Waste-Derived Fine-Milled Bone Char for Apparent Cr (VI) Removal From Water and Preliminary Asphalt-Compatible Processing of the Recovered Residue.

Chromium adsorption transfers contamination to a solid residual that still requires management. This proof-of-concept study evaluated fine-milled bone char (BC; D50 = 5.52 μm) for apparent aqueous Cr (VI) removal from acidic synthetic water and examined asphalt-compatible processing of the recovered residue. Contact-time screening showed > 97% apparent Cr (VI) removal within 30 min; 120 min was retained only as a standardized operational contact time because later archived residual concentrations were very low, the assay lacked independent replication, and the sample-equivalent lower calibration bound could not be reconstructed from the available records. Observed apparent aqueous-depletion-based uptake reached 4.39 mg g-1 in one screening condition. Nonlinear Langmuir, Freundlich, Sips, and Redlich-Peterson models empirically described the refined 120-min dose-response dataset, with Freundlich receiving the greatest Akaike information criterion (AICc) support. Drying the acidified BC/Cr system produced 22.65 g of unresolved additional dry material beyond the initial BC and nominal Cr input, most of which was water-soluble upon rehydration. The resulting process-derived residue was incorporated into asphalt binder at 3 and 6 wt.% without large descriptive shifts in binder or mortar master curves. An adapted nonstandard mortar-cylinder cyclic recovery test showed higher mean recovery with increasing residue dosage, but these descriptive values are not directly comparable with standard binder MSCR results. Leaching, chromium speciation, residue characterization, and independent replication are required before reuse or containment claims.