One of the ways to extract tin from tinplate waste is to dissolve tin in alkaline solutions containing metanitrobenzoic acid, followed by electrolysis. The process solution is a complex multicomponent system. In addition to free alkali and metanitrobenzoic acid, it may contain tin stannates and stannites, as well as various reduction products of nitrobenzoic acid (azoxy-, azo-, hydrazo- and other compounds). The formation of carbonates is inevitable due to the absorption of carbon dioxide from the air. ...