Rapid Field Verification of Organoclay-Sand Blends for Environmental Construction Using Portable X-Ray Fluorescence

Organoclay (OC) is a widely used sorbent for environmental remediation of nonaqueous phase liquids and thus requires rapid construction quality assurance (CQA) verification of OC-sand blends used for sediment capping applications containing up to 50% OC content prior to field placement to ensure continuous construction. Accordingly, this paper outlines a field-based method for quantifying OC contents in OC-sand blends using portable X-ray fluorescence (pXRF). Oven-dried and powdered specimens consisting of OC, Flourosorb 400 (FS) (clay sorbent media designed to treat polyfluorinated alkyl substances), and their blends (OC/FS-sand) were tested. Four mineralogically different sands were used in this study to demonstrate the broad applicability of the pXRF approach. All test media were rapidly crushed to powders using a simple handheld power tool and then readily prepared for pXRF analyses. Using pXRF, 38 linear correlations were developed in the 0%–45% OC/FS blend range. All correlations exhibited R2 ≥ 0.80, with 27 of 38 yielding R2 ≥ 0.95. Correlations were presented via two different approaches: (1) based solely on chlorine (Cl), which is primarily associated with the OC manufacturing process and was thus identified as the main pathfinder element in OC/FS containing media; and (2) based on the naturally occurring elementals in bentonite clay used to manufacture the OC/FS and the commercially available sands. Chlorine showed strong correlations with R2 ≥ 0.98 across all OC-sand blends, enabling a general correlation to estimate OC content without site-specific data. Approach 2 identified 11 media-specific pathfinder elements and linear correlations with R2 ≥ 0.90 for 27 of 33 correlations across four sand types. Once the base correlations were created, rapid CQA verification of the OC content of field-produced OC-sand blends can be obtained in <2 h.