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Lead is often found in
wastewater from printed circuit board factories, electronics assembly plants,
battery recycling plants and landfill leachate. In the printed circuit factory,
solder plating and etching operations is the lead source. In the electronics
assembly operations, the source is solder flux cleaning. In battery breaking,
the lead is found in the sulfuric acid from the battery. In landfill leachate,
it can be found as an organo metallic like tetra ethyl lead.
Since lead hydroxide is moderately soluble, it cannot be treated by pH
adjustment to regulated concentrations. It is often treated by precipitating
lead sulfide or phosphate, using a two step process. It can also be treated by
reduction or by ion exchange. When using ion exchange, it is difficult to remove
the lead from the resin by regeneration requireing the disposal of the spent
resin.
Organo-metallics are particularly difficult to treat since the lead is not free
to form a precipitate. The organic compound must either be oxidized to free the
lead or the compound may be adsorbed on to carbon to remove the lead as the
organic complex. Either way it is difficult and may not be effective.
The equipment used is batch treatment for concentrated wastewater, continuous
precipitation for dilute wastewater. Ion exchange for very dilute solutions or
media filtration in the presence of a reducing agent. For organo-metallic lead,
treatability studies should be done to determine if oxidation or carbon
adsorption is effective at removing the lead.
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