Macroscopic and spectroscopic investigation of interactions of arsenic with synthesized pyrite

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Title: Macroscopic and spectroscopic investigation of interactions of arsenic with synthesized pyrite
Author: Kim, Eun Jung
Abstract: Sulfide minerals have been suggested to play an important role in regulating dissolved metal concentrations in anoxic environments . Pyrite is the most common sulfide mineral and it has shown an affinity for arsenic , but little is known about the arsenic retention mechanisms of pyrite . In this study , interactions of arsenic with pyrite were investigated in an anoxic environment to understand geochemical cycling of arsenic better and to predict arsenic fate and transport in the environment better . A procedure using microwaves was studied to develop a fast and reliable method for synthesizing pyrite . Arsenic -pyrite interactions were investigated using macroscopic (solution phase experiments ) and microscopic (X -ray photoelectron spectroscopic investigation ) approaches . Pyrite was successfully synthesized within a few minutes via reaction of ferric iron and hydrogen sulfide under the influence of irradiation by a conventional microwave oven . The SEM -EDX study revealed that the nucleation and growth of pyrite occurred on the surface of elemental sulfur , where polysulfides are available . Compared to conventional heating , microwave energy results in rapid ( < 1 minute ) formation of smaller particulates of pyrite . Higher levels of microwave power can form pyrite even faster , but faster reaction can lead to the formation of pyrite with defects . Arsenic removal by pyrite was strongly dependent on pH and arsenic species . Both arsenite (As (III ) ) and arsenate (As (V ) ) had a strong affinity for the pyrite surface under acidic conditions , but As (III ) was removed more effectively than As (V ) . Under acidic conditions , arsenic removal continued to occur almost linearly with time until complete removal was achieved . However , under neutral to alkaline conditions , fast removal was followed by slow removal and complete removal was not achieved in our experimental conditions . A BET isotherm equation provided the best fit to arsenic removal data , suggesting that surface precipitation occurred at high arsenic /pyrite ratio . The addition of competing ions did not substantially affect the ultimate distribution of arsenic between the pyrite surface and the solution , but changing pH affected arsenic stability on pyrite . X -ray photoelectron spectroscopy revealed that under acidic conditions , arsenic was removed and formed solid phases similar to As2S3 and As4S4 by reaction with pyrite . However , under neutral to alkaline conditions , arsenic was removed and formed As (III ) -O and As (V ) -O surface complexes , as well as As2S3 /As4S4 -like precipitates . As pH increases , the amount of arsenic that formed As2S3 /As4S4 -like precipitates decreased , while the amount that formed As (III ) -O and As (V ) -O surface complexes increased . Under alkaline conditions , a FeAsS -like phase was also detected .
URI: http : / /hdl .handle .net /1969 .1 /ETD -TAMU -3138
Date: 2009-05-15

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Macroscopic and spectroscopic investigation of interactions of arsenic with synthesized pyrite. Available electronically from http : / /hdl .handle .net /1969 .1 /ETD -TAMU -3138 .

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