Magnesium Hydroxide Slurry – Is it a Solution?
Magnesium hydroxide is ”slightly soluble in water at room temperature”. “If magnesium hydroxide is only slightly soluble in water, how would it function in my treatment process?” Let’s provide an answer to that question!
Martin Marietta Magnesia Specialties produces a high-solids, high-stability magnesium hydroxide slurry. Liquid slurry is magnesium hydroxide particles suspended in water. Magnesium hydroxide slurry is shipped at 61% solids to minimize both chemical freight and storage costs. Slurry is not called ‘solution’ because the suspended particles do not dissolve at the shipped pH value, near 10. Users recognize a milk of magnesia slurry as a milky white liquid that resembles white latex paint. A solution would be visually clear.
Magnesium Hydroxide slurry is a cost-effective source of alkalinity for biological activity and acid neutralization. It is an “alternate technology” because the alkalinity is not released from the particles until they dissolve. Users determine when the alkalinity of the particles is released, because the particles dissolve on demand according to pre-determined parameters. Magnesium hydroxide dissolves best with good mixing and retention time, at low pH, at low temperature, and when biological or chemical reactions consume alkalinity.
Biological waste treatment requires both bacteria “food” (waste) and alkalinity for the process to remove nitrogen or carbon-based wastes. When the microbiological “bugs” consume alkalinity, they cause the particles in the slurry to dissolve and fulfill the needs of the “bugs”. Each particle is made of many molecules of magnesium hydroxide, but eventually each particle of the slurry dissolves as the bacteria and protozoa at the treatment plant complete their task. The slurry releases alkalinity as it is needed. Release is self-limiting – waste pH does not elevate above 9 pH.
In the same way, if alkalinity is required for acid neutralization or metals precipitation, highly acidic water causes the slurry particles to dissolve quickly while slightly acidic water dissolves particles more slowly. Either way, as magnesium hydroxide slurry particles dissolve, the acidity of the treated water drops unless the alkalinity is consumed by chemical or biological reactions. When dissolving ceases but a few undissolved particles remain, the water is “buffered”. Magnesia buffers the pH below 9, which is desirable for controlled discharge pH and for the health of microbiological “bugs” employed to clean the waste stream.
Once alkalinity is consumed, dissolved magnesium remains in solution. Magnesium does not produce scale as calcium treatment agents such as lime do. When treated wastewater is recovered for re-use, magnesium can provide an essential micro-nutrient to agricultural plants, animals, or aquaculture. Magnesium improves sludge dewatering characteristics and decreases operating costs by decreasing sludge volume. Magnesium hydroxide slurry of suspended particles that dissolve on demand, solves many problems for the treatment plant, minimizes waste, and maximizes re-use of water resources.