Silica ~ high range – LaMotte DC1600 Colorimeter User Manual

Page 79

SILICA ~ HIGH RANGE

HETEROPOLY BLUE METHOD

CODE 3687

QUANTITY

CONTENTS

CODE

30 mL

*Silica Reagent #1

*V-4466-G

30 mL

*Silica Reagent #2

*V-4467-G

15 mL

*Silica Reagent #3

*4468-E

Spoon, 0.1 g, plastic

0699

*WARNING: Reagents marked with a * are considered hazardous substances. Material Safety Data Sheets (MSDS) are supplied for

these reagents. For your safety, read label and accompanying MSDS before using.

Silicon dioxide, SiO

, 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 flow. Values may range from 0-75 parts per million (or mg/liter).
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 efficiency

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:

0.0 – 75 ppm Silica

METHOD:

Reactive 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 a plastic containers up to one week

without any change in silica concentration.

INTERFERENCES:

Sulfides and large amounts of iron interfere. Color and turbidity may be removed by

standardizing the instrument with the original water sample.