Extraction of rubidium and cesium from oilfield brine by the two-step adsorption–flotation method

Rb, Cs, and their compounds are important raw materials, and the extraction of Rb+/Cs+ from brine has attracted increasing attention. In this work, the extraction of Rb+/Cs+ from aqueous solutions, such as oilfield brine, through an adsorption–flotation process was evaluated. The effects of various factors on the extraction efficiency (Ee) of Rb+/Cs+ and the floatability of particulate matter were systematically investigated, and the Ee of Rb+/Cs+ was maintained at approximately 80% after five cycles. Because of the difference in the selectivity of ammonium molybdophosphate (AMP) for Rb+ and Cs+, Rb+/Cs+ can be extracted from oilfield brine using a two-step adsorption–flotation process. The Ee values of Rb+ and Cs+ were 18.01% and 90.83%, respectively, in the first step and 80.10% and 8.22%, respectively, in the second step. The adsorption and flotation mechanisms were analyzed using density functional theory (DFT), fourier transform infrared (FT-IR) spectroscopy, and point of zero charge (PZC). The adsorption mechanism could be explained by electrostatic interactions and van der Waals effects between the ions and molybdophosphate, and the flotation mechanism was mainly the electrostatic interaction between the CTAB cations and rubidium molybdophosphate (RMP)/cesium molybdophosphate (CMP) particles.