI, chlorite.

with 40 ml of 100 ppm solution for various periods of time. After centrifuging at 10,000 rpm for 10 min, ABS in the supernatant obtained was determined. The amount of ABS adsorbed was calculated from difference in concentration between reference and equilibrium solutions. The result obtained showed that an adsorption equilib­rium was established in the employed systems within 1 hr. According to this result, the shaking of reaction systems was done for 2 hr in every adsorption experiment.

Forty milliliters of dodecylbenzenesulfonates ranging in concentration from 1 to 1,000 ppm were added to 2.0 g of the soil or 200 mg of the clay in a beaker. The sus­pensions were adjusted to appropriate pH with dilute NaOH or H2SO, solution, and transferred into a polyethylene bottle and subsequently placed on an end-over-end shaker for 2 hr at 25°C. Centrifugation was carried out to obtain a clear supernatant for the estimation of pH and the determination of dodecylbenzenesulfonates. The amount of adsorption was expressed on the basis of the weight of the oven dried soil or clay.

RESULTS AND DISCUSSION

Adsorption of dodecylbenzenesulJonates on soils As shown in Table 2, the amount of dodecylbenzenesulfonates adsorbed on volcanic

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Page 5: Adsorption of dodecylbenzenesulfonates by soil colloids and influence of soil colloids on their degradation

Tab

le 2

. S

oil

prop

erti

es a

nd t

he a

mou

nt o

f do

decy

lben

zene

sulf

onat

es a

dsor

bed

on

soi

ls.

Ads

orbe

d2)

Fre

e ox

ide

Pho

spho

r A

bbre

vi-

pH

C

lay

Hum

us

CE

C

atio

nll

AB

S L

AS

(H

aO)

(X)

(X)

(me/

l00g

) F

eaO

. A

lsO

, R

IO.

abso

rpti

on

Tex

ture

J

pHS)

(p

mol

/g)

(mm

ol/g

) co

effi

cien

t

K-l

3.

6 4.

4 5

.9

29

9.2

15.5

0.

49

0.84

I.

33

2,25

0 L

iC

0.5

905

4.8

5.0

6.

0 29

2.

2 7.

8 0.

24

0.80

1.

04

2,11

0 S

C

0.5

510

3.5

4.1

5.8

19

4.9

7.2

0.43

0.

97

1.40

2,

170

SC

L

0.5

KR

4

.0

5.3

34

22.1

21

. 3

0.57

1.

10

1.67

2,

240

LiC

0.

5 S

J 1.

2 2.

0 5.

6 13

2

.0

8.8

0.07

0.

30

0.37

35

0 S

L

0.7

MK

-2

4.6

4. 7

4.

8 50

0.

3 8.

4 0.

53

0.35

0.

88

1,00

0 H

C

0.5

W-1

l6

0.8

1.5

6.8

24

0.4

25.6

0.

14

0.22

0.

36

1,08

0 S

CL

0.

2 K

A

0.7

1.5

5.3

82

0.1

57.5

0.

09

0.23

0.

32

1,29

0 H

C

0.2

5-1

1.9

3.1

5.9

20

11.3

26

.4

0.27

0.

98

1.2

S

2,11

0 C

L

0.6

5-2

0.3

6.4

3 0.

2 4.

2 0.

13

0.46

0.

59

1,21

0 L

S

0.3

S-3

3.2

4.7

24

14.8

16

.2

0.13

0.

49

0.62

2,

080

CL

0.

7 S

-4

0.9

6. 7

31

0.

5 12

.3

0.40

0.

44

0.84

1,

300

LiC

0.

2 s-

s 3.

5 4.

4 19

15

. I

22.4

0.

26

0.39

0.

65

1,36

0 C

L

1.5

S-6

0.6

5.6

6 0.

4 2.

4 0.

11

0.16

0.

27

240

LS

0.6

S-7

1.1

5.8

31

2.7

12.9

0.

33

0.22

0.

55

600

LiC

0.

6 80

8 2.

2 5

.4

19

4.9

9.8

0.13

0.

39

0.52

77

0 S

CL

O

.S

809

1.7

5.3

2S

3.1

24.5

0.

19

0.19

0.

38

1,01

0 C

L

0.6

8010

1.

1 2.

1 6.

0 53

1.

4 32

.5

0.07

0.

15

0.22

1,

090

HC

0.

5 80

11

1.6

4.8

30

0.2

19.1

0.

22

0.23

0.

45

1,11

0 L

iC

0.4

11 L

ess

than

0.0

2 pm

ol p

er g

ram

of

met

hyle

ne b

lue

acti

ve s

ubst

ance

s w

ere

cont

aine

d in

eac

h so

il a

nd

wer

e di

sreg

arde

d in

the

det

erm

inat

ion

of

the

amou

nt o

f do

decy

lben

zene

sulf

onat

es a

dsor

bed.

I) T

he a

mou

nt o

f dod

ecyl

benz

enes

ulfo

nate

s ad

ded

to s

oils

was

5.7

4 fo

r A

BS

and

5.99

p

mo

l pe

r gr

am s

oil

for

LA

S,

resp

ectiv

ely.

I)

Jp

H=

pH

(AB

S)-

pH

Oh

O}.

\0

""' ~ - Z 0 C sn ~ ~ Z

tr1 ~

5' '" ::s Q

.. ~ -< 0 en :r: a >

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Page 6: Adsorption of dodecylbenzenesulfonates by soil colloids and influence of soil colloids on their degradation

Adsorption of Dodecylbenzenesulfonates by Soil Colloids 95'

ash soils was larger than on non-volcanic soils. And it seems that the adsorption of dodecylbenzenesulfonates is larger on fine texture soils than on coarse ones. Both ABS and LAS would be retained on soils by the same adsorption mechanism. Corre­lation coefficients between the amount of adsorbed dodecylbenzenesulfonates and each soil's properties are given in Table 3. The adsorption of dodecylbenzenesulfonates was related to the content of free sesquioxides and approximately the phosphor absorp­tion coefficient. These relationships suggest that sesquioxides are the most important soil component acting on the adsorption of dodecylbenzenesulfonates on soils. The organic matter content was not so related to the adsorption rate of dodecylbenzene­sulfonates (Table 3). Clay minerals are also a surface active colloidal constituent acting on the adsorption, and are somewhat capable of adsorbing dodecylbenzene­sulfonates. However, the clay content gave a small correlation coefficient to their adsorption. The major clay mineral in examined soils is not always the same (Table 1). The adsorption of dodecylbenzenesulfonates by the clay would differ with different clay minerals. It may be one of the causes which decreased the significance of the correlation between the amount of surfactants adsorbed and the clay content.

KRISHNA et al. (8) reported that LAS adsorption correlated significantly with the organic matter content and the P-fixing capacity of soils, and indicated that a poor relationship existed between LAS adsorption-rate and amounts of Fe, AI, or Fe + Al extracted with citric acid. However, the importance of iron and aluminum oxides in the retention of dodecylbenzenesulfonates was indicated by the highly significant correlation in the present study. Thus it is apparent that sesquioxides in soils influence the adsorption of dodecylbenzenesulfonates. There was less correlation between the rate of adsorption and the other soil characteristics studied such as pH, clay, and organic matter contents (Table 3).

The contribution of organic matter, sesquioxides, and clay minerals to ABS adsorp­tion was investigated through H20 2 and Na-citrate-bicarbonate-dithionite treatments (Table 4). The decline of adsorption rates with removal of organic matter may be

Table 3. Correlation coefficient between soil properties and the amount of ABS or LAS adsorbed on soils.

Soil property Correlation Coefficient (r)

pH(H.O) Clay content Organic matter content Free FeaO, content Free AI.O, content RIO. content CEC Phosphor absorption coefficient

ABS (N=19)

-0.465* 0.065 0.527* 0.639** 0.622** 0.689**

-0.230 0.612**

• significant at 5% level; •• significant at 1% level.

LAS (N=10)

-0.326 -0.253

0.306 0.815** 0.644* 0.780**

-0.658* 0.583

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Page 7: Adsorption of dodecylbenzenesulfonates by soil colloids and influence of soil colloids on their degradation

96

Soil

K-l S10 KR

K. INOUE, K. KANEKO, and M. YOSHIDA

Table 4. Effect of the removal of the organic matter and the sesquioxide on ABS adsorption at pH S.S.

The amount of ABS adsorbed on soilsll (IImol!, soil)

Original soil

4.S9 3.82 4.42

HaO. treated soil

4.30 4.07 4.S6

H,O. treated and deferrated soil

MK-2 4.S1 4.28

1. 12 1. 78 1.43 1.06

11 The amount of ABS added is S.74 pmol per g soil.

attributed to the decrease of anionic adsorption-sites formerly associated with it, while the increase could be explained through ABS adsorption on active iron and aluminum compounds released through the oxidation of organic chelates.

On the other hand, 60 to 70% of their ABS adsorbabilities was lost by following a dithionite treatment. It is suggested that sesquioxides influence the adsorption of dodecylbenzenesulfonates. This result is in accordance with the highly significant correlation between the amount of dodecylbenzenesulfonates adsorbed and the content of sesquioxides.

Effect of pH, anion, ionic strength on the adsorption of ABS The effect of pH was studied by using seven soils and an artificial goethite. From

pH-adsorption rate curves shown in Fig. 1, it appeared that ABS adsorption on soils was strongly affected by pH and decreased with increasing pH in every soil. Changes in the rate of adsorption under acidic conditions may be based on the increase of the positive charge on colloidal surfaces.

Two soils, 510 and MK·2, were used in order to study the effect of anion and ionic

g 80

! :: 60 g .~ 40 o III ... <

20

B

3 4 5 6 7 pH In luperDltantl

Fig. 1. Effect of pH on the adsorption of ABS on soils. A, volcanic ash soils; B, non-volcanic ash soils.

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Adsorption of Dodecylbenzenesulfonates by Soil Colloids 97

Table S. Effect of anion and ionic strength on ABS adsorption.

510 MK-2

Added salt Concentration Supernatant Adsorbed Supernatant Adsorbed (mM) ABS ABS . pH

(pmol/g) pH (pmol/g)

Adsorption experimentU

No salt 6.3 3.46 5.3 4.39 1 6.3 3.32 5.2 4.37

NaCI 10 6.1 3.28 4.9 4.56 100 6.0 3.35 4.S 4.49

1 6.4 2.02 S.3 3.S7 NaISO, 10 6.4 1.95 4.9 2.92

100 6.3 3.00 4.6 3.47 1 6.7 2.11 S.2 3.62

NaH.PO, 10 6.7 0.98 4.7 2.99 100 5.7 1. 74 4.4 3.06

Desorption experiment"

After washing 2.23 3.71 with water

1) The amount of ABS added is 5.74 pmol per g soil. ., The soil and solution remaining in the centrifuge tube under the previous adsorption experiment (in the case of no salt) were weighed and 40 ml of distilled water were added and the system again allowed to equilibrate on the shaker. This procedure was repeated three times in all. The amount of ABS in the solution remaining in the centrifuge tube after the adsorption experiment was subtracted in the calculation of the amount of desorption.

strength on ABS adsorption. Table 5 shows the adsorption of ABS on soils in the presence of salt ranging from 1 to 100 mM. Chlorine ion did not affect ABS adsorp­tion, but SO,,- or HaPO, - did considerable. The relative order of the influence of anion on ABS adsorption was in the order of HaPO,->SO,a->Cl-. Phosphate or sulfonate is chemically adsorbed on soil colloidal surfaces. Therefore, ABS anion may compete with HaPO, - or SO,I- to occupy adsorption sites on the colloidal surface. By addition of SO,2-, the amount of ABS adsorbed was depressed one-half to two­thirds of its initial rate. On the other hand, the amount of ABS adsorbed on the allo­phanic soil was depressed one-forth to one-half by the presence of HaPO, - .

Fifteen per cent of ABS was desorbed by washing with water three times from MK-2-soil, and 36% from 510-soiI. In general, anions are desorbed only by com­petitors which can occupy the site already occupied. ABS adsorbed chemically on soils is never desorbed by water. Therefore the amount of ABS desorbed by washing with water would correspond to the amount of physical adsorption (intermolecular associations). These results show that Cl- does not inhibit the formation of inter­molecular associations but 80,2- or H2PO,- does at the level of 1 to 10 mM. The enhanced adsorption of ABS at the presence of 100 mM 80,2- or HaPO,-, however, may be dependent on the decline of pH in suspensions or the increase of the chemical

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98 K. INOUE, K. KANEKO, and M. YOSHIDA

potential of the surfactant in solution and the collapse of the electrical double layer around clay particles (1).

On the basis of these data, ABS (or LAS) may be adsorbed on colloidal surfaces by the ligand exchange proposed by HINGSTON et al. (4, 5) similar to phosphate or selenite adsorption. The exchange of ABS (or LAS) with aquo groups decreases the surface positive charge according to Eq. 1, whereas the exchange with hydroxy groups does not alter the surface charge, but does alter the pH of the suspension according to Eq.2.

> I ~OH.)+ > I ~ABS (or LAS»)O M +ABS- (or LAS-). I M +11.0 I HI I HI

(1)

> I ~OH )0 > I ~ABS (or LAS)]O M +ABS- (or LAS-) , • M +OH-I HI I H.

(2)

In the previous experiment, the pH values of the supernatant were raised by 0.2 to 1.5 as J pH in every adsorption process (see Table 2). The rise of pH values indicates that hydroxy groups are released from the colloidal sites by the ligand exchange with ABS.

Adsorption isotherm at constant pH Adsorption isotherms of ABS in four soils and an artificial goethite and their

Langmuir plots are shown in Figs. 2, 3, and 4, respectively. The plotting was made according to the adsorption isotherm:

C/X==l/Xm K+C/X.

where C is the ABS concentration in mg per liter at equilibrium, X, the amount of ABS adsorbed in pmol per g clay, X til, the maximum amount of ABS adsorption in pmol

500r----------------~~--------------------~ ";. ~ 400

"" --'0 ! 300

tJ) I:!l < il J> .. o <II

'" <

GT

MK-2

600 800

Equilibrium concentration (ppm)

Fig. 2. Adsorption isotherms of ADS on non-deferrated clays. pH condition: K-l, S.l; SIO, SA; OT, S.B; MK-2, S.6; W-1l6, S.3.

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Page 10: Adsorption of dodecylbenzenesulfonates by soil colloids and influence of soil colloids on their degradation

Adsorption of Dodecylbenzenesulfonates by Soil Colloids

,O~------------------, I

8

6

)(

...... u

4

1

400 600 800 1000 C

400

~ .. .. 300 ~ '0 E ~ Vl 200 III < 1l ~ 100 g '" <

Equilibrium concentration (ppm)

99

600

Fig. 3. Linear Langmuir plot of the data of Fig. 2 used to calculate X ••

Fig. 4. Adsorption isotherms of ABS on deferrated clays. pH condition: S10, 4.7; K-l, S.O; MK-2, S.4; W-116, S.S.

Table 6. Adsorption maxima calculated from Langmuir plots of adsorption data.

Clay

K-l S10 MK-2 W-116 GTlI

1) GT: Artificial goethite.

Adsorption maximum (pmol/g clay)

Non-deferrated

521 422 127

15 476

Deferrated

28 SO 34 7

per g clay, and K is a constant relating to the strength of adsorption. If the bonding energy is approximately equal, the plot of elx against e will give a straight line, the slope of which is 1 I X m and the intercept is slopel K.

The Langmuir plots recalculated from the data in Fig. 2 resulted in a straight line indicating monolayer coverage by ABS (Fig. 3). The adsorption maxima calculated from Langmuir plots of adsorption data are shown in Table 6. In non-deferrated samples. the adsorption maximum for allophanic clays and an artificial goethite ranged 422 to 521 pmol per g clay. . However, the maximum for the montmorillonitic clay was remarkably small, the kaolinic clay, which contained an appreciable amount of ses­quioxides, showed an intermediate adsorption.

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Page 11: Adsorption of dodecylbenzenesulfonates by soil colloids and influence of soil colloids on their degradation

100 K. INOUE, K. KANEKO, and M. YOSHIDA

On the other hand, the adsorption isotherms in deferrated clays were different from those in the non-deferrated ones (Fig. 4), and the adsorption maxima in the for­mer were extremely small. This result suggests that the components dissolved with Na-citrate-bicarbonate-dithionite participate in ABS adsorption.

The allophanic soil adsorbed significantly larger quantities of ABS than the mont­morillonitic or the kaolinic soil. The relatively greater adsorption by MK-2-soil is probably due to the higher contents of clay and Fe20a (Table 2). RENEAU and PEnRy (12) reported the linear relationship between the amount of LAS adsorbed and the concentration of equilibrating solution. A similar relationship was reported for ABS adsorption by FINK et al. (2). However, the adsorption process is more complex and occurs in two distinct steps. In dilute solution, the adsorption of ABS on deferrated clays followed the Langmuir isotherm, reaching a maximum amount, while the enhanced adsorption occurred with increasing ABS concentration (Fig. 4). This enhanced ad­sorption can be attributed to micelle formation at the surface. Similarly in non­deferrated samples, intermolecular associations due to van der Waals force would be formed in higher concentrations of ABS. This is in agreement with the observation of CLEMENTZ and ROBBINS (1), who studied the intermolecular association of a com­mercial grade ABS on Na-montmorillonite. This intermolecular association will be supported by a following flotation effect.

Flotation effects The flotation test was carried out as follows: Non-deferrated Na-clay or defer­

rated Na-clays separated from 510-, MK-2-, and W-1l6-soils were dispersed by means of ultra sonic waves. One milliliter of 0.1% clay suspensions were transferred into test tubes and one ml of ABS solution in concentration from 50 to 1,000 ppm and 1 drop of 0.005 N H2SO, were added. After shaking for a while. the mixture was allowed to stand and then the flotation effect was observed.

The obtained result is shown in Table 7. Within 72 to 287 pmol of ABS adsorbed per g clay, the complex became hydrophobic and floated to the surface. The flotation is caused by the colloidal surface becoming partially hydrophobic. This flotation effect disappeared on further adsorption. It is suggested that adsorbed ABS anions are oriented with their hydrophobic long chain ends directed towards the solution ,

Clayll

S10 (deferrated) MK-2 W-U6 (deferrated)

o

Table 7. Flotation effects.

The amount of ABS added into clay suspensions (pmol/g clay)

72 144 287 717 1.435

+ +

++ +++

± ++ ±

11 Clay samples were saturated with the homoionic Na-ion. +++, very remarkable; ++:­remarkable; +, medium; ±. slight; -. none.

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Page 12: Adsorption of dodecylbenzenesulfonates by soil colloids and influence of soil colloids on their degradation

Adsorption of Dodecylbenzenesulfonates by Soil Colloids 101

sulfonyl groups being strongly bound to positive sites on the colloidal surface. At high levels of adsorption, some ABS anions are orientated in the opposite

direction by van der Waals interaction with the first adsorption layer and the surface reverts to its hydrophillic nature. WATSON et al. (13) observed similar flotation effect for the adsorption of the herbicide 2,4-D on goethite. This flotation phenomenon would be closely associated with the formation of micelle depending upon intermolec­ular associations.

Influence of soil colloids on the degradation of dodecylbenzenesulJonates One gram of each soil and 35 ml of 50 ppm ABS or LAS solution were placed

in a 250 ml polyethylene bottle and were shaken for 2 hours at 25°C. Then 5 ml of the supernatant separated from the sewage in Morioka City was inoculated. Methylene blue active substances were contained at 12.7 ppm in this sewage. After incubating in dark for 2, 4, 8, 16, and 30 days at 25°C, the mixture was centrifuged, and the dodecyl­benzenesulfonates both in the supernatant and in the soil were determined. Dodecyl­benzenesulfonates adsorbed on soils were extracted with 40 ml of 0.01 N NaOH six times from the soils 510 and MK-2, while twice from KA-soil. The recovery of the dodecylbenzenesulfonates ranged from 99 to 108% for ABS and from 87 to 94% for LAS, respectively.

Figure 5 shows the effect of soil colloids on the degradation of dodecylbenzeoesul­fonates. Soils slowed down the degradation-rate of ABS and LAS. About 30% of the added ABS was decomposed after 16 days incubation. Its degradation was de­pressed by the addition of the soils, while a difference among soils could oot be readily detected. On the other hand, LAS was decomposed rapidly in comparison with ABS and the rate of LAS degradation was about 70% after 16 days incubation. As the LAS degradation-rate was considerably affected by the existence of 510 and MK-2 soils,

g 100~r-----------------------------------------------~ i .. ~; ABS ~ .

1 : o;i.<"<,~T>·-<"'·:~:::~.:::: .. :::::::::::::::::::::::·: ~ 40 ••••• •.•••• LAS

\ :0 •...... ,::.::::::::::,.:-.. •• , .....•••... __ ...•

ti .......... , ~ 00 2 4 16 30

Incubated period (days)

Fig. 5. Influence of soils on the degradation of ABS and LAS. 0,510; A, MK-2; A, KA; ., control. Solid lines, ABS; dotted lines, LAS.

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Page 13: Adsorption of dodecylbenzenesulfonates by soil colloids and influence of soil colloids on their degradation

102 K. INOUE, K. KANEKO, and M. YOSHIDA

LAS was partially protected against the degradation in these soils. Soil KA, however. did not protect and more than 90% of LAS was degraded after incubating for a month. By addition of 510 and MK-2 soils, which contain large amounts of allophane and/or sesquioxides, LAS degradation held constant at 40 to 50%. When the amount of remaining dodecylbenzenesulfonates was expressed logarithmically, the remaining amounts decreased rectilinearly according to the lapse of the incubation period. This suggests that the dodecylbenzenesulfonates were microbially degraded.

REFERENCES

1) CLEMENTZ, D.M. and ROBBINS, J.L., Adsorption of dodecylbenzene sulfonate on Na+-montmoril_ lonite: Effect of salt impurities, Soil Sci. Soc. Am. J., 40,663-665 (1976)

2) FINK, D.H., THOMAS, O.W., and MEYER, W.J., Adsorption of anionic detergents by soils, J. Water Pol/ut. Control Fed., 42, 276-281 (1970)

3) HAGIWARA, K., Kogai Bunseki Shishin, Vol. 5, Kyoritsu-Shuppan, Tokyo, 1972. pp. 68-81 (in Japanese)

4) HrNGSTON, P.J., ATKINSON, R.J., POSNER, A.M., and QUIRK, J.P., Specific adsorption of anions • Nature, 215, 1459-1461 (1967)

5) HINGSTON, F.J., AUrNSON, R.J., POSNER, A.M., and QUIRK, J.P., Specific adsorption of anions on goethite, Trans. 9th Int. Congr. Soil Sci. (Adelaide. Australia), 1,669-678 (1968)

6) KOBAYASHI, I., On serious situation and countermeasure of environmental pollution by synthetic cleansers in Japan, J. Jap. Sci., 1, 516-522 (1974) (in Japanese)

7) KOJIMA, M., On the colar of the artificial ferric oxide and its hydrate (Part 1). On the colar of the artificial goethite, J. Sci. Soil Manure. Japan, 30,29-33 (1959) (in Japanese)

8) KRISHNA, M., VOLK, G.S.R., and JACKSON, M.L, Soil adsorption of linear alkylate sulfonate Soil Sci. Soc. Am. Proc., 30,685-688 (1966) •

9) LAW, J.P., Jr. and KUNZE, G.W., Reaction of surractants with montmorillonite: Adsorption mechanisms, Soil Sci. Soc. Am. Proc., 30,321-327 (1966)

10) MEHRA, O.P. and JACKSON, M.L., Iron oxide removal from soils and clays by a dithionite-citrate system butTered with sodium bicarbonate, ClaYI Clay Miner. Proc. 7th Can/., Pergamon Press, London, 1960.pp. 317-327

11) THE MINISTRY OF AGRICULTURE AND FORESTRY, THE AGRICULTURAL LAND DIVISION, NOgyo to KOgai, Chikyu-Shuppan, Tokyo, 1969. pp. 204-205 (in Japanese)

12) RENEAU, R.B., Jr. and PETTRY, D.E., Movement of methylene blue active substances from septic tank effluent through two coastal plain soils, J. Environ. Qual., 4, 370-375 (1975)

13) WATSON, J.R., POSNER, A.M., and QUIRK, J.P., Adsorption of the herbicide 2,4·0 on goethite J. Soil Sci .• 14, 503-511 (1973) •

14) YOSHINO, M., Behavior of surfactants in soils and plants, J. Agr/c. SCi., 19, 63-67 (1974) (in Japanese)

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