Preparation method for D-mannose crystals

The invention provides a preparation method for D-mannose crystals. The method includes adding activated carbon into mannose slurry to perform heating and discoloration, then performing desalination and purification, performing evaporation and concentration, and soaking in absolute ethyl alcohol for purification and drying to obtain high-purity crystal D-mannose. By the aid of the method that the activated carbon is used for discoloration and electrodialysis desalination, evaporation and concentration are performed until the slurry is almost oven dry and the absolute ethyl alcohol is used for soaking the obtained crystals, the problems of viscous mother liquid, small crystals, low yield and the like in the existing D-mannose crystallization process are solved. On the basis of the traditional technology, an advanced electrodialysis desalination technique replaces ion exchange, crystallization time ranges from 20 hours to 30 hours, a technological process is shortened, and energy conservation and consumption reduction are achieved; crystallization times are decreased, and crystallization yield of the mannose crystals is increased.