铝酸钠溶液中硫对低碳（合金）钢的耦合腐蚀行为机理研究

Sulfur transform into sodium aluminate solution for different forms (S2-, S2O32-, SO32-, SO42-) during alumina production process with high sulfur bauxite, which corrosion of equipment seriously, the mechanism is not clear. So, salt spray corrosion method is used to research the influence of sulfur in NaOH solution and sodium aluminate solution on carbon (alloy) steel corrosion respectively. Corrosion potential and corrosion current density of specimen under static and dynamic conditions are monitored by potentiodynamic polarization method and electrochemical impedance spectroscopy, the main factors of sulfur corrosion on the material under complex conditions are explored. The evolution laws of products’ micro-morphology, conformation and composition are analyzed by IR, SEM, EDS and X-ray diffraction. Inhibition mechanism of aluminum on sulfur corrosion in sodium aluminate solution is analyzed theoretically, while coupling corrosion mechanism of different forms sulfur on carbon (alloy) steel for equipment is revealed. And then seed and evaporation conditions are simulated, immersion corrosion test at high temperature is conducted by steel bombs. The inherent laws of passivation film evolution and stability with composition factors is studied. Comparative analysis with former, establishing corrosion kinetics model, forecasting equipment’s corrosion life will promote the application of high sulfur bauxite as well as define the critical value that sulfur do not cause corrosion damage on equipment materials.

高硫铝土矿生产氧化铝过程中硫以各种形态（S2−、S2O32-、SO32-、SO42-）转入铝酸钠溶液，对设备材质造成严重的腐蚀，机理尚未明确。项目首先采用盐雾腐蚀方法，分别研究苛碱溶液与铝酸钠溶液中硫对低碳（合金）钢腐蚀性能的影响规律，通过动电位极化法、电化学阻抗谱法，监测试样在静态和动态条件下的腐蚀电位与腐蚀电流密度，探索复杂条件下硫对材质腐蚀的主要控制因素；采用红外光谱、扫描电镜、能谱仪、X衍射仪等仪器，分析产物显微形貌、结构与成分的演变规律，建立腐蚀速率方程，从理论上分析铝酸钠溶液中铝对腐蚀的抑制规律，揭示各形态硫对设备常用低碳（合金）钢的耦合腐蚀机理；进而模拟种分与蒸发条件，利用钢弹群釜进行高温浸泡腐蚀，研究成分因子与钝化膜演变及稳定性的内在规律，建立腐蚀动力学模型，预测设备的腐蚀寿命，确定铝酸钠溶液中硫对设备材质不造成腐蚀危害的临界值，有助于高硫铝土矿的推广应用。

高硫铝土矿拜耳溶出后铝酸钠溶液中硫以S2-、S2O32-、SO32-、SO42-等形态存在，低价态的硫对设备材质（Q235和16Mn钢）造成较为严重的腐蚀。基于这一现状，本项目开展了系统研究，获得主要结论：（1）研发了一种铝酸钠溶液中各种硫化物测定新方法，在快速、准确测定S2-的基础上，采用硝酸银和醋酸的协同效应测量溶液中S2O32-；（2）S2-与S2O32-同时存在时产生“耦合腐蚀”效应，在纯氢氧化钠溶液中，浓度均为5 g/L时两种钢的耦合腐蚀速率出现峰值； Q235钢的腐蚀产物主要由FeS、FeS2和Fe3O4组成，16Mn钢主要为FeS、MnS、Fe3O4和FeOOH；腐蚀介质中氧化铝浓度增加，腐蚀速率逐渐下降；（3）在含硫铝酸钠溶液中，16Mn钢的腐蚀速率大于Q235钢，S2-和S2O32-浓度分别为4 g/L和3 g/L时腐蚀速率出现峰值；初期腐蚀速率急剧降低，腐蚀速率方程为R=A∙t^n，腐蚀物主要为铁的硫化物；腐蚀5天后的腐蚀速率下降趋于缓慢，腐蚀产物由铁的硫化物逐渐向铁的氧化物转变。腐蚀动力学参数（反应级数n、活化能E_a和速率常数k）揭示了两种钢的腐蚀速率变化规律。（4）电化学研究表明，Q235和16Mn钢在铝酸钠溶液中均发生钝化现象；Q235钢的腐蚀主要受电荷转移控制，而16Mn钢的腐蚀在S2O32-单独存在时受电荷转移控制，其它条件以传质为控制。在耦合条件下，当S2-浓度较低时，两种钢的电极过程由电荷转移及扩散共同控制，当S2-浓度较高时，主要受电荷转移控制。S2O32-浓度对16Mn钢腐蚀动力学的影响相反；（5）Q235和16Mn钢的腐蚀速率影响大小依次：腐蚀时间、S2-浓度、腐蚀温度、S2O32-浓度。对数GM(1,1)修正模型优于开n次方GM(1,1)修正模型。在高硫铝土矿推广过程中，研究结果有利于硫含量的控制及设备材质的选择。