A substitution-based method for chromium (III) leaching from chromium-tanned leather waste (CTLW) without destroying the collagen matrix was proposed. The leaching efficiency of Cr (III) from CTLW using different organic salts was investigated and sodium oxalate (OA-2Na) was considered to be the best Cr leaching agent. The effects of leaching time, temperature, pH, concentration, shaking speed and leather thickness on Cr leaching rate were investigated and a Cr leaching rate of 98% was obtained. Thermodynamic parameters (ΔG0 < 0, ΔH0 > 0 and ΔS0 > 0) were obtained in this study. The kinetic data fitted well with the first-order kinetic equation. The apparent activation energy (Ea = 82.9563 kJ/mol) and the frequency factor (A = 2.96 × 1011) were obtained. The collagen matrix remained intact after Cr leaching by the characterization of SEM and FTIR. A substitution mechanism was proposed that Cr (III) in CTLW was complexed with oxalate and dissociated from the collagen matrix.
Keywords: Chromium (III); Leaching kinetics; Leather waste; Sodium oxalate; Substitution mechanism; Thermodynamics.
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