Interfacial Adsorption Behavior of a Structurally Optimized AMP@MIL-101(Cr) Composite for Efficient Rubidium Recovery from Aqueous Solution

A novel composite adsorbent, AMP@MIL-101(Cr), has been successfully synthesized by integrating ammonium phosphomolybdate (AMP) with the metal–organic framework MIL-101(Cr) for the efficient adsorption of rubidium ions (Rb+) from aqueous solutions. The results of structural characterizations confirmed that the crystalline framework of the adsorbent remained intact after Rb+ adsorption, indicating excellent structural stability. Adsorption kinetics, isotherm, and thermodynamics studies revealed that the adsorption process followed a single-layer chemisorption mechanism and was an endothermic reaction and spontaneous adsorption process with negligible influence from solution pH. The adsorbent exhibited a remarkable Rb+ adsorption capacity, reaching 69.4 mg·g–1 within 5 min in a solution containing 250 mg·L–1 Rb+ at 45 °C. In the Nanyi Mountain Oilfield, the adsorption rate of adsorbent for Rb+ (10.69%) exceeded that of other ions (Li+: 0.75%; Na+: 0; K+: 0.95%; Mg2+: 0.67%). Furthermore, the adsorbent still maintained 86.72% of its initial adsorption capacity after 5 consecutive adsorption–desorption cycles. These findings highlighted the great potential of AMP@MIL-101(Cr) as an efficient and stable adsorbent for the selective recovery of rubidium from aqueous environments.