Equilibrium study of Cr (VI) removal from aqueous solution by stalks from three tobacco species (Nicotiana) grown in Bulgaria

Agricultural and processing activities generate enormous amounts of tobacco waste, and the stalks left after harvesting of the leaves constitute a significant share. The stalks of common tobacco (N. tabacum L.) were considered a promising source for processing and recycling, but very little is known about the properties of the stalks from other Nicotiana species. The aim of present study was to examine the performance of stalk powders from three Nicotiana species grown side-by-side in Bulgaria for the ability to remove Cr (VI) ions from aqueous solutions. The characterization of applied biosorbents was conducted by FTIR analysis. Batch experiments were carried out and the effects of different adsorption process parameters were determined. Maximum removal efficiencies of 99.13±0.55%, 98.33±0.58% and 95.00±0.50% for N. tabacum, N. rustica L. and N. alata Link&Otto, respectively, were obtained at pH 3.0, adsorbent dosage 5 g/L, initial Cr (VI) concentration 10 mg/L, temperature 25.0 ± 0.5oC, agitation speed 200 rpm and contact time 60 min. The Langmuir and Freundlich models fitted well the equilibrium isotherms experimental data. Based on the values determined for the maximum adsorption capacity, the powder from N. alata stalks was found to have higher affinity (9.87 mg/g) for Cr (VI) ions than those obtained from N. tabacum (8.38 mg/g) and N. rustica (6.96 mg/g) stalks.