It sounds as if the water ...

It sounds as if the water will also be quite acidic, so it will surely need to be stabilized to protect the heat transfer piping, pumps, etc.  This can be done with lime or limestone/lime combination, which can precipitate out most of the heavy metals and actually reduce the TDS.  This will however result in a sludge which must be separated and used or disposed of.  The other challenge is that the sulphides/sulphates will not be removed by lime precipitation.  You also don't want to lose heat energy during the treatment process, so you may want to consider a closed system with stabilization coupled with a rapid clarifier such as a magnetic assisted separation using magnetite a a coagulant aid.  It sounds though it can get to be quite complicated. As Daniel Dean says - also depends on the final disposal of the water after use.