Page 58 - Geochemical Remote Sensing of The Sub-Surface

Geoelectrochemistry and stream dispersion 35

q = O, z > v~t (2.10')
qmax

When z and t have values such that (t >_ z/v~ff, z/v~ff--~oo), we obtain,

C 1
= [3 (q .... +C~176 ,z < t (2.11)
-- Veff
Co e I(C~ )) I Velr

From equations (2.9) and (2.11) and Fig. 2-14, it is obvious that the shape of the
concentration-front distribution is stabilised with time and the concentration front moves
with a certain constant speed, vr, determined by the following equation,

C~ v~ff (2.12)
Vf = Co +qmax

For example, if Vef f -- 10 .7 V0 and qmax/C0 = 100, from (2.12) we obtain vf = 10 .9 v0.
That is, under the given conditions of speed of quasi-convection, veff makes up to 10 .7 of
the physical speed of movement of bubbles, v0, and the speed of the concentration front

C/Co
1

0.8

0.6

0.4

0.2

0 50 1 O0 150 200
crn
Fig. 2-14. Concentration distribution of the mobile element forms in a I D convection stream halo
for different moments of time x, hours: 1- 100; 2- 300; 3- 500; 4- 1000; 5- 1500; vefr~lcm/hour;
~qmax/Veff=0.1 cm -1", 13Co/verr=0.1 cm l