--Bryan wrote:
>
> You mean that there are no additional chloride ions added by the
> softener, and that the sodium is in the form of carbonate, since it
> has replaced the calcium or magnesium in their carbonate salts.

The counterion for the sodium is an anionic group attached
to the polymer backbone of the resin beads. That part is
permanently attached to the bead. Sometimes it has sodium
on it, and sometimes it has a metal ion like iron on it.

In dilute solution, iron (or other undesirable metals) can
displace sodium from that site. This liberates sodium with
whatever the iron's counterion was to travel down the pipe
to the consumers of soft water.

In brine, the massive sodium concentration drives the iron
(or other ions) off the sites. During the regeneration cycle,
the brine and stuff trapped on the resin goes to wastewater.