The Effect of Natural Organic Matter on Arsenic Removal Using Iron Oxide Based Adsorbent

  • 傅 立達

Student thesis: Doctoral Thesis


In many regions of the world especially in the densely populated South East Asian deltas the health of millions of people is threatened by arsenic (As)-polluted water Long-term exposure to this toxic metalloid typically through drinking water can have devastating health effects including severe skin diseases cardiovascular diseases and cancers of the skin kidneys lungs and bladder It is now known that the mobility of As in environmental systems is mainly controlled by sorption to as well as desorption from mineral matter and by precipitation of As-bearing mineral phases Depending on the prevailing redox conditions iron (hydr)oxides and sul?de minerals are the main sinks for the metalloid Recent experiments and ?eldwork suggest that natural organic matter (NOM) which is ubiquitous in aquatic and terrestrial systems may interfere with arsenic adsorption But the parameters governing the influences of dissolved natural organic matter are not well understood The main objective of this study is thus to investigate the effect of NOM on As organically complexation speciation fate and transport in environmentally relevant condition Experiments presented in the first stage of this work consist of complexation of two model natural organic fractions humic acid (HA) and fulvic acid (FA) with arsenic species in the absence or presence of iron (hydr)oxides in water systems A two-site ligand binding model was successfully developed to describe the complexation of arsenic on the two natural organic fractions for different concentrations The model showed that the numbers of both types of binding sites were proportional to the HA concentrations while the apparent stability constants defined for describing binding affinity between arsenic and the sites are independent of the HA concentrations In order to build up a more comprehensive understanding of HA influence on As fate and transport in the environment effect of HA on As adsorption and pore blockage on iron-based adsorbent was also investigated The results showed that As uptake was suppressed by HA with the level of suppression increasing with HA concentration HA may partially cover the adsorption sites on the adsorbent as well as change the adsorption energy of arsenic Intragranular pores within the adsorbent may be blocked by HA slowing down the transport of arsenic within the adsorbent Due to the importance of adsorption kinetics and redox transformation of As during the adsorption process additional experiments presented in this thesis elucidated NOM effects on As adsorption-desorption kinetics and speciation transformation Experiments were conducted under different environmentally relevant conditions including the simultaneous adsorption of both As and HA onto iron oxide based adsorbent (IBA) HA adsorption onto As-presorbed IBA and As adsorption onto HA-presorbed IBA to better understand the effect of NOM on redox cycling of arsenic species Different concentrations of HA mediated the redox transformation of As species with a higher oxidation ability than reduction Presence of HA not only reduced the As uptake in the system with the co-presence of HA and As but also caused the release of significant amounts of previously sorbed As into solution The Weber’s intraparticle diffusion model was also used to gain insight into the mechanisms and rate controlling steps in which the results suggested that intraparticle diffusion of As species onto IBA is the main rate-controlling step The overall results indicated significant in?uence of NOM on the fate and transport of As in various environmental systems that must be considered when evaluating the environmental dispersion of the metalloid Knowledge about As-NOM interactions may give insights on the As mobility in NOM-laden groundwater and on the selection of more effective adsorption-based treatment methods for natural waters
Date of Award2014 Nov 18
Original languageEnglish
SupervisorTsair-Fuh Lin (Supervisor)

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