A process for obtaining a product sugar stream from cellulosic biomass is disclosed. In one process, the cellulosic biomass is pretreated at a pH between about 0.4 to 2.0 by adding one or more than one acid to produce a pretreated cellulosic biomass comprising acetic acid. One or more than one base is then added to the pretreated cellulosic biomass to adjust the pretreated cellulosic biomass to a pH of about 4.0 to about 6.0 to produce a neutralized cellulosic biomass comprising inorganic salt and acetate salt. The neutralized biomass is then hydrolyzed by cellulase enzymes to produce a crude sugar stream. Insoluble residue is separated from the crude sugar stream and the resulting clarified sugar stream is treated using ion exclusion chromatography at about pH 5.0 to about 10.0 to produce one or more raffinate streams and a product stream. The raffinate stream comprises inorganic salts and acetate salts, and the product stream comprises sugar. The product stream may then be fermented or otherwise further processed. In an alternate process, a product sugar stream is obtained from a crude sugar stream that is produced from conversion of cellulosic biomass to sugar. The cellulosic biomass may be produced using any suitable method. In this process the crude sugar stream is treated using ion exclusion chromatography at about pH 5.0 to about 10.0 to produce one or more than one raffinate stream comprising sulfate and acetate salts, and a product stream comprising sugar, and the product sugar stream is obtained.