Table of Contents
Jig Acceleration
Rittinger, having found that jigs save galena of smaller sizes than his formula, worked out in his appendix of the theory of acceleration to account for that fact, showing that a particle of galena which is equal-settling with a particle of quartz reaches its maximum velocity in perhaps one-tenth the time required by the quartz. The oft-repeated pulsations of a jig give the galena particles a decided advantage over the quartz, placing beside the quartz, when equilibrium is reached, a much smaller particle of galena than we should expect according to the law of equal-settling particles. He concludes that the excess of jigging-power over that indicated by the law of equal-settling particles is due to acceleration. Unfortunately, he has not given a ratio of diameters of quartz and galena, which represents equilibrium with regard to acceleration.
To test this question of acceleration, I have designed a pulsion- jig or modified Setzpumpe, which is shown in Fig. 8. It consists of a tin funnel, a, with overflow, b, connected by rubber connector, c, to a glass tube, d, cut apart at h for the insertion of a disk of sieve- cloth. The two parts are held together by two clamps, e and f, and two bolts, g, g, and the leaky joint, at h, is made tight by a belt of rubber plaster. The tube has a branch, k, joined by rubber connector, o, to a common plug-cock, p, provided with a gear-wheel, q, which intermeshes with a larger gear, r, having a crank, s, turned by hand. Water is supplied through the rubber hose, t, and the hydrant, u. The lower end of the tube is drawn down to one-quarter inch in
diameter at l, and by rubber connector, m, is joined to a bulb, n, for receiving what passes through the sieve.
The method of operating this pulsion-jig is simply to turn on the water gently at u, and revolve the crank, s, at the speed desired. The revolution of the plug-cock, p, makes and breaks the water-connection, and the rubber tube, t, is elastic enough to act as an accumulator for the instant that the water is shut off. The sand fed in at the funnel, a, quickly falls to the sieve, h, and then receives a series of intermittent upward pulsations from the movement of the water. The sand is therefore subjected to an upward current of water at one instant, which remains stagnant the next instant. These pulsations may be given at almost any rate up to 800 per minute.
This instrument seems well calculated to answer the question. Does Rittinger’s acceleration, due to intermittent upward pulsations, add anything to the effect of Munroe’s interstitial currents ?
Two tests were made with the pulsion-jig, one upon galena and one upon sphalerite, each paired with quartz.
For convenience, when in use, the sieve was removed. This permitted the products to be drawn off by the bulb in series, exactly as they were in the pointed-tube test, and the bulbs so drawn off were sized, and the different little hills were laid out and photographed as before (Plates XIV. and XV.).
The ratio for three columns of hills, computed by the method adopted for the pointed tube, yielded for the two minerals treated, namely, galena and sphalerite, the figures shown in Table XXXIX.
If now we compare these ratios of Table XXXIX. with those obtained by the pointed tube (Table XXXVII.), we see that nothing whatever has been gained by adding acceleration to interstitial currents. But since acceleration must logically produce some result,
there should be some explanation of its apparent failure here. It is quite possible that this is a case of “ parallelism,” just as if two cells of a battery be placed side by side in multiple arc nothing is gained in volts, or, as two horses harnessed side by side are no faster than one horse.
Tables XL. and XLI. give the weights of the hills in three columns each of Plates XIV. and XV., from which the computations in Table XXXIX. were made.
Jig Suction Explained
This law of jigging has not received the attention which it deserves. Munroe says of it, that suction appears to be necessary for jigging through a bed. Hoppe says that suction is very necessary to jigging, and that he has in progress an investigation of it.
In order to test the limits of the law of suction, I have designed a little movable sieve-jig, shown in Fig. 9, which gives a very perfect jigging-action. It consists of a glass tube, a, a, a, a, 5 inches long and 1¼ inches in bore, which is cut at t, t, into two parts, 4 inches and 1 inch long respectively—the 4 inches being above the sieve; a disk of sieve-cloth, t, t, is inserted between them; the parts are held together by the wooden bars, b,b, and the bolts, e,e, with nuts, d,d.
Power is transmitted through the rod hu, the beam, j, oscillating upon a pivot, k, a connecting-rod, l, a small pulley, m, with crank-pin, a belt, n, and a large pulley, o, driven by a crank, p. The cross-bar, f, and the lock-nuts, g, g, are used simply to stiffen the rod, u. The jig is suspended in a glass jar, s, with water-level at r.
By turning the crank, p, an oscillating motion up and down is given to l, received by u, and transmitted to the jig-sieve, t, t. The amount of oscillation may be controlled by connecting u with j, by means of any of the holes, i. The smallest oscillation was 1/8-inch, the largest 5/8-inch. The latter was preferred for the tests.
The effects of pulsion and suction were studied in three different combinations, namely, full pulsion with much, with little, and with no suction.
1. Full Pulsion with much Suction.—When the jig (Fig. 9) is run with the glass tube elevated 1½ inches above the surface of the water at the lowest point of its stroke, the jig operates during the first few pulsations as a lift-pump, elevating the surface of the water within its tube until the inside water-level is, perhaps, one inch above the outside level, the sand-particles acting like so many little valves. Thus, it reaches equilibrium ; and, from this time on, the suction due to the downward rush of water must be equal to the pulsion due
to the upward rush of water. The bed of this jig is tight and only slightly mobile. The strong suction compacts it more or less. Mobility may be restored by using a long stroke.
2. Full Pulsion with Little Suction.—When the jig is run with the glass tube inundated to a depth of 7/8-inch below the surface of the
water at the lowest point in its stroke, then, during the downward movement of the sieve, a full pulsion movement is given to the water as it passes up through the sieve, and the sand settles through it. But, on the upward movement, the sand settles in the sieve, and comparatively little suction results, from the inertia of the water. The reason is, that there is a free discharge of the water at the top of the glass tube. Here, we have full pulsion with little suction. The bed of this jig is loose, and very mobile. There is not enough suction to compact it. A shorter stroke here suffices for mobility.
Full Pulsion with no Suction
When the pulsion-jig (Fig. 8) is used upon mixed sands, it matters not whether we revolve the cock rapidly, giving rapid, small pulsations with short intervals of repose, or, more slowly, giving fewer and stronger pulsations with longer periods of repose—the result is the same. The sands are treated by pulsion without suction. The bed of this jig is extremely loose and mobile, there being no suction to compact it.
In all the tests upon jigging now to be described, unless otherwise stated, the stroke of the jig was 5/8-inch; the layer of quartz was 2 inches thick ; the layer of the added mineral to be separated from the quartz, was 3/16-inch deep, and placed on top of the quartz. When the jig is said to be “elevated,” the top of the glass is 1½ inches above the water at the lowest point of the stroke; and when the jig is said to be “ inundated,” the top of the tube is 7/8-inch below the surface of the water at the lowest point in the stroke. A 16-mesh sieve was used in the jig throughout the tests.
The first series of tests was made with quartz and galena to note the behavior of different sizes of galena with a single standard size of quartz. For this purpose the two minerals were jigged together as follows:
Quartz, in all cases, through 10- and on 12-mesh; average diameter, 0.0683 inch.
Each pair was treated with much suction, with little suction, and with no suction.
The results are given in Table XLII.; and the following conclusions as to the behavior of quartz and galena are indicated:
Light suction is more rapid than heavy suction (tests 1 and 2); no suction is more rapid than light suction (tests 2 and 3). Where the galena is fine, much suction is rapid, but no suction is also rapid (tests 10, 11, and 12) until 60- to 80-mesh is reached (test 15), where galena is in equilibrium with the quartz. With heavy suction there is an interesting maximum reached at .0262-diameter galena (test 7). Here the galena is too fine for equal-settling particles to help it much, and it is too coarse to be sucked down in the interstices of the quartz, hence its slow action. Compare it with .0195-diameter galena (test 10), which is small enough to be sucked down in the interstices. Here heavy suction brings quite a rapid separation.
The second series of tests was made upon quartz and sphalerite (blende), put together in pairs as in the experiments just described. The diameters were the same as those given above for the similar tests with galena.
The results are given in Table XLIII.; and the following conclusions as to the behavior of quartz and sphalerite are indicated:
When the quartz and sphalerite are of the same size, light suction is far more rapid in its action than heavy suction (tests 19 and 20), and no suction is most rapid of all (test 21). As the discrepancy in size increases, heavy suction gains slightly and light suction loses ground slightly (tests 22 and 23, also 25 and 26). No suction breaks down entirely in test 27; equilibrium is here reached. When, however, .0195-diameter sphalerite is reached, there comes a complete reversal; the heavy suction gives a rapid result (test 28), and the light suction is quite slow (test 29). No suction was not tried because the upward current in the previous experiment was too much for a larger-sized sphalerite. From this down the heavy suction is rapid (tests 31 and 34), while the light suction grows weaker in each number of the series towards the lower end (tests 29, 32, and 35), where the rate of jigging had to be diminished in order to lessen the upward current before the sphalerite would go through the sieve at all (see test 32 for example).
We seem, here, to a more marked degree than with galena, to have the measure of the size of the interstices in the quartz of 10- to 12- mesh or .0683-inch diameter, for the sphalerite through 24 on 30- mesh (= .0262 diameter) is settled only with extreme difficulty according to the laws of equal-settling particles and interstitial currents, while sphalerite of 30- to 40-mesh (= .0195 diameter) is drawn down with great rapidity by suction. We may assume, therefore, that this size is the coarsest that can move freely in the interstices of quartz of 10- to 12-mesh size.
The third series of tests was made upon quartz in large grains, with quartz in small grains, to determine the effects of suction and pulsion. For this purpose, the two kinds were jigged by pairs, as follows (the results are given in Table XLIV.).
Quartz passing through 10-mesh and resting on 12-mesh sieve (average diameter, 0.0683 inch) was jigged with quartz of the following sizes:
We conclude with regard to quartz of different sizes, that strong suction can draw down small grains of quartz through the interstices between large grains of quartz (tests 39, 41 and 43), and if there is no intercepting heavy mineral layer below, these small particles will go through the sieve. Light suction, with excess of pulsion, cannot draw small quartz down (tests 40 and 42) so long as the jig is really working. When, however, the pulsions are so slow as not to move the coarse quartz (test 42), then suction equals pulsion and sifting takes place. Strong pulsion with no suction cannot draw down fine quartz through the interstices of 10- to 12-mesh quartz under any circumstances. The quartz will always be graded by size; the coarser below, the finer above, as in the pointed tube.
The fourth series of tests comprised the jigging of mixed sizes upon a number of minerals ranging from copper, at the heavy end of the series, to anthracite, at the light end. Each mineral was mixed with quartz in approximately equal quantity by volume, and the sizes in all cases were from 10-mesh to dust. The pairs were composed of quartz, with copper, galena, antimony, arsenopyrite, chalcocite, magnetite, pyrrhotite, sphalerite, epidote, and anthracite, respectively. The results are given in Table XLV. To aid in interpreting these results, the skimmings or tailings from each of the tests were sifted upon the nest of sieves; each size was spread out upon a sheet of paper, and the quantity of the heavy mineral in it was estimated by the eye, as per cent, by volume or number of grains in one hundred grains. The results of this sifting and valuing process are given in Tables XLVI., XLVII. and XLVIII.
As a means of comparing quickly the final results of these jigging-tests, the phrase “ 5 per cent, in the tails reached up to mesh ” is used. The figures inserted in the blank are taken from Tables XLVI., XLVII., and XLVIII., and will be seen to give a quick and fairly good summing-up of the tests.
The conclusions as to the jigging of mixed sizes are as follows :
In the elevated (heavy suction) tests, the tailings retrograde rapidly from copper towards arsenopyrite. From arsenopyrite on, they retrograde but little. (See Table XLVI.)
Again, in the inundated (light-suction) tests, beginning with copper, the quality of the tailings of each mineral is much poorer than that of the mineral next preceding it, until arsenopyrite is reached. Here again, there is a change—the tailings of arsenopyrite are much worse than those of antimony, and but little better than those of its lighter neighbors to the right.
For testing the pulsion-jig, the corresponding values were obtained by assuming that the pulsion-jig and the pointed tube have practically the same effect. This has been proved at two ends of the series (compare Plate XIV. with Plate II. b, and Plate XV. with Plate X.; also, the tables of figures which correspond).
On this assumption, we take, for example, Plate II.b. Clearly, bulbs Nos. 1, 2, and 3, form the heads of jigging, and bulbs Nos. 4, 5, 6, 7, 8, 9, and 10, form the tails. We estimate the percentage of galena in these different sizes of the tailings. There is no galena in 12-, 14-., 16-, 18-, 20-, and 24-mesh grains. From 30-mesh down, my estimate is given in Table XLVIII., together with estimates made in like manner on Plates I. to XII., inclusive.
Once more arsenopyrite appears as the turning-point in the series ; the tailings of the successive minerals rapidly retrograding in the
series until arsenopyrite is reached, while the tailings of the minerals to the right of arsenopyrite are but little worse than those of that mineral.
Quartz being the heavier mineral, of quartz and anthracite, it is much too good to be in the company it is. The ratio between quartz and anthracite is nearly as great as between quartz and antimony.
The results of this series prove conclusively, that strong suction is more efficient for jigging mixed sizes thau weak suction (compare Nos. 45 and 46, 48 and 49, etc.); and again, that weak suction is more efficient than no suction (compare Nos. 46 and 47, 49 and 50, etc.)
These tests show, also, that in jigging mixed sizes of a series of minerals, we have found, in arsenopyrite, the middle cone of the three (see Fig. 7), the turning-point in the set, where the heavier
mineral grain is just large enough to fill the interstices in the quartz. All the minerals heavier than arsenopyrite jig easily ; all those that are lighter jig poorly when mixed sizes are used.
The turning-point referred to in Fig. 7, where the heavy grain is of a size which just fills the interstices among the lighter grains, is represented by the interstitial factor 3.7 of Table XXXVII. This factor has been arrived at in three places in this investigation, namely, by jigging-tests, Nos. 7 and 10 ; jigging-tests, Nos. 25 and 28, and the facts brought out in Tables XLVI., XLVII., and XLVIII. The factor will probably vary somewhat with the fracture of the minerals; and it also needs confirmation for larger sizes.
While it is a simple matter to make a table of equal-settling factors (Table VII.), of interstitial factors (Table XXXVII.) and of acceleration-factors (Table XXXIX.), no corresponding table of suction-factors can be made. The most that can be said is that suction increases with the length of the plunger-stroke, with the difference in specific gravity of the two minerals, and with the diminishing of the thickness of the bed on the sieve, whether of the heavier minerals only or of both minerals.
Working Principles of jigging are pulsion & suction
The effect of pulsion depends upon the laws of equal-settling particles, interstitial currents, and, possibly, also of acceleration. The chief function of pulsion is to save the larger grains of the heavier mineral, or the grains which settle faster and farther than the waste.
The effect of suction depends upon the interstitial factor of the minerals to be separated (see Table XXXVII. and Fig. 7). If this factor is greater then 3.70, suction will be efficient and rapid. If the factor is less than 3.70, suction will be much hampered and hindered. The use of a long stroke will help to overcome this difficulty. The chief function of suction is to save the particles that are too small to be saved by the laws of equal-settling particles, and of interstitial currents, acting through the pulsion of the jig.
- For jigging mixed sizes, pulsion with full suction should be used.
- For jigging closely-sized products, pulsion with a minimum of suction should be used.
The degree of sizing needed as preparation for jigging, if we are looking for the most perfect work, depends solely upon the interstitial factor of the minerals to be separated. If the factor is above 3.70 (assuming this value to be sufficiently proved), then sizing is simply a matter of convenience. The fine slimes should, of course, be removed ; and, if it is more convenient to send egg-size, nut-size, pea-size, and sand-size, each to its own jig, the suitable screens should be provided for this purpose, and a hydraulic separator for grading the finest sizes. But if, on the other hand, the factor is below 3.70, then, the jigging of mixed sizes cannot give perfectly clean work, and the separation will be approximate only. To effect the most perfect separation, close sizing must be adopted, and the closer the sizes are to each other the more rapid and perfect will the jigging be. There may be conditions where the jigging of mixed sizes of this class will be considered sufficiently satisfactory, as an expedient, under the circumstances. Indeed, it is probable, that as much as 90 per cent, of the mineral was saved in every test recorded in Table XLVI., except that of epidote.
The small scale on which this work has been done may have exaggerated, to some extent, some of the jigging-results. It is hoped, however, that if the reader does not find here the large-scale work exactly pictured, he will find analogies from which he may be able to predict results.
The author is indebted to his assistant, Mr. W. A. Tucker, for the careful and accurate way in which the whole investigation has been conducted; and particularly to Mr. J. B. Seager, graduate of the Michigan Mining School at Houghton, for the help he has given, not only in conducting the experiments, but also in the way of suggestion and intelligent criticism.