a water solution having an increased density is added during the neutralization of crude tall oil soap with carbon dioxide or acidulation of soap oil with sulfuric acid application_number US 82013504 A description as schematically shown in fig1 water 1 and recovery boiler ash 2 are introduced into a dissolving tank 3 in an embodiment the recovery boiler ash is a mixture of about 90 sodium sulphate 9 sodium carbonate and 1 sodium chloride and is separated from the recovery boiler flue gases by using electrostatic precipitators in the dissolving tank 3 a water solution 15 is prepared which has an increased density of 1200 kg m 3 achieved by dissolving ash and dust 2 from the recovery boiler into the water 1 the high density water solution 15 is fed to a vessel 4 further carbon dioxide gas 5 is introduced into the vessel 4 and dissolved in the high density water solution 15 the so prepared high density carbonic acid solution is pumped to the tall oil plant in the tall oil plant crude tall oil soap 6 is neutralized with the high density water solution in a neutralization reactor 7 after this carbon dioxide pre treatment process two phases are formed within the neutralization reactor 7 a bicarbonate brine which collects at the bottom of the neutralization reactor 7 and the soap oil phase on top of the brine due to the inventive use of the high density water 15 the bicarbonate brine has an increased density compared to brine resulting from the state of the art neutralization reactions thus the brine can easily be separated from the soap oil and is returned to the.