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SulfaLock TM HiGel - Detailed information
Mechanism of Acid production and Concrete Corrosion
The generation of acid resulting in sewer corrosion is understood to be a two step process. In the first step, sulphate reducing bacteria in the sewage reduce sulphates sulphides. At the near neutral pH of sewage, the bulk of the sulphide is in the form of molecular hydrogen sulphide which volatilises at the liquid / gas interface and concentrates the sewer headspace. In the second step, gaseous hydrogen sulphide dissolves in the moisture present on the sewer wall where sulphur oxidising bacteria oxidise H2S to sulphuric acid.
The sulphuric acid reacts with the calcium hydroxide in the concrete to form calcium sulphate as a corrosion product. Calcium sulphate is a soft, expansive compound with no binding properties. Unchecked corrosion will eventually lead to the destruction and collapse of the sewer.
SulfaLock TM HiGel Physical Properties
A unique feature of the regular magnesium hydroxide liquid is the combination of low viscosity and high solids content. In addition to this, regular MHL exhibits what is referred to as a gel characteristic. Gelling describes the tendency of the liquid to lose fluidity and form a solid gel structure some hours after the removal of shear whilst upon the application of shear, the gel instantaneously reverts back to its fluid state. This property has been manipulated resulting in a SulfaLock TM HiGel, a low viscosity liquid alkali under moderate shear that gels instantaneously upon the removal of shear. This property enables the pumping and spraying of a relatively low viscosity liquid and the application of a paste like solid. With SulfaLock TM HiGel, a 3 mm high pH magnesium hydroxide coating can be applied in a single spray pass with very little run off.
Benefits of SulfaLock TM HiGel for Sewer Line Corrosion Protection
Extremely Effective Corrosion Protection
Results obtained in an actual acidic sewer application show that SulfaLock TM HiGel can be sprayed on to sewer walls where it forms a very durable alkaline surface coating. Where applied, a pH of between pH 7 and 9 was maintained on the concrete substrate for a twelve month period effectively precluding further concrete corrosion through acid attack. This contrasts strongly with the pH values of 2 - 3 measured in similar unsprayed areas. One year after application, the applied coating continued to provide coverage over the concrete substrate. These results suggest that the spray application of SulfaLock TM HiGel onto sewer walls constitutes a viable solution to the problem of acid corrosion of sewer lines.
Simple and Reliable Technology Replaci
ng Conventional Chemical Dosing
The addition of large quantities of chemicals to the raw sewage has historically been employed in an attempt to effect the prevention of sewer corrosion. Fundamentally, chemical addition attempts to provides corrosion protection by limiting the volatile sulphide levels in the raw sewage. The flow-on effect of this is a reduction in the concentration of gaseous hydrogen sulphide in the sewer head space which in turn limits the amount of sulphuric acid formed on the sewer wall.
However chemical dosing has been found to be intrusive, expensive and as a result of a number of variables, not always effective. Where H2S formation is not completely eliminated the formation of sulphuric acid will still occur.
In contrast, sewer corrosion control by the spray application of magnesium hydroxide onto the sewer wall is achieved by directly curtailing acid generation. The basis of the technology is that the application of an alkaline surface coating firstly neutralises acid present at the concrete surface and further more, ensures that a high pH is maintained on the concrete surface. It is the enduring alkaline surface coating which is believed to constitute the major advantage of corrosion prevention in that under alkaline conditions, further acid formation, and subsequently corrosion, is avoided by significantly retarding the proliferation of the acid forming Thiobacillus concretivourous bacteria. Thus the technology is able to achieve corrosion protection irrespective of the gaseous H2S concentration and unlike chemical dosing, is not effected by changes in temperature, pH, flow and effluent composition.
Cost Effective
In comparison to high capital options, ie epoxy sewer relining and ventilation, and continuous chemical dosing, corrosion protection using the spray application of SulfaLock TM HiGel is a cost effective alternative.
