Evaluation of Chemical Products in Leather Post-Tanning Process and Their Influence in Presence of Neutral Salts in Raw Tannery Effluent

Abstract

In the leather industry, several chemical products are used forthe transformation of the raw hide into the demanded finalproduct. The production flow and the post-tanning of wet-blueleathers may vary according to the available technologies and thetype of final item produced. Previous operations and processesare also relevant, particularly the steps of unhairing-liming andtanning process. During the effluent treatment process, there isa great difficulty in removing soluble salts, such as sodiumchloride and sodium sulfate in conventional effluent treatmentstations. These salts might compromise the biological treatmentof tannery wastewater and adversely impact the receiving waterbodies, causing environmental pollution. Further, the presenceof chlorides and sulfates might interfere in the implementationof the bath reuse system or in the recycling of the treatedeffluents in the post-tanning process. Therefore, this work aimsto investigate the measures used to control the production ofsodium neutral salts, such as the sodium chlorides and sulfates,contained in the chemical compounds uses in the industry thatperforms post-tanning in bovine wet-blue leather, mostly forautomotive and furniture upholstery. The work was carried outfollowing the production of the factory for six months, withapproximately 1485 whole wet-blue leathers being processed perday, with an average production of 7500 m² of crust leathers perday. The work methodology was based on the diagnosis of theinitial situation of the tannery, chemical analyses of the suppliesemployed and in proposals of action based on this initial profile.The work also involves the checking of the water consumptionand the evaluation of the residual baths. The identification of thechemical products in the formulation that contribute directly tothe presence of neutral salts in the gross effluent and theirpresence in the residual baths were among the main results observed in the present work. In order to determinate sodium,chlorides and sulfates, two methodologies were tested (ionchromatography, for chlorides and sulfates; and absorptionspectroscopy, for sodium), showing similar results.