Production of lithium chemicals from spodumene using novel leaching processes

Mahmoud F Alhadad

The sulfuric acid-roast process is the principal technology to refine lithium from β-spodumene. Despite the high lithium recoveries (> 90 %), the process downside includes considerable but controllable contaminants in the leaching fluid, such as Al, Si, Fe, Na, K, Ca, and Mg that necessitate multiple purification steps. However, the overall lithium recovery is reduced due to the subsequent removal of contaminants, mainly aluminium. Additionally, disposal costs of hydrogen aluminosilicate (HAlSi2O6) and sodium sulfate (Na2SO4) by-products are a significant disadvantage that urges researchers to convert them to commercial goods (e.g., zeolites). Furthermore, the process energy footprint, as well as hazardous reactant and by-product intensities, contradict the idea of lithium as a green metal. This research is founded on developing innovative lithium extraction processes from β-spodumene. The study is based on experimental work endorsed with thermodynamic modelling and reaction kinetics. It looks not only to optimise the parametric effects such as reaction time, temperature, liquid to solid mass ratio (L/S), agitation, chemical ratios, and particle size on the Li-recovery but also at the inhibiting factors, process economics, and purification methods. The project incorporated intensive analytical techniques to study feed material, leach residue, leach liquors and produced lithium chemical purity. Distinctly, project data interpretation led to an understanding of reaction mechanisms of the developed processes. The work entails developing a lithium extraction process from β-spodumene that yields zeolites or sodium aluminium silicates in a single leach step using a sodium chloride solution with and without the addition of sodium hydroxide. The process is simple, the optimised conditions extract more than 92 % of lithium and significantly lower impurities due to its extraordinary selectivity. The process yields a commercial by-product of sodium aluminosilicate (NaAlSi2O6) for the food sector, after further processing, when conducted at neutral pH, high NaCl/β-spodumene, and high L/S ratios. The intensified process (low NaCl/β-spodumene and low L/S ratios) demands alkaline pH, resulting in the synthesis of analcime (NaAlSi2O6∙H2O), which has a well-established market in the building industry and is a possible reagent for nitrate removal from groundwater. The findings demonstrate a shift in the reaction mechanism between neutral and alkaline conditions from ion exchange (or replacement interface) to dissolution-precipitation. The low contamination impacts the analcime process with a modest downstream process of resilient potential to produce various lithium chemicals, including but not limited to LiCl, LiOH, Li2CO3 and Li3PO4. In addition, the study proved that a germane process between dissolved KCl and β-spodumene fails for both neutral and alkaline pH. This comes to pass because of lower K+ diffusion compared to Na+ in β-spodumene at neutral pH and slow rate of transformation of β-spodumene to leucite at alkaline pH. The doctoral study optimises the operating conditions to induce selective Li metal precipitation with minimum chemical additions, yielding battery-grade lithium carbonate with a purity of 99.99 wt% of > 90 % precipitation efficiency. The study compares the developed analcime method to the standard sulfuric acid process in all aspects, including impurities, waste management, and economics. The saline method preserves significant selectivity to lithium with minimal impurity ion dissociation, no Al dissolution, and significantly less iron (91.1 % drop) than the H2SO4 option. The research compares the capital and operating costs of the analcime and sulfuric acid processes for refining 200,000 t/y of spodumene. Moreover, the lithium was extracted using carbonic acid from β-spodumene at moderate pH. The dissolution of β-spodumene involves two conspicuous reaction mechanisms, including Li+ ↔ H+ ion exchange and limited dissolution reprecipitation of amorphous silica (SiO2) and Al-oxide/hydroxide. The findings show that a high L/S ratio or sequential extraction processes improve Li-recovery by reducing silicon and aluminium fluid saturation and suppressive layer development. The observation of increased Li recoveries at longer carbonation time suggests that key species (e.g., Li+ and H+) permeate through the precipitated layers.

Production of lithium chemicals from spodumene using novel leaching processes

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