DISSOLUTION OF TIN FROM FE - SN MUD ORIGINATING FROM PRECIPITATION CLEANING OF TECHNOLOGICAL WASTE WATER
Abstract
Production of wastes in industry keeps rising and their production will be progressive until consistent recycling of wastes is put into practise. In the cleaning process of waste waters using precipitation method for undesirable elements removal heterogenous muds rise, which could represent suorces of great importance for recovery of nonferrous metals.
Mud which originates in cleaning of rinsing waters from the electrodeposition of tin on the sheet iron is a good example of such muds. As for the significant content of tin (between 30 to 35 %) this type of mud is getting to be an interesting source of tin recovery.The withdrawing of the main accompanying element - iron with a satisfactory efficiency is not possible to achieve using classical pyrometallurgical method. By hydrometallugical processing of the mentioned mud a solution could be obtained which is suitable for electrodeposition of tin or for production of various tin containing compositions.
This work deals with study of leaching the mud with the purpose of effective dissolution of tin as the first step of tin recycling. Dissolution experiments were run with not treated - wet mud and with treated - dry mud. In the first set of experiments the wet mud was leached stirring during 2 hours in concentrated chloric acid (37%) and in diluted (1:1) HCl at temperatures 20 and 45°C. In concentrated HCl also the effect of leaching time was followed up. The density of the slurry, it means relation between liquid and solid phase (L:S) varied. In the second set of experiments the dependence of tin dissolution efficiency on slurry density was studied. Dissolution tests with dried mud were carried out in concentrated chloric acid at the temperature of 20°C during 2 hours stirring. The contents of Sn and Fe in all products of leaching was analyzed.
It was found from the above mentioned experiments that the efficiency of tin dissolution from the Fe-Sn mud is satisfactory if the leaching process was carried out in concentrated chloric acid at the temperature of 20°C during 2 hours stirring while the relation liquid to solid phase was L:S = 2:1.The use of diluted chloric acid for leaching of the mud is impossible because of tin and iron hydrolysis. This backward reaction decreases the efficiency of tin dissolution and in the same time impairs the technological conditions of filtration. In order not to dilute the hydrochlic acid too much the use of wet (not treated) mud with water content higher than 30% is not recommended. The subsequent step in treatment of Sn-Fe solution will be a search for effective separation of Sn and Fe with effort to get pure tin and product reusable in iron production.
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