Process for treating cassiterite ore
The present invention relates to the enrichment of cassiterite ores by flotation by eliminating part of the gangue by means of an amphoteric collector. 
     Treatments of ores by flotation are known. 
     They are used for ensuring a concentration of the interesting ores by partial or total separation of the elements constituting the gangue. 
     In a treatment of enrichment by flotation, the ore may be previously de-slimed (elimination of the fine particles, particularly the clays, by granulometric cut), then, if necessary, the large elements are ground in order to release the different mineral phases. Attrition may be added to this preparation in order to improve the cleanness of the mineral surfaces. To the mineral pulp thus formed is added a reagent, or collector, which clings to the surface of the particles either of the interesting species or of the undesirable species or gangue, rendering the surface hydrophobic. By insufflating air, the air bubbles cling to the hydrophobic surfaces and carry the particles over in the form of foam or froth representing the floated part. The species which has not retained any collector is not carried over in the froth. 
     The stability of the froth is generally ensured by adding to the mineral pulp so-called foaming reagents. When the form formed is excessive in volume or too stable, it is sometimes envisaged to employ froth regulating agents. 
     In order to avoid (or to activate) fixation of a collector on one of the mineral phases, other so-called depressing (or activating) reagents are sometimes added to the pulp, prior to the addition of the collector, which reagents cling selectively to the surface of the particles of one of the mineral phases. 
     Froth flotation therefore generally comprises the series of the following operations: 
     possible de-sliming 
     grinding and/or attrition 
     conditioning of the pulp with a depressing and/or activating agent 
     conditioning of the pulp with a collector 
     conditioning of the pulp with a foaming agent and/or a froth regulating agent 
     insufflation of air. 
     Cassiterite is an oxide of tin which exists in ores in the state of deposit formations where the mineral is either already released or finely scattered in a gangue. 
     In the first case, separation of the cassiterite is obtained by gravimetrical concentration treatments. In the second case, the ore is firstly ground so as to release the cassiterite. The large fractions are generally subjected to a gravimetrical concentration, whilst the cassiterite present in the fine-grained ores may be recovered by direct flotation. However, in the event of the ore containing sulfides, the latter are previously removed, likewise by direct flotation of the sulfides. 
     For direct flotation of the fine-grained fractions of the ore, carboxylic, phosphonic and arsenic acids have been recommended as collectors of the cassiterite, the latter acids presenting risks of toxicity which are an obstacle to their use. At present, the use of sulfosuccinamates is therefore preferred, as they ensure safer operation. Their use as collectors of cassiterite is described in particular in U.S. Pat. No. 3,469,693. 
     Minerals such as silicates and silico-aluminates (muscovite, chlorites, tourmaline, topaz, . . . ), fluorite, iron oxides and carbonates, particularly siderite, generally constitute a large part of the gangue of the cassiterite ores. The presence of these impurities considerably hinders flotation of the cassiterite by reducing both the selectivity and yield of tin. The lack of selectively obtained brings about the necessity of subjecting the concentrate of cassiterite to an additional treatment consisting either of a high-intensity magnetic separation or an acid lixiviation. 
     It has been found, and this represents the invention, that a substantial elimination of the undesirable impurities could be advantageously obtained by a preliminary flotation treatment using amphoteric collectors comprising at least one basic nitrogen and at least one acid group at the same time. 
     The collectors which may be used according to the invention are the products of formula: ##STR3## in which: 
     R may be R 1 , --R 1  --O-- or ##STR4## where R 1  is a linear or branched, saturated or non-saturated alkyl radical, having 5 to 19 carbon atoms, or an alkylaryl radical, or a poly(oxyalkyl) radical; R 2  being H or CH 3 , with the additional condition that R is a chain of lipophilic character, 
     R&#39; may be H or CH 3  -- or poly(oxyalkyl) or R&#39; is R--(CH 2 ) 3  -- or R&#39; is A q  --Z, 
     R&#34; is H or A q  --Z; in the case of n&gt;1 there may be both substituents H and substituents A q  --Z, 
     Ap and A q  are polymethylene chains containing respectively p and q carbon atoms, p and q being integers from 1 to 4, 
     n is 0 or an integer from 1 to 5, 
     Z is a radical selected from the carboxylic, sulfonic or phosphonic groups. 
     According to the invention, use may particularly be made of the corresponding alkylaminopropionic, alkylaminopropylaminopropionic and alkoxypropylaminopropionic acids of formula: 
     
         R--(NH--CH.sub.2 --CH.sub.2 --CH.sub.2).sub.n --NH--CH.sub.2 --CH.sub.2 --COOH 
    
     where R is CH 3  --(CH 2 ) m-1  or CH 3  (CH 2 ) m-1  O--CH 2  CH 2  CH 2  -- with m: 12 to 22, n=0, 1, 2 or 3 
     &#34;Preliminary flotation&#34; is understood to mean a flotation operation leading to the elimination of part (for example from 3 to 10% by weight) of the treated ore which is carried out on a product having undergone the preliminary operations (de-sliming, grinding) and which, in the conventional process, would be subjected to flotation. 
    
    
     The invention will be more readily understood from the following examples. 
     In these tests, normal flotation was effected according to the conventional technique in two cells; the float of the first is retreated in the second, yielding the final float and a non-float to be recirculated in the first cell where the non-float constitutes the final tailings. 
     Preliminary flotation was carried out in one cell, the float which contains the undesirable elements being eliminated and the non-float being taken up for supplying the normal flotation. 
     EXAMPLE 1 
     Treatment of a cassiterite ore containing, after elimination of the sulfides by flotation: 
     silicates 
     silico-aluminates (muscovite, chlorites, tourmaline) 
     carbonates (calcite, siderite) 
     fluorite 
     quartz 
     Conditions of flotation (nature and consumption of the reagents, expressed in grams per ton of ore supplying the flotation process): 
     
         __________________________________________________________________________
                        Preliminary flotation (according                  
                        to the invention)                                 
                        pH = natural pH 5.7                               
                        N--alkylaminopropionic acid                       
                        (alkyl being with copra chain) =                  
                        150 g/t                                           
                        conditioning: 3 mins                              
                        M.I.B.C. (methylisobutylcarbinol                  
                        20 g/t)                                           
Normal flotation        Normal flotation                                  
Sulfuric acid: 5 kg/t   Sulfuric acid: 2.7 kg/t                           
pH = 2.4                pH = 2.4                                          
Na.sub.2 SiF.sub.6 = 100 g/t                                              
                        Na.sub.2 SiF.sub.6 = 100 g/t                      
                  depressant              depressant                      
Na.sub.2 SiO.sub.3 = 200 g/t                                              
                        Na.sub.2 SiO.sub.3 = 200 g/t                      
Conditioning: 2 mins.   Conditioning: 2 mins                              
Tetrasodium sulfosuccinamate =                                            
                        Tetrasodium sulfosuccinamate =                    
300 g/t                 300 g/t                                           
Conditioning: 3 mins.   Conditioning: 3 mins                              
M.I.B.C. = 40 g/t       M.I.B.C. =  45 g/t                                
__________________________________________________________________________
 
    
     Results: 
     
         __________________________________________________________________________
           Without preliminary                                            
                       With preliminary flotation                         
           flotation   object of the invention                            
           Yield       Yield                                              
           in      Yield                                                  
                       in       Yield                                     
           weight                                                         
               %   in  weight                                             
                            %   in                                        
           %   tin tin %    tin tin                                       
__________________________________________________________________________
Supply preliminary                                                        
           --  --  --  100.0                                              
                            1.87                                          
                                100.0                                     
flotation                                                                 
Float      --  --  --  3.6  0.79                                          
                                1.5                                       
Supply cassiterite                                                        
           100.0                                                          
               1.87                                                       
                   100.0                                                  
                       96.4 1.91                                          
                                98.5                                      
flotation                                                                 
Float (cassiterite                                                        
           7.6 11.32                                                      
                   46.0                                                   
                       7.6  12.43                                         
                                50.5                                      
concentrate)                                                              
Non-float to be                                                           
           14.7                                                           
               4.34                                                       
                   34.1                                                   
                       15.4 4.07                                          
                                33.5                                      
recirculated                                                              
Final tailings                                                            
           77.7                                                           
               0.48                                                       
                   19.9                                                   
                       73.4 0.37                                          
                                14.5                                      
__________________________________________________________________________
 
    
     EXAMPLES II AND III 
     The same ore is treated as in Example 1, the only differences coming from the use of various collectors according to the invention. 
     
         __________________________________________________________________________
Example II                  Example III                                   
__________________________________________________________________________
Preliminary                                                               
      natural pH (6.6)      natural pH (6.6)                              
flotation                                                                 
      N--alkylaminopropionic                                              
                            N--octyloxypropylaminopro-                    
(accor-                                                                   
      acid (alkyl = radical pionic acid (alkyl = chain                    
ding to the                                                               
      of tallow chain) =    having 7/9 carbons) =                         
invention                                                                 
      160 g/t               160 g/t                                       
      Conditioning: 3 mins  Conditioning: 3 mins                          
      M.I.B.C. = 10 g/t     M.I.B.C. = 10 g/t                             
Normal                                                                    
      Sulfuric acid:        Sulfuric acid: 2.8 kg/t                       
flotation                                                                 
      2.7 kg/t                                                            
      pH = 2.4              pH = 2.4                                      
      Na.sub.2 SiF.sub.6 = 100 g/t                                        
                            Na.sub.2 SiF.sub.6 = 100 g/t                  
                    depressant                                            
      Na.sub.2 SiO.sub.3 = 100 g/t                                        
                            Na.sub.2 SiO.sub.3 = 100 g/t                  
      Tetrasodium sulfo-    Tetrasodium sulfosuccinate =                  
      succinate = 300 g/t   300 g/t                                       
      Conditioning: 3 mins  Conditioning: 3 mins                          
      M.I.B.C. = 40 g/t     M.I.B.C. = 40 g/t                             
__________________________________________________________________________
 
    
     Results: 
     
         __________________________________________________________________________
            Preliminary flotation                                         
                          Preliminary flotation                           
            with N--alkylaminopropio-                                     
                          with N--octyloxypropyl-                         
            nic acid (alkyl = tallow)                                     
                          aminopropionic acid                             
            Yield         Yield                                           
            in       Yield                                                
                          in      Yield                                   
            weight                                                        
                 %   in   weight                                          
                              %   in                                      
            %    tin tin  %   tin tin                                     
__________________________________________________________________________
Supply preliminary                                                        
            100.0                                                         
                 1.86                                                     
                     100.0                                                
                          100.0                                           
                              1.87                                        
                                  100.0                                   
flotation                                                                 
Float       2.3  0.68                                                     
                     0.8  1.9 0.79                                        
                                  0.8                                     
Supply cassiterite                                                        
            97.7 1.87                                                     
                     99.2 98.1                                            
                              1.89                                        
                                  99.2                                    
flotation                                                                 
Float (cassiterite                                                        
            7.6  12.26                                                    
                     50.1 7.7 12.63                                       
                                  52.0                                    
concentrate)                                                              
Non-float to be recircu-                                                  
            15.9 3.33                                                     
                     30.4 17.8                                            
                              3.20                                        
                                  30.5                                    
lated                                                                     
Final tailings                                                            
            74.2 0.47                                                     
                     18.7 72.6                                            
                              0.43                                        
                                  16.7                                    
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     EXAMPLE IV 
     Treatment of the same ore using as collector of normal flotation styrenephosphonic acid instead of tetrasodium sulfosuccinamate. 
     Conditions of flotation (nature and consumption of the reagents, expressed in grams per ton of ore supplying the flotation process): 
     
         ______________________________________                                    
               Preliminary flotation                                      
               (according to the invention)                               
               pH = natural pH 5.8                                        
               N--alkylaminopropionic acid (alkyl                         
               being with copra chain = 160 g/t                           
               Conditioning: 3 mins                                       
               M.I.B.C.:10 g/t                                            
Normal flotation                                                          
               Normal flotation                                           
Sulfuric acid: 1.1 kg/t                                                   
               Sulfuric acid: 0.7 kg/t                                    
pH = 4.5       pH = 4.5                                                   
Styrenesphosphonic acid =                                                 
               Styrenephosphonic acid =                                   
390 g/t        390 g/t                                                    
Conditioning: 3 mins                                                      
               Conditioning: 3 mins                                       
M.I.B.C. = 35 g/t                                                         
               M.I.B.C. = 35 g/t                                          
______________________________________                                    
 
    
     Results: 
     
         __________________________________________________________________________
           Without preliminary                                            
                       With preliminary flotation                         
           flotation   object of the invention                            
           Yield                                                          
           in      Yield                                                  
                       Yield in Yield                                     
           weight                                                         
               %   in  weight                                             
                            %   in                                        
           %   tin tin %    tin tin                                       
__________________________________________________________________________
Supply preliminary                                                        
           --  --  --  100.0                                              
                            1.89                                          
                                100.0                                     
flotation                                                                 
Float      --  --  --  5.1  1.12                                          
                                3.0                                       
Supply cassiterite                                                        
           100.0                                                          
               1.84                                                       
                   100.0                                                  
                       94.9 1.93                                          
                                97.0                                      
flotation                                                                 
Float (cassiterite                                                        
           7.8 8.67                                                       
                   36.6                                                   
                       6.3  11.79                                         
                                39.3                                      
concentrate)                                                              
Non-float to be                                                           
           16.9                                                           
               3.98                                                       
                   36.6                                                   
                       14.8 4.84                                          
                                37.9                                      
recirculated                                                              
Final tailings                                                            
           75.3                                                           
               0.65                                                       
                   26.6                                                   
                       73.8 0.51                                          
                                19.8                                      
__________________________________________________________________________
 
    
     EXAMPLE V 
     Treatment of another cassitierite ore containing: 
     silicates 
     silico-aluminates (muscovite, chlorites, tourmaline) 
     carbonates (calcite, siderite) 
     fluorite 
     quartz 
     Conditions of flotation (nature and consumption of the reagents expressed in grams per ton of ore supplying the flotation process): 
     
         __________________________________________________________________________
                        Preliminary flotation                             
                        (according to the invention                       
                        pH = natural pH 6.5)                              
                        N--alkylaminopropionic acid (alkyl                
                        being with copra chain) = 250 g/t                 
                        Conditioning: 3 mins                              
Normal flotation        Normal flotation                                  
Sulfuric acid: 3.5 kg/t Sulfuric acid: 2.3 kg/t                           
pH: 2.4                 pH: 2.3                                           
Na.sub.2 SiF.sub.6 : 100 g/t                                              
                        Na.sub.2 SiF.sub.6 : 100 g/t                      
                  depressant               depressant                     
Na.sub.2 SiO.sub.3 : 200 g/t                                              
                        Na.sub.2 SiO.sub.3 : 200 g/t                      
Conditioning: 2 mins    Conditioning: 2 mins                              
Tetrasodium sulfosuccinamate =                                            
                        Tetrasodium sulfosuccinamate =                    
300 g/t                 300 g/t                                           
Conditioning: 3 mins    Conditioning: 3 mins                              
M.I.B.C. = 45 g/t       M.I.B.C. = 50 g/t                                 
__________________________________________________________________________
 
    
     Results: 
     
         __________________________________________________________________________
           Without preliminary                                            
                       With preliminary flotation                         
           flotation   object of the invention                            
           Yield       Yield                                              
           in      Yield                                                  
                       in       Yield                                     
           weight                                                         
               %   in  weight                                             
                            %   in                                        
           %   tin tin %    tin tin                                       
__________________________________________________________________________
Supply preliminary                                                        
           --  --  --  100.0                                              
                            1.36                                          
                                100.0                                     
flotation                                                                 
Float      --  --  --  9.0  0.87                                          
                                5.7                                       
Supply cassiterite                                                        
           100.0                                                          
               1.40                                                       
                   100.0                                                  
                       91.0 1.41                                          
                                94.3                                      
flotation                                                                 
Float (cassiterite                                                        
           5.7 6.79                                                       
                   27.5                                                   
                       5.5  12.12                                         
                                49.0                                      
concentrate)                                                              
Non-float to be                                                           
           25.3                                                           
               2.91                                                       
                   52.4                                                   
                       24.4 2.07                                          
                                37.1                                      
recirculated                                                              
Final tailings                                                            
           69.0                                                           
               0.41                                                       
                   20.1                                                   
                       61.1 0.18                                          
                                8.2                                       
__________________________________________________________________________
 
    
     The preliminary flotation treatment by means of the collectors according to the invention makes it possible to obtain a significant improvement in selectivity in the course of the subsequent direct flotation of the cassiterite whilst substantially reducing the consumption of acid necessary for maintaining the pH of the flotation (in addition, the residual presence of the amphoteric collector avoids obtaining a considerable volume of very stable froth inherent in the flotation of the cassiterite with the aid of sulfosuccinamates).