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THE REACTIONS AND BECHANISI�'fS OF INORGANIC

PHOSP.Hl.1.TE SORPTION BY SOILS

11. thesis presented in pn.rtinl fulfilnent of

the requirenents for the degree of Doctor of

Philosophy in Soil Science nt N�ssey University

John_Christophor Ryden

1975.

ii

Ab s tl'fl. et

A revie1-r of the li terc.turo relating to the reactions c.nd

nechnnisns involv0d in the sorption of inorgnnic ph0sph.".te (r) by

soils and soil conponents sug-gested scvo rl'. l topics for further resenrch,

the rosul ts 1'.11d interpretn tions of vrhich arc presented in this t hesi s.

Soils 1-rhich contrn��ocl in c ooponcnt s and properties considered to be

inport�nt in P sor ption sorbod between 210 nnd 3350 pG P/g during 40 hr fron 0.1 M }hCl nt a fin.'ll I' conccntr::.tion of 10 pg P/nlo Contrnsting

soils provided a nore rclio.blo basis for the intorproto.tion of do.tn

obtained in invostigntions of the rec.ctions nnd nochnnisQS of P sorption

by soils, Sorption of P was described by four fi rst-order reactions

for each soilo The ro.te constant for a particulc.r ro.::1.ction wc.s c.lso

sioilnr for onch soil, ioplyiJ:1G th..'l t the snne series of rec.ct ions were involved in P sorptiono The d ecronse in extrn�tabil ity o.nd isotopic -

oxch..".nc;eabiJ.i ty of so rbc::d P 1-ri t h increo_sing tir::.c, follO'I·i:i..ng P n.dui tion; coupled vlith incro.2sed ro c ovv ry of P by citrnto-dithionite-bicnrbcmate

extr::tetion indico.tecl th.:d; J.dsorption -vms follevmd by nb sorption .

Elininnticn of the diffo r :,ncos between the o.nounts of P sorbod :fron

vo.:::-ious support ncdia clurir.JG 1).0 hr, when nn estion.te of the equilibriun condit ion vTt:.S !1ade, pointed t o the inplication s of tine-dependent sorption in the in��erprotction of P sorption do.ta. Virtunlly ccnplcte roplaceab-

ili ty by K of Co. ronmrod f:.·o:J solution in respons0 to P sorption vm.s ob-

to.inodo Rotontion of Cn. to b."..lnnco the incrO['.SOd nogntivo cmrge·nris-

ing froo P so rp tion , and not the procipi tntion of n c.�lc iuo phosphnte ,

is indico.todp Tine-dependent sorption nffected si�nificnntly the in­

terprob.tion of P so rption data using the Lnngnuir equntion.,

equilibriuo dntf!., the P sorption isothern for each soil Has described

by three distinct h�nerruir oquntion 8 , onch corresponding to n pnrticul�r

P concentration rn.ne-;o or region ( 0 to 0.02, 0.08 to OoBO, and 1 .0 to

> 20 yg P/nJ. )o The sorption onorcy constant of a Lang.ouir equn-

tion corrosponding to n pnrticul.'lr region -vras very si;:1ilnr for each

soil nnd suggested sinilnr sorption oechnnisus for eo.ch so:i.lo ChD.rge

and pH relationships of P s orption by tlm soils nnd Fe gel dec.onstrnt­

ed t�'lt tlrroo distinct P sorption nechnnisns cnused the dovi.:J.tion of P sorption dntn froo n single Lo..ngr�uir equntion. �ne sane Dechnnisns

iii

vrere involved in P sorption by soils ru1d Fe gel. Dnt.:J. sur;gosted

tho.t tho nochnnisns involved the ligand exchange ronctions -on2+; - - 2-II2PO 4 ; -OH; H2Po!). , .::>.nd -OH; IfPO 4 o. t the hydrous-oxide surf nee.

Those !:::echnnis!:ls nro in o.ccord 1vi th the· three L::>.ngLmir so rption·

energy const.::>.nts obtninod for ench soiL The ren.ctions nnd nechnnisns

of P scrptior. estc.blished hnve i;:1por·tnnt inplic::,tions to the plnnt

nvcilt'.bili ty of soil nnd fertilizer P� rmcl provide o. bnsis for the

interprot.-:ttion of other P sor ption dnt:":o

iv

1\.cknouledgelilents

I 1'i"Ould like to exprass ny sincere th:cnks to

Prof. ICei th Syers for the close personnl cmd 1·JOrking relntionship

thrtt hns L1J.de the lnst four-o.nd-n.-half :yenrs, both in the U.S.A.

nnd New Zenlnnd, such rm enj oynble o.nd revro.rding exper ience.

Dic.nne for her pc'1rt.

v.n.s. vrho has sho-vm Be that it co.n vrork.

Also,

J . R . r�T. for the nuoerous o.nd pro ductive discussions 110 ha.ve had over the po.st year.

Dr. I!Jc.x Turner for his continuetl interest o.nd connonts

The folks in the lnb for puttinp: up vri th BG.

Tholno. for such po.tient typing.

University Grnnts Conoittec for financial support during this study.

Table of Contents

Abstract

Acknmvledgononts

Table of Contents . . .

List of Fi;"DU'CS • •

List of Tables

CHAPTER 1

REVIEW OF LITERATURE

1 .1 Introductio n • • • • • • 0

. . . . . . . . .

. . .

. . .

. . . .

1 . 2 Phosphntc Re tention Gcnernl Consider�t ions . . . . . .

1 .2 .1

1o2o2

The dovelopoe nt of P rete nt ion concepts . . . .

The Th�turc of P retent i o n . . . . . . . . .

1 .2 .2. 1

1 .2.2.2

The validi ty of precipi to.tiom and sorption c oncepts • . . • • • • • • • • • • • •

The tirce dGpcndence of P s orption

V'

ii

iv

V

X:

xiv

2

2

4

4

7

7

1 2

P sorpt ion surfac es in soils • • • • • • • • • • 13

Nature of the P s orption surfr..ce..... 13

Distribution of oxidGs and hydrous

oxides in soils • • • • • 0 • • • • • • • • • • • • 16

The Oxi de-Aqueous Interface • • • • • • • • • • • • • � 1 8

1 • 3� 1 Oxide struc ture and origin of chnree

Charge properties of the interface • •

• • •

. .

Aophoteri c behaviour and pH depend-ence of chr.. ree • • • . . • • • • . • • • • • • •• • •

Points of zero ch�rge for soil eo�

18

1 9

19

ponents and soils ................. 23

1.,6

vi

The electriccl double l1.yer at the interf.::tce 2 5

The Gouy-Chap1:::un nnd Stern nodels 25

Interetction of c ounterions vri th the

Porous intorfnce nodel • • • • • • • • • • !• 30

The Typo and rJiechnnisD of Phosphntc Sorption . . . . " " 3 1

Sorption type . . ... . . 3 2

Non-specific .::,ru:l s).X3cific sorption 32

Exporinontnl verific�tion of specific sorption . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

The nechnnisn of P sorption • • • • • • • • • • 36

pii nnd ch.'l.rge relc.tionships • • • • • • • • 37

The forn of P s orbed • • • • • • • • • • • • . • • 40

Interpretntion of Sorption Dato. • . . . . . . . . . . . . 41

1 • 501

1 .,5o3

1 .5 .. 4

The sorption isot}1ern • •

The Freundlich equo.tion •

The �·uJt;nuir eq_uc. tion • •

• • e • • • • •

. . . . . ..

• 0 • • 0 •

Dorivo.tion nnd test for data fit • . . .

The vc.:.lidi ty of o.pplyinc the h.'1ngnuir

4'f

44

45

4 5

equntion to P sorption . . . ........... ..,.. . 48

P sorption n.ncl desorption isothorns • • • • • • 49

1 .5 •. ')..,2

Application of the knc;:ru.ir cquntion to P sor-pt ion . . . . . . . . . . . . . . . . • . . . . . 49

Inplicntions of nultiple h.'1nermir rclr1tionships . . . . .. . . . . . . . . . . . . . . . .

The n.::tture and inplicntions of P de­sorption is otherns • • • • • • • • • •• • • • • • •

53

56

General Conclusions and Research Needs . . . . . . . . . 58

vii

CHAPTER 2

SOILS AI\lJ) SOIL PROPERT IES • • • • • • • • • • • • • • • • • • 62

Introduction . . . . . . . . . . .

Mnterinls nnd Methods • • . . . . . . . . . . .

Results and Discussion • • • • • • • • • • • • • • • •

CHAPTER 3

62

62

63

EXTENT AND ORIGIN OF TINE DEPENDENT PHOSPHATE S ORPTIOn BY SOILS 69

3.1

3.2

3 .3

Introduction • . . . • .

futerio..ls nnd MGthods • . .

Results . . . . . • . • . .

3.3 .1 Tine dependence of p sorption

3.3.2 F:ro.ctiom tion

Discussion • • • • • •

of

. .

sorbed

. . .

p . .

. • • . • .

• • • .

• • .

. . . . . .

.

. •

. •

. .

• . !'

. • •

. . .

Extent �nd nn turo of tine dependent P sorption

•

69

69

71

7 1

77 80

80

Ori8�n of tine dependent sorption • • • • • • • 81

Inplicntions of nn o..bsorption reo..ction • • • • • 82

CHArTER 4

CATION AND IONIC STRENGT!I RELATIONSHIPS OF PHOSPHATE SORPT ION BY

SOILS . . . . . . . . . . . . . .

4A Oriein of c�tion nnd ionic strength effects on phosphate

85

sorption b y soils • • • • • • • • • • • • • • • • • e • 85

411.� 1 Introduction • • • • • • • • • • • • • • • • • • • • • • 85

��teri�s nnd Methods • • • . . ' . . . . .

Results • • • • • • • • • • • • • • • • • • • • • •

Effect of su1�ort neJin on P sorption • • • . •

Cnuses of support nedin effects on P sorptio�,

L1rAe3e2�1

tJ-11..3 .2�2

4A.3.2 .3

Ionic strength nnd cntion species

pH effects • • • • ••••••••••••••••• •

Kinetic effects • . . . . . . . . . . . . . . . . .

86

87

87

�

�

92

95

Discussion • • • • . . . . . . . . . . .

4B Cnl ciun retention in response to phosphate sorption by

soils • . . . . . . . . . . . .

In trcxiuc tion • . . • . . . . . . . . . • • • • • • .

Mn te rinls nnd TIIcthods •

Re sults •

• • • •

. . . . . . . .

Discu ssion • • • • • • • • • • • • • • • • • • • • •

CH!l.PI'ER 5

INTERPRETi>TION OF PHOSPHATE SORrTION BY SOilS USING THE

LANGr-IDffi EQUATION

viii

97

103

103

1 03

104

104

109

5.1 Introduction • • • • • • • • • • • • • • • • • • • • • 109

:r.hte rinls nnd Methods • • • 110

Results • . . . . . . . . . . . . . . . . . • 111

Equilibriun nnd 40-hr isotherns • • • • • • • 111

Fit of dntn to the Lo.ngr.ru.ir equGtion • • • • 114

Resolution of Ln.Ilo<:>TIUir rcl:J.tionships • • • •

Evaluation of Lnngnuir constants • • • • • •

Dis9ussion • • • • • • • . • • • • • • • • • • • • • •

118

122

125

Equilibriun nnd non-e quilibriun isothe1� • • 125

Inportanco of detailed dntn • • • • • • • • • 126

Inplicntions of sinilar K values • • • • • • 127

CHAFTER 6

CHARGE RELATIONSHIPS AND MECHI\.NISf£ OF PHOSPHATE SORPTION BY

SO ILS. • • • • • • • • • • • • • 131

I ntroduction • . . . . . . . . . . . . . . . . . . . . 131

Mate rials nnd Methods • • • • • • •

Results • • • • • . . . . . . . . .

Sorption isotherns . . . . . .

Chnrge and pH re la tim:.shi ps •

• • • • • • • ! 13"1i

• • • • • • • • 133

• • • • • 133

� • � • • • • 133

Discussion • • • • • • • • • • • • • • • • • • • • • • 142

i:x:

CHAPTER 7

INT:CRPRETATIOIJS • 147

Sw.Jr.\:J.ry • 152

Bibliocrr:phy • • • • • • • • • • • • • 15L'r

FiG• 1 .1

Fig. 1.2

Fig. 1.3

Fie;. 1.4

Fie. 1.5

Fig. 1.6

Fig. 1.7

Fig. 1 .8

Fig. 1.9

Fie. 1 .10

List of Fir;ures

Solubility isotherns for V.'"'.rious phuspho.te

niner:�ls ::s a function of pH, nncl dnt[l. for the

P concentrntions of soil solution extrncts

Scheu�tic ropresentntion of tho hydrntion of o.

broken oxide surfo.cG ;'..nd thG subsGquent develop-

nent of cho.rce

Tit ration curves ( surface chnrge

. . . .

pH rolntion-

ships ) for tvm oxide s . . . . . . . . . . . .

Distribution of cho.rge nnd potenti".l nt o.

posi tivoly-chnr[Sed hydroue-oxide surfa.ce • • •

Schem tic represe nto.tion of .3.niorr- sorption

:X:

Po.eo

8

20

22

27

types at differon t posi ti vely-cho.rt;;od surf.�ces. 29

Two rGrresentntions of the effects of sr�cific

anion sorption on the pH ( p.z.co ) of oxide o.nd

hydrous-oxide surf[l.oes • 411 • • • . . . • •

Rolntionships behreGn P sorption nnd pH • • • •

Isotheros for solute sorption • • . . .

Isothern for P sorption by o. soil shovlinc two

diRtinct lino-�r portions over the finnl P coDoo

centro.tion rn��o of 0 to 8 pe P/ol, usine the

34

38

42

I.uner:ru.ir e qun tion • • • • • • • • • • • • • • 52

Sorption isotho rrm construc ted froo the Lo.��ouir

equation essuoing n unifon1 surface or K vnlue

nnd two distinc t popuL�tions of si tes or K vnlues. 54

Isothen1s for P sorption by soils durin� �0 h r

froo 10-1M NnCl over n filli�l r concentro.tion

range of 0 to 1 0 pc :2/nl • • • • • • • • • • • 66

Fig. ;1ro2'

Fig. 4.4

Rola.tionship behmen solution P concentra.tion

:end tine clurin.:; the sorption of nclded P by

Oko.ih::m and 1/:;.ikn.kahi soils • •

Relationship bohroen solution r concentr:ction

( loc scale ) n.nd tii:'.e during the sor1)tion of

added P by Ok�ih.".u soil . . . . . . . . . . .

Distinct first-order ro�ction relationships

for the sorption of :'.clded P by Ok::cih1.u soil

obtained after the resolution of data. in Fig.·

xi

72

3.2 usiTIG the nethod described in the text • • 75

Relo.tionship behreen a.dded P sorbed betvmon 48 n.nd 1 92 hr, the anount of sorbed ::odded ? cxtro.ct­

ed by two successive 0. HI 1h0II trentnents, tho.t

extro.cted by o. su bsequent CDB treo.tnent, o.nd that '7.2

exchangeable to J P durinG the sa�e 48 to 192 hr

tiEe interv::cl for Ok:--.ih-cu �d Poriru'l. soi:ts • • 79

Isotherns for ? sorpt ion by soils durill[� 40 �� fron v.::.rious support nodir. over r. finnl P

concontrntion ro.nce of 0 1 0 yc/nl • • • • •

Isotherns for r sorption by soils durinG

40 hr fron vo.rious support nedin ov er o. fin.::.l

88

P concentr"..tion rnn;;o of 0-1 pc;/nl c • • • • 89

Re lationship (*) be��een fin2l P concentra.tioiT

and anbiont pH induced by various support nedin

for given additions of P to three soils, �d the

dependence of fi�1.l P concentration na.intnined

in 10-2M Ca. nnd 1 0-1M }h systens upon pH a.djust­

nent over the range of o.nbient pH values induced

by the other support nedia. • e • • • • • • • • • 94

Relntionship between final P concentration in

three support nedia nnd tine over a. period of

40 to 144 hr for �vo additions of P to each soil. 96

Fig. f1re6

Fig. 5.1).

xii

Relo.tionship betueen fin-:!.1 P concontro.tion,

mint.�incd in three support nodio. fro::-1 "highn

ndo.itions of P, rend rcciproc�l of tine; dnshed

linos used to· cxtrc..polo.te the de:. b. to the orclino.te1

i.,o.,; 1/t = 0; i.; = CO to ostino.to equilibriun

P concontro.tion

Relntionship bot1-rocn fj_ru..'11 P concontr:ction,�

r:ninto.ined in thToe s11.pport nodia fro2 HlO'iT" c.cldi tions of P1 r'.:i.1d reciprocr,l of tice i dc:shed

lines used to ex·crnpolate the dato. to the ordinate,

ioo.;, 1 /t = O, t = 00 to estic;l..to equili::>riun

Pnge

98

• 99

Solution P conccn-Grc.:.tion ns ::1. function of tine

(1/t) for vo.riou.3 P l"'.uditiuns to the POl'irun s oil o Dn tn cxtr::tl)Oli"'. tod to ordi.n:o. to ( d.:J.shed line) to

obtain o.n ostic:cto of oquilibriun r concentr;;.tion. 112J

Isothor;:o for P sorptioYJ. by the Poriruo. 1"'.11d

�-Jniknko.hi soils at cquilibriun ::.nd 1).0 hr over

·G>·ro final r concont:·:c.. t ion rnn:::;cs ,

Equilibr:.uu P sorptj_oa isotherns for the Pcrirun

nnd Er���01rc soils obtninod usin�; the 13.;1,:-:-;IJ.Uir

equ:.1 ti:m over 0.n equilibl'iul:.'. r eo nee ntrn. tion

range of npproximtoly 0�002 to Oe05 ws?/D� ; before l"'.nc1 nfter the inclusion of the nnount of

nntivo so:..·bcd P in the vnlue:J of P sorbccl •

Equilibriun P sorption isotherns for the Poriru.:':t

soil over two cquilibriun F concentro.tion ro.ngos

1 13

1 1 6

obtained using' the LnnGDUir equation • • • • • • 1 1 7

Equilibriun P sorption isotherns for Porirun

soil showi�3 tho three h�ngnuir relationships

( regions ) obtnined nfter re soluticn of sorDtion

dntn by successive npproxi��tion ( see Tnble

5o1) . . . . . . . • • • • • 0 • . . 121

Fig. 5.6

xiii

Equilibriun P sorption is otherns for Poriru�

n.nd Ok.'l.iho.u soils over the equilibriun r con­

c entro.tion rnnge 0 to 12 pcP/ru shovrinc

res olved is othorr:s for eo.ch sorption region

nnd the overo.ll isoth ern g-e11ern.ted by sunrn. tion

of tho isothorns for onch region . . . . . . .

Isotherns for the s orption of ncldod P fron 1 o-"rr.r No.Cl by soils .:>.nd Fe Gel durine 40 hr • • •

Re lationship between the difference ( � Nn) be­

tween sodiUTI uptnke, in the presence o.nd absence

of P o. t the so.I:le level of sodiun n.ddi tion, nnd

Page

12T

134

o.dded ? sorbod for soils nnd Fe gel • • • • • • 136

Reln.tionship behveon the degree of flocculntion

sub sequent to P sorption neo.sured by the trans­nission (%T) of Fe g·el susp0nsions o.t 700 nn, the

pH of suspensions subsequent t o P sorption,o.nd

nddod P sorb ed . . . . . . . . . . . . . . . . 141

Table 1.1

To.ble 1 .2

Tnble 1.3

Table

Table 3.1

Table 3.2

Tnblc 4.1

Table 4.2

List of Tables

Tho [' .. P.ount of :· rooovod by .:o.. soil fron

solutions of different initi:::,l J.! conccntr:::,tions

( first troo..tuent ) -".ml tho diotribution of P ro­

noved fron solution durin(; the first trentnent

bah;een soil ,::md solution, o.ftcr roplacine the

finnl solutions fron the first trontocnt vTi th

solutions ini ti,"'..lly containinc; 5 p-c tren tncn t ) .. Dn tn free Hsu ( 1 964) •

r=/nl (second

. . . .

Sorption of P by vnrious soil conpcments a.t

fin;1l I' concontr�,tions of o..pproxiriL toly 3 fG P/nl

under tho experinont[l.l conc1i tions spocj_fiod . "

Values of pH (p.�oc. ) of v:1rious oxides and

hydrous oxides • • • 0 & • • lt • • • • • •

Sono characteristics of the soils used • • . �

&".to constants (t:) for tho four re.'lctions

doscril)inr: the docro.1.so in solution P conccmtro..-­

tion durinc I-' sorption by four contrnstir1t:; soils;

and the tino interv"..ls ovor 1·1hich e'Cch reaction

is donin�nt in over:::,ll ? sorption • 0 • c

Vnlues of th0 ra to constr.:.nt (k4) for the decroo..se

in solution P concontrntien o.t tiLBs eroo..tor than

xiv

10

15

24

65

76

60 hr for various o..ddi tions of P to Po:ciruo.. soil. 78

Anounts of Cc. sorbod fron 1 o-2r-r o..nd 1 o-3M Co.

systens and nnounts of sorbc d �� which a.ro

non-roplaceablo by K • • • • • • 8 • • • • • • 91

Effect of support nedin on suporP�tnnt pWvalues

( a.vornco values over the isothoro ) 93

Te..ble 5.1

Table 5.2

Table 5.3

Tab le 5.4

Table 6.1

Table 6.2

Table 6.3

Anounts of c� �u ? rouovou frou solution

durir-;:-; 'lO hr ·end nnounts of C1- �nd P rolensed

by 1:·1.:lshinc; 'iTi th 1 N KCl • . . . . . . .

Schenatic represent'"'.tion of the stops involved

in the resolution of P sorptio n dnb to ubt.�in

the Lnngnuir sorption cons tnnts K �nd b for P sorption by soils over Cc fin.."Cl P concon-Grn.tion

ro.nc-e of 0 to npproxin1-toly 25 y.g P/nl; us incr

n noth0d of successive approxiuntion . . . .

Values of Lnnr;nuir sorption const;>nts obto.ine<t.

nt successive approxin1-tions of oquilibriun P sorption cl::l.tn.. for Er:;:-Jont soil by tho schEme

shmm in Tnble 5o 1 . . . . . . . . • • •

L'll'lr,Tiuir sorption constc.nts ( K �nd b )

obtained by successive approxiontion of P

sorption data obtnined under equilibriun nnd 11,0-hr conditions for four s cils • • • • • •

Valuos of the Lnncuuir sorption enorcy

constan t K ( :::: Dl/l;l!.S )' for P sorption- by I

vnrious. soils nnd soil conponents over three

concentrr:.tio!1 r.1.:ncos (ror;ions ) . .

Vo.lues of sorption r:nximm (b ) and sorption

e nergy (K) for ench of throo (:r to III) L�ngouir equations ( regions ) describing the

sorption of P by E,c;nont ::md Oknihau soils;

XV

105

119

120

124

128

and Fe gel • • • • • • • • • • • • • • • • 135

Degree of saturation of ench sorption region

for tho overnll levels of P sorption by each

sorbent, dencted n, b and c in Fig. 6.2

nnd 6.3 • . . . . • . . . • • • • • • • . • 138

Values of the I'fl.tio o f 6 lih: P sorbed at

points d and e on the relo.tionship betwean

� No. nnd ndded P sorbed ( Fig. 6.2 ):. 139