2. Material and methods
2.1. Reagents
All reagents were obtained from SIGMA ACS grade and were used as received without any further purification procedure. Heavy metals solutions were prepared at 10 mg/L of Pb(NO3)2, Cd(NO3)2, and Cu(NO3)26H2O in distilled water.
2.2. Cellulose-derivate material
The different cortexes (banana, lemon and orange) were cleaned avoiding any pulp and carpellar membrane, then the different materials were dried in an oven at 40 C during six days. Once dried, cortexes were milled using a mortar and screened to obtain two different particle sizes (1 and 2 mm). The resulting powders were treated for alkalinization with 0.5 N NaOH during 20 min according Navarro et al. (2006). Then passed through gauze and rinsed with distilled water four times to eliminate the excess of NaOH. Finally, the powders were dried again at 40 C. In order to estimate the effect of alkalinization procedure, control materials were also produced in the same way except the treatment with NaOH. Once dried, all the biosorbent powders were kept on a dryer until its use.
2.3. Biosorption process
In this process, 1.5 g of powder were weighed to fill different 100 mm high, 10 mm i.d. glass columns. Then 25 ml of the heavy metal solution were added keeping the column close until complete matrix humidification. After that, the column was open to allow water flow and pressure was applied on the top of the column using a syringe. From the elution, a sample (1.0 ml) was obtained, labeled and stored for analysis and the rest was reloaded into the column to test the amount of metal adsorbed after more than one elution, all the experiments were done by triplicate.