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The use of vegetable tanning materials in leather processing has drawn attention as an alternative to basic chromium sulphate for its natural abundance and environmental aspects. In this work, an attempt has been made to extract vegetable tannins from Xylocarpus granatum bark using different solvents (e.g., water, methanol, ethanol, and chloroform) and compare with conventional vegetable tanning agents such as mimosa and quebracho. The highest extraction efficiency was observed 31.22% by methanol. The presence of tannin content and polyphenolic compounds, e.g. (-)epicatechin (503 mg/100 g dry extract), catechin hydrate (218 mg/100 g dry extract), catechol (29 mg/100 g dry extract) were ensured by UV–Vis, FT-IR spectroscopy and HPLC. Again, condensed tannins, moisture content, and pH of the methanol extracted tannin were found 47.80%, 5.82%, and 3.97 respectively. The leather tanned by Xylocarpus granatum tannin showed a shrinkage temperature of 86.34 ± 1.52 °C. Other properties such as tensile strength, tear strength, grain cracking load, and distention at grain cracking were comparable to conventional vegetable-tanned leather. The cross-sectional morphology of the tanned leathers was also characterized by scanning electron microscopy (SEM) which revealed a compact structure of the leather fibers. In light of the findings from the study, X. granatum bark tannin could be a well alternative to chromium and a new source of vegetable tannin for the leather industry. Graphical Abstract

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Worldwide, tannery sludge management has become a big challenge due to containing heavy metals, especially chromium. In this study, phytoextraction of heavy metals from tannery sludge by Napier grass (Pennisetum purpureum) is presented.Heavy metals-chromium (Cr), copper (Cu), zinc (Zn), and lead (Pb) in tannery sludge were found at 12686, 371, 265, and 66 mg/kg, respectively. Separately, Napier grass was harvested on raw tannery sludge and garden soil and examined for 16 and 20 weeks after the sowing of seeds. Metal extraction from tannery sludge in Napier