Spectrophotometric determination of aluminium in iron ores using solid-phase extraction

In the present paper, a procedure for separation and determination of aluminium in iron matrices is proposed. It is based on the solid-phase extraction of the iron, in the form of thiocyanate complexes, by a polyurethane(PU) foam. The followings parameters were studied: effect of pH and of the thiocyanate concentration on the iron extraction, shaking time required for quantitative extraction, amount of PU foam necessary for complete extraction of iron, aluminium separation from other cations, influence of anions on the iron sorption by PU foam and analytical characteristics of the procedure for aluminium determination using methylthymol blue as chromogenic reagent. The results show that, in the pH range from 1.5 to 4.7, with a thiocyanate concentration of 0.80 mel L-1, by extraction using 1 g of polyurethane foam and a shaking time of 1 min, aluminium (40 mu g) can be separated from large amounts of iron (10 mg), 800 mu g of copper(II), cobalt(II), zinc(TI), mercury(II), tin(IV), manganese(I) and tungsten(V); 100 mu g of titanium(IV) and lead(II); and 50 mu g of vanadium(V). Calcium(II), barium(II), strontium(II) and magnesium(II) can not be separated by this process, but do not react with MTB under the conditions used for aluminium determination. The anions nitrate, chloride, sulfate and acetate do not affect the iron extraction. Phosphate and EDTA. must be absent. The methylthymol blue allowed the spectrophotometric determination of aluminium with molar absorptivity of 1.32 x 10(4) L mol(-1) cm(-1) (528 nm), calibration sensitivity of 0.491 mL g(-1), detection limit of 5 ng mL(-1) and dynamic interval of application of 15 ng mL(-1) to 1.00 mu g mL(-1) and variation coefficient of 0.73%. The proposed procedure was applied for aluminium determination in iron ores and metal-base alloy standards. The obtained results did not show significant difference from the certified values.