Purification process of polar liquid wastes containing suspended solvated particles and flocculating composition therefor

A process to purify polar liquid wastes consists in treating the wastes with a flocculating composition formed by a concentrated suspension of montmorillonite into a polar liquid, and preferably into the same polar liquid waste to be treated. Selected pH and concentration ranges are determined in order to obtain short or very short contact times and a complete purification of the treated polar liquid wastes.

FIELD OF THE INVENTION 
The present invention concerns a process to purify polar liquid wastes 
containing colloidal dispersions of solvated particles, and a flocculating 
composition used in said process. The liquid resulting from said process 
is totally purified from said solvated particles and can thus be 
reintroduced in the environment or recycled into an industrial process 
without undergoing further treatments. 
BACKGROUND OF THE INVENTION 
It is known that the main problem connected to the use of water for 
agricultural, civil and industrial purposes, lies in the huge consumption 
of water which, after having been used, cannot be re-employed due to the 
impurities contained therein, or otherwise creates several pollution 
problems when disposed of in the environment. 
The present international and European Union guidelines on water 
consumption provide for drastic reductions in the water resources for 
agricultural, civil and industrial uses, imposing the partial or total 
recycling of the waste waters resulting from the primary working cycles in 
which the water is used. 
Liquid colloidal dispersions are characterized by dispersions of solids, 
liquids or gases into a homogeneous liquid. Two stability factors enable 
the particles of the different substances to remain in suspension and 
separate so as to form a liquid colloidal dispersion: electric charge or 
salvation. 
Electric charge causes the repulsion of the particles and is determined by 
the absorption of ions onto their surface. 
Solvation is determined by the tendency of many substances to cause the 
molecules of the polar liquid in which they are suspended to strongly 
adhere thereon, forming a coating which prevents them from joining and 
thickening. 
The treatment of liquid colloidal dispersions characterized by electrically 
charged particles involves no particular difficulties, in that the 
addition of electrolytes reduces the dispersion, causing the flocculation 
of the dispersed impurities. 
The problem created by solvated particles is instead more difficult to 
solve, since salvation confers to the colloids a far higher stability than 
electric charge. Solvated particles are practically insensitive to the 
action of electrolytes and, furthermore, polar liquids allow stable 
suspensions to be formed also with relatively large particles (emulsions 
and/or suspensions of bentonites clays kaolin and the like). 
There is hence an unsatisfied demand for a simple and economic process apt 
to efficiently separate solvated impurities from polar liquid wastes 
containing colloidal dispersions thereof, so as to allow the resulting 
clear liquid to be discharged into its natural environment with no 
pollution problems. Since many primary working processes make use of large 
quantities of fresh water, a process of this type would provide the 
considerable advantage of drastically reducing fresh water consumption; in 
fact, once the dispersed impurities have been removed, it would often be 
possible to recycle the water initially used in the primary process. 
Preferably, such impurities should be separated into a non-liquid form so 
as to be easily eliminated. 
Such a process will obviously be the more advantageous, the higher the 
possibilities of its universal use, independently from the nature of the 
solvated impurities. 
SUMMARY OF THE INVENTION 
The Applicant has thus been involved in deep studies in order to seek a 
purification process allowing to obtain clear liquids from polar liquid 
wastes containing colloidal dispersions of solvated particles, to be 
carried out on the widest range of liquid wastes containing this type of 
colloidal dispersions, and to provide the highest reliability with the 
most disparate solvated substances. A further problem having to be faced 
in said process is to use therein only additives which are not apt to 
increase the salt and/or impurity contents in the waste waters being 
purified; moreover, such additives should preferably be food grade ones, 
as many waste waters result from food industries whereby, to recycle the 
purified waste waters in the primary working cycle, the additives used in 
the purification process need to be harmless. 
At the end of his studies the Applicant has surprisingly discovered that 
montmorillonite --commercially known as a thickening agent, to be used in 
combination with flocculating agents in order to increase the weight and 
volume of already formed flocks and favor their precipitation, as 
disclosed for example in FR-A-2640613 / - has instead the capacity to give 
rise, itself to the forming of flocks with solvated particles. In selected 
conditions, said flocculation turns out to be exceptionally effective and 
fast. 
On the basis of such a discovery the Applicant has conceived the present 
invention, which allows to solve all the problems cited heretofore by 
providing a process to purify polar liquid wastes containing colloidal 
dispersions of solvated particles, characterised in that it comprises: 
a first step, wherein a flocculating composition is prepared by: 
dispersing montmorillonite in a polar liquid to form an homogeneous 
suspension; 
keeping or conditioning the pH of said suspension in a range between 5 and 
9; 
leaving said suspension to react, possibly under mild stirring, for a 
period of time sufficient to obtain the aggregation to the montmorillonite 
of most of the solvated particles of said polar liquid and, in any case, 
of at least one hour; and a second step, wherein a complete liquid/solid 
separation is obtained by: 
adding said flocculating composition, free of any additional flocculating 
agent, to said polar liquid wastes and thoroughly mixing the same, up to 
obtaining a mixture having a final montmorillonite concentration of not 
less than 20 ppm; 
keeping or conditioning the pH of the mixture, thus obtained, in a range 
above 2.5; 
stirring the mixture for a predetermined period of contact time; and 
filtering the mixture. 
The invention also concerns the flocculating composition used in said 
process, comprising an homogeneous montmorillonite suspension in a polar 
liquid having a pH in a range between 5 and 9, free of any additional 
flocculating agent and aged for a predetermined period of time sufficient 
to obtain the aggregation to the montmorillonite of most of the solvated 
particles of said polar liquid and, in any case, of at least one hour.

DETAILED DESCRIPTION OF THE INVENTION 
The present invention will be understood more clearly from the following 
description, accompanied by some Examples given by mere way of explanation 
and not to be considered as limiting its scope. 
The purification process of the present invention comprises a first step, 
which consists in preparing a flocculating composition to be added to the 
polar liquid waste to be treated. The composition is prepared by 
suspending the montmorillonite, in a concentration between 0.5% and 15% by 
weight, into a polar liquid; said suspension will have --or %will be 
conditioned so as to obtain --a pH between 5 and 9. This polar liquid is 
preferably a fraction of the polar liquid waste having to be treated, or a 
polar liquid containing a colloidal dispersion having the same solvated 
substances present in the liquid waste. To achieve the best results in 
terms of flocculation speed, the suspension thus obtained is left to react 
for at least one hour possibly under mild stirring, hence obtaining the 
preferred flocculating composition wherein the montmorillonite has been 
"selectively activated" to a full extent. 
It is important to note that, both in the case of the montmorillonite 
having been suspended into a fresh polar liquid, and in the case it has 
instead been preferably suspended into a fraction of the polar liquid 
waste to be treated or into a polar liquid containing the same solvated 
substances, no flocculation nor precipitation takes place either of the 
montmorillonite or of the solvated substances, so that the flocculating 
composition can be preserved, without getting altered, even for long 
periods of time. To obtain this result, the montmorillonite has to be 
added in a high excess in respect of the solvated particles, whereby there 
is no possible formation of flocks having a sufficiently large size to 
settle. It is thus evident that the montmorillonite concentration values 
within the above indicated range will be higher, the greater the content 
of solvated particles in the polar liquid. 
Montmorillonite is a clayish mineral characterized by an expanding 
reticular structure; it comprises a group of minerals (beidellite, 
non-tronite, hectorite and saponite) having, to a different extent, the 
same characteristic. The theoretical formula of montmorillonite with no 
structural substitutions is (OH).sub.4 Si.sub.8 Al.sub.4 O.sub.20.nH.sub.2 
O. 
Montmorillonite is a mineral with three layers; it is in fact formed by 
packed layers comprising two layers of tetrahedrons SiO.sub.4 --with the 
Si atom at the centre --and one intermediate layer of octahedrons --with 
an Al atom at the centre --. 
The silica-alumina-silica units are continuous in the crystallographic 
directions "a" and "b", and they are superposed in the direction "c"; with 
this arrangement the oxygen levels of the neighbouring units get to be 
adjacent; this determines the existence of a weak bond and of a foliation 
between the units. 
The length of the axis "c", between the layers, can vary considerably: from 
9.5.ANG. to 21.4.ANG.. Normally, the extension of the axis "c" takes place 
by absorption --between the single layers of the mineral --of water or of 
other polar molecules, favoured by the very weak bonding forces 
characteristic of montmorillonite. 
In practice, said mineral always has a different composition from the 
theoretical one. In the tetrahedrons layer, silica can often be 
substituted by aluminum and by phosphorous, while the aluminum at the 
centre of the octahedrons of the intermediate layer can be substituted by 
Mg. Fe, Li. 
Once the above flocculating composition is ready for use, having completed 
the "selective activation" of montmorillonite, the process of the present 
invention continues with a second step in which said composition is added, 
under stirring, to the polar liquid waste to be treated, which will have 
--or will be conditioned so as to obtain --a pH higher than 2.5, up to 
reaching a final montmorillonite concentration of not less than 20 ppm, 
and preferably at least 20 ppm higher than the stoichiometric 
concentration apt to flocculate all the solvated particles; by continuing 
to stir only for a few minutes, one obtains the quick precipitation of the 
solvated substances agglomerated to the montmorillonite. By filtration 
--for example --it is then possible to rapidly separate a clear 
homogeneous liquid from a residue, consisting of the solvated impurities 
which have agglomerated to the montmorillonite. 
A possible explanation for this phenomenon --to which, however, the present 
invention should not be limited --is given hereinafter. 
When dry montmorillonite, in relatively high concentrations, is dispersed 
into a polar liquid waste containing a liquid colloidal dispersion of 
solvated particles, part of the residual charge of the montmorillonite 
particles is neutralized, for instance by water (through the hydrogen 
bond); in this way, also the solvated particles (surrounded by water) are 
attracted by the montmorillonite particles, which will extend its 
crystallographic axis "c" up to allowing the inlet into the mineral of the 
solvated particles (impurities), which will confer lyophilic 
characteristics to the montmorillonite. 
Once completed the preparing of the flocculating composition, i.e. the 
aggregation of most of the solvated particles to the montmorillonite, one 
obtains the so-called montmorillonite "activated selectively"; when the 
same is added, under stirring, to the polar liquid waste containing the 
same solvated particles which have allowed the selective extension of the 
axis "c", these last ones are: in part --as in the first step of the 
process --attracted by the residual charge of the particles of the 
montmorillonite "activated selectively", thereby penetrating into the same 
and increasing the lyophility of the montmorillonite surface; and in part 
caused, by constant stirring, to collide with the lyophilic 
montmorillonite particles, hence allowing the lyophilic substances, 
contained in the solvated particles, to diffuse into the lyophilic layer 
which covers more and more abundantly the montmorillonite surface. This 
phenomenon determines the complete aggregation of the lyophilic impurities 
contained in the solvated colloids present in the polar liquid waste, in 
flocks of high volume and weight, thereby allowing an easy and quick 
precipitation thereof. By filtration, for example, it is then possible to 
rapidly separate a clear homogeneous liquid from a residue formed by the 
montmorillonite and aggregated impurities. 
The process object of the present invention is therefore, in its whole, 
quite simple and rapid. It in fact only requires the addition of a 
predetermined quantity of the flocculating composition (proportional to 
the concentration of the solvated substances) under strong stirring; the 
precipitation of the agglomerates formed by the montmorillonite and the 
impurities takes place in a very short period of time --in the range 
between few seconds and some minutes --and the separation of the clear 
liquid is quickly obtained, for instance by filtration. 
The process of the present invention is also characterized by the fact that 
the treated liquid is by no means altered chemically, in that the 
montmorillonite is totally insoluble and is thus fully eliminated by 
filtration and/or other known techniques of liquid/solid separation; this 
characteristic allows to re-employ the clear liquids, obtained with the 
process of the invention, in the primary cycle from which the liquid 
wastes have flown out. 
The present invention can be efficiently applied to all the polar liquid 
wastes containing solvated particles, independently from the chemical 
nature of the particles, seen that the purification process involved is 
essentially of the physical type. 
By way of example, one may treat successfully polar liquid wastes forming 
the effluents of industrial car washers and the like, of sewers, of animal 
breeding, and of industry in general. Using a food grade montmorillonite, 
the process of the invention can be successfully applied also to the 
effluents of the food industry. A further very interesting application 
consists in treating bilge waters, in view to obtain a perfectly clear 
liquid. 
As well as in the full treatment of civil and industrial effluents, the 
process of the present invention has also proved particularly useful in 
the primary treatment of those effluents which must undergo reverse 
osmosis, ultrafiltration or electrodialysis processes, as it allows to 
increase the performances and to prolong the life of the relevant 
membranes. 
The montmorillonite "activated selectively" can be validly used in all the 
aforecited application fields, with the greatest efficiency and 
effectiveness. One of the minerals which has shown the best results is 
characterized by the following main physical parameters: 
Moisture: 10% max 
Limit of liquid state: 450-500% 
Swelling: 30-35 ml/2 g 
Granulometry: 90% below 75 micron. 
when the clear liquid resulting from the process of the invention still 
shows traces of oils --either suspended or emulsified --these can be 
totally eliminated by adopting the oil-separation system, and respective 
apparatus, described in the patent application PCT/EP93/01053 filed by the 
same Applicant. It is just in order to obtain the best results from said 
system that the Applicant has conceived the process and the composition 
according to the present invention. 
EXAMPLES 
Although the invention finds a suitable application in the purification of 
polar liquid wastes containing solvated particles, wherever they come 
from, and in the clarification of bilge waters, reference will be made in 
the following Examples --to simplify the description --only to the 
effluents from industrial car washers, and to bilge waters (after 
gravimetric removal of the free oils), without however wishing to limit to 
these fields the scope of the present invention. 
EXAMPLE 1--Purification of Car-Wash Waste Waters 
A preferred flocculating composition of the invention used for treating 
car-wash waste water, so as to be able to use it again in the successive 
washing cycle, consisted in a 10% montmorillonite suspension into a 
fraction of the polar liquid waste having to be treated, prepared at room 
temperature and conditioned --if necessary --so as to have a pH of about 
6.5; the montmorillonite was left to "activate selectively" for three 
hours, under mild stirring. The suspension was prepared by slowly adding 
the montmorillonite to the liquid waste --kept under strong stirring --and 
by continuing to stir until the mineral crumbs had totally disappeared. 
According to the process of the invention, 100 g of said composition were 
added, under stirring, to a sample of 50 litres of effluent from a highly 
utilized car-wash plant--having the following characteristics: 
pH: 6.8 
Suspended solids: 118 mg/l 
COD: 222 mg/l 
Surfactants (MBAS): 5.25 mg/l 
Total oils: 18.3 mg/l 
so as to reach a final concentration of montmorillonite "activated 
selectively" equal to 200 ppm. The suspension thus obtained was mixed for 
another five minutes and left to react for five minutes. 
A sample of five litres of the mixture thus obtained was filtered with a 
fast filtering paper filter; the filtrate, perfectly clear, showed the 
following characteristics: 
Suspended solids: absent 
COD: 85 mg/l 
Surfactants (MBAS): 1.50 mg/l 
Total oils: traces 
On examining the results reported in the previous Example 1, it can be 
noted that the purification process of car-wash waste waters gives a water 
which--besides abundantly falling within the limits imposed by Table A of 
the Italian law No. 319/76--allows to be advantageously used again in 
successive washing cycles. 
Further subsequent tests on the washing plant have confirmed the rapidity 
of the process of the invention and the fitness of the water resulting 
therefrom to be used again in the successive washing cycles. 
EXAMPLE 2--Clarification of Bilge Waters 
A sample of 10 litres of bilge waters, which contained--inter alia--a 
colloidal dispersion formed by solvated particles, as subjected to 
gravimetric separation of the free oil, which stratified on the upper part 
of the separator and was recovered. A sample of 20 ml of the remaining 
waste waters--rather turbid and having a pH of 6.4--was mixed to 75 ml of 
fresh water to reduce the high concentration of electrolytes, typical of 
sea-water; 5 g of dry montmorillonite were added to said solution. slowly 
and under strong stirring. The montmorillonite was then left to "activate 
selectively" for three hours, stirring the suspension every now and then, 
to produce a flocculating composition. 
To 5 litres of the gravimetrically oil-freed waste water, there were added, 
under stirring, 50 ml of the above composition, so as to reach a final 
concentration of montmorillonite "activated selectively" equal to 500 ppm. 
Stirring was continued for five minutes and the mixture was left to react 
for another five minutes. After filtration--with a fast-filtering paper 
filter--a perfectly clear filtrate was obtained, the surface of which 
showed traces of free oils which were fully separated through the system 
described in the Patent Application PCT/EP93/01053 cited heretofore. 
EXAMPLES 3 AND 4 
Examples 1 and 2 were repeated in a continuous working process, using 
mechanical mixers into which flowed and min-led a main flow formed by the 
polar liquid waste to be treated, and a secondary flow formed by the 
flocculating composition according to the invention, in the wanted flow 
rates. At the end of the filtering operations, the filtrates obtained had 
the same characteristics as those obtained in Examples 1 and 2, while the 
times of contact before filtration were reduced within a range between 2 
and 20 seconds. 
The present invention has been described with reference to some specific 
examples of application, but it is evident that its protection scope 
should be extended in a fully general way to the use of montmorillonite as 
a flocculating agent for colloidal dispersions of solvated particles, as 
defined in the following claims.