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 presen ted 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.
Ab
s tl'fl. etA revie1-r of the li terc.turo relating to the reactions c.nd nechnnisns involv0d in the sorption of inorgnnic ph0sph.".te
(r)
bysoils and soil conponents sug-gested scvorl'.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 cooponcnts and properties considered to be inport�nt in P sorption 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 pgP/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
sorptionby 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�tability o.nd isotopic -
oxch..".nc;eabiJ.i ty of sorbc::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 ovvry of P by citrnto-dithionite-bicnrbcmate extr::tetion indico.tecl th.:d; J.dsorption -vms follevmd by nbsorption.
Elininnticn of the diffor:
,
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 condition vTt:.S !1ade, pointed t o the inplications 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 rption, 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 sorption data using the Lnngnuir equntion.,
equilibriuo dntf!., the P sorption isothern for each soil Has described by three distinct h�nerruir oquntion8, 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 sorption·
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
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 enjoynble o.nd revro.rding experience.
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
Introduction • • • • • • 0. . . . . . .
.
. . .
. . .
.
1
. 2
Phosphntc Re tention Gcnernl Consider�tions . . . . . .1 . 2 .1 1o2o 2
The dovelopoe nt of P rete nt ion concepts . . . . The Th�turc of P retention . . . . .
. 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 surfaces 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 structure and origin of chnreeCharge properties of the interface • •
• • •
. . Aophoteric behaviour and pH depend- ence of chr..ree • • • . . • • • • . • • • • • • •• • •
Points of zero ch�rge for soil eo�
1 8 1 9
19
ponents and soils ... 23
1.,6
The elec triccl d ouble l1.yer at the inter f.::tce 2 5 The Go uy-Chap1:::un nnd Stern nodels 25
Interetction of c ounteri ons vri t h the
Porous intorfnce nodel
• • • • • • • • • • !•30
The
Typo and rJiechnnisD of Phosphntc Sorption
. . . . " "3 1
Sorpt ion type
. . ... . .3 2
Non-spe cific
.::,ru:ls).X3cific s orption 3 2
Exporinontnl veri fic�tion o f s pec ific sorption
.. . . 33 The nechnnisn of P sorption
• • • • • • • • • •36
pii
nnd ch.'l.rge relc.tionships
• • • • • • • •37
The
forn of P s orbed
• • • • • • • • • • • • . • •40 Interpr etnt i on of
Sor
ptio
n Dato. • . . . . .. .
. . . . .41
1
•501
1 .,5o 3
1 .5
.. 4The
sorpti on is ot}1ern
• •The Freundlich
eq uo.tion
•The
�·uJt;nuir
eq_uc.tion
• •• • e • • • • •
.
.
..
. ..• 0 • • 0 •
Dorivo.tion nn d tes t for data fit
• . . .The
vc.:.lid i ty of o.pplyinc t he h.'1ngnuir 4'f
44
45 4 5
e quntion to P s or pt ion .
. . .....,.. . 48 P sorption
n.ncldesorption is othorns
• • • • • •49
1 .5
•.')..,2
Application of the
knc;:ru.ir cqunt
io
nto P sor-pt ion
. . . •. . . 49
Inplicnti ons of nultiple h.'1nermir rclr1tionships
. . . . .. . . .The
n.::tture and inplicntions of P
desorpti on 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 sorption3.3.2
F:ro.ctiom tion Discussion • • • • • •of . .
sorbed . . .
p
.
.. • •
.
• .• • • .
• • .
. . . .
.
..
. •
. •
. .
• . !'
. • • . . . Extent �nd nn turo of tine dependent P sorption
•
69 69 71
71 7780 80
Ori8�n of tine dependent sorption • • • • • • •
81
Inplicntions of nn o..bsorption reo..ction • • • • •
82
CHArTER
4
CAT ION AND IONIC STRENGT!I RELAT IONSHIPS OF PHOSPHATE SORPT ION BY SOILS . . .
.
. . ..
4A
Oriein of c�tion nnd ionic strength effects on phosphate85
sorption by 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 •
Results •
• • • •
. . . . . . . .
Discussion • • • • • • • • • • • • • • • • • • • • •
CH!l.PI'ER 5
INTERPRETi>TION OF PHOSPHATE SORrTION BY SOilS USING THE LANGr-IDffi EQUATION
97
103 103 1 03 104 104
109
5.1 Introduction • • • • • • • • • • • • • • • • • • • • •
109
:r.hterinls 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-equilibriun isothe1� • •
12
5Inportanco 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
• 147Sw.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 Fi
g
.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 represento.tion of .3.niorr- sorption
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
coDoocentro.tion rn��o of
0
to 8 peP/ol,
usine the34 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 sites or K vnlues. 54
Isothen1s for P sorption by soils durin� �0 hr froo
10-1M
NnCl over n filli�l r concentro.tionrange of
0
to1 0 pc
:2/
nl • • • • • • • • • • • 66Fig. ;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 • • 75Relo.tionship behreen a.dded P sorbed betvmon 48 n.nd
1 92
hr, the anount of sorbed ::odded ? cxtro.cted 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 192hr
t iEe 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 in10-2M
Ca. nnd1 0-1M
}h systens upon pH a.djustnent over the range of o.nbient pH valu es 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. f1re 6
Fig. 5.1).
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 equilibriunP
concontro.tionRelntionship 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::>riunPnge
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 soilo
Dn tn cxtr::tl)Oli"'. tod to ordi.n:o. to
(
d.:J.shed line)
toobtain 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 equ ilibl'iul:.'. r eo nee ntrn. tion range of npproximtoly 0�002 to Oe05
; ws?/D�
before l"'.nc1 nfter the inclusion of the nn
o
untof
nntivo so:..·bcd P in the vnlue:J of P s
o
rbccl •Equilibriun P sorption isotherns for the Poriru.:':t soil over two cquilibriun F concentro.tion ro.ngos
1 1 3
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 resoluticn of sorDtiondntn by successive npproxi��tion
(
see Tnble5o1) . . . .
• • • • • 0 •. . 121
Fig. 5.6
xiii
Equilibriun P sorption is otherns for Poriru�
n.nd Ok.'l.iho.u soils over the equilibriun
r
concentro.tion rnnge 0 to 12
pcP/ru
shovrincres 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 fro
n 1 o-"rr.r
No.Cl by soils .:>.nd Fe Gel durine 40 hr • • •
Relationship between the difference
(
�Nn)
between 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 subsequent to P sorption
neo.
sure
d by the transn
ission(%T)
of Fe g·el susp0nsions o.t 700 nn, the pH of suspens
ions subsequent t o P sorption,o.ndnddod 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 ronoved 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-ctren tncn t
)
.. Dn tn free Hsu(
1964)
•r=
/
nl(
second . . . .Sorption of P by vnrious soil conpcments a.t
fin;1l I' concontr�,tions of o..pproxiriL toly 3
fG
P/
nlunder 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.'lctionsdoscril)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 than10
15
24
65
76
60 hr for various o..ddi tions of P to Po:ciruo.. soil. 78
Anounts of
Cc.
sorbod fron1 o-2r-r
o..nd 1o-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 th1
N KCl • . . . . . . .Schenatic represent'"'.tion of the stops involved in the resolution of P sorption 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 incrn 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
I)
' forP
s orption- byvnrious. soils nnd soil conponents over three concentrr:.tio!1 r.1.:ncos
(
ror;ions)
. .Vo.lues of sorption r:nximm
(
b)
and sorptione nergy
(K)
for ench of throo(:r
toIII)
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