Microwave-assisted extraction of Cr from residual tanned leather: A promising alternative for waste treatment from tannery industry

Abstract

In this work, the feasibility of microwave (MW) energy and ethylenediaminetetraacetic acid (EDTA) as complexant for Cr removal from residual tanned leather were evaluated. The Cr-EDTA complex was removed from the leather surface applying washing cycles with hot water (50 ºC). The following experimental conditions were evaluated: complexation time (1–4 min), washing time (1–4 min), number of washing cycles (1−5) and complexant recycling (1–5 cycles). The morphology of untreated and treated residual tanned leather after microwave-assisted extraction (MAE) was characterized by scanning electron microscopy (SEM). After optimization of MAE process, the following conditions were selected: 3 g of residual tanned leather, 75 mL of complexant solution (3 mol L−1 EDTA), 60 °C and 3 min of complexation time. After extraction, 3 washing cycles (each cycle with 50 mL of water at 50 °C for 3 min) were applied reaching Cr removal of 99%. A green analytical procedure index was used to emphasize the greenness of the proposed treatment comparing with the literature, highlighting the suitability of MW for this purpose. Moreover, the proposed process is energy and reagents saving, taking into account the low extraction time and possibility of complexant recycling.