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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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