Calcite, otherwise known as limestone, is found in most regions in Pennsylvania. Limestone rocks are used in Open Limestone Channels (OLCs) to remediate acid mine drainage (AMD). It is expected that basic calcite (CaCO3) will react when it comes in contact with AMD, creating large pits on the surface. Atomic Force Microscopy (AFM) was used within this research and is a technique that allows surfaces to be examined on the nanometer scale. The AFM is a scanning probe microscope designed to measure local properties such as height, friction, and magnetism.The AFM will help determine if the pits are forming and how rapidly they will form. The focus of the experiment is to determine what is happening on the surface of calcite in a low pH solution. Three different solutions were utilized: 1) Millipore water, 2) 5% nitric acid solution at pH 3.35, and 3) 20 ppm aluminum solution at pH 3.18. Calcite was imaged using a nanoScience TraxAFM at Saint Francis University and a Hitachi AFM5100N with a liquid cell AFM at West Chester University. The longer the calcite stayed in solution, the more it reacted and the pits were seen to become deeper. The height of the image spot was 85 nm then transformed into a dark, misshapen hole that had reached the depth of 98 nm. The same process is expected to happen in Open Limestone Channels exposed to AMD. However, upon exposure to AMD, there are concerns about armoring on the limestone rocks. The armoring effect occurs when rocks are covered in precipitate and cannot dissolve correctly within the runoff, thereby failing to raise the pH. This armoring effect is something to be tested in further research.

AFM imaging of calcite surfaces

2019 Spring National Meeting

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