Electrochemical separation of chromium/collagen from wet blue in a single step: recycling of tannery waste to promote a circular economy

• Cr 3+ was separated from wet blue chromium shaving (WBCS) using a three-compartment reactor separated by cationic membranes. • The process involves performing two reactions simultaneously, NaCl electrolysis and WBCS hydrolysis, in the cathode compartment. • 99 % of Cr 3+ was separated as Cr(OH) 3 , which can be recycled to the tanning process. The leather industry produces tons of solid waste containing significant amounts of chromium. Without any safe deposition, these can potentially pollute the environment. This article develops an electrochemical method to remove chromium and separate collagen from wet blue chromium shaving (WBCS). The raw WBCS had an initial content of 28.5 g Cr 3+ /Kg. The process was carried out in a three-compartment electrochemical reactor assembled with cationic membranes, using graphite and titanium as electrodes. The single-stage process produces NaOH by electrolysis of NaCl solution, while OH- hydrolyzes the collagen from WBCS in situ. The influence of NaCl concentration 1–10 g/L, reaction time 0.5 - 5 h, temperature 60 - 99 °C, and current density were studied. The products were analyzed using FTIR, UV–vis spectrophotometry and TGA. NaOH was generated proportional to NaCl concentration and current density. WBCS hydrolysis varied with OH − concentration, temperature, and time. The conditions to achieve the highest chrome-collagen separation were 5 g NaCl/L, pH 11.7, 0.31 A/cm 2 , 90 °C, during 1 - 2 h of reaction. Chromium precipitates as amorphous Cr(OH) 3 at a pH higher than 10, while collagen remains in the aqueous phase. Over 99 % of Cr 3+ extraction from WBCS was achieved. An analysis of the process sustainability was made for byproducts reuse in the tannery.