The precipitation of Cu at pH 7 might depend on various factors like the initial concentrations of Cu, Cd, Zn, as well as the ionic strength of the solution. Check the equilibrium constants and solubility products used in your PHREEQC model, and ensure they are accurate for Cu precipitation at pH 7 under your specific conditions. Adjusting these parameters or considering additional chemical reactions may help simulate the expected Cu precipitation.

If you fix pH at 7, at least Cu(OH)2 precipitates.

DATABASE c:\phreeqc\database\minteq.v4.dat

PHASES

Fix_pH

H+ = H+

log_k 0

SOLUTION 1

pH 7

Cu 1

Cl 2

EQUILIBRIUM_PHASES

Fix_pH -7 HCl

Cu(OH)2 0 0

END

My fault. The right input file is as follows. Cu(OH)2 precipitates

DATABASE c:\phreeqc\database\minteq.v4.dat

PHASES

Fix_pH

H+ = H+

log_k 0

SOLUTION 1

pH 7 charge

Cu 1

Cl 2

END

USE SOLUTION 1

EQUILIBRIUM_PHASES

Fix_pH -7 NaOH

Cu(OH)2 0 0

END

The same:

DATABASE c:\phreeqc\database\minteq.v4.dat

PHASES

Fix_pH

H+ = H+

log_k 0

SOLUTION 1

pH 7 charge # Result: 3.883

Cu 1

Cl 2

END

USE SOLUTION 1

EQUILIBRIUM_PHASES

#Fix_pH -7 NaOH

Fix_pH -7 HCl

Cu(OH)2 0 0

END