FR2900075A1 - Removing mercury components from electronics waste including liquid crystal screens, by fragmenting, eliminating mercury vapor via filter, separating fragments by size and rinsing with liquid - Google Patents

Abstract

A method for removing mercury (Hg) or Hg-containing materials from electronics waste involves fragmenting the waste to break up the Hg-containing components and release Hg vapor and other Hg-containing materials. The volatile Hg vapors are eliminated via a filter; and the non-evaporated Hg and other Hg compounds are eliminated by a combination of (i) multistage separation based on fragment characteristics and (ii) rinsing the fragment surfaces with liquid.

Description

The present invention relates to a process for the removal of mercury and

  mercury-containing substances in electronic waste containing liquid crystal displays containing mercury or other sources of mercury, in which mercury-containing wastes are first fragmented in a device suitable for breaking down mercury-containing components, such that mercury vapors and other mercury-containing substances are released, wherein the volatile mercury vapors are removed by a filter and wherein the unvaporated mercury and other mercury-containing substances are removed by the combination of multiple separation according to a characteristic property of the fragments and a rinsing of the surface of the fragments by means of a liquid.

  Such a method is not known in the literature. It reveals, however, that the most important source of mercury in electronic waste is the backlit luminescent tubes of liquid crystal displays, also known as backlights (A. Mester, Fraunholcz N., A. van Schaik, MA Reuter : Characterization of the Hazardous Components in End-of-Life Notebook Displays, EPD Congress 2005, Ed ME Schlesinger TMS (The Minerals, Metals & Materials Society) San Francisco, CA 13-17 February, 2005).

  The above source also discloses that backlight mercury is present in the fluorescent powder within the luminescent tube and that at least a portion of the mercury is volatile vapors.

  Removal of mercury-containing backlights by manual disassembly of liquid crystal displays is problematic. Backlights are difficult to access because they are often protected by several layers of materials such as the outer surface of the screen, a plastic film and an aluminum plate. Disassembly of backlights requires a lot of time. An aggravating factor is that some older models of LCDs do not have a backlight, other older models often have two backlights, while newer models still come with a single backlight. In addition, the position of the backlights in the LCD 30 differs from one manufacturer to another and sometimes even from one model to another. For all these reasons, manual disassembly is economically unattractive. In the study cited above, 150 LCDs for laptops to be recycled were manually removed. The study indicates that 17% of the backlights in this sample were already broken upon arrival. These backlights were broken during the collection procedure. This means that mercury vapor can be released during the dismantling of such liquid crystal displays, which has important consequences for workplace safety.

  The object of the present invention is to provide a method by which mercury and mercury-containing substances of electronic waste having liquid crystal displays containing mercury or other sources of mercury can be safely and effectively removed.

  To achieve the above objective, the invention provides a method as described in the preamble, characterized in that the treatment begins with a fragmentation of the electronic waste containing mercury. This fragmentation is intended to break down mercury-containing components such that mercury and mercury-containing substances are released.

  In a preferred embodiment, the fragmentation is carried out in steps to allow controlled release of mercury.

  In another preferred embodiment, mercury-free or at least mercury-less components are separated from the fragmented mixture between two fragmentation steps. In this way, the precipitation of mercury and mercury compounds on non-mercury containing electronic waste components is minimized.

  According to the process of the invention, the mercury vapors and volatile mercury compounds released during the fragmentation are removed and captured.

  The amount of mercury vapor released can be influenced by increasing or decreasing the temperature before, during, and after fragmentation from room temperature. More mercury evaporates at high temperatures than at low temperatures.

  According to a preferred embodiment, the mercury vapors released and a portion of the mercury compounds in solid form are aspirated, filtered from the process air and stored in one or more steps.

  According to another preferred embodiment, the mercury vapors are chemically bonded to solid particles.

  According to a particular embodiment, the chemical bonding and removal of mercury compounds resulting from the treatment are carried out at least partially in separate steps.

  According to the method of the invention, fragments from the fragmentation are separated into at least two fractions according to a characteristic particle size. The purpose of this separation is to concentrate the powder containing mercury in a fine fraction. In addition, backlights which may be incompletely fragmented may be taken up in a medium fraction. Fragments of electronic waste components that do not contain mercury sources are concentrated in a coarse fraction. If fragments from fragmentation do not have a significant amount of incompletely fragmented backlights or other mercury-containing components, the formation of an average fraction may be omitted.

  Preferably, the particles of a fraction having the smallest dimensions have a smaller dimension of less than 1 mm and / or the fragments of a fraction of intermediate dimensions have a smaller dimension of between 1 and 10 mm.

  According to the process of the invention, backlights which are optionally incompletely fragmented are crushed selectively during the first stage of fragmentation, so that mercury-containing substances can be removed.

  According to the process of the invention, the nonvolatile mercury compounds are rinsed with a liquid from the surface of the fragmented electronic waste fragments, whereby the mercury compounds can then be separated from the rinsing liquid. using a separation method based on a characteristic particle size.

  According to a preferred embodiment, the rinsing liquid used is water.

  The invention is described below on the basis of a drawing and an exemplary embodiment.

  Figure 1 shows a treatment scheme according to a preferred embodiment of the method of the invention. Treatment begins with fragmentation (A), in which the mercury-containing electronic waste is fragmented such that the mercury-containing components are broken down in the waste and the resulting fragments are largely expelled from the other components. not containing mercury. This can be achieved by means of cutting or percussion movements, or a combination of these two types of movements. For example, a rotating rotary shear may be used for this purpose.

  The mercury vapors (2) possibly released during the fragmentation are sucked up and filtered from the ventilation air (E). A suitable method for this purpose is to pass the mercury vapor through an activated carbon filter. Clean ventilation air (3) can be returned to the treatment or released into the atmosphere. The eliminated mercury (4) is stored and evacuated.

  An excellent absorption of mercury from the ventilation air is obtained in particular with an activated carbon filter impregnated with sulfur.

  The separation of mercury vapors can be further promoted by locally cooling the ventilation air.

  Another way of separating the mercury vapors from the ventilation air is to pass the mercury-containing air stream into a mercury-absorbing liquid, such as, for example, an aqueous solution of potassium dichromate (K 2 Cr 2 O 7).

  After aspiration of the mercury vapors, the pieces from the fragmentation are separated into two, three or even four fractions based on a characteristic particle property.

  A suitable method for this purpose is to separate the particles based on their rate of falling into the air or water. A ballistic separator, air cyclone or zigzag type can for example be used for this purpose. All of these separation methods are described in the literature.

  Another suitable method for the above-mentioned classification is the separation of particles on the basis of a characteristic particle size using a sieve.

  Figure 1 shows an embodiment in which the fragments are separated in air in three fractions (B): a coarse fraction 6, an average fraction 7 and a fine fraction 8. The characteristic size at which the fragments of the classification quoted above are separated is chosen such that the fragments of the coarse fraction (6) do not contain a source of mercury. A portion of the mercury vapor and the mercury-containing powder released during the fragmentation can, however, be deposited on the surface of the fragments.

  For example, the particles of the average fraction 7 have a smaller dimension of between 1 and 10 mm, and the particles of the fine fraction 8 have a smaller dimension of less than 1 mm.

  FIG. 1 shows an embodiment in which the coarse fraction (6) is rinsed with a rinsing fluid, for example water, to remove the mercury deposited on the surface of the fragments. An appropriate installation for this purpose consists of a screen comprising a device for spraying the fragments with clean rinsing liquid and a device for receiving and discharging used rinsing liquid. The openings of the rinsing sieve have a slightly smaller dimension, so that the fragments can not pass through these openings while the rinsing liquid and the mercury-containing substances can, on the contrary, pass through them. The rinsed coarse fraction 9 is a final product of the treatment of the present invention.

  As shown in FIG. 1, the average fraction obtained during the above-mentioned separation is conducted to a second fragmentation step (C) in which optionally incompletely fragmented mercury-containing components are again fragmented to expose the components. containing mercury, the pieces containing no mercury being refragmented as little as possible. For example, a hammer mill may be used for performing such selective fragmentation, wherein the speed of the hammers is selected such that all mercury-containing components (or at least a large part thereof) are crushed, while the mercury-free fragments are not crushed or ground to a lesser extent.

  After the second fragmentation step, the average fraction (16) is rinsed in the same way with a rinsing liquid as described above for the coarse fraction (6).

  The fine fraction of the separation (8) is conducted with the rinsing liquid streams containing mercury (10) and (17) to a separation step (G), in which this fraction is again separated into a coarse fraction (9 ') and a fine fraction (11). The parameters of this separation step are determined so that the particles containing little or no mercury are concentrated in the coarse fraction, which constitutes a second final product of the treatment after removal of the water (9 '). The fine fraction (11) constitutes a suspension in which the mercury-containing substances are concentrated.

  As shown in FIG. 1, the mercury-containing substances are separated from the suspension (11) by an additional separation step (I). This separation can be facilitated by agglomerating the solid particles of the suspension (H) with a suitable flocculant (12) to form larger particles. The clean process water (15) can then be returned to the treatment. The filter cake containing mercury (14) is recovered and discharged.

  EXAMPLE A batch of used laptops produced between 1985 and 2001 was used. A mass of 222 kg of laptops from the aforementioned batch was fragmented into a 4-shaft rotary shear equipped with a 50 mm diameter round-hole internal sieve, with the knife shafts rotating at a speed of 23 rotations per minute. Fragmentation was carried out at an ambient temperature of 6 ° C. An airtight receiving pan was placed under the outlet mouth of the rotary shear to receive fragments of the fragmented computers. All interstices and lateral openings of the rotary shear were covered during the test, except for a small opening in the 100 mm x 440 mm feed funnel to drive the vent air in a controlled manner via the feed funnel and fragmentation chamber to the receiving tray. Ventilation air was then passed through an opening in the side wall of the receiving pan to an activated carbon filter impregnated with sulfur. Mercury concentrations before and after the activated carbon filter were measured regularly using a calibrated mercury vapor probe. In unfiltered ventilation air, mercury concentrations between 10 and 19 g / m3 (n) were measured, while values between 0 and 4 gg / m3 (n) were measured in filtered air .

  After 48 hours of aspiration, fragments of the fractions of different particle sizes were sieved and the mercury content of each fraction was determined using a standardized assay method. A round perforation drum screen was used for screening at 10 mm and square mesh flat vibrating screens were used for screening at 1 mm, 2 mm and 3.5 mm.

  Table 1 shows that 33.0% of the mass of mercury-containing solids is concentrated in the 0 to 1 mm fraction, which contains only 2.2% of the total mass of the fragments. The mercury content of this fraction is 10.8 ppm.

  Table 1 further shows that the mercury content of the 2 to 10 mm fraction is higher than the mercury content of both the 1 to 2 mm fraction and the> 10 mm fraction. The manual sorting analysis shows that the fraction of 2 to 10 mm has incompletely fragmented backlights, whereas no incompletely fragmented backlight was found in fractions of 1 to 2 mm and> 10 mm.

  A rinse test was then performed on 6.4 kg from the fraction> 10 mm to test the removal of the mercury-containing powder adhering to the surface of the fragments. The test set consisted of a flat square mesh vibratory screen with a mesh width of 5 mm, a receiving tray for rinsing water and a spraying device. The material was deposited on the sieve and thoroughly rinsed with a volume of 22 liters of tap water applied with a pinched hose. The mercury content of the sample after rinsing was 0.28 ppm while the mercury content was 0.49 ppm prior to rinsing.

  It will be clear that the invention is not limited to the description which precedes and is shown in the figure.

Claims (13)

  1. A process for removing mercury and mercury-containing substances from electronic waste containing liquid crystal displays containing mercury or other sources of mercury, wherein the mercury-containing waste is first fragmented in a device suitable for breaking mercury-containing components such that mercury vapors and other mercury-containing substances are released, wherein the volatile mercury vapors are removed by a filter and wherein the unvaporated mercury and other compounds of the mercury are removed by the combination of a multiple separation step according to a characteristic property of the fragments and a step of rinsing the surface of the fragments with a liquid.   2. Method according to claim 1, characterized in that the characteristic particle property used for the separation comprises a characteristic dimension of the fragments.   3. Method according to claim 2, characterized in that the characteristic particle size used for the separation comprises the smallest dimension of the fragments.   4. Method according to claim 2 or 3, characterized in that the fragments are separated into at least two fractions.   5. Method according to one of the preceding claims, characterized in that a ballistic separator is used for the separation of the fragments.   6. Method according to one of claims 3, 4 or 5, characterized in that the particles of a fraction having the smallest dimensions have a smaller dimension of less than 1 mm.   7. Method according to one of claims 3, 4 or 5, characterized in that the fragments of a fraction of intermediate dimensions have a smaller dimension of between 1 and 10 mm. 30   8. Method according to claim 7, characterized in that the fragments of intermediate dimensions are subjected to a repeated fragmentation step.   9. 2. Method according to claim 1, characterized in that an activated carbon filter, preferably impregnated with sulfur, is used for the separation of mercury vapors.   10. Method according to one of the preceding claims, characterized in that the unvaporated mercury and non-volatile mercury compounds of the surface of the fragments are rinsed with a rinsing liquid.   11. The method of claim 10, characterized in that the rinsing liquid used comprises water.   12. Method according to one of the preceding claims, characterized in that the mercury-containing substances are separated from the rinsing liquid on the basis of a characteristic property of the mercury-containing substances.   Process according to claim 12, characterized in that the characteristic property used for the separation of the mercury-containing substances from the rinsing liquid has a characteristic particle size.