Abstract:
The invention relates generally to a desludging system for electrolytic cells for metal production in the hydrometallurgical industry. Specifically, it relates to a system for desludging cells, preferably for copper cathodes, which comprises removable collectors for lead sludge accumulated at the bottom of cells. Collectors are located at the bottom of the cell and lead sludge is transported towards trays which are later removed from the cell with the sludge thereon without having to stop the cathode production.

Description:
FIELD OF INVENTION 
       [0001]    The invention relates generally to a desludging system for electrolytic cells for metal production in the hydrometallurgical industry. Specifically, it relates to a system for desludging cells, preferably for copper cathodes, which comprises removable collectors for lead sludge accumulated at the bottom of cells. Collectors are located at the bottom of the cell and lead sludge is transported towards trays which are later removed from the cell with the sludge thereon without having to stop the cathode production. 
       BACKGROUND 
       [0002]    In cathode production processes in the metallurgic industry, including copper cathode production processes, lead anodes oxidize to form lead oxide which separates and precipitates to the bottom of the cell where a sludge is built-up. This sludge must be extracted regularly to prevent lead contamination of the copper cathodes. 
         [0003]    Regular desludging from electrowinning cells requires stopping the direct current which is necessary for metal electrowinning. To avoid contamination, circuit breaker frames are used to isolate the cell to be cleaned while the sludge is being removed. The above implies that the copper cathode production in such cells has to stop. 
         [0004]    One solution applied to cell desludging is disclosed in the Chilean patent application for invention number 987-2002 which describes a process and the equipment for cell desludging in electrolytic process plants where solid particles separate in the electrolyte solution inside the electrolytic cell. The equipment comprises a vacuum that sucks solids without spreading them in the electrolyte solution. Then, the solids are separated by their size and weight, and then the collected sludge is packaged. However, the system costs per cell for desludging are costly, since this desludging process also involves filter saturation and vacuum pump wear out. Additionally, vacuum operation for collecting the mud sediments from the bottom of each cell is very slow. 
       SUMMARY OF THE INVENTION 
       [0005]    The main problem solved by this invention comprises desludging a cell without having to stop current supply during the process. Thus, metal electrowinning on cathodes can continue uninterruptedly and time during final harvest is not wasted. 
         [0006]    In one aspect, the present invention provides a desludging system for electrolytic cells for metal production in the hydrometallurgical industry. In a preferred embodiment, the desludging system operates without having to stop the current supply of cells thereby stopping cathode production. For example, the desludging system may comprise a collector formed by a continuous belt device with a feed roller activated by a driving system and a free roller joint by a pair of parallel rails which join the axles in each roller. In one embodiment, a continuous belt is placed and the sludge from the electrowinning process is deposited thereon. At the ends of the continuous belt device and adjacent to the narrow ends of the electrowinning cell, one or more removal trays may be installed to receive sludge accumulated on the collector continuous belt and such feed is produced by activating the driving system on the feed roller and consequently the free roller. 
         [0007]    These and other aspects of the invention will be better understood by reference to the following detailed description and drawings. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0008]      FIG. 1 : shows an isometric view of the invention, which illustrates two systems installed at the bottom of a cell. 
           [0009]      FIG. 2 : shows an isometric view of the invention wherein the framework and rails where collector belts move can be seen. 
           [0010]      FIG. 3 : shows an isometric view of the invention, as in  FIG. 1 , but including open removal trays. 
           [0011]      FIG. 4 : shows an isometric view of the invention, as in  FIG. 3  but with the removal trays at the bottom of the cell, now open and ready to be desludged. 
           [0012]      FIG. 5 : is a top plan view with a drawing of side elevation view of the belt rotary device. 
           [0013]      FIG. 6 : is a top plan view of the belt rotary device with its driving rollers that make belts rotate. 
           [0014]      FIG. 7 : is an isometric perspective view representing a cell in which the size of the cell only allows one system of the invention to be installed. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0015]    Generally, the invention comprises a system of sludge collectors installed at the bottom of a cell. The collector is a flat, continuous belt which captures lead oxides which separate from the anodes before reaching the bottom of the cells. The lead sludge captured by collectors is accumulated over time. When it is time for desludging, the belts are activated to convey the sludge under the cathodes and anodes towards one or more removal trays which receive the sludge. Then, the removal trays are removed from the cell for its final destination. Once the sludge has been removed from the trays, these are placed back into cells waiting for the next desludging. There may be as many systems installed as cells inside the electrowinning plant, and the number of systems per cell will depend on the size of them. 
         [0016]    In one embodiment according to the invention, it is possible to make only one investment per cell, with just the normal cost of desludging and with minimum of personnel, thus cutting desludge time and cost by half compared to the vacuum technique. That is to say, for the same cost, with this invention, it takes the same time to remove residues from 2 cells compared to the amount of time spent in vacuuming just one cell. 
         [0017]    One process for desludging cells involves extracting lead sludge produced in copper electrowinning cells by stopping production via a circuit breaker frame which stops the electrical supply in 2 or 3 cells to be desludged. During this process, the production is stopped at least 1.5 hour per cell when a run-through operation circuit breaker frame is used, and three hours per cell when only the standard frame is used, with a desludging frequency from two to three months per each cell in the electrowinning plant. 
         [0018]    Individual mining tasks may have their own desludging procedure, based on the available resources. A general desludging procedure may be as follows: 
         [0000]    1. A Gantry Crane is assembled to the Circuit Braker Frame in the cells to be desludged. Current supply is shut-off and the copper electrowinning on stainless Cathodes is stopped.
 
2. All Stainless-steel Cathodes with electro deposited copper are removed by the Gantry Crane.
 
3. All Lead Anodes are removed by the Gantry Crane.
 
4. All anti-fog spheres, which are floating on the electrolyte, are removed manually.
 
5. Then, when the stopper at the bottom of the cell is removed all electrolyte is emptied by gravity.
 
6. When the Cell is completely empty, Lead Sludge settled at the bottom can be observed. This sludge is swept, extracted and placed into special containers.
 
7. The bottom of the Cell is washed with clean water.
 
8. The stoppers are installed again and the process for filling with electrolyte is started.
 
9. Anti-fogs Spheres are added.
 
10. Anodes are placed by the Gantry Crane.
 
11. Cathodes are placed by the Gantry Crane
 
12. The Circuit breaker frame is removed by the Gantry Crane and the current supply is switched-on inside the desludged cells.
 
13. The Circuit Breaker Frame along with the Gantry Crane is taken to other cells to be desludged followed by step 1 and so on until every Cell inside the Plant has been desludged.
 
         [0019]    The present invention separates the desludging process in lead contaminated cells from the copper cathode harvest. Therefore, a gantry crane is not necessarily a required element for the system according to the invention compared to traditional desludging. In this way, the present invention provides for more gantry crane availability for carrying out gantry crane basic tasks such as copper cathode harvesting. This allows for increased copper cathode production per cell, more frequent desludgings, and improved copper cathode quality by reducing lead contamination present in the accumulated sludge. 
         [0020]    In one embodiment, the system of the invention comprises a collector ( 2 ) which consists of a continuous belt device with a feed roller ( 3 ) activated by a driving system ( 10 ) which make the belt move towards narrow ends of the electrowinning cell ( 1 ). Additionally, the continuous belt device comprises a free roller ( 4 ) which guides the belt when the roller ( 3 ) is activated. The continuous belt device comprises parallel rails ( 8 ) which join axles ( 9 ) which are part of the roller ( 3 ) driven by the driving system ( 10 ) and also the free roller ( 4 ). Both rollers are joined by a belt ( 11 ) which makes the rollers move at the same speed, consequently the belt moves at the same speed with the sludge accumulated thereon, as shown in  FIG. 6 . 
         [0021]    At the ends of the continuous belt device and adjacent to the narrow ends of the electrowinning cell are located the removal trays ( 7 ) which receive the sludge ( 12 ) that accumulates on the collector belt ( 2 ). 
         [0022]    In one embodiment according to the invention, the continuous belt device also comprises a framework ( 5 ) formed by lateral bars ( 6 ) supporting parallel rails ( 8 ) which support both the drive roller ( 3 ) and free roller ( 4 ), forming a firm structure where the collector continuous belt moves on ( 2 ). The framework has a rectangular shape so that it includes the complete area where oxides are separated, leaving a space at the ends of the framework to install the removal trays ( 7 ) when desludging occurs. The framework is fitted onto later bars ( 6 ) through dovetails which enable such framework ( 5 ) to keep its position within the system. This framework works as a guide and a support for continuous belts which receive and transport the sludge thereon. 
         [0023]    According to one embodiment of the invention, the removal trays ( 7 ) may remain out of the cell during the period the collector is in its steady state accumulating the sludge thereon. Additionally, a removal tray may have a rectangular shape where its width is slightly narrower than the width of the cell, and its height is such that it enables to incorporate a multiple section labyrinth type cap which helps to encapsulate the sludge transferred by the belt. A tray&#39;s base may have a rubber border throughout the rectangular perimeter which is in contact with the cup in order to seal the tray before it is taken from the cell. 
         [0024]    A high relief border may be incorporated at lateral ends of continuous belts to prevent the sludge from moving sideward, thereby spreading the sludge towards the bottom of the cell. Likewise, this system may comprise at the driving roller zone ( 3 ) a sludge scraper to clean the remaining sludge on the continuous belt. 
         [0025]    In one embodiment, the system according to the invention may be manufactured with materials which are preferably acid resistant materials and which do not conduct electricity like synthetic rubber, polyethylene plastics, polypropylene or the like. 
         [0026]    Depending on the size of the cell, all the systems necessary may be installed, as shown in  FIG. 1  which illustrates a cell with two systems installed.