pH Testing Methods for Sulfidic Mine Wastes

pH tests are useful screening tools for assessing the characteristics of first flush waters draining sulfidic rocks and waste materials at mine sites. Rinse and paste pH tests are part of a suite of static tests used in acid-base accounting assessments. This study presents a comparison of eleven different pH tests (e.g., rinse and paste pH tests as well as soil tests of the International Organization for Standardization ISO 10390:2005, American Society for Testing and Materials ASTM D4972-01(2007) and Standards Australia AS4969.2-2008) using three different sulfidic rock samples and the acid-base accounting standard KZK-1. We show that different rinse and paste pH methodologies using different grain sizes and extraction solutions can result in different risk classification for ARD assessments. We suggest pH testing should be standardized in their grain size and solid to solution ratio. pH tests conducted using unweathered materials (e.g., drill core) should be carried out using a 0.01 M CaCl₂ solution.