FR2864861A1 - Recycling of cathode tubes by extraction and separation of the glass and the electroluminescent constituents of the tubes - Google Patents

Abstract

The integrated recycling of cathode tubes consists of: (A) the opening of the cathode tubes by laser; (B) the dry cleaning of the tubes with surface treatment agents; and (C) the recycling of the luminophores by an acid-basic route in the presence of fluorides.

Description

2864861 1

  The production of electrical and electronic equipment is one of the fastest-growing areas in the Western world.

  Technological innovation and market expansion continue to accelerate the process of replacing products with a shelf life of no more than three years.

  In 2000, French production of end-of-life electrical and electronic waste was estimated at 1.5 million tonnes, half of which came from households. Since then, this figure has increased by 3 to 5% per year.

  It is estimated that 400 000 T / year is the European deposit of this waste, of which 90% is still going to landfill.

  This is why new directives strongly control this waste; the most recent being Directive 2002/96 / EC of 27 January 2003.

  These new management rules for these products impose minimum recycling rates. Now among the electrical and electronic equipment at the end of life, the cathode ray tube represents a relatively large weight.

  To achieve the overall recycling rate it is imperative to achieve high recycling rates for the CRT.

  A color cathode ray tube comprises a slab glass containing, inter alia, oxides of barium and strontium and a glass of cone containing lead oxide in large quantities.

  These two parts are interconnected by a joint and are coated with so-called "functional" layers consisting of metal oxides, rare earths, graphite and iron.

  Metal parts in the form of plates are placed inside the tubes before closing.

  In particular, the layer deposited on the internal face of the slabs consists of electroluminescent materials based on Zinc, Cadmium, Yttrium and Europium.

  All of these compounds tend to impart a toxic character to the entire cathode tube.

  That is why various solutions have been proposed for the treatment of these cathode ray tubes.

  US Pat. No. 4,885,833 describes a process for recycling the tubes by grinding followed by treatment with fluoroboric acid followed by selective separation of the various components.

  This process has several disadvantages by the mixing of glasses, the dissolution of metal parts and the use of fluoroboric acid.

  In particular, this acid has shown its limits in the treatment of waste especially through all attempts to industrialize processes (especially in the recycling of batteries).

  The glasses obtained by mixing the slab (based on barium) and the cone (based on 5 lead) are difficult to recover as they are.

  It was therefore essential to open the tubes and separate the tubes. The first way used is the diamond saw. This technique ensures a good opening but is accompanied by large emissions of glass particles and requires manual operations.

  It is to overcome this drawback that patent DE4234706 describes a method of opening and separating the two components by means of a heating wire.

  This separation can take place only if notches are made on the entire perimeter of the cathode ray tube. This type of operation limits productivity by its rate and requires the very precise laying of the wire after making the notches.

  Moreover, the luminophore layer composed of electroluminescent materials is currently removed by any physical means and the resulting powders are sent to a storage center for toxic waste.

  There is still no operational industrial process that offers an outlet for these powders.

  In general, the oxalate processes for the separation of rare earths have been known for a very long time since they have been proposed since the beginning of the 1900s and have been widely used (C.James, J.Am.Chem.Soc, vol 30 979, 1908). They are effective for mixtures of lanthanum, thorium, yttrium and cerium).

  The complete methods are widely described in Journal of SocChem.Eng, (R. W Urie, 46 (437) year 1947 and ES Pilkington 46 (387) 1947) and in J. Appt. Chem. [ES Pilkington 2 (265) year 1952 and 4 (568) year 19543.

  On the other hand, the presence of zinc, cadmium and yttrium singularly complicates Operations. In addition, the precipitate, very fine, leads to impurities (including the anions of the acid attack).

  Finally, the formation of oxalate complexes with other products, leads to overconsumption of oxalate.

  This is why various processes have been proposed.

  We have already seen that patent US4858833 describes a process for recycling these powders fluoroborically followed by a precipitation of oxalates. In addition to the disadvantages of fluoroboric acid, the production of valuable oxides requires the calcination of oxalates leading to a contribution to the emission of CO2.

  The patent DE19918793 describes a process for recycling these powders by etching with nitric acid followed by a carbonate precipitation and calcination to obtain oxides. Here too, the disadvantages are mainly related to emissions of nitrogen oxides and CO2.

  The present invention aims to overcome these various disadvantages.

  According to three implementations, the invention consists in associating a method of opening cathode ray tubes, a surface treatment method of cone glasses and a phosphor recycling process (FIG.

  1. Opening the cathode ray tubes According to a first application of the present invention, the cathode ray tubes are opened by means of a CO2 laser with a power of between 300 mW and 3 kW and a wavelength of between 10 and 11 pm

  A first advantage lies in the fact that the opening does not require an initial notch which has the effect of considerably reducing the opening time.

  A second advantage is that the power of the laser is sufficient to completely destroy the seal which allows a direct opening to the slab-cone junction while the opening by saw or heating wire leaves about a centimeter of the slab glass which is related to the body of the cone.

  Once the cathode ray tubes open, for a good valuation of the glasses it is important to completely eliminate all the coating products that are located on the inner face of the slab and on the inner and outer faces of the cones.

  In order to protect the operators at the workstation and the effectiveness of the surface treatment, techniques such as direct dry brushing are rejected. In the interest of protecting the environment and eliminating water from large amounts of waste, washing with water is discarded.

  II - Surface Cleaning of the Glasses In a second application of the present invention, the surface oxides are removed by dry treatment using a solid state cleaning agent. The agents used are: - steel shot - sodium bicarbonate - calcite.

  The three products have given satisfactory results insofar as the layers are completely eliminated especially on the layers where they are very adherent; as illustrated in FIGS. 2/7 and 3/7, which take an electron microscope photograph of a cone glass after treatment.

  These three products are chosen for the ease of subsequent processing of the mixed fractions comprising the surface treatment agent and the products resulting from the surface cleaning.

  In the case of the use of the shot for the slab and for the cone, the products obtained are treated by magnetic separation to obtain separately the phosphors or the other oxides on the one hand and the steel shot on the other hand .

  In the case of use of sodium bicarbonate or calcite for the treatment of the slab, these products are removed during the treatment of phosphors, object of the third implementation of the present invention.

  I = - Recycling phosphors According to a third embodiment of the invention, the phosphoric powders are treated by a route comprising neither oxalate nor ammonia.

  The electroluminescent assembly comprises an aluminum foil and a phosphor powders layer. A 500 micron sieve separates the vast majority of the powders.

  The fraction greater than 500 microns consists mainly of aluminum strip as shown in Figures 4/7 (scanning electron microscopy).

  The fine fraction consists mainly of zinc and yttrium with presence of europium, iron and manganese as shown by the observation under the electron microscope (Figure 5/7 and Figure 6/7) associated with a microanalysis. In terms of phase distribution, zinc is involved as sulphide while yttrium and europium are present as oxide and oxysulfides as we have shown by X-ray diffraction analysis. After the sieving operation, the actual chemical process is carried out.

  This process comprises the following steps: i - etching step The powder resulting from the treatment described in II is subjected to dissolution with 2N sulfuric acid at a temperature set at 70 ° C. The concentration of the acid may vary. from 15 to 35%. But for reasons of compromise between reaction rate and dilution it can be set at a value between 17% and 22%.

  The solution resulting from the acid attack is subjected to filtration to separate the liquor containing the metals from the insoluble residues.

  2 - fluoridation neutralization step The liquor is then neutralized to a pH between 2.8 and 4.4 by means of sodium hydroxide, potassium hydroxide, lime or magnesia. The optimal value of neutralization for a good implementation of the subsequent operations was found equal to 3.4.

  The neutralization can advantageously be carried out using soda or potash with a concentration of between 10 and 35%.

  The neutralized solution is then mixed with a solution of alkaline fluoride heated to 50 ° C and in a stoichiometric ratio equal to that of Yttrium + Europium content increased by 10% by weight.

  The precipitate formed is separated and then washed with industrial water at a temperature between 30 and 40 C.

  This washing water is used at the top of the process to prepare 2N acid from concentrated acid.

  3 - Hydroxylation step The solid is then suspended in a 30% sodium hydroxide solution and a whitish precipitate is formed. After filtration, the slightly alkaline fluoride solution is reused in step 2; while the solid is dried at 105 C.

  A schematic diagram of this process is shown in Figure 7/7.

  IV -Recycling glasses Cathodic tubes consist of two types of glass: 35 - a lead glass for the cone a barium glass and sometimes strontium for the screen tile.

  2864861 6 For a good valuation the glasses must be treated separately. To avoid pollutions, in particular barium glass by lead, the melting is carried out in an externally cooled induction coil, thus forming a self-crucible.

  This self-crucible has many advantages including the formation of a layer of glass fixed around the crucible which avoids any use of refractory and any pollution of the glasses.

  To obtain a constant composition at the outlet, the silica, barite and strontium carbonate titers are adjusted by adding them to the crucible.

  The lines of the high frequency electric field cause turbulence in the molten bath which induce the enormous advantage of homogenizing the molten material. This makes it possible to obtain a uniform melting and consequently, at the outlet, a glass of homogeneous composition with a total absence of unmelted material.

Claims (7)

  1- integral recycling method of the cathode ray tubes, characterized in that it allows the recycling of the glasses that make up said cathode ray tubes and phosphors deposited on the internal face of the screens by means of the combination of steps a. opening said cathode ray tubes by means of a laser source b. dry cleaning with surface treatment agents c. phosphor recycling by acid-base in the presence of fluorides.   2- method of integrated recycling of cathode ray tubes according to claim 1 characterized in that the surface treatment of the glasses is carried out by means of surfactant preferably selected from steel shot, baking soda and calcite.   3-method of integral recycling cathode ray tubes according to any one of claims characterized in that the electroluminescent powders are treated sulfuric acid with a concentration of between 15% by weight and 35%, but preferably between 17% and 22% in weight.   4-method of integral recycling cathode ray tubes according to any one of claims characterized in that the separation of yttrium and europium is effected by means of a sodium or potassium fluoride at a pH between 2 , 8 and 4.8, but preferably close to 3.4.   5 - method of complete recycling cathode ray tubes according to any one of claims characterized in that the extraction of yttrium and europium is in the form of hydroxide by alkalinization with soda or potassium hydroxide concentration included between 10% by weight and 35% by weight.   6. The method of complete recycling of the cathode ray tubes according to any one of the preceding claims, characterized in that the extraction of yttrium and europium leads to the regeneration of reusable alkaline fluoride at the head of the process in the separation of said yttrium and europium.   The method of integral recycling of cathode ray tubes according to any of the claims characterized in that the separated glasses are melted by means of an induction crucible designed so as to produce a self-crucible.   8- method of complete recycling cathode ray tubes according to any one of claims characterized in that the composition of the glasses is adjusted by adding silica, baryta and strontium carbonate directly into the melting crucible.