Date of Award

Fall 1997

Project Type

Dissertation

Program or Major

Natural Resources

Degree Name

Doctor of Philosophy

First Advisor

Robert D Harter

Abstract

Radon, a carcinogenic radioactive gas and a contamination in household air and drinking water, has been an environmental issue of great concern in New England, particularly in the Concord and Conway granite areas of New Hampshire. One of the major factors controlling the releases of radionuclide is the weathering rate. In this project, two Conway granite samples collected from the Redstone Quarry, Conway, NH, were weathered in laboratory by several solutions (HNO$\sb3$, H$\sb2$SO$\sb4$, H$\sb2$C$\sb2$O$\sb4$, KHP, catechol, EDTA, and humic acid) using several methods (batch, FBR, and surface titration).

The release of all cations except K follows a typical parabolic pattern. K is first rapidly released then diffuses back into the weathering altered layer and is fixed. The high weathering capability of catechol is due to its preferential dissolutions of Si and Al. EDTA and oxalic acid have combined effects of proton- and ligand-promoted dissolutions. Humic substance has a much lower weathering capability than expected from their cation complexing capacity. The general weathering order is H$\sb2$O $<$ 0.01 M (NH$\sb4)\sb2$C$\sb2$O$\sb4 <$ 0.01 M KHP = 0.01% HA-Na $<$ 0.01 M catechol $<$ 0.01 M EDTA-2Na = 0.01 N HNO$\sb3 <$ 0.01 N H$\sb2$SO$\sb4 <$ 0.01 N H$\sb2$C$\sb2$O$\sb4.$.

The laboratory weathering rates $(kg\ m\sp{-2} s\sp{-1})$ are $2.82 \times 10\sp{-14} - 3.30 \times 10\sp{-12}$ for Conway granite, $2.06 \times 10\sp{-12} - 7.01 \times 10\sp{-12}$ for biotite, $5.21 \times 10\sp{-13} - 5.28 \times 10\sp{-12}$ for perthitic microcline, $5.18 \times 10\sp{-13} - 2.61 \times 10\sp{-12}$ for plagioclase, and $4.18 \times 10\sp{-16} - 1.74 \times 10\sp{-14}$ for quartz, respectively. The converted field rates $(kg\ m\sp{-2}$ watershed $s\sp{-1})$ would be $1.41 \times 10\sp{-10} - 1.13 \times 10\sp{-8}$ for Conway granite, $6.18 \times 10\sp{-10} - 2.10 \times 10\sp{-9}$ for biotite, $1.11 \times 10\sp{-9} - 1.35 \times 10\sp{-8}$ for perthitic microcline, $7.05 \times 10\sp{-10} - 1.67 \times 10\sp{-8}$ for plagioclase, and $7.52 \times 10\sp{-13} - 3.13 \times 10\sp{-11}$ for quartz.

The Conway granite weathering mechanism involves three successive steps: (1) instantaneous exchange of alkali cations and rapid desorption of non-network former cation; (2) gradually build-up of a residual layer depleted in cations but enriched in Si and/or Al; (3) slow dissolution of the residual layer. K reversal diffusion and internal fixation exists during the whole weathering process.

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