DE4328242A1 - Electrolysis body and process for treating waters and waste waters - Google Patents

Abstract

The invention relates to an electrolysis body and a process for removing toxic heavy metal traces and heavy metal components from natural waters and waste waters (effluents) having a low total electrolyte content. By means of a divided cell having an ion-exchanger membrane as a diaphragm and a small spacing between cathode and anode, a reasonable voltage drop is achieved in the electrolysis cell. The waters and waste waters to be electrolysed permeate the porous, precoated, specially formed three-dimensional carbon-fibre-mat cathode and lose during this by electro reduction the majority of their toxic heavy metal components. By means of a special conical shape of the cathode body, a uniform self-regulating utilisation of the total cathode area and operation which is stable in the long term are achieved. The invention is used in the cost-effective treatment of natural waters, waste waters and special waste waters relatively highly contaminated with heavy metals which arise, for example, in galvanic, chemical, pickling and tanning processes and in the printing industry. <IMAGE>

Description

The invention relates to an electrolysis body with specifically designed carbon fiber mat Electrodes and a method for the electrochemical deposition of heavy metal components Water and contaminated waste water as well as for the removal of especially halogen organic com components.

In principle, electrolysis cells and the processes that run in them are particularly well suited for processing separation of metal ions from solutions. For the trouble-free functioning of such electrolysis cells it is necessary to have a sufficiently high concentration of conductive in the solution to be electrolyzed To ensure particles (ions) and the largest possible active electrode surface constructively to train. This is especially necessary to determine the influence of the Nernst diffusion layer on the To minimize separation speed. This problem plays a major role, particularly with electrolysis cells Role that work with very low concentrated solutions or natural waters and wastewater, such as in the recovery of metals or the detoxification of low concentration Leaching. In addition to the extraordinary increase in the internal resistance of the electrolytic cell sufficient residence time of the solution, water or waste water is necessary to achieve the desired Successful depletion or destruction of toxic or disruptive components of the solution in not to reach harmful concentration ranges. (L. Franke, A. Zimmer, Development tendencies of electrolysis processes under the aspect rising raw material and energy prices, Chemische Technik 36 (1984) 401-444; D. Schab, H. Hein, Electrolytic metal recovery in electrolytic cells with moving bulk cathode, chemical Technique 36 (1984) 451-455).

For example, the natural resistance of the cell in natural water and waste water increases 100 KΩ range. Electrode polarization phenomena occurring in parallel take place the desired and necessary reduction or oxidation of troublesome water, waste water or Electrolyte components preferably developed cathodically hydrogen and anodically oxygen, so that the The effectiveness of the electrolytic process remains very limited or is completely ineffective.

To avoid these problems, a strong electrolyte or liquid has already been proposed generate flow through the cell to reduce the boundary layer or the electrodes to which the electochemical processes take place to get moving. It has also been suggested that Electrode, in most cases the cathode as a fluid bed electrode made of a suitable conductive material train and use in the electrochemical process (DE 22 27 084, EP 02 61 747). Farther Numerous electrode arrangements and designs have been described that are as intimate as possible Ensure contact between the electrode and the liquid (DE 26 30 883 C2, DE 30 51 012 C2).

An electrolytic cell with a flat or curved perforated cell has also been proposed or intentionally rough electrode and a fluidized bed of non-conductive particles, for example sand or  spherical particles with a diameter of 0.5-2 mm (DE 24 45 412). Gas is also known forming electrodes the use of diaphragm cells, more recently as a diaphragm besides conventional astbestdiaphragm especially ion exchange membranes are used and have proven (DE 21 26 430).

A process and the technical solution for carrying it out have recently been specified (DE 40 33 016 A1), through the water intended for drinking water with the help of a catalytic Oxidation or reduction of organic substances and heavy metal compounds of all kinds Catalytic reactions on current-carrying electrodes or in their vicinity destroyed or removed become. The constructive design of this cell and the low conductivity of natural water or, if applicable, the waste water, do not allow safe removal of the heavy metal components another electrochemically induced destruction of the disruptive organic components.

The main deficiency consists first of all in the design of the flow volume formed as an electrode space between the cathode and anode. B. the voltage drop ΔU in a cell construction specified in DE 40 33 016 A1 with an electrode spacing between the cathode and anode of 5 cm and typical resistance values of 100 Ω-100 K Ω cm ^-1 with a current flow of 50 A dm ^-2 , ie 0 , 5 A cm ^-2 according to Ohm's law 1-1000 KV, so that such a proposed system could not work practically, especially not within the parameters specified.

Secondly, the hydrogen generated cathodically in the main reaction would of course become anodic are oxidized according to (1) or the anodically generated oxygen is reduced cathodically according to (2).

H₂ → 2H⁺ + 2e⁻ (1)

O₂ + 4 H⁻ + 4e⁻ → 2 H₂O (2)

This would only aim to remove traces of heavy metals and organic components partially or with fluctuating results.

Previous technical solutions or suggestions are not suitable or able to use natural water or wastewater with different levels of conductive electrolyte components long-term stable and economically justifiable to get rid of traces of heavy detail and toxic organic components, that in natural waters drinking water quality and in wastewater such a depletion Heavy metal components and optionally organic substances is achieved that a safe Further use or initiation into natural processes is possible.

The aim of the invention is to provide a continuously operating electrolysis body which is broad Throughput ranges electrochemically from natural heavy metals and heavy water metal-contaminated wastewater removes toxic traces of heavy metal to the extent that natural water  Drinking water quality and, in the case of waste water, discharge quality into natural processes is achieved.

The object of the invention is achieved in that a known electrolytic cell principle of the type of the diaphragm cell with a divided electrode space applied and using a known defined diaphragm material of the type of an ion exchange membrane to the electrolysis body according to the invention is formed. With him it is achieved for the solution of the task according to the invention that the electrolyzed Liquid with a strongly fluctuating content of toxic heavy metal ions to be depleted or their ionogenic complexes such as lead, cadmium, zinc, mercury, chromium and copper ions is safely lowered into tolerable concentration ranges.

The cell of the electrolysis body according to the invention is designed such that the distance between the anode and the cathode is in the range of 10-50 mm and the cathode is in the form of a conical cylinder ( FIG. 1a). It has surprisingly been found that such an electrode configuration works surprisingly constantly with respect to the desired success of the heavy metal ion depletion in the case of strongly fluctuating heavy metal ion and inert electrolyte content in natural water or waste water. As shown in FIG. 1, the electrolyte body is preferably designed in a cylindrical shape in such a way that a cylindrical electrode known per se is used as an anode in a stable cylindrical tube. To reduce polarization phenomena, this electrode is preferably made of RuO₂-TiO₂-coated titanium expanded metal known per se, but also of perforated carbon. The ion austanschermembrane, designed as a diaphragm, is arranged in the immediate vicinity of the inside of the anode, the elevation membrane being fixed in a stable grid made of an inert material, such as polycarbonate or ceramic, to increase the dimensional stability. An analyte circulates in the anode space thus formed, which either itself consists of components of the wastewater or an electrolyte enriched with salts is sufficient for conductivity. In the interior of the electrolysis body, the three-dimensional cathode according to the invention, consisting of a cone-shaped tube formed from carbon fibers, is arranged in such a way that the distance between the ion exchange membrane and the carbon fiber electrode at the beginning of the cell, ie the entry of the water to be treated, is between 5 and 20 mm and at the end between 10 and 50 mm ( Fig. 2).

According to the invention, an increase in the conical hollow cathode of 1:20 - 1: 100 is preferred 1:20 to 1:50, depending on the concentration of the species to be depleted or the total ion content becomes. The steepness decreases with increasing concentration. The total diameter or the total length of the electrolysis body is freely selectable and will only depend on the flow rate rich liquid, d. H. determines and limits the capacity of the system. The invention Cell construction can also be chosen so that an angular arrangement of the components of the Electrolysis cell is selected. The planar cathode shown as described is then in an angle of 2-10 degrees, preferably 2-4 degrees, based on the position of the ion exchanger Diaphragm membrane, employed.  

The structure of the carbon fiber cathode is also in accordance with the invention. It is manufactured in such a way that in a suitable, stable, inert form or in stable, inert partial forms, carbon fiber mats, made of preferably needle-shaped, good to highly conductive carbon fibers, at a pressure of 100 kPa-5 MPa in layers or all at once with a highly conductive metallic grafted tape or wire are pressed so that a laterally and vertically approximately constant conductive cathode with stochastically pronounced pore structures in the size of 0.05-1 mm is formed ( Fig. 3).

This arrangement according to the invention of the electrodes, in particular the cathode and its structure, ensures that a very large inner cathode surface is created for the cathodic process of depleting toxic heavy metal components, which ensures a high effectiveness of the depletion process of toxic heavy metal ions. Despite the low concentration of ions in natural waters, due to the inventive design of the electrolytic cell in the electrolytic body, there is a justifiable small voltage drop in the electrolytic cell, which at a current density of 1-10 A dm ^-2, depending on the total electrolyte concentration in the range of 1-10 V. lies and is so technically easy to master.

With an electrolysis body according to the invention described above, the copper content of a solution containing 50 mg dm ^-3 Cu ²⁺ ions was experimentally achieved in one step to below 1 mg dm ^-3 Cu ²⁺ . The capacity range, based on the toxic heavy metal component or components to be depleted, is given by the current yield, which was determined experimentally in the current density range from 0.1-1 A dm ^-2 to 5-30% depending on the content of heavy metal to be depleted and the total electrolyte content .

According to (3), this corresponds to a deposition rate of ∼1-2 10 ^-6 eq · s · dm ^-2 , ie related for example

Me′⁺ + 2e⁻ → Me (3)

on the Cu ²⁺ depletion ∼1 mg Cu ²⁺ / s ^-1 dm ^-2 cathode surface.

The only major competitive reaction besides the deposition, the cathodic hydrogen winding according to (1), supported by the nascent nature of hydrogen, the purely reductive Implementation of the heavy metal ions and thus causes an additional depletion.

The inventive cell construction of the electrolysis body makes it surprisingly stable Long-term operation with a very good success with regard to the depletion of toxic heavy metal components achieved. This is apparently due to the fact that initially the electrochemical cathodic reaction including the evolution of hydrogen at the sites with the least Total resistance begins, i.e. H. near the inlet of the water to be treated and Sewage. Due to the local increase in resistance that occurs, an activation of Reduction areas with originally higher resistance until a metastable long-term resistant  State automatically. This process only occurs when the carbon fiber cathode was formed according to the invention before use in the field in such a way that in a more concentrated electrolyte solution a very thin layer of heavy metals or heavy metal nuclei, preferably copper, nickel or zinc, be deposited. Particularly efficient cathode structures are created when the cathodes are like this long polarized until about 0.1 monolayer of metal based on the true surface of the Carbon mat is deposited.

For continuous control of the electrochemical deposition process, it is necessary to either remove the anodically generated active oxygen or, preferably, to treat oxygen-consuming wastewater contaminated with organic substances in synchronism with the cathodic process and to replace the water consumed in the anode compartment. This can be done, as shown in FIG. 4, by an electrolysis body adapter detachably connected to the actual electrolysis body.

The electrolysis body according to the invention with the three-dimensional cotode is operated in such a way that natural polluted water or waste water with an overpressure of 5 to 500 kPa, preferably of 10-300 kPa, flows into the interior of the electrolysis body and begins cathodically here is polarized. When it passes through the three-dimensional carbon mat cathode, it becomes toxic Heavy metal ion component deposited almost completely cathodically. Leftovers are by the cemented nascent hydrogen produced in parallel and held in the cathode fiber braid.

According to the invention, a current density of 0.05-100 A dm ^-2 , preferably from 0.05 to 10 A dm ^-2 cathode surface is selected for this process, which is galvanostatically connected to the electrodes of the electrolysis body by means of known electrical and electronic circuits via insulated electrode feeds become. Depending on the content of heavy metal ions to be removed, which can be in the mg to g range per liter of natural water or waste water and the concentration of naturally dissolved electrolyte components and added in the case of waste water, there is a voltage difference of 2-100 V on the cell body according to the invention , usually from 2-10 V, in the cathode range of approx. -2 V. This potential is completely sufficient according to the electrochemical voltage series of the elements to be able to discharge all toxic heavy metal ions under consideration.

For example, with an electrode body according to the invention when using a weakly acidified copper-containing solution and the parameters: current density 1 A dm ^-2 , electrode resistance stood 3.8 Ω, voltage 4.5 V, flow rate ∇ = 13 dm³ h ^-1, a concentration decrease of 350 mg dm ^-3 Cu ²⁺ to 0.31 mg dm ^-3 Cu ²⁺ and in a second experiment depletion from 50 mg dm ^-3 Cu ²⁺ to 0.03 mg dm ^-3 Cu ²⁺ in the laboratory test. It has proven itself based on the tests to choose a thickness of the three-dimensional carbon mat cathode in the range of 5-50 mm, preferably 5-20 mm. The entire structure of the electrolysis body and its electrical and hydrodynamic operation is extremely simple and therefore very easy to integrate into existing water and waste water systems, as shown in FIG. 5.

The flow rate can easily be varied by varying the pressure difference between the two anodes Partial spaces are accomplished. By connecting the electric according to the invention in parallel or in series cleaning capacity and efficiency can be varied in a wide range. The effectiveness of the electrolysis body can be detected by known metal-metal ion sensors and are displayed.

In the event of exhaustion of the cell capacity of the electrolysis body due to the increase in carbon matt cathode mainly due to dendritic metal deposition or other type Signs of clogging, which can be seen at the latest through a greater pressure drop across the three-dimensional Carbon fiber cathode makes a regeneration of the cell body automatically easy by changing the polarity of the cell after the original anolyte has passed through a more conductive one has been replaced. This process continues until about 90-95% of the metal Components were brought into solution on the cathode.

The collected highly concentrated metal-containing solution can then be worked up on the heavy metals. With the electrolysis body according to the invention and the associated process for the treatment of water and waste water, it is possible in many areas of environmental technology and remediation, in recycling processes and in the extraction of uncontaminated substances such as drinking water, inexpensive, easy-to-use and less labor-intensive systems ( Fig. 5 ) that are capable of depleting or completely removing highly toxic and other heavy metal components.

The electrolysis body according to the invention and the method for treating water and waste water will be explained using an exemplary embodiment. In an electrolysis body described in Fig. 1a of 15 cm in diameter and 50 cm in length, provided with two 25 cm strong connections, heavy metal ion-contaminated wastewater with a total concentration of Cu ²⁺ , Cd ²⁺ and Pb ²⁺ of 45 mg dm ^-3 and passed through the cathode compartment with a total electrolyte content of 0.001 eq. dm ^-3 and electrolytically electrolyzed at a flow rate of 60 dm ^-3 h ^-1 . A current of 1 A dm ^{-2 is} maintained, with a voltage between the anode ( 2 ) and cathode ( 1 ) of 18.7-19.5 V. A cylindrical titanium expanded metal body, which is coated with a thin TiO₂ / RuO₂ layer in a mass ratio of 60:40, serves as the anode ( 2 ). The ion exchange membrane diaphragm ( 3 ), which is located on a shaping ceramic holder, is arranged at a distance of 3 mm. The three-dimensional carbon fiber mat electrode ( 1 ), see also Fig. 2, (mean: 8 the carbon fiber mat, 9 the highly conductive coated metal wire or the band, 10 the ceramic body and 11 the power connection of the cathode), which with a pressure of 50 kPa was pressed into two ceramic holders ( Fig. 3, 4th pre-assigned cathode, 7 : cathode after 50 h operation, 6 cathode after 200 h operation) is selected so that its distance from the diaphragm in the constructive arrangement, as in Fig. 1a shown, is 8 mm at the inlet opening and increases to 16 mm at the end of the electrolysis body. The water pressure at the inlet opening is 210 kPa, the pressure drop at the outlet opening is 25 kPa. The heavy metal ion spectrum is depleted to a total concentration of 6 µg dm ^-3 . A circulation pump ( 5 ) moves the anolyte.

Claims (4)

1. Continuously working electrolysis body and method for the electrochemical removal of toxic heavy metal components and component spectra from natural heavy metal-contaminated waters and heavy metal-contaminated wastewater with preferably low total electrolyte concentration according to the divided cell principle with an ion exchange membrane as a diaphragm and separate anolyte circuit, characterized in that an between themselves and cathode between 10 and 70 mm, preferably between 10 and 30 mm, and that the cathode is formed as a three-dimensional electrode made of pre-assigned carbon fiber mats in a preferably tapered cylindrical but also inclined planar configuration, with the distance between the diaphragm and the outer surface the three-dimensional cathode at the inlet opening of the water and waste water to be electrolyzed in the range between 5 and 20 mm and at the end of the cell body It moves between 10 and 50 mm while maintaining an increase in the hollow cathode body or planar cathode mat of 1:20 to 1: 100, preferably 1:20 to 1:50, and that the flow rate of the water to be electrolyzed is so is chosen that a deposition speed of heavy metal components to be removed does not exceed 10 ^-5 · eq s ^-1 dm-2 cathode surface, but is preferably selected in the range of 1-5 · 10 ^-6 eq · s ^-1 dm ^-2 cathode surface. 2. Electrolysis body and method according to claim 1, characterized in that the cathodic heavy metal deposition takes place in a galvanostatic electrolysis regime in the current density range from 0.05-100 A dm ^-2 cathode surface, preferably from 0.05 to 10 A dm ^-2 , cathode surface . 3. Electrolysis body and method according to claim 1, characterized in that the three dimes sional cathode body is so pronounced that the carbon fiber mat cathode in its Configuration is generated by a pressure of 100-5000 kPa and that an uneven distributed pore structure of 0.05-1 mm is selected. 4. Electrolysis body and method according to claim 1 and 3, characterized in that the full constantly shaped, three-dimensional carbon fiber mat cathode before use cathodic with one containing heavy metals, preferably one containing copper, nickel, zinc or lead Solution or a solution from a mixture of the heavy metal components as long as polarized until there is a lot of a heavy metal component or heavy metal components which has a surface coverage of 0.1 to 1 monolayer of real surface, preferably 0.1 to 0.5 monolayer.