1 IntroductionVanadium (V) is a ubi

1 Introduction
Vanadium (V) is a ubiquitous trace element and the
average content of V in soil of the world has been
established at 90 mg/kg [1]. However, high content of V
can be accumulated in soil due to anthropogenic sources,
such as fossil fuel combustion, tailing leakage and metal
plants [2]. Mining and smelting activities, especially for
vanadiferous magnetite, cause V pollution widespread in
many countries [3,4]. For instance, the total contents of
V in soil from the vicinity of V mine in South Africa
varied from 1570 to 3600 mg/kg [5], and the ranges of V
contents in soil are 208