It is known MnO2 ion sieve is an excellent adsorbent for Li (+) recovery from low lithium grade brine containing a high ratio of Mg to Li. However, the concentration of manganese ions dissolved along with Li+ during the desorption process with hydrochloric acid is very high and its mechanism of desorption has still not be elucidates. Here, acetic acid in aqueous solution is evaluated by the first time as an eluent in the desorption process of Li4Mn5O12 powder. A desorption mechanism of Li4Mn5O12 is proposed for the first time throughout analyses and correlations of experimental data, the construction of epsilon-pH diagram for the Mn-H2O system, and changes in its crystalline structures for the first time. The Mn dissolved in acetic acid 0.5 mol.L (-1) has been just 0.01%, which was less than that eluted with hydrochloric acid carried out for the sake of comparison. The desorption process of Li(+ )from Li4Mn5O12 was successfully achieved with a pH around 2.0. Meanwhile, the mechanism found is described by the simple H+-Li+ ion-exchange mainly occurring in the eluent with a high pH value, while both H+-Li+ ion-exchange and redox reactions occur in the eluent with low pH value. The Mn dissolution is mainly caused by the redox reactions.