Chemical characterization of raw and treated agave bagasse and its potential as adsorbent of metal cations from water

Lignocellulosic materials have a very complex configuration that contains a variety of active sites capable, in some cases, of adsorbing contaminants from water. Agave bagasse is a sub-product from the alcohol industry that has been very little studied, but that could have the potential to remove a variety of contaminants from aqueous solutions.Raw and modified Agave salmiana bagasse were characterized, before and after they were tested to remove metal cations, by acid–base titrations, elemental analysis and ATR-FTIR. HCl, HNO3, NaOH, tartaric, citric and oxalic acids were used to modify bagasse to determine if its concentration of active groups could be improved. These materials were then tested for the removal of Cd(II), Pb(II) and Zn(II) ions from water at pH 5, and desorption studies were performed at pH 2 and 4 at 25 °C.The characterization techniques mainly identified carboxyl, hydroxyl, sulfur and nitrogen containing groups in bagasse. It was clear that mainly the carboxylic groups were responsible for metal uptake. Raw bagasse has an adsorption capacity of about 8, 14 and 36 mg g−1 for zinc, cadmium and lead, respectively, and this was improved about 27–62% upon modification with HNO3 and NaOH. Treatments with citric, oxalic and tartaric acid did not have a significant effect in adsorption capacity.Raw agave bagasse has a very acceptable adsorption capacity of metal cations and it can approximately be regenerated in a 45%, since the biosorption mechanism involves ion exchange and complexation.

► Agave bagasse contains carboxyl, hydroxyl, sulfur, and nitrogen containing groups. ► Acids and base pretreatments enhance the natural sorption capacity of raw bagasse. ► Carboxylic groups are involved in the uptake of metal cations. ► The biosorption mechanism involves ion exchange and complexation processes. ► Agave salmiana bagasse has an acceptable adsorption capacity of metal cations.