Stability of a novel synthetic amorphous manganese oxide in contrasting soils

Manganese oxides are known to be efficient sorbents in soils, and thus potentially useful in soil remediation. A novel synthetic amorphous manganese oxide (AMO) was prepared using the first step of the procedure generally used for birnessite synthesis (i.e., omitting the heating step of the gel). Its long-term (90 day) stability was evaluated using a pot experiment in contrasting soil samples (pH 42, 5.4, and 73). Up to 113 mg Mn l(-1) was released into pore water at the beginning of the experiment in more acidic soils, indicating a partial dissolution/alteration of AMO surfaces. Manganese release into the pore water stabilized after 15 days, in agreement with the mass loss measurements. Mass loss decreased again after 60 days of incubation for the neutral soil due to the massive formation of secondary rhodochrosite (MnCO3) and/or kutnahorite [(Ca,Mn)CO3] detected on the AMO surfaces by both X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM). Mineralogical transformations and aggregation of fine-grained AMO particles probably lead to the decrease of binding surfaces. Despite the fact that 10-18% of AMO dissolved during the 90 days of the experiment, the sorbent was found to be relatively stable, primarily in near-neutral soils; consequently, its in situ applications to polluted soils need to be evaluated further. (C) 2013 Elsevier B.V. All rights reserved.