The traditional leather processing cycle is characterised by the production of wastewaters containing various inorganic as well as organic materials which create serious problems in terms of environmental impact. In particular, conventional tannage operations produce exhausted liquors containing significant amounts of tanning substances (such as vegetable tannins and chromium salts) not consumed in the process: so the discharge of the exhausting liquors represents a damage both form economical and environmental point of view. Membrane processes, successfully used on large scale in various industrial processes, are a valid approach for the recovery of the primary resources and for the separation, purification and concentration of the products. In this work a nanofiltration (NF) process was used to increase the tannin/non tannin ratio of exhausted liquors coming from the vegetable tannage and to reuse the retentate solution for the preparation of new tanning baths. A suitable membrane module was identified for the treatment of exhausted baths coming from different tanneries involved in the production of sole leathers. The exhausted liquors were processed according to a batch concentration mode up to reach the desired tannin/non tannin ratio. A technically viable method for recovering chromium salts from exhausted tanning liquors was also investigated. In particular, an integrated process based on a preliminary ultrafiltration (UF) treatment of the exhausted liquor, followed by a NF process of the UF permeate, was studied on laboratory scale. The UF process permitted to obtain a remarkable reduction of suspended solids and fat substances. A tanning solution with a chromium (III) concentration of about 10 g/l was obtained in the NF process. The recovered solutions were employed in experimental tannage tests on skins destined to the production of sole and cloth leather. The experimental skins were compared with control skins treated according to the conventional method. Chemical and physical analyses performed on the experimental skin samples revealed values very similar to those of the control group. The investigated processes permit to rationalize the tanning cycle of the leather industry guarantying a series of advantages such as: simplification of the cleaning-up process of wastewaters, easy reuse of sludges, saving of chemicals and water, reduction of wastewater discharge and pollution load and decrease of disposal costs.
Recovery of tanning substances from exhausting effluents of the leather industry by membrane operations
Cassano A;Drioli E
2007
Abstract
The traditional leather processing cycle is characterised by the production of wastewaters containing various inorganic as well as organic materials which create serious problems in terms of environmental impact. In particular, conventional tannage operations produce exhausted liquors containing significant amounts of tanning substances (such as vegetable tannins and chromium salts) not consumed in the process: so the discharge of the exhausting liquors represents a damage both form economical and environmental point of view. Membrane processes, successfully used on large scale in various industrial processes, are a valid approach for the recovery of the primary resources and for the separation, purification and concentration of the products. In this work a nanofiltration (NF) process was used to increase the tannin/non tannin ratio of exhausted liquors coming from the vegetable tannage and to reuse the retentate solution for the preparation of new tanning baths. A suitable membrane module was identified for the treatment of exhausted baths coming from different tanneries involved in the production of sole leathers. The exhausted liquors were processed according to a batch concentration mode up to reach the desired tannin/non tannin ratio. A technically viable method for recovering chromium salts from exhausted tanning liquors was also investigated. In particular, an integrated process based on a preliminary ultrafiltration (UF) treatment of the exhausted liquor, followed by a NF process of the UF permeate, was studied on laboratory scale. The UF process permitted to obtain a remarkable reduction of suspended solids and fat substances. A tanning solution with a chromium (III) concentration of about 10 g/l was obtained in the NF process. The recovered solutions were employed in experimental tannage tests on skins destined to the production of sole and cloth leather. The experimental skins were compared with control skins treated according to the conventional method. Chemical and physical analyses performed on the experimental skin samples revealed values very similar to those of the control group. The investigated processes permit to rationalize the tanning cycle of the leather industry guarantying a series of advantages such as: simplification of the cleaning-up process of wastewaters, easy reuse of sludges, saving of chemicals and water, reduction of wastewater discharge and pollution load and decrease of disposal costs.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
