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Table 4 MgCl2 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
Bischofite MgCl2 * 6H20 SI 0.00 − 0.19 − 0.40 − 0.75 − 0.75 − 0.40 0.02
Brucite Mg(OH)2 SI 0.51 0.17 − 0.24 − 1.06 − 1.16 − 0.35 0.40
Halite NaCl SI 0.00* 0.00* 0.00* 0.00* 0.00* 0.00* 0.00*
pH    6.9 6.3 5.7 5.2 5.3 5.7 6.9
Cl Cl− mol kg−1 11.6 11.7 11.7 11.9 11.9 11.7 11.6
Mg Mg2+ mol kg−1 5.59 5.59 5.59 5.59 5.59 5.59 5.59
Na Na+ mol kg−1 7.54 × 10–2 1.20 × 10–1 1.92 × 10–1 3.81 × 10–1 2.94e × 10–1 1.92 × 10–1 7.51 × 10–2
ΔHalite Incremental mol kg−1 0 4.47 × 10–2 7.19 × 10–2 1.89 × 10–1 − 8.71 × 10–2 − 1.03 × 10–1 − 1.16 × 10–1
ΔHalite Total mol kg−1 0 4.47 × 10–2 1.17 × 10–1 3.06 × 10–1 2.19 × 10–2 1.16 × 10–1 − 2.80 × 10–4
  1. Italics numbers indicate saturation or supersaturation
  2. *Indicates equilibrium phase.
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