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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.

The treatment of tanning wastewater was studied by means of reverse osmosis and ultrafiltration. Tests were carried out on laboratory scale using membranes of polyamide (reverse osmosis) and of polysulfone (ultrafiltration). The evaluation of the system was performed by chemical analysis, pH measurements and visible spectrophotometry. Effects of the protein contained in the industrial effluent, the applied pressure and the feed temperature on the permeate flux were analyzed. The polyamide membrane used allowed us to obtain permeates with a low chromium (III) content (7–10 mg/L) but with appreciable amounts of SO4= (1–3 g/l), Cl− (9–14 g/L) and Na+ (5–10 g/L). The presence of chromium (III) polymers was determined in the original effluent and in the concentrates obtained by reverse osmosis. Finally, it was established that during the operation of reverse osmosis, the transport of H+(H3O+) from the concentrate to the permeate was produced.

The isothermal and non-isothermal chlorination of a scheelite–wolframite concentrate with chlorine and sulphur dioxide was studied. Tests were made in a vertical reactor with a static bed and upward flow of reactive gases. The behaviour of the chlorination was analyzed from the identification of the volatile and non-volatile reaction products obtained in each case. The main identified reaction products were WO 2 Cl 2 , FeCl 2 , FeCl 3 , S 2 , FeS, CaSO 4 and CaCl 2 . Taking into account the most important physicochemical characteristics of the system, an empirical methodology to make chlorinations was proposed. The validity of the empirical methodology that we used was demonstrated utilizing data obtained under isothermal and non-isothermal conditions. Experimental results showed that the presence of non-volatile reaction products affects the chlorination under isothermal and non-isothermal conditions. A same kinetic dependence was found with both methods. Finally, the apparent activation energy and the rate constant of the reaction were determined through isothermal and non-isothermal methods.

The chlorination of wolframite and of scheelite with chlorine (chlorination agent) and sulphur dioxide (reducing agent) was studied within the temperature range 673–1173 K. The tests were carried out in a vertical reactor with a static bed. The greatest tungsten extractions (1173 K) were 86% from wolframite and 33% from scheelite. The behaviour of the chlorination reactions was analyzed through characterization of the reaction products obtained in each case. The principal reaction products identified were WO 2 Cl 2 , FeCl 3 , CaSO 4 and CaCl 2 . Likewise, size changes, specific surface areas and surface contents of calcium, tungsten, iron and manganese of both ores were studied during chlorination. By means of kinetic models it was determined that the wolframite chlorination is controlled by the movement of an interface and that the presence of reaction products affects the scheelite chlorination. Finally, a possible stoichiometry was proposed to explain the reaction of oxygen contained in the wolframite and in the scheelite.