Browsing by Author "Kwikima, Muhajir M."

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    Hexavalent chromium mobility and distribution behavior in riparian agricultural tropical soils: a column experiment
    (Springer Nature, 2022) Kwikima, Muhajir M.; Said, Alfred
    Ingestion has been identified as a significant source of hexavalent chromium exposure in humans. The metal exposure in a community fed by vegetables cultivated along the Msimbazi River's riparian area has been studied by ascertaining its bioavailability in soil. Through column experiments, the mobility and distribution characteristics of hexavalent chromium (Cr(Vl)) in soils were examined. To achieve saturation flow conditions, influent Cr(VI) solutions of 0.26, 0.52, and 1.04 mg/L were introduced from the upper side of the three columns, respectively, until the effluent solute concentration equaled the influent concentration. The findings demonstrate that the predominant process governing Cr(VI) mobility and dispersion in soils is the reduction to trivalent chromium (Cr(III)), followed by adsorption. The Cr(VI) concentration distribution on the column at the end of the experiment was reasonably even across the columns, with a little drop with depth, which is assumed to be related to the leaching of other minerals that impede Hexavalent Cr reduction/adsorption (VI). According to the findings, the increase in Cr(VI) concentration is proportional to the solute's adsorption in the soil. Furthermore, the time it took for the effluent-influent solute concentration equilibrium to be reached was proportional to the rise in influent Cr(VI) concentration. Given that reduction is the dominant process, vertical mobility, transportation, and dispersion of Cr(Vl) in soils may be argued to have a minimal environmental impact. However, due to the apparent soil's high adsorption capacity for Cr(VI) and hence its bioavailability, the metal may contaminate crops planted in the vicinity. Increases in variables that influence the oxidation of Cr(III) to harmful Cr(VI) in the soil, such as pH, may have a significant deleterious effect.
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    Sorption characteristics of hexavalent chromium in the soil based on batch experiment and their implications to the environment
    (Scientific Research Publishing, 2017) Lema, Meserecordias W.; Kwikima, Muhajir M.
    The objective of this experimental study was to determine the kinetics and equilibrium sorption of Cr (VI) in soils collected from Hengshui City of Hebei Province, China, based on batch experiments. The main concentration for this paper is on the effect of soil pH, solute concentration and ionic strength as the variable factors in the sorption of Cr (VI) in soils and the assessment of their implications to the environment. Atomic Absorption Spectrophotometer (AAS) was used for Cr (III) analysis; UV-VIS Spectrophotometer for quantification of Cr (VI) in soil samples and determination of electrical conductivity and temperature of the soil samples; and Automatic Laser Particle Size Analyzer LS230 for the determination of soil physical characteristics. Results from this study show that adsorption and reduction are major reactions accounting for removal of Cr (VI) from soil solution. It is concluded that chemical reactions such as reduction, strongly influence Cr (VI) mobility in soil. Adsorption kinetics experiments indicated that Cr (VI) removal from soil solution increases with increasing solute concentration, with decreasing pH and with decreasing ionic strength. Adsorption reactions reached equilibrium within 12 hours in batch reactors. Increasing background electrolyte concentration (KCI) decreases Cr (VI) adsorption on soil. The Cr (VI) adsorption isotherm for this soils conforms well to the Langmuir isotherm at constant pH. Two Cr (VI) adsorption parameters: the maximum sorption capacity (Qo) and Langmuir adsorption constant (KL), were determined as 1.0135 × 10−4 mol/g and 0.0622 mg/L, respectively. The reduction of Cr (VI) into less toxic Cr (III), means reduction of significant environmental problems. Finally, this study advises relevant environmental governing authorities to observe periodic monitoring of the status of Cr (VI) in soils.