Rubidium recovery using potassium cobalt hexacyanoferrate sorbent

Abstract

A B S T R A C TRubidium (Rb) is a highly valued and economically important metal present in large quantities in many natural and wastewaters. However, its recovery is hampered by its low concentration and extracting agents' limited selectivity. A batch sorption study showed that a potassium cobalt hexacyanoferrate (KCoFC) sorbent had much higher sorption capacities for Rb and caesium (Cs) than for lithium (Li), sodium (Na) and calcium (Ca). Equilibrium sorption data at pH 7 and 24 ± 1˚C for Rb and Cs satisfactorily fitted to the Langmuir model with sorption maxima of 96 and 61 mg/g, respectively. A fixed-bed column (12 cm height) containing a mixture of 2.2 g KCoFC and 19.8 g granular activated carbon had a breakthrough sorption capacity of 61 mg/g when a solution containing 5 mg Rb/L was passed through the column at a velocity of 2.5 m/h (0.7 L/h). When 1 and 5 mg Cs/L were added to the Rb solution, Rb sorption capacity dropped to 46 and 41 mg/g, respectively. During Rb sorption, K from the KCoFC lattice was released. Leaching the column containing sorbed Rb with 0.1 M KCl for 60 min at a velocity of 10 m/h desorbed 99% of sorbed Rb. A process for recovering Rb from sea water reverse osmosis brine is presented.

Removing rubidium using potassium cobalt hexacyanoferrate in the membrane adsorption hybrid system

“…Moreover, at low pH, H + could have competed with Rb for adsorption in the highly acidic solution where the concentration of H + was high, and consequently adsorption capacity declined. Similarly, at high pH the presence of increased concentration of Na (arising from pH adjustment with NaOH) most likely competed with Rb adsorption, thus reducing Rb adsorption capacity [10,11]. The results also indicated that the difference between the zeta potential with and without Rb increased, and the negative surface charge declined in the presence of Rb as pH increased for both adsorbents (Fig.…”

“…The number of negative charges on the surface of the adsorbent increased with pH. Therefore, the increase in pH elevated the adsorption of positively charged Rb ions by electrostatic adsorption (outersphere complexation) [10,11]. Moreover, at low pH, H + could have competed with Rb for adsorption in the highly acidic solution where the concentration of H + was high, and consequently adsorption capacity declined.…”

“…The methods currently employed for extracting Rb consist of ion exchange/adsorption, evaporation, precipitation, use of emulsion membranes and liquid-liquid extraction techniques [7,8]. Of these, the ion exchange/adsorption process is the most suitable and widely utilised, since it is able to selectively extract low concentrations of Rb from mixed solutions [9][10][11].…”

“…Most of these studies were conducted in batch experiments, and only a few had been reported in fixed-bed column system studies [18]. Of the various adsorbents, potassium cobalt hexacyanoferrate (KCoFC) and ammonium molybdophosphate (AMP) have indicated high adsorption capacity and selectivity for Rb and cesium (Cs) extraction in both batch and column studies [10,11,17].…”

“…These problems can be overcome by either encapsulating the material in a coarser material or physically mixing it with a coarser material such as granular activated carbon [11,19].…”