The purpose of this paper is to clarify the mechanism of adsorption and leaching of mercury to the soil, containg allophane clay which exists in most of all volcanic ash soils in Japan.
Mixing experiment between the soils sampled and 500 ml mercury solutions which indicate pH 2 to pH 8 with the concentration of 1 μ g/ml and infiltration experiment between the soils sampled and 500 ml mercury solutions which indicate pH 7 with the concentration of 1 μ g/ml are carried out. These results, are summarized as follows:
In mixing experiment, the mercury in its solutions with pH 4 to pH 8 is adsorbed by the soil more than 99% and adsorption quantity decreases from 96% for the solutions with pH 3 to 51% for those with pH 2.
It is already reported there are two groups in the allophane, silanol groups (= Si-OH) and (Al-OH) groups. The adsorption of mercury occurs by cation exchange reaction between divalant mercury ion and two hydrogens of silanol group.
Mercury is adsorbed more than 99% in the infiltration experiments, too. The mercury concentration of infiltrated water is in the range of 0.03 ppb to 1.5 ppb. The amount of leached mercury is very small compared to the amount adsorbed in the soil particle.