Note: Descriptions are shown in the official language in which they were submitted.
CA 02282432 1999-08-27
DE19718452A1
Description
The invention relates to new biosorbents for binding metal ions, produced from
residue
of the food industry, and to the production process and use of such
biosorbents.
The biosorption of heavy-metal ions to materials of bio-natural origin - which
is also
referred to as biosorbent - has created considerable, practical interest due
to the easy
and inexpensive accessibility, simple modifiability, partially high binding
capacity to metal
ions and their biodegradability. This biomass is obtained, e.g., as a by-
product or as
residue or waste material in large-scale fermentation, in the form of metal-
binding algae
in oceans, as well as in agriculture and in the forest, paper and food
industry. The use
of such biomass, which is available in large quantities and at low cost as
metal-
immobilizing biosorbents is an appealing alternative for removing heavy metals
from the
environment instead of the conventional ion-exchanger chromatography with
synthetic
polymers or inorganic materials.
Biomasses obtained in industrial processes of large-scale fermentations show
in some
cases a very high metal-binding capacity which, e.g., in some fungi can amount
to 25%
of their biomass, and in certain brown algae of marine origin even up to 30%
of their
biomass (Biotechnol. Prog. 1995, 11, 235-250). Such high binding rates are
generally
not the rule. Due to the fact that the microbial biomass obtained by
industrial means, and
the biomasses obtained by harvesting the algae of the oceans, are a cheap base
material for the production of heavy- metal ion binding biosorbents, more
effective
biosorbents are produced by chemically modifying such biomass.
Carbo-hydrate-containing raw materials, as well as by-products, residue or
waste
materials of the forest and paper industry, are likewise taken into
consideration as
potential biosorbents for metal ions. Even more than bioabsorbers.of microbial
origin,
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such carbohydrate-containing biomasses have first of all to be chemically
modified in order to
result in effective biosorbents. The modification reactions are carried out in
such a way as to
increase the already naturally existing, however very low ion exchange
capacity of these
biosorbents. Such high binding capacity is primarily achieved by introducing
phosphate
groups into the carbohydrate-containing biomasses derived from the forest and
paper
industry. Through phosphorylation with variable phospholating agents phosphate
groups are
convalent bonded, e.g., in cellulose (FA-A-2206977) lignocellulose (WO
93/11196) wood
residue (JP90-122269), saw dust (JP87-267 663), paper pulp (JP86-234-543) and
starch
(JP92-308 078). However, such biosorbents and the production processes thereof
have not
yet been technically applied.
In contrast to the biosorbents of marine and microbial origin and those
derived from the
forest and paper industry, the possibilities of biosorption of metal ions to
residue and waste
materials from agriculture and the food industry have not been examined to any
extent up to
now, and the chemical modification of such regenerative raw materials for the
development
of metal-binding bioabsorbers and their technical use for metal-ion absorption
has not been
considered at all.
Starting out from this premise, it is the object of the this invention to
suggest new biosorbents
for metal ions and a process to produce same on a bionatural basis.
The problem is solved with respect to the biosorbents by biosorbents on a
biological-natural
basis derived from grain grinding residue, and in regard to the production
process of
biosorbents by a method in which the residue is chemically treated to enhance
its metal ion
binding capacity. In a preferred embodiment, the bisorbent in accordance with
the invention
consist of residue from grain grinding in an aqueous system and/or particles
insoluble in
inorganic solvents, which have been modified through treatment with a
combination of the
general formula I
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a,
n c
R2
1
wherein X 0, S or NH
R1 = NH2, NH-NH2, and
R2 = NH2, NH-NH2, NH-CO-NH2, N(HC3)-CH2-COOH,
NH-(CH2)3 -CH(NHZ)-COOH,
and acids, such that the nitrogen content is in the range of 0.1 to 20%, the
phosphor content
in the range of 0.1 to 20%, and the sulphur content in the range of 0.1 to 8%.
In a preferred embodiment of the method of production of the biosorbents, the
residue from
grain grinding is treated at 50 to 200 C over a time span of 1 to 20 hours
with a combination
of the compound of general formula I, as defined above, and an acid, and
subsequently
separated.
Residue from grain grinding forms the basis of biosrobents, according to the
invention. Such
residue, which is obtained by extracting the flour from the grain, accumulates
in large
quantities in flour mills during the flour production process. Due to its high
carbohydrate
content, as well as its nitrogen content of approximately 3%, its
2a
CA 02282432 1999-08-27
phosphorus content of less than 2% and its sulphur content of less than 0.2%,
the
residue has only been used as animal feed up to now and not as a base material
for
useable products, e.g., for obtaining biosorbents for metal-ion binding.
Residue from
the grinding of all kinds of grain, such as wheat, barley, rye, triticale,
millet, as well as
corn and rice can be used to produce the biosorbents, according to the
invention.
Residue of grain grinding itself has - even though it is very low - a metal-
binding capacity
of less than 0.2 milli-equivalents per gram of dry material. In order to be
able to fully
utilize the advantages of the residue of grain grinding, it is necessary to
modify it, if
possible, by simple and inexpensive methods to achieve greater binding
capacities to
metal ions.
The biosorbents for binding metal ions are characterized by consisting
preferably of
spherical particles of residue of grain grinding - which are insoluble in
aqueous systems
and/or organic solvents - i.e. residue of grains from which the flour content
has been
extracted and which are composed of carbon, hydrogen, oxygen, nitrogen,
sulphur and
phosphorus and in which the residue of grain-grinding is modified in such a
way that the
nitrogen content of the biosorbents is 0 to 20% (preferably 4 to 15%), the
phosphorus
content is 0 to 20% (preferably 6 to 15%) and the sulphur content is 0 to 8%.
According to the invention, the ground-grain residue is modified preferably by
reacting
it with carbonic or thiocarbonic acid derivatives, or mixtures of both, of
general formula
(1),
R1
X= C
R2
in organic solvents or watery solutions, or a mixture of both at temperatures
of 50 C up
to 200 C in the presence of an acid, or if necessary, also without acid.
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In another exemplified production process of biosorbents, according to the
invention, 0.1
part by weight of sulphuric acid and 2 parts by weight of an addition compound
of
phosphoric acid and carbonic and/or thiocarbonic acid derivative, or a mixture
of both,
and possible also 0.5 up to 2 parts by weight of sodium triphosphate are
dissolved or
suspended in 20 parts by weight of distilled water. 1 part by weight of
residue of grain
grinding is added to this mixture and worked to a well mixed, dough-like mass
which is
processed as described above.
As a result of such production processes, biosorbents with a very high metal-
ion binding
capacity are obtained. Their typical exchange capacities range from 3 to 6
milli-
equivalents per gram of dry biosorbent. By varying the concentration of the
reaction
components, solvents, reaction temperatures and the reaction time, it is also
possible,
if requested, to synthesize biosorbents with lower exchange capacities than
those
indicated above.
The reaction mixtures are reprocessed in such a way that the solvent is
separated from
the suspensions, and the remaining solid matter is washed with water, diluted
hydrochloric acid and distilled water, and then dried at 100 C. The solid
matter of the
former dispersion is to be suspended in water and likewise washed with water,
diluted
hydrochloric acid and distilled water and subsequently dried.
Biosorbents based on residue of grain grinding can be used very
advantageously,
according to the invention, to absorb metal ions, particularly, however, the
ions of heavy
metals and radionuclides. They have a substantially higher binding capacity of
those
ions than the unmodified residue of grain grinding. The absorption of metal
ions can be
accomplished by way of the batch procedure as well as the column procedure. In
the
batch procedure the biosorbents are suspended in the metalliferrous solutions,
which
should have a pH-value of 4 to 8, preferably 4.5 to 7Ø The solution is
stirred for 0.3
minutes up to 8 hours, preferably 0.5 to 3 hours. Thus, the metal ions become
bound
to the bioabsorber. In the column procedure, the bioabsorbers are filled into
a
chromatographic column. The content of the column is brought -to a pH-value as
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CA 02282432 1999-08-27
described in the batch procedure, and the metalliferous solution of the same
pH-value
is passed continuously through the column. In doing so, the metal ions
likewise become
bound to the biosorbents. According to the dimensioning of the column content
and the
metalliferous solutions of heavy metals, water purified in compliance with
statutory
regulations leaves the column. The metalliferous bioabsorbers can subsequently
be
regenerated with diluted acids and re-used for metal-ion binding purposes.
A special advantage of the biosorbents, according to the invention, is that
the residue
and waste material obtained from the food industry can be used as biosorbents.
Particularly the residue of grain-grinding which accumulates in flour mills as
remainder,
by which is meant the residue of the grain from which the flour has been
extracted, is
a potential material. Such residue has characteristics which make the latter
especially
suitable for the development of biosorbents. Said residue is insoluble in
watery or
organic solvents, and its change in volume is insignificant when subjected to
a change
in the pH-value or in ion strength. Furthermore, such residue is hydrophillic
and can
therefore very well tolerate being wetted with water. Thus, it is suited for
work in
aqueous media without restrictions. Due to the physical properties said
residue is most
suitable for the continuous application of metal-ion absorption in columns for
the flow
chromatography despite its bio-organic nature.
The biosorbents obtained according to the invented process, show a
substantially
improved binding capacity to metal ions, particularly, however, to heavy-metal
ions and
ions of radionuclides than the unmodified residue of grain grinding or the
biosorbents of
marine or microbial origin. Due to standardized production processes,
reproducible
binding rates for metal ions are available with respect to such biosorbents,
which,
however cannot be guaranteed for algae and microorganisms. In the latter case
the
metal-binding rate depends mainly on growth conditions. The biosorbents,
according to
the invention, bind univalent metal ions as well as metal ions of a higher
valence and
surpass in their binding capacity to heavy-metal ions and radionuclides the
conventional
absorbers of organic or inorganic origin.
CA 02282432 1999-08-27
In the compounds of the general formula (1) the following mean:
X = O,S, NH;
R1 = NH2, NH-NH2; and
R2 = NH2, NH-NH2, NH-CO-NH2 N(CH3)-CH2-COOH.
N H-C Hz)3-C H( N HZ)-COO H
The invention relates, in addition, to a production process for biosorbents
for metal ions
on a bionatural basis in which the residue of grain grinding is treated with
the above-
described compound of the general formula (1) and subsequently separated. The
residue
of grain grinding is preferably processed in the presence of an acid. The
duration of the
treatment with the compound of the general formula (1) can range from 1 to 20
hours
at a temperature of 50 to 200 C.
The modification is achieved in an organic solvent, a watery solution or a
mixture of
both.
Aprotic solvents with a higher boiling point, preferably dimethylformamide or
dimethyl
sulphoxide, are used as solvents. As watery solutions, it is preferable to use
either
distilled water or phosphate buffer with a pH-value of 5.0 to 8.0 and an ion
strength
ranging from 0.01 to 1 Mol/L, which may contain, in addition, polyphosphates
and/or the
salts thereof, or mixtures.of the above-mentioned organic solvents and watery
solutions.
Sulphuric acid and/or phosphoric acid and/or polyphosphoric acid are used as
acids.
A preferred production process is characterized by suspending the residue of
grain
grinding either in a solvent which contains a carbonic acid or thiocarbonic
acid derivative
or a mixture of both and possibly a dissolved acid. The suspensions are heated
to 100 C
up to 200 C, preferably to 140 C up to 160 C whilst stirring. The stirring
continues at
the selected reaction temperature for 0.5 to 8 hours or, however, the
suspension is
processed into a disperse dough-like system by using the compounds of the
general
formula (1), which are dissolved in the solvents, and possibly an acid. Such
dough is
subjected for 2 to 20 hours, preferably 4 to 15 hours to a temperature of 60 C
to 100 C,
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preferably 700 to 80 C. The subsequent modification of the residue of grain
grinding at
temperatures of 120 C to 200 C, preferably 140 to 160 C is completed within 1
to 10
hours, preferably 2 to 5 hours. In both cases the duration of the heating
depends on the
selected temperature. The incubation can be accomplished statically or in a
mobile
manner by means of appropriate devices.
The weight ratios of the components to be used for the reactions can be chosen
freely
to a large extent. The weight ratio of the acid to the carbonic acid or
thiocarbonic acid
derivative, or a mixture of both is set to 0.1:2 up to 0.1:20, preferably 1:2
up to 1:6, and
possibly by adding 0.1 up to 5 parts by weight, preferably 0.5 up to 2 parts
by weight of
a polyphosphate or its alkali salt. It is advantageous to produce a
concentrated solution
from the solvent used and the carbonic acid and/or thiocarbonic acid
derivative, or a
mixture of both.
In an exemplified process to produce the new biosorbents, one part by weight
of
phosphoric acid with 6 parts by weight of carbonic acid and or thiocarbonic
acid
derivative, or a mixture of both, are dissolved in 100 parts by weight of
dimethylformamide at 80 C. 10 parts by weight of residue of grain grinding is
added to
this solution, and the modification of the ground-grain residue is carried out
according
to the selected and determined conditions as described above.
In a particularly advantageous production process of biosorbents, according to
the
invention, 1 part by weight of phosphoric acid and 4 parts by weight of
carbonic and/or
thiocarbonic acid derivative, or a mixture of both, and possibly, in addition,
0.5 to 2 parts
by weight of sodium triphosphate are dissolved or suspended in 30 parts by
weight of
distilled water. By adding 15 parts by weight of ground-grain residue to this
solution or
suspension and by mixing the components well, a dough-like mass is produced
which
is kept at 75 C for 15 hours. Thus, the modification of the residue of grain
grinding,
according to the above-mentioned conditions of reaction, is completed.
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The residue of grain grinding required for the production of the biosorbents,
according
to the invention, is easily accessible, cheap by being the remainder of the
grain grinding
process, and easy to modify with inexpensive chemicals.
The invented production process can also be carried out in such a way that no
aprotic,
organic, and in many cases toxic and environmentally hazardous solvents have
to be
used. The metal-loaded biosorbents can be easily regenerated with diluted
acids and
subsequently re-used for metal absorption. Due to their bio-organic nature,
biosorbents
which have become unusable or are no longer completely regenerative can be
combusted as an advantageous means of disposal so that only a small volume of
inorganic material remains as residue. After becoming loaded with particularly
problematic metal ions, e.g., radionuclides, the disposal of the biosorbents
is much
simpler compared to the conventional absorbers for radionuclides based on
sythentic-
organic polymers or inorganic absorbers. In addition, the invented
bioabsorbers are
biodegradable, so that after the binding of the radionuclides and the
entailing removal
of same from the environment, e.g., through composting or anaerobic
fermentation whilst
obtaining methane from bioabsorbers loaded with radionuclide, there is less
special
refuse.
The bioabsorbers derived from regenerative raw materials, preferably residue
of grain
grinding for metal-ion absorption, can be used for the metal-ion elimination
from soakage
water, watery solutions and extracts from soil, sludge, industrial residue and
urban
waste, as well as water from processing, and waste-water from energy-
producing,
material-transforming, municipal and agricultural enterprises.
The invention is explained below in greater detail by six examples.
Example 1
4 g of carbamide phosphate and 1 mL of concentrated sulphuric acid are
dissolved at
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60 C in 100 mL of dimethylformamide, and 10 g of dried residue of grain
grinding is
added to the solution. Whilst stirring, the suspension is slowly heated to 145
C, and at
this temperature the suspension is continued to be stirred for 3 hours. The
solid matter
is filtered off and washed with water, 0.1 n of hydrochloric acid and
distilled water and
dried at 100 C.
This bioabsorber has a nitrogen content of 3.85%, a sulphur content of 0.32%
and a
phosphorus content of 3.15%. 1 g of dry bioabsorber is suspended in 25 mL of
distilled
water and filled into a chromatographic column, and the content of the column
is set to
a pH-value of 5Ø A cupric sulphate solution of the same pH-value is guided
through
the column in order to determine the bonding capacity of the bioabsorber. It
amounts to
46 mg Cu per gram of bioabsorber.
Example 2
A mixture of 4 g of carbamide phosphate and 2 g of sodium triphosphate are
dissolved
at 80 C in 30 mL of water. By adding 5 g of residue of grain grinding to it
and mixing the
mixture well, a dough-like mass is produced. This mass is first of all kept at
75 C for
15 hours and afterwards for 2 hours at 150 C. The dark mass is subsequently
suspended in 150 mL of water, filtered off, and washed several times with
water, 0.1 n
hydrochloric acid and distilled water and dried at 100 C.
This bioabsorber has a nitrogen content of 3.64%, a sulphur content of 0.22%
and a
phosphorus content of 4.11%. The binding capacity is determined as described
in
Example 1. It amounts to 52 mg Cu per gram of bioabsorber or 48 mg Co per gram
of
bioabsorber.
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Example 3
g of thiocarbamide and 30 g of carbamide are dissolved together with 15 g of
ortho-
phosphoric acid at 75 C in 50 mL of dimethylformamide. 15 g of residue of
grain grinding
is added to this solution. By mixing this mixture well, a dough-like mass is
produced.
This mass is first of all kept at 75 C for 15 hours and afterwards at 150 C
for 2 hours.
The dark mass is subsequently suspended in 150 mL of water, filtered off, and
resuspended in a solvent mixture of 100 mL of ethanol and 20 mL of 0.1 n
sodium lye
and stirred at 80 C for one hour. After filtering off again, the solid matter
is washed
several times with water, 0.1 n hydrochloric acid and distilled water and
dried at 100 C.
This bioabsorber has a nitrogen content of 5.17%, a sulphur content of 2.85%,
and a
phosphorus content of 7.55%. The binding capacity is determined as described
in
Example 1. It amounts to 75 mg Cu per gram of bioabsorber or 210 mg Pb per
gram
of bioabsorber.
Example 4
30 g of carbamide and 15 g of ortho-phosphoric acid are dissolved at 75 C in
30 mL of
water. 15 g of residue of grain grinding is added to this solution. By mixing
this mixture
well, a dough-like mass is produced. This mass is first of all kept for 15
hours at 75 C
and afterwards at 150 C for 2 hours. The dark mass is subsequently suspended
in 150
mL of water, filtered off, and washed several times with water, 0.1 n
hydrochloric acid
and distilled water, and dried at 100 C.
This bioabsorber has a nitrogen content of 8.19%, a sulphur content of 0.38%
and a
phosphorus content of 14.02%. The binding capacity is determined as described
in
Sample 1. It amounts per gram of bioabsorber to 145 mg Cu, 245 mg Ag, 165 mg
Ni,
178 mg Co, 122 mg Cr, 117 mg Mo, 150 mg Zn, 132 mg Mn,385 mg Pb, 324 mg Hg,
275 mg Cd, 436 mg U, 356 mg Cs.
CA 02282432 1999-08-27
Example 5
20 g of semicarbazide hydrochloride and 10 g of polyphosphoric acid are
dissolved at
80 C in 30 mL of water. 10 g of residue of grain grinding is added to the
still warm
solution. By mixing the mixture well, a dough-like mass is produced. This mass
is first
of all kept for 15 hours at 75 C and afterwards at 150 C for 4 hours. The dark
mass is
subsequently suspended in 150 mL of water, filtered off, and washed several
times with
water, 0.1 n hydrochloric acid and distilled water, and dried at 100 C.
This bioabsorber has a nitrogen content of 19.10%, a sulphur content of 0.18%
and a
phosphorus content of 3.86%. The bonding capacity is determined as described
in
Example 1. It amounts to 85 mg Cu, 110 mg Ag, 65 mg Co, 201 mg Hg, 98 mg Cd or
197 mg U per gram of bioabsorber.
Example 6
20 g of aminoguanidine hydrogen carbonate, 2 g of sodium triphosphate and 10 g
of
ortho-phosphoric acid are separated from pH value 7.0 in 30 mL of 0.1 m
phosphate
buffer, and the pH-value of the solution is brought with 2 n sodium lye again
to pH-value
7Ø 15 g of residue of grain grinding is added to the solution, and by mixing
the mixture
well a dough-like mass is produced. This mass is first of all kept for 10
hours at 75 C
and afterwards for 5 hours at 140 C. The dark mass is subsequently suspended
in 150
mL of water, filtered off, and washed several times with water, 0.1 n
hydrochloric acid
and distilled water, and dried at 100 C.
This bioabsorber has a nitrogen content of 4.43%, a sulphur content of 0.56%
and a
phosphorus content of 4.81%. The bonding capacity is determined as described
in
Example 1. It amounts to 55 mg Cu, 48 mg Zn, 162 Pb, 74 mg Cd or 148 mg Hg per
gram of bioabsorber.
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