Iron ligands as 1,2-dihydroxybenzenes (1,2-DHBs) have been used to increase the oxidizing ability of Fenton systems. However, these kinds of ligands become toxic quinones in the process creating an environmental problem since these compounds cannot be easily separated from a solution. To avoid this problem, in the present work, water-insoluble tannins, obtained from Pinus radiata bark, were used as a source of 1,2-DHBs to promote the oxidizing ability of the Fenton process. The developed system was tested using atrazine, as a substrate, which is a toxic and recalcitrant compound, present in different sources of water. The best reaction conditions established by the experimental design were as follows: pH of 3.6; 2.4 mmol L of HO; 150 μmol L of Fe(III); and 800 mg L of tannins. A significant increase in the efficiency of the degradation of atrazine by the heterogeneous Fenton process was observed under these conditions. The repetitive use of the insoluble tannins for Fenton-like processes showed a similar oxidizing ability and did not produce the lixiviation of phenols or other aromatic compounds. Together, the results showed that insoluble tannins could be used safely at least five times to promote the reactivity of Fenton systems.