Sustainable Selective Recovery of Sulfuric Acid and Vanadium from Acidic Wastewater with Two-Step Solvent Extraction.

A two-stage extraction process was proposed to recover sulfuric acid and vanadium from simulated acid solution and titanium dioxide waste acid (TDWA). Some extractants were compared and studied, in which the enthalpy changes (Δ) of the extraction process and the extracted complex were analyzed by using thermodynamics. The microscopic characteristics of the loaded organic phase were compared and investigated by infrared spectroscopy (FT-IR), where the extraction mechanism was described. The extraction efficiency of sulfuric acid was more than 99% by three-stage countercurrent extraction with 60% triisooctylamine (TEHA) and 35% -pentanol, in which Δ was -61.31 kJ/mol and the extracted complex of HSO·TEHA·2--pentanol was obtained. The extraction efficiency of vanadium was above 98% by using 20% bis-2-ethylhexyl phosphate (P507) and 80% sulfonated kerosene, where Δ was 14.69 kJ/mol and the extracted complex of VO·2A (vanadium as VO and P507 as HA) was obtained. The stripping efficiencies of sulfuric acid and vanadium were more than 90% and 98%, respectively. The extraction effect of used organic phase after regeneration was equivalent to that of the new organic phase with cycle numbers of less than 10. The real waste acid of TDWA was operated to extract and separate sulfuric acid and vanadium with the same parameters, in which the characteristics of high extraction efficiency and good selectivity were obtained. The technique may provide a new thinking for the separation and recovery of valuable components from TDWA.