US2389727A - Flotation of iron ores - Google Patents

Description

E. C. HERKENHOFF FLOTATION OF-IRON CRES Filed Dec. l0, 1942 ATTOR N EY Patented Nov. 27, 1945 FIDTATION F IRON GRES Earl Conrad Herkenhoil', Stamford, Conn., assignor to American Cyanamid Co N. Y., a corporation of Maine mpany, New York,

Application December 10, 1942, Serial No. 468.524

(cil 209-166) 6 Claims.

This invention relates to the beneiiciation of iron ores by froth flotation. More particularly, the invention relates to a multi-stage dotation lprocess suitable for use on :lines such as are found in the overflow from iron ore washer plants; in waste products from heavy media separation processes, and on those ores which mustl be nely ground 1n order to unlock the iron minerals from the gangue.

Increasing amount of the lower grade iron ores, such as those with which the present invention is concerned, are coming into industrial importance because of the constantly decreasing amounts of available high grade ore. Most of these ores are. too low in iron and too high in silica-bearing gangue to be suitable for use in blast furnaces. Consequently, if they are to be used they must be beneiiciated in some manner. Frequently, calciumcarb'onate and other alkaline earth carbonate minerals are also found in the ores. These, of themselves, are not particularly objectionable, in fact being to a certain extent desirable. In some cases, however, it may be necessary to remove a portion of theseconstituents in order to raise the iron content.

The principal problem, therefore, is one of reducing the impurities and raising the iron content to as high a degree as possible. As was pointed out, this usually involves the removal of silica. The necessary degree of beneciation can be accomplished in any one of several ways, depending on the ore. In some cases, the necessary rise in iron content may be made by merely crushing and washing the ore. Where the iron minerals and the gangue are associated in such manner that this can not be done, but the mineral values can be released with moderately ne crushing, heavy-media separation is particularly useful.

Much of the naturally occurring ore, however. requires line grinding in order to enable separation of the objectionable gangue. After the necessary grinding is done, beneiiciation by froth flotation is perhaps the most useful method of separating the gangue from the mineral values. In addition to the ores of this type, there are the wastes from the washing and the heavy-media processes mentioned above. Although too low in iron content for ordinary use, because of the tremendous volumes involved they represent a very large amount of potentially useful iron mineral.

As pointed out above, one of the principal objectionable constituents is usually a silica-bearing mineral of some type or other. From the point of view of susceptibility to froth notation, this is particularly unfortunate since the iron minerals and these silica-bearing gangues are generally diilcult to separate. Because of this separational difficulty, a flotation process to be successfully carried out requires careful handling, usually also accompanied by a high reagent consumption. All of these factors tend to increase the cost of processing. Yet iron ores, despite the fact that they must be handled in enormous quantities, are intrinsically cheap products and the margin of profit is small. Therefore beneficiation by froth flotation, if it is to be carried out, must be done cheaply, easily and eiiiciently. In this respect, ordinary methods of beneficiating ores by froth flotation when applied tu iron ores leave much to be desired.

Ordinarily, separation of mineral values from silica-bearing gangues by froth flotation takes one oi' two forms. Either the mineral is oated from the silica by the use of an anionic-type reagent or reagent combination, or the silica is oated from the mineral values by means of a cationic-type of reagent. In general, anionic flotation is the easiest and cheapest and is, thereg5 fore, used whenever possible. 'I'he usual procedures are old and well known in conjunction with many ores.

Unfortunately, when applied to ordinary iron ores of the type with which the present invention is concerned, anionic flotation does not work well. The iron minerals and the gangue tend to oat together. By using sufficient care and the necessary amount of reagents a beneficiation can be carried out whereby some 30 to 40% of the iron values can be recovered, but the grade is usually too low. The grade can be improved somewhat at the expense of the recovery, but the net cost is much higher than is practically desirable for the amount of mineral recovered at the corresponding concentrations.

In like cases with other ores, the reverse procedure is useful, i. e., silica is floated from the useful minerals with a cationic promoter. This process, when it can be properly used, is excellent. However, it suffers from several inherent drawbacks which must be capable of being overcome before the procedure can be said to be properly used. First of all, cationic reagents are expensive, the unit cost being several times that oi equal amounts of anionic-type reagents. They depend for competitive success on the fact that if they can be used eiectively, they are highly selective and have great collecting power and so can be used in smaller amounts.

However, they must be very eiiiciently used and this involves a second dii'liculty, that oi' slimes. Cationic reagents are particularly sensitive to the presence of slimes. even a fraction of a percent in the pulp often being suilicient to impair the efliciency of the reagent to a point where the -reagent cost becomes prohibitive. A balance must be made between the cost of preparing the ore such as the grinding, desliming, etc., the reagent cost, andthe amount of mineral recovered. Unfortunately, with most low grade iron ores this balance works out unfavorably. The cost of the preparation required plus the reagent cost raises the total above that which can be expended for the amount of ore recovered if the latter is to be sold in a competitive market.

In general, the recovery of iron from low grade materials tends to be lower than recoveries of non-ferrous metals from their ores. However, as previously stated, recovery is governed by economic factors which may outweigh metallurgical efllciency.

'Ihere remains, therefore, a demand for a suitable beneflciation process whereby the iron content of low grade ores, .particularly the wastes from washer plants and the like, can be carried out at a cost which will permit the process to be used on a large scale. It is the object of the present invention to establish a procedure of froth flotation by the use of which the desirable results of cheaper and more eiective concentration of the iron minerals may be obtained with these low grade starting materials.

In general, the desired object of the present invention is accomplished by a multi-stage flotation. Inv the iirst stage, a major portion of the iron minerals and a part of the silica gangue is floated away from the remainder of the ore by means of an anionic-type promoter. This concentrate is then subjected to a second anionic flotation in the presence of an iron depressant. The tailings from this step are nally subjected to a silica notation with a cationic reagent.

This procedure has a number of advantages. It uses the cheapest reagents on the biggest bulk of material whereby the latter is very appreciably reduced before the more expensive reagents need be employed. In this way the better features of both types of reagent are utilized to fullest advantage. A greater proportion of the iron'minerals can be recovered in a higher grade product than was practically possible with any previously used procedure. On the base of the recovered iron product, the total handling and reagent costs are less than that for any of the previously known and used beneciation methods. 'Ihe process, therefore, is not only highly eilicient as compared with older methods, but is also commercially desirable since it can be readily used on a large scale.

The process of the present invention will be more fully discussed in conjunction with the accompanying drawing in which:

Figure 1 represents a flow scheme of the simplest arrangement involving the essential features of the present invention; and

Figure 2 represents a similar flow scheme' showing alternative flows which may be desirable with certain ores to improve with the grade or the recovery.

The ore, as it is introduced into the process of the present invention, may as shown in Figure 2, be deslimed if necessary. The desliming step, however, as shown in Figure 1 is optional and the ore may ordinarily be passed directly to a conditioning operation in which the pulp is conditioned with the anionic-type promoter and a frother, if the latter is to be used. The conditioned pulp is then subjected to flotation, whereby a concentrate rich in iron but containing a part of the gangue, is obtained. The taiiing, although having a rather high iron assay, usually represents such a small percent of the total iron in the feed that it ordinarily may be discarded without further treatment.

The rougher concentrate may be cleaned, as shown in Figure 2 if so desired, the tailing from which may be either discarded or recycled to the original conditioning step. The rougher and cleaner concentrates are combined and then conditioned with hydrated lime, quicklime or some equivalent alkaline earth oxide or hydroxide. This treatment serves the several purposes of overcoming the effects of any residual fatty acid from the anionic flotation, providing a depressant for the iron minerals and acting in a manner which promotes the silica.

The conditioned pulp is then subjected to the primary silica flotation in which a concentrate high in silica and low in ironis obtained. This primary silica concentrate may be directly discarded or it may be subjected to a cleaning operation, the concentrate from which is discarded.

This cleaning of the primary silica concentrate is not essential to the operation of the process and may be omitted if the iron values in the rougher concentrate are not high enough to warrant carrying out this step.

The tailings from the primary silica flotation and/or the primary silica cleaner operation are passed to a classier, and are washed and deslimed. The slimes are ordinarily discardedbut if it is so desired they may be recycled to the conditioning step just prior to the primary silica flotation. The deslimed sands represent only a small proportion of the total volume of ore fed to the overall process but contain a large proportion of the total iron content.

These sands are then subjected to a secondary silica flotation in the presence of a cationic-type promoter. The tailing from this secondary silica flotation represents the iron concentrate and may be sold directly as ilnished iron product. The silica concentrate from this secondary silica flotation step maybe directlydiscarded or may be given an optional cleaning in which the concentrate is discarded and the tailing is recycled to join the fresh feed in the alkaline-earth metal oxide conditioning step.

It is an advantage of the present invention that despite its being a multi-stage flotation operation the process is in fact quite flexible so that it can be adjusted for different ores. This may be noted, for example, in the optional desliming and cleaning steps. In this regard, the cleaning is preferably done by notation, but it is also possible to use gravity methods of concentration such as tabling or vanning when such methods are advantageous.

Similarly the reagents used may be varied considerably without departing from the scope of the present invention. For example, in the anionic notation. substantially any anionic-type promoter may be used. Excellent results can be obtained using a fatty acid promoter such as oleic acid. However, the invention is not so limited and other promoters may be substituted therefor such as fish oil fatty acids, coconut oil fatty acid, linseed oil fatty acids, cottonseed oil fatty acids, talloel and the like, as well as their sodium, potassium and ammonium soaps and emulsions thereof. In most cases it ls desirable to use a. frother in conjunction with the amonio reagents. Any of the Well known frothers may be used. Among these are pine oil, synthetic pine oil, cresylic acids and certain aliphatic alcohol irothers. These may be used alone or in admixture with each other or with other froth modifying agents.

As was pointed out above, the concentrate from the anionic notation is conditioned with an alkaline earth oxide or hydroxide such as hydrated lime. This apparently serves a double purpose although its action is not thoroughly understood. It does, however, appear to eliminate the undesirable results which are ordinarily obtained in the presence of any excess promoter from the anionic flotation when the latter is followed by cationic notation. In addition, a. distinct depressing action on the iron minerals is observed.

It has been found well to use a small amount of frother in carrying out the primary silica flotation after thepulp has been conditioned with the alkaline earth hydroxide. Again, substantially any commercially available frother may be used. Ordinarily, however, only about one-half as much frother is necessary as in the preceding anlonic notation step and in many cases it may be eliminated entirely.

Similarly, the secondary silica flotation which is carried out in the presence of a cationic promoter is not necessarily limited to the use of any particular reagents. A choice as to the cationic promoter used may be made from among the amines or amine salts such as lauryl amine hydrochloride and the like; quaternary onium compounds such as cetyl trimethyl ammonium bromide many of which are commercially available for the purpose; or the polyalkylene-polyamine reaction products, many of which are also commercially available for the purpose. Again, a, small amount of frother such as pine oil or the like is desirable but not essential.

The invention will be described in greater detail in conjunction with the following specic examples which are illustrative only and not meant to limit the scope of the present invention.

A sample of overflow Waste principally composed of hematite and quartz from an iron ore washed plant, which presented beneiiciation problems typical of those which the present invention is concerned, was made into a pulp containing about 20% solids, conditioned with 0.162 lb. per ton of a pine oil ircther and 0.75 lb. per ton of oleic acid and subjected EXAMPLE 2 A sample of the same ore of Example 1 was then subjected to treatment according to the process of the present invention. The undeslimed feed was conditioned at 23% solids for about 5 minutes in a Fagergren flotation machine using 4 per ton of sodium silicate and 1.5 lbs. per

ton of saponied tallcel. Pine oil, 0.081 lb. per ton, was added and the pulp was floated for 3 minutes. the tailing being discarded. 'I'he concentrate was diluted to about 16% solids and conditioned for 4 minutes with 4 lbs. per ton of hydrated lime and then floated for 5 minutes with 0.054 lb. per ton of pine oil. The silica concentrate was given a 4 minute cleaner notation with an additional 0.054 lb. per ton of pine oil and the cleaned concentrate discarded. The primary sillca otation tail .and the silica cleaner tail were combined and deslimed by hydraulic classification. The overiiow containing the shimes was discarded and the underilow iioated for 4 minutes in the presence of 0.20 lb. per ton of 903-14, a cationic-type promoter marketed by the Emulsol Corporation, and 0.162 lb. per ton of pine oil. The silica concentrate was discarded and the tailing comprising the iron concentrate set aside as product. The results are shown in Table I.

Table l' Percent dis- Percent Percent tribution weight Fe Feed 100.00 Anionic tail 39. 74 Primary silica con 18. 77

1. Secondary silica conc.. 25. Iron conc 14.

EXAMPLE 3 The procedure of Example 1 was repeated on the same. ore with the exception that the ore was deslimed by hydraulic classification Kbefore being subjected to the original conditioning step. From a head assaying 23.84% iron, a concentrate assaying 27.95% iron and containing 37.70% of the total iron fed was obtained. The results although better than those of Example 1 are not even approximately the equivalent of those of Example 2.

EXAMPLE 4 The procedure of Example 2 was repeated on the same ore except that the ore was deslimed before the initial conditioning step and the ore was conditioned for only 2 minutes instead of 5. In the iinal silica flotation 0.10 1b. per ton of an aliphatic amine hydrochloride (approximately Cis) was substituted for the 0.20 lb. per ton of Cationic Reagent 903L. The results are shown in Table II.

Table II Percent distrlbution Percent Percent weight Iron conc EXAMPLE 5 A sample of ore containing hematite and quartz as the principal constituents and assaying 19.73% iron was deslimed by hydraulic classification using 1 lb. per ton of sodium silicate as a dispersant, the slimes being discarded. The sands were diluted to 21% solids and conditioned for 2 minutes with 0.75 lb. per ton of oleic acid and 0.162 lb. per ton of pine oil. The conditioned pulp was oated for 5 minutes and the rougher tail discarded. concentrate was conditioned for '7 minutes with 2 lbs. per ton of hydrated lime after which 0.054 lb. per ton of pine oil was added and the pulp floated for 3 minutes. The silica concentrate was cleaned in a 5 minute flotation using 0.162 lb. per ton of pine oil and the Table III Percent distrlbution Percent Percent weight #l slimes Anlonic tail-H2 slimes.- Primery silica conc Secondary silica conc Iron conc HHN New EXAMPLE 6 A sample of iron ore washer tailings taken from the overflow in a bowl classifier and principally composed of hematite and quartz was dispersed with l lb. per ton of sodium silicate and deslimed by hydraulic classification, the slimes being discarded. The sands were conditioned at 21% solids for 1 minute with 0.50 lb. per ton of saponifled talloel after which an additional 0.75 lb. per ton of saponified talloel and 0.135 lb. per ton of pine oil were added and the pulp floated for 6 minutes, the tailings being discarded. The concentrate was conditioned for 4 minutes at 19% solids with 4.0 lbs. per ton of hydrated lime after which .054 1b. per ton of pine oil was added and the pulp subjected to a 4 minute flotation. The silica concentrate was cleaned for 3 minutes with .0541b. per ton of pine oil and the silica cleaner concentrate discarded. The rougher and cleaner tails were combined, deslimed and the underflow floated for 7 minutes with 0.20 lb. per ton of "Lorol amine hydrochloride (approximately Ciz to C13) and 0.135 lb. per ton of pine oil. The silica concentrate was discarded and the tailings saved as the iron concentrate. Results are shown in Table IV.

Table IV Percent Percent Fe distribution Anionic teil-H2 slime@ Primarysilica conn Secondary silica mm` Iron armi'` 1L Exmu'l The procedure of Example 3 was repeated with several samples of the same ore used in Examples 5 and 6. Enough reagents were used to try to obtain the best possible recovery. Iron concentrates assaying from 33 to 47% iron and representing about 43% of the total iron fed were obtained. As will be seen from a comparison with Tables III and IV, these results do not compare favorably with the grades of products obtained by the practice of the present invention, despite the fact that more reagent was required to obtain the maximum recovery.

I claim:

1. A method of beneciating low grade iron ores containing silicious gangue by froth flotation which comprises the steps of making a pulp of the ore, subjecting the pulp to froth dotation in the presence of an anionic promoter selected from the group consisting of the higher fatty -acids, resin acids, talloel, and the sodium, potassium and ammonium soaps thereof, whereby a concentrate containing a major portion of the iron minerals and a part of the silica-bearing gangue is obtained, conditioning the concentrate with an alkaline-earth oxide in the absence of cationic-type promoters, subjecting the conditioned pulp to a primary silica notation in the absence of additional collecting agents, and subjecting the talling from the primary silica flotation to a secondary silica notation step in the presence of a cationic-type promoter.

2. A process according to claim 1 characterized in that the material used as feed is deslimed before the initial flotation operation.

3. A method according to claim 1 characterized in that the primary silicaA concentrate is subjected to a cleaner flotation, the cleaner tailings being combined with the tailings from the primary silicaflotation before being subjected to the cationic notation.

4. A process according to claim 1 characterized in that the initial flotation concentrate is cleaned, the cleaner concentrate being conditioned with an alkaline earth oxide before the primary silica flotation and the cleaner tailing being recycled to the feed.

5. A process according to claim 1 characterized in that the tailing from the primary silica notation is deslimed prior to the secondary flotation with a cationic reagent.

6. A process according to claim 1 characterized in that the concentrate of the secondary silica flotation is subjected to a cleaning operation, the concentrate from which is discarded and the tailing is recycled to the alkaline-earth oxide conditioning step.

EARL CONRAD I-IERKENHOFF.

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