Note: Descriptions are shown in the official language in which they were submitted.
i3
FIELD OF THE INVENTION
The invention relates to an agent and a method for
the treatment of production cycle and effluent water of the
papermaking and related industries for the purpose of remov-
ing dissolved or colloidally dispersed organic substances.
BACKGROUND OF THE IN~EI~TION
The treatment of paper mill water circulations is
effected today practically exclusively with sedimentation,
flotation, or filtration pulp catchers, in part with the use
of chemical flocculation aids.
In view of exceedingly high costs of effluent puri-
fication and the atte~pt made for that reason to close the
cycle - i.e. to reduce the specific effluent quantity - this
procedure is obsolete. Possibilities of purification as pre-
viously discussed in the waste water sector should be moved
up into the cycle water so as to permit further narrowing of
the water circulation and at the same time to reduce the load-
ing of the residual waste water.
One of the greatest obstacles to further closin~ of
the water circulation in the paper industry is the concentra-
tion of dissolved or colloidally dispersed organic subs-ances
in the cycle water, which because of their predominantly
anionic nature cause considerable production disturbance
and loss of product quality. These substances, therefore,
should be removed from the cycle water to the extent possible,
in order to close the water circulation completely in cases
which are regarded to be impossible today. The second pro-
blem, i.e. the concentration of the electrolytes, should ke
reduced to simply a material problem, since it has been proven
that production and product quality are not notably influenced
by inorganic electrolytes.
~8~3
DESCRIPTION OF THE PRIOR ART
Solid adsorption agents in powder form have already
been used for the treatment of paper mill water circulations.
~or example, the use of alkaline-activated bentonites for this
purpose was disclosed in Wochenblatt fur Papierfabrikation,
105, 799-802 (1977). In the treatment of cycle water, how-
ever, alkaline-activated bentonites must be added to the
water in the form of a suspension and must therefore be re-
moved subsequently by sedimentation or flotation. Direct
filtration treatment is not possible because of the special
properties of the alkaline-activated bentonites.
DE-AS 21 21 198 discloses a method for the recovery
of fiber materials and fillers from effluents from the paper
industry. According to this method a mixture of (a) swelled
layer silicates transformed to the Na, K, NH4 and/or H form
in the usu~l way and (b) water-soluble macromolecular com-
pounds of filamentary molecule structure reacting with the
layer silicates and possibly with the fiber materials and
fillers is added to the effluent in a quantity sufficient
for the formation of total flock. The formed sludge phase
is returned to the papermaking process after separation is
completed. This literature reference, therefore, aims at
removing solid, undissolved substances from the effluent by
flocculation and subsequent filtration, while according to
this invention dissolved or colloidally dispersed organic
substances are to be removed from the production effluent by
adsorption. In the known methods, the use of the macromole-
cular compounds of filamentary molecule structure is essen-
tial, since without them recovery of fibrous and filler sub-
stances by flocculation is not possible. The layer silicate,
~ 3ossibly transformed to the H form, is present in a swelled
orm. Due to the mlld acid treatment, the layer structure
is still largely preserved. In particular the layer lattice
still contains practically the entire aluminum portion.
Accordingly, the sludge phase is contaminated by the macro-
molecular compounds of filamentary molecule structures and
is suitable only for the filling of paper or board of infer-
ior quality. Further the effluent separated from the sludge
phase e.g. by filtration still contains most of the dissolved
or colloidally dispersed org~nic disturbance substances and
therefore is unsuitable as cycle water. J. Weigl teaches in
Elektrokinetische Grenzflachenvorgange9 Weinheim, New York:
Verlag-Chemie 1977, 156 - 157 that a specific asbestos type
(chrysotile asbestos of high specific surface and positive
zeta potential) has good adsorption properties for anionic
organic substances.
I~ is also known that positively charged aluminum
oxide is a good adsorption agent for anionic organic sub-
stances. Industrially, this material is used in granulated
form in adsorption towers, the laden adsorbent being regener-
ated thermally (cf. Prog.Wat.Tech.10, 1978, ~9-96).
The cited :Literature references appear to suggest
that adsorption ag~nts of high specific surface and positive
zeta potential should be suitable for the treatment of paper-
making cycle waters.
It was found, however, that under indus~rial con-
ditions in the treatment of production cycle and effluent
waters of the p~permaking and related industries, that the
named adsorption agents gave unsatisfactory adsorption results,
although in model experiments they had at first proved to be
usable. Surprisingly, it was found that acid-activated clay
minerals, which generally have a negakive zeta potential,
gave in practice, better adsorption results.
SUMMARY OF THE INVE~TION
This invention provides a process for the treatment
of process water containing organic waste materials,
connected with the production of paper from wood pulp,
which comprises the steps of:
A. adding an adsorptive agent, having a negatively
charged surface to said process water, said adsorptive
agent comprising:
1. an acid-treated silicate-layered clay, having
a high surface area of at least 180 m2/gm and a high surface
energy and whic~ contains a major portion of the original
silicate layer in the form of free silicic acid and a minor
portion of the original aluminous constituent of said clay
and only residual amounts of the alkali and alkaline earth
metals originally present in the clay; and
B. separating the adsorptive agent from the
process water.
This invention proposes, then, an agent for the
treatment of production cycle and effluent waters of the
papermaking and related industries for the purpose of re-
moving dissolved or colloidally dispersed organic substances.
The agent is a negatively charged acid-treated clay. The
clay prior to acid-treatment is of the silicate-layered type
which includes the montmorillonite-beidellite series, the
chlorite group and minerals with a series disorder, i.e.
mixed layer silicates. Of particular interest in this in-
vention are the montmorillonite-beidellite series. The
~ 4 --
,~ i
53
silicate-layered clays are treated with acid such as hydro-
chloric or sulfuric so that a major portion of the original
silicate constituent is converted over to silicon dioxide
and free silicic acid. A substantial portion of the original
aluminous constituent is leached out by the acid treatment
and essentially all of the alkali and alkaline earth metal
constituents are removed by the treatment. The treatrnent is
such that the original clay loses much of its original proper-
ties and the silicate layer is converted over to a silicon
dioxide layer containing a substantial amount of free silicic
acid. The finished product has a high specific surface area
of at least 180 m2/gm and more preferably a surface area
in the range of 240-360 m2/gm. The surface has a
1early negative zeta potential and a high surface energy.
The finished product contains the siliceous constituent
in the range of 60-75% by weight expressed a SiO2.
~a -
., . , )
i3
The aluminous cons~ituent is present in the range of from
5-20~ expressed as A12O3 and the remainder consists essen-
tially of compounds of iron, magnesium, and calciu~ in
various proportions. The alkali and alkaline earth metal
constituents are essentially completely removed by the
acid -treatment. Only residual traces remain. The micro-
pore volume of the pores having a pore diameter of <800A
is at least 0.3 ml/gm. The negatively charged acid-treated
clay, having lost its original properties is added to the
process water at one of two different points. The materials
can be added to the water containing the pulp in suspension
- so that upon separation of the pulp from the water the
adsorptive agent, laden with the organic waste materials,
remains with the pulp as a filler. The organic waste
materials, which are either dissolved or colloidally dis-
persed, include proteins, humic acids, lignins, synthetic
retention aids, emulsifiers, dyes, and the like. In
another embodiment of this invention, the adsorptive agen~s
can be added to process water or to waste water prior to
their discharge from the process cycle, and the adsorptive
agent, after the proper processing time, is filtered from
the water, which is then either recycled back to the process
cycle or is discharged as essentially purified waste water.
The filter cake then can be collected and used as a filler
in subsequent batches of paper or paper board.
DESCRIPTION OF THE PREFERRED EMBODI~NT
~ . . _ . . . . _
Acid-activated clay minerals are, per se, known as
adsorption agents. Clay minerals belong to different structure
types. Clay minerals of the kaolinite structure type are
S3
for example kaolinite, nacrite, dickite, anauxite and
halloysite, as well as the serpentine minerals chrysotile,
serpentine, antigorite and amesite. Another structure type
comprises the mica-]ike layer silicates, which in turn are
divided into minerals of the montmorillonite-beidellite series,
vermiculate serles, illite series, and the mica minerals.
Especially important for the present purpose are the minerals
of the montmorillonite-beidellite series. Suitable further
are minerals of the chlorite group and minerals with species
disorder (mixed layer silicates). A general summary of these
clay minerals is found in "Ullmanns Encyklopadie der technis-
chen Chemie", volume 17 ~1966), pages 583 to 597. The acid
activation of these clay minerals is generally effected by
treatment with hydrochloric or sulfuric acid. This treatment
dissolves out the alkali and/or the alkaline earth component
practically completely and also dissolves a large part, (pre-
ferably at least 20 wt.%) of the aluminum and lron portion
present in the octahedral layer of the mineral. There remains
a product consisting predominantly of SiO2 with a high specific
surface of at least 180 m2/g, (preferably 240 to 360 m2/g) a
clearly negative zeta potential and a high surface energy.
Essentially, this product has lost the specific properties
of the clay mineral employed as starting product. The silicic
acid in the product consists in large part of free silicic
acid soluble in weak alkali solution. The product has a
micropore volume (800A) of a-t least 0.3 ml/g.
Acid activation of these clay materials is well
known and suitable acid-activated clays have been described
by the following: Carl-Ernst Hofstadt, et al, in U. S. Patent
3,901,826; Grant A Mickelson, et al, in U. S. Patent 2,981,697
(corresponding to German Patent 1,173,442); L. ~larbort, in
U. S. Patent 3,293,060; Carl J. ~alble, in U. S. Patent
~b
3,557,023; L. Sugahara, in U. S. Patent 3,915,731 (corres-
ponding to German patent 2,203,825); and Y. Sugahara, in
U. S. Patent 3,787,330.
The especially good effect of the acid-activated
clay minerals in the treatment of paper manufacture cycle
waters is surprising because the properties of ~hese products
in comparison to those mentioned before did not suggest such
an effect. Due to their swelling power and the resulting
special layered structure with possible formation of em-
bedded compounds and special charge distribution at the crystalflakes (planes charged negatively, edges positively), alkaline-
activated bentonites are known to be able to also adsorb
negatively charged organic compounds. Clearly, however, the
adsorption of positively charged compounds is preferred.
The above-named products chrysotile asbestos and
aluminum oxide prove effective in the treatment of paper
production cycle waters only if their zeta potential is
positive at the prevailing pH value in the cycle water.
Evidently, there is a connection between the surface charge
of the adsorbent and the charge of the organic substances
to be adsorbed.
The acid-activated clay minerals of the invention,
on the other hand, are employed in known applications for
the treatment of vegetable oils and mineral oils, i.e. in a
purely organic medium, while in aqueous medium they are employed
only for the removal of positively charged proteins from bever-
ages, mainly beer. The mechanism for the excellent adsorption -
according to the present invention, i.e. adsorption of pre-
dominantly negatively charged organic substances from aqueous
paper mill circulation on negatively charged surface of the
acid-activated clay minerals - is not fully understood.
The adsorbed organic substances, according to the
invention which are either dissolved or colloidally dispersed
-7-
"
~ 3
comprise, for example, proteins, humic acids, lignins, synthetic
retention aids, emulsifiers, dyes, and the like.
The preferred agents according to the invention are
acid-activated clay minerals of the montmorillonite ~ype.
The method according to the invention is carried out
preferably by adding the acid-activated clay minerals to the
mixture of substances present in aqueous suspension in the
process water.
According to owr embodiment of this invention, the
laden agent obtained in the treatment of the manufacturing
cycle or effluent water is reused as a filler substance. This
offers the rare case of a purification measure without the form-
ation of solid waste materials which would have to be eliminated.
The efficacy of the agents of the invention and a
comparison thereof with agents otherwise usable for such
treatments is explained in the following examples in a non-
~imiting manner. In Table I below, the properties of the
agents used in the experiments are compared. The acid-acti-
vated clay minera:Ls A to D according to the invention generally
had a SiO2 content of about 66 to 72 wt.%, an A12O3 content
of about 12 to 15 wt.%, and a loss on ignition of about 6 to
10 wt.%. The balance consisted essentially of Fe, Mg and Ca
in varying amounts. The products A to D differ from one
another essentially by their mean grain diameter and by the
pH value. They were obtained by acid digestion of a calcium
bentonite from the Moosburg area.
The comparison substances are generally commercial
products. The chrysotile asbestos is of the HBB type; the
two aluminum oxide types I and II differ primarily by their
specific surface; the alkaline-activated bentonite is sold
by Sud Chemie AG under the trademark "TIXOTON".
Table I. Properties of the test products.
Adsorption agent Spec. Mean Zeta potential mV Pore pH of the
surface grainvol. 1% aqueous
(BET) dia. pH SpH 7 1~ Hg/g suspension
m /g /um
Acid act. clay mineral A 260 2.5 -22 ~27 1.63 3.4
Acid act. clay mineral B 260 2.5 7.4
Acid act. clay mineral C 260 2.5 7.8
Acid act. clay mineral D 240 3.5
Chrysotile asbestos 55 - +32 +45 1.76 9.3
Aluminum oxide I 266 - +12 ~12 2.29 9.2
0 Aluminum oxide II 117 - +25 +20 0.67 5.1
Alkaline act. bentonite 46 * -20 -22 0.64 10.1
*Screen residue on 45 micron ~0.1%
The adsoprtion capacity of the substances listed
on Table I was tested at first on lignin sulonic acid as
model substance for anionic organic substances. Specifi-
cally there was used as model ~ubstance calcium lignin suf-
fonate, purified, mean molecular weight about 10,000. The
adsorption measurements were made on solutions containing
50 mg~lignin sulfonat~ per liter of tap water and wi~h an
ad~lltion of 1.0 g,adsorption agent per liter of solution.
Th~ contact time was 30 minutes; the separation was effected
by centrifuging. The results are summarized in Table II~
.
Tal~,le II. Adsorption of lignin sulfonate.
Adsorption agentAdsorption in %, referred to the con-
centration of the untreated solution
Acid activated clay mineral A 5.4
Acid activatel clay mineral D 8.0
Chryfiotile asbestos 58~7
Aluminum oxide I 44.0
Aluminum oxide II 86.0
30 Alkaline activated bentonite 7.1
_g _
The results show clearly ~hac the anionic organic
subs~ance can be ef~ectively adsorbed only by products with
a positive surface charge. This is as expected.
However, as will be shown in the following examples,
the manufacturing cycle waters occurring in industrial prac-
tice surprisingly behave differently from the model substance
lignin sulfonate.
Example__
In this example the adsorption of organlc substances
from the cycle water of a paper mill is set forth, the con-
tent of organic subs~ance being expressed by the Total
Organic Carbon TOC in mg.C per liter. Corresponding results
are found wi~h the use o~ other parameters for the contam-
ination of water by organic substance, as for example chemi-
cal oxygen requirement COR and biochemical oxygen require-
ment BOR.
The results of th investigations are given in
Table III.
Table III. Adsorption of organic substances from paper mill cycle water.
20 Adsorption agent Total organic carbon, TOC
_ _ mg.C/liter Decrease %
Untreated 210
Acid activated clay mineral A 80 62
Chrysotile asbestos 180 14
Aluminum oxide I 160 24
Aluminum oxide II 200 5
Alkaline-activated bentonite 140 13
For each of the measurements 1 liter of cycle water
was treated with 10 g of the adsorption agen~ to be tested.
In each case the adsorption agent was pre-swelled ~or 2
-10-
~ 3
hours with a little water, as the adsorption agents used
are in part dependent in their action on the degree of
preswelling. After addition of the preswelled adsorption
agent, the cycle water was stirred wlth a vane agitator
for 30 minutes, and then filtered through a glass fiber
filter. The comparison sample (untreated) was likewise
filtered through a glassfiber filter before the measure-
ment.
With this type of treàtment, a large excess of
adsorption agent is added to the water, so ~hat to some
extent ~he maximum possible adsorption output for execu-
tion of a one-stage ~reatment is measured.
The results clearly show that, contrary to expec-
tation, the acid-activated clay mineral gives the best
adsorption effect.
Example 2
In this example, the same investigations as in
Example 1 were carried out on the cycle water of a plant
for the production of mechanical wood pulp used as fiber
material in papermaking. In such a plant, wood is de-
fibered with addition of plenty of water, considerable
portions of organic ~ubstances being released. As the
resulting fiber paste is transferred to papermaking with
a solids content of between 2 and lOV/o, depending on the
technology, considerable amounts of the released organic
substances get into the paper machine cycle.
The treatmen~s are carried out in analogy to Example
1. The results are given in Table IV.
Tab].e IV. Adsorption of organic substances from cycle water of the
mechanical wood plllp department.
Adsorption agent Total organic carbon, TOC
m~C/lite~ Decrease %
. .,
Untreated 510
Acid-activated clay mineral A 290 43
Chrysotile asb~stos 450 12
Aluminum oxide I 450 12
Aluminum oxide II 430 16
Alkaline-activated bentonite 410 20
_ .
Exactly the same result i5 found as in the treat-
ment of paper machine cycle water~ although indubitably
this water shows a distinctly different composition.
Example 3.
It had been noticed in the investigations accord-
ing to Examples 1 and 2 that the treatment with the acid-
activated clay mineral A had shifted the pH value of the
treated sample from starting values of 6.0 in both cases
to 3.8 (Example 1) and 4.2 (Example 2), respectively.
In view of the highly acid nature of the adsorption agent
(Table I), this is not surprising. The other adsorption
agents used for comparison, on the other hand, shift the
pH value in both examples to values above 7~ It is logical
to suspect that the excellent effect of the acid-activated
clay mineral is caused by this pH displacement and could
be obtained similarly also by combination of an acid with
another adsorption agent. To check this assumption, inves-
tigations were carried out on another paper mill cycle
water with all four of the acid-activated clay minerals
listed in Table I. The tests were carried out in the same
manner as in Examples 1 and 2. The results are given in
Table V.
-12-
3~3
Table V. Adsorption of organic substances from paper ~ill cycle
water with consideratioh of the pH value.
Adsorption agent pH Total orga~ic carbon TOC
mg.C/liter Decre~se %
Untreated 6.1 220
Acid activated clay ~ineral A 4.0 140 36
Acid activated clay mineral B 7.2 150 32
Acid activated clay mineral C 7.4 150 32
Acid activated clay mineral D 4.1 145 34
Chrysotile asbestos 7.3 165 25
0 Aluminu~ oxide II 7.3 195 11
The results show clearly that the effect of the
acid-activated clay mineral is not attributable to a pH
value displacement, since Products B and C, which were
acid-activated but neutralized in subsequent processing,
gave practically the same effect.
E~
It was to be xamined to what extent the acid-
activated clay minerals actually absorb anionic organic
substances, which are especially disturbing in papermaking.
The determina~ion of the anionic substances was
effected by TOC measurement before and after a treatment
of the water with a celL].ulose capable of anion exchange~
The difference G~TOC) indicates the C content of the quan-
tity of anionic organic substances contained in the water.
The results are shown in Table VI.
-13-
3~
Table VI. Adsorption of anioni~ organic substances from cycle water
of the ~echanical wood pulp department.
Adsorption agent pH Total organic carbon, Anionic organic substances,
TOC measured on carbon content,
mg,C/liter Decrease ~ ~TOC
_ mg.C/liter _ Decrease % __
Untreated 7.7 515 - 260
Acid act. clay A 5.5 310 40 125 52
Acid act. clay B 7.6 330 36 145 44
Chrysotile asb. 7.9 425 18 225 14
Aluminum oxide I 7.9 440 15 230 12
10 Aluminum oxide II 7.6 420 19 240 8
I~ is found that, surprisingly, the acid-activated
clay minerals not only do absorb anionic substances, but
that they absorb them in much greater measure than the
positivély charged adsorption agents.
According to the invention, therefore, manufactur-
ing cycle waters or waste waters of ~he papermaking industry
and related branches of industry as well as waste waters
of similar composition can be freed from disturbinu organic
substances by addition of acid-activated clay minerals. The
~0 treatment according to the invention can be effect~d by one
or both of the measures stated below:
1. Addition of the adsorption agent to tAle material
present in aqueous suspension from which the prodl~ct (paper)
is produced. The adsorption agent remains in the product
together with the adsorbed organic substance. The water
liberated in the production, which is re-used as cycle water
or is discharged as waste water, contains fewer organic sub-
stances than without addition of the adsorption agent~
2. Treatment of the water liberated in the produc-
tion, which is returned as cycle water or discharged as waste
-14-
water, with the adsorption agent. Here the treatment is
effected preferably in a con~inuous filtration process,
in which an additional treatment step for the separation of
the laden adsorption agent is obvia~ed. The laden adsorp-
tion agent can be added as filler to the product produced
or to another product produced in the same or an adjacent
operation.
The method is characterized by ex~remely simple
technical feasibility, low cost of technical means for its
execution, and an ecologically beneficial treatment process
without occurrence of solid waste materia~s and free of
other polluting emissions.
-15-
