| Contamination often threatens regionalized water sources that are crucial to human survival, a particular problem in developing countries. Oxyanions such as arsenite and arsenate cause difficult remediation challenges, and are often present with a mix of other contaminants including cationic metals such as nickel and zinc. Current remediation strategies are often ineffective, cost-prohibitive or can alter site conditions resulting in immobilization of other contaminants. Understanding and evaluating treatment technologies are critical for efficient and long-term remediation. An emerging technology, surface-functionalized fish bone (FB), may be a good candidate for in-situ treatment strategies by both direct injection into a contaminant source area and use as a reactive material. The material is organic-cleaned hydroxyapatite (HA) from FB reacted with iron-amendments to modify the surface and improve material functionality and sorption characteristics. This research shows significant development of a pretreatment process to increase the effectiveness of HA, processed in the manner described, to sorb oxyanions. This research shows tremendous potential for improvements in cost-effective groundwater aquifer treatment and protection technologies.;A four-step (boil, bubble, bleach and bake; 4B) organic removal process was investigated on a commercial biogenic HA (Apatite II(TM)) product and catfish heads with thermal treatment to 200°C-400°C. Thermogravimetric analysis, the loss-on-ignition method, and total and dissolved organic carbon showed significant removal of organic carbon. The Brunauer, Emmett, and Teller surface area after the 4B process ranged from 58.1 to 126.7 m2/g for the HA with particle size from 2mm to less than 75microm. The 4B process improved sorption with treatment successes of the two HA sources similar, with catfish bone slightly more effective than the commercial HA. Sorption was significantly higher for 400°C thermal treatment compared to 200°C.;The 4B HA was then reacted in an iron solution of either ferrous or ferric chloride between 1.6 to 4.5 pH. The HA pHPZC decreased after iron-modification and suggested the possible prevalence of iron-phosphates instead of and/or in addition to iron-oxides. Batch equilibrium studies of iron-modified HA resulted in increased arsenic removal efficiency, and decreased sorption of cations nickel and zinc when compared to un-amended 4B HA. Ferrous iron-modification proved more effective to remove arsenate and arsenite from the aqueous phase, but less effective than ferric iron-modification to remove nickel and zinc.;The arsenite and arsenate removal efficacy from a synthetic groundwater near neutral pH resulted in the overall best removal by 400°C thermal treatment, catfish bone, ferrous iron-modification and arsenate independent of the other variables. The catfish bones were also tested over a wide pH range and showed arsenite sorption to be strongly pH dependent with significantly more removal above neutral pH. Arsenate was also pH dependent, especially for catfish bone not modified by iron, with iron-modified catfish bones showing strong removal above pH 5. A five-step sequential extraction showed minimal arsenic desorbed during the exchangeable extraction that suggested most arsenite and arsenate was not loosely sorbed. The majority of arsenic, regardless of speciation, was extracted in the carbonate fraction for ferrous iron-modified HA, and in the reduced fraction for ferric iron-modification. Greater than 95% iron was extracted for ferric iron-modified HA during the reduced fraction that targets ferric iron. Only 70% iron was extracted in the reduced phase with 30% of the total iron in the amorphous fraction, which indicated the formation of a secondary iron phase. Results suggested no arsenic was associated with this phase, or that it was loosely sorbed and extracted in an earlier fraction, most likely the carbonate fraction. |
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