THE MORPHOLOGICAL AND CHEMICAL PROPERTIES OF IRON SLAG FROM STANDISH, NY AND THE IMPACT OF WEATHERING

From 1883 to 1907, magnetite was smelted at a facility located in Standish, NY leaving behind a significant pile of slag that covers ~13 acres of land. This study aimed to describe the variety of slag at the site based morphologically and chemically and to better understand how the slag changed due to exposure to a variety of acids, including a simple acid-rain proxy because the Adirondack region has been historically impacted by acid rain. A watershed analysis using ArcGIS Pro was created to show how slag-impacted water flows into the region. The water in this watershed (and from the slag pile) all flows into Standish Brook and ultimately into Upper Chateaugay Lake.

The slag at the site has been classified into 6 broad types based on their physical properties giving rise to types such as “glassy crusted” and “blue massive”. Blue massive slag is the most dominant type found at the site. Six different types were analyzed for both major and trace element concentrations with XRF. In terms of major elements, Standish slag is dominated by SiO2, CaO, and Fe2O3 regardless of the selected slag type. The trace element compositions of all the slag types are dominated by Ba, Sr, and Zr (all >100 ppm).

In the natural setting, weathering causes slags at Standish to become coated by a thin CaO-rich weathering rind. Significant rust also concentrates around pure iron that was not removed during the smelting process. Both the CaO and rust formation exacerbates cracks within slags at the site. Samples of select minimally weathered slag interiors were used in lab-based leach tests. The lab tests included introducing both powdered and non-powdered samples to 2M nitric acid. Powdered samples were also exposed to 2M HCl acid, and an acid rain-like mixture (acetic acid, phosphoric acid, and sulfuric acid). Samples involved in the leaching tests were chemically analyzed by XRF before and after exposure to the acids. In each of the leaching experiments, the pH of the acids increased after interactions with the slag (eg. the acid rain increased from pH 4 to a pH 6). Of the major element oxides, CaO showed the greatest change in concentration from pre to post leached samples. Concentrations of Ba and Sr also shifted significantly due to the leaching tests.