Relationship between Cu(II) sorption and active H+ sorption sites of soils

Sorption characteristics of Cu(II) were investigated using six soils collected in Korea (JUF, JUM, and KHM) and in Japan (KNG, TWD, and ISK). The Cu(II) sorption amount increased with increasing initial Cu(II) concentration. The maximum sorption amount of Cu(II) increased in the order of KHM < ISK < JUM < JUF < TWD < KNG, and was related to the pH and PZSE of soils. The H+ release curves due to Cu(II) sorption apparently were characterized by a two or three step pattern. The amount of H+ released due to Cu(II) sorption increased with the increase in the Cu(II) sorption amount. The amount of protons released per Cu(II) sorbed onto soils with a larger Cu(II) sorption amount tended to be smaller compared with soils with a smaller Cu(II) sorption amount. The H+ sorption amount of the original soils and those with Cu(II) sorption at the PZSE, which was referred to as sigma(P) (Sakurai et al. 1988: Soil Sci. Plant Nutr., 34, 171-182; 1996: Jpn. J. Soil Sci. Plant Nutr., 67, 32-39), was determined by the STPT method proposed by Sakurai et al. (1988: Soil Sci. Plant Nutr., 34, 171-182). The active Hf sorption sites of soils were used for Cu(II) sorption and their amount decreased after Cu(II) sorption because they were covered with Cu(II). Soils with a larger amount of active H+ sorption sites exhibited a higher affinity to Cu(II) than those with a smaller amount of active H+ sorption sites. The Cu(II) sorption created a positive charge in soils, causing the decrease in the amount of active H+ sorption sites.