THIOGUARD in Sanitary Treatment Plants and Collection Systems

Dr. Mark Shand
Premier Magnesia
Premier Research Center
495 Emma Street, Bettsville, OH 44815

THIOGUARD, is an alkaline magnesium hydroxide slurry, Mg(OH)2, that is beginning to be recognized as having many advantages over the more common alkali sources, such as caustic soda and hydrated lime. Technical grade magnesium hydroxide suspensions are akin to the more familiar pharmaceutical grade "milk of magnesia" used to alleviate acid indigestion, and are therefore a safe non-hazardous product that will not cause chemical burns.

Technical grade magnesium hydroxide has found great use in treating industrial metal laden acidic wastewater, where, compared with caustic soda or lime, remove metals at lower pH, produce less sludge volume, and a filtercake that de-waters more readily. However, it is also beginning to be used in the municipal arena. When comparing the physical and chemical properties of magnesium hydroxide with conventional alkalis, hydrated lime and caustic soda, see Table I, several advantages are noted. The first is that fewer pounds of technical grade magnesium hydroxide are required to neutralize the same amount of acid, 37% more for caustic soda and 27% more for hydrated lime. Another unique characteristic, is the maximum pH obtainable during an overdosing situation. Excessive additions of caustic soda and hydrated lime will result in the pH of the waste stream reaching 14 and 12.5 respectively. However, the pH of a technical grade magnesium hydroxide slurry is 10.5, and when used to neutralize acidic waste, will only obtain a pH of about 9.0, even when overdosed. This upper pH limit happens to coincide with the upper limit under the Clean Water Act, 1976.

Property 50% NaOH 30% Ca(OH)2 58% Mg(OH)2
% Hydroxide 42.5 45.9 58.3
Solubility in Water g/100 ml 42 0.185 0.0009
Reactive pH 14 12.5 9.0
Freezing Point °F 61 32 32
Weight Equivalency 137 1.27 1

Technical grade magnesium hydroxide is supplied as an easily pumpable "latex paint like" aqueous suspension, typically ranging from 55 to 65% solids. It can settle and freezes at 32oF, therefore should be stored in agitated tanks. It can also be supplied as a fine powder.

Two new areas where technical grade magnesium hydroxide is being utilized are municipal sanitary collection systems and treatment plants.


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