Beneficiation of metallic ores by froth flotation using polyhydroxy amine depressants
The present invention relates to flotation of minerals from their ores, and more particularly to the recovery of such metallic minerals which are inbedded in a matrix of silica, silicates, carbonates, sulfates, phosphates, etc. 
     The object of this invention is to provide an improved froth flotation procedure in which, through the application of polyhydroxy amines unwanted silicious gangue material and the like acidic gangue minerals are depressed by deactivating the same to the used collectors, and thereby largely eliminating said unwanted guangue material from the concentrate of desired minerals, thus improving the grade of the concentrate to a marked degree. It is also an object of this invention to provide an improved flotation procedure in which, through the application of said polyhydroxy amines a selective separation can be made between two or more valuable minerals by the application different promoters and collectors persevering at the same time the silica, the silicates, the carbonates, the phosphates and the like gangue material dispersed and depressed. 
     Froth flotation is roughly based on the fact that the surface of a given mineral to be recovered can be rendered, by the action of so-called collectors, more or less water repellent, i.e., aerophil, and a mineral-air complex, the specific gravity of which is lower than that of the pulp of mineral slurry, is thus formed with the air bubbles introduced into the pulp of mineral slurry. The binding of the collector to the mineral surface by forces of chemiadsorption, physicaladsorption, etc., is due to electrostatic forces in both of the collector itself and the said surfaces. 
     It is the custom to speak about &#34;differential&#34; flotation, only in the case of polymetallic concentration, but most of the usual monometallic flotations are also differential ones, as the gangue has to be prevented from floating together with the wanted mineral. If the used collector has a tendency to be adsorbed by the gangue (which is particularly the case of paraffinic oils, fatty acids, fatty alcohols, sulfated and sulfonated alkyl compounds, as well as the single amines etc., chiefly used in the flotation of metallic oxide ores and non-metallic ores), the latter must be &#34;depressed&#34;. Roughly, depression consists in the action of preventing the binding of the collecting reagent to the surface of a certain mineral which is not wanted in the concentrate. In the case of monometallic flotation, the gangue minerals which are mostly quartz, silicates, and calcite, rarely sulfates and phosphates, must be depressed. In the case of polymetallic flotation, the gangue, together with other valuable metallic mineral, have to be kept from floating, or a single mineral has to be collected, while others are prevented from concentrating in the froth. 
     It is well known that alkyl amines used in froth flotation practice, many of them commercial products are silica and silicates collectors, because of which amine-flotation has developed as reverse froth flotation in which process the silica and the silicates are floated out as concentrates, while the desired metallic mineral is obtained in tailing, i.e., the procedure is a reverse concentration. Thus, the objective of the present invention is to introduce in the flotation circuit polyhydroxy amines, thus accomplishing a highly hydrophilic surface of silica, the silicates, carbonates, sulfates, phosphates, and the like acidic minerals in which a metal responsive to collector and flotation is bound to an acid radical, which hydrophilicity prevents silica, the silicates, the carbonates, the sulfates, the phosphates and the like minerals to float in the froth, and thus provoke a true froth flotation of desired metallic oxide mineral, leaving said minerals in tailing, which is quite different of the actual amine-flotation. 
     Although the usual gangue minerals when pure and fresh from the mine, are naturally more hydrophilic than the valuable metal-bearing ones, they are easily floated after activation with metallic cations. Thus quartz and most other silicates may be activated by very small amounts of iron, copper, zinc, lead, nickel, titanium, barium and some other cations when floated with fatty acid or fatty alcohol collectors at pH values varying with each activating cation. Since in almost every pulp of mineral slurry there are soluble metallic salts, the gangue is always more or less activated and tends to concentrate in the flotation froth. This is particularly true when anion active high molecular aliphatic acids and alcohols or their derivatives are used as collectors. In order to keep the gangue from floating, it is usual to add alkalies such as sodium carbonate, sodium hydroxide and the like, or sodium silicate, or acids. Alkalies form easily wettable hydroxides with the activating cations and increase the hydrophilic character of quartz and the silicates by their tendency to form soluble alkali-silicates. Sodium silicate forms insoluble metallic-silicates and hydrated metallic silica-gels with the activating cations. The acidification of the pulp of mineral slurry tends to replace the adsorbed metallic cations by more positive hydrogen ions which are hydrophilic, and increases the solubility of certain minerals. In addition to the effect of the alkalies, the use of alkali cyanide for the depression of the gangue is used frequently. Cyanide forms soluble complexes with some activating heavy metal cations removing them by means of this reaction from the gangue surface. The addition of cyanide to a pulp of mineral slurry of a number of metallic oxide ores may be highly deleterious because of formation of highly wettable ferri or ferro metal complex cyanides, thus highly diminuting the recovery. 
     It is therefore obvious, that in the flotation of ores chemical and physical control is directed firstly, toward increasing the floatability of the wanted minerals and, secondly, toward minimizing any flotation tendecy exhibited by the unwanted gangue minerals contained in the admixture. 
     The present invention has the second of these objectives in view and, for the accomplishment of the same, it proposes to add to the flotation pulp of mineral slurry relatively small amounts of certain polyhydroxy amines, which will be described presently, that react with the silicic acid of the silica and the silicates of the gangue minerals, thus preventing the flotation of unwanted gangue minerals of the oxide ore matrix. 
     Broadly, the invention embraces the addition to a flotation pulp of mineral slurry of amine compounds able to form very stable, water insoluble but hydrophilic compounds with silica, i.e., silicic acid, which being adsorbed on the gangue particles prevent or inhibit the same particles from exerting an activating, i.e., promoting effect, thus inhibited from concentrating in the flotation froth. 
     Generally speaking, therefore the flotation of non-sulfide ores, i.e., the metallic oxide ore has been performed with collectors which are mainly unsaturated fatty acids, unsaturated higher aliphatic alcohols, unsaturated hydrocarbons, or derivatives thereof. These collectors unlike for example, the xanthates used in the flotation of sulfides, are not very specific, they have marked tendency to float the ferromagnesian silicates, as well as a gamut of calcium, iron, aluminum, magnesium etc. compounds by forming insoluble soaps. As the aim of froth flotation is selective separation between the valuable mineral and the gangue, the latter has to be depressed. 
     As stated above, silica, the silicates, the carbonates, the sulfates, the phosphates will adsorb polyhydroxy amines of this invention rendering them harmless to the froth flotation of desired metallic mineral. More specifically the polyhydroxy amines will tie up the above said acid radicals bound to a certain metal in a certain mineral, eliminating thus all such minerals as active factors in the process, i.e., the gangue minerals; the quartz, the silicates, the carbonates, the sulfates, the phosphates will therefore exhibit no tendency to contaminate the concentrates. 
     In the field of selective flotation, the present invention makes feasible the specific depression of one or several silicate minerals by the addition of an adequate amount of polyhydroxy amines, of various strength and alkalinity, as desired and needed, for reacting with silicic acid bound in the silicate mineral so as to prevent flotation by rendering said silicate surface hydrophilic or water-avid. 
     This invention is based upon the principle that metallic minerals in which the metal is bound to an acid, the acid radical may be caused to form much more stable undissociable, water soluble or insoluble, but hydrophilic compounds with polyhydroxy amines of various basicity, which will be set forth hereinafter, which are added to the pulp of mineral slurry to depress the gangue minerals. 
     The polyhydroxy amine depressant, which are the specific subject of this invention have the following structural characteristics: 
     
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AMINOBUTANE-TRIOLS  HOCH.sub.2 (CHOH).sub.2 CH.sub.2 NH.sub.2             
such as                                                                   
      Amino-tert.-butylglycerol                                           
                        (HOCH.sub.2).sub.3 C--NH.sub.2                    
      Tris-(hydroxymethyl)-                                               
                        &#34;                                                 
      aminomethane                                                        
AMINOPARTITOLS      AMINO-TETROLS                                         
such as                                                                   
      Xylamine          HOCH.sub.2 (CHOH).sub.3 CH.sub.2 NH.sub.2         
AMINOHEXITOLS       AMINO-PENTITOLS                                       
such as                                                                   
      Glucamine         HOCH.sub.2 (CHOH).sub.4 CH.sub.2 NH.sub.2         
      Mannamine         &#34;                                                 
      Dulcitamine       &#34;                                                 
      Fructamine        &#34;                                                 
AMINOHEPTITOLS      AMINO-HEXITOLS                                        
such as                                                                   
      Perseitolamine    HOCH.sub.2 (CHOH).sub.5 CH.sub.2 NH.sub.2         
      Mannoheptitolamine                                                  
                        &#34;                                                 
      Glucoheptitolamine                                                  
                        &#34;                                                 
AMINOOCTITOLS       AMINO-HEPTITOLS                                       
such as                                                                   
      Glucooctitolamine HOCH.sub.2 (CHOH).sub.6 CH.sub.2 NH.sub.2         
      Mannooctitolamine &#34;                                                 
PENTOSE-AMINES                                                            
such as                                                                   
      Arabinosamine     HOCH.sub.2 (CHOH).sub.2 CH-                       
                        (NH.sub.2)CHO                                     
      Xylosamine        HOCH.sub.2 (CHOH).sub.2 CH-                       
                        (NH.sub.2)CHO                                     
HEXOSE-AMINES                                                             
such as                                                                   
      Glucosamine, Chitosamine                                            
                        HOCH.sub.2 (CHOH).sub.3 CH-                       
                        (NH.sub.2)CHO                                     
      Fructosamine      HOCH.sub.2 (CHOH).sub.2 CH-                       
                        (NH.sub.2)CHO                                     
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     The Examples of investigating the polyhydroxy amines are accomplished with fatty acids such as Acyntol, i.e., tall oil from Arizona Chemical Co., Oleic, Linoleic, and Linolenic acids from Emery Chemical Co., because earth alkaline silicates are responsive to fatty acids. Various natural ores and compositions of minerals, as well as pure silica sand are examined by said polyhydroxy amines in conjunction with said fatty acids. The commercial amines such as ARMEN, DUOMEN, ARMAC, DUOMAC, from the ARMAK Company, which are applied as froth flotation reagents in reverse flotation to float silica and the silicates of various ores are investigated parallel, but here reported only for pure silica sand, pure serpentine, pure calcite, pure barytes, pure apatite, in the amount of 400 g of each as increment in the froth flotation process. 
     Natural chromite in serpentine has given excellent chromite concentrate in which only very very few grains of transparent yellowish and greenish serpentine were observed under the microscope. 
     
                       Table 1                                                     
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                          Recovery by                                     
Example    Collector used weight percent                                  
ore treated                                                               
           gr per ton of ore                                              
                          concentrate                                     
                                    tailing                               
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1.  Silica sand                                                           
               Duomeen  0.05 kg/t                                         
                                95.0    5.0                               
2.  Silica sand                                                           
               Duomac   0.05 kg/t                                         
                                96.0    4.0                               
3.  Serpentine Armeen   0.05 kg/t                                         
                                92.0    8.0                               
4.  Serpentine Armac    0.05 kg/t                                         
                                94.0    6.0                               
5.  Calcite    Duomeen  0.05 kg/t                                         
                                92.0    8.0                               
6.  Barytes    Duomac   0.05 kg/t                                         
                                90.0    10.0                              
7.  Apatite    Armeen   0.05 kg/t                                         
                                90.0    10.0                              
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                       Table 2                                                     
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       Col-                Recovery weight %                              
Example  lector         Depressor                                         
                                 con-                                     
ore treated                                                               
         kg/t    kg/t   kg/t     centrate                                 
                                        tailing                           
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10. Ser-     Tall         Glucosamine                                     
                                   Ser-   Ser-                            
    pentine  oil                   pentine                                
                                          pentine                         
             1 kg/t       0.05 kg/t                                       
                                   2.0    98.0                            
11. Calcite  Oleic        Arabinamine                                     
                                   Calcite                                
                                          Calcite                         
             acid                                                         
             1 kg/t       0.05 kg/t                                       
                                   4.0    96.0                            
12. Calcite  Oleic        Fructamine                                      
                                   Calcite                                
                                          Calcite                         
             acid                                                         
             1 kg/t       0.05 kg/t                                       
                                   5.0    95.0                            
13. Barytes  Linolic      Fructosamine                                    
                                   Barytes                                
                                          Barytes                         
             acid                                                         
             1 kg/t       0.05 kg/t                                       
                                   3.5    96.5                            
14. Apatite  Tall         Glucamine                                       
                                   Apatite                                
                                          Apatite                         
             oil                                                          
             1 kg/t       0.05 kg/t                                       
                                   4.0    96.0                            
15. Silica   --           Glucosamine                                     
                                   Silica Silica                          
    sand                  0.05 kg/t                                       
                                   2.0    98.0                            
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     Table 1, shows that commercial amines are excellent collector-frothers for silica and the silicates, and the investigated acid minerals in which the metal is bound to an acid radical. The recoveries are estimated by weighing the products, being of pure material. The high percentage of tailings relates to a coarse material, which needs further grinding and sizing. All investigated commercial amines yield high recoveries not only because of high responsiveness of investigated minerals but also because of excellent carrying froth developed by said amines. In the tailing there was visible only the coarse material. 
     Table 2, shows that fatty acid collectors are ineffective collectors the gangues in the presence of polyhydroxy amines of this invention which act as depressants for serpentine, calcite, forytes, apatite silica sand. The floated serpentine is a slimy in froth occluded material only. In the case of calcite, barytes and apatite, fatty acids occlude only slimy material which is thoroughly oiled and therefore sticky. In the case of silica sand the depressing and inactivating of the silica sand was genuine. A true froth was not observed nor collected. 
     The comparison of the results shows that the ratio of depressed gangue is considerably lowered in float products by conditioning the pulp of mineral slurry with a polyhydroxy amine of this invention. Therefore, the use, according to the present invention, of polyhydroxy amines for accomplishing the purpose of gangue depression through the application of the same in froth flotation of various minerals of a variety of ores constitutes a marked advance in the art of froth flotation, and is highly advantageous in improving the selectivity of the used collectors, thus improving the grade of concentrate.