Formation of Cr(III) Hydroxides from Chrome Alum Solutions: 1. Precipitation of Active Chromium Hydroxide

The formation of active chromium hydroxide, Cr(OH)₃·3H₂O, was studied through potentiometric titrations and turbidimetric measurements. UV-Vis and IR spectroscopies were also employed to characterize the synthesized solid. The rapid addition of NaOH solution to aqueous chrome alum (KCr(SO₄)₂·12H₂O) solutions caused the immediate precipitation of the active material. Only monomeric Cr(III) species seemed to be participating in the precipitation process; neither chromium polymers nor complexes with anions (SO²⁻₄, Cl⁻, NO⁻₃, ClO⁻₄) influenced the fast formation of Cr(OH)₃·3H₂O. Titration studies allowed the determination of several hydrolysis and precipitation constants for Cr(III). Nevertheless, they cannot be used for the estimate of Cr(OH)⁰₃formation constant.