LaMotte SMART3 Colorimeter - Manual (Page 275)

SILICA – HIGH RANGE
SILICOMOLYBDATE METHOD • CODE 3687-SC
QUANTITY CONTENTS CODE
30 mL *Silica Reagent #1 *V-4466-G
30 mL *Silica Reagent #2 *V-4467-G
15 mL *Silica Reagent #3 *V-4468-G
*WARNING: Reagents marked with an * are considered to be potential health
hazards. To view or print a Material Safety Data Sheet (MSDS) for these reagents
go to www.lamotte.com. To obtain a printed copy, contact LaMotte by e-mail,
phone or fax.
Silicon dioxide, SiO
2
, commonly known as silica, occurs in all natural water. Silica
may be present as suspended, insoluble particles in a colloidal or polymeric state.
It may also be present in a reactive form as silicic acid or silicate ions. Silica is a
major nutrient for diatoms. A silica cycle occurs in many bodies of water containing
organisms, such as diatoms, that use silica in their skeletal structure. The silica
removed from the water may be slowly returned to solution by the decomposition
of the dead organisms. The major source of silica in natural water is from the
decomposition of silicate minerals in the drainage basin from which the waters fl ow.
The presence of silica is particularly objectionable in water used for boiler feed
water purposes, as it may cause the formation of a hard, dense scale which has
unusually high resistance to heat transfer. Serious loss of turbine effi ciency results
from insoluble silica turbine blade deposits caused by vaporization of silica from
boiler water.
APPLICATION: Boilers and cooling towers; domestic and industrial
wastes.
RANGE: 0–75 ppm Silica
MDL: 0.5 ppm
METHOD: Silica forms a complex with ammonium molybdate in an
acidic solution to produce a yellow color in proportion to
the amount of silica present. Phosphate also reacts with
molybdate but the addition of oxalic acid eliminates the
molybdophosphoric acid complex.
SAMPLE HANDLING
& PRESERVATION:
Silica samples may be preserved by refrigeration at 4°C
in plastic containers up to one week without any change
in silica concentration.
INTERFERENCES: Sulfi des and large amounts of iron interfere. Color and
turbidity may be removed by standardizing the instrument
with the original water sample.
PROCEDURE
SMART3 Test Procedures 11.10 SILICA, High Range
Test P
rocedures