Reduction of lead and zinc sulphates by hydrogen

Authors: Stanisław Małecki

Publish Date: 2015/03/18

Volume: 121, Issue: 2, Pages: 861-866

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Abstract

In this paper the results of the thermogravimetric tests reduction of lead and zinc sulphates by hydrogen are presented Tests performed under isothermal conditions allowed to determine the effect of temperature on the formed products of the reaction The temperatures at which the maximum content of sulphides present in the products of reduction were determined For the reduction of lead sulphate value of the activation energy of the process and the participation of partial reactions in the process were determinedThis paper represents a fragment of the research on the reduction of metal sulphates In the literature the problem of thermal reduction of metal sulphates is quite simply treated Research using CO for the reduction is presented only by the authors 1 They concern the reduction of magnesium sulphate The results of the metal sulphates reduction by hydrogen were presented in the papers 2 3 The authors indicate the reduction temperature range and products obtained in these temperatures However these results are rather qualitative without going into the chemical and phase composition of the process products Vijh 4 presents an analysis of the sulphate reduction temperature dependence of the selected physicochemical parametersThis work relates to the research on the reduction of lead sulphate PbSO4 and zinc sulphate ZnSO4 in a hydrogen atmosphere under isothermal conditions The applied thermogravimetric method allowed us to perform calculations of phase composition of the reaction products and determine the contribution of each simple reaction in the whole process This made it possible to determine the temperatures at which in the products is formed the largest amount of sulphidesFor the research were used lead and zinc sulphates of analytical grade Zinc sulphate contains 7 water molecules and before the reduction the process was subjected to dehydration at a temperature of 723 K Preliminary investigations carried out with increasing temperature allowed us to determine the temperature range for isothermal measurements They have been defined the temperature range for the lead sulphate at 873–973 K and for zinc sulphate at 853–973 KInvestigations on reduction of lead and zinc sulphates were carried out by thermogravimetry method using Thermal Analyzer TA1 Mettler A sample of defined mass is placed in a furnace through which flowed hydrogen at the amount of 15 dm3 h−1 The stream of flowing hydrogen was selected so that it did not affect the process rate The temperature in the furnace was controlled by a Pt–RhPt thermocouple placed directly underneath the tested sample The sample was heated to isothermal temperature with rate of 25° min−1 During the process the sample mass change was recorded over time Masses of sulphate samples were practically identical for each temperature measurement and amounted approximately 300 mg Process time was measured from the moment of insertion of the sample into the furnace to establishment of a constant mass Each measurement was repeated three times and the results were averagedThe recorded mass losses indicate that in the case of lead sulphate reduction the total sample mass change is between the values of the reaction course from lead sulphide to lead metal whereas the mass loss of the zinc sulphate reduction is between the values of the reaction course from zinc sulphide to zinc oxide In the first case phase analysis indicated only the occurrence of lead sulphide and metallic lead in products while in the second case zinc sulphide and zinc oxide

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