American Water Works Association
ANSI/AWWA B404-98
(Revision of ANSI/AWWA B404-92)
R
AWWA STANDARD
FOR
LIQUID SODIUM SILICATE
Effective date: Feb. 1, 1999.
First edition approved by AWWA Board of Directors Aug. 5, 1955.
This edition approved June 21, 1998.
Approved by American National Standards Institute Nov. 9, 1998.
AMERICAN WATER WORKS ASSOCIATION
6666 West Quincy Avenue, Denver, Colorado 80235
Copyright © 1999 American Water Works Association, All Rights Reserved.
AWWA Standard
This document is an American Water Works Association (AWWA) standard. It is not a specification.
AWWA standards describe minimum requirements and do not contain all of the engineering and
administrative information normally contained in specifications. The AWWA standards usually
contain options that must be evaluated by the user of the standard. Until each optional feature is
specified by the user, the product or service is not fully defined. AWWA publication of a standard
does not constitute endorsement of any product or product type, nor does AWWA test, certify, or
approve any product. The use of AWWA standards is entirely voluntary. AWWA standards are
intended to represent a consensus of the water supply industry that the product described will
provide satisfactory service. When AWWA revises or withdraws this standard, an official notice of
action will be placed on the first page of the classified advertising section of Journal AWWA. The
action becomes effective on the first day of the month following the month of Journal AWWA
publication of the official notice.
American National Standard
An American National Standard implies a consensus of those substantially concerned with its scope
and provisions. An American National Standard is intended as a guide to aid the manufacturer, the
consumer, and the general public. The existence of an American National Standard does not in any
respect preclude anyone, whether that person has approved the standard or not, from manufacturing, marketing, purchasing, or using products, processes, or procedures not conforming to the
standard. American National Standards are subject to periodic review, and users are cautioned to
obtain the latest editions. Producers of goods made in conformity with an American National
Standard are encouraged to state on their own responsibility in advertising and promotional
materials or on tags or labels that the goods are produced in conformity with particular American
National Standards.
CAUTION NOTICE: The American National Standards Institute (ANSI) approval date on the front
cover of this standard indicates completion of the ANSI approval process. This American National
Standard may be revised or withdrawn at any time. ANSI procedures require that action be taken
to reaffirm, revise, or withdraw this standard no later than five years from the date of publication.
Purchasers of American National Standards may receive current information on all standards by
calling or writing the American National Standards Institute, 11 W. 42nd St., New York, NY 10036;
(212) 642-4900.
All rights reserved. No part of this publication may be reproduced or transmitted in any form or by
any means, electronic or mechanical, including photocopy, recording, or any information or retrieval
system, except in the form of brief excerpts or quotations for review purposes, without the written
permission of the publisher.
Copyright © 1999 American Water Works Association
Printed in USA
ii
Copyright © 1999 American Water Works Association, All Rights Reserved.
Committee Personnel
The AWWA Standards Committee on Scale and Corrosion Control Chemicals,
which reviewed and approved this standard, had the following personnel at the time
of approval:
Robert A. Elefritz Jr., Chair
Consumer Members
J.R. McVeigh, California-American Water Works Service Company,
Chula Vista, Calif.
J.J. Muldowney, Philadelphia Water Department, Philadelphia, Pa.
E.D. Mullen, Elizabethtown Water Company, Bound Brook, N.J.
R.M. Powell, Pinellas County Utilities, Largo, Fla.
C.M. Rogers, City of Richmond, Richmond, Va.
J.C. Thurrott, City of Daytona Beach, Daytona Beach, Fla.
T.M. Tucker, Knoxville Utilities Board, Knoxville, Tenn.
M.M. Vogel, Southeast Morris County Municipal Utilities,
Cedar Knolls, N.J.
(AWWA)
(AWWA)
(AWWA)
(AWWA)
(AWWA)
(AWWA)
(AWWA)
(AWWA)
General Interest Members
R.A. Elefritz Jr., Briley Wild & Associates Inc., Ormond Beach, Fla.
L.L. Harms, Black & Veatch Engineers, Kansas City, Mo.
R.A. Ryder, Kennedy Jenks Consultants, Kentfield, Calif.
L.W. Warren,* Council Liaison, KCM Inc., Seattle, Wash.
J.H. Wilber,* Standards Engineer Liaison, AWWA, Denver, Colo.
(AWWA)
(AWWA)
(AWWA)
(AWWA)
(AWWA)
Producer Members
Kevin Ripp, Consultant, Rocton, Ill.
Marty Watts, Technical Products Corporation, Portsmouth, Va.
* Liaison, nonvoting
iii
Copyright © 1999 American Water Works Association, All Rights Reserved.
(AWWA)
(AWWA)
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Copyright © 1999 American Water Works Association, All Rights Reserved.
Contents
All AWWA standards follow the general format indicated subsequently. Some variations from this format may be
found in a particular standard.
SEC.
PAGE
SEC.
PAGE
Foreword
3
Definitions .......................................... 1
I
I.A
I.B
I.C
II
II.A
II.B
III
III.A
4
4.1
4.2
4.3
4.4
Requirements
Physical Requirements.........................
Chemical Requirements .......................
Impurities..............................................
Uses .......................................................
5
5.1
5.2
5.3
5.6
5.7
Verification
Sampling ...............................................
Suspended Matter ................................
Test Procedure for Determining
Specific Gravity .................................
Test Procedure for Determining
Silica (SiO2) .......................................
Test Procedure for Determining
Sodium Oxide ....................................
Calculation of Weight Ratio ................
Rejection................................................
6
6.1
6.2
6.3
Delivery
Marking................................................. 9
Packaging and Shipping .................... 10
Affidavit of Compliance...................... 10
III.B
IV
V
Introduction........................................ vii
Background......................................... vii
History ................................................ vii
Acceptance .......................................... vii
Special Issues .................................... viii
Discussion.......................................... viii
Safety ................................................. viii
Use of This Standard........................... ix
Purchaser Options and
Alternatives....................................... ix
Modification to Standard..................... ix
Major Revisions.................................... ix
Comments............................................. ix
5.4
5.5
Standard
1
1.1
1.2
1.3
General
Scope ...................................................... 1
Purpose .................................................. 1
Application............................................. 1
2
References ........................................... 1
v
Copyright © 1999 American Water Works Association, All Rights Reserved.
2
2
2
2
3
3
4
5
8
9
9
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Copyright © 1999 American Water Works Association, All Rights Reserved.
Foreword
This foreword is for information only and is not a part of AWWA B404-98.
I. Introduction.
I.A. Background. Sodium silicate solutions have application in the water
treatment industry as an ingredient of activated silica coagulant aids, for the control
of corrosion, and as a stabilizing agent for iron and manganese.
Sodium silicates are water-soluble glasses, manufactured by fusing soda ash
(Na2CO3) and specially selected silica sands at high temperatures. These products
can be identified by the formula Na2O (SiO2)x, where x can range from 0.5 to 4.0.
Sodium silicate solutions (liquid sodium silicates) are usually identified by the weight
ratio of their components, which is x in the formula, and their density is frequently
reported in degrees Baumé (Bé).*
Commercial liquid sodium silicates include a variety of products ranging in ratio
from 1.8 to 3.75, and in density from 35°Bé to approximately 60°Bé (20°C). The most
commonly used product for water treatment is a 3.2 weight ratio liquid, usually sold
at 40° to 41°Bé, which represents the least expensive source of soluble silica. For use
in low pH waters, a lower ratio (more alkaline) silicate is sometimes more useful.
I.B. History. The first edition of this standard for liquid sodium silicate was
prepared under the direction of the AWWA Water Purification Division. The standard
was approved by the Executive Committee of the Water Purification Division and by
the Water Works Practice Committee and received the approval of the AWWA Board
of Directors on Aug. 5, 1955. The text was approved as tentative on Aug. 5, 1955, and
was made standard on Jan. 26, 1958. Subsequent editions were approved by the
AWWA Board of Directors on June 15, 1980, June 14, 1987, and June 18, 1992.
I.C. Acceptance. In May 1985, the US Environmental Protection Agency
(USEPA) entered into a cooperative agreement with a consortium led by NSF
International (NSF) to develop voluntary third-party consensus standards and a
certification program for all direct and indirect drinking water additives. Other
members of the original consortium included the American Water Works Association
Research Foundation (AWWARF) and the Conference of State Health and Environmental Managers (COSHEM). The American Water Works Association (AWWA) and
the Association of State Drinking Water Administrators (ASDWA) joined later.
In the United States, authority to regulate products for use in, or in contact with,
drinking water rests with individual states.† Local agencies may choose to impose
requirements more stringent than those required by the state. To evaluate the health
effects of products and drinking water additives from such products, state and local
agencies may use various references, including two standards developed under the
direction of NSF, ANSI‡/NSF§ 60, Drinking Water Treatment Chemicals—Health
Effects, and ANSI/NSF 61, Drinking Water System Components—Health Effects.
·
*The conversion from degrees Baumé to specific gravity is outlined in Sec. 5.3.4 of the
standard.
†Persons in Canada, Mexico, and non-North American countries should contact the
appropriate authority having jurisdiction.
‡American National Standards Institute, 11 W. 42nd St., New York, NY 10036.
§NSF International, 3475 Plymouth Rd., Ann Arbor, MI 48106.
vii
Copyright © 1999 American Water Works Association, All Rights Reserved.
Various certification organizations may be involved in certifying products in
accordance with ANSI/NSF 60 (61). Individual states or local agencies have authority
to accept or accredit certification organizations within their jurisdiction. Accreditation of certification organizations may vary from jurisdiction to jurisdiction.
Appendix A, “Toxicology Review and Evaluation Procedures,” to ANSI/NSF 60
(61) does not stipulate a maximum allowable level (MAL) of a contaminant for
substances not regulated by a USEPA final maximum contaminant level (MCL). The
MALs of an unspecified list of “unregulated contaminants” are based on toxicity
testing guidelines (noncarcinogens) and risk characterization methodology (carcinogens). Use of Appendix A procedures may not always be identical, depending on the
certifier.
AWWA B404-98 addresses additives requirements in Sec. 4.3.2 of the standard.
The transfer of contaminants from chemicals to processed water or the residual solids
is becoming a problem of greater concern. The language in Sec. 4.3.2 is a
recommendation only for direct additives used in the treatment of potable water to be
certified by an accredited certification organization in accordance with ANSI/NSF
Standard 60, Drinking Water Treatment Chemicals—Health Effects. However, users
of the standard may opt to make this certification a requirement for the product.
Users of this standard should also consult the appropriate state or local agency
having jurisdiction in order to
1. Determine additives requirements, including applicable standards.
2. Determine the status of certifications by all parties offering to certify
products for contact with, or treatment of, drinking water.
3. Determine current information on product certification.
II. Special Issues.
II.A. Discussion. Liquid sodium silicate is generally shipped in metal drums,
tank trucks, or railroad tank cars. Most grades are fluid enough to be pumped easily.
These liquids should be stored in closed, vented tanks. Storage tanks should have
provisions for keeping the silicate from freezing.
Sodium silicates are normally added to water by means of a chemical feed pump.
Diaphragm and piston pumps are satisfactory, but piston pumps should have
lantern-ring water glands around the pistons. For some uses, the silicate solutions
can be diluted with fresh water before use; this is especially advisable if the silicate
is being fed into a brine.
Silica is found to some extent in all natural waters and is believed to be
ecologically harmless. The addition of sodium silicate tends to slightly increase the
pH and alkalinity of water.
II.B. Safety. Sodium silicate solutions are moderately alkaline. They are not
explosive or flammable and are not classified as hazardous in US Department of
Transportation (DOT) shipping regulations.
The principal danger of silicate solutions involves contact with the eyes.
Protective goggles or face shields should be worn when handling these products. If
silicate is splashed into the eyes, flush immediately for 15 min and seek medical
attention.
If splashed on the skin, sodium silicate solution should be washed off with
water—preferably warm water. If allowed to remain in contact with the skin,
irritation may result. Dried deposits of the liquid should be treated with care, since
they can cause skin cuts similar to those inflicted by broken glass. Such cuts should
be washed with water and given appropriate medical attention to prevent infection.
viii
Copyright © 1999 American Water Works Association, All Rights Reserved.
For additional safety information, refer to material safety data sheets (MSDS)
available from the supplier or manufacturer.
III. Use of This Standard. AWWA has no responsibility for the suitability or
compatibility of the provisions of this standard to any intended application by any
user. Accordingly, each user of this standard is responsible for determining that the
standard’s provisions are suitable for and compatible with that user’s intended
application.
III.A. Purchaser Options and Alternatives. The following items should be covered in the purchaser’s specifications:
1. Standard used—that is, AWWA B404, Standard for Liquid Sodium Silicate,
of latest revision.
2. Density required (Sec. 4.1.3).
3. SiO2:Na2O ratio required (Sec. 4.2.2).
4. Quantity required.
5. Form of shipment, bulk or package, type and size (Sec. 6.2).
6. Affidavit of compliance if required (Sec. 6.3).
7. Whether the recommended compliance with ANSI/NSF Standard 60, Drinking Water Treatment Chemicals—Health Effects, is to be required. If this certification is to be required, the purchaser’s specifications shall read, “This material shall
be certified as suitable for contact with or treatment of drinking water by an
accredited certification organization in accordance with ANSI/NSF Standard 60,
Drinking Water Treatment Chemicals—Health Effects.”
III.B. Modification to Standard. Any modification of the provisions, definitions, or terminology in this standard must be provided in the purchaser's
specifications.
IV. Major Revisions. The major revisions made to the standard in this
edition include the following:
1. The format has been changed to AWWA standard style.
V. Comments. If you have any comments or questions about this standard,
please call the AWWA Volunteer and Technical Support Group, (303) 794-7711 ext.
6283, FAX (303) 795-1440, or write to the department at 6666 W. Quincy Ave.,
Denver, CO 80235.
ix
Copyright © 1999 American Water Works Association, All Rights Reserved.
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Copyright © 1999 American Water Works Association, All Rights Reserved.
American Water Works Association
R
ANSI/AWWA B404-98
(Revision of ANSI/AWWA B404-92)
AWWA STANDARD FOR
LIQUID SODIUM SILICATE
SECTION 1: GENERAL
Sec. 1.1
Scope
This standard covers liquid sodium silicate used in the preparation of activated
silica, which is used as a coagulant aid for the treatment of municipal and industrial
water supplies for (1) the control of corrosion, and (2) stabilization of iron and
manganese in water systems.
Sec. 1.2
Purpose
The purpose of this standard is to provide purchasers, manufacturers, and
suppliers with the minimum requirements for liquid sodium silicate, including
physical, chemical, packaging, shipping, and testing requirements.
Sec. 1.3
Application
This standard can be referenced in specifications for purchasing and receiving
liquid sodium silicate and can be used as a guide for testing the physical and
chemical properties of liquid sodium silicate samples. The stipulations of this
standard apply when this document has been referenced and then only to liquid
sodium silicate used in water supply service.
SECTION 2: REFERENCES
This standard has no applicable information for this section.
SECTION 3: DEFINITIONS
The following definitions shall apply in this standard:
1
Copyright © 1999 American Water Works Association, All Rights Reserved.
2 AWWA B404-98
1. Manufacturer: The party that manufactures, fabricates, or produces materials or products.
2. Purchaser: The person, company, or organization that purchases any
materials or work to be performed.
3. Supplier: The party that supplies materials or services. A supplier may or
may not be the manufacturer.
SECTION 4: REQUIREMENTS
Sec. 4.1
Physical Requirements
4.1.1 Description. Sodium silicate is a solution of sodium oxide and silica. It
is generally furnished as a viscous, strongly alkaline liquid. The solution varies in
composition with regard to the ratio between sodium oxide and silica, as well as in
density. It is readily decomposed by acids and acid-forming substances with the
separation of silicic acid.
4.1.2 Suspended matter. The sodium silicate shall contain not more than
0.5 percent by weight of suspended matter.
4.1.3 Specific gravity. The specific gravity of the liquid sodium silicate shall
not be less than 1.370 at 15.6°C for the 40°Bé grade.
Sec. 4.2
Chemical Requirements
4.2.1 SiO2 content. The sodium silicate shall contain not less than 28.0
percent by weight of silica as SiO2 for the 40°Bé grade.
4.2.2 SiO2 to Na2O ratio. The ratio of SiO2 to Na2O is usually 3.25 ± 0.03:1.
The SiO2 component shall not be less than 3.15 in this ratio.
NOTE: By agreement between the manufacturer and the purchaser, material
varying with regard to specific gravity, SiO2:Na2O ratio, and silica content may be
furnished.
Sec. 4.3
Impurities
4.3.1 General impurities. The liquid sodium silicate supplied in accordance
with this standard shall contain no soluble material or organic substances in
quantities capable of producing deleterious or injurious effects on the health of those
consuming water that has been properly treated with liquid sodium silicate.
4.3.2 Product certifications. Liquid sodium silicate is a direct additive used in
the treatment of potable water. This material should be certified as suitable for
contact with or treatment of drinking water by an accredited certification organization in accordance with ANSI/NSF Standard 60, Drinking Water Treatment
Chemicals—Health Effects. Evaluation shall be accomplished in accordance with
requirements that are no less restrictive than those listed in ANSI/NSF Standard 60.
Certification shall be accomplished by a certification organization accredited by the
American National Standards Institute.
Sec. 4.4
Uses
4.4.1 Coagulant aid. To prepare activated silica (used in water treatment as
a coagulant aid) from sodium silicate, any one of the following may be used: sulfuric
acid, aluminum sulfate, chlorine, ammonium salts, or carbon dioxide.
Copyright © 1999 American Water Works Association, All Rights Reserved.
LIQUID SODIUM SILICATE
3
4.4.2 Corrosion inhibitor. Sodium silicate may be added to water to reduce
corrosion. Sodium oxide and carbon dioxide are partially neutralized, and a film
containing silica is deposited on metal surfaces.
4.4.3 Metal sequestering agent. Sodium silicate may be added to water to
stabilize reduced iron and manganese ions. The point of addition of the silicate in
relation to the point of addition of chlorine or other oxidant is important. When
silicate is added for this use, corrosion control may also be accomplished.
SECTION 5: VERIFICATION
Sec. 5.1
Sampling
5.1.1 Sampling point. Samples shall be taken at the point of destination.
Samples shall be taken from 5 percent or more of the containers.
5.1.2 Sampling procedures.
5.1.2.1 Full containers shall be mixed thoroughly by rolling or other suitable
means.
5.1.2.2 When sampling a tank car or tank truck to collect a representative
composite sample, at least five different portions shall be taken. The portions shall
be taken from locations well distributed in depth and area, or at timed intervals
during discharge, in order to obtain a representative sample. The five portions
making up the composite sample shall be mixed in a clean, dry plastic container to
give a composite sample of at least a 3-L volume.
5.1.2.3 Three individual samples shall be poured from the freshly mixed
composite sample into clean, dry, wide-mouthed plastic containers with plastic-lined
screw caps and minimum capacities of 0.5 L. Each sample shall be labeled for
identification and the label dated and signed by the sampler.
5.1.2.4 Two samples shall be retained for not less than 30 days after the date
of receipt for use by the supplier and the referee laboratory if needed. The samples
shall be kept in a cool dry place and kept covered except when portions are removed
for testing. The samples shall be mixed thoroughly before each portion is removed.
Sec. 5.2
Suspended Matter
5.2.1 Apparatus and reagents.
1. Porous-porcelain filter crucible, medium porosity.
2. Distilled water.
3. 50-mL beaker.
4. 10-mL pipette.
5. 400-mL beaker.
6. 500-mL volumetric flask.
5.2.2 Procedure.
1. Weigh 10.0 g of the well-mixed sample from a pipette into a 50-mL beaker.
2. Add 15 mL of distilled water, mix by swirling, and transfer to a 400-mL
beaker with a stream of water from a wash bottle.
3. Stir well and filter with suction through a tared porous-porcelain filter
crucible.
4. Police both beakers thoroughly and wash into crucible. Wash 10 times with
distilled water.
Copyright © 1999 American Water Works Association, All Rights Reserved.
4 AWWA B404-98
5. Make filtrate up to 500 mL in a volumetric flask with distilled water for use
in the determination of silica and sodium oxide.
6. Bake crucible at 105° to 110°C for 1 h, cool in a desiccator, and weigh.
5.2.3 Calculation.
% suspended matter = weight increase, in grams × 10
(Eq 1)
5.2.4 Alternate procedure for suspended matter determination.
5.2.4.1 Apparatus and reagents.
1. Glass fiber filters, 4.7-cm diameter—Whatman grade 934AH, Gleman type
A.E, Millipore type AP40 or equivalent.
2. Desiccator.
3. Drying oven.
4. Analytical balance capable of weighing to 0.1 mg.
5. Filtration apparatus consisting of a vacuum source, frittered disk to support
the filter, suction flask of sufficient capacity for sample size, and membrane filter
funnel and clamp.
6. Graduated cylinder or open-tip pipette to measure sample.
7. Aluminum carrying pan for filter.
5.2.4.2 Procedure.
1. All glassware should be cleaned with detergent, rinsed with tap water
followed by several rinses with distilled or deionized water.
2. Samples should be analyzed as soon as possible after collection.
3. Place a glass fiber filter in an aluminum carrying pan, dry at 550°C for
15 min, cool in desiccator, and weigh the filter only on an analytical balance.
4. Extract a well-mixed aliquot of the sample using either a graduated
cylinder or a broken-tip pipette that will not strain out suspended matter.
5. Filter the aliquot through the prepared glass fiber filter and rinse all
glassware with distilled or deionized water. Rinse water should also be passed
through the glass fiber filter.
6. Place the filter back into the aluminum pan, dry for at least 1 h at 103°C,
cool, and weigh.
7. The gain in weight represents the suspended matter in the original sample.
Calculation:
Weight of filter and residue – Weight of filter
Suspended matter, mg/L = ----------------------------------------------------------------------------------------------------------------------------Volume of sample filtered (in litres)
Sec. 5.3
(Eq 2)
Test Procedure for Determining Specific Gravity
5.3.1 Apparatus.
1. Glass cylinder of sufficient size to accommodate hydrometer.
2. Glass hydrometer, approximately 360 mm long, manufactured and graduated
in accordance with the requirements of the National Bureau of Standards, scaled in
0.001 divisions and calibrated at 15.6°C. This is a short-range hydrometer with a
maximum range of 0.07; that is, 1.35 to 1.42 specific gravity units, and with a
minimum of 120 mm between these points.
Copyright © 1999 American Water Works Association, All Rights Reserved.
LIQUID SODIUM SILICATE
5
3. A glass hydrometer, scaled in degrees Baumé, may also be used. A
convenient range is 39° to 43°Bé, scaled in 0.1° intervals.
5.3.2 Procedure.
1. Pour enough sodium silicate sample from the bottle into the glass cylinder
to float the hydrometer, with at least 25 mm clearance from the bottom of the
cylinder, and place in a water bath maintained at 15.6°C for 1 h.
2. The cylinder should be kept covered when the hydrometer is not in use.
Lower the hydrometer gently into the sample and allow it to sink by its own weight
the final 15 mm. If it drops too low and wets the stem above the final reading mark,
remove the hydrometer, rinse it well and dry it, and repeat the test.
3. Take the reading after two successive 1-min periods have shown no change.
4. Wash the hydrometer immediately after the final reading.
5.3.3 Alternate procedure.
1. Proceed as described in Sec. 5.3.2, except take the hydrometer reading at an
ambient temperature, but above 15°C.
2. Temperatures at the top and bottom of the liquid sodium silicate in the
cylinder are taken before and after the hydrometer reading.
3. If the sample is protected from heating and cooling and the temperature at
the top and bottom differs less than 1°C in 30 min, the water bath may be omitted.
4. To correct the hydrometer reading to 15.6°C, a specific gravity correction of
0.001 must be added for each 2°C that the sample temperature is above 15.6°C.
5.3.4 Relationship between specific gravity and degrees Baumé. Degrees Baumé
can be converted to specific gravity as follows:
145
specific gravity = ------------------------145 – °Bé
(Eq 3)
Specific gravity can be converted to degrees Baumé as follows:
145
°Bé = 145 – ----------------------------------------specific gravity
Sec. 5.4
(Eq 4)
Test Procedure for Determining Silica (SiO2)
5.4.1 Method 1, gravimetric.
5.4.1.1 Reagents.
1. Concentrated hydrochloric acid (HCl).
2. Concentrated sulfuric acid (H2SO4).
3. Concentrated hydrofluoric acid (HF). CAUTION: Use extreme care in handling
hydrofluoric acid.
5.4.1.2 Procedure.
1. Pipette 50 mL of the filtrate (10.0 g in 500 mL), discussed in Sec. 5.2.2, into
a 100-mL porcelain evaporating dish. Add 10 mL concentrated HCl, while stirring
with a short glass rod. Rinse the rod into the sample, cover with a ribbed watch glass,
and evaporate to complete dryness on a steam bath.
2. After 10 min more on the steam bath, add 5-mL concentrated HCl and
50 mL distilled water. Disintegrate the mass with a stirring rod, and continue
heating until only the silica remains undissolved.
Copyright © 1999 American Water Works Association, All Rights Reserved.
6 AWWA B404-98
3. Transfer to a 90-mm filter paper (medium), rinse the evaporating dish, and
wash the precipitate and filter paper eight times with warm 5 percent HCl from a
wash bottle. Give a final rinse with distilled water.
4. Return the filtrate and washings to the same evaporating dish used above,
cover with a ribbed watch glass, evaporate to complete dryness, and bake for 30 min
at 150°C.
5. Cool the dish slightly, add 5 mL of concentrated HCl and 50 mL of distilled
water, and filter through a fresh filter paper as previously described. Scrub the
evaporating dish thoroughly with a rubber policeman, and wash eight times with
warm 1 percent HCl. Give a final wash with warm distilled water.
6. Place both filter papers containing the precipitates obtained into a tared
platinum crucible, cover, heat very slowly to dry, remove cover, and char and burn off
the filter paper. The silica precipitate should be white. Cool the crucible and add one
drop of 50 percent H2SO4. Replace the cover, heat gradually, and finally ignite at full
heat of burner (preferably at 1,200°C) or in a furnace, then cool and weigh.
7. Remove cover and add 1 mL of water, 5 drops of 50 percent H2SO4, and
about 5 mL of HF to a predetermined depth in the crucible. (To determine the depth
in the crucible, use water. Do not forget to add 1 mL and 5 drops to the 5 mL to
determine this depth. Etch the crucible.)
CAUTION: Use extreme care in handling hydrofluoric acid.
Evaporate liquid on a hot plate without boiling, under a well-ventilated hood.
When dry, heat for 15 min at full heat over a burner, cool, and weigh. The silica is
volatilized by hydrofluoric acid.
% SiO2 = loss in weight × 100
(Eq 5)
5.4.1.3 Alternate procedure.
Follow procedure in Sec. 5.4.1.2, omitting hydrofluoric acid (HF) evaporation.
% SiO2 = weight of residue × 100
(Eq 6)
5.4.2 Method 2, volumetric.
5.4.2.1 Introduction.
On addition of an excess amount of sodium fluoride to the solution retained from
the Na2O determination (Sec. 5.5), a reaction occurs with the silicic acid present to
form fluorosilicate and sodium hydroxide. The reaction can be represented as follows:
Si(OH)4 + 6NaF → Na2SiF6 + 4NaOH
The alkali that is liberated is titrated with standard acid, and the titration gives
a basis for calculating the silica in the original sample.
5.4.2.2 Apparatus and reagents.
1. Standard volumetric equipment.
2. Hydrochloric acid 1N, standardized to the nearest 0.001.
3. Sodium hydroxide 1N, standardized to the nearest 0.001.
Copyright © 1999 American Water Works Association, All Rights Reserved.
LIQUID SODIUM SILICATE
7
4. Sodium fluoride neutralized slurry. Prepared using reagent-grade sodium
fluoride, powdered, as given in Sec. 5.4.2.3, item 1.
CAUTION: Exercise due care in handling the poisonous NaF, and observe normal
safety precautions for handling common acids and alkalies.
5. Methyl-red–bromcresol-green indicator. Dissolve 0.08 g of sodium salt of
methyl red in 50 mL of water, dissolve 0.06 g of bromcresol green in 50 mL of
isopropyl alcohol. Mix the two solutions together. Methyl-red–bromcresol-green
indicator may also be available commercially.
5.4.2.3 Procedure.
1. The solution resulting from the Na 2 O determination is used (Sec. 5.5). Add,
by graduated cylinder, sufficient NaF slurry to react all the silicic acid with a slight
excess. To form the slurry, weigh 100 g of reagent-grade NaF into a 1-qt polyethylene
bottle. Fill to the shoulder with distilled water (approximately 950 mL). Add 2 or 3
mL of mixed indicator and mix thoroughly. Add 1N HCl to obtain the gray–green of
neutrality. This usually requires 10 to 15 mL of acid. (The NaF slurry is equivalent
millilitre to millilitre to the necessary standard 1N HCl.)
2. Add six to eight drops of mixed indicator and titrate with 1N HCl to
complete the color change (green to red–purple). NOTE: The sodium fluoride–silicic
acid reaction is pH controlled, requiring excess acid (pH 5.0) to ensure completion.
More NaF slurry may be added as necessary. NOTE: Acid additions that change the
color to a strong red that gradually drifts back to gray–green to green color indicates
insufficient NaF slurry.
3. Back-titrate the excess acid with 1N NaOH to the first definite green end
point preceded by a gray pre-end point. (Complete color change requires two to three
drops of additional NaOH.)
5.4.2.4 Calculations.
% SiO2 = (mL HCl × N – mL NaOH × N) 1.502
(Eq 7)
5.4.3 Method 3, atomic absorption spectroscopy.
5.4.3.1 Introduction.
The silicate is diluted with distilled water to an appropriate range and
determined by atomic absorption spectroscopy using a nitrous oxide–acetylene flame.
The working range for SiO2 is 10 to 320 ppm SiO2.
5.4.3.2 Apparatus and reagents.
1. Atomic absorption spectrophotometer with silicon hollow cathode tube.
2. 100-mL volumetric flasks and transfer pipettes.
3. Concentrated hydrochloric acid.
4. Standard silica solution. A commercially available standard solution
containing 1,000 mg Si/L may be used. Alternately, a standard solution may be
prepared by dissolving 2.36 g of sodium silicate nine-hydrate (Na2SiO3 9H2O) in
approximately 300 mL of distilled water. Add sufficient HCl to bring the pH to
approximately 5, and dilute to 500 mL with distilled water. Store in a polyethylene
bottle. This standard contains 1,000 mg SiO2 /L. Analyze 200 mL gravimetrically
(Sec. 5.4.1) to determine the exact silica concentration.
5. Silica calibration standard, 100 mg SiO2 /L. Dilute 10 mL of the standard to
100 mL with distilled water.
·
Copyright © 1999 American Water Works Association, All Rights Reserved.
8 AWWA B404-98
5.4.3.3 Procedure.*
1. Pipette 10 mL (10.0 g in 500 mL) of the filtrate (Sec. 5.4.2) into a 200-mL
volumetric flask. Fill to the mark with distilled water and mix thoroughly.
2. Establish the following instrument parameters:
light source—silicon hollow cathode lamp,
flame—nitrous oxide–acetylene,
burner—nitrous oxide burner head,
wavelength—251.6 nm,
range—ultraviolet,
slit width—0.2 nm,
filter—out.
3. Aspirate distilled water and zero the instrument. Aspirate the 100 mg/L
silica standard and set the concentration readout to display 0100. Replace the
distilled water and check the zero setting. Aspirate the silicate dilution and obtain
three readings. Repeat with distilled water, then with the 100 mg/L standard. If the
readout does not display 0100 ± 0001, run the silicate dilution again.
4. The silica content of the diluted sample is given by the instrument readout,
as milligrams SiO2 /L.
5.4.3.4 Calculations.
% SiO2 = mg SiO2 /L × 0.1
(Eq 8)
If a commercial standard is used, the working standard will contain 100 mg of
Si/L, and the readout will be in terms of Si. This value can be converted to SiO2 as
follows:
60.09
mg Si /L × --------------- = mg SiO 2 /L
28.09
Sec. 5.5
(Eq 9)
Test Procedure for Determining Sodium Oxide
5.5.1 Reagents.
1. 0.100N HCl.
2. Methyl-orange indicator solution: 0.05 g of methyl orange in 100 mL of
distilled water. (The solution may also be available commercially.)
5.5.2 Procedure.
1. Pipette a 50.0-mL portion of the filtrate obtained in Sec. 5.2.2 into a 250-mL
Erlenmeyer flask.
2. Add one to two drops of indicator and titrate to the salmon-pink end point
with 0.100N HCl.
3. This sample may be used for volumetric silica determination by the method
in Sec. 5.4.2.
*To ensure accurate analysis, always review manufacturer’s instructions for instrument setup
and analyses.
Copyright © 1999 American Water Works Association, All Rights Reserved.
LIQUID SODIUM SILICATE
9
5.5.3 Calculation.
% Na 2O = mL acid × 0.31
Sec. 5.6
(Eq 10)
Calculation of Weight Ratio
The silicate weight ratio is obtained by dividing the percent silica by the percent
alkali as Na2O:
% SiO 2
weight ratio = ---------------------% Na 2O
Sec. 5.7
(Eq 11)
Rejection
5.7.1 Notice of nonconformance. If the liquid sodium silicate delivered does
not meet the requirements of this standard, then a notice of nonconformance shall be
provided by the purchaser to the supplier within 10 working days after receipt of the
shipment at the point of destination. The results of the purchaser’s test shall prevail
unless the supplier notifies the purchaser within five working days after receipt of
the notice of complaint that a retest is desired. On receipt of the request for a retest,
the purchaser shall forward to the supplier one of the sealed samples taken in
accordance with Sec. 5. In the event the results obtained by the supplier on retesting
do not agree with the test results obtained by the purchaser, the other sealed sample
shall be forwarded, unopened, to a referee laboratory agreed on by both parties. The
results of the referee analysis shall be accepted as final.
5.7.2 Removal of material. If the material does not meet the requirements of
this standard, the supplier shall remove the material from the premises of the
purchaser or make a price adjustment agreed on by the supplier and purchaser.
SECTION 6: DELIVERY
Sec. 6.1
Marking*
6.1.1 Required. Each shipment shall carry with it some means of identification. Each unit package shall be legibly marked with the net weight or volume of the
contents, name of the manufacturer, lot number, brand name if any, and other
markings as required by applicable laws and regulations. When shipped in bulk, this
information shall be provided in accordance with applicable regulations.
6.1.2 Optional. At the option of the manufacturer, packages may also bear
the statement, “This material meets the requirements of AWWA B404, Standard for
*Governmental packaging and marking references reflect US requirements. Users of AWWA
B404 in Canada, Mexico, and non-North American countries should verify applicable local and
national regulatory requirements. Because of frequent changes in these regulations, all parties
should remain informed of possible revisions. Provisions of the purchaser’s specifications
should not preclude compliance.
Copyright © 1999 American Water Works Association, All Rights Reserved.
10
AWWA B404-98
Liquid Sodium Silicate,” provided that the requirements of this standard are met,
and the material is not of a different quality in separate agreement between the
supplier and purchaser.
Sec. 6.2
Packaging and Shipping
Packaging and shipping of all sodium silicate shall conform to all applicable
current local, state, and federal regulations.
6.2.1 Containers. Liquid sodium silicate may be shipped in steel drums, tank
cars, or tank trucks. In cold weather, it may be necessary to warm the liquid so that
it will flow.
6.2.2 Weight. The net weight of the containers shall not be less than the
recorded weight nor more than 10 percent greater than the recorded weight. If
exception is taken to the weight of the material received, acceptability or rejection
shall be based on the weight of not less than 10 percent of the containers received,
selected at random from the shipment.
Sec. 6.3
Affidavit of Compliance
The purchaser may require an affidavit from the manufacturer or supplier
attesting that the sodium silicate furnished according to the purchaser’s order
complies with all applicable requirements of this standard.
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