连二硫酸锰碳化干渣热解回收硫酸钠的研究

Study on Thermal Decomposition Mechanisms and Recovery of Sodium Sulfate from Manganese Dithionate After Carbonization

利用软锰矿进行烟气脱硫或湿法冶金技术研究时,因其既可控制大气污染物二氧化硫亦可回收锰资源而备受关注。然而,反应过程会生成影响脱硫尾液中硫酸锰品质的副产物连二硫酸锰(杂质),如何回收或去除该杂质是新技术研发和推广的难题。作者提出了连二硫酸锰先经碳酸氢钠碳化得到连二硫酸钠和碳酸锰,两产物分离后,结合低温热解的方法将连二硫酸钠制备成无水硫酸钠;实验考察了热解制备过程的各产物和控制反应步骤的温度,进而推理出动力学参数和反应机理。热解实验结果表明:255℃是连二硫酸钠热解制备无水硫酸钠的最佳热解反应温度,并且热解反应过程经历脱硫和脱水两大步骤;热解产物的X射线衍射(XRD)和离子色谱(IC)表征结果表明:最终产物为单一相的立方体结构硫酸钠晶体。利用热重示差扫描热分析(TG–DSC)对连二硫酸钠热解过程进行表征,结合Kissinger微分法和Coats–Redfern积分法对热解法脱水和脱硫过程中的活化能进行推算,脱水和脱硫活化能分别在14.75~18.11 kJ/mol和132.61~137.18 kJ/mol范围内。热解尾气测定结果表明:连二硫酸钠热解制备无水硫酸钠时释放出的尾气主要为二氧化硫。因此,经低温热解工艺处理软锰矿脱硫尾液中连二硫酸根的方法是可行的,不仅可以避免液相处理工艺中酸性废水产生的问题,还可以利用热解制备过程中的尾气去除残留的碳化剂(碳酸钠),以达到资源化回收目的。

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 S2O62–,which debase the main product of MnSO4 from the desulfurization solution.In the present work,a large amount of Na2SO4 was prepared by the low temperature pyrolysis of Na2S2O6,which was acquired as the precursor by MnS2O6 that 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 Na2SO4 by 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 Na2S2O6 was characterized by thermo-gravimetric analysis and differential scanning calorimetry analysis(TG–DSC),in which the activation energies(Ea)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 the Ea of 14.75~18.11 kJ/mol for dehydration and 132.61~137.18 kJ/mol for desulfurization.SO2 was 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.