Wastewater from metal plating works was treated with lime - water
suspensions at relatively small concentrations with continuous stirring.
Experiments were designed to allow a direct contact of lime suspension
with the wastewater constituents for a period of time followed by settling
and filtration through a sand filter. The heavy metal content could be
precipitated efficiently from the mother liquor by two mechanisms: reaction
with calcium ions to yield calcium chromate and the precipitation of the
chromium hydroxides in the alkaline medium. Various parameters were
studied to reach the optimum conditions for the removal of chromium from
the wastewater. It appeared that reasonable removal of chromium (80 –
85%) could be achieved with lime: wastewater ratio of 40 mg/ L and 50 min
contact time. After the removal of most of the chromium from wastewater,
the level of the pollutant needed to be reduced to the acceptable limit by
passing water through ion exchange column. This final treatment gave
treated water samples with chromium levels as low as 0.6 - 1.3 mg/L.