The effects of MnO2 on sorption and oxidation of Cr(III) by soils

In the paper, the oxidation of trivalent chromium in soils is presented. The main oxidant responsible for oxidation of Cr(III) compounds in soil is manganese (IV) oxide. The paper examined two aspects of Cr(III) oxidation in soils: (1) the soil oxidation potential and; (2) sorption of Cr(III) on the examples of four soils differing in organic matter content (0.72% to 3.72% of organic carbon) and total and easily reducible Mn. The second consideration was oxidation of Cr(III) by MnO2 itself and in the presence of the soils studied. The experiments were carried out in a batch process for 2 h, in which the soil was mixed with CrCl3 solution at 1:10 ratio. The initial Cr(III) concentration in the solution was 52 ppm. In order to examine Cr(III) oxidation by MnO2, the oxidant was added in three amounts: 0.065, 0.13 and 0.26 g/100 g soil (dry basis). The studies showed that the soil oxidation potential was not detectable in the soils studied. Sorption capacities for chromium (III) were similar for each soil and ranged from 9.72×10−4 to 9.95×10−4mol of Cr(III)/100 g of soil. The oxidation of Cr(III) by MnO2 was slight and progressed with a maximum conversion of 2.66% for the highest dose of oxidant (0.26 g). The presence of the soil decreases Cr(III) oxidation by MnO2; the decrease being related to the soil properties (organic matter, reducible Mn).