The present invention provides methods and compositions for the treatment of ion imbalances. In particular, the invention provides core-shell compositions and pharmaceutical compositions thereof. Methods of use of the core-shell compositions for therapeutic and/or prophylactic benefits are disclosed herein. Examples of these methods include the treatment of phosphate imbalance disorders, hypertension, chronic heart failure, end stage renal disease, liver cirrhosis, chronic renal insufficiency, fluid overload, or sodium overload.