The Influence of Foreign Ions on Determination and Speciation of Cr(VI) and Cr(III) from Water Samples

This study reports: a) the content of Ca, Cd, Co, Cr(III), Cr(VI), Cu, Fe, K, Mg, Mn, Na, Ni, Pb, and Zn in wastewater from metal industries and rivers that flow near the metal processing industries; b) the possibility of quantitative determination of Cr(III) and Cr(VI) in the presence of the following cations: Fe3+, Cu2+, Ca2+, Mg2+, Ni2+, Mn2+; and Zn2+ and anions Cl-, NO3-, and SO42-; c) speciation of Cr(III) and Cr(VI) on silica gel modified with Nb2O5 . Metals were determined by flame atomic absorption spectrometry, except for Na and K, which were determined by atomic emission spectrometry, and Cr(VI) by ultraviolet-visible spectrophotometry. When the concentration of cations is higher than Mg2+ (>25 mg/L), Ni2+ (>100 mg/L), Fe3+ (>250 mg/L), Zn2+ (>500 mg/L), and Mn2+ (>1000 mg/L), an error greater than 10 % is obtained in the measurement of Cr(III) . Silica gel modified with Nb2O5 can be considered as an effective solid phase extraction adsorbent for speciation of Cr species and simultaneous concentration of Cr(III). The proposed method was successfully applied to the speciation and determination of Cr(III) and Cr(VI) in the analyzed samples. The content of almost all analyzed metals has been below the permitted values for wastewaters.