Tin (II) sulfate is an important precursor for tin metal and is used in a variety of applications. It is particularly useful for tinning printed circuits. However, it has not been widely studied.
The present invention relates to a process for preparing tin (II) sulfate from aqueous sulfuric acid. This process is suitable for producing tin (II) sulfate solutions that are moderate to highly concentrated. In the course of the electrolytic process, a tin-containing coating develops at the anode.
The anode and cathode spaces are separated by a diaphragm. Diaphragms have a wall thickness of at least five mm and a pore volume of at least forty percent. They are sintered at a temperature of at least one thousand degrees Celsius.
After the electrode polarity is reversed at specific time intervals, the anode sludge is reworked up into tin compounds. As a result, the anode provides all of the tin needed to conduct the electrolytic reaction.
Tin (II) sulfate in aqueous sulfuric acid is soluble, but the concentration decreases with increasing sulfuric acid. Therefore, the solubility is less than fifteen grams per liter.
Electrolytic processes using organic anion-exchange membranes are suitable for tin (II) sulfate production. Organic membranes have small pore volumes and are permeable to several different ions. These organic membranes can be employed in wet chemical processes. Wet chemical processes are costly and take a long time to process. Nevertheless, they are economical compared to electrolytic processes.
Another disadvantage of organic membranes is the secondary reactions. Some of these reactions are unstable at high temperatures and therefore are not economically beneficial.