A contribution to the adsorption/desorption behaviour of zinc-hexa-fluoro-silicate in different soils
E Melcher, R-D Peek
The estimation of a possible endangering of the groundwater through wood preservatives and thereof deriving measures for the avoidance of secondary damages require among others exact knowledge concerning the behaviour of wood preservative compounds in the soil matrix. Adsorption and desorption behaviour were determined at four soils of different characteristics, which were brought in contact with aqueous solutions of zinc-hexa-fluoro-silicate. For the respective experiments four concentrations were prepared containing 10, 50, 100 and 250 ppm zinc ions. Water of p.a. quality served as reference. As to be expected the soils in question behaved different: the adsorption of inserted ions increased with increasing clay content of the soil. On the other hand significant differences exist also with respect to the adsorption behaviour of the zinc cation in relation to the hexa-fluoro-silicate anion. Within the concentration interval investigated, the same soil adsorbed approximately the same proportional zinc quantity. However, when increasing the hexa-fluoro-silicate-ion concentration a proportional decrease concerning the degree of adsorption was observed. The results show that it is not possible to conclude from partial results achieved with individual preservative compounds to the overall system "wood preservative"-soil and that further investigations are necessary for an inclusive description of the problem.