Page 112 - Geochemistry of Oil Field Waters

100 ANALYSIS OF OILFIELD WATERS

Lead can be extracted from a basic solution with dithizone in chloroform or
carbon tetrachloride in the presence of citrate or tartrate, which prevent the
precipitation of several metal hydroxides. The optimum pH range for extrac-
tion of the lead dithizonate with chloroform is 8.5-11. Cyanide will com-
plex all interfering metals except bismuth, thallium, and stannous tin.
Because these metals are separated by ion, exchange, their interference is
eliminated. Ferric iron can form a ferricyanide that will oxidize dithizone;
however, this reaction can be prevented by adding a reducing agent such as
hydroxylamine hydrochloride.
Excess of calcium, magnesium, and phosphorus retards the lead dithizo-
nate extraction, but thz ion exchange separation excludes phosphorus as well
as much of the calcium and magnesium. The lead dithizonate in chloroform
absorbs at 510 mp. The amount of lead in the chloroform phase should not
be much greater than 2.5 mg/l for optimum results.

Reagents. Hydroxylamine hydrochloride solution : dissolve 10 g of hydroxy-
lamine hydrochloride in water and dilute to 50 ml.
Standard lead solution: dissolve 0.100 g of lead in 10-15 ml of nitric
acid. Dilute to 1 liter volume with water. Pipet a 100-ml aliquot of this stock
solution into another 1-liter volumetric flask, add 10 ml of nitric acid, and
dilute to 1 liter volume with water. This solution contains 10 pg/ml of lead.
Ammonia-cyanide-sulfite solution: add 350 ml of concentrated am-
monium hydroxide, 30 ml of a 10% potassium cyanide solution, and 1.5 g of
sodium sulfite, to a 1-liter volumetric flask and dilute to volume with water.
Dithizone solution: dissolve 0.01 g of dithizone in 200 ml of chloroform.
Chloroform.

Procedure. Transfer a sample of the ion exchange effluent containing up to
80 pg of lead to a 125-ml separatory funnel, and add 5 ml of hydroxylamine
hydrochloride solution, 75 ml of ammonia-cyanidesulfite solution, and 10
ml of chloroform. Shake the mixture vigorously for 1 minute, let the phases
separate, and discard the chloroform phase. Add 1 ml of 0.005% dithizone-
chloroform solution, shake the mixture vigorously for 1 minute, let the
phases separate, and extract the dithizone-chloroform phase into a 25-ml
volumetric flask. If the dithizone-chloroform phase is green or some color
other than cinnabar red, three possibilities exist: (1) there is no lead present;
(2) there is an oxidizing agent present; or (3) an excess of dithizone has been
used. In any event, if the dithizone-chloroform phase is not red, acidify it
with 15 ml of 1:lOO nitric acid, shake the mixture for 1 minute to transfer
the lead to the nitric acid phase, and discard the chloroform. Treat the nitric
acid phase with hydroxylamine hydrochloride solution, ammonia-cyanide-
sulfite solution, and make another dithizone-chloroform extraction using
0.5 ml or less of the dithizone-chloroform solution. If the dithizone-
chloroform phase still does not turn red, take a larger sample of the effluent.
However, if the original dithizone-chloroform extraction did turn red, make