Electrowinning Cell

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General Description

The electrowinning cell converts metal in solution into solid elemental metal. The user specifies the reaction in the normal way using the Reaction Block (RB). In the dynamic mode, the solids are removed separately in a batch process, to emulate the removal of cathodes on a plant. The energy required by the cell is calculated from the heats of reaction and the efficiency of the cell. The excess energy is used to heat the contents of the unit.

Diagram

The diagram shows the default drawing of the Electrowinning Cell, with all of the streams that are available for operation of the unit.

The physical location of the streams connecting to the Electrowinning Cell is unimportant. The user may connect the streams to any position on the unit.

Inputs and Outputs

Label	Required Optional	Input Output	Number of Connections		Description
Label	Required Optional	Input Output	Min	Max	Description
Feed	1 Required	In	1	20	The feed to the Electrowinning Cell
Anolyte	Required	Out	1	1	The Liquid outlet from the unit
Cathodes	Required	Out	1	1	Solids, or cathode, outlet from the unit
Vent	Optional	Out	0	1	Vent Stream (Vapour Only)

Behaviour when Model is OFF

If the user disables the unit, by un-ticking the On tick box, then the following actions occur:

The field MassFracToCath becomes visible and the user may set the fraction of the feed stream that reports to the 'Cathode' outlet. The default is 100%.
All streams connected to the unit will flow out of the 'Cathode' outlet, unless the user has changed the above field from 100%. In which case the user defined fraction of the feed streams will report to the Anolyte stream;
No reactions or heating will occur.

So basically, the unit will be 'bypassed' without the user having to change any connections.

Model Theory

The Electrowinning Cell is represented as a tank in which an electrolytic reaction occurs, resulting in metal being deposited onto a cathode from an aqueous solution. These reactions require energy to proceed, and the energy demand is calculated as follows:

At 100% efficiency, the energy calculated by the model corresponds to the amount needed to maintain the cell contents at the same temperature as the incoming feed. (EW Prod T = EW Feed T)
At less than 100% efficiency, the excess energy contributes to heating the products exiting the cell. (EW Prod T > EW Feed T)
These temperatures together with the energy addition required are shown on the EW Cell tab of the model.

The energy required by the electrowinning cell is determined by the enthalpy of the electrolytic reaction occurring within the unit. This enthalpy can be calculated in one of two ways:

Default Method: Enthalpy of Reaction = Sum of Heats of formation of the products - Sum of Heats of formation of reactants.
- [math]\displaystyle{ \Delta H_{\text{reaction}} = \sum H_f^{\circ}(\text{products}) - \sum H_f^{\circ}(\text{reactants}) }[/math]
- This is the default method of calculating the heat of reaction. The heats of formation of the species are defined in the species database.
Specified Method: The heat of reaction is directly specified in the reaction file. This approach is typically used when the heats of formation are unknown or unavailable.

Note:

The only supported method for user-defined heat addition or removal is the RHX-Power option, which can be added via the Reaction Editor - Adding Heat Exchange.

Flowchart

The following shows the sequence of events if sub model options are switched on. See next heading for more information.

Data Sections

The default access window consists of a number of sections, depending on user specifications. The tabs that may be visible are:

ECell tab - Contains general information relating to the unit.
RB - Optional tab, only visible if the Reactions are enabled in the Evaluation Block.
QFeed - Optional tab, visible if ShowQFeed is enabled. This and subsequent tab pages, e.g. QFeed.. and Sp, shows the properties of the combined feed stream. The tags in the QFeed tab are valid even when the ShowQFeed option is not selected.
Info tab - Contains general settings for the unit and allows the user to include documentation about the unit and create Hyperlinks to external documents.
Links tab, contains a summary table for all the input and output streams.
Audit tab - Contains summary information required for Mass and Energy balance. See Model Examples for enthalpy calculation Examples.