Abstract: This work chose single leaching agent for one-step or multi-step leaching, and a series of leaching agents was used for continuous extraction method to analyze the leaching concentration and toxicity assessment of chromium from chromium tanned, dyed and finished leather scraps. Results showed that the total chromium leaching mass concentration in leather scraps decreased with the extension of the stage. The highest total chromium leaching mass concentration of wet blue leather was 32.58 mg/L. The total chromium leaching mass concentration ranges of the dyed and finished leather were 11.16-16.51 mg/L and 9.43-13.28 mg/L, respectively. Using 1 mol/L sodium citrate for one-step leaching of each sample within 72 h, the total chromium leaching rate in the crushed materials also decreased with the continuation of the process, with leaching rates of 81.9%, 45.8% and 38.1%, respectively. The continuous extraction results showed that the alkali-soluble and acid-soluble chromium contents in samples with total chromium leaching mass concentration higher than the standard value were higher than other samples. Results of scanning electron microscopy, energy dispersive spectrometer and infrared spectroscopy indicated that both dyed and finished leather, treated with organic acid salts, retained the collagen fiber bundle structure, which provides a basis for the assessment of the effect of harmless disposal and recycling of chromium-containing shredded materials.

Key words: chromium-containing leather scraps, leaching toxicity, stability, continuous extraction method