greenwater,
Are you doing any pH adjustment? You should familurize yourself with the relationship between carbonate, bicarbonate and CO2. Once you return the water to "normal" pressure the ratio will be reestablished and you can end up with CO2 being created from the carbonate/bicarbonate. I...
Procman,
Have you looked at membrane technology. The use of standard RO membranes may not be appropriate due to other ions in the solution. There are some new development in the field that could withstand the high concentrations you are looking for. This might not get you to 50% but it could...