# Solvent Extraction Unit

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## General Description

The Solvent Extraction unit is designed for use as a solvent extraction model, which can also be configured to do organic stripping. The model ensures that mainly aqueous phases leave via the aqueous stream and organic phases leave through the organic stream.

The user is responsible for setting up a suite of species which accurately portrays the application that is being evaluated e.g. H2O, H2SO4, Cu, Fe, CuSO4, FeSO4, Fe2[SO4]3, Kerosene, RH, R2Cu, R2Fe, R3Fe. This suite of species is typically set up for chelating type of organic solvents such as the LIX hydroxy oxime copper extractants available from the Henkel Corporation i.e. LIX 64N, 65N, 860, 864, 865, and 622.

The model is capable of the following:

1. The unit will separate the phases based on either Individual Phase or density:
• The user may specify an Individual phase to report to the Organic stream. All solids and other liquid phases will classed as Aqueous; or
• The user may specify the density of separation. The aqueous species are denser than the user defined density of separation and the organic species less dense. e.g. with a separating density of 950 kg/m3, water and all dissolved aqueous species will report to the aqueous phase and the organic species, normally with densities less than approximately 850 kg/m3, will report to the organic phase. Note that solids will also split on density.
2. The user may also specify the entrainment of:
• Aqueous in the Organic stream (this will also include any solids that are in the aqueous phase); and
• Organic in the Aqueous stream.
3. The user would select a primary metallic element of interest that is to be extracted, e.g. Primary Metal 'Cu'
4. The user should supply a reaction which utilises the specified Primary Metal, for example:
$\mathbf{\mathrm {2RH(o) + CuSO4(aq) = R2Cu(o) + H2SO4(l)}}$.
Or, in the case of stripping:
$\mathbf{\mathrm { R2Cu(o) + H2SO4(l) = 2RH(o) + CuSO4(aq)}}$

Method = Isotherms (McCabe-Thiele diagrams):

If the user selects Method = Isotherms, then the Isotherms will be used to determine the extent of the first reaction

1. The model uses the concentration of the primary metal in the streams entering the unit and the extraction (or stripping) isotherm, provided by the user, to determine the required primary metal concentration within the aqueous and organic phases. The model then calculates the extent to which the defined reaction should proceed to give the desired concentrations.
2. The ratio of the organic phase volume flow to the aqueous phase volume flow within the unit also fulfils a crucial role in the equilibrium extraction calculation. It provides the slope of the McCabe-Thiele operating line (a straight line). The Y-intercept is calculated by SysCAD using the data provided by the user. It is called MinOrgConc in the case of extraction, and MinAqsConc in the case of stripping.
3. The model is not currently sensitive to pH and assumes that the pH is correct for a particular equilibrium isotherm.

### Diagram

The diagram shows the default drawing of the Solvent Extraction unit, with all of the streams that have to be connected for the unit to operate.

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

## Inputs and Outputs

 Label RequiredOptional InputOutput Number of Connections Description Min Max. Aqueous Inlet 1 Required In 1 20 Aqueous feed to Solvent Extraction unit. Organic Inlet 1 Required In 1 20 Organic feed to Solvent Extraction unit. Aqueous Outlet Required Out 1 1 Aqueous outlet from Solvent Extraction unit. Organic Outlet Required Out 1 1 Organic outlet from Solvent Extraction unit.

## Behaviour when Model is OFF

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

• All streams connected to the 'Aqueous' inlet will flow straight out of the 'Aqueous' outlet;
• All streams connected to the 'Organic' inlet will flow straight out of the 'Organic' outlet;
• No reactions will occur.

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

## Model Theory

The Isotherm Method of modelling a Solvent extraction unit is based on the McCabe-Thiele method. This assumes that the operating line on the xy diagram, representing a single solvent extraction stage, is linear. The diagram below illustrates the graphical representation of the unit:

The operating line is the ratio of the incoming organic stream to the incoming aqueous stream.

The Equilibrium line is determined from experimental test data.

(This is the Isotherm that the user is required to input to the model. For extraction, the x axis is the concentration of the primary metal in the aqueous phase and the y axis is the concentration of the primary metal in the organic phase. For stripping, the x axis is the concentration of the primary metal in the organic phase and the y axis is the concentration of the primary metal in the aqueous phase.)

If the Metal (in this case Copper) concentration in the incoming Aqueous stream is 1.7 g/l, then, move vertically up the red line to the operating line, then horizontally to the Equilibrium line to find the equilibrium values of the Copper concentrations in the exiting Aqueous and Organic streams.

In this case the Organic Stream will contain 5g/l Cu and the Aqueous 0.4g/l Cu at equilibrium.

The values will be adjusted to take into account the stage efficiency, as the two phases are not usually in contact long enough to achieve perfect equilibrium.

In this example, the user will insert the Equilibrium curve into the model, and then the Reaction file should contain a reaction with the following form:

$\mathbf{\mathrm { CuSO_4(aq) + 2 RH(o) = H_2 SO_4(aq) + R_2 Cu(o)}}$

Extent:Fraction$\mathbf {\mathrm{ CuSO_4(aq) = 0.5}}$

Where (aq) denotes the aqueous phase and (o) the organic phase.

The model will adjust the extent of the reaction to produce the required aqueous and organic Copper concentrations.

## Data Sections

The default access window consists of several sections:

1. SolvExtr-1 tab - Contains general information relating to the unit.
2. RB - Optional tab, only visible if the Reactions are enabled in the Evaluation Block.
3. Isotherm tab - The user can set up and view the isotherm.
4. Info tab - Contains general settings for the unit and allows the user to include documentation about the unit and create Hyperlinks to external documents.
5. Links tab, contains a summary table for all the input and output streams.
6. Audit tab - Contains summary information required for Mass and Energy balance. See Model Examples for enthalpy calculation Examples.

### Solvent Extraction Page

Class: SolvExtr-1 The first tab page in the access window will have this name.

Symbol / Tag

Input / Calc

Description/Calculated Variables / Options

### Requirements

On Tick box If this is enabled then the unit will be in full operational mode. If this is disabled, then unit will be 'inoperative', as described in Inoperative Mode.
SeparationMethod / SeparMethod Density The user selects the Density of Separation. All species (INCLUDING solids) that have a density LESS than this density will report to the organic outlet. All species with a density GREATER than this density will report to the Aqueous outlet.
IndPhase to Organic The user selects the Individual liquid Phase(s) (usually (o)) that reports to the organic phase. All solids and other liquid phases will report to the Aqueous phase.
SeparDensity / SeparRho Input Visible if SeparMethod = 'Density'. The required separation density.
This must be a value between the density of the aqueous and organic streams.
Note: The density of water is a function of temperature, and is often less than 1000 kg/m3; therefore it is safer to specify a separation density below 950 kg/m3.
List of Liquid Individual Phases Tick Boxes Visible if SeparMethod = 'IndPhase to Organic'. The user must select one or more Individual liquid phases that will report to the Organic outlet. Normally, the user will select the 'o', or 'org' phase. All other liquid phases will report to the Aqueous outlet.
(The user defines the Individual phase for each species in the Species Database. Normally organic species are defined to have an individual phase of 'o', or 'org'. Please see Individual Phase Label for information on how to change the Individual Phase of a species)
Entrainment Feed Loss The Aqueous/Organic loss is defined as a percentage of the feed streams.
Product Fraction The Aqueous/Organic loss is defined as mass concentration in the outlet stream, normally in ppm. This method is only available in SysCAD9.2 Build 135.14652 or newer.
AqueousLossReqd / AqsLossReqd Input Visible with the Feed Loss Entrainment method. The mass fraction of Aqueous liquid in the unit lost to the Organic product stream.
Note that solids in the Aqueous phase will also report to the Organic stream when an entrainment value is specified.
OrganicLossReqd / OrgLossReqd Input Visible with the Feed Loss Entrainment method. The mass fraction of Organic liquid in the unit lost to the Aqueous product stream.
AqueousInOrgReqd / AqsInOrgReqd Input Visible with the Product Fraction Entrainment method. User specified the mass concentration of aqueous (normally in ppm) in the organic outlet stream. This method is only available in SysCAD9.2 Build 135.14652 or newer.
Note that solids in the Aqueous phase will also report to the Organic stream when an entrainment value is specified.
OrganicInAqsReqd / OrgInAqsReqd Input Visible with the Product Fraction Entrainment method. User specified the mass concentration of organics (normally in ppm) in the aqueous outlet stream. This method is only available in SysCAD9.2 Build 135.14652 or newer.
ExtractionMethod / Method None The model does not use Isotherms to determine the extent of the extraction or stripping reaction.
The user sets the extent/s of the reaction/s manually.
Isotherm The model uses Isotherms to determine the extent of the extraction or stripping reaction.
Reactions will be switched on by SysCAD if the isotherm method is chosen.
The user must still specify the reaction file and the reaction/s, but the model will set the extent of the extraction or stripping reaction/s manually.
Notes The model will set the extent of the First reaction in the file.
The reaction file may contain more than one reaction.
The user must set the required extents of the other reactions.
The following fields will be visible if the Isotherm Method is chosen.
AllowOveride Tickbox This allows the user to override the reaction extent calculated by the isotherm and manually set the reaction extent on the RB tab page.
Mode Extraction This mode is selected if the unit is used to extract the metal from the aqueous into the organic phase.
Stripping This mode is selected if the unit is used to strip the metal from the organic into the aqueous phase.
StageEfficiency / StageEff Input The efficiency of the solvent extraction stage.
ExtentSpecies / ExtentSp Input The liquid containing the primary metal, e.g. for Extraction it may be CuSO4, and for Stripping R2Cu.

Primary Metal List The user must select the metal of interest from the list of available elements in the project. A valid element must be selected if the "Isotherm" method is selected. It is optional for the method "None", however it is useful to set this so that the feed and product concentrations can be shown.
Reactions List The user may turn the reactions 'On' or 'Off'. If this is 'On' then the RB tab page will become visible. Reactions will be switched 'On' by SysCAD if the isotherm method is chosen.
OperatingP...
Method Atmospheric outlet streams will be at Atmospheric Pressure. The atmospheric pressure is calculated by SysCAD based on the user defined elevation (default elevation is at sea level = 101.325 kPa). The elevation can be changed on the Species tab page of the Plant Model.
AutoDetect If there are any liquids AND no vapours present in the feed, outlet streams will take the highest pressure of the feeds. Else (eg. some vapours present) outlet streams will take the lowest pressure of the feeds.
LowestFeed outlet streams will take the lowest pressure of the feeds.
HighestFeed outlet streams will take the highest pressure of the feeds.
RequiredP outlet streams will be at the user specified pressure.
IgnoreLowQm Tick Box This option is only visible if the AutoDetect, LowestFeed or HighestFeed methods are chosen. When calculating the outlet pressure and temperature of the tank, SysCAD will ignore the low flow feed streams should this option be selected. The low flow limit is set in the field below.
LowQmFrac Input This field is only visible if the IgnoreLowQm option is selected. This is the amount any stream contributes to the total flow. For example, if the total feed to the tank is 10 kg/s, and this field is set to 1%. Then any feed streams with less than 0.1 kg/s will be ignored in the pressure calculations.
PressureReqd / P_Reqd Input This field is only visible if the RequiredP method is chosen. This is user specified pressure.
Result Display The actual pressure used for the sum of the feeds which will also be the outlet pressure (unless further model options change the pressure).

### Results

MinOrgConc OR MinAqsConc Output This field is only visible if the Isotherm Method has been chosen. The Y-intercept of the McCabe-Thiele operating line, MinOrgConc in the case of extraction, and MinAqsConc in the case of stripping.
NOTE this is defined by the feed streams entering the unit operation.
ReactExtent Feedback This field is only visible if the Isotherm Method has been chosen. This is the reaction extent required as appears in the RB tab page.
Displayed here for easy access.
ActReactExtent Feedback This field is only visible if the Isotherm Method has been chosen. This is the actual reaction extent achieved as appears in the RB tab page.
Displayed here for easy access.
MaxLoadedConc Output If the Isotherm Method has been chosen, this field will only be visible if Extraction Mode is chosen. Displays the maximum concentration based on 100% extraction and calculated by mass balance.
This will serve as a warning for incorrectly supplied data if the results differ to those expected.
MaxStripConc Output If the Isotherm Method has been chosen, this field will only be visible if Stripping Mode is chosen. Displays the maximum concentration based on 100% strip efficiency and calculated by mass balance.
This will serve as a warning for incorrectly supplied data if the results differ to those expected.
Feed Conditions
AqueousConcIn / AqsConcIn Calc The concentration of the Primary metal in the incoming Aqueous stream.
OrganicConcIn / OrgConcIn Calc The concentration of the Primary metal in the incoming Organic stream.
Organic/Aqueous
/ OARatio
Calc The calculated volumetric ratio of Organic to Aqueous liquid entering the unit.
Aqueous/Organic
/ AORatio
Calc The calculated volumetric ratio of Aqueous to Organic liquid entering the unit.
Product Conditions
AqueousConcOut / AqsConcOut Calc The concentration of the Primary metal in the outgoing Aqueous stream.
OrganicConcOut / OrgConcOut Calc The concentration of the Primary metal in the outgoing Organic stream.
AqueousInOrg / AqsInOrg Calc The mass concentration Aqueous in the organic outlet stream.
OrganicInAqs / OrgInAqs Calc The mass concentration organic in the aqueous outlet stream.
AqueousLosses / AqsLosses Calc The mass fraction of feed Aqueous to the organic outlet stream.
OrganicLosses / OrgLosses Calc The mass fraction of feed organic to the aqueous outlet stream.

### Isotherm Section

The user types in the Isotherm describing the Solvent Extraction process. Isotherm data points (both Aq and Org or X and Y) are expected to increase in value from the first data point to the last data point entered.

Tag / Symbol Input / Calc Description

The black rectangle is for display purposes only.
The user can configure the Information data to display the Isotherm curve.

Equation + / - This is NOT used.
Information + / - The user clicks on the + to obtain the following buttons, these allow the user to configure the display.
Lin > Log X Button Toggles between normal and log on the x scale
Lin > Log Y Button Toggles between normal and log on the Y scale
Auto>Manual Scale Display Button Toggles between automatic and manual display parameters. If the display is in auto mode, then the model sets the minimum and maximum display parameters. Changing to manual allows the user to set these parameters.
Graph : Width & Height Inputs These numbers determine the size of the graph on this page.
Display Min Display The minimum display point on the graph
Display Max Display The maximum display point on the graph
Lower Boundary Inputs The lower boundary of the actual data points, i.e. the lowest point to which the data may be extrapolated.
Upper Boundary Inputs The upper boundary of the actual data points, i.e. the highest point to which the data may be extrapolated.
Data Points + / - The user clicks here to enter the data points.
The data may be entered in a csv file, or in the two columns on this page. For example, for extraction, x represents the mass fraction of solute in raffinate, and y represents the mass fraction of solute in extract.
The model interpolates linearly between the points and beyond the first and last points.
Load Points Button This will load the points from a CSV file.
Save Points Button This will save the points to a CSV file.
File Input The user may type in the file and path if the points are stored in a csv file.
Length Input The number of data points. If the user wishes to type the data points directly into the model, then this value needs to be filled in. Once a number has been typed in, the X and Y columns will be visible with the required number of lines.
Sort Button This will sort the data points into ascending x values.
X and Y Columns Inputs The X and Y values for the Isotherm.

Tag / Symbol Input / Calc Description
Isotherm Curve
Isotherm...
The user enters the data points in the two columns on this page. For example, for extraction, Aq represents the mass fraction of solute in raffinate, and Org represents the mass fraction of solute in extract.
The model interpolates linearly between the points and extrapolates beyond the first and last points.
Length Input The number of data points. Once a number has been typed in, the Aqueous (Aq) and Organic (Org) columns will be visible with the required number of lines.
Aq and Org Columns Inputs The Aqueous and Organic values for the Isotherm.

## Adding this Model to a Project

Insert into Configuration file

Sort either by DLL or Group.

 DLL: Separ1.dll → Units/Links → Separation: Mixer/Settler OR Group: Mass Separation → Units/Links → Separation : Mixer/Settler

Insert into Project

 Insert Unit → Separation → Mixer/Settler

See Insert Unit for general information on inserting units.