Henryk Zbigniew WREMBEL EXCHANGE OF MERCURY

Henryk Zbigniew WREMBEL
U niversity of Education in Słupsk
EXCHANGE OF MERCURY BETWEEN WATER
AND THE WALL OF A VESSEL AND ITS EFFECT
ON THE RESULTS OF DETERMINATIONS
Contents:
ferences.
1. Introduction, 2. Experim ental, 3. Conclusions; 4. Streszczenie; R e­
1. INTRODUCTION
E xtrem ely high biological activity of m ercury necessitates the assaying
of low levels of the elem ent in the n atu ral environm ent. Assaying v ery
low levels of m ercury in w ater is of particu lar im portance. There are,
however, various processes w hich contribute to the vitiation of th e r e ­
sults of m ercury determ inations in aqueous solutions [2, 4, 5]. In p a rti­
cular. m igration of m ercury from w ater to the walls of vessels used for
sam pling and storage of sam ples as w ell as the reverse process — the
release of m ercury from the walls have a m arked effect on the results
of m ercury determ inations in w ater [1. 6].
This paper presents th e results of investigations (in phenom enolo­
gical form) of the kinetics of exchange of m ercury betw een the w all of
a vessel and its aqueous solution caused by th e physical sorption of m er­
cury on the wall, and th e kinetics of the reverse process — desorption
of m ercury from the wall, for various surface densities of solution. T he­
se processes w ere studied by using th e previously described [7, 8] ato­
mic emission spectrom etry w ith a low -pressure ring discharge.
2. EXPERIMENTAL
The kinetics of the sorption of m ercury from an aqueous solution on th e
w all of a vessel was studied indirectly by analysing variations in th e
m ercury concentration in a sam ple of w ater placed in a proper vessel.
For this purpose, a m ethod described in [6] and the equipm ent reported
in [7] w ere applied.
Oceanologia nr 13(1980)
8 — O ceanologia
The investigations w ere carried out using vessels made from various
m aterials, for various surface densities, the surface_density, dp being
defined by d p = Vr J P z , w here Vr is th e volum e of the aqueous solu­
tion of m ercury and P z is the surface area of th e vessel moistened by
the solution.
C urves shown in Fig. 1 illu strate th e losses of m ercury in time,
from distilled w ater to which given quantities of m ercury w ere added
(w ithout preservatives) due to sorption of m ercury on the w all of the
Time
t , hr'
Upływ czasu
t, godz.
Fig. 1. V ariations in the m ercury level due to physical sorption in sodium glass
vessels, in distilled w ater (without preservatives, at concentration C = 1 ng dm-3
at 20°)
for:
1 — dp =
1.66 cm3 cm -2;
2 — dp = 0.34 cm 3cm-2; 3 —
dp =* 0.12 cm 3 cm-2
Rys. 1. Zm iany zawartości rtęci spowodow ane sorpcją fizyczną, w naczyniach
ze szkła sodowego, dla w ody destylow anej (bez środków stabilizujących, przy stę­
żeniu C = 1 ng/dm 3, itemiperaitiuira t = 20^ 0 dla: 1 — dp = 1,66 cm 3/cm 2; 2 —
dp = 0,34 cm 3/am 2; 3 — dp = 0,12 em 3/cm 2
vessel. The initial concentration of m ercury, C, was 1 ng dm"3 and the
experim ent was carried out at a tem p eratu re of 20°C. W ith various su r­
face densities, th e highest diurnal losses due to this phenom enon, re a ­
ching 40 per cent of the initial m ercury content, occurred at d p —
= 0.12 cm3 cm '2.
It was found th a t w ith subm icro trace levels of m ercury in w ater
a decrease in th e m ercury level by one or even two orders of m agnitu­
de m ay occur w ithin a relatively short period. This w as illustrated in
the experim ental curves shown in Fig. 2 obtained for distilled w ater
Reproducibility of signal
Powtarzalność sygnału
Fig. 2. S ignal for a m ercury solution in d istilled w ater (without preservatives)
stored in a sodium glass vessel at C = 0.1 ng dm-3; dp = 0.34 cm3 cm-2; t — 20°C:
1 — in freshly prepared solution; 2 — after 24-hr storage; 3 — after 1-week
storage.
R ys 2. S ygnał otrzym any dla rozrtiworu mtęci w w odzie destylow anej (bez środ­
ków stabilizujących, przechow ywanej w naczyniu ze sakla sodowego, przy C =
0,1 ng/idm3, cip = 0,34 cm 3/cm 2 oraz t = 20°C: 1 — iw roztworze śiwieżyim, 2 — po
dobowym przechow yw aniu, 3 — po tygodniow ym przechow ywaniu.
Time, t, hr
Upł y w c z a s u t , go dz .
Fig. 3. Losses of m ercury due to sorption on the w alls of th e velsisels for
C = 1 ng dm-3, dp = 0.34 cm 3 cm -2 and t = 20° łn: 1 — sodium g la ss vessels;
2 — polyethytlene vessels; 3 — siliconized vessels; 4‘— quartz vessels.
Rys. 3 W ielkość strat rtąci spow odow anych sorpcją w ściance naczynia, dla
C = 1 ng/dm s, dp — 0,34 cmVorn* oraz t = 20° pow stające w: 1 — naczyniach
ze szklą sodoiwego, 2 — naczyniach polietylenow ych, 3 — naczyniach szklanych
silikonow anych, 4 — naczyniach ze szkła kwarcow ego.
Reproducibility of sigr.?.l
P o w ta r z a ln o ś ć s y g n a łu
Fig. 4. Curvies of a signal after repetition of the m easurem ents w ith sam ples
of fresh ly prepared solution (1), that stored for 24 hrs. in a quartz v essel (2), in
a polyethylene vessel (3), in a sodium glass vessel (4).
Ryis 4. K rzyw e sygnału otrzym ane przy powtórzeniu pom iarów na próbkach
sporządzonych z roztworu świeżego. (2) oraz z roztwo.ru przechow yw anego przez
jedną dobę w naczyniach ze szkła kw arcow ego (2), polietylenu (3) i szkła sodowego
( 4 ).
w ith an initial m ercury concentration of 0.1 ng d m '3 in freshly prepared
solution, after 24 hrs and after keeping th e solution in a sodium glass
vessel for one week, respectively. The signal obtained after one-v/eek
storage corresponds to a decrease of its content by approxim ately two
crders of m agnitude.
The sorption kinetics of m ercury on th e w alls of vessels was stu ­
died by using vessels made from sodium glass, glass siliconized with
chlorosilanes, polyethylene vessels, and quartz vessels at dp = 0.34 cm3
cm-2. The highest losses of m ercury from solution, due to sorption on
the walls, took place w ith sodium glass vessels and th e lowest w ith
quartz vessels (Fig. 3).
V ariations in m ercury concentrations in w ater due to its sorption
on the walls of the vessels are p articu larly large in th e submicro trace
levels (0.01— 1 ng dm-3) of m ercury. The largest variation of a signal
for distilled w ater, free of preservatives, occurs w ith w ater samples
Time, t,
Up-V’W
hr
t, q c d r .
Fig; 5. The effect o f the addition of 0 1 g dm*3 of
stabilization of • a solution of m ercury in distilled w ater
= 1 ng dm-3, t — 20°C, dp = 1.06 cim3 cm_!
1 — variations of the m ercury concentration in a solution
dm3
2 — variations of the m ercury concentration in a solution
KI.
Rys. 5. W pływ dodatku
rtęci w w odzie destylow anej
dp — 1,66 cta’/cm 1;
1 — zm iany stężenia, rtęci w
2 — zm iany stężenia rtęci w
potassium iodide on the
in a glass vessel at C
containing 0.1 g KI per
w ithout the addition of
0,1 g/dm 3 jodku potasow ego na stabilizację roztworu
w naczyiniu szklanym przy C = 1 n^'/drn1, t = 20°C
roztw orze z dodatkiem 0,1 g / d m 3 KJ,
roztw orze bez dodatku KJ.
stored in sodium glass vessels. W ith the initial m ercury concentration
C = 0.1 ng dm-3, at dp = 0.34 cm 3 cm '2, at 20°C, th e drop in th e m er­
cury concentration over 24 hrs. m ay be as high as 1—2 orders of m a‘
gnitude. These variations have been shown in th e form of analytical
curves in Fig. 4, taken in a series of m easurem ents of a freshly prep a­
red solution of m ercury in distilled w ater w ithout preservatives, stored
in vessels made from sodium glass, polyethylene and quartz glass.
The efficiency of the addition of potassium iodide to aqueous solu­
tion of m ercury was also investigated. This salt has been known to p re ­
vent sorption on th e wall. The addition of 0.1 g of potassium iodide to
1 dm 3 of a solution of m ercury in distilled w ater reduced m ercury losses
due to sorption considerably, sim ilar to [3]. Curves shown in Fig. 5
illustrate the losses of m ercury in distilled w ater (initial m ercury con-
T im e
U p ły w c z a s u
.
„
* 3°
Fig. 6. Variations of the m ercury concentration in distilled w ater (with preser­
vatives added, a t dp = 0.34 cm 3 cm-2, t = 20°C) caused by desorption of m ercury
from the waills of a vessel p reviously contam inated w ith m ercury:
1 — in a sodium glass vessel,
2 — in a polyethylene vessel,
3 — in a quartz vessel.
Rys 6. Zm iana stężenia rtęci w w odzie destylow anej (z dodatkiem substancji
stabilizujących, przy dp = 0,34 cm’ /om 2, i = 20°C) w skutek uw alniania rtęci ze
ścianek naczynia skażonego uprzednio rtęcią
1 — w naczyniu ze szkła sodowgeo
2 — w naczyniu polietylenow ym ,
3 — w naczyniu ze szkła kwarcowego.
centration C = 1 ng dm"3; d p = 1.66 cm! cm-2; t = 20°C) sabilized and
not stabilized w ith potassium iodide, stored in a glass vessel.
A reverse process, i.e. desorption of m ercury from the w all of the
vessel and its m igration into the bulk of the solution, was also studied.
By analogy to the sorption, the desorption process was studied by mo­
nitoring variations in the m ercury level in w ater. To contam inate the
vessels w ith m ercury, th ey w ere filled w ith a solution of m ercury
(C = 1 g dm '3) in distilled w ater for 24 hrs. The solution was free of
preservatives. Subsequently the vessels w ere filled w ith distilled w a­
te r w ith the addition of concentrated nitric acid (p.a.) at a ratio of 1 : 9
and 0.1 g d m '3 of potassium iodide. In Fig. 6 th e corresponding v aria­
tions in m ercury concentration in w ater due to desorption have been
shown.
It was found th a t upon prolonged storage of w ater containing u l­
tram icro traces of m ercury (10— 1000 ng d m '3) a gradual decrease in
m ercury concentration occurred even in the presence of preservatives.
A certain anom aly was observed in polyethylene vessels. W ith m ercu-
ry levels of th e order of 10 ng d m '3 in w ater stored in these ves­
sels, a distinct drop occurred in the m ercury level during first
days followed by a gradual increase. W ith a solution of th e ini­
tial m ercury level of 20 ng dm '3 kept in polyethylene vessels, th e
m ercury content increased tw ice w ithin tw o months, w hereas in th e
glass and quartz vessels the content decreased during this period
(Fig. 7). The reason for this was probably leaching by nitric acid of
m ercury left after washing in deeper layers of the wall. However, th e
diffusion of m ercury through th e w all from th e surrounding air can­
not be ruled out.
Time t , risys
U p ły w C2s s u t, dni
Fig. 7. Variations of the m ercury concentration in aqueous solution w ith p re­
servatives added, at an in itial m ercury concentiraiton of C = 20 ng dm-3 -duiring
prolonged storage of w ater in
1 — tpolyethylene vessels,
2 — quartz vessels,
3 — sodium glass vessels.
Ry.s. 7. Zm iany stężenia rtęci w roztworze w odnym z dodatkiem środków
stabilizujących, przy początkowej zaw artości rtęci C = 20 n g /d m 3 przy długotrw a­
łym przechow ywaniu w ody w
1 — pojem nikach polietylenow ych,
2 — naczyniu ze szkła kwarcow ego,
3 — naczyniu ze szkła sodowego
3. CONCLUSIONS
The results of this study reveal the possibility of large errors of de­
term ination of ultram icro- and particu larly submicro trace am ounts
of m ercury in w ater due to m igration of th e m etal betw een th e w all
of the vessel. Of th e vessels tested, the largest errors w ere observed
in the case of the polyethylene vessels. In these vessels, under favo­
urable conditions, the diurnal losses of m ercury may am ount to 50
per cent and even more over the range of ultram icro trace amounts.
The kinetics of th e exchange of m ercury betw een the solution and
the w all of the vessel depends largely on the surface density of the solu"
tion and the m aterial w hich th e vessel is made. Q uartz vessels proved the
most suitable for prolonged storage of w ater containing m ercury, w he­
reas the polyethylene vessels contributed most to errors in th e m e'
asurem ents.
H enryk Zbigniew WREMBEL
W yższa Szkoła Pedagogiczna w Słupsku
WYMIANA RTĘCI MIĘDZY WODĄ A ŚCIANKĄ NACZYNIA
I JEJ WPŁYW N A WYNIKI OZNACZEŃ
Streszczenie
Na w yniki oznaczeń rtęci w w odzie w zakresie ultram ikrośladów poważny w pływ
w yw iera sorpcja i desorpcja fizyczna rtęci w ściankach naczynia. W ykonano ba­
dania tego zjaw iska dla naczyń szklanych, polietylenow ych i kwarcow ych, przy
różnych gęstościach powierzchniowych roztworów rtęci, w w odzie destylow anej.
Przy długotrw ałym przechow ywaniu wodnego roztworu rtęci w naczyniach z od ­
powiednich m ateriałów obserwuje się dość znaczne zm iany stężenia rtęci w roz­
tworze, spowodowane zarówno przez sorpcję, jak i desorpcję rtęci w ściankach
naczynia. Badania świadczą o m ożliw ości pow staw ania w zakresie ultram ikrośladowych, a zwłaszcza subm ikrośladow ych stężeń rtęci w w odzie naw et bardzo
dużych błędów oznaczeń, spowodow anych m igracją rtęci m iędzy roztworem,
a ścianką naczynia użytego do pobierania i przechow ywania próbki. Stw ierdzo­
no, że najw iększe m ożliw ości pow staw ania błędów oznaczeń spowodowanych przez
te zjaw iska w ystępują przy użyciu naczyń polietylenu. W naczyniach sporządzo­
nych z tego m ateriału, w sprzyjających warunkach dobowe zm iany zaw artości
rtęci w zakresie ultram ikrośladów m ogą w ynosić 50%» i w ięcej stanu pierwotnego.
K inetyka w ym iany rtęci m iędzy roztworem a ściankam i naczynia w ykazuje
przy tym dużą zależność od gęstości powierzchniowej roztworu, tem peratury
m ateriału z którego sporządzono naczynie itd.
Spośród badanych naczyń użytych do długotrw ałego przechow ywania wody
zaw ierającej rtęć najkorzystniejsze okazały się naczynia ze szkła kwarcow ego.
U życie do tego celu naczyń polietylenow ych znacznie zw iększa ryzyko pow sta­
nia przypadkowych błędów, spowodow anych stratam i rtęci w w yniku jej m igra­
cji z roztworu do ścianki lub też procesu przeciwnego, m ianow icie w zrostu stę­
żenia rtęci w skutek procesów desorpcji rtęci ze ścianek naczynia do roztworu.
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