Page 108 - Geochemistry of Oil Field Waters

96 ANALYSIS OF OILFIELD WATERS

Acidifying the samples to pH 3.5 with acetic or hydrochloric acid
minimizes precipitation and adsorption. If acetic acid is used, 2 ml of formal-
dehyde per liter of sample should be added to retard mold growth. These
precautions will aid in obtaining representative heavy metal analyses; how-
ever, to obtain optimum results, the samples should be analyzed as quickly
after sampling as possible. If it is necessary to store the samples, they should
be stored in a cool, dark place and should not be moved frequently. Light
accelerates photochemical reactions, and high temperatures and moving
accelerate chemical reactions. Once the seal of the cap of the sample bottle
has been broken, the sample should be analyzed immediately.
A chelating ion-exchange resin such as Dowex A-1 can be used to separate
copper, iron, nickel, and lead from an aqueous solution. Slurry the resin into
a plastic column about 36 cm long and 1.7 cm in diameter. Convert the resin
to the sodium form by washing with 2 volumes of distilled water, 1 volume
being equal to the amount of resin used, followed by 2 volumes of 1N
sodium hydroxide, and then with 10 volumes of distilled water. Because the
resin expands more than 100% when changing from the hydrogen form to
the sodium form, the column must be backwashed frequently to reduce
compaction of the resin and to prevent shattering of the column. Pass the
brine which has been neutralized to pH 7.0 with sodium hydroxide through
the column. 2 liters or more probably will be necessary, depending upon the
amount of heavy metals present in the brine. Elute the chelated metals with
2 volumes of 2N hydrochloric acid and water effluents to a small volume;
cool and adjust to a predetermined volume (for example, 200 ml) with
water. Use aliquots of this solution for determining copper, iron, nickel, and
lead.
The resin must be changed back to the sodium form as soon as the metals
have been eluted, because the resin tends to lose its chelating capacity if left
in the water-rinsed hydrogen form for longer than a few hours. If this
happens, the resin can be regenerated by heating it at 6OoC in a 30-50%
sodium hydroxide solution for 24 hours.
Once the metals are separated from the brine and concentrated, they can
be analyzed using various methods such as atomic absorption spectrometry,
flame spectrometry, emission spectrometry, or colorimetry (Collins et al.,
1962).

The compound 2,9-dimethyl-1 ,lo-phenanthroline, assigned the name neo-
cuproine (Diehl and Smith, 1958, p.23), has the following structure: