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应用旋转环盘电极研究了方铅矿在碳酸铵溶液中直接转化为碳酸铅的反应机理.并根据所拟定的机理,对稳态极化曲线进行了数学模拟.实验指出,当以10mV.s~(-1)扫描速度作暂态极化曲线时,在0.49,0.86及1.19V(SHE)三处出现氧化峰,第一峰产物为PbCO_3及S°,第二峰产物可能为PbCO_■及PbSO_4,第三峰产物可能含有PbO_(2(?))反应过程中经历了一系列硫的中间价态化合物.当以0.2mV.s~(-1)扫描速度作稳态极化曲线时,仅在0.28V处出现一个峰.根据拟定的反应机理进行数学模拟,推导出动力学关系式.

The kinetics of conversion of galena into lead carbonate in(NH_4)_2CO_3 solu-tions was studied using electrochemical method with a rotating ring-disc electrode.Reaction mechanism was proposed based on the results of transient polarizationstudies.A mathematical model was derived to simulate the steady state polariza-tion curves obtained.The oxidation of sulphide to sulphate should be proceeded in a number ofsteps with the formation of intermediate products,A rotating ring-disc electrodewas used to detect the intermediate products with galena as the disc electrode andAg as the ring electrode.Experimental transient polarization curves with a scan-ning rate of 10 mV/s have shown that at 0.49,0.86 and 1.19V(SHE)curfentpeaks were observed on the disc electrode and ring electrode respectively.Basedon the previous work and the experimental results obtained,it has been assumedlthat the first current peak of polarization represents the oxidation of leadsulphide to elementary S with PbCO_3 and S formed on the electrode surface aspassivation film.It is considered that the 2nd current peak of polarization curves representsthe conversion of S to PbSO_4 with lead carbonate and sulphate as the possiblepassivation film.The 3rd current peak has not been studied thoroughly in thepresent work.On steady polarization curves only one current peak(at 0.28V)was found.A kinetic equation for the anodic reaction based upon the mathema-tical model proposed has been derived as follow:(?)The reaction is 2nd order with respect to the NH_4~+ concentration and 1storder with respect to OH~- concentration respectively.When the electric potentialsapplied are rather low,the last two terms of the denominator may be neglected.Calculation based on this simplified equation has been found to represent theexprimental results satisfactorily.