الفهرس 
IntroductionOnly 14 pages are availabe for public view
 |  | from | 179 |  |  |
| | | from | 179 | | |
Abstract
previous studies showed fairly
sometimes contradictory informations
involving phosphorus compounds that
calcareous soils.
little and perhaps
amout the reactions
may take place in
To elucidate the nature of such reactions, CaC03
(chemical compound), fractionated oleitic limestone and a
typical calcareous soil were investigated for their reactivity
with P either from phytic acid or hydroxyapatite in presence
of humic acids derived from three organic-raw materials.
The recovery and characterizations of humic acids
including elementary analysis, infra-red and ultra-violet
spectroscopy were carried out. The ability of humic acids for P
solubilization was compared using H20, NaHC03 and NaOH as P
solvents. Langmuir, Freundlich And Van-Huay equations were
tested for their reliability to assess P adsorption relations
in the systems including; different limestone fractions, three
different humic acids and (calcareous soil + humic acid).
The results obtained are summarized as follows:
a) Recovery and characterization of hnmic acids.
Recovery of humic acids dominated than fulvic acid and
that seems to be dependent on/the total organic carbon content
of organic materials and their rate of decomposition.
The highest and lowest values of total N content of humic
acids were obtained from humic acids derived from peanut and
barley straw, respectively.
The aromatization of humic acid prepared from barley
straw exceeded those originated from other sources.
The infra-red test showed that, the greatest intensity of
humic acids at 3400 cm-1 was obtained in humic acid derived
from barley straw, compared with other sources.
The highest humic acid O/H ratios were the greatest O-H
stretch absorption at 3400 em-I, at 1400 em-I, at 1200 cm-1 and
at 1128 cm-1 when they were treated with KH2P04.
As the surface area of the CaC03 present in the system of H.As
and hydroxyapatite increased, the intensity of infra-red at
3400 cm-1 also, increased.
There were no serious variations between the absorption
at 3400 cm-1 of H.As treated with either hydroxyapatite or
phytic acid.
----------------- ---- ._-- -- As the C/H ratios of H.As increased, the absorption
intensity at 2920-2860 cm-1 also, increased either in presence
or absence of KH2P04.
The absorption of H.As at 1700-1725 cm-1 in the presence
of KH2P04 greatly depends on their oxygen content and their C/O
ratios.
Application of humic acids with phytic acid, mostly
increased their absorption at 1700-1725 cm-1, compared with
those treated with hydroxyapatite. This is probably attributed
to the lower adsorption of phytic acid on both H.A. and CaC03
than hydroxyapatite due to the greater molecule of the former
compared with the later.
The absorption of H.As mixed with hydroxyapatite
increased by increasing the surface area of CaC03 fractions
present in the same system, that may suggest that the amounts
of hydroxyapatite adsorbed on H.As mixed with fine limestone
would be smaller than those mixed with coarse limestone.
The values of H.As intensity at 1300 cm-1 agree with
their total C/N ratios content.
147
The ultra violet spectra indicated that the higher carbon
content humic acid was the greater aromatic condensation and
the more humified humic acid.
b I The ability of acids ou the P solubility uuder the equilibrated systems.
Half normal sodium hydroxide dissolved P, mostly more
than ten times those dissolved by both H20 and O.5N NaHC03 due
to the greater pH of the former, compared with the laters.
Humic acid dissplved in O.5N NaOH extracted mostly more
than ten times and more than one hundred times those extracted
•
by both O.5N NaOH and H20 or O.5N NaHC03, respectively. Calcium
chelation by humic acids !~m calcareous soil and limestone
fractions stimulate P solubilization and decreases its
precipitation as calcium phosphate.
The solubilization of P by different solutes from systems
containing phytic acid and CaC03 greatly exceeded that
solubilized from hydroxyapatite. These results are due to the
higher solubility of phytic acid in the different solutes,
compared with the very low solubility of hydroxyapatite.
Phosphorus solubilization from systems containing the
finest limestone yielded the lowest P values as compared with
all the other systems.
Humic acid in the gel form has a greater capability to
solubilize P, compared with the dried form of humic acid.
C) Phosphorus adsorption isotherms:
Data of P adsorption by different CaC03 sources, showed
complete fitness to Langmuir adsorption isotherm in case of
calcareous soil and oleitic limestone fractions. The previous
equation was of fairly low efficiency in the case of the
chemical compound, CaC03 (c.c.), that may be due to dominancy
of other mechanisms responsible for P sorption rather than to
the one layer adsorption mechanism.
According to Langmuir isotherm, there was no significant
fitness for assessing P sorption in the systems containing
humic acid, meanwhile this reliability was highly significant
in case of either Van-Huay or Freundlich equation, that was the
most reliable isotherm for such systems. The failure of
Langmuir isotherm to describe the relation of P sorption in
presence of humic acid may indicate the dominance of other
reactions requiring higher bonding energy such as chemical
reactions involving replacement of enolic or phenolic O-H
groups.
A close positive relationship between the maximum P
adsorption (b) of Langmuir isotherm adsorbed on active surface
and clay content, whereas a negative relationship with the
affinity constant (K) was also, obtained. It seems that Van-
Huay equation is more efficient for describing P sorption in
such systems.
Finally, it may be concluded that:
humic acids are proved to be effective materials inducing P
solubility in systems involving CaC03 which may suggest a
controlling effect on P solubility due to these acids in such
systems. The tested H.As can be arranged according to their
solubilizing effect on P in the following order: Peanut H.A >
farmyard manure H.A > Barley straw H.A.
As the surface area of limestone fractions increased, the
P solubility of the system decreased and paralley increased the
absorption of l.R at the wave length, characterizing the OH
stretch which represent the main seat of P sorption. This
phenomenon could be explained a basis of increasing the
activity or potentials of Ca ions and hence the H2P04
potentials decreased and/or precipitation reaction of
Ca3 (P04) 2 that may take place at relatively higher P
concentrations.