And of these three compounds, lead carbonate
and lead sulfide are seen to be essentially
insoluble in water. Executing the second step, it
is determined that a relatively inexpensive
source of carbonate ions is common soda ash,
Na2CO3, and a somewhat more expensive
material, sodium sulfide, is a source of sulfide
ions. A promising treatment method for removing
lead from an industrial wastewater, then,
would be to add soda ash and precipitate the
lead as the insoluble carbonate.
Table 8-2 presents a list of heavy metals with
theoretical solubilities of their hydroxides, carbonates,
and sulfides. Figure 8-8 illustrates the
importance of the correct range of pH. Table
8-3 presents a summary of pH range and other
conditions that have been found to produce
good removals of iron, aluminum, arsenic, and
cadmium, respectively, from typical industrial
wastewaters.