Process for Beneficiating Non-Sulfide Minerals

This application deals with a process of use and is related to application Ser. No. 863,032 now U.S. Pat. No. 4,139,482 filed on even date herewith which deals with a collector combination for non-sulfide ores.

This invention relates to an improved process of mineral beneficiation by froth flotation. More particularly, this invention relates to such a process wherein a combination of a fatty acid and an N-sulfodicarboxylic acid asparate is used as the mineral collector.

Froth flotation is the principal means of concentrating phosphate, barite, and fluorite ores as well as a host of other ores. Its chief advantage is that it is a relatively efficient operation at a substantially lower cost than many other processes.

Flotation is a process for separating finely ground valuable minerals from their associated gangue, or waste, or for separating valuable components one from another. In froth flotation, froth occurs by introducing air into a pulp of finely divided ore and water containing a frothing agent. Minerals that have a special affinity for air bubbles rise to the surface in the froth and are separated from those wetted by the water. The particles to be separated by froth flotation must be of a size that can be readily levitated by the air bubbles.

Agents called collectors are used in conjunction with flotation to promote recovery of the desired material. The agents chosen must be capable of selectively coating the desired material in spite of the presence of many other mineral species. Current theory states that the flotation separation of one mineral species from another depends on the relatively wettability of surfaces. Typically, the surface free energy is purportedly lowered by the adsorption of heteropolar surface-active agents. The hydrophobic coating thus provided acts in this explanation as a bridge so that the particle may be attached to an air bubble. The practice of this invention, however, is not limited by this or other theories of flotation.

As a typical example of the beneficiation of non-sulfide ores, phosphate ore containing about 30% BPL (Bone Phosphate of Lime) Ca.sub.3 (PO.sub.4).sub.2 is concentrated in very large tonnages from the Florida pebble phosphate deposits. The ore slurry from strip mining is sized at about 1 millimeter and the coarser fraction, after scrubbing to break up mud balls, is a finished product. The minus 1 mm. fraction is further sized at 35 and 150 mesh. The minus 150 mesh slime is discarded. From the sizing operation the +35 mesh material in thick slurry is treated with fatty acid, fuel oil and caustic, ammonia or other alkali and the resulting agglomerates are separated on shaking tables, spirals, or spray belts. The 35.times.150 mesh fraction is conditioned with the same type of reagents and floated by conventional froth flotation route. Not all the silica gangue is rejected by the fatty acid flotation, so the concentrate is blunged with acid to remove collector coatings, deslimed, washed of reagents and subjected to an amine flotation with fuel oil at pH 7-8. This latter flotation, sometimes called "cleaning," removes additional silica and raises the final concentrate grade to 75-80% BPL.

Although the procedure described above is effective in the recovery of BPL from phosphate rock and similar processes employing fatty acids are effective in the recovery of other non-sulfide ores, there nevertheless exists the need for more effective collectors which will provide increased recovery of mineral values while still providing high grade recovery. In view of the high quantities of non-sulfide ores processed by froth flotation, such a development can result in a substantial increase in the total amount of desirable mineral values recovered and provide substantial economic advantages even when a modest increase in recovery is provided. Accordingly, the provision for an improved process for froth flotation of non-sulfide minerals would fulfill a long-felt need and constitute a notable advance in the art.

In accordance with the present invention, there is provided a process for beneficiating non-sulfide minerals which comprises classifying the mineral to provide particles of flotation size, slurrying the size mineral in aqueous medium, conditioning the slurry with an effective amount of alkali and a collector combination and floating the desired mineral values by froth flotation, said collector combination comprising from about 1 to about 99 weight percent of a fatty acid derived from a vegetable or animal oil and, correspondingly, from about 99 to about 1 weight percent of a compound of the general formula ##STR1## wherein X and X' are members of the group consisting of hydrogen and cationic salt-forming radicals, R is the residue of an aliphatic polycarboxylic acid, R' is a member of the group consisting of alkyl, alkoxyalkyl, and hydroxyalkyl radicals of from 8 to 20 carbon atoms and R" and R'" are members of the group consisting of hydrogen, alkyl and cationic salt-forming radicals.

Use of the specified combination collector provides unexpected improvements in recovery of valuable minerals at high grade (purity) levels under normal froth flotation conditions. The use of an N-sulfodicarboxylic acid aspartate in conjunction with the fatty acid reduces the total quantity of collector needed to provide a given level of recovery. Such use also greatly reduces the requirements for the fatty acids which represent scarce edible oil stocks and thus releases such fatty acids for nutritional purposes as well as other uses.

In carrying out the process of the present invention, a non-sulfide mineral is selected for treatment. Such minerals include phosphate rock, foskorite, apatite, fluorite, barite, taconite, magnetite, hematite and such other non-sulfide ores as are conventionally processed by froth flotation using a fatty acid collector. The selected mineral is sized to provide particles of flotation size according to conventional procedures. Generally, the flotation size will encompass from about 1 mm. to about 150 mesh size.

After the selected non-sulfide mineral has been sized as indicated, it is slurried in aqueous medium and conditioned with effective amounts of collector combination, fuel oil, if necessary, and alkali as required in accordance with conventional procedures. Generally, the slurry is conditioned at pasty consistency in the range of about 50 to 75% solids preferably about 65-70% solids, but such solids may vary widely depending upon the specific non-sulfide mineral being processed. Generally, the collector combination will be in the range of about 0.01 to 1.0 pounds per ton of mineral, although variations in amounts will arise depending upon the specific mineral being processed and the level of recovery desired. Fuel oil and alkali usage, when necessary, will be in accordance with conventional processing. Fuel oil is used to suppress froth formation and will vary as necessary depending upon the extent to which excessive frothing occurs.

Alkali usage will be within conventional limits and is that necessary to provide the pH value at which froth flotation is to be accomplished. The pH value of the slurry is generally on the alkaline side but specific values will vary depending upon the mineral processed and the combination of recovery and grade desired. Generally, the pH value will range from about 6.0 to 12.0, usually from about 8.0 to 10.0.

As the fatty acid present in the collector combination used in the process of the present invention is one that is conventionally used alone in beneficiation of non-sulfide minerals. Generally, such fatty acids are derived from a vegetable or animal oil. Vegetable oils include babassu, castor, Chinese tallow, coconut, cottonseed, grapeseed, hempseed, kapok, linseed, wild mustard, oiticica, olive, ouri-ouri, palm, palmkernel, peanut, perilla, poppyseed, Argentine rapeseed, rubberseed, safflower, sesame, soybean, sugarcane, sulflower, tall, teaseed, tung and ucuhuba oils. Animal oils include fish and livestock oils. These oils contain acids ranging from six to twenty-eight carbons or more and may be saturated or unsaturated hydroxylated or not, linear or cyclic and the like.

Useful N-sulfodicarboxylic acid aspartates present in the collector combination used in the process of the present invention are described in U.S. Pat. No. 2,438,092 issued Mar. 16, 1948 to K. L. Lynch. The useful compounds have the general structure: ##STR2## wherein X and X' are members of the group consisting of hydrogen and cationic salt-forming radicals, R is the residue of an aliphatic polycarboxylic acid, R' is a member of the group consisting of alkyl, alkoxyalkyl and hydroxyalkyl of from about 8 to 20 carbon atoms and R" and R'" are members of the group consisting of hydrogen, alkyl and cationic salt-forming radicals. Preferred compounds of this type are those in which R is the residue of succinic acid. A preferred species is tetrasodium N-(1,2-dicarboxyethyl)-N-octadecyl sulfosuccinamate, since this species is readily available commercially.

In the collector combination used in the process of the present invention, the weight percent of fatty acid may vary from about 1 to 99 and that of the N-sulfodicarboxylic acid aspartate, correspondingly, from about 99 to 1. A preferred composition is about 60 to 97 weight percent fatty acid and, correspondingly, about 40 to 3 weight percent of N-sulfodicarboxylic acid aspartate since such combination enables the total dosage of fatty acid to be reduced by about 80 compared to conventional requirements for fatty acid.

After the mineral has been suitably conditioned with the collector combination and optional additives, it is subjected to froth flotation in accordance with conventional procedures. The desired mineral values will float off with the froth leaving the gangue materials behind.

The invention is more fully illustrated in the examples which follow wherein all parts and percentages are by weight unless otherwise specified. Although the invention is illustrated with phosphate minerals as typical of the non-sulfide class, it is to be understood that similar benefits are obtained with other members of the class defined. The following general procedure is employed in the froth flotation examples given.

Step 1: Secure washed and sized, e.g., from 35 to 150 mesh screen fractions. Typical feed is usually a mixture of 23% coarse with 77% fine flotation particles.

Step 2: Sufficient wet sample, usually 640 grams, to give a dry weight equivalent of 500 grams is washed once with about an equal amount of tap water. The water is carefully decanted to avoid loss of solids.

Step 3: The moist sample is conditioned for one minute with approximately 100 cc. of water, sufficient caustic or other alkali as 5-10% aqueous solution to obtain the pH desired, a mixture of 50% acid and suitable fuel oil and additional fuel oil as necessary. Additional water may be necessary to give the mixture the consistency of "oatmeal" (about 69% solids). The amount of caustic will vary from 4 to about 20 drops. This is adjusted with a pH meter for the correct endpoint. At the end of the conditioning, additional caustic may be added to adjust the endpoint. However, an additional 15 seconds of conditioning is required if additional caustic is added to adjust the pH. Five to about 200 drops of acid-oil mixture and one-half this amount of additional oil is used depending upon the treatment level desired.

Step 4: Conditioned pulp is placed in an 800-gram bowl of a flotation machine and approximately 2.6 liters of water are added (enough water to bring the pulp level to lip of the container). The percent solids in the cell is then about 14%. The pulp is floated for 2 minutes with air introduced after 10 seconds of mixing.

Step 5: The excess water is carefully decanted from the rougher products. The tails are set aside for drying and analysis. The concentrate is placed back in the flotation machine with 10 cc. of 10% sulfuric acid and about 2.0 liters of water. The mixture is agitated 3 minutes in the absence of air feeding to remove the flotation oil. The contents of the cell are removed to a plastic pan, the excess water is decanted, and the rougher concentrate is washed twice using tap water with careful decantation of the excess water.

Step 6: Rougher concentrate is placed in the bowl of the flotation machine and sufficient water is added to bring the pulp level to approximately 0.5 inch below the lip. Amine, kerosene, and frother are introduced and the pulp is agitated until all sand froth disappears. Usually 3 drops of kerosene, 1 drop of frother and from 1 to 2 cc. of 2% amine solution are required for an acceptable float.

Step 7: The products are oven-dried, weighed, and analyzed for percent P.sub.2 O.sub.5 or BPL. The cleaner tails are combined with the rougher tails for assay. Steps 5 and 6 may be omitted if it is desired to obtain rougher concentrate recovery only. Additional analyses for CaO, MgO, Fe.sub.2 O.sub.3, and Al.sub.2 O.sub.3 are sometimes required but are not necessary to determine rougher concentrate recovery. Recovery of mineral values is calculated using the formula ##EQU1## wherein W.sub.c and W.sub.t are the only dry weights of the concentrate and tailings, respectively, and P.sub.c and P.sub.t are the weight percent P.sub.2 O.sub.5 of the concentrate and tailings respectively. Recovery values for rougher concentrate are calculated in the same way whether or not steps 5 and 6 are performed.

Using a phosphate ore obtained from Hooker's Prairie Mine, the General Procedure was followed using in one run a tall oil fatty acid alone as the conditioner and in a second run a combination of the same fatty acid and tetrasodium-N--1,2 dicarboxyethyl)-N-octadecylsulfosuccinamate was used. In each run recycled motor oil was used in conjunction with the conditioner and sufficient caustic to provide a pH of 9.0. Results and dosage levels of the ingredients are given in Table I which follows.

Using a phosphate ore obtained from the Brewster, Florida deposits, the General Procedure was again followed. In one run a tall oil fatty acid was used alone as conditioner and in another run a combination of the same fatty acid and tetrasodium N-(1,2-dicarboxyethyl)-N-octadecylsulfosuccinamate was used. In each run No. 5 Fuel Oil was used in conjunction with the conditioner and sufficient caustic to provide a pH of 9.0. Details and results are given in Table II which follows.

Again, the booster action of small amounts of an N-sulfodicarboxylic acid aspartate of the present invention is shown, a 20% increase in recovery.

The ore of Example 1 was again used. In one run the ore was treated using a tall oil fatty acid, recycled motor oil and ammonia to pH 9.0. In other runs, half of the standard quantity of fatty acid was eliminated and in its place was used a small quantity of an N-sulfodicarboxylic acid aspartate of the invention. Details and results are given in Table III which follows.

These results again show the booster action of N-sulfodicarboxylic acid aspartates when used in conjunction with fatty acids.

Following the procedure of Example 3, a series of flotations were run using a crude tall oil fatty acid alone and in combination with tetrasodium N-(1,2-dicarboxyethyl)-N-octadecyl sulfosuccinamate to show the synergistic results obtained with the combination. Details and results are shown in Table IV.

Following the procedure of Example 3, a number of additional N-sulfodicarboxylic acid aspartates are evaluated as boosters for fatty acid collectors. In each instance, a boostering effect is obtained. The compounds evaluated in each example number are listed below.

Example 5--Tetrasodium N-(1,2-dicarboxyethyl)-N-hexadecylsulfosuccinamate.

Example 6--Tetrasodium N-(1,2-dicarboxyethyl)-N-tetradecylsulfosuccinamate.

Example 7--Tetrasodium N-(1,2-dicarboxyethyl)-N-dodecylsulfosuccinamate.

Example 8--Tetrasodium N-(1,2-dicarboxyethyl)-N-decylsulfosuccinamate.

Example 9--Tetrasodium N-(1,2-dicarboxyethyl)-N-octylsulfosuccinamate.