Overview Data Input Data Output DIC Charge Balance Physico-Chem Params Reactions Redox Mineral Phases

Charge-Balance Adjustment

Step 1:  Calculate the Charge Balance Error

The first thing aqion does when you click on the button Start is to calculate the charge-balance error (CBE) of the input water. The screenshot below shows the CBE of the example water ib.sol.¹

The output panel displays:

• CBE in percent
• sum of cations in meq/L
• sum of anions in meq/L

The user can now select a chemical parameter, which will be re-adjusted to establish charge balance. The following parameters are available in the drop-down list:²

•  pH value	(default)
•  Ca
•  Mg
•  Na
•  K
•  SO4	[S(6)]
•  DIC	[C(4)]
•  Cl
•  NO3	[N(5)]
•  NH4	[N(-3)]
•  … etc.

Note: The button Details opens a guidance for charge-balance adjustment. It provides a hint which parameter, cation or anion, should be selected to establish charge balance.

Step 2:  Adjust Charge Balance

The example above has an error of -1.89. If we select the parameter “DIC” and click on button next ≫, the right screenshot pops up. It tells us that DIC is decreased:³

   5.894 mM ⇒ 5.455 mM

The line below displays the amount added (as the difference of both values):

   ΔDIC = -0.439 mM

A positive (negative) Δ-value signals addition (removal) of the element. The obtained solution is fully charge-balanced (and is referred to as Output 1).

In addition, aqion performs a second calculation (Output 2) to check whether minerals precipitate or not. In this example, the equilibrium solution is supersaturated with two minerals: calcite and siderite. The precipitation causes the final pH change from 7.00 to 6.95.

Remarks