METHOD AND DEVICE FOR ZINC ELECTROWINNING FROM SULFATE SOLUTIONS
The invention relates to a method and a device for electrowinning of zinc from sulfate solutions. The electrolyzer for zinc extraction according to the invention includes a bath-reactor which is equipped with power supply buses, a pipeline of two pipes for supplying the electrolyte, cathodes, anodes, plastic strips along the height of the anodes, an overflow for electrolyte discharge by gravity. The cathodes have an area of 3.5-10 m2. The height of the electrolyzer is at least two times greater than its width, and the length of the electrolyzer depends on the number of the electrodes. The bottom of the electrolyzer is divided by a groove along the length of the bath.
The invention is related to a method and a device for zinc electrowinning from sulfate solutions.
BACKGROUND OF THE INVENTIONVarious methods and devices are known for obtaining electrolytic zinc and 90% of its production is realized by hydro-electrometallurgy. In the conventional electrolytic baths the process is carried out with current densities of ˜400÷600 A/m2, cathode surface ˜1.0÷1.6 m2 and manual stripping of zinc cathodes from the cathode sheets in 24 hours. A novelty in this direction, the application of which began approximately 25 years ago, are the so called Jumbo baths and electrodes of an area of ˜2.60÷3.40 m2, each bath charged with ˜80÷120 cathodes. This technology is now being used by the modern electrolytic zinc plants and zinc stripping is done mechanically by various devices in every 48 hours at ˜3100÷3500 kWh/t energy consumption.
The disadvantage of all known processes and apparatus, regardless of the relative increase in productivity, is the main factor of effectiveness in electrowinning of metals, namely electricity consumption. The latter represents ˜70% of the total processing costs for zinc extraction, along with those for electrode management, electrolyte cooling, labor costs, consumables, etc.
TECHNICAL DESCRIPTION OF THE INVENTIONThe essence of the method and the device according to the invention or the new technology and equipment for zinc electrowinning is the creation of a new generation of electrolyzers regarded as a kind of rectors. This is dictated by the process which is a complex function of electric potentials, oxi-reduction acts and hydro-aerodynamic environment in which the bath (reactor) is conditionally divided into upper and lower and, respectively, left and right symmetric zones. This design and, respectively, the process are consistent with the electrode potentials, productivity, electrode configuration, fixation and positioning of the cathodes and anodes, their formation and processing, the electrolyte circulation system and other factors. Besides, the separated gases—oxygen on the anodes and hydrogen on the cathodes—create a peculiar “fluid bed” and contribute to the movement of the electrolyte between the electrodes from the bottom to the top and vice versa apart of them. Furthermore, the charging of the fresh solution at the pressure of ˜1.5÷2.0 atm., its leading away by means of an overflow as a waste solution and the anode fixing devices have favorable effect on the movement of the solution (
In principle the electrolyzer can be formed longitudinally by two, connected by an overflow, baths, charged by a common circulation line, so that the velocity of the circulation doubles and it is possible to place additional cathodes and anodes (
The aim of the method and the device according to the present invention of a new generation of zinc electrowinning is, while maintaining high productivity, to increase process efficiency by reducing energy costs by ˜20÷30% and other related processing costs as a whole at comparable investment costs for construction, machinery, equipment and installation (engineering).
This is achieved by the introduction of a new design of an electrolysis bath and, respectively, electrodes, loaded into it compared to the existing ones so far.
What is characteristic here is that, while comparatively maintaining the accepted in practice width and length of the electrolyzer, its height is doubled, i.e. the mentioned upper and lower zones are already formed (
The used anodes 4 (
A version of the offered device, according to the present invention, is the twin electrolyzer, or two baths connected in a common system (
The bottom of the electrolyzer (
FIG. 1—General view of the device of the present invention;
FIG. 4—Plastic (PVC, PPL, etc.) strip-clamp for fixing the electrodes of the present invention;
Electrowinning is realized in an electrolyzer of the volume of ˜30 m3, height—3.5 m and width—1.6 m, fed with 60 cathodes 3, each one having an area of ˜6 m2. The density of the supplied current is ˜300 A/m2. The electrolyte enters the bath-reactor 5 through two (diffusion) pipes 1 at the speed of ˜500÷700 l/min and exits along its entire short side through overflow 2. The lead anodes 4 are formed by two symmetrical parts and their surface is shaped like stepped grooves with tapered lower part and at least 80% of anode 4 is fixed by plastic strips, which are supplemented by plastic washers 10 at the middle and lower end of anode 4. The mixed electrolyte enters the reactor, containing 70 g/l zinc and 180 g/l sulfuric acid at the temperature of ˜30° C. (˜37° C. at the outlet) with the necessary additives; yield is 90% and energy consumption—˜2600 Kwh/t zinc.
The duration of the cathode cycle is ˜72 h; metal purity is 99.995% Zn.
Example 2The process is carried out in a twin electrolyzer, formed by two baths with an intermediate wall, connected by a siphon, along their entire width. The baths are charged with 62 cathodes each, i.e. ˜124 cathodes with an area of ˜6 m2 each; circulation is achieved with 4 pipes—diffusers (two at each inlet) in their upper parts and in the middle, overflowing between them top-down at the speed of ˜800÷1200 l/min. Anodes configuration and fixing elements are the same as in Example 1. Current density is ˜300 A/m2 and the cycle of zinc deposition is 72 h. The yield is ˜90%, energy consumption—˜2700 Kwh, purity ˜99.995% Zn with the same electrolyte. Effective sludge removal is done in ˜30 days.
Claims
1. An electrolyzer for zinc electrowinning, characterized in that it includes a bath-reactor (5), equipped with power supplying buses (6), a pipeline of two pipes (1) for feeding the electrolyte, cathodes (3), anodes (4), plastic strips (8) along the height of the anodes (4), an overflow (2) for electrolyte exit by gravity, where the cathodes (3) have an area of 3.5-10 m2 and the height of the electrolyzer is at least two times greater than its width. The length of the electrolyzer depends on the number of the electrodes, and the bottom of the electrolyzer is divided by a groove (11) along the length of the bath (5).
2. An electrolyzer according to claim 1, characterized in that the anodes (4) are made of pure lead, alloyed with 0.3 to 1.0% Ag.
3. An electrolyzer according to claim 1, characterized in that the height of each anode (4) is divided into two equal parts and their total effective area is greater than that of the cathode (3), and the thickness of the anode (4) is 12-18 mm.
4. An electrolyzer according claim 1, characterized in that power feeding buses (6) are made of copper and there is a copper bar (7) fixed on them.
5. An electrolyzer according claim 1, characterized in that the plastic strips (8) are installed so as to cover the edges of anode (4) to at least 80% of the height and in the middle and the lower part the anodes are fixed by a plastic disc washer (10) between anode (4) and cathode (3).
6. An electrolyzer for zinc electrowinning, characterized in that it consists of two connected electrolyzers according to claim 1, where between the two baths is provided a siphon-overflow (9) for the solution, leaving the first bath by gravity and entering the second bath from the bottom to the top.
7. A method for zinc electrowinning with a device according to claim 1, characterized in that it consists of:
- feeding process electrolyte solution, containing zinc, sulfuric acid ˜120-200 g/l and additives as an option at the temperatures of 25-32° C. at the inlet and 36-38° C. at the outlet, and pressure 1.5-2 atm., through a pipeline (1) into the bath-reactor (5) and electric power by means of the buses (6);
- electrolysis at the current density of 250-500 A/m2, maintaining electrolytic solution circulation speed of 1.5÷3 bath volumes per hour, where the anode-to-anode distance is ˜80-86 mm and the duration of the cathode cycle is 72 hours (48-96 hours), and the temperature of the electrolyte at the exit is 36-38° C.
8. A method according to claim 7, characterized in that the process electrolytic solution contains 120-200 g/l sulfuric acid.
Type: Application
Filed: Feb 2, 2012
Publication Date: Dec 5, 2013
Applicant: KCM '2000' AD (Plovdiv)
Inventors: Ivan Enchev (Plovdiv), Nikola Dobrev (Plovdiv), Gencho Bozhilov (Plovdiv)
Application Number: 13/983,386
International Classification: C25C 7/00 (20060101); C25C 1/16 (20060101);