Iron-catalyzed degradation of atrazine with persulfate from synthetic oxides and highly weathered soils with contrasting mineralogy.

The intensive use of herbicides in agriculture has caused contamination of soil, surface waters and underground waters. The presence of atrazine (ATZ), an herbicide widely used in soybean, wheat, and corn crops, is particularly relevant. This study evaluated the degradation of ATZ by persulfate (PS), using Fe oxide activation of two highly weathered soils (Oxisol and Alfisol), with contrasting hematite (Hm) and goethite (Gt) contents. To better predict the mechanisms involved in PS activation and ATZ degradation, tests were also conducted with synthetic ferrihydrite (Fh), Gt, and Hm. The soils were subjected to sequential extractions to obtain residues free of: i) more soluble forms of iron (pyrophosphate - PYR); ii) low crystalline oxides (ammonium oxalate - AO); iii) well-crystalline oxides (citrate-bicarbonate- dithionite - CBD). The decomposition rate of PS by synthetic Fe oxides decreased in the following order (L-1 min-1): Fh - 0.168 > Gt - 0.024 > Hm - 0.011. Positive effects of PS and Fh concentrations and negative effects of pH were observed on the degradation of ATZ. The best experimental conditions were PS 700 mg L-1; Fh 12 mg and pH 3.5. Oxisol and Alfisol and their sequential residues were less efficient in ATZ degradation than synthetic Fe oxides. The maximum percentage of ATZ removal for Oxisol occurred in PYR residue (20%). To successfully remediate highly weathered soils contaminated with ATZ, periodic and continuous supplementation of PS is necessary. The high proportion of crystalline Fe should favor the continuous and long-term heterogeneous process in the soils.