• To participate in the 911Metallurgist Forums, be sure to JOINLOGIN
  • Use Add New Topic to ask a New Question/Discussion about Electrowinning, Smelting or Refining.
  • OR Select a Topic that Interests you.
  • Use Add Reply = to Reply/Participate in a Topic/Discussion (most frequent).
    Using Add Reply allows you to Attach Images or PDF files and provide a more complete input.
  • Use Add Comment = to comment on someone else’s Reply in an already active Topic/Discussion.

Improve Plant Mixer Efficiency (4 replies)

Ace Levy
9 months ago
Ace Levy 9 months ago

How do you improve the plant mixer efficiency both in organic and aqueous phase apart from flows, turbine speed? Lab test is more of batch than continuous process and equilibrium is reached/assumed.

John Koenig
9 months ago
John Koenig 9 months ago

In addition, I would look at agitator mounting and support, impeller type, impeller height in the solution, tank baffling, and tank dimensions (L/D). A good reference might be Liquid Mixing and Processing in Stirred Tanks by Holland and Chapman (1966).

Bill Rico
9 months ago
Bill Rico 9 months ago

Under a prescribed set of chemical conditions, metal transfer will occur more quickly if you have smaller droplets as you will achieve a larger surface area to volume ratio. Of course this will be expected to lead to greater levels of entrainment resulting from the process. You might be able to hasten metal transfer by altering chemical conditions, e.g. copper extraction at a higher pH, or stripping at higher acidity, or changing reagent composition, but these come at additional cost and/or consequences.

In terms of equipment, I think there is great opportunity to investigate opportunities to optimize the needs for SX systems (e.g. generating more smaller drops, but not excessive ultra-fines), and this specific area is one of the foci for the SXT3 proposal we are currently putting together for consideration by industry. As I look at the latest draft, one of the headings is "Designs for mixer box furniture to reduce the quantity of ultra-fine droplets entering the settler". Sponsors of SXT2 will know that we have already been looking at settler designs/furniture in a similar manner. Our CSIRO team has extensive experience in both mixing systems and SX systems, using both physical and computational models. I am excited by the prospect of SXT3 rounding out the settler story (and of course delivering feasible solutions to Industry) and getting our teeth stuck into the mixing side of things. 

Marshal Dienes
9 months ago
Marshal Dienes 9 months ago

I agree that there is always a conflict between mass transfer intensification during the mixing, and an ease of emulsion separation afterwards. A good mass transfer requires intensive mixing, while the phase separation requires formation of droplets that coalesce easily. Chemical modifiers are problem-plagued too – many of mass transfer enhancers reduce the interfacial tension dramatically, preventing coalescence, and many coalescence inducers make too large droplets.

We have developed auxiliary mixers using a different approach – SX mixers that use high energy for mixing and create very few small droplets. The excellent mass transfer is achieved due to high mixing energy, and the fast separation due to absence of small droplets. So one can decrease entrainment, increase mass transfer, and increase flows through existing mixer-settlers. We have recently installed and retro-fitted industrial scale commercial units at plants in the USA and in Central Asia that appear to be successfully achieving these goals.

As a good starting point I’d recommend the excellent article of Treybal (AICHE J. 1958, Vol. 4(2) pp. 202-207).

Maya Rothman
9 months ago
Maya Rothman 9 months ago

I think everyone has given you a good direction. I suggest you also make sure that you are mixing the phases at A/O close to 1 and that you have a residence time of 2-3 minutes in each mixer tank based on total flow.

Please join and login to participate and leave a comment.