The table below compares
Hi-Chem Mag-50 with caustic soda. As you can see, the area of greatest
concern with cuastic soda is its aggressive corrosivity. It poses
a threat to the safety of your personnel, is environmentally destructive,
and can be difficult to handle.
In contrast, Hi-Chem Mag-50 is non-corrosive, safe to people
and the environment, and can be handled in higher concentrations
from the other neutralizers at lower temperatures.
Because of the hazard of caustic soda, costly safety equipment
and procedures are necessary; and because a 50% solution freezes
at 57oF
, heating equipment is usually called for. Hi-Chem Mag-50, on
the other hand, requires no special safety equipment. Heating
equipment is not necessary as a general rule, since the freezing
point is the same as that of water.Reaction time poses a trade-off.
Caustic soda is a very fast neutralizer, but overdosing can produce
a pH as high as 14! Hi-Chem Mag-50 takes somewhat longer to react,
due to its having two Hydroxyl (OH-) ions per molecule, where
caustic soda (and most other neutralizers) have only one . However,
when metals are present in the waste effluent, a fast reacting
neutralizer will produce precipitate particles which are too
small to be effectively settled or filtered. The longer reaction
time with Hi-Chem Mag-50 promotes larger particle formation which
provides a more readily settled, filtered, and dewatered sludge.
Lower volume and less weight of sludge means reduced handling
and disposal costs!
Incidentally, accidental overdosing with Hi-Chem Mag-50 cannot
produce a pH higher than 9.5.
| Neutralizers |
Magnesium Hydroxide |
Caustic Soda |
| Equipment Costs |
Less than for caustic soda even with an agitator to prevent
settling in storage tanks. |
Greater than for magnesium hydroxide because of need for
heated system and safety equipment. |
| Residence Time (Reaction Speed) |
Moderately fast acting to 95% of neutral. Slower above
pH 6, resulting in more controllable process conditions and
enhancing flocculent performance in solids settling. |
Extremely fast - acting with most acids. Difficult process
control conditions and inefficient solids removal frequently
occur when neutralization takes place very rapidly. |
| Dissolved Solids Effluent* |
1.31 tons tons per ton of HCl. 1.23 tons per ton os sulfuric
acid. Generates only soluble salts. |
1.61 tons per ton of HCl. 1.45 tons per ton of sulfuric
acid. |
| Maximum pH if overtreated |
Usually no higher than pH 9, the limit set by the Clean
Water Act. |
Can reach pH of 14. |
| Sludge |
With a wide range of acids and metals, creates a sludge
that is very dense, fast-settling, and easily filtered and
dewatered. |
If effluent contains heavy metals, creates large quantities
of gel-like slow-settling sludge that is difficult to filter
and dewater. |
| Safety |
Comparatively safe to handle. Contact with eye may cause
temporary injury to the cornea. Contact with skin rarely
causes irritation. |
Extremely hazardous to handle. Contact with eye may cause
permanent loss of vision. Contact with skin may cause severe
burns. Breathing vapor may cause damage to the upper respiratory
tract and the lungs. |
| Environmental Effects |
Relatively harmless. Magnesium Hydroxide is a natural mineral
that poses no unusual threat to the environment. |
Because caustic soda is highly corrosive, it can cause
severe physical injury to plant and animal life if it escapes. |
| Ease of Handling |
Supplied as a ready-to-use slurry. Requires no special
equipment except an agitator in the slurry storage tank to
prevent settling. Low temperatures create no special problems,
because the slurry freezes at the same temperature as the
water being treated. |
Requires elaborate safety equipment and rigorous, time-consuming
safety procedures. Workers must be trained in safety and
wear special clothing and goggles. Low temperatures can create
major problems, because a 50% solution freezes at 57oF.
Often requires temperature sensors and heaters throughout
the distribution system. |
| Availability |
Available in abundance from several locations in the U.S.A.
It's not produced as a by-product but by a "primary process." |
Because caustic soda is coproduced with chlorine, the supply
varies widely from surplus to shortage. Price varies accordingly. |
*Based upon Stoichiometric ratios.
Actual usage may vary.
| Neutralizing One Ton Of Hydrochloric
Acid |
|
|
| Pounds of Neutralizer Required |
Pounds of Dissolved Solids in Effluent |
|
| Neutralizing One Ton Of Sulfuric Acid |
|
|
| Pounds of Neutralizer Required |
Pounds of Dissolved Solids in Effluent |
|
|
