Clean removal of silicon (IV) and vanadium (V) from high concentration chromium (VI) solutions in the chromate production processes

How to effectively and environmentally purify chromate solutions containing impurities such as silicon and vanadium, and avoid the generation of Cr(VI)-containing residues are important issues to be solved urgently. Herein, a novel Cr2O3 center dot 2.7H2O adsorbent with stable three-dimensional nanoflower structure was fabricated using the hydrothermal method, which was successfully implemented in the removal of Si(IV) and V(V) from dichromate system. Batch adsorption experiments revealed that the saturated adsorption capacity of Si(IV) was 140.06 mg/g at pH 9 and 132.98 mg/g V(V) at pH 2. Furthermore, density functional theory (DFT) calculations revealed that V(V) anionic species exhibited high adsorption energies (-990.70 kJ/mol,-697.10 kJ/mol) and small adsorption distances from the beta-CrOOH(012) (approximate to 1.89 angstrom, 1.98 angstrom), verifying the selective adsorption of Cr2O3 center dot 2.7H2O on V(V) in Cr(VI)-Si(IV)-V(V) ternary systems. The integrated mechanisms of electrostatic interaction, coordination, polymerization and precipitation for the removal behaviors were proposed via FT-IR, XPS and DFT calculations. In the real Na2Cr2O7 complex solutions, the simultaneous removal rates of 88.48% Si (IV) and 80% V(V) were achieved, with optimal adsorption conditions at a pH of 8 and a temperature of 333 K. Furthermore, the desorbed Cr2O3 center dot 2.7H2O can be effectively converted into high-value nano Cr2O3, indicating the potential of this new green adsorbent. Therefore, this study not only imparts theoretical and practical insights into the purification of chromate solutions but also contributes to the advancement of cleaner chromium com-pound production by facilitating the high-value conversion of the adsorbent.