CHARACTERIZATION OF THE COLLOIDAL PHASE OF ABANDONED MINE DRAINAGE IN PENNSYLVANIA STREAMS

Colloids in abandoned mine drainage (AMD) play a significant role in the rate of deposition of Fe to the streambed as reactive intermediates between the initial oxidation of Fe²⁺ and the precipitation of macroscopic ferric oxyhydroxides. As reactive surfaces for the adsorption of metals, colloidal particles also affect the fate and transport of contaminants. In order to better understand the stability of the colloidal phase in AMD, the evolution of the mineralogical composition was investigated in the laboratory as a function of pH, temperature, age, light exposure, and air exposure. Samples from Sterling Discharge, an abandoned anthracite coal mine air shaft in Shamokin, Pennsylvania, were coarse-filtered and concentrated using tangential flow ultrafiltration. The concentrated colloidal phase was characterized using Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR) without drying the sample. Absorbance features in the ATR-FTIR spectra indicated the presence of iron-based schwertmannite and goethite in the freshly prepared samples. In general, as the samples aged in the laboratory, the colloidal phase became a more amorphous conglomerate of schwertmannite and goethite, as evidenced by the broadening of their characteristic peaks in the ATR-FTIR spectra. Preliminary laboratory mixing studies using a ferrous sulfate solution to simulate AMD were conducted to study the evolution of the colloids and compare it to that of the natural AMD waters collected.