Efficient Removal of Sr2+ by a Layered Metal Sulfide K1.36Cd1.12Bi2.80S6 via Ion Exchange

As a fission product of 235U or 239Pu, 90Sr is a β-emitting radionuclide with a relatively long half-life (t1/2 = 28.9 years). Due to its high solubility, easy environmental mobility, and propensity for bioaccumulation within the food chain, the development of efficient materials for the selective capture of 90Sr2+ is critical for the safe disposal of nuclear waste and environmental protection. In this study, a layered metal sulfide, K1.36Cd1.12Bi2.80S6 (denoted as KCBS), was synthesized via the high-temperature solid-phase method using K2CO3 as the potassium source. KCBS demonstrates high adsorption performance towards Sr2+, achieving a maximum adsorption capacity (qmSr = 77 mg·g−1). Moreover, it can maintain high adsorption efficiency (RSr > 84.15%) across a broad pH range of 2.98–12.01. In addition, KCBS exhibits the outstanding selectivity for Sr2+ removal in the presence of excessive Na+ ions and even in actual water samples. KCBS also possesses regenerability, maintaining its superior adsorption capacity for Sr2+ ions over three cycles. The mechanism study by energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) analyses indicates that the efficient Sr2+ capture is attributed to the ion exchange between Sr2+ and interlayer K+ ions in KCBS. This research further highlights the potential of layered metal sulfide ion exchange materials for radionuclide remediation.