Liquid purification or separation – Processes – Liquid/liquid solvent or colloidal extraction or diffusing...
Patent
1999-03-04
2000-10-17
Popovics, Robert J.
Liquid purification or separation
Processes
Liquid/liquid solvent or colloidal extraction or diffusing...
210800, 210511, 210513, 210801, B01D 1104, B01D 17028
Patent
active
061326151
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a method for controlling solution flows in liquid-liquid extraction in a space where two mutually mixed solutions proceed and simultaneously separate into two layers owing to the effect of gravity. The invention also relates to a settler for realizing the method, in which case the depth and flow baffle structures of the settler are designed so that the flow speed of the organic solution is adjustable to be clearly higher than the flow speed of the aqueous solution, but the phases can still be separated as pure, without the entrainment of the other solution rising to a disturbing level.
By means of the method and apparatus of the invention, the mutually separable solutions are made to proceed at an even speed both in transversal and vertical directions in circumstances provided for the separation, where an essential requirement is that the solutions are made to proceed in the fashion of a plug flow, from the front end of the separation tank to the final end thereof. Another purpose of the invention is to speed up the separation of the solutions and to improve the final degree of separation, i.e. to decrease the entrainment of both solutions in the other solution. It is typical of the method and apparatus of the invention that they retain the solutions from flowing directly forwards, so that in the front end of the separation tank, there are arranged several narrow flow spots provided with direction changes. The method and apparatus according to the invention are particularly well suited to very large copper extraction plants.
BACKGROUND OF THE INVENTION
In copper extraction, where the employed extraction solution is for instance hydroxyoxime dissolved into kerosene, it has been proved that the linear flow speed of the organic solution must not surpass the speed of 45-60 mm/s. In other cases the volume of entrainment, i.e. the amount of small water drops left in the extraction solution, begins to grow to a disturbing extent, even to the order of 1000 ppm, when a conventional separation method in a simple settler is applied. The linear speed can be decreased only to a limited extent by increasing the layer volume of the organic solution, because when the layer volume is increased, there is respectively needed more of the expensive organic reagent. This problem is generally solved so that there is used a 250-350 mm thick layer of organic solution, and the linear speed of the extraction solution is reduced by adding the width of the flow field of the separable solutions. Nowadays the width of the employed settler may be as large as its length, even larger. When the total volume of the solution flow is about 2,000 m.sup.3 /h, the settler width is of the order 25 m and its area 600-800 m.sup.2.
The Finnish patent application 93 5393 introduces a method and apparatus whereby the pumping and mixing units in extraction plants can be improved, so that the previous maximum flow can be increased to be even 2.5-fold. In addition to pumping and mixing, said method and apparatus also relate to conducting the dispersion flow from the mixer into the settler, to the shape of the adjusting gate and picket fence arranged at the front end of the settler, as well as to the separation of organic solution at the final end of the settler.
According to a prevailing notion, the linear speed difference between the extraction solution and the aqueous solution must be small in order to avoid a remixing of the solutions owing to boundary surface turbulence and a resulting increase in the entrainment levels. As a solution for this problem, there are used low separation tanks, where the aqueous solution layer is not essentially thicker than the extraction solution layer. For instance in traditional copper extraction, the employed thickness of the aqueous solution is 400-450 mm, and the thickness of the corresponding extraction solution layer is 250-350 mm, so that the ratio of the thicknesses of the extraction and aqueous solution layers, particularly at the discharge end of the s
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Hultholm Stig-Erik
Kuusisto Raimo
Lilja Launo
Lyyra Juhani
Nyman Bror
Outokumpu Technology OYJ
Popovics Robert J.
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