This paper presents the efficacy of zerovalent iron nanoparticles (ZVINs), magnetic iron oxide nanoparticles (MINs), zero-valent iron nanoparticles/ sugarcane bagasse (ZVIN-SB) composite and magnetic iron oxide nanoparticles/sugarcane bagasse (MIN-SB) composite in immobilizing chromium present in tannery sludge. The optimized values for the immobilization of chromium by the adsorbents were found to be 48 h, 100 g/kg and 7, respectively, for time, adsorbent dosage and pH. The maximum uptake capacity was found to be 429.75, 539.25, 587.25 and 625.8 mg/kg, respectively, for ZVIN, MIN, ZVIN-SB and MIN-SB. The desorption study of the unamended sludge and sludge amended by ZVIN, MIN, ZVIN-SB and MIN-SB was carried out with three different desorbing media (0.1 N HCL, DIW and 0.1 N NaOH). It was found that the cumulative concentration of leachate chromium was more in basic condition than in neutral and acidic conditions. In column studies, the concentration of leachate chromium attained 0 mg/L at 24, 15, 18 and 14 pore volumes, respectively, for the sludge amended by ZVIN, MIN, ZVIN-SB and MIN-SB. The experimental adsorption data fitted well with pseudo-first-order kinetics. The zero-order kinetics accurately predicted the experimental desorption capacity (q e ) of the sludge amended by ZVIN, MIN, ZVIN-SB and MIN-SB. The Fourier transform infrared spectroscopy (FTIR) analysis showed that the amine, carboxyl, iron compounds, etc. present in the adsorbents were the chief causes for the immobilization of chromium. The X-ray diffraction (XRD) analysis of the sludge showed the presence of trivalent chromium compounds at a higher concentration. Nomenclature q t Amount of contaminant adsorbed/desorbed from sludge at time (min) (mg/kg) C 0 Initial concentration of the chromium (mg/L) C e Final concentration of the chromium (mg/L) V Volume of the solution (L) M Mass of the adsorbent (kg) C t (mg/ L) Concentration of the contaminant in the liquid at varying contact time W Weight of the sludge (kg) R 2Correlation coefficient q e Experimental uptake capacity/desorption capacity (mg/kg) Water Air Soil Pollut (2015) 226: 204 Calculated uptake capacity/desorption capacity (mg/kg) k 1 First-order kinetic rate constant (1/min) h Initial adsorption rate (mg/kg/min) t 1/2 Half-life time (min) k 2 Rate constant of pseudo-second-order equation (kg/mg/min) α Elovich kinetic constant initial adsorption rate (mg/kg/min) β Elovich kinetic desorption constant (kg/mg) k Rate constant of the power function (mg/kg/ min) kv Power kinetic specific adsorption rate at unit time (mg/kg/min) k 0 Zero-order rate constant (mg/kg/min) k p Parabolic diffusion rate constant (kg/g/ min 0.5 )
