Comparative studies of the speciation patterns of nickel and chromium in surface-, ground- and wastewater systems in Botswana

Results of speciation studies of nickel and chromium in wastewater, surface and groundwater systems using flame atomic absorption spectrometry (FAAS), graphite furnace atomic absorption spectrometry (GFAAS) and differential pulse adsorptive cathodic stripping voltammetry (DPAdCSV) are presented. Dimethylglyoxime (DMG) and diethylenetriaminepentaacetic acid (DTPA) were used as complexing agents for DPAdCSV determination of nickel and chromium, respectively, at a hanging mercury drop electrode (HMDE). Total nickel was in the range 3091-3201 mg L^-1 in wastewater from an electroplating plant, 8.1-14.4 μg L^-1 in surface water (freshwater) and 6.38-16.95 μg L^-1 in groundwater. Total chromium was in the range 34.99-37.03 mg L^-1 in electroplating wastewater and 15.8-571.0 mg L^-1 in tannery effluents. Trace levels of chromium were detected in surface water (3.09-17.42 μg L^-1) and groundwater (18.01-36.39 μg L^-1). While most of the metal forms were found to be present in the CSV-labile fraction in the wastewater from the electroplating plant (mean of 67.9% for Ni and 79.8% for Cr), less than 5% of the total metal was present as CSV-labile fraction in tannery effluents, surface and groundwater samples. The tannery effluent was found to have very high complexation capacity (about 3 mg of Cr/L of effluent, i.e. 57.8 μM Cr). This complexing capacity of tannery effluent may have a potential application in environmental remediation.