Recyclable process modeling study of hexavalent chromium elimination by thiol-based electron donor: Implications for practical applicability

Recently, extensive researches implemented to decontaminate hexavalent chromium from industrial effluents. Even though, these processes were not comprehensively addressed in various environmental conditions. This paper investigated the reduction plus adsorption mechanism of [Cr₂O₇]^2-by thiol-based composite in wide range pHs. In this system, firstly the reduction of [Cr₂O₇]^2-to Cr³⁺occurred and Cr species adsorbed by -SH, -NH₂, -OH functional groups in different degrees. The pH 2.0 medium underwent partial reduction of [Cr₂O₇]^2-to Cr³⁺, besides three-quarter of [Cr₂O₇]^2-were reduced to Cr³⁺and also Cr species adsorbed onto the composite in pH 3.0 medium. The extremely fast reduction occurred within 5 min, which helped the application in the fixed-bed column while diminished the column's residual time. Interestingly, mild acidic pHs have prompted the composite to a well-expanded structure, which further controlled the hydraulic resistance and column blockage. Inspiringly, the [Cr₂O₇]^2-- composite system can be treated 13 L of 19.87 mg L^-1[Cr₂O₇]^2-to the Environmental Protection Agency's (EPA) discharge limit by 2.27 g of composite in pH 3.0 with 383 mL of an eluent. As per the Bohart-Adams model, a liter of a fixed-bed column may effectively capture around 60 g of Cr from industrial effluent in pH 2.0 - 3.0. This collective system is an efficient catalytic cycle technique to treat oxyanions from wastewater where replacing toxic oxidants with environmentally friendly catalytic wastewater treatment processes.