Download Effects of Organic Matter on Solubilities and Crystal Form of

AM. ZOOLOGIST, 9:681-688 (1969).
Effects of Organic Matter on Solubilities and Crystal Form of Carbonates
YASUSHI KITANO, NOBUKO KANAMORI, AND AKIRA TOKUYAMA
Water Research Laboratory, Faculty of Science, Nagoya Unixjersity,
Chikusa-ku, Nagoya, Japan
SYNOPSIS. The results of a study of the role of organic compounds in the formation of
carlxmate crystals in marine biological systems are reported. In an increasing concentration of certain organic compounds which complex calcium ions, the proportion of
aragonite decreases and that of calcite increases. In increasing concentrations of
magnesium ions the proportion of aragonite increases and that of calcite and vaterite
decreases. When the influence of organic compounds is greater or smaller than that of
magnesium ions, only calcite or only aragonite is formed, respectively. Organic
compounds forming a strong complex with calcium ions cause the formation of
magnesium-rich calcite, and with an increase in temperature and the concentration of
magnesium ions, the magnesium carbonate content of precipitated magnesian calcite
increases. When the influence of organic compounds is almost equivalent to that of
magnesium ions, in increasing or decreasing temperatures, the proportion of calcite
decreases or increases, respectively, and the proportion of aragonite increases or
decreases, respectively. The concentration of magnesium ions in the body fluids of
marine calcareous organisms seems to differ little from that of other organisms, and
seems to be similar to that of sea water. Only the presence of certain organic
compounds brings about the formation of the carbonate crystals observed in marine
biological systems. The very important role of organic matter in the formation of
crystals found in skeletal carbonates is emphasized.
A large amount of carbonate sediments
is distributed very widely on the surface of
the earth. These sediments have collected
as carbonate fossils during a long geologic
time.
Most sedimentary carbonates are derived
from the skeletal parts of calcareous marine organisms. The major component is
calcium carbonate, which has three different crystalline forms: calcite, aragonite, and
vaterite.
In marine biological systems calcites
(Mg-poor calcite and Mg-rich calcite) and
aragonite are found, but vaterite is not
(Kitano, 1964). Magnesium carbonate in
skeletal calcites is present as a solid solution between calcite and dolomite or magnesite (Kitano and Furutsu, 1959). And
Mg-rich calcite (which is called magnesian
calcite) and aragonite (poor in magnesium carbonate) are unstable relative to
Mg-poor calcite under natural conditions
of temperature and pressure (Jansen and
Kitano, 1963).
The mineralogical composition of carbonate could indicate the physicochemical nature of the environment, that is, the
temperature or the salinity of sea water in
which the carbonate was formed (Kitano,
1967). The crystal form of carbonate
greatly controls the content of minor elements of carbonate, a matter of great geochemical significance. In this regard, there
is need to know what factors control the
formation of the three crystals in marine
biological systems. Two approaches have
been used in the past to determine these
factors: (1) field observations to learn the
relationships between the crystal forms of
carbonate skeletons collected and the
physicochemical nature of the environment in which the skeletons have been
formed; (2) laboratory experiments on the
synthesis of carbonate crystals found in
marine biological systems from simple solutions the properties of which are very
close to those of media for calcification in
marine biological systems. In the present
investigation the authors studied the controlling factors using the second approach.
Certain characteristics which are very
difficult to observe in inorganic systems,
but are familiar in biological systems, e.g.,
the formation of Mg-rich calcite at low
681
682
YASUSHI KITANO, NOBUKO KANAMORI, AND AKIRA TOKUYAMA
•;—-oo-n
1 00
80
60
KJC
'
40
20
10
20
Temp
IIC. I. A plot of per cent aragonitc vs. environmental temperature in the skeletal parts of marine
calcareous organisms. • , Foraminiferans, sponges,
echinoderms, asteroids, ophiuroids, crinoids, crustaceans, barnacles, alcyonarian corals, pelagic algae,
hrachiopods, and others: O, Madreporian corals,
gastropods, pelecypods, bryozoans, benthic algae,
annelids, and others; X, Serpulids, Schizoporella,
Mytilus, I.ittorina, pelecypods, annelids, gastropods,
bryozoans, and others.
temperatures and pressures, are dependent
on the presence of organic substances in
the parent medium.
The present paper reports the results of
a study of the role of organic materials in
the parent medium on the formation oE
carbonate crystals in marine biological calcification.
OBSERVATIONS
The crystal form of carbonate in the
skeletons of the three representative
groups of marine calcareous organisms is
plotted in Figure 1. Represented are (1)
organisms which secrete skeletal parts composed only of aragonite in the range of
biological temperatures, and (2) organisms which form calcite in the same range
of temperature. With increasing sea water
temperatures, the magnesium carbonate
content of calcite increases. The rate of
increase in the magnesium carbonate content with temperature varies with the phylogenetic level of the organism. Furthermore, with increasing concentration of
magnesium ions in sea water, the magnesium carbonate content of skeletal calcite
increases. (3) Certain organisms which de-
posit calcite in one portion and aragonite
in another portion of their skeletons are
included. With increasing temperature of
the sea water, the proportion of aragonite
increases, that of calcite decreases, and the
magnesium carbonate content of the calcite portion increases.
The formation of the three carbonate
crystals is controlled by biological species,
temperature, and the concentration of
magnesium ions in sea water.
RESULTS OF LABORATORY EXPERIMENTS
The formation of carbonate as either
aragonite, Mg-poor calcite, or Mg-rich calcite is probably influenced by the following
factors (Kitano, 1964): (1) the presence
of certain inorganic ions and compounds
in the parent solution, (2) the presence of
certain organic matter in the parent solution, (3) the temperature, (4) enzymes
(carbonic anhydrase) and bacteria, (5)
the mechanical conditions for forming carbonate, including the rate of formation,
(6) nuclei for forming carbonate, and (7)
the transformation of the crystal of carbonate after the carbonate has been
formed.
Factors 1-6 are related to the rate at
which carbonate is formed.
The following basic chemical reaction
was used for making calcium carbonate, to
learn the influence of the factors listed
above: carbonate was precipitated from
calcium bicarbonate solution with escape
of carbon dioxide gas to the atmosphere.
The reaction was used because it is one of
the homogeneous precipitation reactions,
and calcium bicarbonate solution does not
dissolve any other matter than calcium and
carbonate.
The crystal forms of precipitated carbonate were identified and compared with
those of skeletal materials.
The calcium bicarbonate parent solution should contain inorganic materials
present in sea water and organic matter
found in the body fluids of marine calcareous organisms. Enzymes were not added
to the parent solution in the present
683
SOLUBILITIES AND CRVSTAL FORM OF CARBONATES
experiment, and the rate of carbonate
formed was controlled by changing the
rate of escape of carbon dioxide from the
solution mechanically.
The laboratory experiments showed that
the most important factors are 1-3.
The influences of various inorganic ions
and compounds such as H + , Li+, Na+, K+,
Rb+, Cs+, Mg2+, Cu2+, Zn2+, Mn2+,
Hg2+, Ca2+, Sr2+, Ba2+, Pb2+, O H - C1-,
NO 3 - SO 4 2 -, HCO,,-, CO/- and CO2
on the crystal form of precipitated carbonate were reported by Kitano (1962«).
In the experiment, calcium carbonates
were precipitated from calcium bicarbonate solutions into which inorganic ions
and materials had been added in various
proportions, and the crystal forms of precipitated carbonates were identified.
From the previous work it was expected
that inorganic ions having a possible influence in marine biological systems would be
sodium, magnesium, chloride, sulfate, and
bicarbonate ions in the parent solution.
The results indicate that magnesium ions in
the parent solution have the greatest influence (Fig. 2). Magnesium ions favor the
formation of aragonite, and hinder the
formation of calcite and vaterite (Kitano
and Hood, 1962; Kitano, 1962&).
In the laboratory experiment, the proportion of aragonite increases and that of
calcite decreases with increasing temperature, as observed in skeletons (Kitano,
19626).
80
0.
60
o
g1 <o
NoCI
0
20
40
FIG. 2. Salt content in calcium bicarbonate mother
solution, mcq/l. Influence of salt in mother solution on crystal type of formed calcium carbonate
(28 ± 3°C)'.
Ci'to|e,Pyfuvoie
SO
¥/
V \
*""
^^Glutamote
-—- " Galoctose,Aceiatt
Dextr ose . Serine
•
Glycine
'. Tourine
Organic material in mother solution ( g / | )
( 27+2*C)
FIG. 3. Polymorphic composition of calcium carbonate formed from calcium bicarbonate solution
containing organic material and magnesium chloride.
Kitano and Hood (1965) reported the
results of preliminary experiments concerning the influence of organic matter
present in a parent solution on the crystal
form of precipitated carbonate (Fig. 3).
Selection of various organic compounds
used in the experiment was based on previous reports on the mechanism of calcification and the distribution of organic matter in calcareous organisms. Calcium, bicarbonate, organic compounds, and magnesium chloride solutions were mixed in various proportions in an Erlenmeyer flask,
plugged with cotton, and allowed to stand
at room temperature for 2 to 8 weeks. The
rate constants in the reaction with the
first type order were calculated (Fig. 4).
The following results were obtained:
(a) Organic compounds such as citrate,
malate, pyruvate, and glycogen form a
complex with calcium ions, enlarge the
solubility of calcium carbonate (Fig. 5),
reduce the rate of precipitation of carbonate, and favor the formation of the
stable form, calcite, even in the presence of
magnesium ions which greatly hinder the
formation of calcite.
This would suggest the possibility of the
precipitation of magnesian calcite at low
temperatures and pressures. In the laboratory, calcites could be formed from calcium
bicarbonate solutions containing magnesium ions and certain organic compounds
684
YASUSHI KITANO, NOBUKO KANAMORI, AND AKIRA TOKUYAMA
9.0
10.0
Organic material added ( g / l )
PIG. 4. Rate-constant in the reaction Ca (HCO3). -»
CaCO3 + CO2f -f H2O in the presence o£ specific
such as sodium citrate, malate, or pyruvate
by allowing the solutions to stand still at
low temperatures and pressures (Kitano
and Kanamori, 1966). The precipitated
calcites from the solutions contained magnesium carbonate. The values for the difference in spacing of (0114) reflection between pure calcite and precipitated calcites
were plotted against magnesium carbonate content as chemically determined
(Fig. 6). The linear relationship between
these variables indicates magnesium carbonate is contained as a form of a solid
solution between calcite and dolomite
(magnesian calcite).
Figures 7 and 8 show the magnesium
carbonate content of magnesian calcites
precipitated from calcium bicarbonate solutions containing magnesium chloride
and sodium citrate. The figures indicate
that an increase in the concentrations of
magnesium ions and organic compounds,
such as citrate, and an increase in temperature, cause a Mg-richer calcite. The
presence of sodium citrate or malate favors
the formation of Mg-rich calcite, probably
by complexing calcium ions, enlarging the
organic compounds (temperature 27 ± 2°C).
O
o
O
O
AIR
0
2-5
5
7-5
ORGANIC M A T E R I A L ADDED
10
(g/l)
FIG. 5. Solubility of calcium carbonate in solutions
containing specific organic compounds in contact with one atmosphere of CO2 gas and air.
SOLUBILITIES AND CRYSTAL FORM OF CARBONATES
solubility of calcium carbonate and on the
rate of carbonate precipitation, have little
effect on the crystal form of precipitated
carbonate.
(c) Organic compounds which enlarge
the solubility of calcium carbonate and reduce the rate of carbonate precipitation to
a moderate degree have only a moderate
influence on the crystal form. Their influences were different: chondroitin sulfate,
succinate, and lactate favor the formation
of calcite, and taurine favors the formation
of aragonite.
0.06
j 0.05
cP
CD'
| 0.04
"s 0.03
o oooc
oo
o
685
oo
I 0.02
0.01
S 10
n
10
20
Weight per cent MgCOFIC. 6. The relation between magnesium carbonate content and interplanar spacing.
solubility of calcium carbonate, reducing
the rate of formation, giving a stable calcitic lattice configuration and causing a
capture of magnesium in the calcitic lattice.
Many other organic compounds were examined for content of magnesium carbonate (Kitano and Kanamori, 1966). It
is known that the content of magnesium
carbonate differs with the kind and the
concentration of organic compound.
(b) Compounds such as galactose and
dextrose, which have little effect on the
'\ 800 mj/500 ml
Mg' f , 600 mg/500 ml
Mg'+ 400 mj/500 ml
- O - Mg H . 200 mg/500 nil
0 100 !C0 300 400 SCO
10CO
W0
Na citrate concentration (citrate ions content, mj/500 mil in the mother
solution (500 mil CalHCftl, + MgCI. + Na citrate
FIC. 7. MgCO3 content of magnesian calcite formed
from the Ca (HCO3) 2 solution containing MgCl2 and
sodium citrate (20 ± 1°C).
»p
9
I 8
I 1
I 6
2. 5
citrate ions
200mg/500.ml
citrate ions
100mg/500ml
citrate ions
50mg/500ml
f4
o
" 2
» 1
0
FIG.
from
(500
and
ml) .
5
20
30
Temperature (°C) of mother solution
8. MgCO3 content of magnesian calcite formed
the calcium bicarbonate mother solution
ml) containing MgCl2 (Mg2*, 400 mg/500 ml)
sodium citrate (citrate ions, 50-200 mg/500
These results were obtained when the
parent solution was undisturbed during
the process of precipitation. When the solution was stirred, the results were not so
simple; the effects of stirring on the crystal
form and the mechanism remain unsolved.
Concerning the role of organic compounds dissolved in a parent solution, the
following interesting facts have been observed first in our laboratory experiment.
Heavy metal ions such as copper, zinc,
nickel, or manganese favor the formation
686
YASUSHI KITANO, NOBUKO KANAMORI, AND AKIRA TOKUYAMA
0D0I
Me'(m§q/i)
FIG. 9. Mineralogical composition of carbonate
formed from calcium bicarbonate solution conlain-
in" metal nitrate at 38 -+• 2°C.
of aragonite much more than do magnesium ions in a parent solution (Fig. 9). The
extent of their influence on the forming
of aragonite increases in the following sequence, although the influences of zinc
and manganese dissolved in the parent solution are very complex: C u 2 + > Zn 2 +>
N i 2 + > M n 2 + > Mg 2 +. This sequence is in
agreement with that of the second ionization potential value, in other words, that
of the value of the stability constant of
complex between metal ions and carbonate
ions in solution. Thus, we would expect
that metals dissolved as both complex and
free ionic forms are much more favorable
for aragonite formation than those dissolved in either complex or ionic form. We
have examined also the influence of metal
ions, coexisting- with organic matter which
forms complexes with the metal ions, on
the crystal form of precipitated carbonate.
Figure 10 shows a plot of the proportion of
aragonite in precipitated carbonate against
the concentration of zinc dissolved in the
calcium bicarbonate parent solution with
glycine. The value of the stability constant
between zinc ions and glycine, [Zn2 + ] X
[Glycine-]-y[Zn-Glycine 2 "], is 10-»-4. Figure 10 shows that the influence of zinc
in the parent solution on the formation of
aragonite increases with increasing concentration of glycine added to the parent solution up to a certain concentration, and
then decreases with a further increase in
the concentration of glycine. This indicates
that metal dissolved in the parent solution
in both complex and free ionic forms is
much more favorable for the formation of
aragonite than in either complex or free
ionic forms alone.
Although such an interesting mechanism
has not been clarified completely, the basic
data given here on the role of organic
matter in a parent solution seem to help in
understanding the factors controlling the
formation of carbonate crystals in marine
biological systems (Kitano, 1964). The
major factors seem to be (1) the concentration of magnesium ions in a parent
medium, (2) the concentration of certain
organic materials which complex calcium
ions in a parent medium, (3) the temperature of a parent medium, and (4) the rate
of deposition of carbonate in relation to
the presence of enzymes such as carbonic
anhydrase.
With increasing concentration of certain
organic materials which complex calcium
ions, and with decreasing temperature, the
687
SOLUBILITIES AND CRYSTAL FORM OF CARBONATES
100
o
g
50
0.001
Zn (mea/L)
FIG. 10. Mineralogical composition of carbonate
formed from calcium bicarbonate solution contain-
o
«
spotted circle
double circle
A
X
ing metal nitrate and glycine at 36 ± 2°C. Concentration of glycine (meq/1) :
total glycine
glycine"
0
1.4 x io-3
1.4 X 10"
1.4 X 10i
4.1 X 10i
1.4 X 10=
0
2.3 X 10-5
2.3 X 10-5
2.3 X 10"1
6.8 X lO-i
2.3 X 101
proportion of aragonite decreases and that
of calcite increases.
With increasing concentrations of magnesium ions in a parent medium, the proportion of aragonite increases and that of
calcite and vaterite decreases.
When the influence of organic material
is greater or smaller than that of magnesium ions, only calcite or only aragonite is
formed, respectively. And it is noted that
organic material forming a stronger complex with calcium ions in a parent medium causes the formation of a Mg-richer
calcite, and that with increase in the temperature and the concentration of magnesium ions in a parent medium the magnesium carbonate content of precipitated
magnesian calcites increases.
When the influence of organic material
is almost equivalent to that of magnesium
ions, with increasing or decreasing temperature, the proportion of calcite de-
creases or increases, respectively, and the
proportion of aragonite increases or decreases, respectively.
The concentration of magnesium ions in
the body fluids of marine calcareous organisms seem little different from that of other organisms. It seems to be similar to that
in sea water.
If the term "biological species" in the
section on "Observations" is exchanged for
the phrase "kind and concentration of organic material in a parent medium", the
observed facts are completely in accordance with the results of the laboratory experiments (Kitano, 1968).
Only the presence of certain organic materials accomplishes the formation of carbonate crystals observed in marine biological systems. We must emphasize the very
important role of organic material in the
formation of crystals found in skeletal carbonates.
688
YASUSHI KITANO, NOBUKO KANAMORJ, AND AKIRA TOKUYAMA
REFERENCES
Jansen, (., and Y. Kitano. 1963. The resistance of
recent marine carbonate sediments to solution. J.
Oceanogr. Soc. Japan 18:208-219.
Kitano, Y., and T. Furutsu. 1959. The state of a
small amount of magnesium contained in calcareous shells. Bull. Chem. Soc. Japan 33:1-4.
Kitano, Y. 1962a. The behavior of various inorganic
ions in the separation of calcium carbonate from
a bicarbonate solution. Bull. Chem. Soc. Japan
35:1973-1980.
Kitano, Y. 1962i>- A study of the polymorphic
formation of calcium carbonate in thermal
springs with an emphasis on the effect of temperature. Bull. Chem. Soc. Japan 35:1980-1985.
Kilano, Y., and D. W. Hood. 1962. Calcium carbonate crystal forms formed from sea water by
inorganic processes. J. Oceanogr. Soc. Japan
18:141-145.
Kitano, Y. 1964. On factors influencing the poly-
morphic crystallization of calcium carbonate
found in marine biological systems, p. 305-319. In
Recent researches in the fields of hydrosphere,
atmosphere and nuclear geochemistry. Maruzen
Co., Ltd., Tokyo.
Kitano, Y., and D. VV. Hood. 1965. The influence of
organic material on the polymorphic crystallization of calcium carbonate. Geochim. Cosmochim. Acta 29:29-41.
Kitano, Y., and N. Kanamori. 1966. Synthesis of
magnesian calcite at low temperatures and pressures. Ceochem. J. 1:1-10.
Kitano, Y. 1967. Paleo-chemical composition and
paleo-temperature of ocean water. Kagaku,
Iwanami Co., Ltd. 37:366-372.
Kilano, Y. 1968. Factors controlling the crystal form
and the minor element content of carbonates
formed in marine biological systems—the geochemical significance of carbonate fossil. Chem.
and Chem. Industry 21:1017-1028.