连二硫酸锰碳化干渣热解回收硫酸钠的研究

Nowadays, there is an interest in fully applying on the reaction solution, such as desulfurization by pyrolusite or leaching pyrolusite with sulfur dioxide, for the purpose of controlling air pollution and the recovery of manganese salt. However, some researchers aimed at studying on the technological problem that there was a byproduct of S₂O₆^2-,which debase the main product of MnSO₄from the desulfurization solution. In the present work, a large amount of Na₂SO₄was prepared by the low temperature pyrolysis of Na₂S₂O₆, which was acquired as the precursor by MnS₂O₆that was carbonated by the carbonization reagent (NaHCO₃). During the thermal decomposition process of Na₂S₂O₆·2H₂O, the reaction products and the temperatures of the key steps of reaction processes were investigated and both of the reaction mechanisms and the kinetic parameters were deduced. The thermal decomposition experiments showed that 255 ℃ was the optimum temperature for the preparation of Na₂SO₄by the thermal decomposition of Na₂S₂O₆, which underwent two steps including dehydration and desulfurization. The characterization results of X-ray diffraction (XRD) and Ion chromatography (IC) showed that the decomposition product was the pure and single phase cubic sodium sulfate. The thermal decomposition process of Na₂S₂O₆was characterized by thermo-gravimetric analysis and differential scanning calorimetry analysis (TG-DSC), in which the activation energies (E_a) of dehydration and desulfurization were calculated by the combining Kissinger differential method and the Coats-Redfern integral method, respectively. The processes of dehydration and desulfurization of Na₂S₂O₆·2H₂O were controlled by phase boundary reaction model fitting shrinking sphere equation with theE_aof 14.75～18.11 kJ/mol for dehydration and 132.61～137.18 kJ/mol for desulfurization. SO₂was observed as the main decomposition gas. Finally, the reaction equations were demonstrated combined with the chemical analysis method. Based on realizing the resource recovery, this technology of the thermal decomposition of Na₂S₂O₆·2H₂O is feasible and used to avoid the acidic wastewater problem within the liquid-phase method, from which decomposition gas could reacted with sodium bicarbonate again during the process of thermal decomposition.