AU666309B2 - Process for removing silica from aqueous liquors - Google Patents

Description

OPI DATE 08/01/93 APPLN. ID 18738/92 AOJP DATE 25/02/93 PCT NUMBER PCT/AU92/00241 I Il 1111111111 1 111 AU9218738 .tEATY (PCT) (51) International Patent Classification 5 (11) International Publication Number: WO 92/21618 C02F 1/60, 1/52, 1/28 Al (43) International Publication Date: 10 December 1992 (10.12.92) (21) International Application Number: PCT/AU92/00241 (74)Agent: MUNT, Gregory, Richard; Griffith Hack Co., 601 St. Kilda Road, Melbourne, VIC 3004 (AU).

(22) International Filing Date: 27 May 1992 (27.05.92) (81) Designated States: AT (European patent), AU, BE (Euro- Priority data: pean patent), CA, CH (European patent), DE (Euro- PK6312 27 May 1991 (27.05.91) AU pean patent), DK (European patent), ES (European patent), FR (European patent), GB (European patent), GR (European patent), IT (European patent), JP, LU (Euro- (71) Applicant (for all designated States except US): HOEFER, pean patent), MC (European patent), NL (European pa- Dawn, Annette [AU/AU]; Trustee of Modern Environ- tent), SE (European patent), US.

mental Service Trust, Lot 5, O'Brien Road, Gidgegannup, W.A. 6555 (AU).

Published (72) Inventor; and With international search report.

Inventor/Applicant (for US only): BROWNE, Geoffrey, Robert [AU/AU]; Lot 26, Orchard Road, Gidgegannup, W.A. 6555 (AU).

666309 (54) Title: PROCESS FOR REMOVING SILICA FROM AQUEOUS LIQUORS (57) Abstract A process for removing silica in dissolved or colloidal form from an aqueous liquor comprising, precipitating/adsorbing the silica with or onto a precipitant/adsorbent, typically a compound containing aluminium, magnesium, or iron, forming floccs of the precipitated/adsorbed silica, and separating the floccs from the liquor.

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PCT/AU92/00241 WO 92/21618 1 PROCESS FOR REMOVING SILICA FROM AQUEOUS LIQUORS The present invention relates to a process for removing silica from aqueous liquors.

It is known that soluble and colloidal silica present in water that is used in cooling water circuits in gas or coal fired power stations or other applications is undesirable since it tends to form extremely hard deposits that progressively reduce the heat transfer efficiency of the cooling water circuits.

SSUBSTITUTE SHEET r77LJ I WO 92/21618 PCT/AU92/00241 2 There are a number of known chemical and physical means for removing the silica deposits. However, all these known means have disadvantages. For example, one physical means comprises projecting a scraper bullet through the tubing in cooling water circuits to scrape I away the deposits. The disadvantage of this technique is that there is an unacceptable risk of damage to the cooling water circuits.

An object of the present invention is to provide a process for removing soluble and colloidal silica from aqueous liquors to minimise the extent of the silica deposits.

According to the present invention there is provided a process for removing silica in dissolved and/or colloidal form from an aqueous liquor comprising: precipitating/adsorbing the dissolved and colloidal silica with/onto a precipitant/adsorbent; adding a flocculent to the liquor to form floccs of the precipitated/adsorbed silica and any other suspended solids in the liquor and ji the flocculent; and separating the floccs from the liquor.

The term "precipitant/adsorbent" is understood herein to mean any element or compound in soluble or insoluble form that is capable by mechanisms of precipitation or adsorption of changing dissolved and/or SSUS'T I7TE T SiUELT WO 92/21618 7 1 WO 92/21618 pCr/AU92/00241 i,

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3 colloidal silica into a state that can be separated more readily from the liquor.

It is preferred that step comprises adjusting the pH of the liquor to promote precipitation/adsorption.

It is particularly preferred that step comprises adjusting the pH to be equal to or greater than It is more particularly preferred that step (a) comprises adjusting the pH to be equal or greater than Typically, step comprises adjusting the pH to be equal or greater than It is preferred that the process further comprises the step of adding an inert particulate carrier prior to or at the same time as the step of adding the flocculent.

It is particularly preferred that the inert particulate carrier is added prior to the addition of the flocculent.

It is preferred that the process further comprises, after step agitating the floccs to break up the floccs and separating the inert particulate carrier for recycling in the process.

It is preferred that the precipitant/adsorbent comprises a compound containing one or more of aluminium, magnesium, and iron. It is noted that in some situations the precipitant/adsorbent may already be in the liquor

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International application No.

PCT/AU92/00241 -INrERNATIONAL SEARCH R-PORT A. CLASSIFICATION OF SUBJECT MATTER Int. C15. C02F 1/60, 1/52, 1/28 WO 92/21618 PCT/AU92/00241 4 and the pH adjustment is required to promote precipitation/adsorption of the dissolved or colloidal silica with/onto the precipitant/adsorbent. It is also noted that in other situations it may be necessary to add the precipitant/adsorbent to the liquor, with or without pH adjustment.

It is particularly preferred that the precipitant/adsorbent is a soluble aluminium salt such as sodium aluminate, aluminium sulphate or aluminium chloride.

It is particularly preferred in situations where the precipitant/adsorbent is a soluble aluminium salt that the process comprises, after step lowering the pH of the liquor to 7.5 or less to precipitate any soluble aluminium retained in the liquor.

The term "liquor" is understood herein to include aqueous and non-aqueous liquors.

The term "inert" as used herein in relation to "particulate carrier" is understood herein to mean that the particulate carrier is not substantially attacked by i the liquor. In other words, the term "inert" means that the particulate carrier exhibits both suitable chemical r and physical stability in the liquors.

It is preferred that the inert particulate carrier garnet, magnetite, hematite, ilmenite, and calcite.

The term "suspended solids" is understood herein to I include organic and inorganic material.

SLEST!TE S| WO 92/21618 PCI/AU92/00241 It is preferred that the flocculent is a polyelectrolyte flocculent.

The term "polyelectrolyte flocculent" as used herein is understood to mean any suitable cationic, non-ionic and anionic flocculent.

The process of the present invention is described further by reference to the following examples.

Example 1 A series of experiments was carried out on water from the cooling water circuit of the Muja coal-fired power station in Collie, Western Australia. The water was at pH 8.0 and contained a total of 69 ppm silica in dissolved and colloidal form.

A number of samples of the water were tested to investigate the effect of the following parameters on the removal of silica from the water.

1. Precipitant/adsorbent, the following [j precipitants/adsorbents were tested: soluble iron or aluminium containing S":i 20 compounds; soluble aluminium containing compounds; and rTUBSTITTE SHEET m WO 92/21618 PCY/AU92/00 2 4 1 6 a combination of soluble iron and aluminium containing compounds and lime.

2. pH.

3. Contact time of precipitant/adsorbent and water prior to addition of inert particulate carrier.

4. Inert particulate carrier (IPC).

The 1 below.

results of the experiments are set out in Table I~r With reference to Table 1, the experiments Tl to T7 and T10 to T24 were carried out in accordance with the following sequence of steps.

1. Addition of precipitant/adsorbent to liquor.

2. Adjustment of pH.

3. Addition of inert particulate carrier and polyelectrolyte flocculent (Zetag 92 in a cationic flocculent produced by Allied Colloids) after prescribed contact time of precipitant/adsorbent and water.

4. Separation of floccs of precipitated/adsorbed silica, inert particulate carrier, polyelectrolyte flocculent and suspended solids in the liquor.

the the The experiments T8 and T9 were carried out without addition of precipitant/adsorbent and in the case of experiment T8 without adjustment of pH.

SUBSTITUT SI:Ei TABLE 1 Test Precipitant/ pH- Batch IPC Silica Silica Adsorbent Contact Used Assay Removal (ppn) Tim PP) Fe+ 3 A1+ 3 Cao (hrs:mins) Ti 77 -10 0:45 Magnetite 4 94 T2 77 9.5 0:45 tv22 68 T3 77 9.2 0:17 it24 T4 20 10 0:45 It30 56 77 8.0 0:45 it18 74 T6 20 8.5 2:0 it41 41 T6 20 8.0 14:0 of44 36 T7 77 9.5 0:01 If22 68 T8 8.0 0:00 to 53 23 T9 9.5 0:10 59 14 T1O 92 9.5 0:15 1 99 T13 45 9.5 0:15 8 88 T14 77 9.5 0:45 Silica 18 74 92 9.3 0:15 it<1 99 T16 92 9.3 0:40 Magnetite 1 99 T17 100 60 0.2 9.6 1:10 it29 66 T18 100 60 0.2 9.6 1:10 it6 93 T19 50 30 0.1 8.9 1:10 of4 50 30 0.1 8.7 1:10 27 68 T21 50 30 0.25 9.0 2:10 II5 94 T22 25 15 0.2 9.1 2:10 16 81 T23 25 9.6 0:15 9, 9 89 T24 25 9.6 0:15 fI 18 79 WO 92/21618 PCT/AU92/00241 8 The results for experiments T5 and T8 and for experiments T2 and T9 in Table 1 indicate clearly that the addition of a precipitant/adsorbent to the water at the feed level of pH 8.0 followed by the addition of inert particulate carrier and polyelectrolyte flocculent produced a significantly higher removal of silica from the water than the addition of inert particulate carrier and polyelectrolyte flocculent without the addition of precipitant/adsorbent.

It can also be seen from Table 1 that an increase of the pH of the water above the feed level of pH following the addition of a precipitant/adsorbent and prior to the addition of inert particulate carrier and polyelectrolyte flocculent produced a further increase in the removal of silica from the water. In this regard, the results for experiments Tl, T10, T15, T16, T18, T19 and T21 indicate that in excess of 90% of the silica in the water was removed by such a process.

In summary, it can be seen from Table 1 that generally there was an increase in the removal of silica: with an increase in the addition of precipitant/adsorbent at a given pH (cf the results of experiments T10/T13 and T1/T4); and S. with an increase in the pH at a given concentration of precipitant/adsorbent (cf the results of experiments T4/T6).

Example 2 A further series of experiments was carried out on SUBSTITUTE s:-:L7 j Ir W092/1618PCU/AU92/00241 9

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water from the cooling water circuit of the Muja coal-fired power station.

The experiments focussed on the use of alumina as the precipitant/adsorbent and the inert particulate carrier. The following is a brief outline of the experimental procedure.

1. Addition of calcined or hydrated alumina to water.

2. Adjustment of pH to be higher than 0 3. Agitation of water/alumina.

4. Addition of polyelectrolyte flocculent (Zetag 92).

Agitation of water/alumina/flocculent.

6. Separation of floccs of precipitated/adsorbed silica, alumina, and polyelectrolyte flocculent.

The results of the experiments are set out in Table 2 below.

U~2 So ci ETA wjZdliU PCU/AU92/00241 WO 92/2i1618 Table 2 10 rest Alumina Comments Silica Silica (ppm) (ppm) Removal 1 100 pH increased to 9.2 0.1 99 and then +24 hr agitation 2 100 As for 1, but only 2.1 97 hr agitation after pH adjustment 3 100 Alumina washed at pH 2.7 96 11.5, decanted water then added alumina to water resultant pH 10.2, 0.5 hr agitation following addition of alumina 4 100 Alumina washed at pH 2.1 97 11.5 and then filtered and added to water resultant pH 9.3, hr agitation following addition of alumina The results in Table 2 indicate that the addition ii 25 of a precipitant/adsorbent, followed by adjustment of pH to be higher than 9.0, and subsequent addition of a polyelectrolyte flocculent substantially removed the silica from the water.

Example 3 A further series of experiments was carried out on water from the cooling water circuit of the Muja coal-fired power station. The water contained a total of ppm silica in dissolved and colloidal form.

S SU STiTUTE SH EET L WO 92/21618 PCT/AU92/00241 hi

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f, 11 The experiments fociused on the effect of pH on the removal of silica from the water.

The experiments were carried out in accordance with the following sequence of steps.

1. Addition of 10 ppm or 20 ppm of a soluble aluminium containing compound as precipitant/adsorbent.

2. Adjustment of pH.

3. Addition of inert particulate zarrier and polyelectrolyte flocculent.

The results of the experiments are set out in Table 3 below.

Table 3 )H Residual Silica (ppm) ppm precipitant/ adsorbent 20 ppm precipitant/ adsorbent SST "F T E h PCr/AU92/0024' WO 92/21618 12 The results in Table 3 above indicate that at a given concentration of precipitant/adsorbent there was an increase in the removal of silica with an increase in the pH.

In particular, the results for the experiments based on the addition of 20 ppm precipitant/adsorbent indicate that there was a significant increase in silica removal at pH levels equal to and above Example 4 A series of experiments was carried out on water from the cooling water circuit of a Queensland Nickel Pty. Ltd. plant at Gladstone, Queensland.

The make-up water to the cooling circuit contained 72 ppm dissolved and colloidal silica and the cooling tower water contained 278 ppm dissolved and colloidal silica.

The experiments focussed on the effect of the amount of the addition of precipitant/adsorbent on the removal of silica from the water.

The experiments were carried out in accordance with the following sequence of steps: i i Addition of soluble aluminium containing compounds as precipitant/adsorbent.

Adjustment of pH to 9.6.

Addition of inert particulate carrier and polyelectroly.e flocculent.

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WO 92/21618 PCT/AU92/00241 13 The results of the experiments are set out in Table 4 below.

Table 4 it Li i Precipitant/adsorbent Addition (ppm) Residual Silica (ppm) Make Up Cooling Tower 0 72 278 64 210 22 214 40 8 78 80 18 8 The results in Table 4 above indicate that at a given pH there was an increase in the removal of silica with an increase in the addition of precipitant/adsorbent.

By way of summary, the experimental results presented in Examples 1 and 2 establish that it is possible with the process of the invention to substantially remove soluble and colloidal silica from water. This is a significant outcome in relation to the coal and gas fired power station industry in particular and for industry in general which relies on the use of cooling water circuits.

S L!EaTe 1 TUTt WO 92/21618 PC~/AU92/00241 14 Many modifications may be made to the process of the present invention as described above without departing from the spirit and scope of the present invention.

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Claims (9)

1. A process for removing silica in dissolved and/or colloidal form from an aqueous liquor comprising: adjusting the pH of the liquor to be equal to or greater than 8 to precipitate/adsorb the dissolved and colloidal silica with/onto a precipitant/adsorbent; adding a flocculent to the liquor to form floccs of the precipitated/adsorbed silica and any other suspended solids in the liquor and the flocculent; adding an inert particulate carrier prior to or at the same time as the step of adding the flocculent; and separating the floccs from the liquor.

S2. The process defined in claim 1, wherein step (a) Scomprises adjusting the pH to be equal or greater than

3. The process defined in claim 2, wherein step (a) comprises adjusting the pH to be equal or greater than

4. The process defined in any of the proceeding claims, Swherein the inert particulate carrier is added prior to the addition of the flocculent.

The process defined in any one of the preceding claims, further comprising, after step agitating the floccs to break up the floccs and separating the inert particulate carrier for recycling in the process. staffluanlkeep/18738.92 30.10.95 I i i; i i~ i ii 16

6. The process defined in any one the preceding claims, wherein the precipitant/adsorbent comprises a compound containing one or more of aluminium, magnesium, and iron.

7. The process defined in claim 6, wherein the precipitant/adsorbent is a soluble aluminium salt such as sodium aluminate, aluminium sulphate or aluminium chloride.

8. The process defined in any one of the preceding claims, wherein the inert particulate carrier is selected from the group consisting of sand, alumina, magnetite, hematite, ilmenite, and calcite..

9. The process defined in any one of the preceding claims, wherein the flocculent is a polyelectrolyte flocculent. DATED THIS 31ST DAY OF OCTOBER 1995. DAWN ANNETTE HOEFER By her Patent Attornsys: GRIFFITH HACK CO Fellows Institute of Patent Attorneys of Australia st: "'jan/keep/18738.92 30.10.95 r i :I rll- 1- rr I :j r I: SITERPNATIONAL SEARCH REPORT International application No. PCT/AU92/00241 A. CLASSIFICATION OF SUBJECT MATTER Int. Cl 5 CO2P 1/60, 1/52, 1/28 According to International Patent Classification (IPC) or to both national.classification and IPC B. FIELDS SEARCHED Minimum documentation searched (classification system followed by classification symbols) IPC: C02F 1/60, 1/52, 1/28; C02B 1/14, 1/20, 1/24; C02C 5/02. Documentation searched other than minimum documentation to the extent that such documents are included in the fields searched AU: IPC as above Electronic data base consulted during the international search (name of data base, and where practicable, search terms used) DERWENT; CHEMICAL ABSTRACTS "SILICA' OR "SiO2"; "WATER" or "AQUEOUS" OR "H20"; "PRECIPIT:" OR "ADSORB:" C. DOCUMENTS CONSIDERED TO BE RELEVANT Category X X X Citation of document, with indication, where appropriate of the relevant passages AU,B, 82623/91 (617290) (HOEFER; DAWN ANNETTE) 21 November 1991 (21.11.91). Whole document FR,A, 1168036 (THE DOW CHEMICAL COMPANY) 3 December 1958 (03.12.58). Page 1 column 2 lines 1-31, page 2 column 2 lines 1-10, examples 2 and 6 Relevant to Claim No. 1-12 1-12 1, 3, 9, 10, 12 US,A, 3516932 (MONSANTO COMPANY) 23 June 1970 (23.06.70). Claims 1-16, example 1 Further documents are listed Se patent family annex. in the continuation of Box C. Speciai categories of cited documents later document published after the international filing date or priority date and not in conflict document defining the general state of the art which is with the application but cited to understand the not considered to be of articular relevance principle or theory underlying the invention earlier document but published on or after the document of particular relevance; the claimed international filing date invention cannot be considered novel or cannot be document which may throw doubts on priority claim(s) considered to involve an inventive step when the or which is cited to establish the publication date of document is taken alone another citation or other special reason (as specified) document of particular relevance; the claimed document referring to an oral disclosure, use, invention cannot be considered to involve an exhibition or other means inventive step when the document is combined document published prior to the international filing date with one or more other such documents, such but later than the priority date claimed combination being obvious to a person skilled in the art document member of the same patent family Date of the actual completion of the international search Date of mailing of the international search report 21 August 1992 (21.08.92) '7 SEP 1992 Oq 92.) Name and mailing address of the ISA/ Authrc fficer AUSTRALIAN PATENT OFFICE PO BOX 200 WODEN ACT 2606 AUSTRALIA J. BODEGRAVEN Facsimile No. 06 2811841 Telephone No. (06) 2832281 Form PCT/ISA/210 (continuation of first sheet (July 1992) A c. _j INTERNATIONAL SL r (otnUto) kRCH REPORT International apjiliation No. PCT/AU92/00241 DOCUMENTS CONSIDERED TO BE RELEVANT Category x x x Y Y Citation of documnst, with indication, where appropriate of the relevant passages Relevant to Claim No. USPA, 3723310 (INTERNATIONAL MINER-ALS CHEMICALS CORPORATION) 27 March 1973 (27.03.73). Whole document. DERWENT ABSTRACT ACCESSION NO.56133C132, CLASSES D15, E36, JP,A, 55-084588 (EBARA INFILCO KK) 25 June 1980 (25.06.80) DERWENT ABSTRACT ACCESSION NO. 28184C/16, CLASSES E36, 108, JP,A, 55-031437 (JAPAN METAL AND CHEM (YOKO-)) 5 March 1980 (05.03.80) PATENT ABSTRACTS OF JAPAN, C222, page JP,A, 59-16588 (KOGYO GIIUTSUIN (JAPAN)) 27 January 1984 (27.01.84) US,A, 4046684 (EBA: -k INFILCO KABUSHEKI KAISHA) 6 September 1977 (06.09.77). Whole document. 1-5, 9, 10, 12 1-3, 6, 7,9-12 1,2, 1- 12 1-12 I Form PCT/ISA/21O (continuation of socond sbect)(July 1992) L' .1 I- I I I I I L L nimbMWEENA INTERNATION.AL SEARCH PEPIORT International application No. PCT/AU92/00241 Form PCT/ISA/21O(patent family annex)(Juiy 1992) COPLCC This Annex lists the known publication level patent family members relating to the patent documents cited in the above-mentioned international search report. The Australian Patent Office is in no way liable for these paticulars which are merely given for the purpose of information. Patenit Document Cited in Search Patent Family Member Report AU 91/82623 FR 1168036 us 3516932 us 3723310 CA 926797 us 4046684 END OF ANNEX For PCT ISA/210 (continuation of second sheet)(July 1992)