Abstract:
A method and apparatus are disclosed for separating target particles from surrounding materials such as separating gold particles from the clays in placer deposits. The enveloping material is converted to a slurry, then pumped into a collision chamber through pairs of opposing nozzles. Sets of slurry collide, dislodging target particles from surrounding material. The outgoing slurry is then further processed to separate the particles dislodged by the collision.

Description:
FIELD OF THE INVENTION 
     The invention relates generally to the methods and apparatus for separating hydrous slurries into two or more fractions through collision scrubbing. High velocities are created for attrition collisions to facilitate particle separation. 
     BACKGROUND OF THE INVENTION/PRIOR ART 
     Various methods and apparatus have been used to separate slurries containing solids into several fractions to aid in extraction of the target mineral. Many sizing and classifying methods employ gravity separation, the separation being dependent on the difference in the settling rates or settling velocities of the particles in a relatively quiescent body of water. The different settling velocities of the solid particles of the slurry may be by virtue of particles differing in size, particles of different substances differing in their densities, or both. 
     Methods and apparatus of this type are subject to certain disadvantages and limitations. For example, the separation may not be as sharp as desired, particularly for certain types of slurries. The sharpness of separation tends to be subject to variations, which generally occur when there are changes in the solids content of the feed or in the relative amounts of the solids in the feed having different settling velocities. Also, the apparatus may be excessively elaborate in structural detail and size for the capacity or sharpness of separation desired. For a given processing capacity, the size of such equipment is relatively large. 
     Beyond gravity separation, other means of separating mineral ore involve various mechanical and chemical processes. Mechanical processes include: rotary scrubbers, which roll and tumble rock in water; log washers, which have paddles to scrub and transport the material from one point to another; pebble attrition or autogenous mills, which are rotary turning barrels that tumble the rock and particles in water and pass the same on to the next process; wet vibrating screens, which hydrate the material during agitation; high speed paddle blenders, which are batch mixes and not suited for continuous flow; and pulverization. 
     The disadvantages to these processes include the rate at which ore can be processed and the expense. Alluvial ore deposits require thousands of tons of raw material to be mined, processed, and refined daily. The current methods and apparatus either cannot efficiently process the large amounts necessary in mining or are cost prohibitive. 
     An object of the invention is to improve upon hydraulic separating methods and apparatus, particularly with respect to providing an efficient and economical means to separate mineral ore at a desired sharpness of separation. 
     Another object of the invention is to provide an apparatus that is relatively simple in construction and operation, which provides for changes in the character and rate of feed slurry. 
     SUMMARY OF THE INVENTION 
     When alluvial or placer deposits of ore are mined, large amounts of unwanted material surround the target mineral. For example, gold particles or granules are encased in the local variety of clay. In many types of such ore processing, it is customary to add water to the ore mixture to produce a slurry that facilitates mechanical processing. The present invention is an efficient way of dislodging the unwanted material from the target mineral carried in the slurry. The invention also permits changes in the flow rate and viscosity of the slurry mixture using a simple and economical apparatus. The flow rate of the slurry mixture can be adjusted to accommodate different particle sizes and varying viscosity and to promote effective scrubbing of mineral-bearing ore. 
     In one embodiment of the invention, a hydrous slurry mixture of the ore is pumped via hydrostatic and other pressure at a continuous flow rate into a receiving cylinder. Then, the mixture is pumped through two small openings on opposite walls of a hollow tube inserted into the receiving cylinder. These openings are positioned so that a jet of slurry flows from each hole and the jets collide in the center of the tube. This collision occurs at atmospheric pressure and causes clay and other particles to be dislodged from the mineral ore. The flow into the tube is controlled by the size of the nozzle, and the incoming pressure which may be adjusted to the required velocity for the collision. The dislodged material and scrubbed particles then fall out of the tube for further processing. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a side view of the system illustrating the preferred embodiment of the apparatus in accordance with the present invention. 
     FIG. 2 is a cross-sectional top view illustrating the nozzle configuration. 
     FIG. 3 a  is a detail in section illustrating a nozzle, nozzle receptacle and nozzle retainer. 
     FIG. 3 b  is a detail in section illustrating a nozzle. 
     FIG. 4 is a flow chart schematically depicting a preferred embodiment of the process of the present invention. 
     FIG. 5 depicts an arrangement in which four units of the apparatus are integrated into a refining operation through the use of a manifold. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention generally provides for a container with an opening at the top by which a pressurized slurry mixture is introduced into the system and jets at the bottom through which the slurry mixture is pumped. 
     FIG. 1 is a diagrammatic representation showing a vertical cross-section of the device. This embodiment of the invention has a chamber or receiving cylinder  15  made of steel or another adequate material to withstand the high pressure needed to separate particles from the mineral ore. For a prototype purpose and implementation in a small-scale operation, a standard five gallon propane cylinder in common use has proven satisfactory. A prototype operation was set up with four cylinders attached to a steel manifold for even distribution of slurry to each scrubber. See FIG.  5 . Two stages of scrubber are used, and the system is capable of processing 30 tons per hour of ore. 
     The chamber has an entry opening  10  the same size as the end of a low friction feed line (not shown). The end of the feed line fits securely over the entry opening  10  and allows a hydrous slurry of mineral ore to pass into the chamber. The feed line should be have a sufficient diameter and be made of a durable material to withstand a pressurized slurry mixture to be fed into the chamber or receiving cylinder. 
     At the lower end of the receiving cylinder there is a discharge tube  20 , capped at the top  21  and open at the bottom  22 . The discharge tube has pairs of nozzles  30 , which are positioned directly across from each other. The discharge tube is unrestricted, centralized and strong enough to withstand the pressure difference between the charged chamber and atmospheric pressure. The nozzle  30  should have a sufficient diameter and be made of a durable material to allow the slurry mixture to pass at high velocity without clogging or obstruction. A plurality of discharge nozzles may be positioned so that a jet of slurry flows from from each nozzle and collides in the center area  25  of tube  20  as shown in FIG.  2 . 
     FIGS. 3 a  and  3   b  show an enlarged representation of the nozzle and nozzle assembly. Nozzle  30  must be constructed of a material strong enough to withstand the wear and pressure. For the prototype operation, standard  ¾-10 × steel bolts with 1″ hex heads  31  were drilled lengthwise to create a ⅜″ diameter barrel  32 . The bolt is counterbored with a {fraction (9/16)}″ shaft  33  from the intake  34  to a distance of about 1-1¼″, allowing a shoulder  35  to remain in the bolt head  31  short of the discharge outlet  36 . An insert  37  of a suitable smooth and durable lining material, preferably polyurethane or carbide, with the same inside diameter as the barrel  32  and the same outside diameter as the counterbored shaft  33 , is inserted into the shaft, bonded and shouldered up. In the prototype, the insert has a ⅜″ inside diameter, {fraction (9/16)}″ outside diameter and is bonded to the bolt shaft with epoxy  38 . Preferably, the insert has a rounded entry  39  to make inflow into the nozzle more efficient. 
     The nozzle retainer in the prototype is a ¾-10 steel hex  40  nut which is centered over a {fraction (9/16)}″ hole  41  in the discharge tube and welded  42  to the inside surface of the discharge tube  20 . The nozzle bolt  30  is threaded into the retainer nut  40  for a tight fit that is flush with the outer surface of the discharge tube  23 . Optionally, a flat washer  43  may be used between the bolt head and the nut. When the insert wears out, the nozzle is unscrewed from the retainer and replaced. The retainer nut and nozzle bolt may be selected so that a range of nozzle barrel sizes can be accommodated. 
     For an apparatus on the scale of the described prototype, the nozzle lengths are optimally about one inch and the barrels ⅜ inch or ¾ inch. The combination of nozzle size and input pressure should be set to achieve a nozzle exit velocity of about six meters per second. Bore diameters must accommodate the largest expected solid particles in the slurry. 
     The unit may contain two nozzles, but should optimally contain four nozzles. Larger scale apparatus may include more nozzles. The nozzles are positioned in pairs directly across from each other, so that a jet of slurry is forced from opposing holes and the jets collide in the center of the tube. It is important to optimal operation that the particles collide with each other and not with the nozzles or other parts of the apparatus. 
     Once the apparatus is constructed according to the foregoing specifications, a feed slurry of the particulate ore material is pumped via hydrostatic, hydraulic or other pressure at a continuous flow rate into the entry opening  10 . The hydrous slurry fills the chamber  15  and is forced through the nozzle assemblies  30 , causing the expelled jets of material to collide in the center area  25  of discharge tube  20  at atmospheric pressure. Clay and other particles are thereby dislodged from the mineral ore by the force of the collision. The separated particles drop out the bottom  22  of discharge tube  20  to the next processing step which may be, for example, mesh screen separation or still water gravity concentration. 
     A laboratory test should determine the size of particles, the type of clay and type of verities present, and the ratio of clay to mineral solids in the ore to be processed. Successful recovery has been accomplished with slurries containing 3% to 15% clay in solids and gold concentrations between one gram and one-half ounce per ton. Slurry densities of 5% to 40% were tried, and the best results were achieved at 25% to 30% slurry density. 
     Particle size may be ascertained by sieve analysis of the input slurry. Gold particles larger than ⅜″ can be scrubbed in another device. Particles between ⅜″ and 20 mesh would be scrubbed in a hydroattrition device with ¾″ nozzles. Smaller sized particles will be processed with the ⅜″ nozzles. Table 1 shows the relationship of nozzle pressure, flow rate and collision requirements for 25% to 30% slurries with target particles small enough for a ⅜″ nozzle. 
     
       
         
               
               
               
             
               
               
               
             
           
               
                   
               
               
                 Nozzle Pressure 
                 ⅜″ Nozzle 
                   
               
               
                 Lbs/sq.in. 
                 Gal/per min. 
                 Required Collisions 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                    10 
                 13.3 
                 multiple - 60 min. 
               
               
                 15 
                 16.3 
                 multiple - 45 min. 
               
               
                 20 
                 18.7 
                 multiple - 30 min. 
               
               
                 25 
                 21.0 
                 multiple - 15 min. 
               
               
                 30 
                 23.1 
                 multiple - 08 min. 
               
               
                 35 
                 25.0 
                 multiple - 04 min. 
               
               
                 40 
                 26.6 
                 one collision 90% 
               
               
                 45 
                 28.2 
                 one collision 95% 
               
               
                 50 
                 29.9 
                 one collision 99% 
               
               
                   
               
             
          
         
       
     
     The table shows the number of cycles through the hydroattrition scrubber needed at various pressures to liberate at least 90% of the target materials in the slurry. For nozzle pressures between 10 psi and 35 psi, the slurry had to be recycled through the scrubber to achieve the desired liberation percentage (60 times at once per minute at 10 psi and four times at once per minute at 35 psi). A single collision at 40 psi liberated 90% of the target materials, while a single collision at 50 psi liberated over 99%. 
     The hydroattrition scrubber is useful at several stages of a refining operation. FIG. 4 shows a process flow for a sample gold refiner for placer deposits, in which seven hydroattrition scrubbers  1  to  7  are incorporated. FIG. 5 illustrates the use of multiple hydroattrition scrubbers  1  in parallel, connected by a manifold  25  fed by master input hose  26  to increase the throughput at a particular stage of the ore processing. 
     Although the present invention has been described in detail with reference to certain preferred versions thereof, those skilled in the art will note that the spirit and scope of the appended claims is not limited to the preferred version.