Biosorption of indigo carmine from aqueous solution by Terminalia Catappa shell

[Display omitted] •Terminalia catappa shell was used as biosorbent for indigo carmine removal from aqueous solution.•The optimum conditions were pH 2, contact time 30 min and initial concentration 600 mg L−1.•The biosorption capacity of the biosorbent for indigo carmine was 26.77 mg g−1.•Pseudo-second order kinetics and Freundlich isotherm model were the best fit.•The biosorption process was spontaneous and exothermic. Synthetic dyes from liquid waste can harm people or the environment, even at low concentrations. This research investigated the utilisation of Terminalia catappa (TC) shell as biosorbent in the removal of Indigo carmine (IC) dye from aqueous solution. TC shell was modified by soaking in 0.01 M nitric acid for two hours. The biosorbent characterised by Fourier Transform Infra-Red Spectroscopy (FTIR), X-ray Fluorescence spectroscopy (XRF), Scanning Electron Microscope with Energy Dispersive Spectroscopy (SEM-EDX) and Brunauer-Emmett-Teller (BET) analysis. Batch experiments carried out at a biosorbent particle size of ≤ 36 μm and 100 rpm of agitation speed. The optimum conditions for TC shell biosorption of IC were at pH 2, contact time 30 min, and an initial concentration of 600 mg L−1. The adsorption capacity of the biosorbent for IC was 26.77 mg g−1. The kinetic and isotherm study of IC dye biosorption revealed that the pseudo-second-order model and Freundlich isotherm were the best fit. Thermodynamic parameters for the biosorption showed that the process was spontaneous and exothermic. The removal efficiency only dropped from 73 % to 64 % after 3 cycles of use using 30 % glycerol as eluent. The removal efficiency of IC dye from the real wastewater using TC shells was 60.13 %. The results indicated that TC shell was a potential biosorbent to reduce IC concentration in aqueous solutions.