polishing treatments

Two primary techniques can be used to limit the metal concentrations in the discharges: tertiary filtration and polishing resins.

tertiary filtration

Subsequent to sedimentation, we may wish to reduce further the total metal concentrations prior to discharge, particularly by completely eliminating suspended solids which typically consist of hydroxides of those metals. Additionally, we can also reduce the soluble fraction of these metals by acting a chemical precipitation agent (organic sulphides, phosphates…).

Pressure filtration through sand will then produce excellent results. Coagulation through the filter may be necessary.

polishing resins

This technique is implemented as tertiary filtration and often following a sand filter to prevent premature fouling of the resins. The objective is to trap soluble residual metals on specific resins (usually cationic).

In this instance, two exchangers are set up in series in order to achieve maximum metal concentration capacity with the first and good polishing with the second. Regeneration wastes are returned to the plant inlet. This will produce quality effluent with metal levels of a few ppb, irrespective of the metals involved.