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• <br />Vanadium V <br />1 <br />0.9 <br />0.8 <br />0.7 <br />0.6 <br />M <br />La 0.5 <br />a 0,4 <br />0.3 <br />0.2 <br />0.1 <br />0 <br />11 <br />pH <br />Figure 2 - Vanadium (+5) speciation as a function of pH (alpha is the fraction of the <br />total dissolved vanadium m (+5) consisting of the given species). <br />A predominance-area (Eh-pH) diagram for the various vanadium species is shown in <br />Figure 3. As mentioned previously, V(+4) is only predominant below a pH of 5.87, at <br />which point the stability field pinches out. In general, the predominant vanadium <br />species tend to be negatively charged when the Eh is positive. Therefore, under <br />relatively oxidizing conditions, vanadium tends to adsorb to positively charged surfaces <br />in a similar manner to other oxyanions such as arsenic (+5). Under more reducing <br />conditions, the predominant species is neutral at ph values greater than 5.19 and does <br />not adsorb in response to coulombic forces (i.e. the attraction of negative and positive <br />charges to each other). <br />0 <br />0 2 4 6 8 10 12 14