Soda residue is a kind of waste produced by the ammonia-soda process for soda ash production.It is very difficult to use soda residue due to the existence of a lot of chlorine ions.In order to solve this problem,the microstructure and chlorine ion dissolution characteristics of soda residue are investigated.The results show that ( 1) soda residue is mainly composed of two components,one is porous calcium carbonate formed through binding and bonding of nano-sized calcium carbonate,and the other is dihydrate gypsum particle; ( 2) there is a well-developed pore structure in soda residue,and the pores include the voids between calcium carbonate congeries particles and dihydrate gypsum particles,the micron-sized pores between the aggregates in calcium carbonate congeries and the nano-sized pores in calcium carbonate aggregates; ( 3) the vast majority of chlorine ions in soda residue exist in the voids between particles and the micron-sized pores within calcium carbonate congeries; and ( 4) adding water to break soda residue and then separating the solid from the liquid is an efficient method to remove chlorine ions from soda residue.