A Novel Recycling Technology for Chrome Shavings Application of Non-Swelling Acids during Dechroming Process

Abstract

To separate and recycle collagen fibers and chromium from chrome shavings is important for the sustainable development of leather industry. However, the requirement of chromium content for a wide range of industrial applications of the recycled collagen fibers is limited to 50 mg/kg, which is challenging for the current dechroming methods. Hence, the goal of this work was to establish an efficient dechroming method to address this problem based on the OH- replacement and non-swelling acid application principles. In this study, the types of aromatic sulfonic acids and the parameters of the dechroming processes were optimized, and the tanning performance of the recycled chromium was investigated. The results indicated that disposal of the alkali treated chrome shavings with a mixed acids exhibited high dechroming extent and low extent of collagen hydrolysis, and the optimal ratio of sulfuric acid (20%) to optimized non- swelling acid-sulfone sulfonic acid was 7:1 at pH 1.0 and 25°C. The resultant collagen fibers retained their fiber structure and had a maximum hydrolysis extent of 10.6%, with a chromium content of 39.9 mg/kg. Additionally, the chromium in the dechroming filter liquor displayed good alkali precipitation property, and the chromium concentration of the precipitate’s supernatant satisfied the requirements for direct discharge, approximately 1.05 mg/L, and the recovered chromium exhibited good tanning performance. Therefore, the newly developed salt free chrome shavings treatment method is a promising resource recycling technology and may be helpful for the sustainable development of the leather industry