Preliminary Evaluation of Glass Microfiber Filter Effects on the Chemistry of Synthetic Precipitation Leaching Procedure Extracts

Abstract

The synthetic precipitation leaching procedure (SPLP) is commonly used to measure the potential for release of constituents from soils and wastes by natural precipitation. However, experience has shown that SPLP extract pH values obtained from commercial laboratories are often elevated beyond that expected based on sample mineralogy and sometimes exceed environmental standards. This study was conducted to examine the effects of glass microfiber filters (GMFs) on pH values and metal concentrations of SPLP extracts. In a control experiment, GMF filtration increased the pH of standard SPLP extraction fluids (Eastern extraction fluid, pH 4.2, and Western extraction fluid, pH 5.0) to approximately 10.0 in the first 100 mL of filtrate. Filtration using GMFs also produced substantial pH increases in SPLP extracts from a variety of geologic materials, although dissolved metal concentrations were less affected. Laboratory analysts should be conscious of artificially elevated pH values in SPLP extracts caused by GMF filtration and consider using techniques to minimize these effects, such as (1) prerinsing GMFs with deionized H2O and pH monitoring of the resulting filtrate prior to SPLP filtration and (2) filtering the maximum volume of SPLP extract practicable.