Effects of acidification on metal mobility in a papermill-ash amended soil

Elevated soil pH due to papermill ash application has adverse effects on forest soils. Column leaching studies were conducted to determine the effects of acidification on trace metal mobility in a papermill-ash amended soil. Two types of ash, aged and fresh, were used. The aged ash-soil profile was collected from the field,there the ash was mixed with the surface soil to a depth of 47 cm at rates of 896 and 1792 mt ha(-1) and left to stand for 1.5 yr. The fresh ash-soil profile was prepared by mixing fresh ash with the surface soil at the same rates as the aged ash-soil profiles. The pHs of the ash-soil profiles were adjusted from 9-10 to 7 and 6 using dilute HNO3. Leachate concentrations of As, Ca, Cd, Cr, Cu, Na, Ni, Se, and dissolved organic carbon (DOC), and pH were measured at the end of 7 and 35 d. Acidification of the aged ash-soil profiles elevated concentrations of Se, As, Cd, and Ni in leachate possibly due to the dissolution of CaCO3 and release of metals adsorbed to CaCO3. Reduced Cu concentrations were possibly due to reduced DOC concentrations at reduced pH. On the other hand, acidification greatly reduced the amount of metals leached through the fresh ash-soil profiles (except Ca and Cd), mainly due to significant reduction in the mobilization/solubilization of organic matter. The high metal mobility in the unacidified fresh ash-soil profiles could have been due to DOG-facilitated metal migration.