Tanigels were prepared according to the basis of Nakano et al.
[9]. Five grams of tannin extract were dissolved in 32mL of NaOH
(PANREAC) 0.125 mol L−1 and 30mL of distilled water at 80 ◦C.
When mixture was homogeneous, certain amount of aldehyde
were added and reaction was kept at the same temperature for 8 h
until polymerization was considered completed. Then, the apparent
gummy product was lead to complete evaporation of water
remain and dried in oven (65 ◦C) overnight. After drying, tannin
rigid gels were crushed and sieved to produced 38–53m diameter
particles. They were washed successively with distilled water
and HNO3 0.01 mol L−1 (PANREAC) to remove unreacted sodium
hydroxide. Finally, the adsorbent was dried again in oven. Differences
are found between this preparation way and the description
made by Yurtsever and Sengil [17], mainly concerning the amount
of formaldehyde.