As with other construction materials, coal fly ash contains trace metals that can leach into the natural environment. As part of a broader effort to encourage appropriate coal combustion product use in infrastructure applications (e.g., road construction, stabilization, and structural fill), this study evaluated traditional and low-cost adsorbent alternatives for their capacity to attenuate trace metals. Batch sorption tests were used as a preliminary screen for a wide variety of low cost (e.g., steel byproducts, rubber dust, and compost) and innovative materials (e.g., kudzu, biofilm, and pond weed) as well as conventional materials (activated carbon, alumina, and zeolites). The removal rates were demonstrated in this study by observing the calculated distribution coefficient (K d) which were determined using a program called MATLAB. Limestone and steel byproducts were found to be particularly effective with large K d values of 15,740, 1,520, and 540 L kg −1 for cadmium, chromium, and selenium and, for ladle refractory and mill scale, K d values of 3,910, 670, and 1,760 L kg −1 were observed. Among the three metals tested for this study, it was observed that most low cost and innovative materials removed cadmium quite efficiently; however, the removal of selenium and chromium depended on the substrate and prevailing pH. In general, these results suggest that alternative materials may have relevance in niche applications where leaching is a concern that can be addressed through enhanced attenuation capacity via blending or layering of adsorbents. K E Y W O R D S distribution coefficients, heavy metals, low cost adsorbents, MATLAB 1 | INTRODUCTION Coal fly ash (CFA) is commonly used in structural fills and embankments, with such applications representing second only to concrete in terms of amount used (ACAA, 2016). A structural fill or embankment may be defined as a raised mass of material that is used as part of an engineered facility (USEPA, 2013). When used in these applications, CFA is typically placed in direct contact with existing soil or even after excavation. Fill materials can be used for a variety of different applications such as roadways, earth retaining walls, abutments for bridges, and even parking lots. Fill material is generally required to raise the height of the existing topography to some design elevation. CFA is particularly attractive as a fill material because of its low unit weight and reasonably high strength. Less weight translates into less deflection or settlement in each application. It has been observed that the mechanical properties of a Class F CFA are similar to those of natural sandy soils (Kim & Prezzi, 2008). Numerous projects have been completed using CFA without geotechnical or environmental concerns. For example, the Federal Highway Administration (FHWA) summarized data from 21 construction projects that used two million or more cubic yards of fly ash without any significant adverse environmental concern (FHWA, 1998). Many other product categories involve placing or blending ...
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