Abstract:
A method of enhancing the magnetic separation of ores is disclosed in which a sulfonated polymeric dispersant is added to an ore slurry just prior to or during the magnetic separation operation. The sulfonated polymeric additive inhibits heterogeneous flocculation during the magnetic separation operation.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention is directed to the benefication of magnetic ores. More particularly, the present invention is directed to the benefication of low-grade ores via magnetic separation wherein the magnetic separation process is enhanced by the addition of sulfonated polymer dispersants to the magnetic separation operation.  
         BACKGROUND OF THE INVENTION  
         [0002]    The present invention is directed to the benefication of low grade, finely divided ores via a magnetic separation process. Such ores are typically upgraded by magnetic separation followed by flotation. The settling of particles in the solutions which have relatively high concentrations of suspended solids is a problem in such ore processing. For example, magnetic separators take advantage of the difference in magnetic properties between ore minerals and is used to separate valuable minerals from non-magnetic gangue or non-magnetic minerals. The efficacy of a magnetic separation process can be greatly reduced by adsorption or agglomeration of non-magnetic particles around magnetic particles. That is, heterogeneous flocculation of the finely divided ore can hinder magnetic particles from separating in the magnetic fields, thereby reducing the recovery of the desired magnetic ore concentrate. Alternatively, impurities attached to magnetic ore particles can be recovered with the concentrate, thereby reducing the grade, or purity, of the magnetic ore concentrate.  
           [0003]    The use of dispersant materials in ore processing is known. U.S. Pat. No. 4,298,169 discloses the addition of dispersants such as tannins, lignin sulphonates and alkaline phosphates to maintain a uniform dispersion of ore in water when the ore is ground. Thereafter, a flocculating agent is added to induce selective flocculation of magnetite and the flocculated ore is subjected to magnetic separation. U.S. Pat. No. 4,219,408 discloses a process of magnetic separation of minerals in which a dispersed aqueous slurry of ore is admixed with a system of ferromagnetic seed particles to enhance the magnetic separation process. The aqueous slurry is dispersed with dispersants such as sodium silicate, sodium hexametaphosphate and sodium polyacrylate/sodium hexametaphosphate. U.S. Pat. No.5,307,938 discloses a method of increasing iron ore recovery by adding a dispersant polymer or copolymer containing at least one acrylic functional group to the ore during the grinding operation. The polymer is added to deslime thickeners (settling tanks) where the ore is allowed to settle and silica is decanted and removed as overflow.  
         SUMMARY OF THE INVENTION  
         [0004]    The present invention is directed to a method of enhancing magnetic separation processes for ore recovery. The method comprises the addition of sulfonated polymeric dispersants to an ore slurry just prior to or during magnetic separation. The addition of sulfonated polymeric dispersants just prior to or during the magnetic separation operation has been found to inhibit heterogeneous flocculation in the magnetic separation operation which adversely impacts the efficacy of the magnetic separation process.  
         DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
         [0005]    Although the method of the present invention is applicable to all ores which may be separated by selective flocculation and magnetic separation, the invention is illustrated by specific reference to iron ores. The present invention proceeds according to existing processing of ore in which selective flocculation and magnetic separation processes are employed.  
           [0006]    In typical iron ore processing, the discharge from the grinding mill is diluted to between 5 and 40 percent solids and mixed with a flocculating agent to induce selective flocculation of iron oxides on nuclei of particles containing residual magnetite. The flocculating materials are selected to cause selective flocculation of the iron oxide in preference to silica materials. Examples of flocculants are carbohydrates such as corn starch, potato starch and other natural and modified starches; ammonium algenate; carboxomethyl cellulose; cellulose xanthate; and synthetic polymerized flocculents such as polyethylene oxide, polyacrylamides and polyacryls nitrites. In the prior art, the suspension of ore and flocculents are agitated briefly. The selectively flocculated ore pulp is then fed to a magnetic separation operation such as a magnetic surface or porous ferro magnetic matrix.  
           [0007]    The present inventors have discovered that the magnetic separation of the iron oxide of the prior art can be enhanced by the addition of sulfonated copolymers or terpolymers or mixtures thereof to the ore slurry just prior to or during the magnetic separation operation. The addition of sulfonated copolymers or terpolymers just prior to or during the magnetic separation operation was discovered to disperse the suspended iron particles and reduce or eliminate undesirable heterogenous flocculation in the magnetic separation operation.  
           [0008]    In the present invention, the sulfonated copolymers or terpolymers are added to the ore slurry just prior to or during the magnetic separation operation. The sulfonated copolymers or terpolymers act as dispersants that inhibit heterogeneous flocculation in the magnetic separation operation. By inhibiting heterogeneous flocculation, the efficacy of the magnetic separation operation is enhanced.  
           [0009]    The sulfonated copolymers or terpolymers are added to the aqueous ore slurry in a concentration of from abut 1 to about 200 parts active polymer per one million parts aqueous ore slurry (ppm). Preferably the sulfonated copolymers or terpolymers are added to the aqueous ore slurry in a concentration of from about 5 to about 60 ppm.  
           [0010]    The dispersant efficacy of the sulfonated copolymers or terpolymers of the present invention is demonstrated by the following example. The following example is intended to be illustrative of the present invention and not restricting the scope of the present invention.  
       
    
    
     EXAMPLES  
       [0011]    The dispersant efficacy of a variety of materials on a mineral ore slurry containing 8% suspended solids was evaluated. The mineral ore slurry was placed in turbidimeter cells, shaken to ensure complete dispersion of the solids and inserted into a Hach turbidimeter. Turbidity readings were taken over a ten hours. For treatments that exhibited a drop in dispersing efficacy, readings were terminated in less than ten hours. Treatment performance was compared to a control in which no treatment was added. Tables I and II summarize the results.  
                                             TABLE I                       Treatment   Dosage   Turbidity (NTU)   Timed Reading (hours)                                AA/AHPSE (3:1,low MW)   10 ppm   9911   10       Sodium Hexametaphosphate   10 ppm   6729   10       Lignosulfonic acid,   10 ppm   6041   10       ammonium salt       Sodium Polymethacrylate   10 ppm   2668   10       AA/PEGAE (2.%:1, 10 moles EO)   10 ppm   1712   4.92       Carboxymethylcellulose   10 ppm   1320   10       AA/AHPSE (3:1, high MW)   10 ppm   1297   10       PIPA   10 ppm   1149   5.83       Sodium Tripolyphosphate   10 ppm   929   1.84       Lignosulfonic acid, sodium   10 ppm   911   2.71       salt       Control    0 ppm   234   2.02       Control    0 ppm   157   1.75       Polyoxyethylene thioether   10 ppm   151   3.45                  
 
         [0012]    [0012]                                   TABLE II                                       Ter(acrylic acid/t-   5 ppm   8979.7   10           butylacrylamide/AMPS),           MW = 5000           AA/AHPSE (3:1, low MW)   5 ppm   8872   10           AA/AHPSE (6:1)   5 ppm   2703.9   10           AA/AMPS   5 ppm   1967.9   10           Diisobutylene maleic   5 ppm   1914.4   10           anhydride copolymer           Ter(acrylic acid/t-   5 ppm   1202.2   10           butylacrylamide/AMPS),           MW = 4500           Sodium Hexametaphosphate   5 ppm   1101   3.4           Polyacrylic acid   5 ppm   964.57   10           Control   0 ppm   828   4.92           Lignosulfonic acid,   5 ppm   739   2.21           ammonium salt           Sodium polystyrene   5 ppm   590.35   5.82           sulfonate           Dicarboxyethyl N alkyl   5 ppm   245.84   3.07           (C 18) sulfosuccinate           Control   0 ppm   145.4   3.42           Polymaleic acid   5 ppm   32.54   7.59                        
         [0013]    In tables I and II, AA/AHPSE is Acrylic acid/ allylhydroxpropyl sulfonate ether, AA/PEGAE is Acrylic acid/polyethylene glycol allyl ether, PIPA is polyisopropylene phosphonic acid, AA/AMPS is Acrylic acid/acrylamide methylpropane sulfonic acid.  
         [0014]    The data is tables I and II shows that sulfonated copolymers or terpolymers exhibit surprising efficacy at improving dispersion of the ore slurry which will result in improved efficacy in the magnetic separation operation. The non-sulfonated materials tested did not exhibit comparable efficacy in dispersing the ore slurry.  
         [0015]    While the present invention has been described with respect to particular embodiments thereof, it is apparent that numerous other forms and modifications of the invention will be obvious to those skilled in the art. The appended claims and this invention generally should be construed to cover all such obvious forms and modifications which are within the true spirit and scope of the present invention.