[0001] The invention relates to a process for the preparation of a solid carbon-containing
material having a sorption capacity for metal ions. The preparation of a solid carbon-containing
material having a sorption capacity for metal ions is known in itself. In the Netherlands
Patent Application 6 805 305, for instance, a process is described in which polymers
of vinyl aromatic hydrocarbons are reacted with a compound made up of sulphur and
chlorine in the presence of a catalyst and the resulting polymer sulphides or polymer
polysulphides are oxidized or reduced.. Reduction results in the formation of thiol
resins which have a high affinity for ions of heavy metals. A disadvantage to the
known metal adsorbing material is its high price. This is due both to the high price
of the starting materials and the relatively complex process to be used for the preparation
of the desired thiol resins.
[0002] Particularly, when a material is considered which does not qualify for regeneration
once it is spent, the known process must be regarded as costly.
[0003] Surprisingly, is has now been found that a solid carbon-containing material having
a sorption capacity for metal ions can be obtained in an inexpensive and simple manner
by mixing the carbon-containing starting material with sulphur, heating the mixture
for some time to a temperature of about 120
o-500
o C., and subsequently treating it with an aqueous solution of alkali metal hydroxide
an a temperature not exceeding about 200° C. Tt should be
[0004] treatment with sulphur of a carbon-containing starting material, viz. a synthetic
rubber and/or natural rubber, in order to obtain an active carbon is known in itself
from the Netherlands Patent Applicaticn 7 210 632. Besides sulphur, however, a great
many inorganic and organic compounds are mentioned, the use of which is apparently
preferred since no example is given in which sulphur is employed. After pyrolysis
the resulting active carbon can be further activated by burning the carbon. Both from
the way in which further activation takes place and from the applications mentioned,
such as the treatment of water, sugar juices, etc., it further appears that for the
active carbon described in the last-mentioned patent application a mainly physical
adsorption is envisaged.
[0005] For the process according to the invention various carbon-containing starting materials
may be used. As examples of suitable materials may be mentioned waste materials such
as waste rubber, but also peat, liqnite, coal, asphalt or petroleum coke. They are
preferably used in a finely divided state, in the form of for instance chips or grains
having a diameter of not more than a few millimeters. The rubber to be used may be
of synthetic or natural origin. It will generally occur in the form of worn tyres
of automobiles or other motor vehicles or means of transport, and in the form of worn
objects that are partly or entirely made of rubber, such as conveyor belts. The rubber
objects may be cut up or ground in any convenient manner, possibly after removal of
metal parts, for instance from the beads of automobile tyres. The process according
to the invention is usually so carried out that before, during or after the carbon-containing
starting material is cut up, it is mixed with 0.1 to 5 parts by weight of sulphur
and subsequently heated for a number of hours in an oven at a temperature in the range
of about 120 to 500
o C. Preference, however, is given to a treatment with 0.5 to 1.5 parts by weight of
sulphur per part by weight of starting material at a temperature between about 200
and 300
o C. '
[0006] The subsequent treatment of the sulphurized material with an aqueous solution of
an alkali metal hydroxide can suitably be carried out at a temperature not exceeding
about 200 C.; above 100 C.the treatment is usually done in an autoclave. It is preferred
that use should be made of a sodium hydroxide solution, for instance a 10% NaOH solution,
by which with proper stirring the treatment can be completed within a few hours at
a temperature of 800C. or higher.
[0007] It has further been found that in the treatment with an aqueous sodium hydroxide
solution the formation of thiol groups can still be considerably furthered when in
the sodium hydroxide solution there is also dissolved an alkali metal sulphide. Depending
on the amount of sulphur previously added to the starting material such a sulphide
solution may already be sufficiently formed in situ, so that the sodium hydroxide
solution used also may with advantage be employed for treating a fresh batch. In many
cases, however, it is advisable, that the sulphide should be dissolved in the aqueous
sodium hydroxide solution beforehand, for instance 10% Na
2S in a 10% NaOH solution.
[0008] The material successively treated with sulphur and an aqueous solution of NaOH is
finally filtered and/or washed with (acidified) water, after which it is ready for
use.
[0009] The physical appearance of the novel adsorbing materials according to the invention
may vary from gel form to porous solid matter.
[0010] For example the material obtained by treating cut up automobile tyres at a temperature
between 180
o and 280
o C.has a gel like structure. Treatment of the same starting material at a temperature
above 400° C. results in obtaining a material having a porous structure.
[0011] The material produced with the process according to the invention not only shows
the property of a cation exchanger, but is also capable of binding metals that occur
in the form of anionic complexes.
[0012] Moreover, the material according to the invention appears to have a high reducing
capacity, which is particularly manitest in the sorption of ions of noble metals,
such as gold and silver, and cf metals of the platinum group. It is also found possible
for instance to reduce Cr0
42- to Cr
3+. This means that the novel material according to the invention can also be looked
upon as an inexpensive reducing agent. Another useful application of the material
according to the invention consists in the removal of mercury from concentrated sulphuric
acid, as obtained by roasting zinc sulphide.
[0013] 
from it, if desired, by dry distillation.
[0014] It has further been found that the practical applicability of the material prepared
by the process according to the invention can still be considerably improved upon.
[0015] To that end the invention also provides a process in which prior or subsequent to
thermal treatment the starting material is subjected to a treatment with sulphur or
oleum, or still heated in the presence of air or some other oxygen-containing gas.
[0016] By this additional treatment there are introduced a small number of more or less
polar groups such as sulphonic acid groups and/or carboxyl groups, which promote the
swelling cf the material in water. In practice the treatment with sulphuric acid
will as a rule be carried out by bringing 1 part by weight of the material to be treated
into contact for some time with 1 to 4 parts by weight of 96% by weight H
2S0
4, Upon completion of the reaction the material is centrifuged and washed with water.
It is preferred that the treatment with air should take place in a fluid bed. The
present invention will be further described in the following examples. These examples
are, of course, only meant to illustrate and not to limit the invention.
Example 1
[0017] By cutting up old autombile tyres rubber chips measuring 1 to 2 mm were obtained.
Of these chips 100 parts by weight were mixed with 120 parts by weight of sublimed
sulphur. The resulting mixture was subsequently heated in a rotating steel oven for
eight hours at a temperature of 230° C. Next, the temperature was increased to 280°
C. over a period of 8 hours. There were obtained 130 parts by weight of hard grains.
[0018] Half of the resulting material, while in the fluidized state was subsequently heated
in air at 350
o C. over a period of 6 hours and thereafter stirred for 4 hours at 30
o C. in an aquecus solution containing 10% NaOH and 10% Na
2S. The chips were then filtered off and washed with water. After the material had
been acidified with a solution of 5% by wieght and washed with water, a product IA
was obtained whose ien exchanging properties are given in Example VI and Example IX.
The other half of the material, instead of being heated in air, was heated for 4 hours
to 90°C. with stirring in the presence per part by weight of. granules of 3 parts
by weight of concentrated (95% by weight) sulphuric acid. After the acid had been
washed out with water, the same treatment was carried out as described above for the
first batch of chips. The ion exchanging properties of this product IB are given in
Example VII and Example IX.
Example II
[0019] Brown coal briquettes were crushed and ground into grains measuring 1 to 2 mm.
[0020] After drying in an oven at 105
o C.100 parts by weight of the grains made up of brown coal and pitch were mixed with
50 parts by weight of sulphur and introduced into a rotating steel oven whose temperature
was raised to 350
o C.over a period of 4 hours. There were obtained 90 parts by weight of hard grains
which were heated for 2 hours at 90
0 C in an aqueous solution containing 10% by weight of NaOH.
[0021] The grains, which had strongly swollen in the aqueous NaOH solution, were successively
washed with water and acidified with dilute sulphuric acid (5% by weight of H
2SO
4). After they had again been washed with water, their properties were determined.
The results are given in Example VIII and Example IX.
Example III
[0022] 100 parts by weight of coal grains (containing 24% volatile material) measuring 1
to 2 mm were mixed with 100 parts by weight of sulphur and subsequently heated for
8 hours in a rotating steel oven, with the temperature being gradually raised from
120°C to 300° C.
[0023] After cooling it was found that the yield of


[0024] the mixture thus obtained was heated for 4 hours at 300° C. Finally, the resulting
grains were still heated for 5 hours at 90 C.with an aqueous solution of 10% by weight
NaOH and 10% by weight Na
2S. Next, as in Example III, the grains were successively washed with water, excess
acid and water.
[0025] The results are given in Example IX.
Example V
[0026] 100 arts by weight of asphalt were heated, with stirring, with 100 parts by weight
of sulphur. At a temperature of 200° C.H
2S escaped. Upon continued heating to 260° C the viscosity of the mass increased. 4
hours the mass was left to cool down, followed by crushing it into grains measuring
0.5 to 1.5 mm. Subsequently, 100 parts by weight of the sulphurized material were
treated for 16 hours at 100° C. with 200 parts by weight of 96% by weight H
2SO
4. After the material had been cooled and the concentrated H
2SO
4 been centrifuged off, it was washed with water until acid free and treated with an
aqueous NaOH/Na
2S solution in the way indicated in Example IV. NaOH/Na
2 S solution in the way indicated in Example IV.
[0027] Upon analysis it was found that this material contained strongly acid groups in an
amount of as little as 50 meq/l. When 25 ml of grains had been introduced into a 20
cm column, they were found capable of sorbing all silver from a fixing bath containing
1 g Aq per litre.
Example VI
[0028] To illustrate the strong metal adsorbing capacity of the material prepared by the
process according to the invention the product prepared in Example I A was tested
for its capacity of retaining mercury from a HgCl
4 ions-containing solution.
[0029] Hg Cl
4 2- ions-containing solution.
[0030] Through a column of the product prepared in Example I A 20 cm in bed weight and having
a bed volume of 25 ml there was passed an aqueous solution containing 100 mg Hg
2+ and 10 grammes of NaCl per litre.
[0031] Over a period of 30 hours 10 titres of 400 bed volumes of this solution were passed
through the column. Next, it was found upon analysis by flame spectrometry that the
effluent still contained only as little as about 1 ppb (part per billion) of mercury.
Comparative experiments in which use was made of frown coal briquettes (particle size
0.5 to 1.5 mm) treated with an aqueous solution of NaOH and of coal grains also areated
with such a solution and fluidized in air ("Oxycoal") yielded

[0032] These materials, however, were not capable of retaining mercury a Hg Cl
4 ions-containing solution.
[0033] This capacity is not obtained until the material has been

Example VII
[0034] The product prepared in Example I B was introduced into a 20 cm as used in Example
VI. Through the column there was passed a sulchirie acid solution (pH = 1) containing
chromium in the form of Cro. in an amount of 35 mg/l. After the passage of 20 litres
or 800 volumes the yellow solution was still found to get entirely

Example VIII
[0035] 25 ml of granular material prepared in the way described in Example It were introduced
into a 20 cm column, as used in Example VI

Through the column there was passed a solution of 1 mg Cu in 25% by weight sulphuric
acid. After a passage of 40 bed volumes over a period of 8 hours no copper could be
found in the effwens of the column.
[0036] The solution was subsequently replaced by a 5% sulphurie acid

containing about 100 mg Ag per litre.
[0037] Here too, after a passage of 1 litre over a period of 9 hours, silver could be detected
in the effluent of the column, Finally, the silver solution was replaced by a sulphuric
acid gold solution (about 100 Au
3+ per litre). After 1 litre of this solution nad (about 100 mg Au per litre) . After
litre of this solution nad been passed through over a period of 8 hours, this metal
ion

found to be completely adsorbed. The sorptions were attended

reduction of the metal ions.
Example IX
[0038] 
[0039]
