US2288237A - Process for concentrating phosphate ores - Google Patents

Description

-Patenteii June 30, 1942 PROCESS FOR CONCENTRATING PHOSPHATE ORES Ernest W. Greene, Plant City, Fla., assignor, by mesne assignments, to Phosphate Recovery Corporation, Chicago, 111., a corporation of Delaware No Drawing. Application December 1, 1939, Serial No. 307,059

.4 Claims.

This invention relates generally to a process of concentrating ore by selective flotation of the constituents thereof, and more particularly concerns itself with the preconditioning of ore pulps to make the same more, susceptible to selective flotation reagents. While the process herewith disclosed is broadly applicable to flotation separation of many kinds of ores, both metallic and non-metallic, this invention is particularly adaptable to-the concentration of fine Florida phosphate ore. The major constituents of this type of ore. consist largely of silica gangue and bone phosphate of lime.

The art of concentrating fine phosphate ore is restricted in practice to the type of separation in which the phosphate particles are selectively oiled with a soap and an inert oil, or with a caustic alkali, a fatty acid and an oil, such as fuel oil. These chemical reagents render the phosphate constituent surfaces non-wettable and thus amenable to a flotation separation from the silica or gangue.

The patent art contains a number of descriptions of a reverse type of separation in which the ore is treated with reagents adapted to selectively coat the silica gangue constituent and render it non-wettable and thus amenable to a flotation separation from the phosphate constituent. This method of concentration has not been used in practice because the reagent requirements have been either too large or too expensive for a low priced material such as phosphate.

My co-pending application Serial No. 291,683, filed August 24, 1939, relates to a dual process which discloses the preliminary flotation of only the finer part of the silica constituent of this type of ore followed by the flotation of the phosphate from the remaining coarser silica. This process is very effective in producing maximum grades and recoveries through the medium of first removing the flne silica gangue which reduces concentrate grades when the usual concentration methods are employed. Although only a part of the silica is floated in this process, in the preliminary step of the same, and the silica reagent consumption is consequently greatly reduced below that required for a complete separation, still the commercial utilization of the process of this disclosure is questionable due to the present high cost of the silica flotation reagents.

Pre-conditioning the ore'pulp according to the teaching of the present invention increases the efficiency of either the silica selective reagents or the phosphate selective reagents. Thus, the

amount of material floated by the same amount of reagent may be increased from two to as high as ten times. My results have shown that the effect produced on silica flotation is more pronounced than it is on phosphate flotation. This brings the silica flotation processes into the realm of practical commercial possibilities, and removes the diificulties encountered in my dual process hereinbefore mentioned.

As a consequence of the practice of thejherewith disclosed invention, it has been discovered that phosphate ores which have been pre-conditioned with small amounts of flotation reagents adapted to selectively coat the phosphate constituent, but restricted in amount and under such conditions that the phosphate surfaces are not sufiiciently oiled or coated to float to any appreciable extent, and if the conditioned ore is then washed or the water carrying the excess reagent is decanted, such ores are rendered much more susceptible to reagents adapted to selectively coat and float the opposite or silica gangue constituent. Conversely, it has also been discovered that phosphate ores which have been pre-conditioned with a small amount of selective silica flotation reagents, and then washed, are rendered more susceptible to phosphate reagents. This is an unusual result, as one would not expect to pre-condition an ore pulp with flotation reagents which are selective toward the constituent in the pulp which it is desired to wet or retain in a non-floatable condition.

The reason for the striking results of this process of conditioning an ore pulp follow logically from a consideration of the physical and. chemical forces involved at the mineral surfaces when the wetted phosphate mineral is treated for example with selective silica flotation reagents. The molecules of these reagents will be physically adsorbed at all surfaces present in the ore pulp, whether phosphate or gangue. Those molecules which are adsorbed on the silica gangue surfaces toward which the reagent is selective will then attach themselves chemically to those surfaces in such a particular oriented way as to render the surface non-Wettable and the gangue floatab-le. On the other hand, these molecules which are adsorbed on other surfaces, such as phosphate, will remain in a physically adsorbed state and will not be oriented to render the surfaces non-wettable. All reagent adsorbed on phosphate surfaces in this physical manner will be lost for the purpose of floating the gangue, and will constitute a Waste of reagent. In accordance with the teaching of the present invention, if the ore pulp is first treated with a small amount of reagent which is selective toward the phosphate constituent, its molecules will become attached in part to these phosphate surfaces in an oriented chemical manner. If reagents selective toward the silica gangue constituent are then added to the pulp, their molecules will not be physically adsorbed on the conditioned phos phate surfaces, at least to anywhere near the amount which would be adsorbed on conditioned ore. As a result, much more of the selective silica reagent is available for attachment to the silica surfaces, and consequently more mineral is floated with a given amount of reagent.

In the practice of the present invention, it is necessary to keep the amount of the conditioning reagent below that required to float any appreciable quantity of the phosphate constituent of the ore. However, it has been found that the closer the amount of the conditioning reagent approaches that required to just float some phosphate the more effective it is in reducing the requirement on the actual needed amount of the silica flotation reagent to be employed.

Throughout this application the wording: phosphate reagents; phosphate flotation reagents; selective phosphate reagents"; phosphate selective reagents"; refer to either single reagents or combinations of reagents adapted by proportions and pulp conditions such as acidity or alkalinity to selectively condition the phosphate surfaces to render them non-wettable by water, if used in suflicient quantity, but restricted in amount to prevent any appreciable proportion of these phosphate surfaces becoming water repellent to an extent that would cause flotation. Among such reagents may be mentioned soaps, various combinations of alkali and fatty acids, and other reagents which are used under such conditions that they have a specific collecting action on phosphate surfaces. The important thing is that the reagent or reagents be used under conditions which will cause them to act as phosphate collectors but in insuflicient amount to actually collect. The frothing properties of collectors and the fortifying properties of inert oils such as fuel oil are unnecessary although not detrimental.

This invention is not concerned with the types of reagents used to effect the flotation of silica gangue after the pulp has been conditioned in the manner described. The conditioning processes of the invention will reduce the amount of reagent required to float any desired amount of silica from a phosphate ore. Experimentally, work has been done with silica reagents of the class of organic ammonium compounds such as the high molecular Weight alkyl amines and their salts.

When pre-conditioning a phosphate ore in preparation for the reverse type of flotation, that is phosphate flotation, the above described organlc ammonium compounds have been found to be effective as conditioning reagents. In this type of conditioning treatment, it is preferred to treat a dilute pulp with these reagents in a manner in which they tend to selectively coat the silica surfaces with a water repellent coating, but in such amounts that these surfaces are not sufflciently water repellent to float. After de-watering a phosphate pulp which has been conditioned in this manner and treating with phosphate flotation reagents, the phosphate will float with a minimum of the usual phosphate reagents.

Conditioning the phosphate surfaces according to the manner of my invention is much more effective than conditioning the silica gangue surfaces, because the phosphate surfaces are of such a nature that they are more adsorbent physically to surface active compounds than are the harder and smoother silica surfaces. conditioning method applied to the phosphate constituent will reduce the required amount of silica flotation reagents to a greater extent than the reverse type of conditioning will reduce the phosphate reagent requirement.

The conditioning reagents can be mixed into the ore pulp in any convenient manner with the pulp either comparatively dense or well diluted with water. As a rule, I- have found it best to mix the phosphate conditioning reagents into dense pulps, while the silica reagents have been dissolved of dispersed in water with which the pulp is then diluted. When the conditioning reagents are mixed into dense pulps it is necessary to subsequently wash the pulp with water before the flotation reagents are added to it in order to obtain the best results. This washing operation can be carried out with or without agitation, and

may be simply a dilution followed by a de-watering. In case the conditioning reagents are added to a well diluted pulp, it is only necessary to dewatcr the conditioned pulp.

The following examples serve to illustrate the beneficial results of my present method for preconditioning phosphate ores for either phosphate or silica flotation processes as compared to ores which have not been so conditioned.

Example 1 A sample of de-slimed phosphate heads representing the debris from a washing and screening operation which had passed an .028 inch woven wire screen was transferred to a laboratory flotation cell containing water, which carried in solution the equivalent of 0.3 pound of laurylamine hydrochloride per ton of heads. Agitation and aeration produced no appreciable amount of silica float. The cell was discharged and the water decanted. The dense pulp was then treated with 21.8% of the weight of the original heads. Treatation, and floating the same in the manner described produced a phosphate concentrate which weighed only 13.1% of the original heads.

Example 2 A similar sample of de-slimed phosphate heads was mixed as a dense pulp with 0.19 pound of caustic soda and 0.30 pound of a fatty acid, expressed as pounds per ton of heads. The pulp was then diluted in the flotation cell and agitated and aerated for one minute. Practically no phosphate float appeared, although a few particles of phosphate could be seen on the surface of the water before diluting. The cell' was then discharged and the water was largely decanted off. The pulp was then returned to the flotation cell containing water which carried the equiva-' lent of 0.3 pound of laurylamine hydrochloride per ton of heads. On completing dilution and agitating and aerating, a copious silica bearing Consequently, the

froth was produced. The silica concentrates were collected and dried, and were found to weigh 50.9% of the weight of the original heads. subjecting another portion of the same original heads to an identical flotation operation with the same amount of laurylamine hydrochloride, and

Example 3 Another portion of the same sample of heads which was used in Example 2 was mixed as a dense pulp with 0.10 pound of caustic soda, 0.30 pound of a fatty acid, and 0.19 pound of fuel oil, all per ton of original heads. The pulp was then diluted in the flotation cell and agitated and aerated for one minute; The cell was then discharged and the water was largely decanted off. The pulp was then returned to the flotation cell containing water which carried the equivalent of 0.3 pound of laurylamine hydrochloride per ton of heads. On completing dilution and agitating and aerating, a copious silica bearing froth was produced. The floated silica amounted to 27.1% of the weight of the original heads. This represented five times the amount of silica floated from the same pulp with the same amount of laurylamine hydrochloride. Example 4 A similar sample of heads was mixed as a dense pulp with 0.19 pound of caustic soda and 0.30 pound of a fatty acid per-ton of heads. The pulp was then diluted in the flotation cell and agitated for one minute. The cell was then discharged and the water was largely decanted off. The pulp was then returned to the flotation cell containing water which carried 0.2 pound of a high molecular weight alkvl amine and 0.125

pound of pine oil per ton of heads. Agitation and aeration produced a copious silica bearin froth. The floated silica amounted to 55.0% of the weight of the original heads. subjecting another portion of the-same original heads to an identical flotation operation with the same amount of the high molecular weight alkyl amine and pine oil, and without the conditioning treatment, produced a silica concentrate weighing only 12.5% of the original heads.

While I have described what I considerto be a practical and desirable manner of carrying out my invention, it is obvious that many changes in the method of practicing my invention could be made without departing from the spirit thereof, and I, therefore, do not limit myself to anything less than the whole of my invention as herelnbefore set forth, and as hereinafter claimed.

I claim as my invention:

1. In a process for concentrating phosphate tion of the silica constituent, the steps which comprise desliming the ore, pre-treating the deslimed ore with a phosphate collecting reagent comprising a fatty acid and an alkali so proportioned with the ore as to leave the phosphate in substantially non-floatable condition, decanting the water from the thusly pre-treated ore, then conditioning the pre-treated ore in an aqueous pulp with a silica-collecting reagent comprising a high molecular weight alkyl amine so proportioned with the ore as to make the silica constituent floatable, subjecting the thus conditioned ore to a froth-flotation operation and removing the froth, and collecting the non-floated phosphate constituent of the ore as a concentrate.

2. In a process for concentrating phosphate ore in which silica is contained, by selective flotation of the silica constituent, the steps which comprise desliming the ore, pre-treating the deslimed ore with a phosphate collecting reagent comprising a fatty acid and an alkali so proportioned with the ore as to. leave the phosphate in substantially non-floatable condition, decanting the water from the thusly pre-treated ore, then conditioning the pre-treated ore in an aqueous pulp with a silica-collecting reagent comprising lauryl-' amine hydrochloride so proportioned with the ore as to make the silica constituent floatable, subjecting the thus conditioned ore to a frothflotation operation and removing the froth, and collecting the non-floated phosphate constituent of the ore as a concentrate.

ore in which silica is contained, by selective flota- 65 3. In a process for concentrating phosphate ore in which silica is contained, by selective flotation of the phosphate constituent, the steps which comprise desliming the ore, pre-treating the deslimed ore with a silica collecting reagent comprising laurylamine hydrochloride so proportioned with the ore as to leave the silica in substantially non-floatable condition, decanting the water from the thusly pre-treated ore, then con-' ditioning the pre-treated ore'in anaqueous pulp with a phosphate-collecting reagent comprising a fatty acid and an alkali so proportioned with the ore as to make the phosphate constituent floatable, subjecting the thus conditioned ore to a froth-flotation operation and removing the froth as a concentrate.

4. In a process for concentratingv phosphate ore in which silica is contained, by selective flotation of the phosphate constituent, the steps which comprise desliming the ore, pre-treating the deslimed ore with a silica collecting reagent comprising a high molecular weight alkyl amine so proportioned with the ore as to leave the silica in substantially non-floatable condition, decanting the water from the thusly pre-treated ore, then conditioning the pre-treated ore in an aqueous pulp with a phosphate-collecting reagent comprising a fatty acid and an alkali so proportioned with the ore as to make the phosphate constituent floatable, subjecting the thus conditioned ore to a froth-flotation operation and removing the froth as a'concentrate.

ERNEST W. GREENE.