Study of Sulfate Reduction
251
funnel e first 1-2 ml of isobutanol with ethanol 1 : 1 mixture is added to prevent
foam. It is sequenced with 10% HzS04 added in small portions via the funnel
. d. First portions of acid decompose the carbonates and the evolving COz drains
a main stock of H z 35 S formed during the decomposition of AVS. This soft procedure of HzS extraction prevents the formation of pyrite and So, which can
occur in an aCId medium. When the visible gas evolving ceases, an excess of
sulfur acid is added and the N2 gas flow increased. After 20-25 min of this a
distillation, all clamps are closed and the content of the absorber is discharged
into the calibrated 25-ml cylinder. The remains are washed from it with a
weak alkaline solution if Zn-Cd mixture is used as absorbing substance, or
with methoxyethanol for a hyamine solution. The volume of liquid in the cylinder is recorded. Then the radioactivity of S2- is assayed in its exact portions as
precipitates of Zn-Cd sulfides, which are collected through the membrane
filters, or as 5 ml of hyamine solution injected directly into the scintillation vial
with 15 ml of toluene cocktail. With ZnS precipitates the Instagel cocktail is
preferable. The values of radioactivity thus measured are calculated per whole
volume of absorbing liquid in the cylinder to find the value of the radioactivity of 35S2- produced in the experimental vessel during its incubation from the
labeled sulfur (R;).
When the processing of all the experimental series is completed, the
killed control is also processed. After its distillation ends, the absorbing
liquid is discharged and three counting samples are prepared as follows.
One control sample is prepared as described above to account for any radioactive contamination of absorbing liquid during the procedure of H 2S distillation (Ro). The other two subsamples are used to measure the radioactivity
of sulfate in the water with added working solution, which has been used to
fill the experimental vessels, in order to estimate its inverse specific radioactivity (Sr) under conditions equal to those by measuring of Rrvalues (the
radioactivity of 35S2- produced). This water is diluted 1 :20 with 0.1 % Na2S04
solution. Then two parallel 0.3-0.5 portions of this dilution are injected into
the scintillation vials. When using hyamine solution as absorber, 3-5 ml portions of the latter are added into them and are radioassayed. The measured
radioactivity is calculated per 1-1 of the water used for filling the experimental vessels (Rs). If using ZnS04 + Cd-acetate as absorbing substance, several
drops of 10% BaC12 are added to the scintillation vials with the abovementioned portions of dilution injected into them, and they are kept at 80°C
to evaporate the liquid. Then the filters with the Zn-Cd sulfide precipitates are
placed into them. After filling them with the Instagel cocktail, the precipitates
in them are resuspended with the aid of a glass stick and they are radioassayed
to measured the same Rs value. Having determined the content of sulfate
sulfur in this water (Ks), the specific radioactivity of sulfate sulfur (Sr) is calculated as the ratio of K,IRs and expressed as f-lgScpm-1 or f-lg at Scpm- I .
Because the Rs value is measured under identical conditions with the R;,
quenching corrections are not needed. The rate of sulfate reduction (As) is
then calculated as follows:
251
funnel e first 1-2 ml of isobutanol with ethanol 1 : 1 mixture is added to prevent
foam. It is sequenced with 10% HzS04 added in small portions via the funnel
. d. First portions of acid decompose the carbonates and the evolving COz drains
a main stock of H z 35 S formed during the decomposition of AVS. This soft procedure of HzS extraction prevents the formation of pyrite and So, which can
occur in an aCId medium. When the visible gas evolving ceases, an excess of
sulfur acid is added and the N2 gas flow increased. After 20-25 min of this a
distillation, all clamps are closed and the content of the absorber is discharged
into the calibrated 25-ml cylinder. The remains are washed from it with a
weak alkaline solution if Zn-Cd mixture is used as absorbing substance, or
with methoxyethanol for a hyamine solution. The volume of liquid in the cylinder is recorded. Then the radioactivity of S2- is assayed in its exact portions as
precipitates of Zn-Cd sulfides, which are collected through the membrane
filters, or as 5 ml of hyamine solution injected directly into the scintillation vial
with 15 ml of toluene cocktail. With ZnS precipitates the Instagel cocktail is
preferable. The values of radioactivity thus measured are calculated per whole
volume of absorbing liquid in the cylinder to find the value of the radioactivity of 35S2- produced in the experimental vessel during its incubation from the
labeled sulfur (R;).
When the processing of all the experimental series is completed, the
killed control is also processed. After its distillation ends, the absorbing
liquid is discharged and three counting samples are prepared as follows.
One control sample is prepared as described above to account for any radioactive contamination of absorbing liquid during the procedure of H 2S distillation (Ro). The other two subsamples are used to measure the radioactivity
of sulfate in the water with added working solution, which has been used to
fill the experimental vessels, in order to estimate its inverse specific radioactivity (Sr) under conditions equal to those by measuring of Rrvalues (the
radioactivity of 35S2- produced). This water is diluted 1 :20 with 0.1 % Na2S04
solution. Then two parallel 0.3-0.5 portions of this dilution are injected into
the scintillation vials. When using hyamine solution as absorber, 3-5 ml portions of the latter are added into them and are radioassayed. The measured
radioactivity is calculated per 1-1 of the water used for filling the experimental vessels (Rs). If using ZnS04 + Cd-acetate as absorbing substance, several
drops of 10% BaC12 are added to the scintillation vials with the abovementioned portions of dilution injected into them, and they are kept at 80°C
to evaporate the liquid. Then the filters with the Zn-Cd sulfide precipitates are
placed into them. After filling them with the Instagel cocktail, the precipitates
in them are resuspended with the aid of a glass stick and they are radioassayed
to measured the same Rs value. Having determined the content of sulfate
sulfur in this water (Ks), the specific radioactivity of sulfate sulfur (Sr) is calculated as the ratio of K,IRs and expressed as f-lgScpm-1 or f-lg at Scpm- I .
Because the Rs value is measured under identical conditions with the R;,
quenching corrections are not needed. The rate of sulfate reduction (As) is
then calculated as follows: