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tiziano

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  1. Oops, I realized that I was mistaken. I had assigned 1 to the k-feldspar activity instead of albite. Problem solved. I apologize for the false alarm! 🙂
  2. Let me illustrate it by assigning activity_Na+ = 0.2 and activity_K+ = 0.3. Considering the logarithm of the ratio, we have: log K = log[(0.2*1)/(0.3*0.891)] = -0.126. Considering the relationship log K = log(0.2)+0+0.05012-log(0.3) = -0.126. On the contrary, if we consider the relationship log K = LOG(0.2)+0-0.05012-LOG(0.3) = -0.226; i.e., we get a different number if we have -0.0512.
  3. Hi Jia, thank you for the quick answer. I still have a doubt, because taking your formulation: logK = log activity(K-feldspar) + log activity(Na+) - log activity(albite) - log activity(K+) then it would be logK = log activity(1) + log activity(Na+) - log activity(0.891) - log activity(K+) logK = 0 + log activity (Na+) − (−0.05012) - log activity (K+) So: log⁡(K)= log ⁡activity(Na+) + 0.05012 − log ⁡activity(K+)) In other words, there should be +0.05012 because we have -(-0.05012). Thank you
  4. Dear GWB users, I have noticed something weird in the RXN tool. Specifically, writing the reaction: albite_low + K+ = k-feldspar + Na+ and assigning an activity of 0.891 to k-feldspar, the logK is calculated as: logK = -0.0501 + logNa - logK However, in reality, the logarithm of the equilibrium constant should be: logK = +0.05012 + logNa - logK because: logK = log[(Na/(K*0.891)] = logNa - log(K*0.891) = logNa - logK - log(0.891) = logNa - logK + 0.0512 Is that not correct? Or perhaps I am making a mistake somewhere? I would like to specify that I am using version 12.0.9.
  5. Hi, I am using GWB 12.0.6. These are the results obtained by Spec8: Temperature = 13.9 C Pressure = 1.013 bars pH = 7.997 Ionic strength = 0.005059 molal Charge imbalance = -0.000267 eq/kg (-3.873% error) Activity of water = 0.999995 Solvent mass = 1.0000 kg Solution mass = 1.0003 kg Mineral mass = 0.00000 kg Solution density = 1.021 g/cm3 Solution viscosity = 0.012 poise Chlorinity = 0.000132 molal Dissolved solids = 291 mg/kg sol'n Elect. conductivity = 326.08 uS/cm (or umho/cm) Hardness = 164.64 mg/kg sol'n as CaCO3 carbonate = 164.64 mg/kg sol'n as CaCO3 non-carbonate = 0.00 mg/kg sol'n as CaCO3 Carbonate alkalinity= 172.96 mg/kg sol'n as CaCO3 Water type = Ca-HCO3 Bulk volume = 980. cm3 Fluid volume = 980. cm3 Mineral volume = 0.000 cm3 Inert volume = 0.000 cm3 Porosity = 100. % Permeability = 98.7 cm2 Water is fresh (TDS = 291 mg/kg sol'n), so I am very surprised to obtain a calculated density of 1.021 g/cm3. This latter value is typical of seawater or an NaCl brine. Indeed, using PHREEQC and density calculation by Pizer.dat dataset, I have obtained Density (g/cm³) = 0.99950. Thank you.
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