US1425186A - Separating process - Google Patents

Description

R. ELLIS. SEPARATING PROCESS.

APPLICATION FILED APR.2. 1919.

Pafendmg. 8, 19222 AQJLS,

naeaise.

PATENT @EETCCE' METTE@ STATES IDSIDALE ELLES, 0F @AK PARK,

SEEABLATING PCESS.

Specification of Letters Patent.

JILEJINIS.

- EEUSSUEE Patented Aue, S, 11922.,

@riginal application led. .april 15,1918, Serial No. 22,623. Divided and. this application illeti April E, wie. Serial No. 27,030.

To all whom it may concern.'

lBe it known that i, RIDSDALE ELLIS, a citizen of the United States, and a resident of Uak Park, in the county of Cook and State of illinois, have invented certain new an useful Improvements in Separating Processes, of which the following is a specification.

My invention relates to processes for concentrating parts of masses of composite character, such as metalliferous ore, by treating the comminuted mass with a fluid adapted to aid in the separation of certain of the comminuted particles from others having diHerent qualities.

rlihis application is a division of my copending application Serial No. 228,623, filed April 15, 1918, and a continuation in part of my co-pending application Serial No. 75,430 filed January 31, 1916.

Broadly my invention includes the use of means for producing certain changes in the fluid and the particles of the mass whereby the separation of certain of the comminuted particles from others having dierent qualities is aided. Preferably such means include the use of substances adapted when dissolved in fluid, preferably an ionizing fluid, to bring about certain electrical changes, and to this end to give polyvalent ions for aiding in the separation of certain of the particles from others by means of a fluid having a preferential afiinity for certain of the particles.

More particularly, in its preferred form, my invention relates to processes for con-k centratingmetalliferous ores by means of the combined action of gaseous bubbles and oil, or other substances soluble or insoluble, adapted to aid in the formation of a froth containing the metalliferous constituents of the ore.

My invention' is particularly adapted for the concentration of sulphide ores, but is also applicable to the concentration of other ores, such as oxides, carbonates or hydroxides, either unchanged or after a sulphiding or other treatment, native or precipitated co per, gold, and for the concentration of grap s ite and other. similar materials.

The principal objects of my inventionQare in general to enhance the eiiiciency of concentrating processes as hitherto carried out;

to increase the percentage extraction and rate of separation of the metalliferous constituents; to improve the grade of concentrate; and in particular to improve froth flotation processes for the concentration of ores and similar comminuted materials of diverse character. .o

To this end my invention contemplates the use of electrolytes of various types and the modification of the flotation processes' as commonly carried out to enable the beneficial action of such electrolytes to be more fully obtained.

The effect produced by electrolytes may be conveniently classified according as they are due to purely physical phenomenon or to chemical reactions in which the electrolytes added react chemically or electrochemically with the constituents of tne ore.

rllhe physical laction of electrolytes, more particularly inorganic electrolytes, appears to be dependent upon the valence (andto a lesser extent on the mobility) of the ions produced by the solution of the electrolytes in an ionizing fluid and is consequently electrical in its nature.

i have found that the results of such physical action may be modified by changing the time of addition of the electrolytes. rllhus certain types of electrolytes give improved results when addedprior to oiling and other types better results when added after oiling v Therel is also a very important relation between the physical action of such electrolytes and the size of the'particles. A

While the e'ects produced by electrolytes of various types arev readily demonstrablev the cause lof these e'ects is far more complex. n

In order, however, that the invention may be more fully understood I give a statement of the general principles underlying the formation of a froth and the action of electrolytes in aiding or hindering the separation of metalliferous matter by froth dotation processes.

Practice carried out by me has shown that results obtained by the use of electrolytes vary considerably according to the way in which the gaseous bubbles are introduced to form a froth. Bubbles may be introduced in two general ways: ln the first place, the bubbles may be forced in from without, and secondly, the bubbles of gas may be generated, or otherwise produced in the liquiditself. As examples of methods of introducing gas mechanically from the outside, the me-` bubbles. As these minute air bubbles have a much 'higher solution tension than larger air bubbles, the water becomes supersaturated so 4far as bubble formation -on a sulphide or oil surface is concerned and as a result air comes out of solution on the sur! face ofthe oiled sulphide particles. The result of the violent mechanical a itation is .therefore two-fold, first, the intro uction of air bubbles bodily from the external air and second, the generation of air bubblesv ab initio on the surface of the oiled particles of sulphide.

In the pneumatic agitation recess the generation of bubbles 1n the pu p does not appear to take place to any great extent.

In the formation of a froth where liquid oil is used, there appear to be two important operations, first the coating of the metalliferous particles with oil and second, the formation of a viscous bond between such oiled particles and the gaseous bubbles.

In these operations electrolytes may act in four amongst other ways:-

First in determining the readiness with which the oil can come into physical contact with the particles of sulphide.

Second in changing the readiness with which the oil after contact with the particles of sulphide will spread over the surface of the latter and the tenacity with which the oil adheres to the sulphide surfaces. Third in determining the readiness with which the gaseous bubbles can come into physical Contact with the oiled particles of sulphide.

Fourth in changing the readiness with which the oil after contact with the gaseous bubbles will spread over the surface of the latter.-

The changes produced by electrolytes in any one or more of the above ways may be the resultqof either (a) Changes in the electrical conditions;

s examples of thel maare@ (b) Chemical lchanges at the surface of the articles to be Hosted;

el; Changes in surface tension due to absorption of the electrolyte at the oil-water,

particle-water or air-water interfaces.

In the case of inor anic salts surface tension measurements indicated that (e) is negligible and this is confirmed by the fact that where the action of electrolytesv does not follow .certain laws based on the valency or number of electrical charges carried by the ions formed by the solution of the electrolytes the deviation from these laws may be attributed in most, if not all, instances, to chemical action between the electrolyte and the constituents of the ore..

With the majorit of ores the most important function o electrolytes in aiding flotation appears to be the yproduction of favorable electrical conditions.

In this respect it is not the molecules of the electrolyte which are active but the ions produced by the dissociation of the electrolyte when dissolved in an ionizing fluid suchl as water.

All electrolytes, whether salts, acids or alkalies, when dissolved in an ionizing fluid produce ions to an extent depending upon the degree of dissociation of theelectrolyte. The valence of these ions may range from one to six and possibly, though not probably, even seven or more.

The simplest combination of ions is M* R where M represents the cation or positive ion and R represents the anion or negative acid radicle ion. Now the valence of the cation or anion may each be increased separately or the valence of both may be increased simultaneously. These three changes may be represented graphically as follows:

As the valence of the ions increases their effect on'the contact and frictional electrification of the oil, sulphide and gangue particles` and gaseous bubbles also increases, whether the ions are posit-ive or negative, and these changes i the sign and magnitude of the electrificatio of theI constituents of the ore p'ul produce very marked results in the formation of a froth and the separation of the metalliferousmatter by such means.

Solid or liquidparticles gifall kinds ac quire a contact potential when suspended in pure water of from 0.03 to 0.06 volts, the particles being almost invariably (with the exception of oxides, hydroxides and some carbonates) negative with respect to the water. Gases, on the other hand, may be /the Aconcentration required to 'duce reversal, and the greater electried in at least two dilierent Ways which are essentially distinct l'irst, frictional electritication, and second, Contact electrification. lf air is blown through Water it becomes electrically charged by friction With the Water, and electricity may be collected from the air and also from the Water. The potential of the Water may reach several volts. llt a bubble ot air is in stationary contact with Water7 it acquires a contact potential of the same magnitude as that acquired by solid or liquid drops suspended in Water, namely, 0.03 to 0.06 volts.

ln contact electrication the conversion of the original negative charge onV aI particle suspended in water (Whether solid, liquid or gaseous) into a positive charge is brought about by means of polyvalent cations; the higher the valence of the cations, the smaller the concentration of the electrolyte required to bring about the reversal, and the greater the positive charge which can be produced thereby. lf a polyvalent anion is present,

produce reversal is increased, and also the maximum positive charge which can be obtained is re' duced. 'llhis inhibiting action of the anion increases as the valence increases.l 0n the other hand, the original negative charge may be increased by polyvalent anions; the higher the valence of the anion the greater the increase in the negative charge which can be produced. Cations inhibit this increase in negative charge in proportion to their valence.

ln frictional electriication the valence ota the ions appears to have exactly the reverse eltect to what they have in contact electrification. ln order to produce a strong positive charge polyvalent anions must be use rlllhe greater the valence of the anion, `the smaller the concentration required to prothe positive charged which is produced. Polyvalent ca.- tions have an. exactly analogous edect .to polyvalent anions in the case 'of contact electriication as they increase the concentration of polyvalent anions required to bring about the reversal, and the effect of cations in this respect increases asfthe valence increases. i

While the spreading of a drop of oil over a sulphide or similar surface is no doubt due to differences in surface tension at the oil-Water, oil-particle, and Water-particle the oil must first be brought into actua-l physical contact With the Asulphide particle before it `can spread. Now it is the electrical factors which largely determine Whether or not such physical contact takes'place readily or diflicultly.

lln pure Water an oil globule is strongly charged negatively5 a( sulphide particle very weakly negatively. Under these conditions there is a slight'electrical repulsion; add a salt ot the type or sodium pyrophosphate and the nega-tive charge on both oil globule and sulphide particle will be increased so that the electrical repulsion is also increased. 0n the other hand it a. small amount of acid isadded the potential of the sulphide becomes positive While yreducing but not reversing the negative potential on the oil, under these circumstances electrical attraction occurs.

ln both cases it the oil globule once comes in contact with the sulphide particle it will probably spread substantially independently of the sign and magnitude ot the electrical charges on the two materials, but in the first case it is relatively dilicult to giet the initial contact olf'v the oil and sulphi e and so allow the surface tension forces to come into play while inthe second case it is relatively easy. l

Consequently as sodium pyrophosphate tends to increase the negative c arge ot both oil and sulphide it will inhibit"oiling. just as acid aids oiling by reversing the sign of the charge on the sulphide.

Although an anion, particularly a high valent ion, ten s to change the contact potential `of any solid or liquid particles suspended in anionizing fluid in the same direction there is a reat dierence in the natural tendency o? various substances to acquire and retain a negative or lpositive charge. rlhus oil is normally strong y negatively charged and a much higher concentration of acid is required to neutralize and reverse this charge than in the case of the much more weakly negatively charged sulphide particles.

Further with salts ot the type ot sodium pyrophosphate the ne ative contact potential ot oil, sulphide and other substances increases to a maximum and then decreases and the position of vthis maximum oint depends on the chemical nature of t e substance. With oil thispoint is reached with a higher concentration ot salt than with either sulphides or silica or silicates.

llt a salt is used which is adapted-to give anions and cations both having a relatively high valence, such as aluminum pyrophosphate it is possible to give the sulphides a positive charge' Without reducing the nega tive potential of the oil to the same extent as When acid only is used to give the sulphides a positive charge. As oil acquires' and retains a negative charge much more readily than do sulphides, a trivalent cation like ill lllli aluminum has a much greater edect on the metalliferoils particles, on the other-hand it is not the most eflicienttypefor oiling. Such a salt may, however, be used in relatively hi h concentrations to take advantage of the di erence in the maximum potential points of oil and sulphide respectively. Further, a salt adapted to give both high valent cations and anions may be used to reverse the sign` of the potential on the sulphides without lowering the negative potential on the oil to the same extent as the acid alone. Again, oiling may be caused to take lace in plain water or acidied water an the sodium pyrophosphate or similar salt added after oilin and immediately prior to flotation.

De aying the time of addition of the sodium pyrophosphate does not entirely eliminate its' inhibiting eect on the oilingfor the reason that in the mechanical agitation process, and to -a much smaller extent in the `pneumatic agitation process, the oiling, is in part atleast, a reversible operation, possessing therefore a position of equilibrium. Wlth mechanical agitation, therefore, the fact that the oil originally adhered to the sulphides is not suficient and it is desirable, if possible, that conditions' during flotation should be as favorable as possible for reoiling.

The greater the alin-ity' of oil for the metalliferous particles the more tenaciously will the oil adhere once it has been brought into contact with the particles and the more-irreversible will the operatlon become.

rlhe aftnit of oil for sulphide particles may be c anged by salts, usually to reduce the .adhesions (employed in preferential ilotation),but in some casesfto increase it. Such changesappear to be dueto chemical rather than electrical causes.

rlhe difference between the chemical and the electrical action of -salts is well illustrated by the action of potassium ferrocyanide onI the flotation of copper ores. ln neutral solutions this salt acts as a owerful poison owing to the formation of insoluble copper ferroc anid on the surfaces of the sulphide artic es. On the other hand with an alkaine solution of the same salty very beneficial results are obtained since in the presence of alkali insoluble copper ferrocyanide is not produced so that the beneficial action of the quadrivalent anion is obtained.

Copper sulpiate has a very marked chemical action. ith zinc ores its use is very beneficial, with pyrite ores it is deleterious.

With zinc ores it is more beneficial than theA valency of the ions it forms would warrant and while coppersulphate and acid under certain circumstances appear to be more eilcient than either aluminum or sodium pyrophosphate and acid, a combination of the latter salts with acid and copper sulphate gives better results than copper sulphate and acid alone. i l

The next factor to be considered is the air-sulphide adhesion. At the first moment of adhesion between the oiled sulphide particle and an air bubble there must .be actual physical contact irrespective of the conditions which occur afterwards.

For ecient flotation both air-bubble and particle must be oiled. rlhis may be done in one of three ways.

(1) Sul hides are oiled and air bubbles get their film of oil from the sulphides.

(2) Air bubbles are oiled (as in the case of oil vapor process) and the sulphides receive their oil from the air bubbles.

(3).(y Both sulphides and air bubbles are oiled independently. The first of these is the method used incirculating mechanical agitation apparatus in which oil is added in liquid form. A

As already indicated, a salt of the type of sodium pyrophosphate gives the oil an increased negative charge and the air a Strong frictional positive charge (dependent upon the rate of movement of the air relatively tothe water) thereby producingan silicates is also increased by a salt of the type of sodium 1pyrophosphate, an increase in the amount o gangue floated would also be expected. Practice'shows this to be the tant feature then sodium pyrophosphate will 'give higher extractions with the mechanical than with the pneumatic agitation process, owing to the much more vio ent agitation in the former than inthe latter case. -This is also confirmed by practice.

The relative movement of the Ibubbles of gas and water producesa positive or nega same si as that on the .metalliferous particles w 'ch it is desired to unite to the bubbles of as and consequently it is desirable to get rid of the charge on the water Ias it If frictional electrication is an impor llli tocante@ charge may be advantageously eliminated,

preferablyby grounding the flotation apparatus so as to connect the Water electrically With the earth.

l have also `found that the action ot electrolytes is greatly modified by the size of the particles in the ore pulp. With relatively coarse feedf-say 80 to 100 meshthe addition ot' sodium pyrophosphate even before oiling greatly increases the extraction Whereas with slimes the addition ot this salt before oiling may even decrease the extrae? tion.

This is due to the ifa/ct that the smaller the particles the more important become the electrical factors in oiling. t

ln the pneumatic agitation process, unlike the mechanical agitation process, l have found that. salts of the types of thorium chloride or aluminum p rophosphate are, under some conditions, istinctlydeleterious, kWhereas a salt of the type of sodium pyrophosphate is very useful though not producing as advantageous results as in the mechanical agitation process. Further, While acid aids the action ol salts in mechanical agitation alkali is preferably used in the pneumatic agitation process. Y

There appear to 'be various reasons for this diderence between the mechanical and pneumatic agitation recesses.

Thus a reduction o the negative potential I of the oiled sulphides is'particularly deleterious inthe pneumatic agitation process as much less frictional electricity is generated on the air than in the mechanical agitation process, owing to the less violent a tation. This is due to the fact that while the sign of the charge on-the air depends upon the ions present in solution, its ma itude is largely dependent upon the spec at which the air bubbles are lmoved through the solution.'

Then the production ot conditions advan- V t-ageous to oiling are more important in the mechanical than in the pneumatic agitation process and such conditions are aided byy aff-id or polyvalent cations.

Further in the mechanical atation process somegeneration of gas bub les ab initio on the sur-face of the oiled sulphides occurs. The acquisition of a positive-charge appears to favor the formation of a bubble ab initio in Water since it has been shown that bubbles of gas are often, if not usually, positively charged when they have been generated from a solution which would not give a positive charge to a bubble of gas introduced bodily from an external source.

Arm-really, theaters.

hydrogen or high valent cations are uselulas either directly or indirectly providing positive nuclei tor bubble formation.

For carrying out my invention apparatus of well known types, may be employed 'with such modifications in construction and arrangements as may be needed to enable my improvements to be employed to best advantage. `As dot-ation apparatus of the type proposed tor use with my salts and other improvements are so vvell known to those skilled in the art detailed description vvill be unnecessary. Consequently in the accompaiiying drawing ll have given only a diagrammatic illustration ot one construction and arrangement adapted tor carrying out my improvements.

' ln the drawings l represents the tube mill to which ore is fed by means of a chute or launder 2. @il and such reagents as may be employed to aid flotation and in particular the oilng of the metalliferous articles, for exam le an acid solution containing such a quan ity ot sulphuric acid and aluminum or titanium pyrophosphate that the pulp con-- taining the slimes after separation from the sands will contain in the case of copper sulphide ores about 4l lbs. of?v acid per ton of Vdry slime ore (for an cre which normally requires 8 lbs. of acid when used Without added salt) and about 0.25 lbs. or aluminum pyrophosphate or 0.10 lbs. of titanium pyrophosphate, ore as it enters the tube mill by means of pipes 3 and t. .l

The crushed and oiled ore passes from the tube mill through pipe 5 to a Dorr or other classifier 6. As the ore is ordinarily ground With a much smaller amount of Water than is used for dotation the additional amount of Water may conveniently be added to the pulp in the classifier. This classifier is provided With an inclined bottom 7 up which the sands which settle out lare moved by means of rakes (not shown) until they pass over the lip or Weir 8 into the pipe 9. At the opposite end of the classifier an overflow lip or Weir t3 is provided at a lower level than the lip 8 so that the Water in the classifier carrying the slime'material in suspension Will all flow over the lip t3 While the rakes in moving the sands over the lip will litt them out of the Water and deliver them to the pipe 9 very largely dewatered. By this arrangement the electrolytes employed in aiding oiling, which-are mre especially useful' inthe flotation of slimes, are removed from the sands and retained in the slimes.

The slimes pass from the lip t3 into a pipe 10 which discharges into the agitation chamber 11 of a machine which may conveniently be ot the mechanical agitation type. Asthe pulp dovvs into the pipe 10 further additional quantities of reagents,

are conveniently added to the- Stil MDO

lil@

such for example as a solution of aluminum or titanium pyrophos hate, may be added bymeans o f pipe 12. n the agitation chamber a rotatable propeller 13 is provided driven by gearing from a shaft 14. The aerated ore pulp passes through the a erture 15 into the spitzkasten 16 in which t e bubbles of air carrying metalliferous particles form a layer of froth 17 while the sands fall 10 to the bottom and can be discharged through the pipe 18 to the tailing pond or another machine for'retreatment. The froth flows over a weir into a launder 19 from which the concentrates may be discharged.

Frequently vit is desirable to introduce frothing agent with the air or other gas employed for forming the froth either in addition to or in place of liquid oil or a soluble frothing agent. For this purpose the 20 upper part of. the agitation chamber 11 and spitzkasten 16 are enclosed by a cover 21 at opposite 'ends of which pipes 22 and 23 are provided for ingress and egress of air carryfing a frothing agent such as oil vapor.

Preferably the machine just described is employed merely as a roughing cell and the concentrates discharged by pipe 20 are retreated in a cleaning cell, as 24.

With most ores this cleaner cell 24 is preferably of the Callow or pneumatic agitation type yhaving a porous bottom 25 through which air may be blown from pipe 26. kThis air may, if desired, be charged with a frothing agent such as oil vapor. To allow the B5 unutillzed portionsV of the oil vapor to be conserved the upper part of the cell is enclosed at 27 so that the air liberated by the breaking of the bubbles in the froth may be` y/led away by pipe 28 for reintroduction 4o through the pipe 26 with such further additions of air and (or) oil vapor as maybe re uired.

s the concentrates only contain a small percenta e of water additional water may be intro uced into the cell 24 by means of pie 36. he froth flows over weirs into launders along each side of the cell in the usual way and the concentrates, and any froth which does not break down in the launders, passes out through the pipe 29.

The flow ofthe tails into the pipe 30 is controlled by a valve 31 operated in wellknown way Vby a float 32. These cleaner v tails contain considerable quantities of metalliferous matter and so they are preferably returned to the rougher cell by substantial means such as a centrifugal pump 33 and pipe 34. The cells, particularly the rougher cell, are preferably electrically grounded in any suitableway as illustrated diagrammatically at 35.

The sand may conveniently be treated by a similar arrangement of 'mechanical agi Macnee tation rougher and pneumatic agitation et cleaner cells to those employed for treating However, the method of handling the 'circuit water is preferably vsomewhat different in the case of sands than of slimes for the reason that the sands are substantially dewatered by the classifier and further, .the tails are readily dewatered as the sands settle quickly. These facts greatly facilitate the operation of the rougher and cleaner cells on a closed cycle'so far as the l circuit water is concerned. This is particularly advantageous with sand since for particles of large size relatively large quantities .of a salt of the type of sodium pyrophosphate is employed for-aiding in the production of a collective float'of the values in the ores. ln many cases it is desirable that oiling take place in acidified waterV and dotation in alkaline water and the dewatering of the sands by the classifier reduces the amount of alkali required to' neutralize the acid in the water still adhering to the sands. and to give the water the desirable alkalinity. .V

For `copper sulphide ores a convenient concentration of sodium pyrophosphate 6 lbs. per ton of ore and if desired free 95 alkali ma be employed in addition. The amount o alkali, such as sodium hydroxide, may conveniently range from 0.01 to 0.2 lb. per ton of ore in excess of that required to f neutralize any acid adhering to the parti- 100 cles of ore as they leave the classifier.

In the first place, instead of discharging the tails from the pipe 18 to the tailing pond they may to'advantage be transferred to a settllng cone 37, from which the circuit water may be drawn offend returned to the system by ipe 38, centrifugal pump 39 and pipe 40. 1g portion of the circuit water passmg throu h the pipe 40 may conveniently be iverted by pipe 41 to the cleaner cell 24. With this arrangement flotation takes place in the same solution in both rougher and cleaner cells.

Additional quantities of water, salt and (or) alkali may be supplied as required by 1pipe42.

or purpose of illustration I give in detail the results of practice with a pross of the mechanical a itation froth type.

The amounts of e ectrolyte employed are given merely as examples of concentrations foundl suitable for certain ores, since, as is well known to. those skilled in the art, the exact proportions of those substances which may be used in {lotation processes vary somewhat according -to the nature of the ore treated. n-

AS itis usually lmore convenient to addthe For emulsication or oiling prior to flotation separation the ground ore was mechanically agitated with three times its weight of water, 0.3% to 0.4% of its weight of oil, and the desired quantity of electrolyte. rlhe percentages of electrolytes used are based on the ore and' not on the water.

Using salts of a monovalent acid, i. e. hydrochloric acid, l found that the highest recoveries were obtained with the following percentages of sodium chloride, calcium chloride and aluminum chloride (each used alone without acid) respectively Sodium chloride, NaCL'. 0. 40% Calcium. chloride, CaCl2 0. 27%

Aluminum chloride, A1Cl3 0.06%

rllhis table clearly shows that the higher the valence of the cation the smaller the quantity of salt required to give the best results for that particular salt. llt was further found that not only did the amount of salt required decrease as the valence of the cation increased, but also the amount of sulphide floated increased as the valence of the cation increased. The froth obtained with aluminum chloride was not only thicker, but also much firmer, finer and cleaner than the froth obtained with calcium chloride, and still more so than that'v obtained with sodium chloride, and, further, the difference between the floats obtained with aluminum chloride and calcium chloride, respectively,

was much greater than between calcium chloride and sodium chloride, respectively.

However, for theA particular ore used, the separation of sulphides, even in the case of aluminum chloride, was inferior to that obtained with sulphuric acid both as regards quantity and quality of concentrate.

llsing salts of a trivalent metal with acid radicles of different valence, the highest recoveries were obtained with the following concentrations Sodium chloride NaCl 0. Lt0% Sodlum phosphate NalPU4 (above) 0. 064% Sodium pyrophosphate NaPZU,..- 0. 016% llVith both sodium and aluminum salts increasing the valence of the anion not only decreases the amount of salts required to produce the best results, but also increases the efficiency of separation. lt will be observed that the smallest concentrations were obtained when the valence of both the cations and anions was the greatest, namely, when aluminum with sodium pyrophosphate was used. f

ln connection with sodium pyrophosphate ll have found that there are two points of maximum extraction, one about 0.016% and the other abovev 0.3%. tential of oil steadily rises to a maximum obtained with concentration of sodium pyrophosphate above 0.3% so that the existence of the first maximum point is probably due to the fact that the difficulty with which oiling of the sulphide particles can occur increases to a'maximum and then decreases y.

as the concentration of sodium pyrophosphate is increased from zero to 0.3%. 0f the two points of maximum extraction the higher concentration has been found b practice to be the most efficient, and this 1s probably due to the fact that not only is the contact potential on the oil much greater, which means that the oiled sulphide particles will have a more powerful attraction for the positively (frictionally) charged air, but also because at the higher concentration the difficulty of oiling appears to be less than at the lower concentration.

Using sulphuricv acid alone, the best results were obtained with a concentration of 1.2%. When, however, mixture of salts and acid were used it was found that the amount of acid which would give the best results in conjunction with the salts was approximately one-half that required when acid alone was used in the ca'se of salts adapted to give trivalent ions, either positive or negative, or both positive and negative, as will be seen from the table given below. lin the case of salts adapted to give quadrivalent ions, either negative or positive, it was found that the amount of acid could be advantageously increased beyond this amount (i. e. 0.060%.) For instance, with titanium sulphate, increasing the concentration of acid up to 0.711%, gave a'steadily increasing yield, so that the best results would be obtained with the even higher concentration of acid. than that just referred to. Similarly with sodium pyrophosphate, the best results were obtained with a concentration of acid y in excess of 1%.

When the valence of both cation and anion are increased above two the amount of acid which can be usefully employed falls on' below 0.60%. rllhe figures for the best concentration of the salt and acid, respectively, in each case are given in the follow- It y,Will be seen that in each of the'above acid and salt mixtures there is a relatively much greater numberof hydrogen ions than polyva ent ions produced by the dissociation of the salt, whether such ions are positive or negative.

lin thel above practice, both with and without acid, salts were used in the absence of heat and of material, such as bichromates adapted to inhibit flotation of certain sulphides.

l have further found that an acid solution of sodium pyrophosphate-0.3% Nazlz@7 and 1.00% HZSUr-gives better results than the above acid solution of sodium pyrophosphate, namely :-0.016% NaPfz, and

1.00% NZSO..

llt was found that the aluminum pyrophosphate gave higher extractions rthan either aluminum chloride or titanium sul-v phate. With most ores neutral sodium pyrophosphate gave higher extractions than aluminum pyrophosphate, and in practically all cases a strongly acid solution of sodium pyrophosphate give much better results than either 'neutral sodium pyrophosphate or aluminum pyrophosphate.

Conse uently it appears that of the foregoing so utions the one generally most eilicient for the mechanical agitation process is a strongly acid solution of sodium pyrophosphate. Such a solution not only increases the extraction but also raises the maare@ Atice was ground to pass 80` mesh but if the more readily it floats but when a saltpf thev type of sodium pyrophosphate is present during oiling poorerfresults `may be obtained with slimesthan with sands.

This difference is much more marked with zincores than with'copper ores, doubtless due to the smaller ailinity of oil for blende than for sulphides of copper.

Preferably, therefore, prior to flotation treatment the ore is classified in order that the sands or larger particles may be oiled and floated in a different electrolyte `than the slimes or fine particles. For the sands the electrolyte may be of the type specially adapted to aid the flotation of the particles when oiled, e. g. sodium pyrophosphate. In the case of the slimes the electrolyte may be of the type specially adapted to -aid the oiling of the particles, e. g. an acid solution of aluminum pyrophosphate:

This classification treatment has the further advantage that it facilitates the recovery of the sodium pyrophos hate Vfor further use. It is comparative y easy 'to dewater sands as they settle rapidly and can be readily separated from water by means of drainage belts or the like. Slimes, on the other hand, require much longer time to settle and more careful treatment to separate the water.

The amount of aluminum pyrophosphate required is so much smaller than the quantity of sodium pyrophosphate needed to give best results that the de-watering of the slimes is not nearly as important as the dewatering of the sands.

In addition to classifying the oreaccording to size of particle l have found it useful with certain ores to employ mechanical agitation rougher cells in combination with pneumatic agitation cleaners.

In practice using a low grade copper ore ground with oil and floated in the presence of 6 lbs. of sodium pyrophosphate by the mechanical agitation process an extraction of 97.5% was obtained with a concentrate weighing 25% of the original feed. On the other hand, using the pneumaticagitationprocess and the same amount of such salt. the extraction was only 93% instead of 97.5%, but the concentrate only weighed 16%' of the original feed instead of 25%. Accordingly, I propose to employ the two processes in conjunction in order to cornbine the good features of each. .I have found that the above concentration of such salt gives very beneficial results in both forms of process so that the same solution may be used in both rougher and cleaner cells.

Further, l may employ sodium pyrophos- Ult 1 salt was added prior to y phate or inname 'concentrate may be as important as the edect ot these salts in increasing the extraction.

Tn practice with zinc ores ll have found that a salt such as copper sulphate having a beneficial chemical or electrochemical action should be employed in addition to acid and pyrophosphate, `Whether sodium or aluminum.

The concentrations of sodium pyrophosphate found most benecial with zinc ores appear to be very considerably lower than in the case of copper and other ores.

With relatively coarse feed a change in the time of addition has only a slight edect on the extraction. This was shown in the dotation ot a copper ore assaying 1.00% Cu ground 16% on 80 mesh.

When the ore and oil were both ground and subselguentl lloated in the presence of 0.10% alll2 7 solution (on the Water) the tails assayed 0.11% instead of 0.88% when ground with plain Water and then floated in a solution of sodium pyrophosphate of that strength. The same ore, both ground and floated in plain water, gave a tail containing 0.25% Cu.

With smaller concentrations of salt` the effect is more pronounced. lFor instance, with a 0.003% solution (on the Water) of Na4P207-on a sample of ore assaying 1.92% Cu, the tails assayed 0.55% Cu when the grinding and 0.d2% Cu when the salt was added after grinding as compared with 0.47% Cu tor plain water. This is probably due to the maximum negative potential or the sulphides bein reached in much lower concentrations than 0.10% sodium pyrophosphate. Tt this is the case., then in a 0.10% solution, the negative potential of the sulphide will be brought' to a value approachin zero.

The edect of changing the tlme of addition ot the sodium pyrophosphate is much more marked in the case of sllmes. i

lin the case of a copper ore slime assaying about 0.02% lbs. per ton) the tails contained 0.07% Cu. When sodium pyrophosphate- (10 lbs. per ton) was added with the acid prior to oiling the copper ...in the tails increased to 0.13% but when added alter oiling (acid added before oiling) it decreased to 0.045%. This change in the time of addition also increased the grade of rougher concentrate from 8% Uu to 17% Cuas Well as very materially hastening the rate of separaion.

As the addition of alkali to a solution containing a salt of the type of sodium pyrophosphate greatly aids the latter in 1ncreasing the negative charge on the oil T Cu using acid alone (H2504 7.

may, especially alter oiling in acidiedsolution, make the solution alkaline by the addition of caustic alkali simultaneously vvith the introduction ot sodiumv pyrophosphate. Caustic alkali in very small concentrations (up to about 0.001 normal) itself increases the negative potential of oil as Well as increasing the amount of high valent anions produced by the dissociation of the sodium pyrophosphate.

The use ot various salts adapted to give `v..;

high valent ions has been referred to, and

in particular, sodium and aluminum yrophosphates. @ther similar salts mig t be used although these two appear to e the most readily available.

As in general the anion ap ears to be more important than the cation tlie available salts capable of givin anions having a high valence will be consi ered first.

As examples of hexavalent anions the tetraphospliates such as NalPlm and hexametaphosphates such as NaalPOm may be referred to. As instances ot salts capable of giving quadrivalent anions may be mentioned the pyrophosphat/es such as Na4l3207, ferrocyanides such as K Fe('CN)6, pyroarsenates such as Nalsz, and pyroantimonates such as KSbZUr Similarly for trivalent anions phosphates such as Na3P04, iierricyanides such as KQFMCN) or arsenates Naarlso4 might be used.

llt valence were the only factor to be considered the tetraphosphates and hexametaphosphates would be superior' to salts which give quadrivalent or trivalent anions. ll-lowever, tor is the extent to which the salt and the corresponding acid dissociates, as this determines the number of high valent anions furnished by a given amount of salt. Any polybasic acid or salt of such acid disse# ciates in stages. Tn other words, cations are given oil progressively With` the formation of negative ions of increasing valence. For instance p rophosphoric acid (H4P2O7) dissociates ist to form HBPZO] ions, a certain number of which then split up to form llllzPzUf' ions a certain number of which split up to form 20,"- ions, anumber ol which split up to form PZOf'" ions. The dissociatlon constants of the first second, third and fourth hydrogen ions of pyrophosphoric acid are respectively 1.a 101, 1.1 1c2, sexie-f and sexie-D. Cqonsequently the amount of quadrivalent P26," ion formed is much less than thev amount of the trivalent ion, which in turn is very much less than the amount of the divalent ion which in turn is less than the amountof the monovalent ion. The irst and seconddissociationv constants are less than those of sulphuric acid so that pyrophosphoric acid 1s an even stronger lacid than' sulphuric. @rthophosphoric acid on another, almost equally important taclCO til@

i divalcnt and as many divalent as the latter y aociation.

gives trivalent ions. Consequently even though pyrophosphoric acid did not give a quadrivalent ion while phosphoric acid Vcan onl give a trivalent ion pyrophosphoric aci would be much superior to phosphoric acid Lon account ofthe much larger number of diand trivalent ions it gives on disllhe dissociation of the acid correspu- .ding to the salt added is very important since, particularl when the electrolyte is added prior .to oi ing, acidied solutions in general give better results than neutral soutiens. Especially after oiling, and this, of course, includes the cleaning of rougher concentrates, the solution may to advantage be made slightl alkaline. Not only do hydroxyl ions tendy to increase the negative char@ on the oil but also the addition of alkali greatly increases the concentration of high valent anions. v

rlhis .latter edect results from the fact that the product of the concentrations of the hydrogen and hydroxyl ions is always 10,

lin a solution containing only 0.05% ot' sulphuric acid the hydrogen ion concentration (assuming complete dissociation is 1)(102. lin a solution containing0.05% of sodium hydroxide the hydroxyl ion concentration (assuming complete dissociation) is 1.2)(10'2 so. that the hydrogen ion concentration will be less than 10'.

The change from acid to alkaline solution involves a change of hydrogen ionconeentration from 1)(102 to 1 10'12 which will result in greatlv increasing the dis'- ,sociation et the ILMO, HPQOf" and similar ions.

ln view of the importance of the hydrogen ion concentration and the dissociation constents `of the lirst, second, etc.,l hydrogen ions of the acid corresponding to the salt used it is usuall advisable to employ salts of inorganic acids in preference to those ot organic acids as the dissociation of the acids formed in the presence of sulphuiic acid is much greater in the case of inorganic acids veo than of o nic acids. c v

Relative v little is known of tetraphos'- horic acidi: but the fact that it has been ound that over ten ti'ines the amount of sodium ltetraphosphate is needed to produce the same edect on dotation as a given amount of sodium pyrophosphate indicates that the salt and acid dissociate far less completelyV than do the pyrophosphates.

` insane@ K Ferrocyanic acid is a strong acid and its salts suc as tassiuin4 ferrocyanide 've very good resu ts in dotation where the ormation of insoluble ferrocyanides can be avoided. ln view, however, of the fact that pyropho'sphoric acid does not readily form injurious insoluble com unds its use is ordinaril to be preferr ar as trivalent salts are concerned, these would be superior to pyrophosphates only lif `they dissociated to an unheard of degree. Phosphates have been shown to be far inferior to pyrophosphates and probahi t the same is true of the arsenates.

e ferricyanides are in general open to the saine objection as the ferrocyanides,

namely the formation ot insolub e compounds" which poison flotation.

llt appears therefore that the pyrophosphates are the most suitable source of high valent anions for dotation. Sodium pyrophosphate, which appears to be the most generally useful yrophosphate Acan be very cheaply and casi y prepared from the conimon gies hate of soda of commerce (NazH U4? by simply heating it to drive oh' water.

Since in connection with some ores and slime material in particular it may be found advisable to use a salt adapted to give cations and anions, both of high valence, the availability of suitable high valent cations will he considered.

While in the case of polyvalent anions the dissociation constants of the corresponding acid appears to be one 'of the most important, factors2 in the case of polyvalent cation the mobility of the ions appears to be a very important factor. For instance, the aluminum ion has a greater mobility than the ferric ion, and it is found that alumimim salts are much more effective in dotation than are ferrie salts For instance when ferrie sulphate was used in conjunction with acid, the best results were obtained with a concentration of l-0.16% of the salt as compared with 0.000% of aluminum sullos nio"

phate. This diderenee between the mobility r of the aluminumy and the ferrie ions is in part if not entirely due to the smaller atomic weight of the aluminum ion, since according to the kinetic theory the velocity of movement of the ions in solution is in-Y versely proportional to the square 4root` of their masses, consequentl since the atomic weightlof aluminum is 2 and that of iron et slowing nasales has two waters of hydration, the potassium ion averages 9.6 Water of hydration, vvhile the lithium ion has 2t Waters of hydration. This attached Water has, ot course, the edect up the action ot the ions in solution, so that whereas the hydrogen ion With an atomic Weight ot lhas a mobility of 318, and the potassium ion with an atomic Weight of 39, a mobility of 65.3 the lithium ion with an atomic Weight of 7, has a mobility of yonly A334:. ther things being equal, therefore, ions having a high mobility should be selected in preference to those having a'low mobility.

Aluminum has an atomic weight smaller than any other tri-valent metal, and since with the exception of iron its salts are cheaper than those of other trivalent metals, its salts are particularly suitable for use in flotation.

There are a number of metals which under certain conditions are quadrivalent, the most common being titanium and tin.

Some of the rare earth metals also give uadrivalent cations, such as ermanlum, t orium, vanadium, uranium an zirconium. 0f all these metals the cheapest is titanium, since the oxide, rutile or ilmenite is found in considerable quantities. Titanium has also the smallest atomic Weight as its atomic weight is only t8 as compared with 118 for tin and 230 tor thorium. Titanium sulphate producin only a divalent anion was found to be in erior to aluminum pyrophosphate and when titanium pyrophosphate was prepared it was found to be largely colloidal 1n character, so that, although theoretically it should be superior to alumlnum pyrophosphate, the number ot positive and negative quadrivalent ions produced was apparently not suihcient to enable it to give superior result to aluminum pyrophosphate. The pyrophosphate of other quadrivalent metals might possibly be used to advantage it their cost is not prohibitive.

There are also a number of metals which form pentavalent salts thev principal of these being tungsten. This metal is also hexavalent under certain conditions. However, man of these salts do not appear to exist in e presenceV of water, at least to any appreciable extent. For instance tun?,- sten pentachloride on treatment with large quantities of water is at once'decomposed almost entirely into blue oxide W26), and 1hydrochloric acid with the evolution of ieat. Y

While l have referred to the employment of oil as a rothing agent, l may use a soluble organic trothingt agent such as amyl alcohol either alone or inl conjunction with oil.

Further, although oleic acid and similar fatt acids and resinous` acids might be use ll prefer not to employ such substances Celi.

as are capable of forming insoluble compounds vvith the aluminum or other similar salts used tor aiding dotation.

With certain ores the use et an organic u frothing agent may be wholly dispensed with and a troth formed by the aid ot inoranic material, more particularly salts of t e tylpe of sodium pyrophosphate.

Alt ough in the foregoing description of actual practice air only was employed in other ractice carried out by me other gases have rw employed and in particular air with additions of readily condensable gases. As a general rule, the readiness with which a gas will condense upon a surface de ends on the ease with which the gas can be iquetied. For instance, carbon dioxide condenses to a reater extent on a sulphide surface than oes air for the reason that the critical temperature ot carbon dioxide is +3l C. whereas that ot oxygen and nitrogen are, respectively, 118 C. and 146 C.

lin some cases l may therefore em loy air or other gases containing as la rothing agent a readily condensable vapor, such as the vapor of a hydrocarbon oil, gasolene for example, or a more volatile member et the same series. Further, in place of oil vapor, l may use the vapor ot a soluble organic compound such as amyl alcohol.

Such oil or vapor may be employed either in substitution tor or in addition to the use oil oil in the liquid state or the introduction ot a soluble organic frothing agent independently of the air or other gas required to operate the process.

E ectrolytes are preferably vadded to the ore pulp to aid the separation of the metalliterous constituents when such frothing vapor is used.

l claim:

1. The process of concentrating ores which includes mixing the comminuted ore `vvith oil in the resence ot an acid, then aerating the so-oi ed ore pulp to form a collective froth and separating the froth trom the remainder by dotation and which further includes the addition subsequent to the oiling treatment of material adapted to change the contact potential ot the oil to a potential more negative than before for aiding the formation of a collective froth.

2. The process of concentrating `ores which includes mixing the comminuted ore with oil in the presence of material adapted torchange the contact potential of the particles ot ore to a potential more positive than before, then aerating the so-oiled ore pulp to form a collective troth, and separating the froth trom the remainder by dotation and which further includes the addition subsequent to ciling treatment ot material adapted to change the. contact potential ot oil to a potentlal more negative than before lll@ lllti give hi her va .tial more negative than before and a for aiding in the formation of a collective froth.

3. The process of concentrating ores which includes mixin the comminuted ore with water and an oi y liquid, aerating the mixture to form a vfroth, and separating the froth from the remainder h dotation, and which further includes aciiyin the ore pulp prior to oiling and the ad ition subsequent to oiling of material adapted to reduce the hydrogen ion concentration and to give anions havlng a greater valence than two for aiding the formation of a froth.

4. The process of concentrating ores which includes mixin the comminuted ore with water and an on y liquid in the presence of acid to oil the metalliterous particles, then aeratin the mixture to form a froth and separating the froth from the remainder by dotation, and which further includes the addition intermediate the oiling and aeration treatments of sodium pyrophosghate.

5. he process of concentrating ores which includesl mixin the comminuted lore with water and an oily liquid, aerating the mixture to form a froth and separating the froth from the remainder b flotation and which further includes 'aci ifyin the ore pul prior tfroilingl and the a dition of alka-i lntermediate t e oilingand aeration treatments forl aiding in the formation of a froth.

6. The process of concentrating ores which includes mix'in the comminuted ore with water andan oily li uid in thepresence of acid to coat the meta liferous particles with oil, then adding an electrolyte adapted to ent anions lthan cations to aid in ty e dotation of the particles so oiled, -luently` aerating the mixture to form a trot and w :rating the froth from the remainder by dotation.

7. 'lhe process of concentrating comminuted masses of. comite-character which includes the treatmentof the mass with an ionizing liquid and a s, said liquid containing in solution wances adapted to change the contact potentialo the constituents of the composite mass to be separated m those ot diderent character to apotenapted simultaneously to produce a positive frictional electrical charge on the gas and which further includes the movement of the gas` relatively to the vliquidand the substantial elimination of the electric charge produced on the liquid by such movement.

8. The process of separating composite comminuted masses which includes va preliminary dotation treatmentby mechanical agitation, separation of the froth produced by such agitation and a secondary recleaning dotation treatment of such froth by fluid pure agitation, and which further inanaal includes the treatment of the mass with an` ionizing liquid and a as, said liquid containing in solution su tances adapted to 'produce an electrical charge on the gas of opposite sign to that on the constituents of the composite mass to bel separated from those of diilerent character, and which further includes the movement of the gas relatively to the li uid and the substantial elimination of the e ectric charge produced on the liquid by such movement.

10. The process of concentrating comminuted masses of composite character which includes the treatment of the mass with an ionizing liquid and' a gas, said liquid containi in solution negative ions having a valelilz greaterthan two, said gas having an electrical charge of opposite sign to that on the constituents of the composite mass to be separated from those of different character, and which further includes -the morement of the gas relativel to the liquid and the substantial elimination of the electric charge produced on the liquid by such movement.

11. The proce of concentrating comminuted masses of composite character which includes the treatment of the mass with an ionizing liquid and a gas, said li uid containing in solution negative ions aving a Ithe movement of certain of the comminuted particles relative to others having different qualities, and which further includes the use of a solution containing a salt of pyrophosphoric acid and a monovalent cation for inlncreasing the selective act-ion of the fluid.

13. The process of concentrating comminuted masses of composite character which compvrises mixing the mass with an ionizing li uid containing negative /ions having a v ence greater than three, and passing bubbl of gas upwardly through the mixture in the substantial absence of violent mechanical agitation whereby certain of the comminuted particles are separatedr from others et cludes the use in each agitation treatment of having dierent'qualities.

nannies Ll@ 14h Ilhe process of concentrating sulphide particles are separated trom the particles of ores which comprises mixing the cornmgan-gue, noted ore with oil and a solution containing 16. The process oi concentrating commianions having a valence greater than three nnterl naaes of composite character which 20 and passing bubbles ol air upwardl through eomprisis the formation of a non-permanent the mixture in the substantial a ence of yroth hy mixing the ma with an ionizin violent mechanical agitation whereby the liquidi2 and passing bubbles orv gas throng sulphide particles are separated `from the the mixture to torni a relatively non-permagangue. nent froth with certain or the comminuted 25 l5. 'lhe process of concentrating sulphitle particles having a fpreferential anity for ores which comprises mixing the commi such gas buhhles an separating the froth so nuted ore with oil and a solution containing formed from the remainder of the ore, and anions having a valence greater than three which further includes the use of anions and passing a gaseous tlui through the mirhaving a valence greater than three for inao ture in the substantial ahsence or violent creasing the said preferential anit mechanical agitation whereby the sulphide RlDSlDALlE E LlS.

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