Abstract

Manganese is one of the most difficult elements to be recovered from its respective solutions, due to its high solubility in both acid and neutral conditions. However, metal carbonate precipitation as manganese carbonate can be an effective way for its recovery. In this study, manganese carbonate (MnCO₃) was precipitated by mixing an aqueous solution of manganese sulfate (MnSO₄ containing 85% Mn²⁺) and sodium carbonate (Na₂CO₃) in different proportions. The maximum (∼72%) manganese was precipitated as MnCO₃ at a pH value of 3 for 5 g Na₂CO₃ at 80 °C and 40-min reaction duration. X-ray diffraction of precipitated sample confirmed the formation of single-phase rhodochrosite (MnCO₃). The observed microstructure comprised coarse grains composed of 15.69 wt.% C, 41.78 wt.% O, and 30.8 wt.% Mn along with Na and S as minor impurities. FTIR confirmed the presence of the characteristic MnCO₃ band at 724 cm⁻¹ corresponding to the C–O (CO₃^2–) bond. The kinetic study of the process indicated that the reaction process followed the first-order kinetics. The reaction rate constants were observed to gradually increase with increasing reaction temperature, and the apparent activation energy was calculated to be 27.338 kJ.mol⁻¹ demonstrating the existence of energy barrier between the reactants and products. A spontaneous and an endothermic nature of chemical reaction has been revealed by the thermodynamic parameters of activation (ΔH^#, ΔS^#, and ΔG^#), accompanied by the entropical changes at solid solution interface during precipitation.

摘要

锰是最难从其各自溶液中回收的元素之一，因为它在酸性和中性条件下均具有很高的溶解度。然而，作为碳酸锰的金属碳酸盐沉淀可以是其回收的有效途径。在这项研究中，通过混合不同比例的硫酸锰（MnSO ₄含有 85% Mn ²⁺）和碳酸钠（Na ₂ CO ₃）的水溶液来沉淀碳酸锰（MnCO ₃）。对于 5 g Na ₂ CO ₃，在 pH 值为₃时，最大 (~72%) 锰以 MnCO _{3 的形式}沉淀。在 80 °C 和 40 分钟的反应时间。沉淀样品的 X 射线衍射证实了单相菱锰矿 (MnCO ₃ ) 的形成。观察到的显微组织包括由 15.69 wt.% C、41.78 wt.% O 和 30.8 wt.% Mn 以及作为微量杂质的 Na 和 S 组成的粗晶粒。FTIR 证实了在 724 cm ^-1处存在与 C-O (CO ₃ ^2- ) 键相对应的特征性 MnCO _3带。该过程的动力学研究表明，反应过程遵循一级动力学。观察到反应速率常数随着反应温度的升高而逐渐增加，表观活化能为27.338 kJ.mol ^-1证明反应物和产物之间存在能垒。活化的热力学参数（ΔH ^#、ΔS ^#和 ΔG ^#）揭示了化学反应的自发和吸热性质，伴随着沉淀过程中固溶体界面的熵变化。