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Manganese oxide adsorbent (H1.6Mn1.6O4) was synthesized from precursor Li1.6Mn1.6O4 that was obtained by heating LiMnO2 at 400 °C. LiMnO2 was prepared by two methods:  hydrothermal and reflux. The crystallite size of Li1.6Mn1.6O4 and its delithiated product was slightly higher by the hydrothermal method as compared to the reflux method. The adsorbents prepared by the two methods were compared in terms of physical characteristics and lithium adsorption from seawater. The maximum uptake of lithium from seawater by the adsorbent was 40 mg/g, which is the maximum value among the adsorbents studied to date.

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A new type of adsorbent, MnO 2 ‚0.5H 2 O, was synthesized from Li 1.6 Mn 1.6 O 4 followed by acid treatment. The hydrothermal reaction of monoclinic type γ-MnOOH with LiOH solution at 120 °C resulted in a H + /Li + ion exchange, giving orthorhombic LiMnO 2 . The orthorhombic LiMnO 2 was transformed to cubic Li 1.6 Mn 1.6 O 4 (Li 2 Mn 2 O 5 ) at a temperature higher than 400 °C. The conversion of Li 1.6 Mn 1.6 O 4 to MnO 2 ‚0.5H 2 O by acid treatment resulted in contraction of the lattice constant a 0 from 8.14 to 8.05 Å with little dissolution of manganese. The new adsorbent showed a markedly high ion-exchange capacity (7.5 mmol/g) for lithium ions due to its ion-sieve property. The pH titration study suggested the formation of large numbers of uniform sorption sites having relatively high acidity. The uptake of Li + ions from lithium-enriched seawater was found to be 5.3 mmol/g (37 mg/g), which is the maximum among the adsorbents studied to date.

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