Solid leather wastes as adsorbents for cationic and anionic dye removal

The removal of anionic and cationic dyes from aqueous solutions was investigated by different leather shavings, which are solid wastes generated in the leather industry. Wet-blue leather shavings (WB), vegetable-tanned leather shavings (VT), pickled hide (not tanned) shavings (PIC) and wet-white leather (pre-tanned) shavings (WW) were used. The cationic dye was Basic Red 2 and the anionic dye was Acid Brown 414. Point of zero charge, functional groups, shrinkage temperature and adsorbent surface area were characterized. The point of zero charge was 4.0, 6.0, 3.9 and 4.1 for WB, VT, PIC and WW, respectively. The specific surface area showed low values which was expected for this type of material. Tanning agent influence was verified through shrinkage temperature analysis of leather shavings. Main functional groups of the acid dye and the collagen structure of the solid wastes were determined. The tests with Basic Red 2 solutions showed only VT had a considerable removal for this cationic dye (96.7%). The tests with Acid Brown 414 were carried out with different contact times and adsorbent mass. Results showed high efficiency of WW and PIC, whose percentages of dye removal were above 96% at contact time of 30 min and above 90% using 20 mg of adsorbent. In this way, the final dye removal was 98.1% and 98.3% for contact time tests and 97.7% and 98% for adsorbent mass tests for WW and PIC, respectively. These results highlight the promising use of leather shavings as alternative adsorbents for the treatment of wastewater containing dyes.