Vegetable tannins and chromium solutions are used in the leather industry in order to convert hides and skins into leather. Unfortunately, these compounds do not react completely with the skins so that, at the end of the process, their concentration in the exhausted liquor is still significant. Tannins and chromium recovery from exhausted tanning baths has a significant advantage in terms of their reuse in the production cycle and for the simplification of the depolluting processes of tannery wastewaters. In this work a nanofiltration (NF) process was studied in order to increase the tannin/non tannin (T/NT) ratio of exhausted liquors coming from the vegetable tannage and to produce a retentate solution suitable for the preparation of new tanning baths. A NF membrane module was identified for the treatment of exhausted liquors coming from different tanneries involved in the production of sole leathers. An integrated membrane process was also studied for the recovery of chromium from exhausted liquors of the chromium tannage. A preliminary ultrafiltration (UF) of the chromium liquors permitted to remove the most part of total suspended solids (TSS) and fat components from the exhausted liquor. The permeate, containing about 3 g/l of chromium (III), was submitted to a NF process in order to obtain a retentate solution suitable for its reuse in the chromium tannage. The permeate, containing a high chloride concentration, was reused in the pickel operation before the tannage. The proposed process have significant advantages in terms of: saving of water and chemicals, reduction of environmental impact, simplification of depolluting processes of tannery wastewaters, reduction of energetic consumption. The quality of the finished leathers treated with the recovered solutions was very similar to that of skins treated with conventional solutions, as confirmed by chemical and physical analyses performed on control and experimental skins.
Tannins and chromium recovery in the leather industry by membrane operations
A Cassano;E Drioli
2005
Abstract
Vegetable tannins and chromium solutions are used in the leather industry in order to convert hides and skins into leather. Unfortunately, these compounds do not react completely with the skins so that, at the end of the process, their concentration in the exhausted liquor is still significant. Tannins and chromium recovery from exhausted tanning baths has a significant advantage in terms of their reuse in the production cycle and for the simplification of the depolluting processes of tannery wastewaters. In this work a nanofiltration (NF) process was studied in order to increase the tannin/non tannin (T/NT) ratio of exhausted liquors coming from the vegetable tannage and to produce a retentate solution suitable for the preparation of new tanning baths. A NF membrane module was identified for the treatment of exhausted liquors coming from different tanneries involved in the production of sole leathers. An integrated membrane process was also studied for the recovery of chromium from exhausted liquors of the chromium tannage. A preliminary ultrafiltration (UF) of the chromium liquors permitted to remove the most part of total suspended solids (TSS) and fat components from the exhausted liquor. The permeate, containing about 3 g/l of chromium (III), was submitted to a NF process in order to obtain a retentate solution suitable for its reuse in the chromium tannage. The permeate, containing a high chloride concentration, was reused in the pickel operation before the tannage. The proposed process have significant advantages in terms of: saving of water and chemicals, reduction of environmental impact, simplification of depolluting processes of tannery wastewaters, reduction of energetic consumption. The quality of the finished leathers treated with the recovered solutions was very similar to that of skins treated with conventional solutions, as confirmed by chemical and physical analyses performed on control and experimental skins.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
