Revalorization of chromium-tanned leather shavings into carbon materials and re-tanning solution

Tannedleather is a product of high intrinsic value and a sign of luxury. Chromium-tanned leather shavings are abundantly produced wastes which contain chromium that could be revalorized. The present research proposes the use of alkaline hydrolysis, aided by an inorganic anion, to promote the hydrolysis of the Cr–O bond. De-chromed solids were employed to synthesize carbon material, which subsequently was applied for dye removal from aqueous solution, while the chromium-rich solution was used as a re-tanning agent. The results demonstrated that it is possible to develop a method of chromium-protein separation, with a minimum degree of hydrolyzation. When an activating agent was employed, the prepared carbon had a surface area of 585 m²/g, with trace levels of chromium (< 0.1%), present mainly as Cr₂O₃ particles. The materials displayed an adsorption capacity of up to 47.60 mg/g and 27.58 mg/g for methylene blue and Congo red respectively. The chromium-rich solution contained proteins and amino acids that aid in its employment as a re-tanning agent. Leather that was re-tanned with this solution had a similar tear strength and a superior and tensile strength (38%), superior elongation at break (10%), and improved elongation at break (47%) than traditional Cr33-tanned leather. The present study represents a major step in the development of cleaner production of leather. Graphical abstract: [Figure not available: see fulltext.].