Hello,
We have not tried using RNase R in the aqueous phase from Qiazol preparation. The buffer condition in the aqueous phase may not be suitable for RNase R digestion. If you want to save a column, after RNase R treatment you may use phenol chloroform extraction method and precipitate the RNA using co-precipitant like Glycogen or Glycoblue (ThermoFisher SCientific).