JPH037731B2 - - Google Patents

Description

[Detailed description of the invention]

Gold electroplating processes have become extremely important in the electronics and computer industry due to gold's low contact resistance, corrosion resistance, and solderability. Although platers can formulate plating baths from commonly available raw materials, most contain small to significant amounts of alloying elements such as antimony, tin, nickel, copper,
It relies on proprietary formulations that typically contain silver, indium, cadmium and cobalt. Gold is traditionally plated from cyanide baths, but several other metals including silver, cadmium, copper and indium are plated as well. Cyanide baths can be divided into three types: alkaline, neutral and acidic, of which acidic baths are the most advantageous.
These baths initially contain between 2 and 16 g/g/g, usually present as potassium gold disyanide (KAu(ON) ₂ ).
It can contain up to 100% of gold. As the plating reaction progresses, the concentration of impurities in the gold solution increases until the solution can no longer be used. Gold is recovered from such spent solutions using electrolytic recovery methods. However, electrolytic recovery methods are not practical for dilute solutions with low dielectric constants. In processing, the gilding bath is removed, the gilding bath is treated with a "wash-out" tin liquor, and finally rinsed with cold water. The gold concentration washed out by this process is typically about 300 PPm. Depending on the process, this gold concentration can be as high as 1000 PPm (1 g/). Anionic gold compounds have also been recovered from dilute solutions through the use of strongly basic anion exchange resins containing quaternized aliphatic amino groups. However, the anionic gold is so strongly bound by such resins that it can only be recovered by burning off the polymeric resin substrate. It would therefore be desirable to provide a polymeric ion exchange material in the form of a filter cartridge that can be effectively complexed and extract low concentrations of metals from aqueous solutions and easily regenerated into a metal-free active form. This is the object of the invention. It is a further object of the present invention to provide a method for recovering gold from an acid cyanide plating bath. It is a further object of the present invention to provide a method for producing pure gold metal from plating wastewater without being contaminated by metal-containing sludge by-products. It is a further object of the present invention to provide an ion exchange material in the form of a filter cartridge that does not exhibit the normal wear associated with ion exchange resins when exposed to hot metal-containing solutions of high alkalinity or acidity. be. BRIEF DESCRIPTION OF THE INVENTION It is an object of the present invention to contact an acidic aqueous solution containing an anionic metal cyanide complex with a weakly basic anion exchange resin formed by irradiation grafting of pyridinyl functional groups onto a polymeric felt. This is achieved by letting The complex formed when the pyridine nitrogen atom interacts with the negatively charged metal cyanide anion is easily destroyed by washing the complexed ion exchange material with a water-soluble base.
The metal can then be recovered from this basic solution by known electroplating methods, and the ion exchange material can be washed with water and reused. DETAILED DESCRIPTION OF THE INVENTION The ion exchange materials of the present invention are prepared by radiation grafting a substrate hepyridinyl moiety containing a fiber polymer felt. A method useful for radiation grafting hydrophilic monomers, including the preferred vinylpyridine, onto inert polymeric substrate films to form membranes for electrochemical cells is described in U.S. Pat.
It is disclosed in specification No. 4230549. A preferred polymeric felt for use as the ion exchange material substrate is 0.069 mm (2.7 mil) fiber polypropylene, commercially available as No. 1488 from Kendall Mills, Walpole, Mass., USA. Contains non-woven felt. Other porous polymeric woven or non-woven felts or sheets may be suitable for use as substrates having a porosity after grafting that allows effective flow rates through which the feed and elution solutions flow, as described below. . Thus, suitable polymeric felt fibers also include polymeric felt fibers made from nylon, cellulosic materials, polyethylene, polytetrafluoroethylene, and mixtures thereof. The grafted cartridge substrate is prepared by rolling a nonwoven sheet with an absorbent paper interlayer and dipping the roll into a solution of pyridine monomer in a suitable solvent. Organic solvents suitable for the grafting monomers include chlorinated hydrocarbons, such as methylene chloride, carbon tetrachloride, 1,1,1- or 1,
1,2-trichloroethane; aromatic solvents such as toluene or xylene, or mixtures thereof. Useful monomers that, when grafted onto a polymeric substrate, impart ion exchange activity to the substrate include pyridinyl functional groups. Preferably, the pyridinyl group is attached to one or more vinyl or ethylene groups forming the polymer matrix by coupling via a free radical reaction when excited by the incident radiation. The most preferred pyridinyl monomers are 2- and 4-
It is vinylpyridine. The monomer used in the grafting step is approximately 10% based on the total grafting solution.
~60% by weight. Other methyl-substituted vinyl-pyridine monomers can also be used. After immersion in a solution of the monomer, the polymer felt is ionized as provided by a Co-60 source until it is grafted to an extent of about 10-1500%, preferably about 100-1000%. irradiation by a source of radiation; The grafted felt substrate is then removed from the monomer bath and treated with water and dilute mineral acid, i.e.
Wash with sulfuric or hydrochloric acid to remove any homopolymer. The pyridinyl group is then activated to become ion-exchange active by washing the grafted substrate with a water-soluble dilute base to form the corresponding free pyridinyl group. The ion exchange substrate thus prepared is a weakly basic compound that functions to extract metal cyanide anions, i.e. gold disyanide anions, from acidic aqueous solutions (PH of about 0.5-6) by complexation. It can be identified as an anion exchange material. The ion exchange substrate in the form of a salt of the acid, which is gradually formed in the acidic bath, also functions to trap the gold disyanide anion. The complexed Au(ON) ₂ anion is
It can be eluted from the cartridge material by treatment with excess water-soluble base (optimal PH of about 11-13). Thus, gold salts can be removed from acidic solutions containing contaminants, such as chelating agents, buffers, other metal ions, etc., by exposure to the ion exchange material of the present invention, and further remove said contaminants. It is possible to elute into a basic solution substantially free of substances. Subsequently, metallic gold can be recovered in a relatively short time and in a highly pure state by electrodeposition of gold onto a suitable metal cathode using methods well known to platers. . The base form of the ion exchange material is then washed with water for further processing of the gold-containing solution. Typically, a filter cartridge is formed from the grafted felt by wrapping the grafted felt strip onto a cylindrical core of inert material, and the filter cartridge is then inserted into a pressurized filter housing. , one end of which is covered by an inlet member and the other end by an outlet member. The ion exchange cartridge manufactured according to the present invention is 15/
Approximately 1PPm to
99% from a solution containing as little as 500PPm of gold
It was discovered that more money could be recovered. When manufacturing filter cartridges using this method, 1~
Gold present in a solution containing 500PPm gold
Filter cartridges can be made to capture more than 99.5%. For each, approx.
18m (60ft) long, 51cm (20in) wide, 0.71mm
(28mil) thick vinyl pyridine grafted polypropylene felt filled
One cartridge is approximately 160g (5 troy ounces)
The ability to capture gold in amounts of metal up to a maximum of about 5.0 PPm, preferably about 0.1 to 1.0 PPm, with an endpoint gold concentration in the capture solution in the bypass.
It is. The gold disyanide anion can be rapidly removed from the acidic scavenging solution and further removed from the ion exchange cartridge by passing the aqueous alkali metal hydroxide solution through the filter bed. Preferably, the pH of the eluent (recovery solution) is approximately 10-13 using sodium or potassium hydroxide.
This adjusted eluent was adjusted to about 7 to 15%
Pass through the cartridge at a flow rate of min and circulate through a suitable plating bath. A typical plating bath for recovery from a cartridge assembly with a capacity of 30 to 40
Holds ~40 metal hydroxide-containing electrolytes. The plating bath is equipped with a rotating stainless steel cathode, a platinum-niobium anode, and has a temperature of approximately 37.8 to 82.8°C (100 to
Operating at an electrolyte temperature of 180㎓), voltages up to about 30 volts and currents up to about 30 amperes. When operated in this manner, a useful plating bath will recover at least about 99.0% of the captured gold in about 8 hours or less;
Meanwhile, the gold concentration of the basic eluent-electrolyte is approximately 0.1
-15 PPm, preferably down to about 1-5 PPm. Gold recovered in this manner is typically over 99% pure. At this purity, no further purification steps are required, which increases the economic potential of the method. As previously mentioned, the present ion exchange materials and methods are effective in recovering other metals, including silver, copper, iridium, palladium, etc., which form useful cyanide complexes that can be plated from cyanide-containing acidic baths. It is expected that this will happen. Therefore, in use, typical gold recovery equipment:
It can include two ion exchange cartridges prepared as described above and arranged in series. Approximately 30 mL of a spent lacquer solution containing acidified (PH of approximately 4.0 to 6.0) potassium gold disyanide was added to the
Circulate through the column at a flow rate of 0.7 to 10/min. Bypass (gold concentration in recovery solution eluent
PPm) is approximately 0.25PPm if the column holds 31g (1 troy ounce);
bypass is approximately 0.5PPm for 155g (5 troy ounces) (maximum optimal capacity)
In the case of , the bypass is about 1.0PPm. captured
To recover 99.8% of 93 g (3 troy ounces) of gold as metal in a plating bath, a minimum of approximately 37.8 ~
PH about 11.5~ heated to 43.3℃ (100~110〓)
It takes about 8 hours using a 0.1 to 0.2 M potassium hydroxide recovered aqueous solution of No. 12.5, and the final gold concentration in the eluent is about 5.0 PPm or less. When the recovered gold was analyzed by atomic absorption spectroscopy, it was found to be 99.9 plus%.
purity. If desired, a second series of cartridges can be connected to the bath of gold-containing solution to allow continuous processing of large volumes of solution. Therefore,
while eluting and precipitating the gold in the first column apparatus;
The flow of gold-containing capture solution can be switched to a second column device. After the gold is recovered from the first column apparatus and the filter is regenerated, the flow is returned to the first column apparatus for continuous gold anion capture and metallic gold recovery. The invention is further illustrated by the following detailed examples. Example: Preparation of ion exchange material According to the conventional method described in U.S. Pat. No. 4,230,549, an ion exchange material was prepared as follows.
It was made from 0.069 mm (2.7 mil) polypropylene nonwoven felt (No. 1488, manufactured by Kendall Mills, Walpole, Mass., USA). The felt was rolled with an absorbent kraft paper interlayer and the roll was immersed in a solution of 40% by volume 4-vinylpyridine and 60% by volume methylene chloride. This felt roll was then exposed to 1.20 Mrad at a dose rate of 9000 rad/hr using a Co-60 radiation source.
A total dose of 700% of the graft was irradiated. The roll was removed from the bath and the grafted felt was washed with water to remove the homopolymer. The grafted felt was washed with 10% aqueous sulfuric acid to remove unreacted monomer. Grafted felt resin is 0.71mm
(28 mils) thick. EXAMPLE...GOLD RECOVERY 18 m (60 ft) of 51 cm (20 in) wide grafted felt prepared as described in the example was
(2.0ft) long and 1.91cm (0.75in) PVC core material to produce a filter cartridge, which is then wrapped around a 0.76m (2.5ft) and 15cm (6.0in) PVC pressure filter. It was inserted into the housing to create one column device. Two such columns arranged in series exhibited a total solution holding capacity of 37. The system is filled with water, and the cartridge is adjusted by repeated washing with dilute acid and dilute alkali.
The cartridge was then made basic with a 5% potassium hydroxide wash. 11.4 containing 93.30g gold
volume of 0.0285M potassium gold disyanide solution,
A flow rate of 4.8/min was circulated through the system from the holding tank. After one step through the system of two columns, the concentration of gold in the eluent was 0.45 PPm, which means that the capture of gold by the column was 93.06 g.
(99.96% capture). The solution in the column was evacuated and water flowed through the system to fill 30 plating vessels with 76.1 cm ² (11.8 in ² ) stainless steel cathodes and niobium-coated platinum anodes rotating at approximately 1500 rpm. . Add 250ml of 8M potassium hydroxide solution to this tank to adjust the pH of the electrolyte.
11.5 and heated the contents of the bath to 50°C (122°C). The basic electrolyte was then circulated through the column at a flow rate of about 10/min while the plating bath was operated at 11.0 volts and 7.5 amperes.
After 8.0 hours, 93.135 g of 99.82% pure gold was deposited on the cathode. This represented 99.9% gold recovery. The gold concentration in the circulating 0.134M potassium hydroxide electrolyte dropped to 5.0 ppm. After the plating step, the column is washed with water to remove the base and can be used directly again in the capture step. Running the system for 20 steps under these conditions showed no appreciable decrease in column performance. Table 1 summarizes examples illustrating gold recovery methods for recovering gold from commercially available plating solutions using one or two of the example columns. The table shows the plating baths available commercially.
Figure 2 illustrates the effectiveness of the ion exchange material of the present invention in recovering high purity gold without the need for any pre-treatment of the solution to remove chelating agents, contaminating metal components, etc. The column apparatus of Examples 2-8 also function effectively to recover gold from acidified potassium gold disyanide containing small amounts of gold, from 1 to 500 PPm. Therefore, the ion exchange material of the present invention is expected to effectively recover gold from spent plating solutions and drained plating solutions as well as from pre-processing solutions to remove the bulk of the gold. Ru. Although the invention has been described with respect to various specific and preferred embodiments and methods, it should be understood that many variations and modifications can be made within the scope and spirit of the invention.

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Claims (1)

[Scope of Claims] 1. A method for recovering metal, comprising: (a) a monomer having a pyridinyl functional group,
%; and (b) contacting said anion exchange material with an acidic aqueous solution containing a metal cyanide anion. A method for recovering metals comprising removing said anion from a solution by forming a complex between said anion and a pyridinyl group. 2 further comprising: (a) decomplexing the metal cyanide anion by contacting the ion exchange material with an aqueous base; and (b) recovering the metal from the aqueous base by electrodeposition. 2. The method of claim 1, comprising: 3. The method of claim 1 or 2, wherein the metal is selected from the group consisting of gold, silver, copper, palladium, cadmium and indium. 4. The method of claim 3, wherein the metal is gold and the noble metal cyanide anion comprises a gold disyanide anion. 5 The monomer is 2-vinylpyridine or 4
- vinylpyridine, and the polymer felt comprises a polypropylene nonwoven felt. 6. The method of claim 2, wherein the water-soluble base comprises sodium hydroxide or potassium hydroxide. 7 (a) forming a weakly basic anion exchange material by irradiation grafting 2-vinylpyridine or 4-vinylpyridine onto a polymeric felt substrate to the extent of 100 to 1000%; and (b) contacting the polymeric resin with an acidic aqueous solution containing gold potassium disyanide to form a complex between the pyridine group and the gold disyanide anion, thereby removing the anion from solution; A method according to claim 1. 8 further comprising: (a) decomplexing the anionic complex by contacting the ion exchange material with an aqueous solution of potassium or sodium hydroxide; and (b) decomplexing the anionic complex from the water-soluble base by electrodeposition. 8. The method of claim 7, comprising recovering money. 9. The method of claim 7 or 8, wherein the polymeric felt comprises a polypropylene nonwoven felt. 10. Before contacting the aqueous solution of potassium or sodium hydroxide with the ion exchange material,
9. The method of claim 8, wherein the method is heated to about 100-180 degrees Fahrenheit.