Extraction of rare earth elements using synergist extractant in solvent extraction and synergist extractant immobilised resin in adsorption / Nur Nadiatul Hidayah Shaikh Rohmat

Faculty of Chemical and Process Engineering Technology

Thesis (Doctor of Philosophy in Chemical Engineering) -- Universiti Malaysia Pahang – 2019

Includes bibliographical references

The extraction of rare earth elements (REE) mostly conducted in solvent extraction due to it ability to handle large volumes of aqueous solution but possess several drawbacks that give poor extraction efficiency and selectivity. The main possible reason is due to poor contact between extractant with the rare earth metal ions from aqueous phase which lead to the application of supporting material for the extractant in adsorption. The aim of this research is to determine the most effective synergist extractants from solvent extraction method and compare the extraction efficiency of synergist extractant immobilised resins (SEIRs) and blank resins in adsorption. From the comparison study, the most feasible adsorbent was selected and studies on the adsorption kinetics and mechanisms were carried out to determine the best adsorption condition. The research methodology includes the preparation of the novel synergist exractants like A336-[C2mim][NTf2] and A336-[C4mim][NTf2] for REE extraction of praseodymium (Pr), gadolinium (Gd), and dysprosium (Dy) in solvent extraction. The best synergist extractant was then used to prepare SEIRs like AE11, AE216 and AE1B and the performance of SEIRs were compared with blank resins like CR11, PK216 and SK1B in adsorption of Pr, Gd and Dy. The feasible extractant and method were decided based on the comparison conducted according to aspects such as extraction performance, availability, selectivity and material cost thus proceed with study on kinetics and mechanism studies. In solvent extraction, A336-[C2mim][NTf2] is the most influential synergist extractant discovered in extraction of Pr, Gd and Dy after synergist probably due to [C2mim][NTf2] acts as diluent to A336 thus enhance the physiochemical. Apparently, not all resins are compatible with A336-[C2mim][NTf2] as supporting material as only AE11, AE216 and AE1B showed adsorption capability after immobilisation. The adsorption of Pr, Gd and Dy using supporting materials use up to 90% less extractant with at least 30 times fold efficiency than synergist extractant in solvent extraction. The adsorption capacity is higher in SEIRs of AE11, AE216 and AE1B than blank resins of CR11, PK216 and SK1B at higher loading. However, after all aspects considered, PK216 is selected as the best adsorbent due to its excellent performance, low in cost, robust and constant availibity. The adsorption kinetic and mechanism studies showed that higher loading enhance the adsorption capacity but the pH and temperature adjustment have minor effects as the adsorption is constant between pH values of 1-6 and temperature 25 to 85 ℃. The thermodynamic parameters are spontaneous reaction with exothermic reaction for Pr and Gd while Dy is endothermic reaction. This probably due to the characteristic of Dy is high in hydration enthalphy compared to Pr and Gd which requires additional energy from surrounding to dissociate from the aqueous phase into PK216 phase. PK216 fits Langmuir model and fits Pseudo second order which show adsorption of Pr, Gd and Dy are monolayer coverage and chemisorption. The diffusion is both intraparticle and film diffusion as it fit Boyd kinetic model instead of Weber-Morris intraparticle model. In conclusion, adsorption is clearly the best method to oversome issues on the poor contact area occurred in solvent extraction. AE11, AE216 and AE1B have better adsorption capacity than CR11, PK216 and SK1B but PK216 is the most feasible extractant to extract REE in adsorption method.