Liquid–Liquid Extraction and Reductive Stripping of Chromium to Valorize Industrial Effluent

Liquid–liquid extraction of chromium from industrial effluent has been investigated using tributyl phosphate as a potential extractant. Variation of parameters such as the extractant dosage, acid concentration, temperature, and organic-to-aqueous (O/A) ratio revealed that extraction took place through outer-sphere complexation. The adduct formation was further supported by Fourier-transform infrared analysis of the organic phase and the determined enthalpy value (ΔH°, − 18.8 kJ/mole). As predicted by the McCabe–Thiele diagram, quantitative extraction of approximately 5.0 g/L Cr6+ was achieved by two-stage countercurrent extraction at O/A ratio of 1/1.5. Subsequent stripping of the extracted metal in reduced form (as Cr3+) was carried out using ≥ 1.5 M ascorbic acid with 30 min of contact time. Finally, the critical metal was precipitated to recover Cr(OH)3 by pH swing of the stripped solution using NH4OH.