Yoshitaka Miyai

Recovery of lithium from seawater by manganese oxide adsorbent

Abstract Ion-sieve (microporous) type manganese oxide (HMnO) was prepared by acid treatment of lithium-introduced manganese oxide which was obtained from γ-type manganese oxide and lithium hydroxide. The HMnO showed high selectivity for lithium ions in seawater. The maximum lithium uptake by the HMnO from seawater reached 7.8 mg/g which corresponded to a lithium content of 1.7% as Li2O. The adsorbed lithium could be easily eluted with 0.01 or 0.05 M hydrochloric acid solution. The adsorptive capacity for lithium ion scarcely changed during five repetitions of the adsorption-elution cycle. The column test was carried out by using granulated HMnO which was prepared with polyacrylic hydrazide as a binder.

Recovery of Lithium from Seawater Using a New Type of Ion-Sieve Adsorbent Based on MgMn2O4

Abstract A new type of ion-sieve manganese oxide, HMnO(Mg), was prepared by an acid treatment of MgMn2O4. The HMnO(Mg) showed a remarkably high selectivity for lithium ions among alkali metal and alkaline earth metal ions. The selectivity sequences were Na ≑ K ≪ Li for alkali metal ions and Mg ≤ Ca ≤ Sr ≤ Ba for alkaline earth metal ions at pH 8. The HMnO(Mg) showed a high selectivity for lithium ions in seawater. The lithium uptake increased with increasing solution pH and adsorption temperature. The maximum lithium uptake from native seawater reached 8.5 mg/g, corresponding to a lithium content of 1.8% in the form of Li2O. The adsorbed lithium could easily be eluted with a dilute acid solution. The adsorptive capacity for lithium ions gradually decreased through repeated adsorption/elution cycles. The HMnO(Mg) after 4 cycles showed a lithium adsorptivity which was about 60% of the initial value.

Kinetic properties of a Pt/Lambda-MnO2 electrode for the electroinsertion of lithium ions in an aqueous phase

Kinetic properties of a Pt/{lambda}-MnO{sub 2} electrode for the electrochemical insertion of lithium ions were studied in t aqueous phase by cyclic voltammetry (CV) and potential step chronoamperometry (PSCA). The cyclic voltammogram showed that the electrochemical insertion reaction of lithium ions proceeds in two steps in the potential range between 0.6 and 0.98 V (vs. saturated calomel electrode). The chemical diffusion coefficients of lithium ions in the manganese oxide the authors evaluated from the PSCA data using a finite diffusion model. They were in the range of 6.6 {times} 10{sup {minus}11} to 1.4 {times} 10{sup {minus}10} cm{sup 2}/s, depending slightly on the applied potential. The activation energy of the diffusion was evaluated as about 44 kJ/mol from the temperature dependence of the PSCA. These results suggested that lithium ions diffuse by a hopping mechanism in the spinel phase. The diffusion coefficients, transfer coefficients, and standard rate constants also were estimated from the CV data. The diffusion coefficients agreed reasonable, well with those obtained by PSCA.

Equilibrium Potentials of Spinel‐Type Manganese Oxide in Aqueous Solutions

Equilibrium potentials of spinel-type manganese oxide, λ-MnO 2 , were measured in various aqueous solutions. The Pt/λ-MnO 2 electrode showed a near-Nernstian response to lithium ions and not to other alkali metal and alkaline earth metal ions in the concentration range between 3×10 -6 and 0.5 mol/dm.. The selectivity coefficents for lithium ions against sodium, and potassium ions and protons were found to be: log k LiNa pot =-4.8, log k LiK pot =-4.6, and log k LiH pot =+1.9. The equilibrium potential was stable and pH-independent over a wide pH range (pH 4 to 9.5) in a solution with a lithium ion concentration above 5 mmol/dm 3

LITHIUM-ION SIEVE PROPERTY OF λ;-TYPE MANGANESE OXIDE

ABSTRACT The adsorptive properties of A-Mn02for mono and divalent metal ions were investigated by pH titration and by measurements of the distribution coefficients(Kds) of the metal ions. The pH titration curve showed an apparently monobasic acid type for a H+-Li+exchange. Those for H+-K+and H+-Cs+exchanges were nearly the same as that for blank titration. The lithium ion uptake increased with increasing solution pH and reached 5 meq/g at pH 11. X-ray diffraction analyses showed that the adsorption of lithium ions caused an increase in the lattice constant of a cubic unit cell. The potassium and cesium ion uptakes were nearly zero over a pH range between 4 and 11. A-Mn02showed a remarkably high Kd value for lithium ions, compared to a cation exchange resin. The selectivity sequences were Na+< K+< Rb+< Cs+<< Li+for alkali metal ions, Mg2+< Ca2+< Sr2+< Ba2+for alkaline earth metal ions, and Ni2+< Zn2+< Co2+< Cu2+for transition metal ions.

Electrochemical recovery of lithium ions in the aqueous phase

Abstract The electrochemical insertion of lithium ions into a Pt/λ-MnO2 electrode was investigated in various metal chloride solutions. The Li+ insertion occurred effectively in LiCl solutions with higher concentration than 10 mmol/dm3, but it could hardly occur in a 0.1 mmol/dm3 LiCl solution. Alkaline earth metal ions showed a stronger inhibition effect against the Li+ insertion into the Pt/λ-MnO2 electrode than alkali metal ions. However, since only Li+ ions were taken up from a mixed solution of lithium and alkaline earth metal chlorides, a high selectivity of the electrode for lithium ions was shown. It was possible to recover lithium ions from geothermal water by this electrochemical method using the Pt/λ-MnO2 electrode; the lithium uptake was 11 mg/g-MnO2.

Ion-Exchange Properties of lon-Sieve-Type Manganese Oxides Prepared by Using Different Kinds of Introducing Ions

Abstract Three ion-sieve-type manganese oxides, HMnO(Li), HMnO(Na), and HMnO(K), were prepared by acid treatments of Li+-, Na+-, and K+-introduced manganese oxides, respectively. Three oxides were obtained from γ-MnO2 and the corresponding alkali metal hydroxides by heating at 600°C. The ion-exchange properties of the adsorbents were investigated by pH titration, Kd measurements, and the adsorption of metal ions from seawater. The selectivity sequences of alkali metal ions were Na+ < Cs+ < Rb+ < K+ < Li+ for HMnO(Li) and Li+ Na+ < Cs+ < K+ < Rb+ for HMnO(Na) and HMnO(K). The high selectivity of Li+ on HMnO(Li) can be ascribed to an ion-sieve effect of spinel-type manganese oxide which was produced from LiMn2O4 Since HMnO(Na) and HMnO(K) had [2 × 2] tunnels of edge-shared [MnO6] octahedra, the high selectivities of K+ and Rb+ on these samples were used to explain that the sizes of the [2 × 2] tunnels were suitable for filling ions of about 1.4 A in radius in a stable configuration. The order of metal-ion u...

FRACTIONATION OF LITHIUM ISOTOPES IN ION EXCHANGE CHROMATOGRAPHY WITH TITANIUM PHOSPHATE EXCHANGER

ABSTRACT Ion exchange chromatography of lithium was carried out to study the lithium isotope effect in an aqueous ion-exchange system, using titanium phosphate exchangers granulated with polyvinyl chloride or an inorganic binder. The sample granulated with PVC showed significant isotope fractionations when a 0.05 M (NH4)2CO3 solution was used as an eluent. The lighter isotope 6Li was preferentially fractionated into the exchanger phase. The isotope separation factor was roughly evaluated as 1.007, which is smaller than that (1.017) obtained by batch experiment in a preceding paper. The smaller separation factor could be explained by the fact that the number of sites effective for Li+ exchange is less than the number evaluated from the ion exchange capacity. The exchanger granulated with an inorganic binder did not show lithium isotope fractionation in spite of its large capacity for retention of lithium.

Preparation and ion-exchange properties of ion-sieve manganese oxide based on Mg2MnO4

A new type of ion-sieve manganese oxide (HMnO(2Mg)) was prepared by extracting magnesium from Mg2MnO4 with aqueous acid. The preparation conditions of HMnO(2Mg) and its ion-exchange properties were examined. The extraction of magnesium from Mg2MnO4 caused a decrease in the lattice constant of a spinel structure. The HMnO(2Mg) showed a selective adsorption of lithium from seawater when the Mg/Mn ratio of the sample was less than 1. The pH titration curve showed an affinity order of Cs ≒ K < Li above pH 3.5. The lithium-ion uptake increased with increasing solution pH and reached 3 meq/g at pH 12. The selectivity sequence was Na < Li < K < Rb < Cs for alkali metal ions at pH 3.1, while it changed to Na < Rb ≒ Cs < K < Li at pH 8. The selectivity sequences were Mg < Ca < Sr < Ba for alkaline earth metal ions and Ni < Zn < Cu < Co for transition metal ions at pH 3.1. The Li+-selective property is discussed based on the ion-sieve effect of the protonated octahedral sites at the cubic closed-packed oxygen framework of HMnO(2Mg).