Hydrometallurgy: Leaching in Heap, Vat, CIL, CIP, Merrill–Crowe, SX Solvent Extraction

Hydrometallurgy: Leaching in Heap, Vat, CIL, CIP, Merrill–Crowe, SX Solvent Extraction 2017-04-04T06:57:36+00:00
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(PLS) Pregnant Leach Solution pondtemperature (14 replies)

Dizzy Flores
2 years ago
Dizzy Flores 2 years ago

Will decreasing PLS temperature to less than 10 centigrade affect on copper ion exchange between organic and aqueous phase and their phase separation? If yes, what is the solution?

Carmen Ibanz
2 years ago
Carmen Ibanz 2 years ago

You can certainly expect poorer phase separation, increased entrainment (organic in the raffinate, PLS in the loaded organic). As well, your strip feed which I presume is spent electrolyte, should be coming in warm and if the advancing organic is that cold. I am not sure about this, but you may need to adjust the thermal balance in EW so that EW runs in the right temperature range.

Dizzy Flores
2 years ago
Dizzy Flores 2 years ago

Can you explain more about scientific reason for this phenomena?

Helena Russell
2 years ago
Helena Russell 2 years ago

I agree that the temperature increased organic losses and impurities in electrolyte, increased separation time and decreased the kinetics in extraction stages.

Put a coalesce system like a honeycomb into the extraction stages helps to decreased the entrainments.

Alan Carter
2 years ago
Alan Carter 2 years ago

The entrainment and phase separation issues you will face are mostly attributable to an increase in organic phase viscosity at lower temperatures. The extraction kinetics are potentially going to suffer because for the extractant to coordinate a copper ion out of your PLS, there is an activation energy involved (rather low, but still). At colder temperatures, that means that it will take longer to reach equilibrium of copper in the organic vs. aqueous phases.

Carl Jenkins
2 years ago
Carl Jenkins 2 years ago

Why would you decrease the temperature of PLS? It must be decreased???

Dizzy Flores
2 years ago
Dizzy Flores 2 years ago

Pregnant Leach Solution PLS temperature decreased because of cold weather.

Carl Jenkins
2 years ago
Carl Jenkins 2 years ago

I see. The decreasing will affect the copper ion exchange.

The phases still can separate, is right? It will take longer to separate phases.

Have you take methods to warm the feed liquid or raise the plant temperature?

Ace Levy
2 years ago
Ace Levy 2 years ago

The comment is accurate regarding the effects of temperature drop in the PLS. What is of concern is not the 100 C (Some SX plants operate with PLS at 2-40 C), but the minimum PLS temperature that the plant was designed.

David Kano
2 years ago
David Kano 2 years ago

The most probable reason for this phenomena is increase of viscosity:

http://en.wikipedia.org/wiki/Stokes%27_law#Terminal_Velocity_of_Sphere_Falling_in_a_Fluid

http://en.wikipedia.org/wiki/Hadamard%E2%80%93Rybczynski_equation

There are many other factors that usually change slower than viscosity with change in temperature: interface tension, activity of surfactants, specific gravity and so on. Hence, they have much smaller influence on separation rate.

Carmen Ibanz
2 years ago
Carmen Ibanz 2 years ago

The issue regarding phase separation is viscosity. The more extractant your organic phase contains and the higher you load it with copper, the higher your viscosity will be. So, if you are treating a dilute copper PLS with a few % of extractant in the organic phase, you may still be OK or at least not as badly hurt by the drop in temperature. If your PLS contains higher copper levels, say from an agitated leach process, and your organic contains more extractant, you are sure to have problems. One option might be to decrease the organic loading when you encounter cold weather by increasing the O/A advance ratio in your circuit, but this is by no means ideal and the effect may not be sufficient. And production will drop because you will likely need to lower the PLS flow rate in order to keep (or even increase because of the cold) the mixer and settler residence times.

Another option, at least on paper, would be to use a less viscous diluent. Practically, this means switching to a diluent with a lower boiling point. As your extraction stages are colder, your volatile losses may not increase there, but your strip stages will still be warmer because they are coupled with EW so you will evaporate more diluent in stripping that before. You will need to monitor the extractant concentration closely with regular max load test so that you can add diluent makeup. Otherwise, a starting concentration of x% extractant will be 2x% in a couple of weeks because of preferential evaporation of the diluent, phase separation will disappear and it will just be a mess.

All of this does not address what others have pointed out, the poorer extraction rates and probable equilibrium shifts that lower temperature will cause. Increasing the advance O/A ratio might compensate somewhat because there is more extractant around per mole of copper being extracted, but is again not the ideal situation.

Clearly the best thing you can do is to heat your feed in any way that you can, heat exchangers, direct steam injection of whatever might be practical at your operation.

Bill Fraser
2 years ago
Bill Fraser 2 years ago

As you may know, the extent to which copper is extracted follows an extraction equilibrium isotherm curve. Since this is temperature dependent ("iso-therm"), from a practical perspective if you change the temperature you change the position of the curve and hence the degree of extraction; and lower temperatures afford lower levels of extraction.

PDT's suffer to due to the increase in viscosity. Both O in A and A in O entrainments increase due to this effect depending upon your mixer phase continuity.

What to do about it? Some options include reducing flow rates, or increasing mixer and settler residence times.

Carl Jenkins
2 years ago
Carl Jenkins 2 years ago

Yes. I didn’t agree with you more. That's why I said try to heat the PLS or warm the extraction plant.

Had you tried to warm the PLS or raise the extraction plant temperature?

Ace Levy
2 years ago
Ace Levy 2 years ago

If entrainments increase beyond manageable limits as a consequence of a sustained drop in the PLS temperature, to maintain production quality within marketable limits probably the only alternative in the short term is to reduce the PLS processing rate.

The trade-off is not easy to assess: risk of 100% plant production not meeting quality specifications versus 5-20 %(?) lower, marketable production. The second option is not liked by management amidst a price drop scenario, but it involves only delayed production with no reprocessing costs.

Tony Verdeschi
2 years ago
Tony Verdeschi 2 years ago

To warm PLS should be the best option but it can increase the costs. A cheaper but slower solution could be to avoid heat losses in PLS piping and trench flowing. In some high altitude projects I worked before good results was achieved by covering trenches with hype, piping isolation or soil covering, proper irrigation systems, etc. A slow increase in plant heat level can be achieved at marginal cost.Dynamic thermal simulation can help to identify the optimal heat conservation actions.Not only viscosity, loss of transfer efficiency, and other problems the fellows warn... even undesirable precipitation of some impurities can even affect pipeline integrity.


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