Beneficiation of low-grade manganese ore by hydrochloric acid leaching and high-value regeneration of acid medium

Nowadays, the high-grade manganese ore resources available in the world are run out gradually, while the demand for manganese is increasing; therefore, it is of great significance to research how to exploit and utilize abundant low-grade manganese ore resources economically and effectively. Aiming at the low-grade manganese ore in Indonesia, the process of beneficiating manganese ore by hydrochloric acid leaching and high-value regeneration of acid medium was proposed in this paper. Process mineralogy analyses were performed using X-ray diffraction, optical microscopy, and electron microscopy. The results show that the mineral composition mainly contains calcite and pyrolusite, followed by a small amount of pyrolusite, limonite, and kaolinite. The results of sieve analyses demonstrate that the manganese content in the manganese ore increases with the decrease of particle size. After coarse crushing, manganese middlings with manganese content of 33.32% (mass fraction) can be obtained by screening at 2 mm. The optimum conditions for leaching manganese middlings directly by hydrochloric acid are as follows: leaching pH is 3.0, leaching time is 1.5 h, rotating speed of agitator is 200 r·min⁻¹, and liquid-solid ratio is 4∶1 mL·g⁻¹. The grade of manganese concentrates obtained under the optimum conditions is 54.50% (mass fraction), and the calcium content is 0.57% (mass fraction). Dihydrate gypsum whiskers can be produced by the regeneration of hydrochloric acid at a common temperature, and the length-diameter ratio can be over 50. The regenerated hydrochloric acid is returned to leach manganese middlings. The grade of manganese concentrate and calcium content are 52.16% and 1.39% (mass fraction), which verifies the feasibility of this technological process. The X-ray diffraction (XRD) and scanning electron microscopy (SEM)/energy dispersive X-ray spectroscopy (EDS) results show that the main component of the manganese concentrate is pyrolusite, and the impurities are a small amount of limonite and kaolinite. Impurities will accumulate gradually as acid medium circulates, and they can be removed by hydrolysis precipitation method when Mg²⁺ concentration accumulates to 96.74 g·L⁻¹.