System and method for the concentration of a slurry

Abstract

The present invention relates to a system and a method for the concentration of slurry, especially mineral containing slurry. The invention provides a system comprising an electrophoresis unit and a separation unit, where the separation unit comprises a recipient, preferably of half cylindrical form, with adjusted flanks for separating the solid material or cake from the rotating anodes and a sliding carriage suitable for closing the recipient and stripping resting solid material from the flanks into the recipient before the solid material or cake is pressed out of the recipient by a piston.

Claims

1. A separation unit for use with a device for the concentration of slurry, the separation unit comprising a recipient and a piston adapted to the recipient form, wherein the recipient has shoulders dimensioned to act as scraping flanges for cake material, the piston is dimensioned for pressing cake material out of the recipient, the separation unit has a sliding carriage with a cover for closing the recipient and collecting residual cake material from the shoulders into the recipient while closing it, the recipient has a half cylindrical or half rectangular form, and the separation unit has a pneumatic cylinder that drives the piston pneumatically.

2. The separation unit according to claim 1, wherein the separation unit is made of poly-tetra-fluoroethylene.

Description

DETAILED DESCRIPTION OF THE FIGURES

(1) The invention will be further described by figures and examples without being limited to the described embodiments:

(2) FIG. 1 Plot of the solid content of the deposition cake against the voltage applied to the electrodes

(3) FIG. 2 Plot of the specific deposition rate against the voltage applied to the electrodes

(4) FIG. 3 Plot of the specific energy consumption against the voltage applied to the electrodes

(5) FIG. 4 Plot of the solid content of the deposition cake against the distance of the electrodes

(6) FIG. 5 Plot of the specific deposition rate against the distance of the electrodes

(7) FIG. 6 Plot of the specific energy consumption against the distance of the electrodes

(8) FIG. 7 Plot of the solid content depending on the retention time

(9) FIG. 8 Plot of the specific deposition rate depending on the retention time

(10) FIG. 9 Plot of the specific energy consumption depending on the retention time

(11) FIG. 10 Separation unit

(12) FIG. 11 A, B: Arrangement of the separation units and anode discs

(13) FIG. 12 Electrophoresis cell with inlet and overflow

(14) FIG. 1 shows that the voltage applied to the electrodes has a considerable influence on the solid content of the deposition cake resp. the osmosis. Solid content and deposition rate (FIG. 2) increase with raising the voltage, but the energy consumption (FIG. 3) increases disproportionally. The reason for this effect is an increase in electrolysis of the contained water. It is a serious problem that the electrophoresis of the water content leads to the production of hydrogen and oxygen, which form an explosive mixture with the surrounding air. It is not possible to reduce the voltage to a level that no hydrogen is produced.

(15) Consequently, a compromise had to be determined allowing a good productivity with reasonable energy consumption. Most experiments were done with a voltage of 20 V, although the voltage might range from 10 to 60 V.

(16) Further experiments were performed in order to determine a distance of the electrodes with regard to the solid content (FIG. 4), specific deposition rate (FIG. 5) and the specific energy consumption (FIG. 6). The distance of the electrodes can usually only be changed with an immense effort, e.g. with movable cathodes, so that it is import to know an optimal distance of the electrodes for the construction of an electrophoresis device.

(17) The results shown in FIGS. 4 to 6 were obtained by applying a voltage of 20 V. It is clearly visible that a short distance of the electrodes correlates with an increase of efficiency of the electrophoresis, viz. solid content and deposition rate increase with a decrease of energy consumption. This means that a short distance of electrodes has to be preferred.

(18) It has to be taken into account that the deposition cake on the anode reduces the opening between cathode and anode. The experiments showed a physical thickness of the anode cake of about up to 10 mm. It has to be guaranteed that the residual opening between the electrodes is suitable for the flow through of the slurry. In FIG. 5 a stagnation of the deposition rate can be observed for a distance of electrodes above 20 mm. This might reflect the effect of minimizing the opening between the electrodes by the anode cake.

(19) By using rotating anodes different modes of performing the electrophoresis can be applied. The anodes can rotate continuously or in intervals. The increasing anode cake on the anode disc 50 leads to an increase of the electrical resistance as the solid cake has a higher electrical resistance than the slurry. As a consequence the deposition rate decreases (FIG. 8) and the energy consumption increases (FIG. 9), while the solid content of the anode cake still increases (FIG. 7).

(20) The results of the experiments for determining a reasonable retention time as shown in FIGS. 7 to 9 were performed with a voltage of 20 V, an electrode distance of 40 mm and an angle of rotation of 45.

(21) Angle of rotation and retention time are important parameter with regard to the total amount of anode cake deposited on the anode disc 50. The volume of the anode cake has to correlate with the volume of the separation unit in order to avoid overfilling of the separation unit, as this would lead to remaining solid particles on the anode disc 50. The skilled man would adapt the degree of rotation according to the thickness of the cake on the anode, i.e. the thicker the cake is, the smaller the degree of rotation of the anode before the recipient 40 is filled.

(22) Some restrictions have to be taken into account while defining the parameters for the construction of the device and performing the electrophoresis. Applying high voltage to the electrodes should be avoided since the side effect of hydrogen production has to be reduced for safety reasons. The distance of electrodes is basically predefined by the concept of the multi compartment slurry container 60 as shown in FIG. 11. The remaining parameters have to be chosen in order to optimize solid content of the anode cake and obtain a high deposition rate.

(23) Table 1 shows the parameters that have been chosen for a device according to the invention.

(24) TABLE-US-00001 Starting parameter spec. spec. energy (preferred solid content deposition rate consumption parameter) (%) F.sub.FS (.sup.kg/.sub.m.sup.2.sub.h) F.sub.AR (.sup.kWh/.sub.t) F.sub.EV U = 20 V 42.3 29.4 49.9 H = 40.0 mm 41.5 1.000 31.1 1.045 42.2 0.988 (H = 37.5 mm)* (41.5) (32.5) (41.7) t.sub.v = 4 min 42.5 0.988 27.0 1.056 52.8 0.985 (t.sub.v = 3 min)* (42.0) (28.5) (52.0) = 45 38.9 1.131 19.7 1.131 46.7 0.642 ( = 10)* (44.0) (24.0) (30.0) Preferred 47.3 39.5 31.2 operating cond. Values not corresponding exactly to measured values have been extrapolated according to the curve progression (*). Starting point for the calculation has been taken from the results obtained for the variation of the voltage, shown in the top line of table 1. The changes of solid content, deposition rate and energy consumption were taken from experiments varying electrode voltage, retention time and angle of rotation. Using the preferred parameters in preferred operating conditions, results in the solid content, deposition rate and energy consumption shown in the line at the bottom. The voltage should be adjusted to 20 V and the electrode distance H chosen according to the construction of the slurry container 60. The retention time should be about 4 min and the angle of rotation 45 in order to optimize solid content, deposition rate and energy consumption.

(25) FIG. 10 shows a separation unit that comprises a recipient 40 for receiving the cake material from a rotating anode 50. The shoulders 30 of the recipient 40 are dimensioned to act as scraping flange for taking off the solid material or cake from the anodes 50. Collected material will be pressed out of the recipient 40 by a piston 20 which is driven by a pneumatic cylinder 21 that is regulated through valves 22. It is intended that the recipient could be closed with a sliding carriage 10. The sliding carriage 10 comprises a cover 11 and guiding rods 12.

(26) It is further intended that the sliding carriage 10 for closing the recipient 40 has a wiper at the front, for collecting residual material from the shoulders 30 into the recipient 40 while closing it.

(27) FIG. 11 shows the arrangement of the separation units and the anode discs 50. In FIG. 11A the recipients 40 are closed in order to press the collected solid material out by moving the piston 20. In FIG. 11B the recipients are open and ready for collecting solid material from the rotating anodes 50. In order to open or close the recipient 40 all recipients 40 which are arranged next to anode discs 50 are connected via a connection bar 6. At their ends the connection bars 6 are connected with the pneumatic cylinders 21 that are mounted onto the frame 5. The anode discs 50 are rotating vertically in the container 60. The anode discs 50 are fixed on a drive shaft 7 that is rotated by a single drive 8 being mounted on a stationary table 9. The recipients can be closed with the sliding carriage 10 comprising cover 11 and comprising guiding rods 12.

(28) FIG. 12 shows an electrophoresis cell with inlet 61 and overflow 62. A vertical rotating anode disc 50 rotates within a compartment of a multi compartment container 60. Slurry is filled in at the inlet openings 61 and the dewatered slurry leaves the container via the overflow 62. It is intended to arrange the inlet openings 61 at the bottom of the container 60 and the outlet 62 at the upper margin of the container 60.

(29) It is possible to fill each compartment of a multi compartment container 60 with fresh slurry by equally dividing the flow of fresh slurry. It is advantageous that only one pump might be used for this way of filling an electrophoresis cell. Another possibility is to fill a compartment with the overflow slurry of the previous compartment, resulting in a solid content gradient in a row of compartments. It has to be noted that the formation of solid material on the anodes 50 stops below a solid content of the slurry of about 9 to 10%, so that a slurry with a solid content below this value might be supplemented with solid material from a buffer storage or has to be removed from the process.

REFERENCE NUMBER LIST

(30) 5 frame 6 connecting bar 7 drive shaft 8 single drive 9 stationary table 10 sliding carriage 11 cover 12 guiding rod 20 piston 21 pneumatic cylinder 22 valve 30 shoulder 40 recipient 50 anode disc 60 container 61 inlet 62 overflow