COOLING CORROSION ION EXCHANGE MOLYBDATE WASTEWATER

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Abstract

Molybdate is used in water treatment as a corrosion inhibitor. Molybdenum is directly underneath chromium on the periodic table, which means the two elements have similar properties and react in a similar fashion. When chromate was banned due to its very high toxicity, molybdate was initially thought to be a promising substitute (1). However, while soluble molybdate is a good corrosion inhibitor only at fairly high concentrations (2), it still has moderate toxicity (3), and is generally too expensive to use in open (evaporative) cooling water systems. Despite drawbacks in open cooling systems, molybdate chemistry has been widely used in smaller closed loop high-temperature cooling systems. Although discharge of molybdate is not federally regulated, its presence in sludges used in Land Applications is limited to 75 milligrams per kilograms (mg/Kg) (40 CFR 503 ﾖ Subpart B). This limit has caused some states to prohibit discharge of molybdate-containing water from cooling towers. Other states have established voluntary limits. In places where it is no longer permissible to discharge molybdate, it is necessary to remove molybdate from the cooling water, prior to discharge or possible reuse.

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