Dissolution of Amorphous Matter from Soils by Hydrogen Peroxide Treatment and Its Effect on the Consistency Limits

Abstract

The change of carbon content, pH, dissolution of amorphous matter, and its effect on the consistency limits of soil by H₂O₂ treatment were measured using andosols and hedoros, or lake bottom muds. When 30 cm³ of 6% H₂O₂ was used on 10 g of soil, the pH of the topsoil of andosol lowered from 5.8 to 4, and Hachirogata hedoro from 6.4 to 3.3. These pHs recovered when treated with an increased amount of H₂O₂. Oxalic acid formed by H₂O₂ treatment lowered the pH, and as it was combined with aluminum or iron in the soil, the pH gradually recovered, In relation to the pH drop amorphous matter dissolved. More than 80 % of aluminum as free oxides or hydroxides were dissolved from hedoros during the H₂O₂ treatment. Hachirogata hedoro greatly changed in the plasticity chart by air-drying, but showed only a little effect of that after the H₂O₂ treatment. On the contrary, the effect of air-drying on the topsoil of andosol did not show any substantial change before and after H₂0₂ treatment. Free oxides and hydroxides were found to have a great effect of air-drying on Hachirogata hedoro.