CORROSION INHIBITION BY SILIPHOS
Water missing certain natural ingredients or having an unfavourable composition
(buffer capacity, calcium amounts, neutral salt contents, etc.), cannot form a corrosion
inhibiting layer inside the pipes. The phosphates contained in SILIPHOS consist of a
well balanced blend of many species of food grade organic phosphates, authorized to
be used for potable water treatment. Because of their well balanced composition they
inhibit the cathodic and corrosion process, leading to a synergistic effect.
In presence of calcium and iron, phosphates form a dense, uniform, hard to dissolve
layer separating the water and the oxygen in the water from the iron-metal. For the
formation of this corrosion protective layer the total composition of the water is of minor
importance.
The real mechanism still remains unexplained, but following are some assumptions of
a possible mechanism:
1. |
2Fe2+ |
+ 2H2O + O2 |
2Fe(OH)2 |
|
2. |
2NaHPO4 |
+ Ca(HCO3)2 |
Ca(H2PO4)2 |
+ 2NaHCO3 |
3. |
Ca(H2PO4)2 |
+ 2Fe(OH)2 |
CaFe(PO4)2 |
+ 4H2O |
A slowly soluble calcium iron phosphate is deposited on the pipe surface, forming the
desired corrosion inhibiting layer.
SCALE INHIBITION BY SILIPHOS
SILIPHOS acts as "Threshold Inhibitor" in sub-stoichiometric amounts, thus stabilizing
water and preventing CaCO3-scale from forming.
As a guideline it can be said that SILIPHOS prevents CaCO3-scaling up to water
hardness of 360 ppm as CaCO3 and up to a water temperature of 80° C.
Removing Existing Scale
Actually SILIPHOS is not a fast descaler. SILIPHOS will prevent new iron
oxide/hydroxide scale formation, and loosen/soften existing scale deposits, which thus
are flushed off by the natural turbulence of the water flow.
Mechanism of Fe2O3 scale formation:
I. |
Fe2+O2 + H2O |
FeOOH (scale) |
II. |
FeOOH scale |
wash out |
Reaction I is faster than reaction II.
Mechanism of Fe2O3-scale removal by SILIPHOS:
I. |
Fe2+O2 + H2O |
FeOOH (corrosion inhibition) |
II. |
FeOOH + SILIPHOS |
softening scale |
III. |
FeOOH (loose scale) |
wash out |
It is to be noted that the descaling process by SILIPHOS is very slow, thus the Fe3-
content in water will not increase during the initial treatment, above levels encountered
before using the SILIPHOS treatment. The time needed for the descaling process
depends on many factors like composition and amount of scale and is hard to be
forecasted. Time may vary from 4 days to 6 months or even more.
Setting up a special treatment schedule for each case is a must. BKG Water Solutions
and the representing distributors are any time willing to assist.
As a general guideline it can be said that, in general, brown scale (iron
oxide/hydroxide) can be totally or partially removed, whereas it is hard to remove white
scale (calcium carbonate, calcium silicate). As far as white scale is concerned in most
cases only further build-up increase of scale is prevented.
Plugging Effect
Old pipeline systems often contain invisible holes only plugged by loose iron oxide
deposits, through which water leaks. SILIPHOS will harden this deposit plug and to
some extent, prevent the leaking of water, but it will definitely prevent the small holes
from increasing in size. This effect is uniquely achieved with the composition of several
phosphates contained in SILIPHOS.
DECOLORIZATION OF BROWN WATER
Brown water (containing Fe2O3 below 0.3 ppm as Fe3+) can be decoloured by addition
of SILIPHOS. This effect is very important during the initial treatment and in case the
incoming water contains already a certain Fe3+-load. SILIPHOS is adsorbed to the
small iron oxide/hydroxide particle, thus preventing them from agglomeration and
colouring the water brown.
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