Magnesium hydroxide as a substitute for caustic soda and lime

1) Safety is the driver

Caustic soda and lime are historically the two most industrially available choices for wastewater pH control, however, both have significant limitations. Caustic freezes at 15ºC to plug feed lines and is extremely hazardous to handle, causing severe chemical burns.

Lime is even better known for the plugging of feed lines, as well as wastewater transport lines due to the formation of calcium mineral scale, and over-exposure can also result in severe burns to operators’ hands.

3) Improved solids settling

The wastewater stream for many industrial processes can be quite unpredictable and inconsistent. Dramatic changes in pH can have adverse effects on the settleability of suspended solids. To stabilize the pH, the wastewater is commonly neutralized with alkalis. The nature of the alkali selected can have a dramatic impact on the ability to settle suspended solids. Caustic soda typically provides no settling benefit and often results in gelatinous sludge that does not dewater easily. With lime (Ca(OH)2) there is typically a significant increase in sludge volume due to the formation of calcium minerals, like calcium carbonate (CaCO3).

In contrast, magnesium hydroxide assists with solids settling, providing a more compact sludge with a boost in alkaline pH to improve subsequent secondary treatment and anaerobic digestion performance.