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Table 3 NaCl 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 − 0.46 − 0.14 0.10 0.33 0.26 0.10 − 0.46
Bischofite MgCl2 * 6H20 SI − 6.58 − 6.38 − 6.20 − 6.00 − 6.07 − 6.20 − 6.58
Brucite Mg(OH)2 SI − 6.51 − 6.48 − 6.19 − 5.84 − 5.94 − 6.19 − 6.50
Carnallite KMgCl3:6H2O SI − 7.41 − 7.63 − 7.74 − 7.80 − 7.79 − 7.74 − 7.41
Glauberite Na2Ca(SO4)2 SI − 1.02 − 0.71 − 0.48 − 0.27 − 0.32 − 0.48 − 1.03
Goergeyite K2Ca5(SO4)6H2O SI 0.32 − 1.54 − 2.59 − 3.47 − 3.21 − 2.60 0.32
Gypsum CaSO4:2H2O SI − 0.16 − 0.22 − 0.30 − 0.51 − 0.41 − 0.30 − 0.16
Halite NaCl SI 0.00* 0.00* 0.00* 0.00* 0.00* 0.00* 0.00*
Kieserite MgSO4: H2O SI − 5.99 − 5.64 − 5.19 − 4.42 − 4.72 − 5.16 − 5.99
Polyhalite K2MgCa2(SO4)4 * 2H2O SI − 8.82 − 9.01 − 9.73 − 11.9 − 10.9 − 9.7 − 8.82
Sylvite KCl SI − 1.98 − 2.24 − 2.42 − 2.63 − 2.56 − 2.42 − 1.98
pH    7.0 6.3 5.9 5.7 5.8 6.0 7.0
Ca Ca2+ mol kg−1 2.59 × 10–2 2.59 × 10–2 2.59 × 10–2 2.59 × 10–2 2.59 × 10–2 2.59 × 10–2 2.59 × 10–2
Cl Cl− mol kg−1 6.74 6.85 7.09 7.57 7.37 7.01 6.74
Fe Fe3+ mol kg−1 2.76 × 10–6 2.76 × 10–6 2.76 × 10–6 2.76 × 10–6 2.76 × 10–6 2.76 × 10–6 2.76 × 10–6
K K+ mol kg−1 1.78 × 10–2 1.78 × 10–2 1.78 × 10–2 1.78 × 10–2 1.78 × 10–2 1.78 × 10–2 1.78 × 10–2
Mg Mg2+ mol kg−1 5.02 × 10–4 5.02 × 10–4 5.02 × 10–4 5.02 × 10–4 5.02 × 10–4 5.02 × 10–4 5.02 × 10–4
Na Na+ mol kg−1 5.47 5.58 5.81 6.29 6.10 5.82 5.47
S SO42− mol kg−1 3.69 × 10–2 3.69 × 10–2 3.69 × 10–2 3.69 × 10–2 2.856 × 10–2 3.69 × 10–2 3.69 × 10–2
ΔHalite Incremental mol kg−1 0 1.11 × 10–1 2.39 × 10–1 4.79 × 10–1 − 1.96 × 10–1 − 2.82 × 10–1 − 3.48 × 10–1
ΔHalite Total mol kg−1 0 1.11 × 10–1 3.50 × 10–1 8.29 × 10–1 6.33 × 10–1 3.51 × 10–1 3.33 × 10–3
  1. Italics numbers indicate saturation or supersaturation. Solutions is considered at equilibrium with halite.
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