Summary
The solvent extraction (SX) phase flip detector emits a warning when the phase continuity in a mixer unit changes.
Background
The SX Mixers normally operate with aqueous suspension (dispersion) in organic continuous phase. “Flip” is the event where the continuous and the suspended (dispersed) phase swap. The importance of the mixing continuity is not an issue during the mixing phase of the SX operation, however it does have an impact on the extent to which the phases separate AFTER they exit the mixer and are settled out into their two respective phases in the associated settler.
Figure 1: Simplified diagram of SX Mixer Settlers with mixers operated in Organic and Aqueous Continuous Phase Regimes
Mixer phase flips create instability in the SX circuit and are especially detrimental to the efficiency of transferring copper from the incoming PLS to the exiting advance electrolyte. As an example when there is aqueous entrainment from the Strip stage transferred with the stripped organic to the E2 extraction stage (first rteceiving stage for stripped organic), this aqueous has two qualities that are detrimental to the extraction equilibrium isotherm - high copper at high acid concentration -in some instances this impact is so severe that no copper is able to be transferred from the aqueous in E2 onto the organic, and as a result copper is “leaked” out undesirably to the raffinate aqueous and either has to be returned to the leach circuit or is lost via neutralization to tailings, as a true loss of copper.
Intended users
The phase flip detector was designed with the needs of the plant operator in mind.
Principles
Data used
The model takes the history of the following variables. The length of the history depends on the actual unit being monitored. It is usually around ten-fifteen minutes.
current drawn by the motor of the mixing unit
Data Quality Requirements
If either of the data quality requirements below is not met the phase flip detector does not try to attempt to decide whether the phase is flipping. It will returns a null, which will be seen as a gap in the plot of the alerts.
there should be no data gap in the history
the current drawn must be within a range
Outputs
The detector outputs the following quantities:
phase flip indicator has a value of one if the detector assumes that the phase continuity changes. Otherwise it is zero.
Where to Find the Output?
The outputs of the detector is placed in the widget and dashboard to best suit the needs of the client. As such, the exact location may change site-to-site. As a default, the "SX Plant Dashboard" dashboard would contain the widget displaying the detector outputs.
The widgets "<Mixing unit name> Stability -- Jump Detector" contains the alerts. They are plotted as continuous lines for each mixing units separately as shown in Figure 2.
Click on the "SX Plant Dashboard" and scroll to the bottom of the screen.
Figure 2. The phase flip detector output (blue line). Values at one indicate possible phase flips. Zero indicate stable phases. The discontinuities are due to either model refusal or data gaps.
Limitations
The developers are conscious of the following areas where the detector can be improved
False negatives: instances where phase flip is happening but the detector indicates otherwise.
False positives or false alarms: instances where the detector deems the phase continuity to be changing despite it is being stable.
The rates of the false and missed alarms depend on the specific site and mixing unit. The exact numbers are always communicated to the client.