The alkaline leachate
of the roasted concentrate was subjected to the precipitation of silica and
alumina; it was then left to stay overnight to allow the crystallization of
sodium sulfate as a purification step. The filtrate was divided into two parts;
the first was used for the direct precipitation of vanadium, whereas the second
was used for the ion-exchange separation.
Precipitation of silica and alumina
leachate of the roasted titanium concentrate of 79%TiO2 has pH <13. It was analyzed via wet chemistry and instrumental techniques which revealed the presence of 22000 ppm Si, 3200 ppm Al and 800 ppm V while Ti, Fe, Mn and Zr were not detected. The alkaline leachate was treated with conc. sulfuric acid (98%) at a ratio of (10:1) (v/v) to reach pH of 8 where silica and alumina were precipitated together leaving V in solution. It is well known that silica plays an important role in different industries ECETOC JACC Report No. 51, 2006. The separated SiO2 resulted from this step was crystalline after ignition at 1000oC in two forms; Tridymite and Cristobalite as analyzed by XRD, Fig. 10 chart 1. The filtrate containing V was left to stand overnight to allow the crystallization of sodium sulfate (Thenardite), where a pure byproduct was detected by XRD, Fig. 10 chart 2. This step was used to clarify the V filtrate from almost sodium ions which reduce the quality of the vanadium products. In the meantime, sodium sulfate has various uses which made its separation as a pure compound is of interest (Garrett, 2001; Kostick, 2013). 3.4.2. Precipitation of vanadium The resultant filtrate contained V with traces of Si, Al and Na ions. This filtrate was divided into two parts; the first was used for the direct precipitation of vanadium. It was agitated at 80oC with gradual addition of NH4Cl(s) aiming to reach the pH of 5 at which V precipitation occurred as NH4VO3 (Chmielewski et al., 1997; Habashi, 1997; Liu et al, 2013; Navarro et al., 2007; Vitolo et al., 2000). The precipitate was washed with bi-distilled water producing ammonium metavanadate (NH4VO3) ASTM card No. 009-0411 as was confirmed by XRD, Fig. 10 chart 3.