CA2161864A1 - Regeneration of used cleaning solution - Google Patents

Abstract

A method is provided for regenerating spent cleaning solutions, whether they be alkaline, acidic, or neutral. The method involves the sequential steps of first preconditioning the spent solution. Then, an absorbent material is added to the preconditioned solution to provide an interactive solution. The precipitating of the undesirable materials from the interactive solution is accomplished by adding an anionic polymeric flocculating agent and a cationic polymeric flocculating agent thereto, in the following sequence of steps, namely (i) adding either the anionic polymeric flocculating agent or the cationic polymeric flocculating agent to the interactive solution to provide a reactive solution, (ii) thoroughly mixing the reactive solution, and (iii) adding the other of the cationic polymeric flocculating agent or the anionic polymeric flocculating agent, (respectively), thereby precipitating insoluble salts as large-sized and hard flocs. Finally, the solution containing the precipitated flocs is subjected to a solid/liquid separation.
This regenerated solution is virtually indistinguishable from a fresh-made cleaning solution which is made from caustic and water, or acid and water.

Description

CA 02161864 1998-0~-19 (a) TITLE OF THE rNVENTION
REGENERATION OF USED CLEANING SOLUTION

(b) TECHNICAL FIELD TO WHICH THE rNVENTION RELATES
This invention relates to the regeneration of used cleaning solution which may be ~lk~lin~, neutral or acidic.

(c) BACKGROUND ART
Cleaning is a complex technology whose efficacy is governed by four parameters, namely time, temperature, concentration, and shear. Some cleaning solutions contain d~lelgellls to remove soils, and/or compounded alkalis and c~ tics to react upon organic residues. Other such cle~ning solutions may contain acids to remove inorganics and minerals.
It is known to clean and clarify water by adding one or more coagulating agents to water to combine fine particles therein into flocs and thereby to sediment the flocs by gravity. In this known method, water is separated into a floc phase and an aqueous phase. The thus sep~ted flocs are removed from the treating vessel and are dewatered, i.e., dehydrated, and the solids discarded. The separated water is finally returned to rivers.
It is also well known that metal ions dissolved in water can be removed by the addition of various tre~tm~nt agents which react with the metal ions and precipilale them as insoluble salts. This is of use in the treatment of co.~ ted water when, for example, the addition of calcium hydroxide (lime) to hard water will cause the precipitation of metal carbonates and so remove the metal and bicarbonate ions from the water. This precipitation method can be further improved by the addition to the water of a polyelectrolyte which promotes the flocculation of the solid particles and a weighting agent, e.g., calcium carbonate, which increases the specific gravity of the floccul~ted matter and therefore increases the rate of se lim~nt~tion and thus the rate of clarification of the liquor.

It is also known to remove suspended solid m~teri~l~ from water by the - addition of coagulants, e.g., aluminum sulphate, iron chloride etc., which are normally employed along with lime in conjunction with sefiiment~tion and/or filtration procedures. The coagulants, and frequently a coagulant aid, assist the building of a floc to a proper size for settling; setlim~nt~tion units permit the separation of the relatively slow settling floc thus formed from the purified water.
As noted above, the approach to tre~tm,ont of cont~min~t~ water and effluent - has in the past comprised the precipitation of the metal salts followed by their separation and then the removal of unwanted gases or vapours from the liquor by storing the liquor in a shallow lagoon where it is aerated. This method is not particularly efficient because the shallow depth of liquor in the lagoon does not allow the oxygen supplied to the liquor to be under s~lfficient pressure to saturate the liquor.
The patent lil~ld~ure also purports to be directed to the problem of purifying of solutions.
British Patent No. 2,095,226 describes a composition which is of use in the pmific~tion of water and which contains an ~lk~line earth metal hydroxide and ananionic oligomeric polyelectrolyte and may additionally contain a weighting agent and a cationic polyelectrolyte. However, although it stabilizes the composition, theanionic polyeleckolyte is not particularly effective as a flocculant and when a cationic polyeleckolyte is also used, the anionic polyelectrolyte may counteract its effect. The amount of calcium hydroxide or sodium carbonate added to the water will depend on the conce-ntr~ti~-n of bicarbonate or sulphate ions in the water.
British Patent No. 2,157,278 described a method of treating water using a composition cont~inin~ calcium sulphate as a weighting agent, an electrolyte having ~ 21~186~

a multivalent cation, e.g., iron (III) or aluminum and either a cationic or an anionic polyelectrolyte. As taught in such patent, the polyelectrolyte used was not both a cationic and an anionic compound. As taught in this patent the polyelectrolyte used is cationic and it is stated that cationic polyelectrolytes stabilize the compositions.
S C~n~ n Patent No. 428,472 p~tented July 3, 1945 by H.L. Olin provided a multi-step procedure for the cl~rifis~tion of water. The first step involved preparing a sol of sodium bentonile in water. The second step involved incorporating such sol in the body of water to be cl~rifiY~ The third step involved ~ ling the sodium benlol ile to form a first flock and to thereby entrain negative dispersoids in the water. The fourth step involved separating the water from the first floc and theentrained m~tPri~l The fifth step involved adding polyvalent ionizable material to the water in ~luanlily s--fflcient to effect flocculation of bentonite subflocs. The final step involved se~al~hlg a purified water from the second floc.
~n~ n Patent Application No. 2,006,512 published May 15, 1991 by A.
Timmons, provided a method for the purification of cont~min~ted water. The treatment involved the application to the water of anionic and cationic coagulants at different stages. Between the application of the coagulants, precipitation agents were added to precipitate the conl;.",i~nt.c which typically were metal ions in solution.
The coagulants were polyelectrolytes. It was taught that the adding of the respective coagulants before and after the addition of the tr~tment agents produced a much denser precipitate which was much more easily separated from the liquor. It was postulated that the reason was because the addition of the first coagulant inclllced a charge on the particles suspended in the liquor and so when a coagulant of the opposite charge was added, precipitation and coagulation of the charged particles was 8 ~ ~

faster and more efficient Separation followed and the s~a.dled solids were passed to a sludge thickening tank, while the sep~r~ted liquid could be filtered to provide clean water which could be returned to a stream or river.
The specific reagents taught by this patent application included: The anionic S coagulant could be selected from anionic polyacids and salts thereof and could, for example, be an aLt~ali metal salt of a simple or complex oligomer of acrylic or methacrylic acid, low-viscosity sodium carboxymethylcellulose or an oligomeric sulphonate. The cationic coagulant could be a polyamide. The tr-e~tment agents used could be an ~lk~line earth metal hydroxide and calcium carbonate as a weighting agent. Preferably the ~lk~line earth metal hydroxide was c~lcium hydroxide. Other tre~tment agents, e.g., sodium carbonate or sodium hydroxide could also be used.Other tre~tment agents, e.g., an electrolyte having a multivalent cation and calcium sulphate as weiPhtin~ agent could also be used. The multivalent metal cation could comprise iron (III) or aluminum, and the electrolyte could be iron (III) sulphate, iron (III) chloride or ~ minllm sulphate.
C~n~ n Patent Application No. 2,012,201 pllbli~h~ March 14, 1990 by S.
D. K~m~to et al, provided a method for treating water which include l adding a first chemical cont~ining an allcali metal or ~lk~line earth metal oxide or hydroxide to the water to be treated, thereby rendering muddy water ~lk~line. A second chemical cont~ining an anionic polymer coagulant was added to the water, either simultaneously with, or after, the addition of the first chemiç~l A third chemical co~,l;,h~h~g a sulphate was then added, thereby rendPrin~ the water weakly ~lk~line.
Finally, a fourth chemic~l cont~ining an anionic polymer coagulant was added to the muddy water. As a result, large-sized and hard flocs were produced. When the - ~ ~
CA 02161864 1998-0~-19 the water was in the weakly ~lk~lin~ state, and an anionic polymer coagulant was added to the muddy water to cause lc.llAi~ g fine particles, the hydroxide and the metal ions to be combined, resulting in larger-sized and harder flocs.
U.S. Patent No. 4,783,265, p~tent~d November 8, 1988 by A. Timmons, 5 provided a composition to flocculate and separate solids from water to yield asubstantially clear supcllldL~l. The composition included an electrolyte in an amount which was sufficient to coagulate suspended solids in the water being treated, e.g., iron (III) sulphate, iron (III) chloride, or ~ll.. i.. , (III) sulphate, calcium sulphate weighting agent, in an amount which was sufficient to provide weight to suspended solids which 10 were formed by the action of the electrolyte, and a cationic or anionic polyelectrolyte.
The composition further could include a clay, e.g., benlollile or kaolinite, and/or an organic titanate, and/or a component, e.g., c~lcillm hydroxide or calcium carbonate to m~int~in the pH of the water to which the composition was added.
U.S. Patent No. 4,655,934, p~t~.~lecl April 7, 1987 by G. Rose et al, provided 15 a composition for clarifying water. The composition was a low-viscosity, polynuclear ~ll.. i... compound.

(d) DESCRIPIION OF THE INVENTION
In spite of these teacllings, there is still a need for further hl~lovelllents, and, in particular, there is a need for the regeneration of used ~lk~lin~ or acid cleaning solutions.
However, as disclosed previously, because cle~ning is a complex technology, whose efficacy is governed by four parameters, namely time, lelllpeldLule, concentration, and shear, some clç~ning solutions contain detergell~ to remove soils, and/or compounded alkalis and c~ tirs to react upon organic residues. Other such cleaning solutions may contain acids to remove inorganics and minerals.
Accordingly, it is an object of one aspect of the present invention to provide a - - -CA 02161864 1998-0~-19 method for the regeneration of spent ~lk~line, acid or neutral cleaning solutions, which method is simple to operate, and provides effective floccul~tilln of the solid salts which are preci~ilated when ch~omir~l treatment agents are added to the solution.
It is an object of another aspect of the present invention to provide a method for regenerating spent ~lk~linr, acidic or neutral cleaning solutions, wherein large-sized and hard flocs can be formed by the use of small amounts of r.h~omir.~
An object of yet another aspect of this invention is to provide a method for regenerating spent ~lk~lin~, acidic or neutral cleaning solutions, wherein dispersed residues, which have been removed from dirty surfaces, are removed, so that the residues do not react with caustic or acid, which would thus tend to reduce cleaning efficacy, and so that the available active caustic or acid concentration remains higher with less top-over needed to .,.~ ; in co~ct;ll~ldlion.
An object of yet another aspect of this invention is to provide a method for regen~,.dLing spent ~lk~lin~, acidic or neutral cle~ning solutions, wherein the soil load is kept at low level, so that such cle~ning solutions are more active and clean faster.
An object of still another aspect of this invention is to provide a method for regelle~aling spent ~qlk~lin.o, acidic or neutral cle~ning solutions in which organic soil, which has low heat llA.~...iLl~nre and tends to foul heating surfaces, is removed so that the legenelated solutions may be heated while using less energy and while not fouling 20 surfaces.
An object of a still further aspect this invention is to provide a method for regeneldling spent ~lk~lin~, acidic or neutral c!e~ning solutions, in which solutions co.~l~inil-g soil therein, which have higher viscosity that impa* soil penetration and removal, are treated to remove the soil so that regelleldted solutions flow better and 25 penetrate more efficiently.
The present invention broadly provides a method for regenerd~ g spent ~lk~lin~, acidic or neutral clean*ng solutions. F*stly, the spent cle~ning solution is preconditioned as will be specifically described hereillarler. Secondly, an absorbent material, as will be CA 02161864 1998-0~-19 specifically described heleillarl~l, is added to that precol1dilioned solution to provide an interactive solution. Thirdly, suitable agents, as will be specifically described helei~rlel, are added to that interactive solution to precipitate undesirable materials from that solution. This third step takes place in at least three stages. In the first stage, a 5 polymeric flocc~ ting agent, which is either a cationic polymeric flocclll~ting agent or an anionic polymeric floccnl~ting agent, is added to the interactive solution to provide a conditioned solution. In the second stage, that conditioned solution is ~git~te~ in order to i.-l~....ix the added polymeric flocc~ ting agent with the conditioned solution to provide a mixed conditioned solution. In the third stage, a dirr~lelll polymeric10 floccul~ting agent, which is either an anionic polymeric flocc~ ting agent or a cationic polymeric floccul~ting agent which is opposite in sign to the first polymeric flocculating agent which was added in the first stage, is added to the mixed conditioned solution, thereby to complete the provision of such large-sized and hard flocs. In the final step, the mixed conditioned solution co..l~ining such flocs is subjected to a final solid/liquor separation.
Thus, by one broad aspect of this invention, a method is provided for regenerating a spent ~ lin~, acidic or neutral cleaning solution, comprising the steps of pre-conditioning the spent solution, adding an absorbent material to the preconditioned solution to provide an interactive solution, precipilaling undesirable materials from the interactive solution by adding a soluble polymeric floccul~tin~ agent which is selected from the group con~i~ting of an anionic polymeric floccnl~ting agent and a cationic polymeric flocclll~ting agent thereto, in a sequence of steps con~i~ting essentially of (i) adding one of the anionic polymeric flocc~ ting agent or the cationic polymeric flocclll~ting agent to the interacthe solution to provide a reactive solution, (ii) thoroughly mixing the reactive solution to provide a mixed reactive solution, and (iii) adding the other of the anionic polymeric floccul~ting agent or the cationic floccul~ting agent to the mixed reactive solution, thereby to ple~i~,i~te insoluble salts as large-sized and hard CA 02161864 1998-0~-19 flocs, and subjecting the interactive solution co~ -g the flocs to a solid/liquid separation.
By one variant of such method, the method in~ es the additional step of adding a dirr~.e.ll polymeric flocclll~ting agent, which is either an anionic polymeric flocc~ ting 5 agent or a cationic polymeric flocc ~l~ting agent which is opposite in sign to the second added polymeric floccul~ting agent, to the mixed reactive solution, thereby to complete the provision of the large-sized and hard flocs.
By one variation of such method and the variant thereof, the spent solution is ~lk~lin~, and the precol~dilioning is carried out by the addition of an agent which is 10 selected from the group con~i~ting of alkali metal ~ es, alkali metal ferrates, alkali metal hydroxides, alkali metal carbonates, ~lk~lin~ earth metal salts, ~lk~line earth metal hydroxides, ~lk~lin~ earth metal carbonates, and ~lk~lin~ earth metal oxides, and ules thereof. By specific variations thereof, the ~lk~lin~ metal is sodium; or the ~lk~linP earth metal is c~lcillm or m~g,~.osill...; or the ~lk~lin~ earth metal hydroxides are 15 calcium hydroxide or m~g~si~l... hydroxide; or the preconditioning agent is calcium oxide; or the preconditioning agent is sodium carbonate.
By another variant of such method and the variant and variations thereof, the spent solution is neutral or acidic, and the preconditioning agent is selected from the group con~i~ting of salts of Group III of the Periodic Table, and salts of the first 20 transition series of the Periodic Table. By one specific variations thereof, the preconditioning agent is alum, ~ll~...i.,~.,, sulphates, iron sulphates, polyall.,,,i,,.l.~-chloride or ~lll.,,i,,~..,, acetate.
By another specific variation thereof, the anionic polymeric flocc~ ting agent is chitosan.
By yet another variant of such method and the variant and variations thereof, the cationic polymeric flocclll~ting agent is selected from the group consisting of a polyamide, and a polyacrylate, and lni~lules thereof.

CA 02161864 1998-0~-19 By still another variant of such method and the variant and variations thereof, the spent solution is ~lk~lin~, acidic or neutral, and the preconditioning step is provided by oxidation of the solution. By specific variations thereof, the oxidation is carried out by the addition of an agent which is selected from the group co~ g of a peroxyborate, 5 a peroxycarbonate, a peroxide and a persulphate to the solution; or the oxidation is carried out by the addition of an agent which is selected from the group consisting of sodium peroxyborate, sodium monoperoxycall,ollales, sodium diperoxycarbonates, hydrogen peroxide, sodium peroxide, barium peroxide and sodium peroxydisulphate to the solution.
By still a further variant of such method and the variant and variations thereof, the spent solution is neutral or acidic, and the preconditioning step is carried out by heating the solution to a telllpelalure above 50~C.
By a still further variant of such method and the variant and variations thereof, the preconditioned step is carried out in the presence of a weighting agent. By specific variations thereof, the weighting agent comprises calcium carbonate; or the weighting agent comprises diatolllaceous earths.
By still a further variant of such method and the variant and variations thereof, the absorbent material colll~lising is selecte~ from the group con~ g of a bellloniL~ and an attapulgite. By specific variations thereof, the bentonite is sodium bentonite.
By still further variants of such method and the variant and variations thereof, the soluble polymeric flocc~ ting agents are used in ~ g added charges progressing from anionic to cationic; or the soluble polymeric floccul~ting agents are used in alternating added charges progressing from cationic to anionic; or the soluble polymeric floccul~ting agents are used in all~"~ g added charges progressing from anionic to cationic to anionic; or the soluble polymeric flocc ll~ting agents are used in ~lt~ tin~
added charges progressing from cationic to anionic to cationic.
By specific variations thereof, an anionic polymeric floccul~ting agent is addedto the interactive solution to provide a reactive solution, the interactive solution is -CA 02161864 1998-0~-19 thoroughly mixed to provide a mixed reactive solution, a cationic polymeric floccul~ting agent is added to the mixed reactive solution to cause plecipi~lion of insoluble salt, and the precipitated insoluble salts are separated from the mixed reactive solution; or a cationic polymeric flocc~ ting agent is added to the reactive solution to provide a reactive solution, the interactive solution is thoroughly mixed and to provide a mixed reactive solution, an anionic polymeric floccul~ting agent is added to the mixed reactive solution to cause pl~eci~,i~lion of insoluble salts, and the precipitated insoluble salts are separated from the mixed reactive solution; or a first anionic polymeric floccul~ting agent is added to the reactive solution to provide a reactive solution, the interactive solution is thoroughly mixed to provide a mixed reactive solution, a cationic coagulant is added to the mixed reactive solution to provide an interm~ te reactive solution which has been subjected to at least partial precipitation of insoluble salts, a second anionic polymeric floccul~ting agent is added to the interm~ te reactive solution to cause subst~nti~lly-complete pleci~ilalion of insoluble salts, and the preci~ilaled insoluble salts are separated from the int~rm~ te reactive solution; or a first cationic polymeric flocc~ ting agent is added to the interactive solution to provide a reactive solution, the reactive solution is thoroughly mixed to provide a mixed reactive solution, an anionic polymeric flocc~ ting agent is added to the mixed liquid solution to provide an intermediate reactive solution which has been subjected to at least partial precipitation of insoluble salts, a second cationic polymeric flocc~ ting agent is added to the interm~ te reactive solution to cause substantially-complete precipitation of insoluble salts and the preci~i~led insoluble salts, are sep~aled from the intermediate reactive solution.
By still further variants of such method and the variant and variations thereof, the anionic polymeric flocc~ tin~ agent is selected from the group con~i~ting of alginic acid, ~lgin~te~, sodium algin~te, sodium polyacrylate, maleate copolymers, partial hydrolyzates of polyacrylamide, anionic polyacids and salts thereof, an alkali metal salt of a simple CA 02161864 1998-0~-19 oligomer of acrylic acid, an alkali metal salt of a simple oligomer of acrylic acid, an alkali metal salt of a complex oligomer of methacrylic acid, a low-viscosity sodium carboxymethylcellulose, and an oligomeric sulphonate, and ~ ules thereof.
By still further variants of such method and the variant and variations thereof, the S cationic polymeric floccul~ting agent is selected from the group consisting of a polyamide, and a polyacrylate, and mixtures thereof.
By still further v~iants of such method and the variant and variations thereof, the separation is achieved by filtration.
By specific variations thereof, the filtration is carried out using a filter member which is selected from the group con~i~ting of a fine sand filter, a membrane filter, a stainless steel membrane filter, and a coarse sand filter.
By specific variations thereof, the method inrlll-1es the use of a filter aid to inhibit clogging of the openings of the filter. By another specific variation thereof, the filter aid is selected from the group con~i~ting of diatomaceous earth, perlite, siliceous materials, carbon, fibrous cellulose, and powdered active m~gn~sillm oxide.
By still further v~i~ls of such method and the variant and variations thereof, the separation is achieved by a filtration step which includes a substantially simnlt~n~ous oxidation step. By specific variations thereof, the oxidation step is a catalytic oxidation to complete the oxidation of any further hll~uli~ies in the solution.
By another specific variation thereof, the filtration step is achieved by ultra-filtration which is carried out to remove particles having a size of S to 0.1 ~.By a specific variant of this method, the method comprises the steps of preconditioning the spent solution by adjusting the tellll~eldlule to above 50~C;
introducing a solution of calcium nitrate therein; ~git~ting the solution for a first period of time; introducing a slurry CO~ g sodium belllonile and sodium carbonate thereinto, thereby to provide the reactive solution; allowing a suitable time for reaction; introducing a dispersion of a strong anionic polyacrylamide polymer thereinto; ~git~ting the solution CA 02161864 1998-0~-19 for a second period of time, thereby to provide the mixed reactive solution; introducing a dispersion of a strong cationic polyacrylamide polymer thereinto; allowing a sufficient time for agitation and settling; ffltering the ~ u~e through a carbon/sand filter; and then readjusting the solution for caustic concelllldlion. By a specific variation of such specific S variant, the solution of calcium nitrate is used in an amount of 0.1 and has a concentration of 50% by weight; the agitation for a first period of time is for 2 lnillules;
the slurry contains 12% sodium bentonite and 3% sodium carbonate which is added in an amount of 0.4% by weight; the suitable time for reaction is 2 .~ es; the dispersion of the strong anionic polyacylamide polymer has a concellllalion of 0.4% and is added in an amount of 0.5%; the agitation for a second period of time is for 2 minules; the dispersion of a strong cationic polyacylamide polymer has a concentration of 0.5% and is added in an amount of 0.4% by weight; the sufficient time for agitation and settling is for 2 ...i....~es; and the caustic concentration is 2.5%.
By a specific variant of this method, the method comprises the steps of 15 preconditioning the spent solution by adjusting the temperature to above 50~C;
introducing a solution of calcium chloride thereto; ~git~ting for a first sufficient period of time; introducing a slurry cont~ining sodium bentonite and sodium carbonate thereinto;
allowing a sufficient reaction time; introducing a dispersion of a strong cationic polyacrylamide polymer thereinto; ~git~ting for a second suitable period of time;
20 introducing a dispersion of a strong anionic polyacrylamide polymer thereinto; ~git~ting for a third sufficient period of time; allowing a sufficient time for settling; filtering through a carbon/sand filter; and then readjusting the solution for caustic concentration.
By a specific variation of such specific variant, the solution of calcium chloride is 30%
by weight and is added in an amount of 0.2%; the agit~ting for a first sufficient period of time is for 2 .. ;.. ~es; the slurry contains 12% sodium btlllonile and 3% sodium carbonate, which is added in an amount of 0.24% by weight; the sufficient reaction time is 2 ...i....~es; the dispersion of the strong cationic polyacylamide polymer has a CA 02161864 1998-0~-19 concentration of 0.4 % and is added in an amount of 0.5%; the ~git~ting for a second suitable period of time is for 2 ~ es; the dispersion of a strong anionic polyacylamide polymer has a co~cellllalion of 0.4 %, and is added in an amount of 0.5% by weight; the sufficient time for settling is for 10 to 30 ",i".~es; and the caustic concentration is 2.0%.
By a specific variant of this method, the method comprises the steps of adjusting the le~ eldlule to above 50~C; introducing a slurry colll;lil-il-g sodium bentonite and sodium carbonate thereinto; allowing a first sufficient holding time; introducing a dispersion of strong cationic polyacrylamide polymer thereinto; ~git~ting for a sufficient period of time; allowing a second sufficient holding time; filtering through a coarse filter;
filtering through a carbon/sand filter; and then readjusting the solution for caustic concentration. By a specific variation of such specific variant, the slurry contains 12%
sodium belllonile and 3% sodium carbonate, which is added in an amount of 0.4 % by weight at a rate of 165 ml/min. into a caustic flow set at a rate of 35 L/min; the first sufficient holding time is 15 seconds; the dispersion of the strong cationic polyacylamide polymer has a concentration of 0.4 % and is added at a flow rate of 46 ml/min; the z~git~ting for a sufficient period of time is for 2 mimltes; the second sufficient holding time is 30 seconds; the coarse filtration is through a 100 ~m filter; and the caustic concentration is 2.0%.
By a specific variant of this method, the method comprises the steps of adjusting the tell~eldlule to above 50~C; introducing a slurry coll~ g sodium belllo~
thereinto; z~git~ting for a first suitable period of time; introducing a dispersion of a strong anionic polyacrylamide polymer thelehllo; ~git~ting for a second suitable period of time;
settling for a suitable period of time; filtering through a carbon/sand filter; and then readjusting the solution for caustic concelllldlion. By a specific variation of such specific variant, the slurry contains 12% sodium belllonile which is added in an amount of 0.8%
by weight; the z~git~ting for a first suitable period of time is for 2 minutes; the dispersion of the strong anionic polyacylamide polymer has a conc~lllldlion of 0.4% and is added CA 02161864 1998-0~-19 in an amount of 0.5%; the ~git~ting for a second suitable period of time is for 2 llliuules;
the settling for a suitable period of time is for 10 to 30 lllhlules; and the caustic concentration is 2.5%.
By a specific variant of this method, the method comprises the steps of adjusting S the temperature to above 50~C; introducing a slurry co~ g sodium belllollile thereinto; :3gitz~ting for a first suitable period of time; introducing a dispersion of a strong anionic polyacrylamide polymer thereinto; ~git~ting for a second suitable period of time;
introducing a strong cationic polyacrylamide polymer thereinto; settling for a suitable period of time; filtering through a coarse filter; and then readjusting the solution for 10 caustic concentration. By a specific variation of such specific variant, the slurry contains 7.5% sodium bentonite which is added in an amount of 1-1.5% by weight; the z~git~ting for a first suitable period of time is for 2 .~.i..~.les; the dispersion of the strong anionic polyacrylamide polymer has a concentration of 0.4% and is added in an amount of 0.25%; the ~it~tin~ for a second suitable period of time is for 2 ...i....~es; the dispersion 15 of a strong cationic polyacylamide polymer has a concentration of 0.4% and is added in an amount of 0.25% by weight; the settling for a suitable period of time is for 10 to 30 ...i....~es; the coarse filtration is through a 100 ~m mesh filter; and the caustic concentration is 5.5%.
By a specific variant of this method, the method comprises the steps of introducing a thioc~l,alllale metal ple~ thereinto; allowing a suitable reaction time;
introducing a slurry co.~ -g sodium bclllonile and citric acid thereinto; settling for a suitable period of time; filtering through a coarse filter; filtering through a carbon/sand filter; and readjusting the solution for acid concentration. By a specific variation of such specific variant, the solution of thiocarbamate metal precipi~le is 30% by weight, and is added in an amount of 0.3%; the suitable reaction time is 20 seconds; the slurry contains 12% sodium benlollile and 3 % citric acid, which is added in an amount of 0.25-0.5% by weight; the dispersion of the strong anionic polyacylamide polymer has a CA 02161864 1998-0~-19 concentration of 0.4% and is added in an amount of 0.25 %; the settling for a suitable period of time is for 10 to 30 ~--i--"~es; the coarse filtration is through a 100 ,um mesh filter; and the acid concentration is 5.7 %.
By a specific variant of this method, the method comprises the steps of introducing thioc~l,alllate metal precipitant thereinto; allowing a suitable reaction time;
introducing a slurry co"~ il-g sodium belllollile and citric acid thereinto; agit~ting for a first suitable period of time; introducing dispersion of a strong anionic polyacrylamide polymer thereinto; ~gitating for a second suitable period of time; introducing a dispersion of a strong cationic polyacrylamide polymer thereinto; aEitating for a third suitable period 10 of time; settling for a suitable period of time; filtering through a coarse filter; filtering through a carbon/sand filter; and readjusting the solution for acid concentration. By a specific variation of such specific variant, the solution of thiocall,alnate metal precipitate is 30% by weight, and is added in an amount of 0.3%; the suitable reaction time is 20 seconds; the slurry coll~ins 12 % sodium belllonile and 3% citric acid which is added in an amount of 0.25-0.5 % by weight; the dispersion of the strong anionic polyacrylamide polymer has a concentration of 0.4% and is added in an amount of 0.25 %; the ~git~ting for a first suitable period of time the agit~ting for a second suitable period of time and the agitating for a third suitable period of time are each for 2 ~--i----~; the settling for a suitable period of time is for 10 to 30 ~ es; the coarse filtration is through a 100 ~4m mesh filter; and the acid concentration is 5.7 %.
In other words, in the first or preconditioning step, the procedure depends to some extent on the nature of the solution. If the solution is ~lk~lin~, such preconditioning may be carried out by the addition o suitable chemicals, e.g., the salts or hydroxides of the ~lk~lin~ earth metals, e.g., calcium salts or hydroxides and m~ sill~" salts or hydroxides. Other agents which may further be used in the preconditioning, and/or absorbent and/or precipilalion steps, include an ~lk~lintq earth metal hydroxide. One suitable ~lk~lin~ earth metal hydroxide may be calcium hydroxide.
Other suitable lle~lllelll agents, e.g., sodium carbonate, may also be used. Yet other suitable materials include alkali metal c~l,ollates and ~lk~lin~ earth metal carbonates, CA 02l6l864 l998-0~-l9 e.g., Na2CO3, ~lk~lin~ earth metal hydroxides, e.g., Ca(OH)2, ~lk~lin~ earth metal oxides, e.g., CaO, alkali metal al~ es, alkali metal ferrates, and mixtures thereof.
Organic pl'eCipi~ S may also be used.
If the solution is neutral or acidic, salts of Group III of the Periodic Table or of 5 the first transition series of the Periodic Table may be used. Examples include alum, all.. "i".. sulphates, and iron sulphates. In addition poly~lll.. i.. chloride or alll,,,i,,,l,,, acetate may also be used.
The rh~omir~l precipitation may also be accompanied by the conjoint use of weighting agents, e.g., calcium carbonate or diatomaceous earths.

~ 21~864 The preconditioning may alternatively be carried out by oxidation using a suitable oxi~1i7ing agent. Examples include peroxyborates, e.g., sodium peroxy-borate; peroxycarbonates, e.g., sodium mono- or di-peroxycarbonate; peroxides, e.g., hydrogen peroxide, sodium peroxide, and barium peroxide; and persulphates, e.g., sodium peroxydisulphate.
Still further, the preconditioning may be achieved simply by heating the spent clP~ning solution to a temperature above 50~C.
In the second step to provide the interactive solution, among the absorbent m~t~ l.c which may be used are those which function to absorb some of the soluble 0 m~t~ri~ and to provide a nuclei to gather suspended particles of a~plvpliate charges.
Among such m~t~ri~l are bentonite, e.g., sodium bentonile, calcium bentonite and attapulgite clay.
One suitable bentonite is sodium belltollile, a plefelled sodium bentonite being the Wyoming or Black Hills type of swelling bentonite. This type of bentonite is composed almost entirely of particles of montmorillonite that expand or swell greatly when dispersed in water.
The Wyoming or Black Hills-type benlolliles are colloidal particles which are typically hydrophillic in character. That is, each particles is hydrated or solvated, and made bulky and loose-textured by firmly bound water which penetrates between, and expands greatly, the lattice sheets making up each unit of a bentonite particle.
The bound water also forms a thick seal which encloses each unit.
Sodium bentonite possesses the following characteristics which relate more specifically to the practice of the present invention: When suspended in water which contains unsubstantial qll~ntiti~s of electrolytes or ionizable substances, sodium ! 21618~

bentonite swells to as much as thirty times its original volume to form a gelatinous paste which, upon further dilution with water, if need, can be dispersed by stirring to form a colloidal sol. In this sol the disperse phase comprises negatively charged, highly hydrated bentonite particles of the type hereinabove described. In the absence S of some suitable flocculating agent, such a sol will show no sc;~d~ion of the disperse phase for an indefinite period of time due to the mutual repulsion of the outer,eationic portion of the eations being carried by the "bound" water surrounding eaeh bentonite partiele. If however, an electrolyte, or ionizable m~tP.ri~l capable of furnishing eations, be added is suitable proportion to sueh a bentonite sol, there ensues a sllfficient neutralization of the anions, the anions being carried by the bentonite partieles themselves, and eoneomitant reduction in their mutual repulsion, so that groups of the partieles co~lPsce to form aggregates of varying sizes. In the case of a majority of the bentonite particles, this aggregation extends until there is a rapid formation of visible flocs. The sodium bentonite may be used in conjunction lS with sodium carbonate to help p~ e excess m~gn~Psillm and/or calcium ions.
In the third, or precipitation or flocculation step, polymeric flocculating agents may be used. However, this ~ltPrn~tive is not always necess~ry to achieve flocs of s~ti~f~tory texture. An important feature in this precipitation step in the present invention is the prerefled or not es~enti~l use of ~ltern~ting charges in the flocculating agents added, i.e. either anionic and then cationic, or cationic and then anionic.
Anionic polymer coagulants which may be used singly or in combination include, for example, alginic acid, ~lpin~tPs, e.g., sodium ~lgin~t~, sodium polyacrylate, m~le~te copolymers, and partial hydrolyzates of polyacrylamide, anionic polyacids and salts thereof, e.g., an alkali metal salt of a simple or complex oligomer of acrylic or r! 216~ 4 methacrylic acid, low-viscosity, sodium carboxymethylcellulose or an oligomeric sulphonate.
In neutral or acid solutions, chitosan may also be used as the anionic coagulant.
The cationic coagulant may be a polyamide or a polyacrylate.
In one way of carrying out such precipitation step, one coagulant (e.g., the anionic coagulant) is added to the incoming preconditioned and absorbent-treatedsolution. Such solution is then thoroughly mixed. The other coagulant is then added to the liquor to cause precipitation of the insoluble salts, as large sized and hard flocs, which are then separated out. This order of addition of coagulants may, or course, be reversed, i.e., first cationic and the anionic.
The final solids/liquids sep~r~tion step also may include an oxidation step.
The solids/liquids separation may be achieved by filtration to remove particles of 5-0.1 ,u, using, e.g., carbon and sand, a natural membrane, or a st~inless steel membrane. Various types of membranes include ceramic, st~inl~s~ steel, carbon, etc.
Conventional filter sands may also be used. A catalyst, e.g. a conventional redox catalyst or a powdered metal catalyst or metal oxide catalyst, may be added to complete the oxidation of any further impurities in the solution.
As generally understood, filtration is the removal of suspended particles from a liquid, e.g., by forcing the liquid under pressure dirfelellLial through a filter medium. Slow sand filters were the first water filter structures devised to accomplish this on a large scale and in many ways ~imul~t~A percolation through naturally occurring sand such as that of the banks or ~lleries along the edges of rivers or other water sources.
-' 2~ 61~64 Filtering may also be achieved through structures cont~ining much coarser sand acting largely as straining devices, (lcnown as"rapid sand filters"). It is to be appreciated that filters have little inherent clarifying capacity of themselves and the basis for cl~rific~ti-~n has been provided by prior tre~tnlent appropliate chemicals as above described. That is, the suspended matter therein was treated to collect orco~lesce into s~lfficiently large agglomt~r~t~s so as to settle out and be subst~nti~lly removed, (e.g., by primary filtration) in advance of the secondary filtration. Such a method may include absorption by means of active agents, flocculation by a flocculating polymer, setting in sedimentation basins to remove the agglomer~tes, and finally the primary filter, which takes out the larger sized cont~min~nt~.
In order to prevent clogging of the openings and eventually slowing down or completely stopping the flow of liquid through the filter, a small amount of filter aid may be added to the liquid to be filtered.
In order to increase the initial Pfficiency of the filt~ring method, a pre-coat of filter aid particles may be provided on the filter in addition to the incorporation of particles within the liquid to be filtered. The m~tt ~ most generally used as filter aids include diatomaceous silica, perlite, other siliceous m~t~ri~l~, carbon, and fibrous matter, e.g., cellulose.
Other filter aids involve the step of preconditioning the filter feed by adding thereto small amounts of powdered active m~gne~ m oxide and pulverulent filter aids, earlier described, preferably in a pre-filter tank having mild agitation and nominal retention. Any standard type of filter acid technique may be used in thefiltPring step.

CA 02161864 1998-0~-19 (e) DESCRIPIION OF THE FIGURE
The acco~ ~lyhlg single figure of the drawings is a flow chart of the regeneration method of one aspect of the present invention.
As seen in the drawings, after the cleaning solution is used in the cle~ning step S 11, it results in a spent solution, at 12, to be regelleraled. The regellelalion take effect in zone 13.
The first step, in zone 13, is to provide a preconditioned solution 14 by the addition of suitable agents, as previously described, at 15, or by the heating of the solution also as previously described.
The absorption step, at 16, also, as previously described, involves the additionof a suitable absorbent material, as previously described, at step 17.
The next step, the precipitation of undesirable materials and subsequent flocc~ tion at step 18, is carried out by the addition of suitable reagents, as previously described, at step 19. This also inrllldes the progressively allelll~ g use of flocc~ ting agents, in any order from anionic to cationic, from cationic to anionic, from anionic to cationic to anionic and from cationic to anionic to cationic.
After the flocculation step at 18 the solution is subjected to a final solids/liquids separation step. This may be achieved progressively by a settling step 20 followed by a primary filtration step 22 in primary filter 21, to provide a filtered solid waste at 23, which may be discarded as desired, at 24, and a prelhllin~y filtered solution at 25.
The next step involves the final separation and oxidation stage at 27 in zone 26.
The residue from the solution so filtered may also be adequately disposed of as desired at 28. This results in a regenerated solution at 29.
The regeneration solution 29 may be subjected to the optional step of chemic~l make-up at 30 by the addition of concell~ated ch~mir~l~ at 31. This, then, provides a reusable cleaning solution at 32.

CA 02161864 1998-0~-19 (f~ AT LEAST ONE MODE FOR CARRYING OUT THE INVENTION
The following are examples of the present invention.
Example 1 Regenerated Cleaning Solution:
App. 2.5% caustic solution in water, cont~ining milk proteins and milk sugars, as well as a heavy soil load from a milk evaporator.
Treatment:
1. adj~lstment of the te~ )el&lule above 50~C;

2. introduction of 0.1% of a 50% solution of calcium nitrate;
10 3. agitationfor2 Illill.lles;
4. introduction of 0.4% of a slurry co~ -g 12% sodium bentonite and 3%
sodium call,ondte;
5. two l"il,.lles of reaction time;
6. introduction of 0.5% of a 0.4% dispersion of strong anionic polyacrylamide polymer;
7. two ~ ..les agitation;
8. introduction of 0.5% of a 0.4% dispersion of strong cationic polyacrylamide polymer;
9. two ~ ..les agitation;
20 10. ten to thirty ,,,i,,,~les settling; and 11. filtration through a carbon/sand filter;

,. 21~1g64 The solution is then readjusted for caustic concentr~tion. If required ~ hel~tin~
additives are then added.
This regenerated solution is virtually indistinguishable from a cl~nin~ solutionmade first from caustic and water.
Adding of the respective coagulants before and after the addition of the treatment agents produced a much denser pre~ir)it~t~ which was much more easily separated from the liquor. It was postulated that the reason was because the addition of the first coagulant induced a charge on the particles suspended in the liquor and so when a coagulant of the opposite charge was added, precipitation and coagulation of the charged particles was faster and more efficient Example 2 Regenerated Cleaning Solution:
app. 2 % caustic solution in water, cont~ining milk fats, milk proteins and milksugars, as well as a heavy soil load from a cheese forms washing machine.
TrP~tmP.nt 1. adjllctment of the temperature above 50~C;
2. introduction of 0.2% of a 30% solution of c~lcil-m chloride;

3. agitation for 2 minutes;

4. introduction of 0.25% of a slurry cont~ining 12% sodium bentonite and 3%
sodium carbonate;

5. two minutes of reaction time;

6. introduction of 0.5% of a 0.4% dispersion of strong cationic polyacrylamide polymer;

7. two IllinULt~S agitation;

~ 21618fi4 8. introduction of 0.5% of a 0.4% dispersion of strong anionic polyacrylamide polymer;

9. two minutes agitation;

10. ten to thirty minutes settling; and 11. filtration through a carbon/sand filter.
The solution is then readjusted for caustic concentration. If required l~.hel~ting additives are then added.
Adding of the respective coagulants before and after the addition of the treatment agents produced a much denser precipitate which was much more easily separated from the liquor. It was postul~ted that the reason was because the addition of the first coagulant inducecl a charge on the particles suspended in the liquor and so when a coagulant of the opposite charge was added, p~ ion and coagulationof the charged particles was faster and more ~fflcient Example 3 Regenerated Cleaning Solution:
app. 2% caustic solution in water, becr yeast protein residues from a "Clean In Place" system in a brewhouse.
Tre~tment- (Continuous Method) 1. adj~-stment of the te-l~peldture above 50~C;
2. introduction of a slurry co~ ini~l~ 12% sodium bentonile and 3% sodium carbonate at the rate of 165 ml/mn into the caustic flow set at 35 1/mn;
3. after a miniml-m holding time of 15 seconds, introduction of a 0.4%
di~p~r.~ion of strong cationic polyacrylamide polymer. Flow rate: 46 ml/mn;
4. two mim-tes agitation;

! ~161864 5. after a minimum holding time of 30 seconds, coarse filtration through a 100 ,um mesh filter; and 6. filtration through a carbon/sand filter.
The solution is then readjusted for caustic concentration. If required chel~ting5 additives are then added.
Example 4 Regenerated Cleaning Solution:
app. 2.5 % caustic solution in water, cont~inin~ milk proteins and milk sugars as well as a heavy soil load from a milk e~/~oldtor.
10 Treatment:
1. adj~-stmPnt of the te.,.pe,~dlllre above 50~C;
2. introduction of 0.8% of a slurry co~ g 15% sodium bentonite;
3. agitation for 2 minutes;
4. introduction of 0.5% of a 0.45~ dispersion of strong anionic polyacrylamide polymer;
5. two minutes agitation;
6. two Inillules agitation;
7. ten to thirty "~ utes settling; and 8. filtration through a carbon/sand filter.
20 The solution is then readjusted for caustic conc~ntr~tion. If required chel~t1ng additives are then added.

~61864 Example 5 Regçner~ted Cleaning Solution:
app. 5.5% caustic solution in water, cont~ining beer and up to 1.5% paper fibres from a beer bottle washer.
Tre~tnn~nt-1. adj~tment of the temperature above 50~C;
2. introduction of 1 to 1.5% of a slurry co~ ing 7.5% sodium bentonite;
3. agitation for 2 minutes;
4. introduction of 0.25% of a 0.4% dispersion of strong anionic polyacrylamide polymer;
5. two mim~tes agitation;
6. introduction of 0.25% of a strong cationic polyacrylamide polymer;
7. ten minlltPs settling; and 8. coarse filtration through a 100 ,um mesh filter.
Turbidity reading of the solution in~ t~d an 855~o tr~n~mitt~nce as compared to water. This corresponds to an almost complete removal of suspended particles.
The solution is then readjusted for caustic concentration. If required, chel~ting additives are then added.
Adding of the respective coagulants before and after the addition of the tre~tment agents produced a much denser precipitate which was much more easily s~ d from the liquor. It was post~ t~ that the reason was because the addition of the first coagulant induced a charge on the particles suspended in the liquor and so when a coagulant of the opposite charge was added, pr~;i~ tion and coagulation of the charged particles was faster and more efficient.

~ ~i6~64 Example 6 Regenerated Cleaning Solution:
app. 5.7% active citric acid based metal clP~ning solution.
Tre~tm~nt-1. introduction of 0.3% of a 30% thiocarbamate metal precipitant that known by the trademark METALSORBTM ZT from Diachem Chemicals);
2. 20 seconds reaction time;
3. introduction of 0.25 to 0.5% of a slurry cont~ining 12% sodium b~;ntolliLe and 3% citric acid;
4. introduction of 0.25% of a 0.4% dispersion of strong anionic polyacrylamide polymer;
5. two minutes agitation;
6. ten to thirty minllt~s settling;
7. coarse filtration through a 100 ,um mesh filter; and 8. carbon/sand filtration.
Results of the Tre~tm~nt Before After Active Ingredient 5.7% 3.8%
Cu++ mg/L 7.0% 0.1%
Zn++ mg/L 6.6% 0.4%
Total OFG 15% 5%
Example 7 Regenerated Cle~n~ing Solution:
app. 0.7% active sodium nibite-based metal cle~ning solution.

~ 2161864 Tre~tnnent-1. introduction of 0.3 % of a 30~o thiocarbamate metal precipitant (METALSORBTM ZT from Diachem Chemicals);
2. 20 seconds reaction time;
3. introduction of 0.25 to 0.5% of a slurry cont~ining 12% sodium bentonite and 3 % citric acid;
4. agitation for 2 minutes;
5. introduction of 0.25% of a 0.4% dispersion of strong anionic polyacrylamide polymer;
6. two minutes agitation;
7. ten minutes settling;
8. coarse filtration through a 100 ,um mesh filter; and 9. carbon/sand filtration.
Results of the Trç~tm~nt Bçfore After Active Ingredient 0.7 % 0.7 %
Cu++ mg/L 73.8 % 1.5 %
Zn++ mg/L 32.5 % 20.5%
Total O F G 93 % 3.8 %
Important advantages of the present invention include the following:
Regener~te~ and recycles spent aLkaline, acid or detergents solutions and their additives.
~r~int~in~ cle~ning solutions at peak efficiency.
Si~nific~ntly reduces chemical, organic, and BOD/COD pollution.

8 6 ~

Saves on chemical usage.
Saves on water usage.
Saves on energy.
Reduces cleaning time to increase overall productivity.
Decrease or elimin~te the need for waste water tre~tment f~t~.iliti~

Claims (6)

1. A method for regenerating a spent alkaline, acidic or neutral cleaning solution, comprising the steps of:
(a) pre-conditioning said spent solution;
(b) adding an absorbent material to said preconditioned solution to provide an interactive solution;
(c) precipitating undesirable materials from said interactive solution by addinga soluble polymeric flocculating agent which is selected from the group consisting of an anionic polymeric flocculating agent and a cationic polymeric flocculating agent thereto, in a sequence of steps consisting essentially of (i) adding one of said anionic polymeric flocculating agent or said cationic polymeric flocculating agent to said interactive solution to provide a reactive solution, (ii) thoroughly mixing said reactive solution to provide a mixed reactive solution, and (iii) adding the other of said anionic polymeric flocculating agent or said cationic flocculating agent to said mixed reactive solution, thereby to precipitate insoluble salts as large-sized and hard flocs; and (d) subjecting the said so-formed mixed reactive solution containing said flocs to a solid/liquid separation.

2. The method of claim 1, including the additional step of adding a different flocculating agent, which is either an anionic polymeric flocculating agent or a cationic polymeric flocculating agent, which is opposite in sign to the second added polymeric flocculating agent to the mixed reactive solution, thereby to complete the provision of said large-sized and hard flocs.

3. The method of claim 1 or claim 2, wherein said spent solution is alkaline, and wherein said preconditioning is carried out by the addition of an agent which is selected from the group consisting of alkali metal aluminates, alkali metal ferrates, alkali metal hydroxides, alkali metal carbonates, alkaline earth metal salts, alkaline earth metal hydroxides, alkaline earth metal carbonates and alkaline earth metal oxides, and mixtures thereof.

4. The method of claim 3, wherein said alkali metal is sodium.

5. The method of claim 3, wherein said alkaline earth metal is selected from the group consisting of calcium and magnesium.

6. The method of claim 3, wherein said alkaline earth metal hydroxides are selected from the group consisting of calcium hydroxide and magnesium hydroxide.7. The method of claim 3, wherein said preconditioning agent is calcium oxide.
8. The method of claim 3, wherein said preconditioning agent is sodium carbonate.
9. The method of claim 1 or claim 2, wherein said spent solution is neutral or acidic, and wherein said preconditioning agent is selected from the group consisting of salts of Group III of the Periodic Table, and salts of the first transition series of the Periodic Table.
10. The method of claim 10, wherein said preconditioning agent is selected from the group consisting of alum, aluminum sulphates, iron sulphates, polyaluminum chloride and aluminum acetate.
11. The method of claim 9 or claim 10, wherein said anionic polymeric flocculating agent is chitosan.
12. The method of claim 9, claim 10 or claim 11, wherein said cationic polymeric flocculating agent is selected from the group consisting of a polyamide, and a polyacrylate, and mixtures thereof.
13. The method of claim 1 or claim 2, wherein said spent solution is alkanine, acidic or neutral, and wherein said preconditioning step is provided by oxidation of said solution.
14. The method of claim 13, wherein said oxidation is carried out by the addition of an agent which is selected from the group consisting of a peroxyborate, a peroxycarbonate, a peroxide and a persulphate to said spent solution.
15. The method of claim 13, wherein said oxidation is carried out by the addition of an agent which is selected from the group consisting of sodium peroxyborate, sodium monoperoxycarbonates, sodium diperoxycarbonates, hydrogen peroxide, sodium peroxide, barium peroxide and sodium peroxydisulphate to said spent solution.

16. The method of claim 1 or claim 2, wherein said spent solution is neutral or acidic, and wherein said preconditioning step is carried out by heating said solution to a temperature above 50°C.
17. The method of any one of claims 1 to 16, inclusive, wherein said preconditioned step is carried out in the presence of a weighting agent.
18. The method of claim 17, wherein said weighting agent comprises calcium carbonate.
19. The method of claim 17, wherein said weighting agent comprises diatomaceous earths.
20. The method of any one of claims 1 to 19, inclusive, wherein said absorbent material is selected from the group consisting of a bentonite and an attapulgite.
21. The method of claim 20, wherein said bentonite is sodium bentonite.
22. The method of claim 1, or any one of claims 3 to 21, inclusive, wherein said soluble polymeric flocculating agents are used in alternating added chargesprogressing from anionic to cationic.
23. The method of claim 1, or any one of claims 3 to 21, inclusive, wherein said soluble polymeric flocculating agents, are used in alternating added charges progressing from cationic to anionic.
24. The method of any one of claims 2 to 21, inclusive, wherein said soluble polymeric flocculating agents, are used in alternating added charges progressing from anionic to cationic to anionic.
25. The method of any one of claims 2 to 21, inclusive, wherein said soluble polymeric flocculating agents, are used in alternating added charges progressing from cationic to anionic to cationic.
26. The method of claim 22, wherein an anionic polymeric flocculating agent is added to said interactive solution to provide a reactive solution; wherein said interactive solution is thoroughly mixed to provide a mixed reactive solution; wherein a cationic polymeric flocculating agent is added to said mixed reactive solution to cause precipitation of insoluble salts; and wherein said precipitated insoluble salts are separated from said liquid solution.

27. The method of claim 23, wherein a cationic polymeric flocculating agent is added to said interactive solution to provide a reactive solution; wherein said reactive solution is thoroughly mixed to provide a mixed reactive solution; wherein an anionic polymeric flocculating agent is added to said mixed reactive solution to cause precipitation of insoluble salts; and wherein said precipitated insoluble salts are separated from said so formed mixed reactive solution.
28. The method of claim 24, wherein a first anionic polymeric flocculating agent is added to said interactive solution to provide a reactive solution; wherein said reactive solution is thoroughly mixed to provide a mixed reactive solution; wherein a cationic coagulant is added to said mixed reactive solution to provide an intermediate reactive solution which has been subjected to at least partial precipitation of insoluble salts; wherein a second anionic polymeric flocculating agent is added to said intermediate reactive solution to cause substantially-complete precipitation of insoluble salts; and wherein said precipitated insoluble salts are separated from said so-formed intermediate reactive solution.
29. The method of claim 25, wherein a first cationic polymeric flocculating agent is added to said interactive solution to provide a reactive solution; wherein said reactive solution is thoroughly mixed to provide a mixed reactive solution; wherein an anionic polymeric flocculating agent is added to said mixed reactive solution to provide an intermediate reactive solution which has been subjected to at least partial precipitation of insoluble salts; wherein a second cationic polymeric flocculating agent is added to said intermediate reactive solution to cause substantially-complete precipitation of insoluble salts; and wherein said precipitated insoluble salts are separated from said so-formed intermediate reactive solution.
30. The method of any one of claims 1 to 29, inclusive, wherein said anionic polymeric flocculating agent is selected from the group consisting of alginic acid, alginates, sodium alginate, sodium polyacrylate, maleate copolymers, partial hydrolyzates of polyacrylamide, anionic polyacids and salts thereof, an alkali metal salt of a simple oligomer of acrylic acid, an alkali metal salt of a simple oligomer of acrylic acid, an alkali metal salt of a complex oligomer of methacrylic acid, a low-viscosity sodium carboxymethylcellulose, and an oligomeric sulphonate, and mixtures thereof.
31. The method of any one of claims 1 to 30, inclusive, wherein said cationic polymeric flocculating agent is selected from the group consisting of a polyamide and a polyacrylate, and mixtures thereof.
32. The method of any one of claims 1 to 31, inclusive, wherein said separation is achieved by a filtration step.
33. The method of claim 32, wherein said filtration step is carried out using a filter member which is selected from the group consisting of a fine sand filter, a membrane filter, a stainless steel membrane filter, and a coarse sand filter.
34. The method of claim 32 or claim 33, including the use of a filter aid to inhibit clogging of the openings of said filter.
35. The method of claim 34, wherein said filter aid is selected from the group consisting of diatomaceous earth, perlite, siliceous materials, carbon, fibrous cellulose, and powdered active magnesium oxide.
36. The method of any one of claims 32 to 35, inclusive, wherein said filtration step includes a substantially simultaneous oxidation step.
37. The method of claim 36, wherein said oxidation step is a catalytic oxidation to complete the oxidation of any further impurities in the solution.
38. The method of any one of claims 32 to 35, inclusive, wherein said filtration step is achieved by ultra-filtration which is carried out to remove particles having a size of 5 to 0.1 µ.
39. The method of claim 1, comprising the steps of: preconditioning said spent solution by adjusting the temperature to above 50°C; introducing a solution of calcium nitrate therein; agitating said solution for a first period of time; introducing a slurry containing sodium bentonite and sodium carbonate thereinto, thereby to provide said reactive solution; allowing a suitable time for reaction; introducing a dispersion of a strong anionic polyacrylamide polymer thereinto; agitating said solution for a second period of time, thereby to provide said mixed reactive solution; introducing a dispersion of a strong cationic polyacrylamide polymer thereinto; allowing a sufficient time for agitation and settling; filtering said mixture through a carbon/sand filter; and then readjusting said solution for caustic concentration.
40. The method of claim 39, wherein: said solution of calcium nitrate is used in an amount of 0.1 and has a concentration of 50% by weight; wherein said agitation for a first period of time is for 2 minutes; wherein said slurry contains 12 % sodium bentonite and 3% sodium carbonate which is added in an amount of 0.4 % by weight;
wherein said suitable time for reaction is 2 minutes; wherein said dispersion of said strong anionic polyacylamide polymer has a concentration of 0.4 % and is added in an amount of 0.5%; wherein said agitation for a second period of time is for 2 minutes;
wherein said dispersion of a strong cationic polyacylamide polymer has a concentration of 0.5 % and is added in an amount of 0.4 % by weight; wherein said sufficient time for agitation and settling is for 2 minutes; and wherein said caustic concentration is 2.5 %.
41. The method of claim 1, comprising the steps of: preconditioning said spent solution by adjusting the temperature to above 50°C; introducing a solution of calcium chloride thereto; agitating for a first sufficient period of time; introducing a slurry containing sodium bentonite and sodium carbonate thereinto; allowing a sufficient reaction time; introducing a dispersion of a strong cationic polyacrylamide polymer thereinto; agitating for a second suitable period of time; introducing a dispersion of a strong anionic polyacrylamide polymer thereinto; agitating for a third sufficient period of time; allowing a sufficient time for settling; filtering through a carbon/sand filter; and then readjusting said solution for caustic concentration.
42. The method of claim 41, wherein said solution of calcium chloride is 30%by weight and is added in an amount of 0.2 %; wherein said agitating for a first sufficient period of time is for 2 minutes; wherein said slurry contains 12% sodium bentonite and 3% sodium carbonate, which is added in an amount of 0.24 % by weight; wherein said sufficient reaction time is 2 minutes; wherein said dispersion of said strong cationic polyacylamide polymer has a concentration of 0.4 % and is added in an amount of 0.5 %;
wherein said agitating for a second suitable period of time is for 2 minutes; wherein said dispersion of a strong anionic polyacylamide polymer has a concentration of 0.4 %, and is added in an amount of 0.5% by weight; wherein said sufficient time for settling is for 10 to 30 minutes; and wherein said caustic concentration is 2.0%.
43. The method of claim 1, comprising the steps of: adjusting the temperature to above 50°C; introducing a slurry containing sodium bentonite and sodium carbonate thereinto; allowing a first sufficient holding time; introducing a dispersion of strong cationic polyacrylamide polymer thereinto; agitating for a sufficient period of time;
allowing a second sufficient holding time; filtering through a coarse filter; filtering through a carbon/sand filter; and then readjusting said solution for caustic concentration.
44. The method of claim 43, wherein: said slurry contains 12% sodium bentonite and 3% sodium carbonate, which is added in an amount of 0.4% by weight at a rate of 165 ml/min, into a caustic flow set at a rate of 35 L/min; wherein said first sufficient holding time is 15 seconds; wherein said dispersion of said strong cationic polyacylamide polymer has a concentration of 0.4% and is added at a flow rate of 46 ml/min; wherein said agitating for a sufficient period of time is for 2 minutes; wherein said second sufficient holding time is 30 seconds; wherein said coarse filtration is through a 100 µm filter; and wherein said caustic concentration is 2.0%.
45. The method of claim 1, comprising the steps of: adjusting the temperature to above 50°C; introducing a slurry containing sodium bentonite thereinto; agitating for a first suitable period of time; introducing a dispersion of a strong anionic polyacrylamide polymer thereinto; agitating for a second suitable period of time; settling for a suitable period of time; filtering through a carbon/sand filter; and then readjusting said solution for caustic concentration.
46. The method of claim 45, wherein: said slurry contains 12% sodium bentonite which is added in an amount of 0.8% by weight; wherein said agitating for a first suitable period of time is for 2 minutes; wherein said dispersion of said strong anionic polyacylamide polymer has a concentration of 0.4% and is added in an amount of 0.5%; wherein said agitating for a second suitable period of time is for 2 minutes;
wherein said settling for a suitable period of time is for 10 to 30 minutes; and wherein said caustic concentration is 2.5%.

51. The method of claim 1, comprising the steps of: introducing thiocarbamate metal precipitant thereinto; allowing a suitable reaction time; introducing a slurry containing sodium bentonite and citric acid thereinto; agitating for a first suitable period of time; introducing dispersion of a strong anionic polyacrylamide polymer thereinto;
agitating for a second suitable period of time; introducing a dispersion of a strong cationic polyacrylamide polymer thereinto; agitating for a third suitable period of time;
settling for a suitable period of time; filtering through a coarse filter; filtering through a carbon/sand filter; and readjusting said solution for acid concentration.
52. The method of claim 51, wherein said solution of thiocarbamate metal precipitate is 30% by weight, and is added in an amount of 0.3%; wherein said suitable reaction time is 20 seconds; wherein said slurry contains 12% sodium bentonite and 3%
citric acid which is added in an amount of 0.25-0.5% by weight; wherein said dispersion of said strong anionic polyacrylamide polymer has a concentration of 0.4% and is added in an amount of 0.25 %; wherein said agitating for a first suitable period of time, wherein said agitating for a second suitable period of time, and wherein said agitating for a third suitable period of time are each for 2 minutes; wherein said settling for a suitable period of time is for 10 to 30 minutes; wherein said coarse filtration is through a 100 µm mesh filter; and wherein said acid concentration is 5.7%.