Procedure and means for separating plastic particles electrically from solutions, in particular from cellulose and paper fibre solutions

Plastic particles are separated from liquid mediums having the same distributed therethrough, in particular cellulose and paper fiber-containing mediums by electrolytic separation. The liquid medium is introduced into a container provided with an anode, a cathode and a reference electrode, with the plastic particles being separated from the liquid medium by controlling the potential of the anode and the cathode so that the potential of the anode is at most 2800 mV S.C.E., preferably +1200 to -300 mV S.C.E., and the potential of the cathode is at least -3500 mV S.C.E., preferably from +120 to -2100 mV S.C.E. The control of the potentials of the electrodes is effected to such ranges that gas production is selectively provided on the electrodes for cleaning thereof.

BACKGROUND OF THE INVENTION 
Plastic particles are present as harmful substances in various liquid 
mediums such as those containing cellulose. The separation of these 
plastic particles from the liquid is very difficult. 
Electrical procedures for the removal of harmful plastic particles have 
been used primarily only in connection with some clarification procedures 
of waste water, floatation and in connection with certain plastic testing 
procedures. Such electrical procedures have not been used for the removal 
of plastic from among cellulose fibers. Instead, the removal of plastic 
from liquids containing cellulose fibers has in the past been accomplished 
primarily based on the density of the plastic, either in a liquid phase or 
by centrifugal procedures. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, plastic particles are 
electrically separated from liquids containing the same and also 
containing cellulose particles and/or paper fibers. 
It is a primary object of the present invention to provide a method which 
permits the separation of plastic particles from liquid mediums containing 
cellulose particles and/or paper fibers. 
It is another object of the present invention to provide electrical means 
for accomplishing this method. 
Other objects and advantages of the present invention will be apparent from 
a further reading of the specification and of the appended claims. 
The electrical conductivity of plastic is in general poor because plastics 
are insulating materials. The surface resistance of plastics varies within 
the range of 10.sup.10 to 10.sup.16 .phi., as a result of which the 
adhesion properties of the plastics are poor and moisting of the same is 
difficult. Because of the poor electrical conductivity, local charged 
areas are left in plastics in general as a result of working, abrasion and 
other treatment. Still further, the mobility of electrons in plastics is 
poor as a result of which the potential differences in different parts of 
the product are not able to discharge. 
Plastics constitute an electrical voltage series of their own, which is 
presented roughly in Table 1 below: 
TABLE 1. 
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Triboelectric Series 
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+ Rabbit hair 
Bakelite 
Cellulose acetate 
Glass 
Quartz 
Hair 
Wool 
Nylon 6 
Nylon 66 
Cat hair 
Viscose 
Cotton 
Leather 
Wood 
Paper 
Amber 
Metals 
PVC 
Ebonite 
Polystyrene 
Polyethene 
Teflon 
- Cellulose nitrate 
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Thus, it is still a further objection of the present invention to remove 
harmful plastic particles electrically from liquid mediums containing the 
same 
The method and means of the invention is mainly characterized in the 
separation of plastic particles present in a liquid medium containing the 
same, particularly liquid mediums also containing cellulose particles 
and/or papers fibers, by inserting an anode, a cathode and a reference 
electrode into the liquid, and controlling the potential of the anode and 
the cathode so that the potential of the anode is at most 2800 mV S.C.E. 
preferably +1200 to -300 mV S.C.E. or the potential of the cathode is at 
least -3500 mV S.C.E., preferably +120 to +2100 mV S.C.E.

DESCRIPTION OF PREFERRED EMBODIMENTS 
In accordance with the method of the present invention, a liquid medium 
containing undesired plastic particles is passed between two electrodes. 
The harmful plastic particles thus adhere to one of the electrodes. The 
electrode potential used to achieve adherence of the plastic to the 
electrode depends on the type of plastic. However, in all cases, the 
potential of the anode should not be greater than 2800 mV S.C.E., or the 
potential of the cathode must be at least -3500 mV S.C.E. 
In accordance with a further embodiment of the present invention, the 
potential of the electrodes is controlled in such manner as to selectively 
produce gas at the electrodes. 
FIG. 1 sets forth the results of a series of tests following the process of 
the present invention. In the tests series, stainless steel was used for 
the cathode material, and the plastic particles were distributed in an 
aqueous solution. A buoyancy angle of 45.degree. was used in the test 
series. The X axis in the figure depicts the potential, and the Y axis, 
the number of plastic particles which adhered to an electrode, as well as 
the percentage of the particles which adhere to the electrode with respect 
to the total number of particles in the solution. 
The graph confirms that at certain values of the potential, almost all 
plastic particles adhered to the electrode, 
The following markings were used in FIG. 1 for the various tests: 
Test 
52-69 
70-77 
78-91 
92-114 
The most suitable material for the electrode in carrying out the process of 
the present invention is stainless CrNi steel, an aluminum mixture, or 
metallic copper. In addition, electrode made from inert metals or coated 
therewith can be used for the process of the present invention. Still 
further, the electrode material may be graphite or carbon fiber. 
In those situations in which the liquid medium flows, the electrodes are 
installed in an optimum position and should have an optimum configuration 
selected from the particular conditions, for example, lamella, reticular 
or plate-like configuration. 
FIG. 2 diagrammatically illustrates a device for carrying out the process 
of the present invention. As shown therein, the liquid substance 1 
containing plastic particles distributed therethrough is placed in a 
container 5 or the like. By means of a power supply 10, a voltage is 
provided through poles 20 and 30 to electrode 2 and 3, respectively. When 
the neccesary potential difference exists between the electrodes 2 and 3, 
the particles adhere to the electrode provided with the appropriate 
potential. With the aid of a reference electrode 4, the potential of the 
other electrode is monitored and the information is transmitted to a data 
unit 12, which in turn transmits the measuring results to a conclusion 
unit 11. The conclusion unit 11 controls the functioning of the power 
source 10 so that the requisite potentials on both of the electrodes are 
appropriately maintained. A voltmeter 13 is connected to one of the 
electrodes for the monitoring of the voltage of the electrode. 
In the device of the invention, the cleaning of the electrodes 2 and 3 can 
be carried out by so controlling the potential between the electrodes, 
that vigorous gas formation takes place on the electrodes. This potential 
differs considerably from the potential used in the separation process. 
While the invention has been described with respect to a particular 
embodiment thereof, it is apparent that variations and modifications 
thereof can be made, and the invention is not meant to be limited to the 
specific details of the embodiment disclosed.