Mastodawn

The “Hydrochemical Gap”: why manual saturation indices don’t work
Many Kryvbas studies still estimate calcite saturation as if high-salinity waters behaved like distilled water.
This plot shows the opposite.

🔵 Blue line: textbook Ksp for calcite.
🔴 Red points: actual ion activity product (IAP) for real samples (PHREEQC).

Key facts:

1️⃣ At 30–40 g/L salinity, real IAP is 1.5–1.6 log units lower — meaning free Ca²⁺ activity is ~38× lower than concentration-based formulas predict.

2️⃣ The dip at 2–5 g/L marks the mixing zone, where ionic strength and ion-pairing change non-linearly and break simple calculations.

3️⃣ Main reason:
• high ionic strength suppresses activity,
• Ca²⁺ forms complexes,
• multicomponent interactions are non-linear.

Result:
Manual SI calculations suggest “precipitation,” but real activity shows undersaturation and aggressive water.
Only thermodynamic modelling reveals the true behaviour.

#Hydrogeochemistry #Geochemistry #Mining #PHREEQC #RStats #SvystunovaGully #Kryvbas #SvystunovaGully

Eugene Dec 8

🧪 The “Oversaturation Illusion” in Kryvbas Mine Waters

While modeling Kryvbas water chemistry (R + PHREEQC), I found a fundamental issue in how saturation is often evaluated.

We usually calculate calcite equilibrium from ion concentrations — fine for fresh water.
But Kryvbas mine waters are brines, where ionic strength and complexation dominate.

📉 Results from ~1000 samples (minteq.v4):
- Once salinity exceeds ~3 g/L, Ca²⁺ activity drops sharply.
- At 15–20 g/L, calcium activity coefficient is ≈ 0.35.

Meaning: more than half of the “calcium concentration” is inert — a dead load that cannot form precipitates.

This explains why traditional methods predicted oversaturation where the water was actually aggressive and dissolving rocks.

Modeling: PHREEQC + minteq.v4 (US EPA), Davis equation.

#Hydrogeochemistry #WaterChemistry #PHREEQC #Geochemistry #Groundwater
#Mining #Tailings #IonActivity #Thermodynamics #Kryvbas #OpenScience #RStats #SvystunovaGully