Evaluation of the Sorption Properties of Diatomite for Capture of Radioactive Barium, Cobalt, and Zinc

Sorption is a well‐known method for radionuclide removal, but the high cost of synthetic sorbents constrains its application. This study investigates the potential of locally sourced diatomite from Kariandusi, Kenya, as a cost‐effective sorbent for capturing barium (Ba), cobalt (Co) and zinc (Zn) from radioactive liquid waste. Characterization of diatomite was done by analysing its chemical, mineralogical, radiological and particle size composition using X‐ray fluorescence, X‐ray diffraction, gamma spectroscopy and mechanical sieving, respectively. The cation‐exchange capacity of diatomite was determined using the SW‐846 test method 9081. Sorption experiments were conducted to assess the impact of diatomite concentration, initial concentrations of target ions, time of sorption and pH. The chemical and mineralogical analysis indicated the presence of 91.64 ± 2.99% silica with cristobalite as the major mineral phase. The radiological safety was confirmed, with a radium equivalent activity of 77.96 ± 13.56 Bq/kg, falling below the internationally accepted safety limit of 370 Bq/kg. Particle size analysis showed that 10% of particles were finer than 171 μm; 50% were finer than 589 μm, while 90% were finer than 1523 μm. The CEC of diatomite was found to be 7.94 ± 0.83 meq/100 g, lower than typical values, possibly due to pH and clay content variations. The sorption studies indicated that increasing diatomite mass concentration enhanced sorption efficiency by providing more sorption sites. Higher pH and longer sorption times improved sorption due to stronger electrostatic attraction and longer interaction time, respectively. The sorption capacity was also higher at higher initial concentrations of target ions due to enhanced mass transfer between the sorbate and the sorbent. At selected sorption parameters, diatomite achieved removal efficiencies of 99.83% for Zn, 99.14% for Ba and 94.27% for Co. These findings suggest that diatomite is an effective and affordable alternative to synthetic sorbents in capturing Ba, Co and Zn from radioactive liquid waste.