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Table 5 A NaCl + MgCl2-brine heat exchange fluid composition and mineral saturation indices (SI) during heating and cooling processes as determined using PHREEQC 3 and Pitzer.dat

From: Evaluation of NaCl and MgCl2 heat exchange fluids in a deep binary geothermal system in a sedimentary halite formation

Mineral Formula   Heating (injection) Max Cooling (extraction)
10 °C 40 °C 70 °C 120 °C 100 °C 70 °C 10 °C
Anhydrite CaSO4 SI 0.00 − 0.43 − 0.94 − 1.91 − 1.50 − 0.76 0.01
Bischofite MgCl2 * 6H20 SI 0.00 − 0.21 − 0.42 − 0.76 − 0.62 − 0.34 0.01
Brucite Mg(OH)2 SI − 0.07 − 0.41 − 0.83 − 1.64 − 1.30 − 0.69 − 0.08
Carnallite KMgCl3:6H2O SI − 0.69 − 1.44 − 2.06 − 2.85 − 2.56 − 1.86 − 0.68
Glauberite Na2Ca(SO4)2 SI − 3.49 − 4.09 − 4.76 − 6.06 − 5.51 − 4.52 − 3.49
Goergeyite K2Ca5(SO4)6H2O SI − 0.41 − 6.38 − 11.5 − 19.0 − 16.1 − 9.86 − 0.37
Gypsum CaSO4:2H2O SI − 0.44 − 1.16 − 1.90 − 3.20 − 2.66 − 1.64 − 0.43
Halite NaCl SI 0.00* 0.00* 0.00* 0.00* 0.00* 0.00* 0.00*
Kieserite MgSO4: H2O SI − 0.49 − 0.94 − 1.25 − 1.62 − 1.48 − 1.15 − 0.48
Polyhalite K2MgCa2(SO4)4
* 2H2O
SI − 5.42 − 8.28 − 11.6 − 17.9 − 15.3 − 10.4 − 3.5
Sylvite KCl SI − 1.84 − 2.23 − 2.53 − 2.92 − 2.77 − 2.43 − 1.43
pH    6.7 5.9 5.4 4.8 5.1 5.6 6.7
Ca Ca2+ mol kg−1 5.76 × 10–3 5.76 × 10–3 5.76 × 10–3 5.76 × 10–3 5.76 × 10–3 5.76 × 10–3 5.76 × 10–3
Cl Cl mol kg−1 11.4 11.5 11.6 11.8 11.7 11.6 11.5
Fe Fe3+ mol kg−1 3.00 × 10–7 3.00 × 10–7 3.00 × 10–7 3.00 × 10–7 3.00 × 10–7 3.00 × 10–7 3.00 × 10–7
K K+ mol kg−1 1.93 × 10–3 1.93 × 10–3 1.93 × 10–3 1.93 × 10–3 1.93 × 10–3 1.93 × 10–3 1.93 × 10–3
Mg Mg2+ mol kg−1 5.61 5.61 5.61 5.61 5.61 5.61 5.61
Na Na+ mol kg−1 7.53 × 10–2 1.20 × 10–1 1.92 × 10–1 3.81 × 10–1 2.94 × 10–1 1.64 × 10–1 7.48 × 10–2
SO4 SO42− mol kg−1 6.95 × 10–3 6.95 × 10–3 6.95 × 10–3 6.95 × 10–3 6.95 × 10–3 6.95 × 10–3 6.95 × 10–3
ΔHalite Incremental mol L−1 0 4.47 × 10–2 7.21 × 10–2 1.89 × 10–1 − 8.75 × 10–2 − 1.30 × 10–1 − 8.92 × 10–2
ΔHalite Total mol L−1 0 4.47 × 10–2 1.17 × 10–1 3.06 × 10–1 2.19 × 10–1 8.87 × 10–2 − 5.00 × 10–4
  1. Italics numbers indicate saturation or supersaturation
  2. *Indicates equilibrium phase