Process for separation of Ca- or Mg-sulfite spent liquor to yield crystalline xylose

A process for the separation of a xylose-containing, lignosulphonate-containing Ca-sulfite spent liquor is provided. The process comprises a first step of: (A) chromatographic separation of the Ca- or Mg-sulfite spent liquor using a single pass through a batch-type long resin bed chromatography column having a strong acid cation exchange resin as a separation medium. The ratio of the bed length:mean resin bead diameter of the column is 10,000-40,000. This step yields *a first xylose-rich fraction having a xylose content 50-70 wt. % based on dry solids and * a lignosulphonate-rich fraction. The process further comprises a step of: (B) crystallizing xylose from the first xylose rich fraction by using a crystallization method comprising (i) boiling crystallization; (ii) cooling crystallization or (iii) a combination of (i) and (ii) to obtain a first batch of crystalline xylose and a first xylose run-off. The process provides a simplification of existing methods, and at the same time allows advantages such as improved xylose yield and improved xylose purity.