| As a kind of rare metals, rubidium is often used to prepare special glass, photomultiplier tubes, thermoelectric converter, organic catalysts and antidepressants. Rubidium forms no minerals of its own, hence, it often coexists with other alkali metals in lepidolite, pollucite, lithium pollux, natural carnallite, and underground brine. Especially in underground brine, rubidium coexists with large amount of sodium and potassium. The challenge of isolation and purification of rubidium from brine is its separation from potassium which has similar physical and chemical properties.A spherical composite adsorbent AWP-CaALG was prepared by the carrier of calcium alginate (CaALG) and adsorbent of ammonium tungstophosphate (AWP).The composite adsorbent was characterized by XRD, IR and TG-DTG-DTA, it proved that the crystal structure of AWP wasn’t destroyed and the adsorption ability of the composite adsorbent couldbe retained up to120℃. Effects of adsorbent dosage, adsorption time, pH, temperature, concentration of Rb+and K+were investigated by batch experiments. The results showed that the adsorption capacity of the composite adsorbent was20.64mg/g. The adsorption rate of Rb+increased within creasing adsorbent dosage; Adsorption equilibrium was gained after24h; when the pH value was neutral, the adsorption rate was the highest; with the rise of temperature, the adsorption rate decreased; Increasing the concentration of Rb+would help to improve the adsorption capacity; when CK+:CRb+=16:1, the adsorption rate of Rb+could still be up to94.1%and the Rb/K separation coefficient was86.In order to improve the adsorption capacity and mechanical property of AWP-CaALG, material ratio, CaCl2concentration, aging time and drying temperature were investigated and optimized using the adsorption capacity of rubidium as an evaluation index. The adsorption capacity of the adsorbent toward rubidium was determined to be43mg/g under the preparation conditions of mNaALG:mAWP=1:2, concentration of CaCl2was0.5mol/L, aging for24h, being dried at105℃. The research of thermodynamic was carried out using Langmuir isotherm model and Freundlich isotherm model for description of experimental data, the free energy(△G), enthalpy(△H) and entropy(△S) change of adsorption were evaluated, the result showed that:The process of adsorption of Rb+by AWP-CaALG could be described by Freundlich equation. The adsorption of Rb+was spontaneous and was exothermic process, therefore, low temperature was advantageous to the adsorption. The study of kinetic was conducted using pseudo-first-order kinetic model, pseudo-second-order kinetic model and shell progressive model for description of kinetic data, the result showed that:The adsorption of Rb+could be described by the pseudo-second order kinetic model and was controlled by the chemical reaction.The repetitive property of the composite adsorbent and effects of flow rate, height-diameter ratio, eluent concentration on the separation of rubidium and potassium was carried out using column test. The result showed that:The better conditions of column process were flow rate=2.06BV/h, height-diameter ratio=6.66. Under this condition, adsorption capacity of the adsorbent towarded Rb+was16.34mg/g, breakthrough volume was57.26mL with feed solution of CRb+=lg/L, CK+=10g/L, pH=1. RbCl with the purity of96.93%was gained using gradient elution with lmol/L HCl-0.005mol/L NH4Cl and lmol/L HCl-0.5mol/L NH4Cl. The first column was saturated and the second column without breakthrough by connecting two-column in series. The adsorbent remained good adsorption and elution performance after repetitive operation for3times. |
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