Treatment of salt from hides curing stage by electrocoagulation for use in the pickling stage of the tanning industry

Luana Sarinho; Pedro Carvalho; Diana Patoilo; João Peres Ribeiro; José Baião da Cruz; Joaquim Gaião; Catarina Marques; Maria Isabel Nunes

doi:10.1016/j.envres.2023.117095

Treatment of salt from hides curing stage by electrocoagulation for use in the pickling stage of the tanning industry

Environ Res. 2023 Nov 15;237(Pt 2):117095. doi: 10.1016/j.envres.2023.117095. Epub 2023 Sep 6.

Authors

Luana Sarinho¹, Pedro Carvalho², Diana Patoilo³, João Peres Ribeiro⁴, José Baião da Cruz⁵, Joaquim Gaião⁵, Catarina Marques⁴, Maria Isabel Nunes⁶

Affiliations

¹ CESAM - Centre for Environmental and Marine Studies, Department of Environment and Planning, University of Aveiro, 3810-193, Aveiro, Portugal; CICECO - Aveiro Institute of Materials, Department of Chemistry, University of Aveiro, 3810-193, Aveiro, Portugal; DAO - Department of Environment and Planning, University of Aveiro, 3810-193, Aveiro, Portugal.
² CICECO - Aveiro Institute of Materials, Department of Chemistry, University of Aveiro, 3810-193, Aveiro, Portugal.
³ DAO - Department of Environment and Planning, University of Aveiro, 3810-193, Aveiro, Portugal.
⁴ CESAM - Centre for Environmental and Marine Studies, Department of Environment and Planning, University of Aveiro, 3810-193, Aveiro, Portugal; DAO - Department of Environment and Planning, University of Aveiro, 3810-193, Aveiro, Portugal.
⁵ CTIC - Centro Tecnológico das Indústrias do Couro, Apartado 158, São Pedro, 2384-909, Alcanena, Portugal.
⁶ CESAM - Centre for Environmental and Marine Studies, Department of Environment and Planning, University of Aveiro, 3810-193, Aveiro, Portugal; DAO - Department of Environment and Planning, University of Aveiro, 3810-193, Aveiro, Portugal. Electronic address: isanunes@ua.pt.

PMID: 37683784
DOI: 10.1016/j.envres.2023.117095

Abstract

The raw materials for the tanning industry, namely hides and skins, are preserved (curing stage) and carried with common salt, i.e., sodium chloride (NaCl). Proceeding to conversion into leather, pickling is a key stage of the tannery process, which entails high demand of water and salt. In this work, the salt-derived brine (SdB) generated from the curing of hides was treated by iron-driven electrocoagulation (EC), aiming at its later application in the pickling stage of the tanning industry, promoting a transition to zero waste emission policy. Focusing on reducing the brine's total organic carbon (TOC), central composite rotational design and response surface methodology were adopted to study the effect of electrolysis time (6.2-14.2 min) and current density (74-431 A·m^-2) on the treatment of the SdB (≅ 7.5 % wt. NaCl). The quality of the treated brines was then assessed in pickling trials and compared with virgin brine. 68-83 % removal of TOC from the SdB were achieved under electrolysis time ranging 6.2-14.2 min and current density ranging 126-252 A·m^-2. Under these operating ranges the quality of the wet-blue leathers was guaranteed. Lowest power consumption (0.44 kWh·m^-3) was achieved under electrolysis time of 6 min and current density of 126 A·m^-2, yielding 68 % removal of TOC. Moreover, the shrinkage temperature of the hides was improved with treated brine (103.5 °C-110.5 °C) compared to virgin brine (103.0 °C). The present study provides strong evidence that contaminated salt from the curing stage can be valorised within the tanning industry through electrocoagulation treatment and then used in another production stage, instead of being landfilled.

Keywords: Contaminated salt; Electrocoagulation; Pickling; TOC; Tanning; Valorisation.