Unit 08a : Advanced Hydrogeology. Aqueous Geochemistry. Aqueous Systems. In addition to water, mass exists in the subsurface as: Separate gas phases (eg soil CO 2 ) Separate nonaqueous liquid phases (eg crude oil) Separate solid phases (eg minerals forming the pm)
Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.
Aqueous Geochemistry
mg/kg = mg/L / solution density (kg/L)
Na2SO4 = 2Na+ + SO42
where mc is mass concentration in g/kg;
r is in kg/m3; and
FW is in g.
Na2SO4 = 2Na+ + SO42
m = (mc/FW)/(1 – TDS)
where mc is mass concentration in g/kg;
TDS is in kg/kg and
FW is in g.
meq/L = mg/L / (FW / charge)

105o
+
Structure of WaterSoluteWater
GasWater
Hydrolysis of multivalent ions (polymerization)
AdsorptionDesorption
MineralWater Equilibria
Mineral Recrystallization
Secs Mins Hrs Days Months Years Centuries My
Reaction Rate HalfLife
Reaction RatesAfter Langmuir and Mahoney, 1984
aA + bB = cC + dD
K = (C)c(D)d
(A)a(B)b
where K is the equilibrium constant and (A),(B),(C), and (D) are the molal (or molar) concentrations
[A] = ga(A)
K = gc(C)c gd(D)d =[C]c[D]d
ga(A)a gb(B)b [A]a[B]b
log gi =  Azi2(I)0.5
where A is a constant, zi is the ion charge, and I is the ionic strength of the solution given by:
I = 0.5 SMizi2
where (Mi) is the molar concentration of the ith species
log gi =  Azi2(I)0.5
1 + Bai(I)0.5
where B is a further constant, ai is the ionic radius
0.9
0.8
0.7
0.6
Activity Coefficient
0.5
DebyeHuckel
0.4
Extended
0.3
0.2
Davis
0.1
Pitzer
0
0.001
0.01
0.1
1
10
Ionic Strength
Divalent IonsIAP =[C]c[D]d = products
[A]a[B]b reactants
aA + bB = cC + dD
SI = log(IAP/K)
IAP = [Ca2+][CO32] = 0.57x3.37x104x0.56x5.50x105
[CaCO3] 1.0
= 6.56 x 109 and log(IAP) = 8.18
{IAP/K}calcite = 6.56/4.90 = 1.34
log{IAP/K}calcite = 8.31  8.18 = 0.13
log[Ca2+] = 3.67 log[Mg2+] = 4.32 log[CO32] = 4.51
log(IAP)=log([Ca2+][Mg2+][CO32]2)= 3.674.329.02= 16.31
log{IAP/K}dolomite = 16.57 – 17.01 = 0.44
k1
aA + bB = cC + dD
k2
where k1 and k2 are the rate constants for the forward (L to R) and reverse (R to L) reactions
rA = dA/dt; rB = dB/dt; rc = dC/dt; rD = dD/dt;
rA/a = rB/b = rC/c = rD/d
rA = k1(A)n1(B)n2 + k2(C)m1(D)m2
where n1, n2, m1 and m2 are empirical or stoichiometric constants
14C = 14N + e
d(14C)/dt = k1(14C) + k2(14N)(e)
d(14C)/dt = k1(14C)
Fe3+ + SO42 = FeSO4+
d(Fe3+)/dt = k1(Fe3+)(SO42) + k2(FeSO4+)