Graduation Year

2009

Document Type

Thesis

Degree

M.S.

Degree Granting Department

Geology

Major Professor

Thomas Pichler, Ph.D.

Keywords

Pyrite, Trace metal, Carbonates, Hydrogeology, Mineral stability

Abstract

The mineralogic associations of arsenic (As) and antimony (Sb) were investigated for the Avon Park Formation (APF) in central Florida to determine its viability for aquifer storage and recovery (ASR). Rock samples were taken from fourteen different cores and samples were taken according to core length, interval samples, and based on areas suspected to contain high levels of arsenic and antimony, such as molds, dissolution fractures, pyrite, clays, and organic matter, targeted samples. Permeable samples were also taken from high permeability zones. In total 373 samples were described in hand specimen and analyzed for bulk rock chemistry. Inductively coupled plasma optical emission spectrometry and hydride generation atomic fluorescence spectrometry were used to determine Fe, Al, Si, Mg, Ca, S, P, Mn, Sr, Mo, As, and Sb in bulk samples, while electron-probe microanalysis was used to analyze Sb, As, Fe, S, Zn, Ca, Mo in discrete minerals.

The mineralogic and geochemical investigation showed: (1) bulk As and Sb concentrations within the APF are low; (2) As values range from < 0 .1 to 30.8 mg/kg and Sb from < 0.1 to 6.76 mg/kg; (3) average values are 2.24 mg/kg As and 0.28 mg/kg Sb; (4) pyrite is present as framboids, hollow framboid rings, "honeycomb" pseudo-framboids, small irregularly shaped pieces with topography, and euhedral crystals; it is typically associated with oxidized organic laminations, fractures, and molds; (5) the framboid rings may have been precipitated by a bacteria making them biogenic; (6) euhedral pyrites contain significantly less As than other morphologies while irregular pyrites have the most; (7) individual pyrites range from < 0.1 to 5820 mg/kg As while Sb ranges from < 0.1 to 2470 mg/kg; (8) the samples from zones of high permeability have lower As and Sb averages than those of the other samples: 1.02 mg/kg As and 0.15 mg/kg Sb versus 1.32 mg/kg As and 0.19 mg/kg Sb for interval and 3.16 mg/kg As and 0.37 mg/kg Sb for targeted samples;

(9) As is found mainly in pyrite but is possibly from organic matter and clay; (10) overall As concentrations and correlations may be low but individual cores and zones have high values; (11) the APF has appropriately permeable zones for ASR; (12) the success of ASR in the APF formation depends on the degree of geochemical alterations, presence of competing anions and simple organic ligands, and the amount of trace metals sorbed to surfaces versus coprecipitated.

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