电位滴定测定石煤焙烧物及其浸出液中三价、四价和五价钒

VANADIUM VALENCY STATE RESEARCH IN CARBONACEOUS SHALE-POTENTIOMETRIC TITRATION OF V(III), V(IV) AND V(V) IN CARBONACEOUS SHALE

钒的价态测定是近几年来提出的一项重要研究课题,不同价态钒的测定方法已有评述。为了能在溶液状态下测定样品中钒的价态,通常采用惰性气氛、低温、选择适宜的熔剂、分解试剂及络合剂等措施,以确保原有价态的稳定。 KCrO电位滴定V(Ⅲ)、V(Ⅳ)或V(Ⅴ)时,V(Ⅲ)不稳定。

A potentiometric titration procedure has been developed for the determination of V(III), V(IV)and V(V)with potassium dichromate solution in carbonaceous shale. Two potential breaks are observed in the titration curve. The first corres- ponds to the oxidation of V(Ⅲ) to V(Ⅳ), and the second to the oxidation of V(Ⅳ) to V(Ⅴ).The determination of V(Ⅴ) in a mixture of V(Ⅳ) and V (Ⅴ) is accomplished as follow: 1) Both V(Ⅳ) and V(Ⅴ) are reduced to V(Ⅲ) by Fe (Ⅱ) and titrated V(Ⅲ) with K2Cr2O7. Thus the total amount of V(Ⅳ) and V(Ⅴ) is determined. 2) The amount of V(Ⅳ) in the mixture can be determined separately. 3) The difference between the two amounts is the amount of V(Ⅴ). Under the conditions proposed for the titration of V(Ⅲ), V(Ⅳ) and V(Ⅴ). Ca(Ⅱ),Mg(Ⅱ), Al(Ⅲ),Fe(Ⅲ),Cr(Ⅲ),Cu(Ⅱ), Ni(Ⅱ),Cd(Ⅱ), Mo(Ⅵ), W(Ⅵ), F-,Cl- and SO42- do not interfere, but Fe(Ⅱ), Ti(III) and NO3- interfere. The relative error of the method is±1%.