Copyright is owned by the Author of the thesis. Permission is given for a copy to be downloaded by an individual for the purpose of research and private study only. The thesis may not be reproduced elsewhere without the permission of the Author.
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
