The study will start with the screening period, and all baseline parameters should be measured/collected up to 1 day prior to administration of first dose of study drug on Correction Phase Day 1. Subjects with 2 consecutive i-STAT potassium values ≥ 5.1 mmol/L will enter the Correction Phase and receive ZS 10 g TID for up to 72 hours, depending on potassium values. Once normokalemia (i-STAT potassium between 3.5 and 5.0 mmol/L, inclusive) is restored (whether after 24, 48 or 72 hours), subjects will be entered into the Maintenance Phase to be dosed with ZS at a starting dose of 5 g QD. Potassium (i-STAT and Central Laboratory) will be measured Days 1, 2, 5, 12, 19 and 26 throughout the first month of study and every 4 weeks thereafter until Day 362 (Visit 23) then patients will be required to complete the EOS visit which is 7±1 days after the last administration of study medication. For patients who do not enter the Maintenance Phase the last visit will be 7±1 day after the last treatment dose in the Correction Phase. The total expected study duration for an individual patient is approximately 53-54 weeks.