Encyclopedia of Membranes

2016 Edition
| Editors: Enrico Drioli, Lidietta Giorno

Leather Industry, Unhairing-Liming

  • Alfredo Cassano
Reference work entry
DOI: https://doi.org/10.1007/978-3-662-44324-8_1349

The aim of the unhairing-liming step is to remove from the raw skin all the components which are not transformed into leather, such as the superficial epidermis including the hair and the subcutaneous adipose layer. The liming step introduces chemicals such as lime (Ca(OH)2) and sodium sulfide (Na2S) or sodium hydrosulfide (NaHS) which open the fibrous structure of the skin. Consequently, exhausted effluents are highly polluted for the presence of sulfide, amines, organic matter coming from degradation of hairs and epidermis, and high concentration of alkalis. The COD of exhausted effluents ranges between 20,000 and 40,000 mg/L of consumed oxygen.

The UF treatment of the exhausted unhairing liquor has been one of the first membrane approaches introduced in the leather industry (Molinari 1995). It can be exploited to recover sulfide and solubilized lime together with low molecular weight proteic substances in the permeate stream in order to reuse the purified solution for the...
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References

  1. Cassano A, Drioli E, Molinari R (1998) Integration of ultrafiltration into unhairing and degreasing operations. J Soc Leath Technol Chem 82:130–135Google Scholar
  2. Molinari R (1995) Application of membrane separation techniques to the treatment of tanneries wastewaters. In: Caetano A, De Pinho MN, Drioli E, Muntau H (eds) Membrane technology: application to industrial wastewater treatment. Kluwer, The Netherlands, pp 101–122CrossRefGoogle Scholar

Copyright information

© Springer-Verlag Berlin Heidelberg 2016

Authors and Affiliations

  1. 1.Institute on Membrane Technology, National Research Council of Italy, ITM-CNRRendeItaly