Making of iron(III) tanning salts from a waste of the titanium recovery by the sulphate process

Abstract

The making of iron(III) tanning salts from iron(II) sulphate heptahydrate, sulphuric acid and potassium acid tartrate (cream of tartar) was studied. The iron(II) sulphate heptahydrate was obtained from the titanium recovery by the sulphate process. The manufacture started with the thermal oxidation of the iron(II). Then, iron(III) soluble complexes were formed with the addition of sulphuric acid and cream of tartar. The tanning salts were obtained in form of fine particles by spray drying. The stability (texture and chemical composition) of the tanning salts so prepared was evaluated by physicochemical parameters. Whereas, the tanning capacity of these salts was determined from the tannage of goat skins. The analysis of the wet brown leathers elaborated was carried out by means of the hydrothermal shrinkage temperature. The prepared salts had an acceptable tanning capacity but its stability was unsuitable. To improve this fact, the formation of the iron(III) soluble complex into the reactor where the tannage occurs was performed. The new methodology was easy to be made and with this alternative it was possible to avoid the troubles produced in the tanning salts obtained in the form of fine particles.