MIL-HDBK-1005/9A
to oxidize excess sulfide to sulfate. Alternatively, use
ferrous sulfide (FeS) slurry as the sulfide source to eliminate
formation of hydrogen sulfide gas.
(3) Sedimentation. Sedimentation is required
following precipitation reactions unless metal precipitate
levels are low enough for direct filtration. Use direct
filtration only if performance has been verified by pilot plant
studies. Evaluate polymer conditioning to enhance sludge
settleability. For continuous flow systems, use circular or
rectangular clarifiers with or without inclined parallel plate
(or tube) settling assistance. Provide a means for scum and
float removal so that scum discharges to the sludge holding tank
or returns to treatment process. Provide complete access for
plant operator to manually scrape down plate settlers. Consider
air agitation and scour beneath plate or tube settler to
blowdown sludge plugging to underflow while clarifier effluent
valve is temporarily closed. For batch settling processes, use
either chemical reactor or separate clarifier tank. Provide
multiple drawoff ports or telescoping valve for supernatant
withdrawal.
(4) Filtration. Filtration following
sedimentation may be required to satisfy low discharge metal
limits or if metal precipitate coagulates and settles poorly.
Evaluate polymer and alum coagulation for enhanced settleability
before using filters. Consider pH effect on cementation of
filter media.
(5) Sludge Dewatering. Since metal sludge will
usually be classified as a hazardous waste, select dewatering
equipment to optimize cake solids concentration and to minimize
volume and weight for ultimate disposal. Use fixed or variable
volume plate and frame press for mechanical dewatering if cake
disposal follows immediately. Consider centrifuge, vacuum
filter, or belt filter press for thickening prior to dewatering
on permitted sand drying beds.
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