Inclusion Criteria:  Participant must be ≥18 years of age at the time of signing the informed consent. Participants with prevalent HK (S-K+ >5.5 mmol/L at the end of LIDI) not requiring acute treatment. Receiving haemodialysis 3 times a week with stable vascular access for at least 3 months before screening visit. Participants who have and are able and willing to use smart phone (android or iOS) nutrition app.  Contraceptive use by men or women should be consistent with local regulations regarding the methods of contraception for those participating in clinical studies.  Female participants of childbearing potential must have a negative pregnancy test. Female participants must be 1 year post-menopausal, surgically sterile, or using 1 highly effective form of birth control (defined as one that can achieve a failure rate of less than 1% per year when used consistently and correctly). They should have been stable on their chosen method of birth control for a minimum of 3 months before entering the study and willing to remain on the birth control until 12 weeks after the last dose. Capable of giving signed informed consent, which includes compliance with the requirements and restrictions listed in the Informed Consent Form (ICF) and in the protocol.  Exclusion Criteria:  As judged by the investigator or sponsor, any medical condition (including active, clinically significant infection) that may pose a safety risk to the participant in this study, may confound safety or efficacy assessments and jeopardise the quality of data, or may interfere with study participation. Myocardial infarction, acute coronary syndrome (ST-elevation myocardial infarction, non-ST-elevation myocardial infarction, or unstable angina), stroke, seizure, thrombotic/thromboembolic event (eg, deep vein thrombosis or pulmonary embolism, but excluding vascular access thrombosis), percutaneous transluminal coronary angioplasty, or coronary artery bypass graft within 12 weeks prior to screening visit. Severe leucocytosis (>20 × 109 /L) or thrombocytosis (≥450 × 109 /L) during screening. Polycythaemia (haemoglobin >14 g/dL) during screening. Severe constipation, bowel obstruction, post-operative motility disorders. Scheduled date for living donor kidney transplant. Participants with a life expectancy of less than 6 months. Females of childbearing potential, unless using contraception as detailed in the protocol or sexually abstinent. Currently pregnant (confirmed with positive pregnancy test) or breast-feeding. Presence of cardiac arrhythmias or conduction defects that require immediate treatment at HCP discretion. History of alcohol or drug abuse within 2 years prior to screening visit. History of QT prolongation associated with other medications that required discontinuation of that medication. Congenital long QT syndrome or QT interval corrected for heart rate (QTc) using Fridericia's method (QTcF) >550 ms. Symptomatic or uncontrolled atrial fibrillation despite treatment, or asymptomatic sustained ventricular tachycardia. Subjects with atrial fibrillation controlled by medication are permitted. If the participant has evidence of Coronavirus disease 2019 (COVID-19) within 2 weeks prior to screening (see Appendix D), the participant cannot be enrolled in the study. Participants treated with SZC, sodium polystyrene sulfonate (SPS: Kayexalate™; Resonium™ A), calcium polystyrene sulfonate (CPS: Calcium Resonium™), or patiromer (Veltassa™) 1 within 4 weeks before screening. Participants with a known hypersensitivity or previous anaphylaxis to SZC or any of the excipients of the product. Participants unable to take oral SZC. Prior/Concurrent Clinical Study Experience Participation in another clinical study with an investigational product administered during the month before screening2 . Involvement in the planning and/or conduct of the study (applies to both AstraZeneca staff and/or staff at the study site). Judgment by the investigator that the participant should not participate in the study if the participant is unlikely to comply with study procedures, restrictions, and requirements. Previous enrolment in the present study.