CA1279293C - Multi-stage apparatus for separating mixtures of solids of differentspecific gravity, particularly for the mining industry - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

The invention relates to an apparats for separating mixtures of solids of different specific gravity, particularly for the mining industry, characterized by consisting of at least one hollow shell divided by transverse walls into at least three consecutive separation chambers which communicate with each other through axial tubes disposed in said transverse walls, an axial inlet tube being disposed in the front wall of said first chamber opposite the first of said transverse walls, and an axial outlet tube being disposed in the front wall of the last chamber opposite the last of the transverse walls, each chamber being also provided with a tangential inlet tube at one of its ends, and with a tangential outlet tube at its opposite end.

Description

The present inventlon relates to a multi-stage apparatus for separating mixtures of solids of different specific gravity, particularly for the mining industry.

In separating mixtures of solids of different specific gravity, particularly mineral particles, it is known to use separators which employ a dense medium or fluid formed from an aqueous suspension of finely ground heavy substances such as ferrosilicon or magnetite, the dense medium creating a centrifugal field inside the separator. Know cylindrical u separators for industrial application are substantially of two types, namely those comprising a single separation chamber and those comprising two separation chambers.

The two-chamber separator described in the Canadian 1~ pat. No 1,117,903 granted on 9, 02, 1982 was designed specifically to obtain a rough separation ~particularly necessary when the quantity and content of useful metal varies in the ore feed) in the first chamber, and a more precise final separation in the second chamber. The first chamber thus enables the 2U unfavourable effect of the variability of the ore to be attenuated, if not eliminated.

In both experimental and lndustrlal practlce lt has been observed that although the two-chamber separator ls certainly more effective than the slngle chamber separator, it is unable to satlsfy certain requirements in this field when a very precise separation ls necessary.

Obtalnlng hlgh separation preclsion increasingly more important ln relation to the requirement of recoverlng the 3 maximum amount of useful substance given the shortage of raw materlals and increasi~g energy costs.

The present invention originates from a theoretical study which proved that a multl-stage cyllndrlcal separator ~at ~ .

least three, and preferably four or more stages) enables a considerably more precise separation to be obtained than with separators of the known art. The present invention therefore provides an apparatus for separating mixtures of solids of different specific gravity, partlcularly for the minlng industry, comprising at least one hollow shell divided by transverse wall into at least three consecutive separation chambers which communlcate with each other through axial tubes dlsposed in said transverse walls, an axial inlet tube belng disposed int he front wall of the first chamber opposite the first of said transverse walls, and an axial outlet tube being disposed in the front wall of the last chamber opposite the last of the transverse walls, each chamber being also provided with a tangential inlet tube at one end of lts ends, and wlth a tangential outlet tube at- its opposite end.
l!;
The advantages of the invention and its various modified forms will be more apparent from the detailed description of practical embodiments thereof given herein after with reference to the accompanying drawings in which:

2~ Figure 1 is a longitudinal axial section through an apparatus of the invention;

Flgures 2 to 10 are views analogous to that of Flgure 1 showlng nlne modlfled embodiments;
2~
Flgure 11 shows a general separation curve; and Flgures 12 and 13 show compa~ative separation curves for different 3U .

~2 .

1.

types of separstion.
With reference to the figure6, the appsratus of Figure 1 consi6ts essentially of a hollow cylindrical shell indicated overall by 10.
Two transverse walls 22 and 23 divide the interior into three chambers S A, B and C, which in the case illustrated are of equal dimensions but can also be of different dimensions.
The cylindrlcal shell 10 can be tisposed inclined as ln the figure or horizontally. An axial inlet tube 17 i8 disposed ln the front wall 21 of the first chamber A, and an axial outlet tube 20 i6 disposed in the front wall 24 of the last chsmber C. The tangential inlet tubes 11, 12 and 13, for the first, second and third chamber respectively, open tangentially into the chanbers in the vicinity of the walls 22, 23 and 24 perpendicular to the axis of the apparatus.
The tangential outlet tubes 14, 15 and 16 branch respectively from the first, second and third chamber in the vicinity of the walls 21, 22 and 23.
The tubes 11, 12, 13, 14, 15 and 16 can be either in the form of tubes inserted tangentially into the cylindrical shell 10 or can be formed from duct~ which are ~oined to the wall of the cylindrical ~hell 10 as volutes, ln accordance with the known srt.
The mineral to be treated is fed into the chamber A of the apparatus through the axial tube 17. The dense medium (suspension) is fed separately into the three chambers A, B and C through the tubes 11, 12 and 13. The heavy fraction which ~eparates ln each chamber is di~charged through the tangential outlet tubes 14, 15 and 16. Finally the final light fraction (which represents the tailings if the useful mineral is contained in the heavy fraction) is discharged from the apparatus through the axial outlet tube 20, which extends from the third chamber C.
The light fraction separated in the chamber A together with a part of the dense medium pass from the chamber A to the chamber B through 5 an axial outlet tube 18 which connects the two chambers A and B
together. Likewise, the light fraction separated in the chamber B
together with a part of the dense medium pass from the chamber B to the chamber C through an axial outlet tube 19 which connects the two chamber~ B and C together.
Figure 2 shows a cylindrical separator analogous to that of Figure 1, and for which the same description applies, but in addition - comprises a fourth chamber D communicating with the chamber C through ~- an axial tube 20 in6erted through a transverse separation wall 24.
The chamber D i8 also provided with tangential tubes 26 and 28 for the inlet of the dense medium and the outlet of the heavy fraction respectively, and with a front end wall 27 through which an axial discharge tube 25 for the final light fraction is inserted.
Likewise, a separator with five or more chambers could be formed, depending on separation requirements.
Figure 3 shows for example 8 cyllndrical separator with a single 6hell divided into six chambers. In addition to the details shown in Figure 2, in this case there are a further two chambers E and F, with thelr relative transverse walls 27 and 35,fronted wall 37, tangential inlet tubes 31 and 32, tangential outlet tubes 33 and 34 and an axial outlet tube 38.
Figure 4 shows a further modified embodiment of the invention in which the separator consists of two hollow cylindrical shells 10 and 10' of the type shown in Flgure 1, each divlded into three cham-bers and suitably connected in series by way of the axial outlet tube 20 of the shell 10 and the axial inlet tube 17' of the shell 10'. For the remaining reference numerals of this figure, reference ;- 5 should be made to Figure 1.
Figure 5 shows 8 further embodiment of the invention in which the separator consists of a hollow cylindrical shell 10 identical to that of Figure 1, upstream of which there is disposed a cylindrical separator 39 of known type with a single separation chamber. The separator 39 is composed of a cylindrical chamber G provided with an axial inlet tube 40 and outlet tube 41,-and tangential tubes 42 and 43. The two separators 39 and 10 are suitably (for example by means of flanges) connected in series by way of the tube 41 and tube 17.
In the modified embodiment of Figure 6, upstream of a separator 10 of the type shown in Figure 1 there is series-disposed a separator of known type comprising a hollow cylindrical shell 44 divided into two chamber H and I by a transverse wall comprising an axial tube 46 which connects the two chambers together (8ee the above mentioned patent) . The separator 44 is also provided with an axial inlet tube 45 and outlet tube 47, and tangential tubes 48, 49, 50 and 51.
The further modified embodiment of Figure 7 consists of a separator of the type shown in Figure 1, in which the intermediate transverse walls 22 and 23 sre replsced by corresponding double walls 22a and 22b, and 23a and 23b, through which the axial tubes which connect the chambers together are disposed.
Between each pair of said walls annular interspaces are defined which lZ79293 communicate wlth the outside through drain tubes 29 and 30 respec-tively. The usefulness of this latter embodiment of the invention is apparent on considering what can happen if in an apparatus of the type shown in Figure 1 the transverse walls 22 and 23 become worn or perforated after a certain number of hours of operation. This leads to a fall-off in efficiency, the reason for which is not immediately clear as it is not apparent from the outside. To prevent this drawback, the apparatus of Figure 1 can be constructed in the form shown in Figure 7, in which the presence of double transverse walls produces an interspace which can be connected to the outside by drain tubes 29 and 30. If one of the transverse walls becomes perforated, the dense medium flows through the tubes 29 and 30 and this is immediately apparent from the outside.
Alternatively, the embodiment of Figure 8 can be used, which differs from ehe preceding embodiment only in that the wall of the hollow shell 10 is interrupted in the zones between the transverse walls 22a, 22b and 23a, 23b. This modification, which with regard to the operation of the apparatus does not differ from the preceding, can lead to the advantage of greater constructional æimplicity and greater ease of assembly and dismantling.
It need only be noted that the distances d and d' between the pair of tranæverse walls of Figure 8 must be suitably limited such that the axial tubes 18 and 19 are not fiO long as to lead to a ~ubstantial loss of rotational kinetic energy in the dense medium streams which pass from the first to the second chamber and from the second to the third chamber.

According to the invention, the chambers into which each hollow shell ~279Z9 of the separator i8 divided can, instead of being cylindrical, be of another shape such as conical or conical-cylindrical as shown for example in the embodiments of Figures 5 and 10. Briefly, Pigure 9 corresponds to the embodiment of Figure 1 but with conical-cylindrical chambers. Figure 10 corresponds to the embodiment of Figure 8 but with substantially conical chambers.
Again, a separator according to the invention can be formed with chambers of unequal lengths. In fact, for certain separation problems unequal lengths are definitely required. For example, the initial stages can advantageously be shorter because of thelr coarse separation function, and the final stages can advantageously be longer because of their so-called scavenger function.
In order to better clarify the advantages of the present $nvention and its varlous embodiments as heretofore described, some introductory remarks are appropriate. The separation precision (on the basis of the constltuent particles of the mineral) is known to be defined by the so-called separation curve or Tromp curve, shown for reference in Figure 11 of the accompanying drawings.
The ordinate axi~ represents the percentage which goes to the heavy product or sink (which ls the concentrate if dealing with a metalli-ferous ore) of each infinitessimal class of density repre6ented by the sbscissa axis.
The more the separation curve approaches the vertlcal, the more precise is the separation. In order to express this precision by means of an invented parameter, the "probable error" Ep is used, defined as in the figure by:

Ep ' 75 d25 where d75 and d25 are the densities corresponding to the 75% and 25%
ordinates.
The 6eparatlon can be defined not only by the separation curve but also by a vector, the elements of which are formed by the ordinates of the separation curve Ri corresponding to defined abscissa values of the density di.
If R is a general value of the separation curve ordinates for single stage separation, then for two, three or four stage separation the values R2, R3 and R4 can be calculated to define the corresponding ordinates of the 6eparation curves.
The calculations give:
- for two stages R2 ' R[l+(l-R)]

- for three stages R3 ~ R[l+(l-R)+(l_R)2~
- for four stages R4 - R[l+(l-R)+(l-R)2+(1-R)g]
By a comparison with the expression for the sum of the terms of a geometrical progression, the general term Rn corresponding to the ordinate of the separation curve for n stages becomes:
R ~ l-(l-R) (1) Applying equation (1) to actual separation curves, the re~ults 6hown in Figures 12 and 13 of the accompanying drawings are obtained.
Figure 12 shows the 6eparation curve a for one stage (ie cylindrical 6eparator with a single separation chamber), and this was used to calculate from equation (1) the curves b, c and d for two, three and four stages (ie for two, three and four separation chambers in serles).

lZ79Z93 It can be seen that on increa6ing the number of stages the separation curves become steeper, ie they spprosch more to the vertical, and thus correspond to a more precise separation. This greater precision also appears from the calculation of the probable error Ep, of which if Ep - 0.045 for a single stage as in Figure 12, the values for the larger number of stages are as follows:
- two stages Ep - 0.034 - three stages Ep - 0.027 - four stages Ep ~ 0.024 Obviously, for a still larger number of stages Ep will be smaller and thus the precision considerably greater.
The usefulness of a larger number of stages, certainly greater than two, is particularly apparent in a case which very often arises in separation processes, and which is illustrated in Figure 13.
lS The separation curve a for one stage in Figure 13 is not symmetrical, and does not attain the lOOX ordinate.
This means that about 80% of the heavy fractions is recovered in the sink, whereas the remainder goes into the light product or float, ie where it should not go. Thls can be due for example to entrain-ment of heavy particles by flows within the separator, and this can happen particularly in the case of particles of smallest dimensions or of a somewhat flat shape. In any event, this phenomenon is extre~ely disadvantageous in that it corresponds for example to a loss of heavy ore which is discharged together with the tailings in the float, or if the float consists of washed coal lt corresponds - to a contamination of the float with heavier mineral.
Applying the multi-stage principle, and in particular equation (1) lZ79293 to the single-stage curve of Figure 13, it can be seen that a substantial correction to the separation curve can be obtained. In this respect, even with only two stages (curve b) approximately 95Z
of the hesvy material is recovered in the sink (as opposed to the approximately 80% which was recovered with a single stage). However the important thing to note is that using only three or four stages (curves c and d) the disadvantage inherent in the initial ~eparation curve is substantially nullified.
If the four-stage separation curves of Figures 12 and 13 are super-imposed, it can be seen that they practically coincide even thoughthey are derived from two separation curves for a very different single stage. The first is a regular curve, whereas the second is a defective curve which allows the loss of much heavy ore with the float.
The equations illustrated up to this point have been derived for separation curves which are equal in the various separation stages.
However, analogous equations can be derived, which are a little more complicated from a formal viewpoint, for separation curves which are different in the different stages. Conclusions are obtained whlch entirely correspond to those already given, provlded the - separation denslty d50 (the denslty corresponding to the 50% ordinates ; of the separation curve) is not excessively different for the different stages.
On the basis of the aforesaid theoretical considerations, it is apparent that a separator with at least three chambers according to the invention is particularly useful when the separation curve is of the type shown in Figure 13, which does not reach the 100~ ordinate lZ79293 st hlgh den~ltles, such that hlgh-density granules contalning heavy materlal would be entralned into the float if operating with only one stage or even with two stages. Experlence shows that this case frequently occurs, particularly under two conditions:
- when the proportion of dense medium flow going to the float is hlgh, and thls often happens when the float quantity ls considerable compared with the feed quantity - when flnes are treated, particularly under a size of 1 mm, because these are heavily entrained towards the float due to the high ratio of surface forces to mass forces.
This latter condition is gradually becoming increasingly more important, in that whereas previously it was sufficient to carry out separation using dense medium down to a minimum size of 1-2 mm, it is currently desirable to process finer ore granules down to a size of about 0. 1-0. 2 mm. In this manner, when the finsl ore concentratlon has to be attalned by flotatlon, lt is possible to preconcentrate a larger quantity of mine-run output using a dense medium system.
Con6equently the processlng cost ls reduced, as i6 the energy consump-tion for the grlnding prlor to flotatlon. In any event, even ifthere is no flotatlon, but only the dense medlum 6eparation system for commercial concentrates, a larger quantity of ore can be processed (because the fines are also included) to give greater recovery levels of useful raw materials.
Stlll better results can be obtalned wlth more than three stages, for example four as in Figure 2, or with still more stages, as in Figures 3 and 4.

~Z79293 A lsrge number of stages is particulsrly useful when two different separations or two different densities are to be handled with the separator.
For example the separator of Figure 1 could be used by feeding the first chamber with dense medium of density Dl and the second and third chamber with dense medium of density D2. This method can be used if the first separation (carried out only in the first chamber) does not have to be very precise, whereas it is more important for the second separation (carried out in the second and third chamber together) to be more precise. Alternatively, the separator of Figure 2 can be used by feeding the first two chambers with the density Dl and the last two chambers with the density D2. In this : manner, each separation is carried out in two chambers. To obtain two very precise separations, another version of the inven~ion could be used such as that shown in Figure 3 comprising six chambers in serles.
The first three chambers would be fed with the density Dl and the last three chambers with the density D2. Instead of the separator of Flgure 3, two separators in series could be used of the type shown in Figure 1, connected as shown in Figure 4.
The apparatus which implements the invention can also be used for performlng separations with three densities Dl, D2 and D3.
For example in the separator of Figure 3 the first two chambers can be fed with the density Dl, the second two with the density D2 and the last two with the denfiity D3.
Alternatively, three separators in series of the type shown in Figure 1 can be used, or a separator such as that of Figure 1 lX79Z93 followed by a separator such as that of Figure 3. In thls case, the separator of the type shown in Figure 1 would be fed with dense medium of density Dl, and the separator of the type shown in Figure 3 would be fed in its first three chambers with the density D2 and in its last three chambers with the density D3.

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Claims (8)

1. An apparatus for separating mixtures of solids of different specific gravity, particularly for the mining industry, comprising at least one hollow shell divided by transverse walls into at least three consecutive separation chambers which communicate with each other through axial tubes disposed in said transverse walls, an axial inlet tube being disposed in a front wall of the first chamber opposite the first of said transverse walls, and an axial outlet tube being disposed in the rear wall of the last chamber opposite the last of the transverse walls, each chamber being also provided with a tangential inlet tube at one of its ends, and with a tangential outlet tube at its opposite end.

2. An apparatus as claimed in claim 1, in which said hollow shell is cylindrical.

3. An apparatus as claimed in claim 1, in which said hollow shell is conical.

4. An apparatus as claimed in claim 1, in which said hollow shell is conical-cylindrical,

5. An apparatus as claimed in claim 1, consisting of a single hollow shell.

6. An apparatus as claimed in claim 1, consisting of two hollow shells connected in series, of which at least one is divided into at least three chambers.

7. An apparatus as claimed in claim 1, in which each of said transverse walls is composed of a pair of walls between which an interspace is defined.

8. An apparatus as claimed in claim 7, in which said cylindrical shell has no outer wall at said interspace.