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[Relation between average oxidation state of Mn of birnessite and the amount of Pb2+ adsorbed].

Vacant sites in Mn oxides, commonly occur in soils, play an important role in their heavy metal adsorption behavior. The dependence of Pb2+ adsorption capacity for the synthesized birnessites and their d110-interplanar spacing on the respective Mn average oxidation state (AOS), and the relationship between Pb2+ adsorption and the Mn2+, H+, K+ released during adsorption were investigated. The results show that Mn AOS of birnessites apparently reflects their amount of vacant sites which largely account for the Pb2+ adsorption. Significant positive correlation between Pb2+ adsorption capacity and the Mn AOS of corresponding birnessites (r = 0.9779 > 0.6614, n = 14, alpha = 0.01), negative correlation between d110 spacing and the Mn AOS (r = -0.9035 < -0.6614, n = 14, alpha = 0.01), and significant positive correlation between Pb2+ adsorption and the Mn2+, H+, K+ released during adsorption(r = 0.9962 > 0.6614, n = 14, alpha = 0.01) are found. The vacant sites amount increases with Mn AOS for birnessites, which causes the increase of Pb2+ adsorption. Therefore, the Pb2+ adsorption capacity of birnessite is largely determined by the amount of vacant sites, from which Mn2+, H+, and K+ released during adsorption are mostly derived.