Vanadium (V) is widely used industrially, and plays an important role in the biosphere. Sensitive and reliable analytical methods to determine V in various kinds of samples are of extensive interest. Mainly two spectrophotometric methods developed in the last decade are discussed, namely complex formation methods and catalytic methods. The former is based on either oxidation or reduction of V leading to coloured complexes with proper reagents; they are applicable to determination of V at the mg L⁻¹ level. Catalytic methods are based on the ability of V to catalyse the oxidation of various organic dyes and are applicable to determination at the μg L⁻¹ level. Both methods are used for determination of V in environmental and biological samples.

Vanadium (V) is a toxic metal, which dominantly exists as V⁵⁺ in an aquatic environment. Rice straw, which is an abundant agricultural by-product throughout China was used to treat V⁵⁺ containing wastewater as an adsorbent after phosphoric acid treatment. The effects of initial V⁵⁺ concentration, solution temperature, pH and reaction time on V removal by phosphoric acid modified rice straw (AcM) were systematically assessed. A pH range of 2.0–3.0 was favorable for V removal and the adsorption capacity of V by AcM increased with elevated solution temperature. The maximum adsorption capacity for water containing 500 mg V⁵⁺ L⁻¹ was 24.70 mg V g⁻¹dry matter under the optimum operation (3.33 g L⁻¹ AcM, pH = 2.0, 50 °C, and 200 rpm for 4 h). Adsorption experiment data fitted well to pseudo-second-order kinetic and Langmuir adsorption isotherm models. In the presence of coexisting ions, Na⁺, Cu²⁺, NO₃⁻ and Cl⁻ had no significant (P > 0.05) effect on V removal. These results indicated that AcM derived from agricultural waste was effective to remove V⁵⁺ from aqueous solution.