column leaching

A laboratory method that involves passing water, acids, or other leaching solutions through a stationary solid waste or another solid sample to model the dissolution of contaminants from the sample. The leaching process uses a plastic or glass column. The column is periodically recharged (usually at the top) with the leaching solution. The solution passes through the solids and is collected at the bottom of the column, usually filtered, and then analyzed for contaminants. Leachate collection may occur over days, weeks, or even months. Column leaching tests provide estimates of the types and concentrations of contaminants that are likely to mobilize from a wetted solid sample and move into the environment. Unlike batch leaching, no agitation of the column occurs and the system is open and more closely resembles subsurface conditions in many natural environments and contaminated sites. Although the procedures tend to be more expensive, time-consuming, and labor intensive than batch leaching, column leaching methods have the advantages of allowing observers to study longer term chemical interactions between solid samples and leachates, to note changes in the permeability of solid samples with time, and to evaluate how chemical reactions may change once more soluble compounds are flushed out of the solids (compare with leaching, batch leaching, leaching test, sequential batch leaching, and serial batch leaching).