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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.