The influence of metal ions on the adsorption /desorption of roxarsone on goethite surface

  • 王 少暐

Student thesis: Master's Thesis


Aromatic organoarsenical roxarsone (ROX) is a common feeding additive found in livestock This arsenic containing pollutant could be discharged into the environment through agricultural application of animal manure and pose potential threats to the population and our environment In this study the influence of pH competing anions and metal ions on the adsorption/desorption of ROX on goethite were examined in order to understand their mobility in the environment The adsorption of ROX on goethite is favorable at acidic pH In contrast adsorption reaction decreases dramatically with increasing pH from 6 to 10 This can be explained by that the negative charge density of the goethite surface increases with the high concentration of hydroxide which leads to a stronger electrostatic repulsion force between ROX and goethite surface The result suggests that surface charge greatly affects the surface adsorption sites on goethite Significant desorption of ROX from goethite surface occurs at high pH level as well as the presence of phosphate Both hydroxide ion and phosphate are common substances in the environment and are both potential competing anions for ROX The competition experiment was thus conducted to study which ion is more pronounced on ROX desorption The addition of phosphate desorbed more ROX than the addition of hydroxide ion at low pH As pH increases phosphate does not show much different effects from the addition of hydroxide ion The result provides a strong support that the presence of phosphate will greatly increase the mobility of ROX especially at low pH In addition to hydroxide ion and phosphate many metal ions were present in soils and animal excrements Six common metal ions including Zn2+ Cu2+ Fe3+ Mn2+ Mg2+ and Ca2+ were tested All spiked metal ions enhanced the stability of ROX adsorption on goethite surface and lead to less desorption when hydroxide was added The results demonstrate that metal ions may form complex or surface precipitate with ROX to enhance its adsorption The effects from Fe3+ and Cu2+ are more pronounced than other metal ions For example the adsorbed amounts of ROX were increased about 10 % and 5 % in the presence of Cu2+ and Fe3+ respectively However further studies are necessary to better understand the effects from different metal ions Although the addition of metal ions can enhance the affinity between ROX and goethite surface the effect caused by the pH change is more important Result of this research may shed lights on the environmental fate and transportation of aromatic organoarsenicals in soil and help predict and control the mobility of arsenic contaminants in geochemical environments
Date of Award2014 Aug 26
Original languageEnglish
SupervisorWan-Ru Chen (Supervisor)

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