Magnetic potassium cobalt hexacyanoferrate nanocomposites for efficient adsorption of rubidium in solution

Rubidium (Rb) is an important resource with economic value. However, extracting Rb resources from nature faces enormous challenges due to its low concentration and being in a complex system. In this study, a novel magnetic potassium cobalt hexacyanoferrate composite (MKCoFC) was synthesized, which had excellent adsorption properties for Rb+ and allowed rapid separation from the liquid phase by outside magnetic force. The effective grafting of potassium cobalt hexacyanoferrate on magnetic carriers was verified by analyzing chemical composition (FTIR, XPS), crystal structure (XRD), and micromorphology (SEM, TEM) of the material. The effects of various factors (pH, concentration, time and temperature for adsorption) on the extraction capacity of MKCoFC towards to Rb+ were explored by batch experiments. The adsorption process was explained quite easily by the Langmuir model, and the actual adsorption performance (208.8 mg/g) was consistent with it. The adsorption was a monolayer process and the active sites were uniformly located. MKCoFC maintained the brilliant adsorption performance of KCoFC by the in situ grafting technique. In addition, the pseudo-second-order model agreed with the sorption behavior, which was governed by the ion exchange mechanism of Rb+ with K+ in the lattice. MKCoFC displays promising selectivity, with high adsorption for Rb+ and hardly any adsorption for Na+, Mg2+, Li+ and Ca2+ in coexisting solution. Furthermore, MKCoFC can be regenerated by 1 mol/L KCl and maintains 92.1% adsorption efficiency (relative to initial adsorption) after five adsorption–desorption cycles.