There must be a drain somewhere if there was a softener there already. Possibly floor drain, sump pump, standpipe with a trap in another room. It may have run upstairs to a laundry tub. Do NOT run the drain in to the toilet drain. All softeners need a proper "AIR GAP" to prevent waste from backing up and possibly contaminating the system. Look in the ceiling around the basement to see if there may be a standpipe with a trap for the softener. Yes softeners take out calcium, lime magnesium (hardness minerals) and some ferrous (dissolved) iron.