Determination of total mercury in bauxite and bauxite residue by flow injection cold vapour atomic absorption spectrometry

A simple method for precise and accurate determination of total mercury in bauxite and bauxite residue was developed by using the flow injection mercury system. Samples of the solid materials were first microwave digested in acidic and oxidising conditions to convert all mercury to an aqueous ionic form. Following filtration and dilution, ionic mercury was reduced to elemental mercury with acidic SnCl2 to produce a cold mercury vapour. The mercury absorbance calibration graph was linear up to 20 μg·kg− 1 with R2 > 0.999. The detection limits were determined to be 23 ng·kg− 1 and 17 ng·kg− 1 for bauxite and bauxite residue respectively. The relative standard deviation for 1 μg·L− 1 mercury standard solution (n = 27) was 1.5%. In the absence of a certified bauxite reference material, accuracy of the method was tested with the closest available zinc concentrate reference material. Spiking known amounts of mercury in bauxite and bauxite residue samples was also tested; 95-111% recovery was obtained for both samples. The method developed in this paper is recommended for measuring total mercury in bauxite and bauxite residue.