Determination of Low-content Iron Carbonate in Stream Sediments by Flame Atomic Absorption Spectrometry with Aluminum Chloride Extraction

Potassium dichromate titration (othophenanthroline spectrophotometry) with ammonium chloride extraction is a reliable technique to determine the high-content iron carbonate (7.5%-80%) in samples. However, the traditional methods have the disadvantages of complicated operation, large reagent consumption and analytical error. Moreover, due to the low-content iron carbonate in stream sediments, the interferences caused by other ferrous minerals easily leads to the increase of measurement error. A highly sensitive and selective method for determination of low-level iron carbonate (0.1%-6.0%) in stream sediments has been developed by Flame Atomic Absorption Spectrometry (FAAS) combined with aluminum chloride extraction in water bath and is reported in this paper. Extraction conditions were optimized so that iron carbonate in stream sediments could be completely extracted when the concentration of aluminum chloride is 100 g/L, the heating time is 60 min for water bath, and extract dosage is 80 mL. The addition of aluminum chloride with the same concentration in the standard curve can eliminate matrix interference. The detection limit of iron carbonate was 0.0015 μg/mL, the relative standard deviation (n=12) was 2.3%-4.0% and the recovery ranges from 95.0% to 107.5%. Some ferrous minerals in stream sediments such as hematite and magnetite have negligible interference on the determination of iron carbonate and the interference from pyrrhotine could be also effectively eliminated by mercuric chloride. Compared with the chemical method, the proposed method is simple and easy to operate and has high accuracy and precision.