Recovery of chromium(III) from wastes of uncolored chromium leathers. Part II. Solvent extraction of chromium(III) from alkaline protein hydrolyzate

Experimental studies were made on the solvent extraction of chromium(III) with Aliquat 336 from the protein hydrolyzate obtained by the alkaline hydrolysis of wastes of uncolored chromium-tanned leathers. The effects of NaOH concentration in the protein hydrolyzate, contact time of the organic and aqueous phases, the aqueous/organic phase volume ratio, and temperature on the extraction of chromium(III) and collagen proteins/peptides were examined. Stripping of chromium(III) from the loaded organic phase is also presented. Chromium(III) can be efficiently removed (99%) from the alkaline hydrolyzate by the solvent extraction with Aliquat 336 after 60–90 min at temperature 50 °C and at the aqueous/organic phase volume ratio equal to 5/1. Moreover, it was found that during one cycle of the alkaline hydrolysis followed by the extraction and stripping operations, chromium(III) can be separated from the source leather wastes with the total yield over 90%. The final products are: the protein hydrolyzates contaminated with traces of Cr(III) (less than 5 ppm) and the solutions of chromium(III) sulfate containing small quantities of protein substances.

► Alkaline protein hydrolyzate with Cr(III) results from leather wastes decomposition.
► Extraction with Aliquat 336 enables removal of 99% of Cr(III) from feed hydrolyzate.
► Onestep process: alkaline hydrolysis-extraction-stripping gives two final products.
► First one protein hydrolyzate contaminated only with less than 5 ppm of Cr(III).
► Second one chromium(III) sulfate solution with small amounts of protein substances.