Acidic metal-bearing wastewaters are treated to produce a finished water
of sufficient purity to meet discharge standards while recovering metals
removed in forms which are commercially valuable. The metals are
selectively precipitated, either in a batch or in a continuous system,
for removal of individual metal products in a specific sequence of steps
from the wastewater. In each step, the pH is adjusted to the specific pH
range and sulfide ion is introduced to precipitate the metals, excepting
the removal of ferric iron and aluminum which is achieved using hydroxide
precipitation. Bioconversion process using unique equipment converts
sulfate in the wastewater to the hydrogen sulfide gas required for the
precipitation process. This bioconversion process reduces the sulfate in
the wastewater so that the water can be directly discharged or used for
agricultural applications.