Polyphosphates for scale and corrosion control are among the few recognized substances which can be safely added to potable water to produce a significant improvement in many water quality parameters.
Bimetallic Zinc Polyphosphates Less Aggressive, Moderately Hard Waters
Zinc polyphosphates offer a variety of benefits. In addition to some of the traditional benefits offered by zinc orthophosphates, the polyphosphate component prevents scale and stabilizes soluble iron, manganese and calcium by sequestering these ions. Limited lead protection is obtained through hydrolysis of the polyphosphate to orthophosphate ion. Products in this category consist of a zinc salt combined with hexametaphosphate in a dry state.
Ortho Polyphosphate Blends Aggressive and Scaling Waters
These formulations consist of orthophosphates and polyphosphates blended together with approximately 30 to 70 percent orthophosphate content on a typical basis. The products are stabilized to ensure that the product maintains the ortho poly blend ratio as manufactured and require a somewhat lower treatment dosage compared to traditional applications used primarily for colored water and scale control.
Linear Chain Polyphosphates Scaling Waters
The linear chain types are the most effective sequestering agents and at sufficient dosages can "scour" a distribution line and remove existing deposition.
Silicate Phosphate Blends Aggressive and Scaling Waters
Primarily used in corrosive Eastern U.S. waters when use of zinc and phosphate is limited, silicate phosphate blends provide sequestering, moderate corrosion control, and limited lead and copper protection.
Orthophosphates Aggressive Waters
Used exclusively in aggressive waters, straight orthophosphates can be considered somewhat an extension of the zinc ortho's in that the blend ratio is so high that zinc has virtually been eliminated.
Zinc Orthophosphates Aggressive Waters
Zinc Orthophosphates as a technology provide the most effective and comprehensive corrosion inhibition. Zinc orthophosphates have traditionally been used to stop colored water caused by bleeding tuberculation and have a long history of success. This technology is very effective in aggressive waters with no source iron and manganese to sequester and where calcium stabilization and scaling are not a concern. Zinc orthophosphates have demonstrated particular effectiveness in providing effective lead and copper protection. Zinc orthophosphates reduce asbestos fiber counts and protect cement pipe.
These formulations consist of a zinc salt (either chloride or sulfate) combined with orthophosphate formulated in a wide variety of zinc to phosphate ratios ranging from 2:1 to 1:10. They function by two distinct mechanisms - film formation and electrochemical passivation. Zinc orthophosphates should never be fed to a water with a pH above 8.1 due to premature zinc precipitation.