MIL-HDBK-1005/9A
given to utilizing "cascade" or direct recirculation systems for
noncontaminated cooling waters, particularly in water short
areas. In a cascade system, cooling water discharged from one
unit may be utilized in another process where temperature of
incoming water is not critical. Direct recirculation systems
require a cooling tower to dissipate the net heat load.
2.6.2.2
Reclamation. There are a number of processes and
equipment, most of them proprietary, that may be utilized for
reclaiming metals in plating wastes or removing materials so
that the reclaimed water can be reused. Manufacturers should be
consulted for design criteria.
a) Demineralization. The five methods available for
demineralization of wastewaters are ion exchange, selective
metal recovery using immobilized ligands, reverse osmosis,
electrodialysis, and distillation. These processes are
generally too costly to consider except where reuse is a
necessity. Distillation appears to be the most feasible method
for regenerating wastewaters in polar regions (refer to NCEL AD
282520, Sanitary Waste Disposal for Navy Camps in Polar
Regions).
b) Evaporation. Evaporation systems, such as the
waste heat or vapor compression evaporation process, can be used
to recover heavy metals from plating solutions. Concentration
and reuse using evaporation is particularly applicable to
chromic acid solutions. The distilled water from evaporation
can be reused as process rinse water, and the high purity water
results in low rinse water use.
c) Ion Exchange. Ion exchange can be applied to
chromium rinse waters with use of other membrane technologies.
A system that contains a cation exchange bed followed by an
anion exchange bed can remove the contaminants of concern from
the chromium-bearing wastewater stream. The cation exchange
resin will remove the metal ions under optimal conditions. The
anion exchange resin under optimal conditions will remove the
chromate ion (CrO4-2) from the solution. With the addition of
electrodialysis (ED) and advanced reverse osmosis (ARO), a
closed looped system can be designed. Electrodialysis will
recycle the H2SO4 to the cation exchange column while the metals
are removed as sludge. The anion exchange column effluent will
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