3.9. Desorption studies
Desorption efficiencies were generally low (o25%), H2O was obtained to have the best desorption efficiency, desorption
efficiency follows the order H2O4HCl4CH3COOH for the RH-RhB system. Desorption efficiency obtained for RH were
23.81%, 7.94% and 6.35% for H2O, HCl and CH3COOH respectively. This result further affirms that uptake of RhB onto RH is via
physisorption. Low percentage desorption of RhB from RH surface may be attributed to a possibility of large net adsorption
energy because of several contact points between large dye molecules and biosorbents [40].
3.10. Cost analysis
RH is a waste thus readily available at no cost, however the cost of transportation for its collection, water and energy for
processing would amount to 0.021 USD/kg (21 USD/ton). Comparing the cost of RH with previous report, chemical activation
of readily available adsorbent may result into about 24 times increase in cost while commercial activated carbon is about
1143 times more expensive than RH [41]. Thus RH gives a good economic advantage over modified adsorbents and commercial
activated carbon.