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Fig. 7. Comparison of 2,4-D adsorption ability among metal-humate complexes. (A) humic acid (HA) was complexed in the presence of 0.01 M CaCl2 (•), 0.1 M CaCl2 (
), 0.01 M FeCl3 (
), and 0.01 M AlCl3 (
). (B) Comparison between Al-humate complex (humic acid was complexed in the presence of 0.01 M AlCl3, ) and Al hydroxides (0.01 M AlCl3 was precipitated by adding NaOH in the absence of HA, 
). Reaction time, 4 h; initial 2,4-D concentration, 22.6 µM (5.0 mg L–1); humic acid added, 2.0 mg; COOH added, 8.14 µmol; Al or Fe added, 50 µmol; Ca added, 50 or 500 µmol.
