Owino , Charles O., et al. “Removal of Cr3+ From Tannery Wastewater Using Unmodified And Acid-Modified Arabica Coffee Husk Adsorbent”. International Journal of Scientific Research in Chemical Sciences, vol. 8, no. 5, Oct. 2021, pp. 4-9, https://ijsrcs.isroset.org/index.php/j/article/view/102.