Evaluating Lead Chemistry Under Variable Water Quality Conditions
Mackenzie Lee Davies
10.25394/PGS.11950134.v1
https://hammer.purdue.edu/articles/thesis/Evaluating_Lead_Chemistry_Under_Variable_Water_Quality_Conditions/11950134
<p>Lead has long been identified as a health issue in the
United States. Government regulations limit the amount of lead allowed in
distribution pipes, fittings and residential plumbing systems, but lead
leaching problems persist as water quality changes or new technologies are
implemented. In this work, experiments were developed to determine the effect
of temperature, ionic strength, and carbonate concentrations on soluble lead
concentrations over relevant pH ranges. Equilibrium models were developed to
predict changes in soluble lead and the predominating solid(s) that form under
these varied water quality conditions. Additional experiments were also
performed to verify how effectively PbO<sub>2(s)</sub>, a lead(IV) solid, could
be measured using a colorimetric method. Results for the kinetic experiments
tested over a period of 48 hours found that an increase in temperature from 25°C to 55°C brought a decrease in soluble lead (i.e.
increased lead precipitation) across a pH range of 3.0-9.8. Increasing ionic strength
(NaCl) as well as increasing the total carbonate concentrations in these
solutions at 25°C
resulted in higher measured soluble lead over 48 hours at pH 7.0 than the same
kinds of experiments without these variables. In the solutions containing lead
with and without NaCl and NaHCO<sub>3</sub>, no solid was modeled to predominate
in equilibrium (6 week analysis). Since several of the 6-week experiments measured
lower levels of soluble lead than originally added, the systems were unlikely
to be at equilibrium. Additionally, the previously developed iodometric method
proved to be a feasible method of quantifying PbO<sub>2(s)</sub> in water with
80-88% accuracy. These findings may have important implications towards how
lead behaves in in-home water heaters or softeners.</p>
2020-03-06 19:14:33
lead
carbonate system
equilibrium model
kinetic analysis
equilibrium analysis
ionic strength
temperature change
lead(IV) analysis
residential water heater
residential water softener
Environmental Engineering Design
Environmental Engineering Modelling