CA1126124A

CA1126124A - Stabilised solutions

Info

Publication number: CA1126124A
Application number: CA320,984A
Authority: CA
Inventors: Tom L. Cordey
Original assignee: Tioxide Group Ltd
Current assignee: Tioxide Group Ltd
Priority date: 1978-03-15
Filing date: 1979-02-05
Publication date: 1982-06-22
Also published as: FR2419743A1; DE2910047A1; GB1572386A; AU4382979A; ZA79535B; ES478209A1; AU522220B2

Abstract

Abstract of the Disclosure "STABILISED SOLUTIONS"

An aqueous solution of a cationic flocculant containing less than 10 grams per litre of the flocculant is stabilised by the addition of free acid in an amount sufficient to render a solution pH of from 1:5.5. The stabilised solutions can be stored without deterioration of the flocculating agent and are of value, particularly in the manufacture of titanium dioxide pigments.

Description

This invention relates to stabilised solution and particularly to a stabilised solution of a cationic flocculat-ing agent.
In accordance with one aspect of this invention there is provided a stabilised solution of a flocculant which comprises an aqueous solution of a cationic flocculating agent containing less than 5 grammes per litre of said flocculating agent and containing free acid in an amount sufficient to confer on the solution a pH of from 1 to 4.5 and said solution being substantially free of suspended inorganic solids.
In accordance with another aspect of this invention there is provided a process for the manufacture of a stabilised solution of a flocculant which comprises diluting an aqueous solution of a cationic flocculating agent to produce an aqueous solution containing less than 5 grammes pe~ litre of said flocculating agent and adding to the solution free acid in an amount sufficient to confer on the solution a pH of 1 to 4.5 with the aqueous solution of the cationic flocculating agent and the acid being substantially free of suspended inox-ganic solids.

: . . .:

z~
-la-Cationic flocculating agents usually are sold as aqueous solutions containing about 5% by weight of the agent often requiring dilution prior to use. The storage of the diluted solutions often causes a deterioration of the floc-culant with a resultant diminution of the effectiveness ofthe flocculant when used. It has now been found that acidification of the diluted solutions reduces considerably the deterioration of the flocculant during storage thus avoiding the inconvenience and wastage associated with the use of stock solutions of short useful life.
Cationic flocculating agents are commonly polymers of cationic esters of acrylic compounds which are soluble in water. The fIocculant may be a copolymer of the-cationic acrylic compound with one or more water soluble monomers.

.

.
~:
.
, . . .
-:: ' . : - .
-, .
- . - , Typicall~ the flocculating agent`is prepared ~y reacting an acrylamade cont ~ g polymer, a seccndary amine and formaldeh~de. m e cationic polymer floccula,ing agent of this type preferably ccntains at least 50 mole per cent of aminated acryla~ide moncm.er units and typicall~ the molecular welght of the acrylamide polymer used to produce the flocculant is between 5 million an~ lO millions.
Examples of suitable acxylamide c~ntaining polymers are polymethacrylamide, ccpolymers of acrylamide and acrylic acid, methacny1;c acid, alkali metal salts of the foregoing acids, ; ~ styrene sulphonate, N-vinyl-pyrrolidone, N-vi~yl pyridine

2 amin oe thyl ac~ylate and copolymers of acrylamide or matha~rylamide with wate~-insoluble moncmers such as methyl ac~ylate, methyl methacrylate acrylonltrile, styrene, vinyl methyl ether and vinyl aoe tate.
The amine used is a secondary amine and preferabl~
cantalns not more than 4 or 5 carbon atcms in each hydrocarbon group~ Preferably ~he amine is dimethylamlne, or diethylamine.
A particularLy useful ~locculant which can be stabilised according to the invention is a high molecular weight water-soluble copolymer containing within the molecular ~hain N-methylol acrylamide ~tts c~nd N-aminGmetkyl ac~ylamide units in the molar ratio 3:1 to 1:2.3 and optionally acryla~tde units ~ ~ acrylic acid or acrylate units Pre~erably the molecular we.ight is g~eater than l,000,000 and most pre~ercibly is greater than 5,000,000.

., ' -Typically the flocculant is prepared by reacting a particular acrylamQde polymer with the amlne ~nd formaldehyde in aqueous solution. ~s previously mentioned the product is often sold in the fonm of an aqueous solution containing about 5~ by weight of the flocculant and usually contains not more than lO~ by weight of the flocculating age~t.
Prior to use the aqueous solution of the flocculat mg agent is diluted with water and stabilised ~y adding sufficient acid to produce a solution pH of from 1 to 5.5. Preferably the solution is acidified to pH 2.5 to 4.5.
Preferably the acid is ml~ed with the dilution water prior to muxing with the flocculating agent.- If desired, hcwever, the acid can be added directly to the dlluted solution m~ediately following dilution.
Usually the acid is a mlneral acid with sulphuric acid being the preferred acid. Conveniently the acid may be waste acid obtam ed from the hydrolysis stage of the "sulphate"
~rocess for the preparation of titanium dioxide pig~ent but unused acid can be employed if desired. Iypically the acid added to the solution o the flocculating agent has a con oe ntration of about lO per cen-t by v~lume in water.
Ihe acidificaticn reduces the deterioration of the dlluted ~lccculant solu~ion on storage and ~he efec~ is of value with dilute solutions of flo~culating agents containing less than 10 grammes per litre of the floc~llating agent.

,.. .

' : ': : . ' Preferably the diluted solutions contain less than 5 grammes, and most advantageously less than 2.5 grammes per litre of the flocculating agentv Usually the dilute~ solution will contain more than 0.5 gra~m~s per l;tre of the - -floccula~ing agen~. The stabilised solutions are acidic and as such are likely to be more corrosive than the unstabilised alkaline solutions. Ccnsequently care should be taken m selec~ing materials of oonstruction of storage and mete~ing equipment.
lG m e stabilised solutions of the flocculating agents are particularly useful in the clarification of black liquor cbtained in the "sulphate" process for th~ manu~acture of pigmentdry titanium dioxide. The acidified stabil1sed solutions retain their flocculating ability even after storing .
~; 15 ~ for~l4 days at 20& to 24C whereas unacidified solutions lose a substa~tial proportion of their flocculating ability on storage for only a few days.
The invention is illustrated in the following Ex~iples :
E~UPIE 1 20 g.rams of a polya~ylamide ~nol. wt greater than 5 x 106~ were dissolved in loOo mls water. To this were added 6.3 g.rarns dirnethylamine ~as a 27% aqueous solution) and 12.7 gr2uns onna1de~yde ~as a 38~ a~leous solution), these additions w~re equivalent to 0.5 moles N~l (CH3)2 and 1.5 n~les ~ICE~ per rnole amide group in the polyac~ylamide.

,~

. ~ -.. . . .... . . .

. ~ . , - , , , , , ~ : - -.. ~ ~ . . . ..

~he mixture was well stirred, and ~aintaLned at 50& in a water bath for 4 hours.
The resulting solution was analysed for its dry solid content ~ie solids nonvolatile at 105C), and two poxtions taken from the solution were diluted to 1 gpl dry solids content : the first portion wi~h pura water, and the second portion simultaneously with water and enough sulphuric acid solution to reduce the pH of the diluted second portion to about 3. ~The sulphuric acid used was actually 'waste' filtrate acid obta m ed ~xom the hydrolysis stage of the 'Isulphat~" process for the manufacture of titanium dioxide and had a concen~ration of about 10% by volu~e).
Samples of these dilub3d "working" solutions of the ~loccullnt w~re testel as described belcw for their usefulness in flocculating the insoluble solid residues remaining in a test liquor which was a ccmmercial titaniumriron-sulphate solution obtained by dissolving the reaction product of sulphuric acid and high titanium conte,nt slag intended for the production of titaniwm oxide pisments by the "sulphate route.
Other samples of the "worklng" solutions ~of the flocculant~ were then stored at ambient laboratory temperature ~20-24C) for 16 days, being tested peric~ically by the sam~
procedure. Results quoted in Table 1 kelow show that not only was the acidified ~orking solutio~ m~rginally better , initially in performance as a floccula~t, but that the solution retained its efficiency substantially unchanged for the 16 days storage period, whereas the working solution stored at its "natural" pH of 9.2-9.6 had become virtually unusable within a storage period of 5 days.
~E~r MEr~CD
Test liquor comFosition ~typical) S.G. 1.52 at Test temperature 50-55 C
Soluble TiO2 195 gpl "Active" H2S04 Content 345 gpl. ~Including fxee H2S04 and that combined with TiO2 but not that combined with iron) Insoluble dispersed solids 30 gp1 (Unattacked slag, insolubles etcj.
The mRasured dose of work~ng solution of flocculant was added slowly to a well agitated standard volume of the test liquor, which was allowed to settle in a warm draught free place for 30 mu~utes. Samples of the cl æified liquor abcve the sludge were t~ken after 30 munutes, for determination of its residual solids content ~s) and for a filtration test 1~ which the time ~t) taken to filter a volume ~v) through a standard filter under standard conditions of temperature, vacuum etc was me~sured. PerfoLmance efficiency is inversel~ proportional to "s" and "t"~

,, , " ~
. , :

~2~

~ 1 (Days) _ 1 2 _ 5 = _ _ 16 pH 9.6 2.9* 9.6 2.9* 9.6 2.9* 9.2 3.0* 9.2 3.0*
~s)Residual solids 0.81 0.56 0.60 0.50 1.3 0.71 1.8 0.59 1.9 0.73 ~t)Filt-tiateoneCS 72 68 75 40 220 78 240 67 240 44 ~v)Volume l fil~PrPd 50 50 50 50 S050 40 50 30 50 ~nls) _ __ _ ~
*Acldified -EX~MPLE 2 ~.
- A saxple o a co~rcial flocculant based on a ~-.. -polyacrylamide and a seconda~y am me and sold as Tio~loc B38 was diluted 30 tim~s to make a working solutian containing about 2 gms per litre of solids determined b~ dry mg at 105C
cvernight. ~he pH of this solution was found to be 9.4, and a portion was then acidified to pH 3.1 by the additio~
of a pure sulphuric acid ~10% V~V), A second series of wor~ing solutions was made up similarly but contalnlng about 1 gm per litre solids as defined above, and respectively with pEI values of abcut 9.4, 5.8, 4.0, 3.0, 2.6.
All these working solutions were stored in the lab at temperatures 2C-24C and tested periodically by the titanium li~uor clarification test described in Ex3mple 1, and with similar titanium liquor.

- .
:
:

~z~
.

Scrutiny of test results quoted in Tables 2, 2A, shcws quite cle æ ly that the solu~io~s acidified to pH4 or belcw have retained their usefulness ~uch longer than those of pH 5.8 and 9.4 especially the latter.
~ABLE 2 Working Solution Solids Conben~
~!~=~ . .

Ag mg Time ~days) t 35 _. 1 _ 3 _ 3 = - 14 10 Solution pH 9.4 3.1~ 3.~ 3.1* 9.4 .2* 9.4 3.2~ 3.4 3.2* 9.~ 3.1* : -~s) Residual solids .
~gpl~ 0.~ ~.5 ,c 0.5 1.~ ~.~ 2.1 ~.5 ~.5 ~.5 : :
~t) Filtration time . ~
~secsl 34 9 6 48 6CC ~6 36C 63 43 3 ~v) ~olume filtered :
~nl) 50 50 ;0 50 4c 5026 50_ 50 ;0 * Acidified ~ .

"

. . " . , . .:

:, ' ' . ~ ' :, ' r - ~

~ n O ~

o ~ o o r~
o ~ n r~ .~ ~r O ~
- ~ - ~----~- - -- -~ o u~ ~

r~ - *~ ~ ~ o # r~~ ~' :
~ o~ ~ O
I ~ ~ 1 erq~ ~ ' ' ~ ~ ~ a ~

%~

EX~MPLE 3 _ A sa~,ple of another ccmmercial flocculant sold as Superfloc C 255 WD and based on a n~dified acrylamide polymer was tested as described in Exa~ple 1 but in this case the .
working solution was tested using a cammercial titaniumr iron "sulpha~e" solution of approximate ccmpositions : ;
SG60 = 1.51 Soluble TiO2 = 135 gpl Active H2S04 = 250 gpl ~including free H2S04 and acid) Soluble Fe = 120 gpl ccmbined with titanium as sulphate Undisolved solids = 15 gpl but not as iron sulphate) The dcse used was 200 parts per million of flocculating agent solids with respect to Ti02. The results are shcw~
ln Table 3 and these demcnstrate that acidi~ication of the dilute ~worklng~ solution substantially improves its storage qualities.
I~BLE 3 Storage period (s) Solids zesidue ax Solution pH 9 Solution pH 3.5 ~cidifled) 1 day 0.48 0.32 2 days 0.46 0~38

3 days 0.74 0.38 7 days . .. .~ 0.40 - -.
: , : .

Lf~ 2~c EX~MPLE 4 A sample of a commercial flocculant, sold as 'Separan CP 35 and based on a polyacrylanlde resin was tested by a similar technique and with a simil æ crude titanium-iron "sulphate" liquor to that spe d fied in Exa~ple 1. ~he results shown in Table 4 demonstrate that the acid treatment substantially imprcves the keeping prcpeLties of the diluted flccculant solution.
The working solutions had a solids ccntent o~
flocculating agent of 2 gms per litre and were used in a~3unts equivalent to 60 paLts p~r million flocculating agent per TA~E 4 StorageResidual Sollds Filtraticn Test mls .
~davs) gpl auoted time in seconds , _ _ pH 9.3 pH 3.1* pH 9.3 pH 3.1*
~) ~) ~v) (t) (v) (t) . _ ___ _ Lessithan 1 0.24 0.17 50 25 50 29 2 1 012 0 4~ 50 510 50 30 13 days useless 0.64 useless 50 58 * ~cidified with waste sulphuric acid fron TiO2 process ., . . ~ - ~
.

~LZ~

12 !
.
EXA~PLE 5 .
k sample of a commercial flocculant sold as NALC0 R3B
and based on a polyacryl a de resin was tested as m Example 4. The results quoted in Table 5 dem~nstrate the S usefulness of the acidification technique in stabilizing dilute "~or~ing" solutions of this material.

Storage Residual Solids gpl Filtratio~ data .
pericd ~ pH 2.8* pH 10.0 pH 2.8~
~days~ ~ ~s~ (v) (t) (v) ~t) .
~ . _ mls secs mls secs : T~qs than l-0.80 0.46 50 80 50 31 Useless l,06 Useless 50 54 : ~ :
* Acidified lS
.

.
;. :. ~' . :
- - ~ . ~: ' ' :

Claims

What is claimed is:

1. A stabilised solution of a flocculant which comprises an aqueous solution of a cationic flocculating agent containing less than 5 grammes per litre of said flocculating agent and containing free acid in an amount sufficient to confer on the solution a pH
of from 1 to 4.5 and said solution being substantially free of suspended inorganic solids.

2. A stabilised solution according to claim 1 in which the amount of the said flocculating agent is less than 2.5 grammes per litre.

3. A stabilised solution according to claim 1 in which the amount of the said flocculating agent is at least 0.5 grammes per litre.

4. A stabilised solution according to claim 1 in which the acid is present in an amount sufficient to confer on the solution a pH of 2.5 to 4.5.

5. A stabilised solution according to claim 1 in which the acid is sulphuric acid.

6. A stabilised solution according to claim 1 in which the cationic flocculating agent is a polymer or co-polymer of an acrylic compound.

7. A stabilised solution according to claim 6 in which the flocculating agent is a reaction product of an acrylamide-containing polymer, a secondary amine and formaldehyde.

8. A stablised solution according to claim 7 in which the flocculating agent contains at least 50 mole % of aminated acrylamide monomer units.

9. A stabilised solution according to claim 7 in which the secondary amine is dimethylamine.

10. A stabilised solution according to claim 7 in which the secondary amine is diethylamine.

11. A process for the manufacture of a stabilised solution of a flocculant which comprises diluting an aqueous solution of a cationic flocculating agent to produce an aqueous solution containing less than 5 grammes per litre of said flocculating agent and adding to the solution free acid in an amount sufficient to confer on the solution a pH of 1 to 4.5 with the aqueous solution of the cationic flocculating agent and the acid being substantially free of suspended inorganic solids.

12. A process according to claim 11 in which the acid is dilute sulphuric acid containing about 10% by volume of H2SO4.

13. A process according to claim 11, in which the acid is mixed with the aqueous solution of the cationic flocculating agent to be diluted simultaneously with water to effect the dilution.

14. A process according to claim 11, in which the acid is mixed with water and the mixture so obtained is then added to the aqueous solution of the cationic flocculating agent to effect the dilution and stabilisation of the solution.

15. A stabilized solution of a flocculant which comprises an aqueous solution of a cationic flocculating agent containing less than 5 grammes per litre of said flocculating agent and containing waste sulphuric acid obtained from the hydrolysis stage of the "sulphate" process for the preparation of titanium dioxide pigment, said waste sulphuric acid being present in an amount sufficient to confer on the solution a pH of 1 to 4.5 and said solution being substantially free of suspended inorganic solids.