Effect of colloidal potassium alum formation on vanadium recovery from acid leach solutions of stone coal

The nattier-blue colloidal particles precipitated out from the sulfuric acid leach solution of stone coal were identified to be potassium alum (KAl(SO4)2 · 12H2O). The particles were characterized through X-ray diffraction (XRD), scanning electron microscopy (SEM) and theoretical analysis with thermodynamics of ion crystallization. The results show that the particles belonged to potassium alum with micro-scale granular surfaces. The colloidal potassium alum formed with the temperature of the leaching solution cooling to 45 °C. This observation could lead to 27.6% vanadium loss in the vanadium extraction process, which might be attributed to the chemical adsorption of vanadium in the form of the species of VO2 + on the potassium alum surfaces.