Leonardite powder as an efficient adsorbent for cationic and anionic dyes

This paper aims to investigate the uses of leonardite powder (LP) as an effective adsorbent for the removal of basic red 18 (BR18) and reactive red 180 (RR180) dyes. LP was characterized using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), Zeta potential, Brunauer-Emmett-Teller (BET) analysis, Fourier transform infrared spectroscopy (FTIR), and X-ray fluorescence (XRF). The adsorption process was assessed based on pH, size and the amount of the adsorbent, BR18 and RR180 concentration, and the contact time. BR18 dye was completely adsorbed onto the LP (the removal efficiency equals 100%) after 45 min at the optimum condition (original pH [6.5], the particle size of 45 μm, the adsorbent dose of 0.25 g/L, and the initial concentration of 10 mg/L). For RR180, the maximum removal efficiency (74%) was obtained when 1 g/L LP with 45 um size was added to an RR180 solution of 10 mg/L concentration. Temkin isotherm was used to explain the adsorption of BR18. In contrast, RR180 adsorption was described by the Freundlich model. The adsorptions of both dyes followed the pseudo-second-order kinetics. The reusability of the LP was assessed. For BR18, the efficiency decreased to 96% in the second cycle and reached 42% in the fifth cycle. In RR180, LP was not able to be reused efficiently. As a result, the LP ability for BR18 removal is higher than the RR180 in terms of uptake and reusability. PRACTITIONER POINTS: BR18 and RR180 dyes elimination was carried out with leonardite powder (LP). The maximum removal efficiencies for BR18 and RR180 were 100% and 74%, respectively. The LP ability for BR18 removal is higher than the RR180 in terms of uptake and reusability.