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Title:
METHOD OF BULK IRIDIUM DISSOLUTION IN HYDROCHLORIC ACID MEDIA
Document Type and Number:
WIPO Patent Application WO/2015/010667
Kind Code:
A1
Abstract:
The solution according to invention consists in a plasma-chemical method for dissolving bulk Iridium metal and/or Iridium alloy in hydrochloric acid, comprising following steps a) providing an electrolytic cell divided into the compartments by either porous ceramic diaphragm or by ion exchange membrane, b) providing an anode in said anode compartment is made of Iridium metal and/or Iridium alloy containing body to be dissolved, c) placing a portion of 8-13M hydrochloric acid in said anode compartment, d) filling the said cathode compartment with 8-13M hydrochloric acid or its mixture with salts thereof, e) placing into said cathode compartment cathode that has at least 10 times larger surface than said Iridium anode, f) applying potential from 60 to 350 Vd.c. between anode and cathode, g) developing glowing plasma discharge on the submerged surface of said Iridium anode.

Inventors:
BOUSA MARTIN (CZ)
BOUSA DANIEL (CZ)
Application Number:
PCT/CZ2013/000087
Publication Date:
January 29, 2015
Filing Date:
July 26, 2013
Export Citation:
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Assignee:
SAFINA A S (CZ)
International Classes:
C01G55/00; C22B1/04; C22B3/00
Foreign References:
JPS6483527A1989-03-29
Other References:
DATABASE WPI Week 199023, Derwent World Patents Index; AN 1990-175823, XP002716421
SCHREIER G ET AL: "Separation of Ir, Pd and Rh from secondary Pt scrap by precipitation and calcination", HYDROMETALLURGY, ELSEVIER SCIENTIFIC PUBLISHING CY. AMSTERDAM, NL, vol. 68, no. 1-3, 1 February 2003 (2003-02-01), pages 69 - 75, XP004409422, ISSN: 0304-386X, DOI: 10.1016/S0304-386X(02)00194-9
"Electrochemical dissolution of metals of the platinum group by alternating current, Physical Chemistry Laboratory, South Parks Road, Oxford, GB", JOURNAL OF APPLIED ELECTROCHEMISTRY, vol. 25, 1995, pages 490 - 494
METALS REVIEW, vol. 22, no. 3, 1978, pages 98 - 99
PERRY L.D.: "Handbook of Inorganic Compounds", 1995
Attorney, Agent or Firm:
KRMENCIK, Vaclav et al. (Praha 2, CZ)
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Claims:
CLAIMS

1. A plasma-chemical method for dissolving bulk Iridium metal and/or Iridium alloy in hydrochloric acid, comprising following steps: a) providing an electrolytic cell divided into the compartments by either porous ceramic diaphragm or by ion exchange membrane, b) providing an anode in said anode compartment is made of Iridium metal and/or Iridium alloy containing body to be dissolved, c) placing a portion of 8-13M hydrochloric acid in said anode compartment, d) filling the said cathode compartment with 8-13M hydrochloric acid or its mixture with salts thereof, e) placing into said cathode compartment cathode that has at least lOtimes larger surface than said Iridium anode, f) applying potential from 60 to 350Vd.c. between anode and cathode, g) developing glowing plasma discharge on the submerged surface of said Iridium anode.

2. The plasma-chemical method as defined in Claim 1, wherein the method operates at 130 to 230Vd.c. and current density of 80 to 120 A/dm2 at the temperatures from 70 to 90°C.

3. The plasma-chemical method as defined in Claim 1 or claim 2, wherein hydrochloric acid contains 5-75% by volume of nitric acid.

4. The plasma-chemical method as defined in any Claim 1 to 3, wherein hydrochloric acid contains dissolved Iridium chloride.

5. The plasma-chemical method as defined in Claim 1 or claim 2, wherein Iridium content in the alloy with other metals in said anode contains at least 15% by weight of Iridium.

6. The plasma-chemical method as defined in Claim 1 or claim 2, wherein cathode is selected from the group of materials consisting of Titanium, Carbon or Iridium.

7. The plasma-chemical method as defined in claim 1 or claim 2, wherein the polarity of the plasma-chemical cell is changed whereby said Iridium is used as a cathode and an original cathode is used as the anode.

8. The plasma-chemical method as defined in Claim 7, wherein instead of direct voltage alternating voltage is used to develop glowing plasma discharge on said Iridium electrode.

Description:
METHOD OF BULK IRIDIUM DISSOLUTION IN HYDROCHLORIC ACID MEDIA

Field of the Invention

The invention relates to a plasma-chemical process, generally known as Contact Glow Discharge Electrolysis (CGDE) or also as Asymmetric Plasma Electrolysis (APE) for dissolution of bulk iridium electrodes and/or metallic Ir scrap and/or its alloys with other metals in aqueous hydrochloric acid media.

Background Art

Iridium is known as most corrosive resistant metal out of all metals towards aqueous inorganic acids like for example hydrochloric acid, nitric acid and their mixtures. It is virtually insoluble in these acids and this property makes dissolution of Iridium for its further refining or chemical salts production very complicated.

Today methods to dissolve Iridium comprise mostly in alloying Ir metal or scrap with other precious metal, namely Platinum, to reach concentration of Iridium lesser than 12% by weight in such alloys. This alloy can be dissolved by conventional techniques in either Aqua Regia or HC1/C12 systems. The use of Platinum as an alloying element with Iridium is generally known to precious metals industry. However, to dissolve one (1) kilogram of Iridium one needs to add and keep in the refining circle more than 8kg of Platinum and this is very costly.

Tanaka Precious Metals Industries has filed the patent No. : JPS 6483527, 1989. According to this patent bulk Iridium is first alloyed with Manganese metal to the content lower than 30% by weight of Iridium, resulted alloy is digested in e.g. sulphuric acid to leach out Manganese and to obtain Ir black powder. This powder is washed dried and homogenized with mixture of sodium chloride and active carbon. This mixture is than sparged with gaseous Chlorine at temperatures above 350°C and finally digested with water to get solution of sodium chloroiridate. In further steps this sodium chloroiridate has to be hydrolyzed to produce hydrated Iridium oxides, these are filtered out and converted to Chloroiridic acid. This is required Ir salt that can be used for further refining of production of chemicals. As explained this process is very lengthy, laborious and expensive.

Russian scientist A.D. Styrkas has published a process for dissolution of PGM including Iridium powders in hydrochloric acid using alternating current applied in glass "U" tube (Electrochemical dissolution of metals of the platinum group by alternating current, Physical Chemistry

Laboratory, South Parks Road, Oxford, GB in Journal of Applied Electrochemistry 25(1995) 490-494). Though it is claimed the Iridium dissolves at the speed of 6mg/cm2.min, this method does not work with bulk Iridium at all. Thus Iridium has to be converted to the powder first and high currents exceeding 500A/dm2 must be applied.

Electrolytic dissolution of Iridium anodes in molten mixture of KCl/LiCl is described in the Metals Review 1978,22,(3), 98-99 at temperatures above 450°C In the same article electrolytic dissolution of Iridium anode in molten cyanide salts is described.

Perry L.D. in his Handbook of Inorganic Compounds, 1995 mentions possibility to attack the Iridium by fluorine at elevated temperatures. In our experience also dry Chlorine attacks Iridium at temperatures exceeding 600°C and under the strong light. However, Iridium chloride made by this way is not soluble in either water or hydrochloric acid.

All described prior art processes are represented by substantial disadvantages: high cost, low Iridium recovery, laborious process, necessity to work with Iridium powder and long Iridium lock up in the process. In addition these processes are mostly not so much friendly to the environment.

Summary of the Invention

This invention provides fast, efficient and cheap process for direct dissolution of bulk Iridium in hydrochloric acid and/or its mixtures with nitric acid. It takes place in simple equipment at temperatures up to 100°C. The method of dissolution is driven by plasma-chemical effect.

Therefore, according to the present invention, the dissolution method of bulk Iridium metal and/or Iridium alloys, in particular with Pt, Pd, Rh, Ru and Au, in aqueous hydrochloric acid and/or its mixtures with nitric acid, is characterized in that the dissolution process takes place in plasma-chemical cell subdivided into two compartments by porous ceramic or ion exchange membranes under temperatures between 5-100°C and controlled direct current voltage of 60- 350Vd.c. and current density of 10 to 180A/dm 2 . Furthermore, the dissolution occurs only under the condition when plasma glow discharge is developed by suitable electrodes arrangement on the submerged Iridium electrode. The Iridium dissolution takes place when Iridium is used as either anode, cathode or even under alternating current conditions. However, best results have been achieved when Iridium has been used as anode or cathode. As Iridium dissolves, it is obvious that dissolution takes place also in the mixture of hydrochloric acid and/or its mixture with nitric acid and with dissolved Iridium chloride formed.

In the plasma-chemical cell, the surface of Iridium electrode is at least 10 times smaller than the surface of opposite electrode. Although the process takes place in electrolytic like cell, the dissolution mechanism is plasma-chemical and hence Iridium electrode is used as either anode or cathode as the process is not dependent on the Iridium electrode polarity. Both cell compartments are filled with pure 5-13M (concentrated) hydrochloric acid or its mixture with nitric acid where content of nitric acid is 5-75% by volume.

A process according to this invention operates preferably at 130-230Vd.c. and current densities of 80-120A/dm 2 at temperatures 70-90°C. The solutions in both compartments are heated by Joule heat developed during the dissolution process. Te electrode opposite to the Iridium is preferably made out of the porous carbon or titanium gauze and best results has been achieved when opposite electrode surface was 105 times bigger that the surface of the Iridium electrode.

To prevent losses of hydrochloric acid through evaporation the cell is equipped with condenser that returns condensate back into the cell.

Beside alloying metals like Pt (Platinum), Pd (Palladium), Rh (Rhodium), Ir (Iridium), Ru (Ruthenium) and Au (Gold) also other impurities can be contained in the Iridium electrode. These impurities are represented mainly but not limited to: Cu (Copper), Fe (Iron), Ni (Nickel), Si (Silicon), Sb (Antimony), As (Arsenic), Se (Selenium), Te (Tellurium), Cd (Cadmium), Zn (Zinc), Sn (Tin), Zr (Zirconium), Ti (Titanium), W (Tungsten), Mo (Molybdenum) and Mn (Manganese). The present invention is characterized by following advantages: It is the only method to dissolve directly bulk Iridium metal in hydrochloric acid media, it uses simple and cheap equipment, it is fast, non-laborious and can be easily automated. Therefore also represents safe and

environmentally sound process especially on the side of waste waters disposed in technologies described above. Comparing to other processes it locks up Iridium for short time and reaches extraordinary high recovery rates.

Examples Example 1

Bulk Iridium wire as a fine metal 1,5 mm in diameter is used as anode and submerged into the concentrated hydrochloric acid in anode compartment. Cathode compartment is filled with concentrated hydrochloric acid too. As cathode Titanium mesh having surface 10 times greater than submerged part of Iridium anode is used. Voltage of 140V is applied to develop glowing plasma discharge on the submerged Iridium electrode. Both compartments are separated with ceramic micro porous diaphragm. Iridium starts immediately to dissolve due to the plasma chemic reaction as indicated by dark brownish color of Iridic acid. Dissolution process has taken 60 minutes and dissolution speed of Iridium of 1812g/h.m 2 has been achieved. Dissolution speed has been calculated by measuring weight at the beginning and at the end of the reaction. The system sets its own temperature during the dissolution due to developed head.

Example 2

Dissolution of bulk Iridium according to the Example 1 while Iridium has been used as cathode. The voltage of 80V has been applied and dissolution speed achieved was 1 181g/hm 2 .

Example 3

Dissolution of bulk Iridium according to Example 1 while alternating voltage of 120 V has been applied. Dissolution speed achieved was 1342g/hm 2 .

Example 4 Dissolution of bulk Iridium according to the Example 1 while iridium anode of diameter 5mm has been used and as anolyte hydrochloric acid with 10% by volume of nitric acid has been used. Cathode compartment has been filled with 5M NaCl solution acidified by 1M hydrochloric acid. Voltage applied was 198V. Dissolution speed achieved was 5318g/hm 2 .

Example 5

Dissolution of bulk Iridium according to Example 4 while Teflon ion exchange membrane has been used as separator of anode and cathode compartments. As cathode porous graphite wool has been used. Voltage applied was 233V. Dissolution speed has been 4598g/hm 2 .

Example 6

Dissolution of bulk Iridium according to Example 1 while Iridium alloy containing 52% by weight of Iridium, 47% by weight of Platinum and 1% by weight of Gold has been used. Ir anode has been made by pressing Ir scrap into the mold having cross-section 10x10 mm. As the anolyte hydrochloric acid with 5% by volume of nitric acid has been used. Applied voltage was 195 V and dissolution speed achieved was 7328g/hm 2 .

Example 7

Dissolution according to Example 6 while Iridium anode was prepared by pressing Iridium powder into the mold with cross-section of 10 10mm and sintered at 1200°C for one hour.

Voltage applied was 208V and dissolution speed achieved was 8521g/hm 2 .

While the invention has been illustrated and described in the text and examples above it is not intended to be limited to the details shown, while different modifications and structural changes may be made without departing away from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of present invention that others can readily adapt for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention.

What is claimed is set forth in following claims.