CA1114079A - Process for clarifying aqueous suspensions of particulate solids - Google Patents

Abstract

24,729 ABSTRACT OF THE DISCLOSURE

The clarification of specified types of aqueous sus-pensions of finely divided solids by the use of polymeric floc-culating agents is markedly enhanced if, in conjunction with specified types of polymeric flocculating agents, the suspen-sions are treated with an aqueous acid colloidal solution of a melamine/formaldehyde resin containing from 2 to about 12 moles of formaldehyde per mole of melamine.

Description

14(~79 The present invention relates to the clarification of water suspensions of finely divided solids. More particularly, it relates to an improved process for the 10oculation and separation of suspended particles, both organic and inorganic, in aqueous dispersions including raw water, raw sewage and various industrial process and waste waters.
The term "clarification" as used herein includes conventional means of separating the flocculated suspended matter from the aqueous phase, such as filtration, settling, centrifugation, flotation, etc., or ccmbinations thereof.
The separation of suspended solids in aqueous systems has kecome a problem of considerable importanoe . For example, present anti-pollution laws require that the solids content of waste water be reduced ;
to a fixed maximum value befoi-~ discharge into a river or stream. In many cases, due to the stability of the suspensions and the small size of the suspended particles, sedimentation and filtration procedures are relatively ineffective insofar as meeting the imposed anti-pollution standards without prior flocculation of the suspended matter. musl it has naw hecome the practioe in the art to treat the suspensions with chemical flocculating agents which cause the fine particles to agglomerate thus converting them into larger particles having an increased tendency to settle and which at the same time have less tendency to plug the filter medium.
r~nicipal sewage treatment, for example, requires the separation and disposal of large quantities of water frcm sewage sludge. Flocculating agents have heen used to good advantage in the settling and filtration of such sludges in sewage treating plants.
Another difficult industrial pro~lem is the clarification of industrial wastes which would otherwise cause pollu-~ .

lA~7~9 tlon Of l~nds ~nd 8tre~m~. ThU~, W~8tes~ re8ultlng from indu~-trial operations, such a8 coal mlnlng, ore processing, chemical manuracturlng and the llke, comprlse suspenslons of ~lnely dlvided sollds in water. These suspensions remaln fitable for days 80 that if the sollds are not removed the water cannot be reused and a dlsposal problem 18 presented. In coal plant operations, for example, the coal wash water contains finely divided coal and clay particles whlch must be separated out prlor to reu~e or dl8po8al of the water ln a river or stream.
Also, the proce6sing Or ores results in the productlon Or large guantities of fines (or slimes), through attritlon grinding.
After removal ~r the mineral values, the slimes must, in many lnstanCe8, be dewatered ~or further processing or disposal.
Bettling or ~lltration, or a combination thereof, have been used to ~eparate such rine suspensions and the efficiency Or the 8eparation8 ha8 been greatly improved by the use o~ flocculat-lng agent8.
Another problem whlch has developed i~ that Or supply-lng the increasingly large amounts Or clean water required for ~drinking and various industrial uses. Thus, the natural sources Or ~water supply, i.e., lakes, rivers and streams, are constantly becomlng less available due to pollution which has been built up in these sources by discharge of industrial wastes therein over the~year8. The clarification of such raw waters, whlch 25~ ~ Contain flnely 8u8pended pollutants, has been ef~ected by settl-ing and/or ~iltratlon processes and flocculants have been used to improve the~e processes. However, the clarities achieved by the heretoPore employed flocculants or flocculant comblnatlons àre ~requently lnadequate for these use6.
30;~ It~ls the obJect Or this inventlon to provide an lmproved method ~or clarifylng aqueous suspenslons Or finely dlvided solids. It 18 a rurther ob~ect to provide a method for the ~locculation and 5ettllng Or the flne partlcles ln such

- 2 -4 0~9 suspens10ns whereby the ~upernatent water thus provlded 18 of markedly hlgher clarlty than obtalnable by flocculatlon and settllng methods known heretofore.
As has been brought out herelnabove, flocculatlng agents have been used ln the clarlflcation of aqueou3 suspen-slons. Of the various flocculatlng agents which have been used, those whlch have proved most effectlve are moderate to high molecular welght polymers, i.e., polymers havlng molecular welghts ranglng from about lO,000 up to about 30 mlllion or hlgher. Polymers whlch have been used, for example, are (a) acrylamide polymers, including polyacrylamides and copolymers of acrylamide with up to about 70 mole percent acrylic acid or lts aIkall or ammonium salts and partlally hydrolyzed polyacryl-amldes contalning up to about 70 mole percent sodlum acrylate groups; (b) hydrolyzed polyacrylonitriles contalning up to about 70 mole percent sodium acrylate groups; (c) cationlc vlnyl addl-tion polymers such as (l) copolymers of acrylamide with from 1 bo about 30 mole percent of a monomer such as dlallyldimethyl-~mmonium chloride, the methyl chloride or dimethyl sulfate ~quaternary of dimethylamlnoethyl methacrylate, vinyl pyrldine or its substituted derlvatlves or other copolymerlzable amine or quaternary amlne, (2) polydlallyldimethylammonlum chlorlde, ~3) polyvlnylpyrldlne, (4) polyvlnyllmidazollne; (d) amino-alkylated polyacrylamldes; and (e) condensatlon polymers of (1) aIkylene dihalides and polyalkylene polyamines? (2) amines and halohydrlns and (3) halohydrins and polyalkylene polyamlnes.
Whlle, as a~ore-lndicated, the varlous polymer floccu-lants have proved useful in the clarlficatlon of the variou~
aqueous suspeAslons, ~till, the clarlties requlred ~or many 30 -; ~munlclpal ~nd lndustrlal uses have elther not been attalned or h~ve requlred the use of relatlvely large amounts of the polymer ~flocculants. Thus, ln the case of coal wash waters, for example, the use of polymer flocculants alone have not provided the ~:
.. . . . .

11~4(~79 :--clarities desired.
According to the present invention, there is provided a method for clarifyin~ an aqueous suspension of finely divided solids, said suspen-sion beingselected from the group consisting of (1) ooal wash water (2) coal oe ntrate

(3) iron ore slime

(4) raw water and

(5) raw sewage, CQmprising treating said suspension with a polymeric flocculating agent and an aqueous said colloidal sollution of a meLamine/formaldehyde resin containing fram 2 to about 12 moles of formaldehyde per mole of melamine provided that:
(I) in treating said suspension (1), the polymeric flocculating agent is selected fmm the group consisting of an anionic partially hydrolyz-ed polyacrylamide, an anionic partially hydrolyzed polyacrylonitrile and an anionic copolymer of acrylamide and acrylic acid or its salts; and the aqueous acid colloidal solution of melamine/formaldehyde resin contain from 4 to about 12 moles of formaldehyde per mole of melamine;
(II) in treating said suspension (2), the polymeric flocculating agent is selected from the group consisting of an anionic partially hydrolyzed polyacrylonitrile, an anionic partially hydrolyzed polyacrylamide., an anionic copolymer of acrylamide and acrylic acid or its salts and a non-ionic polyacrylamide containing less than 1% carboxyl groups; and the aqueous acid colloidal solution of melamine/formaldehyde resin contains from 4 to about 12 moles of formaldehyde per mole of melamine;
(III) in treating said suspension (3), the polymeric flocculating agent is selected fram the group consisting of a cationic polydiallyldi- : . :
methylamm~nium chloride, a cationic amine/epichlorohydrin polymer, cationic polyacrylamides, cationic aIkylene polyamines and a non-iQnic polyacrylamide c~ntaining less than 1~ carboxyl groups; and the a~ueous acid colloidal solution of melamine/formaldehyde resin contains from 4 to about 12 moles of formaldehyde per mole of melamine;
(rV~ in treating said suspension (4~, the polymeric flocculating agent is selected fram the group consisting of a cationic amine/epichloro-hydrin polymer, a cationic aminoaIkylated polyacrylamide, an alkylene polyamine polymer and a cationic acrylamide/vinylamine copolymer; and the aqueous acid collodial solution of melamine/formaldehyde resin contains from 2 to about 12 moles of formaldehyde per mole of melamine;
(V) in treating said suspension (5), the polymeric flocculating ~ agent is a cationic aminoaIkylated polyacrylamide, a cationic amine/epi-chlorohydrin polymer, a cationic acrylamide/vinylamine copolymer or a cationic aLkylene polyamine; and the aqueous acid colloidal solution of melamine/formaldehyde resin contains from 2 to about 12 moles of formalde-hyde per mole of melamine.
In accordan oe with the present invention, it has now been found that the clarification of aqueous suspensions by the uæ of polymer floc-culating agents is greatly improved if, in conjunction with the polymer flocculant, the suspension is also treated with either a melamine/formalde-hyde acid colloid or a formaldehyde-fortified, melamine/formaldehyde acid colloid as defined hereinafter. Thus, it has been found that the use of such an acid colloid in conjunction with the polymer flocculant in so~e instanoe s provides suFernatant clarities not obtainable by the use of the polymers alone, even at high dosages; and generally, permits the use of substantially reduced amounts of the polymer flocculant without sacrifi oe of the clarity obtained using the polymer flocculant alone. Accordingly, it will be appreciated that the use of the acid colloid in cambination with the polymer flocculant in accordan oe with the invention provides not only improved water clarities over those attainable by the use of the polymer flocculants alone but can also provide considerable savings in polymer usage. That the use of the acid colloid in conjunction with the polymer flocculant would provide such ~arkedly superior results as ccmpared to the use of the polymer flocculant alone was surprising sin oe the acid colloid itself would not ke e~pected to exhibit flocculating activity due - 4a -' - . . .

- 1~140~9 to its lcw molecular weight. Applicant does not kncw for certain why the acid colloid provides the improved results. Without limiting the invention to any theory, however, it is considered that the acid colloid, which is highly cationic, effectively neutralizes the negative charges usually associated with the suspended particles thereby making them more readily flocculated by the polymer flocculant.

The Melamine/Formaldehyde Acid Colloids Ihe melamine/formaldehyde acid colloid and the - 4b -.~ .
.. . . , . - .
.

7~9 form21dehyde-fortified, mela~ine/formaldehyde acid colloid employed in the invention are well-known materials. The mela-mine/formaldehyde acid colloid is shown in United States No. 2,345,543.
Thus, as shcwn in the patent, the colloid is prepared by reacting the melamine with formaldehyde in the presence of a defined amount of -acid and sufficient water to provide an aqueous solution of a melamine/
formaldehyde condensation product (resin) having a pH of from about 0.5 to about 3.5 when measured at 15% solids and then aging the acid solution until the resin is converted to colloidal form as evidenced by the appearance of a blue colloidal haze in the solution. The colloidal resin solution thus provided contains about 2 - 3 moles of formaldehyde per m~le of melamine.
Alternatively, the colloid resin solution may be pre-pared by first forming the melamine/formaldehyde (trimethylol melamine) resin in the absen oe of the acid and then converting the resin to the colloid by dissolving it in an aqueous acid of the required pH and aging the acid solution until colloid formation is effected.
m e formaldehyde-fortified, melamine/formaldehyde acid colloid used in the invention is disclosed in United Stated Patent No. 2,986,489. Thus, as shown in the patent, this colloid is formed by reacting the melamine/formaldehyde resin acid cDlloid solutions described in Uhited States No~ 2,345,543 with addi-tional formaldehyde and aging the solution until the resulting formaldehyde-reacted resin is converted to colloidal form.
Alte m atively, a melamine/formaldehyde (trimethylol melamine) resin prepared in the absenoe of aqueous acid (i.e., in non-colloid fonm) may be reacted with the additional formal-dehyde and then converted to colloidal form by dissolving in acid solution and aging to form the formaldehyde-fortified colloid.

~ .

111407~

For the purpose Or the present lnventlon, the amount Or formaldehyde reacted with the melamlne/formaldehyde resln 1~ ~rom about 2 to about 10 moles per mole of comblned mel~mlne ln the resln and preferably from 3 to 8 mole~ since these amounts provide formaldehyde-fortifled products which are the most effectlve for use ln the present lnventlon. Thus, as opposed to the unfortiPled mel~mlne/formaldehyde colloid, whlch contalns 2-3 moles of formaldehyde per mole Or melamlne, the ~ormaldehyde-fortifled collold contalns a total of from about 4 to about 12 moles, preferably from about 5 to about 10 moles, Or formaldehyde per mole of mel~mine.
A typlcal formaldehyde-fortified, acid colloid prod-uct ~or use in the present lnventlon was prepared as follows:
To 114 p~rts Or commerclal spray-drled trlmethylol melamine in 69B parts of hydrochlorlc acid of such strength as to provide 0.5 mol o~ HCl per mol o~ comblned melamlne present there was added 188 part~ o~ 37% aqueous ~ormaldehyde solution (5 mols per mol of combined melamlne in the acid solution). After gentle stlrring for a few mlnutes, the regulting solution was aged for 16 hours at room temperature, during which time the solutlon had developed a blue haze characteristic of the acid collold. The resultlng formaldehyde-fortified, melamine/form-~ aldehyde acid colloid solution (pH = 1.3) 18 identifled here-; ~ lnarter as "Colloid Solutlon A".
A typlcal, non-formaldehyde-fortified catlonic mela-mlne/formaldehyde acld colloid used in the invention was pre-pared as follows: A solution Or 114 parts of commercial spray-drled trlmethylol melamine in 886 parts of hydrochloric acid of such strength as to provide o.65 mols of HCl per mol of com-`:
30~ bined mel~mine present was prepared and permitted to age for 16 hours at room temperature during whlch time it had developed the blue haze characteristic o~ the acld collold. Thl 8 collold solution 18 identlfied herelnafter as "Collold Solution B".

- 6 :

~ 11 4 ~7 ~

The marked lmprovement in the flocculatlon and clari-flcatlon of varlous types of solld suspenslons when the afore-descrlbed acid collolds are used ln conJunction wlth particular type~ Or hi~h molecular welght polymer flocculants, a8 found by the present lnventlon, i8 lllustrated by the ~ollowing exam-ples. It will be appreciated ~rom the examples that the ~orm-aldehyde-fortl~led collold, ln conJunctlon with the specl~ied polymer ~locculants, provldes superlor clarltles to tho~e pro-vlded by the unfortl~ied colloid in the treatment of high solids sUspenslon~ i.e., su8penslons contalnlng more than about 0.5%
by welght o~ suspended sollds, such as coal wash water, coal centrate and iron ore sllmes (Examples 1-6).
It wlll be further appreclated ~rom the examples that elther one of the collolds of the lnventlon, when used in con-~unctlon wlth the speclfled polymer ~locculants, provldes 8uperlor clarltles to those provlded by the employment of the polymer8 alone ln the treatment o~ low solld8 su8penslons, l.e., tho8e contalnlng less than about 0.5~ by welght Or suspended 8011ds, such a~ raw water and raw sewage (Examples 7-11).
Accordingly, for the treatment o~ these suspenslons, melamlne/-formaldehyde acld collolds having from 2 to about 12 moles of ormaldehyde per mole of melamlne may be used.

Clarl~lcatlon tests were conducted on spent coal wash ~;~;25 water, from a West Vlrglnia coal preparation plant, containing 3-4% sollds comprised o~ about 90~ clay and about 10% ~ine coal part~cles, by treatlng the wa~h water with typical commercial polymer flocculants alone and In combination wlth a typical forxaldehyde-fortifled~melamine/~ormaldehyde cationic acid col-30~ 101d of~bhis inventlon, vlz., Colloid Solution A (CS-A). The polymer flocculants used were as ~ollows.
Polymer C: An anlonlc, hydrolyzed polyacrylonitrlle havlng ~ molecular welght o~ approximately 200,000 and contaln-ing about 70% carboxyl and about 30~ acryl~mide groups.

- 7 Polymer D: An anlonic hydrolyzed polyacrylamide hav-lng a molecular welght of 12-15 mllllon containlng about 35 carboxyl groups, The te~t procedure was as follows: A given amount of the polymer ~locculant ln the rorm of a dilute aqueous solu-tlon thereof and/or the collold of the inventlon (as Collold Solutlon A, i.e,, CS-A) 18 added to a l-llter sample of the coal wQsh water in a l-llter graduate cyllnder. The treated sample 18 then stroked up and down slx tlmes wlth a perforated metal plunger to ~orm a substantlally homogeneous mlxture. It i8 then permitted to stand until the compacted solids are at the 200 cc. level at whlch polnt the turbldlty o~ the supernate 18 measured uslng a Helllge Turbidlmeter.
The test results are glven in Table I. (In Table I
8nd all o~ the followlng Tables, the concentration of CS-A or CS-B 18 gIven ~8 ppm. calculated as trlmethylol melamlne.) TABLE I
Amount Added ~P~m.) ( ) Test No. Polymer CPolymer D CS-ATurbidity(2) l --- --- 4 1500 2 2 -__ __ 365 3 l --- 2 90 ~, ~. . , 4 1.2 2.6 -- 175 ~5 1.2 1.3 4 50 . : 6 o. 6 1.3 4 117 )Ba~ed on total volume (1 llter) of suspension; l ppm.
e~uals 1 milligram per liter.
(2)Parts per mllllon o~ suspended solld~.

As can be 6een from Table I, while the formaldehyde-.
a~ for;tlrled colloid itsel~ 18 relatively lne~ective, it markedly lmprove~s~the~erfectlvenes~ of the polymer flocculants. Thus, r` the u8e of the relatively inexpenslve colioid agent affords a conslderable economlc advantage from the ~tandpoint of reduced u~uage Or the relatively expenslve polymer flocculants.

.

4 ~7 -A serles o~ rlocculatlon tests were conducted on a centrlruge centrate ~rom the Mohave generatlng statlon ln Nevada, whlch resulted rrom the dewatering o~ a 70~ slurry of coal rlnes in water. The centrate contalned 4% sollds (about 95% coal and 5% clay) and had a pH ad~usted to 6.8 wlth H2S0~.
The te~t procedure was the same as ln Example 1. In thls series one of the polymer flocculants used was a polyacrylamlde containlng less than 1% carboxyl groups and having a molecular weight of 12-15 million (Polymer E). The test result~ are 8hown ln Table lI.
TABLE II
_ Amount Added (~pm.) Test No.Polymer C Polymer E CS-ATurbidity 1 30 15 __ 460 10 lo ?0 45 Here again, as in Example 1, it i8 seen that the ~ormaldehyde-~orti~ied acid colloid markedly lmproves the ~ef~ectiveness of the polymer rlocculants, provlding superlor reaults at reduced flocculant d~sages.
EXAMPLE
: .
As has been stated hereinabove, the formaldehyde-~ortlf1ed melamine/formaldehyde acid collold employed ln the ~` present lnventlon ls markedly superior to the unfortified melamlne/formaldehyde acid colloid a8 a ~locculant aid for use ln con~unction with polymer flocculants for thé treatment of high sollds suspensions. This superiority is shown by the fol-lowlng tests in which the fortifled colloid, Collold Solution A
30~ (CS-A3 and the un~ortified colloid, Colloid Solution B (CS-B) wer~ used in con~unctlon with two typical commercial polymer locculants, ~iz., Polymer C (supra) and Polymer L, a copolymer of 70~ acrylamlde and 30% ~cryllc acld having a molecular welght : _ g _ 111407~9 1 ^
o~ about 5 million. The testa were made on the s~me type of coal refuse slurry tested in Example 1 usine the test procedure of Example 1. The results are shown in Table III.
TABLE III
Amount Added (Ppm~) Test No. Polymer C Polymer L CS-A CS-B Turbidit~
1 3.o ______ ___ 1200 2 2.0 --- 2.0 --- 65 3 , 2.0 -__ ___ 2.0 115 4 ___ 2.0 --_ ___ 1500 --- 1.0'3.0 --~ 175 6 ___ 1.0 --- 3.0 45 As shown in Table III, Colloid A improves the e~fi-clency o~ the polymers to a much greater extent than does Collold B. ', The super10r1ty of the ~ormaldehyde-~ortl~ied colloid : Or the inventlon over conventional, non-colloldal, catlonic ' r-slns as ~locculant aids 18 evldent ~rom tests conducted on the ,~ 20 ~same type of coal refuse slurry used in Example 1. m e resins tested were (a) ~ urea-~ormaldehyde-diethylenetrlamine cationic 'oondensation resln (Resin I) and (b) an adiplc acid-diethylene-'trlamine-epichIorohydrln catlonic condensatlon resin (Resin II).
~"'~ The;~locculant polymer used was Polymer C (supra). The tests 25 ~ were~conducted as in Example 1. The results are ~hown ln T~ble ~V.
~ , ABLE IV
Amount Added (ppm.) Test~No.~ Polymer~C;~ CS-A ;Resln I Resln II Turbidity 2 ~ }.0 2.0 ~ - go ,, 3 ~ l. o: ; --- 3. o ___ 610 4~ .o --- --- 2.0 630 . . . . . . .. .

`79 -Whlle, aB shown in Table IV, the other reslns glve improved clarlty, the lmprovements are not nearly as good as that obtalned wlth the collold.

A serles of tests were conducted on a taconlte (lron ore) ~lime from Mlnnesota contalnlng 3-4~ sollds by the same procedure used ln Example 1. In thl~ serles the polymer ~loc-culants used were (a) polydlsllyldlmethylammonlum chlorlde (p-DA~M), a catlonlc polymer, (b) a nonion$c polyacrylamlde havlng a molecular weight of 3-5 mlllion (Polymer F) and (c) a cationic amlne/epichlorohydrln condensatlon polymer (A/E~I).

TABLE V
Amount Added l~m.) 15 Test No. ~ymer F ~-DADM A/EPI CS-A Turbidity 1 0.15 ---- ---- 530 2 0.10 ---- ____ 0.25 115 3 ---- 0.50 ---- ---- 390 4 ____ 0.25 ~ 0.25 175 ___ ____ o,50 __ _ 325 ~6 ---- _-__ 0.25 0.25 145 As shown ln Table V, a marked improvement in super-natant;clarlty is obtained by uslng the formaldehyde-fortified acid~collold ln con~unotion with the polymer flocculants.
~ ~ EXAMPLE ~
It 18 also observed that the formaldehyde-~ortified . ~ .
melamlne/~ormaldehyde acid collold provldes superlor clarlty, ove-r the un~ortlfled collold ln conJunction with polymer floc-culànts, ~or;treatment of iron ore 611mes. The superiority is shown~b~the~following~test re8ults in whlch the fortifled ;collold,;~Collold~Solution A (CS-A) and the un~ortified colloid, Collold Solution B (CS-B) were used in con~unctlon with two typ~cai commerclal polymer ~locculant~, vlz., Polymer F and a .. , , . . . _ . .
.

4 ~7 ~
catlonlc amlne/eplchlorohydrln polymer (Polymer G) The te~ts were made on the s~me iron ore sllme as Exnmple 5 by the same procedure u~ed in ~xample 1. The results are glven ln Table VI.

TABLE VI

Amount Added, (ppm.) Test No. Polymer F Polymer G CS-A CS-~ Turbidity 1 0 2 ~ - 325 2 0.1 ---- 0.3 ~ 90 3 0.1 ---- ---- 0.~ 175 4 --- 0.50 ---- ---- ~25 --- 0.25 0.25 ---- 145 6 ___ 0.25 ____ 0.25 230 When polymer~ alone are used to clarify low solid~
~u6pension8, a llght haze is usually left in the treated water, even at optimum polymer dosage. In the followlng te~ts, Colloid Solutlon A (CS-A) was used in con~unction wlth a commercial catlonic amlne-epichlorohydrin condensation polymer (Polymer G, sUpra) to clarify samples of water ~rom Lake Houston, Texas, having an initlal turbidity of 100 Jackson Turbidlty Units (JTU) as measured on a Hach, Model 2100A turbidimeter calibrated with Formazin 601ution. In each case, the polymer was added prior to the colloid. The test procedure was as follows. One-lit~r samples o~ water were stirred wlth an electrlc paddle 8tirrer at 100 rpm for one minute after each reagent was added, then at 30 rpm for 15 minutes. The su~penslon was allowed to settle ~or 30 minutes~a~d turbldities of the supernate measured.
The re~ults are sh~Wn in T~ble VII.
, ':

.

.
.. . . - . . . : . . . ::

`` lil4079 ABLE VII
Amount Added (ppm.) Test No. Polymer G CS-A Turbldity fJTU) 1 3 0 5.5 ` 2 2 1 3.0 3 4 0 4.6 4 3 1 2.

6 0 2.8 6 4 1 1.8 7 10 0 2.6

8 6 1 1.0

9 4 5 0.59 0 2.7 11 10 1 0.74 12 10 5 o.45 As shown in Table VqI, the formaldehyde-fortified acid collold markedly improves the effectivenesæ oi the polymer, pro-vldlng superior results at reduced polymer dosages; and, ln some lnstances, at lower total reagent dosages.
~ EXAMPLE 8 ;~ 25 Similsr tests to those oi Example 7 were run on : another highly colloidal sample of Lake Houston water which had . an lnitial turbldlty o~ 56 JTU and the results are shown ln Table VIII.

~: :30 ~
.

.

40q9 TABLE VIII
Amount Added (ppm.) Test No. Polymer G CS-A CS-B Turbldlty (JTU) 1 . 20 2 0 7.7 2 20 0 2 8.2 3 20 4 o 3,5 4 20 o 4 3,~

8 o 1.7 6 20 0 8 1.7 . It i8 e~ident from the data ln Table VIII that the regular acld colloid and the ~ormaldehyde-~ortified acld colloid are equally effectlve ln clarifying thls raw water.

Followlng the procedure of Examples 7 and 8, tests were carrled out on samples of Ml~sisslppi rlver water whlch had an inltlal turbldlty of 18 ~TU. In these tests, the floccu-lant polymer u~ed was a commerclal catlonic amine-epichloro-hydrln conden~ation polymer (Polymer G, supra). The test results ~re shown ln Table IX.
~ TABLE IX
: Amount Added (~pm.~
Test No. Pol.vmer G CS-B Turblditv (JTU) 2 0.5 0 7~3 3 0.5 1.0 ~.6 4 1.0 0 7.0 1.0 1~0 2.8 6 2.0 0 8.5 Agaln, the co-use of the regular acid colloid produces tr~ated water wlth better clarltle~ than can be obtalned no m~tter how much of the catlonlc polymer is u~ed.

.. . . .
: . .

~ ` 111407~

Low turbldity water~ are extremely dl~ficult to clarlfy with polymerlc flocculants. Te~ts ~ollowlng the same procedure as ln Examples 7-9 were conducted on samples o~
Rlppowam River (Conn.) water (lnltlal turbldity 1.5 JTU~ uslng Polymer K ln comblnatlon wtth Collold Solution A and ln comblna-tlon wlth Collold Solution B. No improvement in turbidlty at all was observed at any dosage when Polymer K, a catlonlc amlno-alkylated~;polyacrylamlde, was used alone. The results with the co-use o~ the acid collold are glven ln Table X.
TABLE X
Amount Added (~m.) Tost No. Polymer K CS-A CS-B Turbldlty (JTU) 1 0.5 1 0 0.7 2 0.5 0 1 0.74 3 0.5 4 0 0,40 4 ; 0.5 0 4 0.45 . !
Remarkably clearer water resulted by use of the catlonic collolds along wlth Polymer K and no difference in , , porrormance could be observed between the use of CS-A or CS-B.

~ . .
The polymer flocculants alone are of limlted effec-tlvenesa for the re~oval of the very flne particles from raw ~25~ sewage, even at la~rge dosages. However, by using the formalde-hyde-rortirIed acld collold in comblnatlon with the polymer, ~;~ the e~rcctivenes~ o~ the polymer i8 greatly increaaed as shown by t-sts~made~on raw~ewage from a municipal sewage treatlng p ~ ~havlng~an~lnltlal turbidity of 38 JTU. Two commercial 0~ polymer~locculants~were used in these;tests, viz., a hlgh molecul~r~welght cationlc amlnoalkylated polyacrylamide tPolymer K) and an~anlonic hlgh molecular weight polyacrylamlde (Polymer~D~supra). The test procedure was the same as in ~ ~.
. .

lllA07~ .

Example 7. The results arc given ln Table XI.

TABLE XI
Amount Added (P~m.) Test No. Polymer K Polymer D CS-A Turbidlty_(JTU) l- l.O --- 0.0 18 2 0.1 --- 2.0 15 3 0.1 --- 5. 5-~
4 o.l --- 8.o 1.7 --- 0.5 0.0 17 6 --- 0.1 5.0 6.6 As evidenced ~rom the foregoing Examples, the catlonic melamine-formaldehyde acid colloids markedly improve the floccu-latlng effectlveness o~ specific types of polymer rlocculat1ng agents, when empioyed in conJunction with the polymers, in the ~ieatment of specific types of aqueous solids suspension. In the case of cationic and nonionic polymers, the improved floccu-latlng effect is achleved whether the colloid 18 added to the ~u~pension to be clarl~ied before, after or simultaneously with the polymer flocculant; however, in the c~se of anionic floccu-l~ants, tho colloid must be added separately (either before or after the polymer addition) in order to avold electrostatic lnteraction of the oppositely charged materials. The amount of the polymer used will, of course, vary depending on the particu--lar polymer and the suspension being treated. Generally, only very small amounts are required, i.e., from about 0.1 to about 50~parts per mi}llon, and usually from about 0.10 to about lO
parts per million. In practice, the optimum amount ln any g1ven case can be readily determined by test. The amount o~ the -oolloid to be used ln conJunctlon with the polymer flocc~lant will also vary wlth the polymer u~ed and the suspenslon belng treated. Oenerally~ effective (enhancing) amounts wlll range . ," , . .

.. j .. ... . .. . ..... . . .

----` lllAC~79 ~rom about one-tenth the amount of the polymer used up to 200 tlmes the ~mount of polymer used, and the optlmum amount can, of course, be determined by test.

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Claims (6)

C L A I M S

1. A method for clarifying an aqueous suspension of finely divided solids, said suspension being selected from the group consisting of (1) coal wash water (2) coal concentrate (3) iron ore slime (4) raw water and (5) raw sewage, comprising treating said suspension with a polymeric flocculat-ing agent and an aqueous acid colloidal solution of a melamine /formaldehyde resin containing from 2 to about 12 moles of formaldehyde per mole of melamine; provided that:
(I) in treating said suspension (1), the polymeric flocculating agent is selected from the group consisting of an anionic partially hydrolyzed polyacrylamide, an anionic par-tially hydrolyzed polyacrylonitrile and an anionic copolymer of acrylamide and acrylic acid or its salts; and the aqueous acid colloidal solution of melamine/formaldehyde resin contains from 4 to about 12 moles of formaldehyde per mole of melamine;
(II) in treating said suspension (2), the polymeric flocculating agent is selected from the group consisting of an anionic partially hydrolyzed polyacrylonitrile, an anionic par-tially hydrolyzed polyacrylamide, an anionic copolymer of ac-rylamide and acrylic acid or its salts and a non-ionic poly-acrylamide containing less than 1% carboxyl groups; and the aqueous acid colloidal solution of melamine/formaldehyde resin contains from 4 to about 12 moles of formaldehyde per mole of melamine;

(III) in treating said suspension (3), the polymeric flocculating agent is selected from the group consisting of a cationic polydiallyldimethylammonium chloride, a cationic amine/epichlorohydrin polymer, cationic polyacrylamides, cat-ionic alkylene polyamines and a non-ionic polyacrylamide con-taining less than 1% carboxyl groups; and the aqueous acid colloidal solution of melamine/formaldehyde resin contains from 4 to about 12 moles of formaldehyde per mole of melamine;
(IV) in treating said suspension (4), the polymeric flocculating agent is selected from the group consisting of a cationic amine/epichlorohydrin polymer, a cationic aminoalkyl-ated polyacrylamide, an alkylene polyamine polymer and a cat-ionic acrylamide/vinylamine copolymer; and the aqueous acid colloidal solution of melamine/formaldehyde resin contains from 2 to about 12 moles of formaldehyde per mole of melamine;
(V) in treating said suspension (5), the polymeric flocculating agent is a cationic aminoalkylated polyacrylamide, a cationic amine/epichlorohydrin polymer, a cationic acryl-amide/vinylamine copolymer or a cationic alkylene polyamine;
and the aqueous acid colloidal solution of melamine/formalde-hyde resin contains from 2 to about 12 moles of formaldehyde per mole of melamine.

2. A method for clarifying an aqueous suspension of a coal wash water comprising treating said coal wash water with a polymeric flocculating agent and an aqueous acid colloidal solution of a melamine/formaldehyde resin containing from 2 to about 12 moles of formaldehyde per mole of melamine; provided that:
in treating said coal wash water the polymeric flocculating agent is selected from the group consisting of an anionio partially hydrolyzed polyacrylamide, an anionic par-tially hydrolyzed polyacrylonitrile and an anionic copolymer of aarylamide and acrylic acid or its salts; and the aqueous acid colloidal solution of melamine/formaldehyde resin contains from 4 to about 12 moles of formaldehyde per mole of melamine.

3. A method for clarifying an aqueous suspension of a coal concentrate comprising treating said suspension with a polymeric flocculating agent and an aqueous acid colloidal so-lution of a melamine/formaldehyde resin containing from 2 to about 12 moles of formaldehyde per mole of melamine; provided that:
in treating said suspension the polymeric floccula-ting agent is selected from the group consisting of an anionic partially hydrolyzed polyacrylonitrile, an anionic partially hydrolyzed polyacrylamide, an anionic copolymer of acrylamide and acrylic acid or its salts and a non-ionic polyacrylamide containing less than 1% carboxyl groups; and the aqueous acid colloidal solution of melamine/formaldehyde resin contains from 4 to about 12 moles of formaldehyde per mole of melamine.

4. A method for clarifying an aqueous suspension of an iron ore slime comprising treating said suspension with a poly-meric flocculating agent and an agueous acid colloidal solution of a melamine/formaldehyde resin containing from 2 to about 12 moles of formaldehyde per mole of melamine; provided that:
in treating said suspension the polymeric floccula-ting agent is selected from the group consisting of a cationic polydiallyldimethylammonium chloride, a cationic amine/epichlo-rohydrin polymer, cationic polyacrylamides, cationic alkylene polyamineq and a non-ionic polyacrylamide containing less than 1% carboxyl groups; and the aqueous acid colloidal solu-tion of melamine/formaldehyde resin contains from 4 to about 12 moleq of formaldehyde per mole of melamine.

5. A method for clarifying an aqueous suspension of a raw water comprising treating said suspension with a polymeric flocculating agent and an aqueous acid colloidal solution of a melamine/formaldehyde resin containing from 2 to about 12 moles of formaltehyde per mole of melamine; provided that:
in treating sald suspension, the polymeric floccu-lating agent is selected from the group consisting of a cationic amine/epichlorohydrin polymer, a cationic aminoalkylated poly-acrylamide, an alkylene polyamine polymer and a cationic acryl-amide/vinylamine copolymer; and the aqueous acid colloidal solution of melamine/formaldehyde resin contains from 2 to about 12 moles of formaldehyde per mole of melamine.

6. A method for clarifying an aqueous suspension of a raw sewage, comprising treating said suspension with a polymeric flocculating agent and an aqueous acid colloidal solution of a melamine/formaldehyde resin containing from 2 to about 12 moles of formaldehyde per mole of melamine; provided that:
in treating said suspension, the polymeric floccu-lating agent is a cationic aminoalkylated polyacrylamide, a cationic amine/epichlorohydrin polymer, a cationic acrylamide/-vinylamine copolymer or a cationic alkylene polyamine; and the aqueous acid colloidal solution of melamine/formaldehyde resin contains from 2 to about 12 moles of formaldehyde per mole of melamine.