To CLASS PAGE:
||To measure zinc (Zn) sorption on the three soils and soil fractions as a function of concentration at constant temperature.|
|I. Experimental Design:|
|Initial concentrations of 0, 7.64, 15.3, 76.5,
153, and 1.53 × 103 µM
Zn (0, 0.5, 1, 5, 10, and 100 ppm) will be reacted with your soil and
soil fractions at their native pH. The Zn stock solution will be
0.0765 M (5,000 ppm), so
appropriate volumes of this stock will be added to each centrifuge tube
with enough 0.01 M NaCl to equal 36 mL total volume. Zinc
sorption will also be measured on your sand, silt, and clay fractions
for the 0, 15.3, 153, and 1.53 × 103 µM Zn treatments.
|1.) Weigh out
2 g (in duplicate) aliquots of your air-dried soil into 12 labeled
(labeled with the treatments
described above) 40 mL centrifuge tubes. Add the calculated amount of Zn stock to achieve the above
initial concentrations of Zn. Then add enough 0.01 M NaCl to yield a final volume of 36 mL.
|2.) Weigh 0.20 g of sand, silt, and clay into labeled 40 mL tubes and repeat as above.|
samples will be equilibrated for 24 h on a shaker.
equilibrium pH using a calibrated pH meter on all reacted
|5.) The solid
and solution will be separated by centrifugation for 15 minutes at 8000
rpm. If the supernatant is
not clear, pass the solution through a 0.2µm pore size membrane filter using 25 mm filter holders and 10
mL syringes into labeled test tubes.
|6.) Prepare Zn
standards of 0, 1.53 (0.1ppm), 7.64 (0.5ppm), 15.3 (1ppm), 22.95
(1.5ppm), and 30.6
(2ppm) µM Zn.
|7.) The equilibrium Zn
concentration will be measured using flame atomic absorption
against your standards. The amount sorbed will be calculated by difference between solution
concentration before and after equilibration.
|II. Data Analysis:
the amount sorbed on an oven-dried weight basis and plot the data
according to the sorption
equations discussed in lecture.
|2.) Input Zn
concentrations and pH into MINEQL+ program and determine any Zn
containing solid phase
which may be controlling solution phase Zn following addition of various levels of Zn to these soils