PRECIPITATION OF LEAD FROM A STORAGE BATTERY
MANUFACTURING WASTEWATER
James R. Wallace, Engineer
Camp Dresser and McKee
Boston, Massachusetts 02108
Philip C. Singer, Professor
Department of Environmental Sciences and Engineering
University of North Carolina
Chapel Hill, North Carolina 27514
Lead is used as an industrial raw material for storage battery manufacture, printing,
pigments, fuels, photographic materials, and matches and explosives manufacturing. The
storage battery industry is the largest consumer of lead, followed by the petroleum industry
in their production of gasoline additives. In the storage battery industry, the highest concentrations of lead originate in the plate-forming area. The resultant wastewater has a very
low pH, in the range of 1.3 to 2.6, which leads to relatively high concentrations of lead
(e.g., 4 to 5 mg/1).
Lead is a consent decree pollutant. In addition to its detrimental impact on aquatic
life in receiving waters, lead can inhibit biological wastewater treatment or sludge digestion
processes. Furthermore, sludges containing lead may be classified as hazardous and are,
accordingly, difficult to dispose of. The maximum contaminant level for lead in drinking
water is 0.05 mg/1.
These problems associated with lead have prompted the setting of pretreatment standards
for the discharge of industrial wastes into publicly owned treatment works (POTW's).
The current standard for lead is a one day maximum concentration of 0.6 mg/1 and a
30-day average of 0.3 mg/1 [ 1 ].
Removal of soluble lead from acidic wastewaters is usually accomplished by neutralization and precipitation. The pH of the lead-containing wastewater is generally raised by
the addition of caustic (NaOH), lime (CaO), sodium carbonate (Na2C03) or sodium bicarbonate (NaHC03), resulting in the formation of insoluble lead oxide (PbO), lead carbonate (PbC03), or lead sulfate (PbS04) in sulfate-bearing wastewaters. All of these
chemicals are acceptable for raising the pH and rendering the lead insoluble, except that
in the presence of high concentration of sulfate, voluminous amounts of calcium sulfate
(CaSO.)) may result if lime is used for neutralization.
Selection of the appropriate base for treatment should be based upon the following
criteria: (a) solubility limits of lead in the neutralized wastewater; (b) settleabdity and
filterabdity of the resultant precipitate; (c) solids handling, e.g. dewaterabdity and ultimate
disposal potential of the resultant sludge; and (d) cost. Solids handling following precipitation of lead from the wastewater stream must be considered, but is often overlooked.
Sludge handling and dewaterabdity depend upon the nature of the solids. For example,
particle size and shape, nature of the solids phase (amorphous or crystalline), and density
of the precipitate all affect the dewaterabdity of the sludge. One method for solids handling
is dewatering of the sludge and disposal of the concentrated solids in a landfill. Another
method is to dewater the sludge and reclaim the lead for recycle as a raw material back
into the manufacturing process. The effectiveness of dewatering processes depends upon
the type of precipitate formed.
The purpose of this study was to evaluate the use of sodium hydroxide, sodium carbonate, and sodium bicarbonate in treating a storage battery manufacturing wastewater.
Three criteria were used in evaluating the bases: (a) the residual lead concentration of the
resulting supernatant after sedimentation was measured to evaluate the settleabdity of
the resultant precipitates: (b) the treated water was filtered and the soluble lead measured,
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