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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
top related