White Paper: Utilization Of Magnesium Compounds For Wastewater Management In The Electronics Industry

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As environmental regulations become more stringent on the quality of effluent discharged into natural waterways and municipal treatment facilities, electronic component manufacturers must employ effective treatment methods to meet these more strict discharge requirements. One treatment method which has proven itself as a viable technology for approaching zero discharge is the utilization of magnesium compounds for neutralizing acid waste streams and removing metals such as zinc, trivalent chromium, lead, nickel, iron, copper, and cadmium from wastewater via chemical precipitation and adsorption. Magnesium compounds, such as magnesium hydroxide and magnesium oxide, have been used in the treatment of acid rinse water from drag-out stations, process solutions from etching baths, floor spills, spent plating baths, and other wastewater streams generated by printed circuit board manufacturers, semiconductor manufacturers, electroplaters, and metal platers. The benefits of magnesium compounds over the other commonly used alkalis such as caustic soda, lime, and soda ash make it a cost-effective alternative for acid neutralization and metal precipitation.

Conventional Alkalis
Acid neutralization of wastewater is generally accomplished by adding a conventional alkali such as caustic, lime, soda ash, or one form of the magnesium compounds to raise the pH of the waste stream. Caustic soda, or sodium hydroxide (NaOH), is the most commonly used chemical for acid neutralization due to its ease of addition by relatively straightforward and inexpensive feed systems. However, caustic is a toxic and corrosive chemical that must be handled cautiously. Workers that use caustic must strictly adhere to safety procedures and wear appropriate protective clothing and goggles. One inadvertent splash of caustic in the eye can cause permanent loss of vision, while contact with the skin can cause severe burns. In addition, caustic spills must be cleaned up immediately by a hazardous clean-up crew to prevent environmental damage since sodium salts entering the environment can cause adverse effects in animals and vegetation. With a relatively high freezing point of 13.9°C (57°F), 50% caustic requires indoor storage or heat-tracing equipment (Teringo, 1990).

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