Dissolution behavior of Pb-free solders due to exposure to bulk precipitation and throughfall

摘要

Pb-free solders containing rare metals were exposed to precipitation at open canopy (bulk precipitation) or under tree canopies (throughfall), and the dissolution processes were investigated in relation to the chemical properties of the precipitation. The dissolution rates of metals varied greatly between the metal species, decreasing in the order In>Sn>Bi> Ag. Metal dissolution was significantly accelerated in throughfall, which contains dissolved organic matter released from trees, compared with bulk precipitation. The accelerated dissolution in thronghfall varied with the tree species, in the order Q. myrsinaefolia>P. densiflora>C. japonica>C. obtusa. Dissolved organic matter in throughfall that has a high metal complexing capacity is likely to have in creased the metal dissolution, due to chelation with the metals. Under Q. myrsinaefolia, the dissolution of metals, especially Bi and Sn, showed remarkable seasonal variation, being high in May and June, and gradually decreasing after summer.