Extracting value from tobacco waste through activating the carbon in tobacco stalks
Tobacco is an economically important crop accounting for over 20 % of export receipts in Zimbabwe. This crop is grown by well over 173 000 growers on a hectarage of over 100 000. However, in Zimbabwe only the leaf is currently valuable as stalks have no economic use. Elsewhere, due to the high lignin and cellulose content, tobacco stalks are being used for the production of energy briquettes among other uses, giving the crop additional value. The objective of this trial was, therefore, to investigate the possibility of using tobacco stalk material as a precursor for activated carbon preparation as a new means of enhancing value. The preparation of activated carbon using tobacco stalks and microwave heating was studied and optimised. The prepared activated carbon was further applied as an adsorbent for methylene blue (MB) and lead removal from water. The optimised conditions for activated carbon preparation were a radiation power of 280 W for a period of six minutes having impregnated the precursor material with 30 % ZnCl2 for 24 hours. The activated carbon yield was 49.43 % with an iodine number of 1264.51 mg/g and a point of zero charge of 5.81. The adsorption kinetics for both MB and lead followed the pseudo second order kinetic model with the intra-particle diffusion model suggesting a two-step adsorption mechanism. Experimental adsorption data for both MB and lead also fitted well within the Langmuir adsorption isotherm model. It can, therefore, be concluded that tobacco stalks can be turned into an economically important product through the production of activated carbon which compares favourably with commercial products on the market.