WO2011137268A1

WO2011137268A1 - Method for recovering tellurium from module comprising cadmium telluride

Info

Publication number: WO2011137268A1
Application number: PCT/US2011/034410
Authority: WO
Inventors: Jungang Zhang; Yongwei Sun; Chengquian Zhang; Qunjian Huang; Wei Cai; Peter Louis Andresen
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 2010-04-30
Filing date: 2011-04-29
Publication date: 2011-11-03
Anticipated expiration: 2012-10-30
Also published as: CN102234811A; CN102234811B

Abstract

A method for recovering tellurium from a module comprising cadmium telluride, comprises: contacting the module comprising cadmium telluride with an electrolyte solution at a pH greater than about 9; contacting a counter electrode with the electrolyte solution; and applying a voltage differential between the module and the counter electrode; whereby tellurium migrates from the module and is deposited on the counter electrode.

Description

METHOD FOR RECOVERING TELLURIUM FROM MODULE COMPRISING

CADMIUM TELLURIDE

BACKGROUND

[0001] The invention relates generally to a method for recovering tellurium from a module comprising cadmium telluride. The invention specifically relates to a method for recovering tellurium from a photovoltaic waste device comprising a cadmium telluride film.

[0002] Photovoltaic devices, e.g., cadmium telluride solar cells, utilizing sustainable, clean and recyclable solar energy are more and more welcome due to more and more stringent shortage problems of non-recyclable energy resources. Recycling technologies to retrieve tellurium and cadmium from cadmium telluride solar cell wastes, e.g., spent cadmium telluride solar cells and manufacturing wastes of cadmium telluride solar cells, is thus a hot topic too.

[0003] Currently available recycling approaches majorly involve crushing cadmium telluride solar cell wastes, reacting crushed cadmium telluride solar cell wastes with acidifiers and/or oxidizers, and separating and collecting tellurium and cadmium. These methods are usually achieved in multiple steps and are thus complicated. In addition, these methods crush the cadmium telluride solar cell wastes to recover <0.05% fractional weight metals from a relatively large glass/plastics matrix and seem not economical.

[0004] It is reported that an electrochemical cell using sulfuric acid as an electrolyte may be applied to remove cadmium telluride from the cadmium telluride solar cell waste and to retrieve on one electrode a cadmium telluride film of composition ranged from nearly stoichiometric cadmium telluride to a 1 :6 ratio for cadmium/tellurium, depending on the applied potential, stirring rate and cadmium concentration in the electrolyte. The report does not detailedly describe how experiments are done, so it is hard to reproduce the experiments. Simulation experiments, however, have been tried and show that it is hard to get cadmium telluride of the quality to be used directly as material for manufacturing the cadmium telluride solar cell. In addition, when trying to recover tellurium individually in the simulation experiments, it is found that pure tellurium can only be achieved in a very narrow low pH value range of the electrolyte, possibly because both tellurium and cadmium exist in the electrolyte in ionic phases in sulfuric acid and both have tendencies to deposit on the electrodes on similar conditions, thereby becoming contaminations to each other, especially when the ionic concentration in the electrolyte changes with the progress of the deposition. It is usually difficult to maintain a very narrow range of pH values of the electrolyte in industrial applications and in turn it is difficult to get reliable qualities of pure tellurium.

[0005] Therefore, a new method needs to be developed. BRIEF DESCRIPTION

[0006] In one aspect, the invention relates to a method for recovering tellurium from a module comprising cadmium telluride, comprising: contacting the module comprising cadmium telluride with an electrolyte solution at a pH greater than about 9; contacting a counter electrode with the electrolyte solution; and applying a voltage differential between the module and the counter electrode; whereby tellurium migrates from the module and is deposited on the counter electrode.

[0007] In another aspect, the invention relates to a method for recovering tellurium from a solar cell waste comprising a cadmium telluride film, comprising: contacting the solar cell waste comprising the cadmium telluride film with an electrolyte solution at a pH greater than about 9; contacting a counter electrode with the electrolyte solution; and applying a voltage differential between the solar cell waste and the counter electrode; whereby tellurium migrates from the solar cell waste and is deposited on the counter electrode.

DETAILED DESCRIPTION

[0008] In the following description, well-known functions or constructions are not described in detail to avoid obscuring the disclosure in unnecessary detail. [0009] Approximating language, as used herein throughout the specification and claims, may be applied to modify any quantitative representation that could permissibly vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as "about" or "substantially", is not to be limited to the precise value specified. In some instances, the approximating language may correspond to the precision of an instrument for measuring the value.

[0010] Any numerical values recited herein include all values from the lower value to the upper value in increments of one unit provided that there is a separation of at least 2 units between any lower value and any higher value. As an example, if it is stated that the amount of a component or a value of a process variable such as, for example, temperature, pressure, time and the like is, for example, from 1 to 90, preferably from 20 to 80, more preferably from 30 to 70, it is intended that values such as 15 to 85, 22 to 68, 43 to 51, 30 to 32 etc. are expressly enumerated in this specification. For values which are less than one, one unit is considered to be 0.0001, 0.001, 0.01 or 0.1 as appropriate. These are only examples of what is specifically intended and all possible combinations of numerical values between the lowest value and the highest value enumerated are to be considered to be expressly stated in this application in a similar manner.

[0011] In one aspect, the invention relates to a method for recovering tellurium from a module comprising cadmium telluride, comprising: contacting the module comprising cadmium telluride with an electrolyte solution at a pH greater than about 9; contacting a counter electrode with the electrolyte solution; and applying a voltage differential between the module and the counter electrode; whereby tellurium migrates from the module and is deposited on the counter electrode.

[0012] In some embodiments, the module is a photovoltaic waste device and comprises a cadmium telluride (CdTe) film and an encapsulation glass layer adjacent to the cadmium telluride film. The method further comprises removing the encapsulation glass layer by heating the photovoltaic waste device to expose the cadmium telluride film before contacting the module with the electrolyte solution. [0013] In some embodiments, the electrolyte solution comprises alkali, such as sodium hydroxide and potassium hydroxide. The temperature of the electrolyte solution is about 80 °C and the voltage differential is about 2.5 V.

[0014] Electrolysis reactions on the module and the counter electrode while applying the voltage differential between the module and the counter electrode include:

On the module: CdTe - 6e^" -> Cd²⁺ + Te⁴⁺

Te^2" - 2e^" ->Te - 2e^" ->Te²⁺ - 2e^" ->Te⁴⁺

On the counter electrode: Te⁴⁺ + 4e^~— > Te

Te⁴⁺ + 2e^" ->Te²⁺ + 2e^" -->Te

[0015] In such a way, cadmium telluride dissolves from the module and tellurium migrating from the module is deposited on the counter electrode.

[0016] On the other hand, after migrating from the module, cadmium tends to precipitate out from the electrolyte solution as cadmium hydroxide because of the low solubility of the cadmium hydroxide, while tellurium tends to form HTe03^~, or H₂Te0₄ ^2". In such a way, cadmium will not compete with tellurium for deposition and pure tellurium may be recovered on the counter electrode. Cadmium hydroxide may be purified by techniques known by persons having ordinary skill in the pertinent art to obtain pure cadmium.

[0017] The counter electrode may be made of any electrically conductive materials suitable for use in a counter electrode in the electrolyte solution. For example, the counter electrode may comprise at least one of platinum, graphite, copper, aluminum, and iron.

[0018] The electrolyte solution may be any suitable ionic solution and may comprise, for example, at least one of sodium hydroxide solution, sodium sulfate solution, potassium sulfate solution, N-butylpyridinium tetrafluoroborate, N-ethylpyridium bromide, 4-amidinopyridinium chloride, 3-amidinopyridinium chloride, 1- acetonylpyridinium chloride, and 1 -aminopyridinium iodide. [0019] In some embodiments, reaction conditions, such as temperature and pH value of the electrolyte solution and voltage differential applied between the module and the counter electrode may be adjusted according to actual needs to facilitate dissolving of cadmium telluride from the module and deposition of tellurium on the counter electrode and shorten the reaction time.

[0020] The following examples are included to provide additional guidance to those of ordinary skill in the art in practicing the claimed invention. Accordingly, these examples do not limit the invention as defined in the appended claims.

General process

[0021] The experiments were carried out in lab scale equipments.

[0022] A CHI electrochemical workstation (from Shanghai Chenhua Instrument Co. Ltd., China) was used to apply the voltage differentials and control reaction times in the experiments.

[0023] Thin film cadmium telluride solar panels (supplied by First Solar, Inc., FS- 272, 72.5 W) were cut into pieces of 2x10 cm² sizes. After cutting, the cadmium telluride panel pieces were heated at 450 °C for 10 minutes to remove an encapsulation glass layer and expose the cadmium telluride film.

[0024] The cadmium telluride panel piece without the encapsulation glass layer was put into and contacted with the electrolyte solution to be used as an electrode. A platinum foil having a size of 2x10 cm² was put into and contacted with the electrolyte solution to be used as a counter electrode.

[0025] A voltage differential was applied between the cadmium telluride panel piece and the platinum foil using the CHI electrochemical workstation to cause electrolysis, i.e., tellurium migrating from the cadmium telluride panel piece and deposited on the platinum foil.

[0026] After electrolysis, energy disperse spectroscopy (EDS) and/or inductive coupled plasma emission spectrometer (ICP) analysis were used to analyze materials deposited on the counter electrode (platinum foil) and the weight percentage of deposited tellurium versus all of the deposited materials were given out.

Comparative Example 1 :

[0027] A series of experiments was conducted where aqueous sodium sulfate solution (analysis rate (AR), 0.2 M, from sinopharm chemical reagent Co., Ltd. (SCRC), Shanghai, China) was used as the electrolyte solution. Sulfuric acid was added to adjust the pH value of the electrolyte solution. Silicon oil bath was used to increase the temperature of the electrolyte solution where the temperature was not room temperature (RT).

[0028] Voltage differentials applied between the electrodes, the temperatures of the electrolyte solutions, and the pH values of the electrolyte solutions in this series of experiments are shown in table 1 below. Each of the experiments was completed within about 5 hours. Weight percentage of tellurium on the counter electrode in each of the experiments was obtained after ICP analysis except the last one experiment used EDS analysis instead of the ICP analysis and are all shown in table 1.

Table 1

2 80 1 67

2.5 80 0.5 100 (EDS)

[0029] As is seen from table 1, when the pH values of the electrolytes were in a range of 0.5 to 2.1, pure tellurium (e.g., higher than 85 wt%) was only obtained in a relatively narrow low pH value range of from 0.5 to 1.5 and the average weight percent of deposited tellurium decreases with increasing the pH values of the electrolyte solutions. In other words, the difficulty of obtaining pure tellurium increases with increasing the pH values of the electrolyte solutions.

Comparative example 2:

[0030] Another series of similar experiments was conducted at room temperature, in which sodium sulfate solution was used as the electrolyte solution and the pH values of the electrolyte solutions are 7.

[0031] Voltage differentials applied between the electrodes and the concentrations of the electrolyte solutions in this series of experiments are shown in table 2 below. About 20 hours were taken in each of this series of experiments. Weight percentage of tellurium deposited on the counter electrode in each of the experiments is obtained after ICP analysis and is shown in table 2.

Table 2

[0032] As is seen from table 2, while pH values of the electrolyte solutions weight percentages of deposited tellurium were very low, i.e., lower than 45%.

Example: [0033] Another series of similar experiments was conducted, in which sodium hydroxide solution (analysis rate (AR), from sinopharm chemical reagent Co., Ltd. (SCRC), Shanghai, China) was used as the electrolyte solution and was changed in concentrations thereof to adjust the pH values. Silicon oil bath was used to increase the temperature from room temperature to the desired temperature. Voltage differentials applied between the electrodes, and the temperatures and the pH values of the electrolyte solutions, and the percentages of deposited tellurium (obtained after ICP analysis) are shown in table 3.

Table 3

[0034] As is seen from table 3, while the pH value of the electrolyte solution is 8.5, very low weight percentage of tellurium was obtained on the counter electrode. However, in the experiments with the electrolyte solutions having pH values greater than 9, pure tellurium were unexpectedly recovered on the counter electrodes. It took from about 3 hours to about 20 hours to finish this series of experiments. This series of experiment results shows that pure tellurium, e.g., higher than 85% wt, were obtained unexpectedly in a relatively broad range of greater than 9.

[0035] Thus, this process is relatively easy to control because of its applicability in a relatively broader range of pH values and is therefore suitable for industrial applications.

[0036] While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.

Claims

CLAIMS:

1. A method for recovering tellurium from a module comprising cadmium telluride, comprising: contacting the module comprising cadmium telluride with an electrolyte solution at a pH greater than about 9; contacting a counter electrode with the electrolyte solution; and applying a voltage differential between the module and the counter electrode; whereby tellurium migrates from the module and is deposited on the counter electrode.

2. The method of claim 1, wherein the module comprises a cadmium telluride film.

3. The method of claim 2, wherein the module is a photovoltaic waste device and comprises an encapsulation glass layer adjacent to the cadmium telluride film.

4. The method of claim 3, further comprising heating the phototovaltaic waste device to remove the encapsulation glass layer and expose the cadmium telluride film before contacting the module with the electrolyte solution.

5. The method of claim 1, wherein a temperature of the electrolyte solution is about 80 °C and the voltage differential is about 2.5 v.

6. The method of claim 1, wherein the electrolyte solution comprises sodium hydroxide.

7. The method of claim 6, further comprising purifying a precipitate from the electrolyte solution to obtain cadmium.

8. A method for recovering tellurium from a solar cell waste comprising a cadmium telluride film, comprising: contacting the solar cell waste comprising the cadmium telluride film with an electrolyte solution at a pH greater than about 9; contacting a counter electrode with the electrolyte solution; and applying a voltage differential between the solar cell waste and the counter electrode; whereby tellurium migrates from the solar cell waste and is deposited on the counter electrode.

9. The method of claim 8, wherein the electrolyte solution comprises sodium hydroxide.

10. The method of claim 8, wherein a temperature of the electrolyte solution is about 80 °C and the voltage differential is about 2.5 v.