JPS5941500A - Purification of trivalent chromium plating bath - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION In a broad sense, misfire + Ifi relates to trivalent chromium plating baths, especially nickel and zinc that occur during commercial operations.

To purify and restore the performance of plating baths that are no longer capable of plating of commercially acceptable quality due to increased concentrations of fouling metal ions such as iron, iron, and lead. Regarding the method. When one or all of these metal ion impurities adversely affect the performance of the plating solution, the resulting plating film becomes black, cloudy, or hazy, and sometimes even a spongy film appears, impairing the plating. This is accompanied by a decrease in the coating ability of the liquid, resulting in an industrially unfavorable result.

In order to overcome the disadvantages caused by contamination by such metal ions in trivalent chromium plating baths, a method is disclosed in US Pat. No. 4,038,160. Although this purification method has been found to be effective in many cases, the residual ferrocyanide can adversely affect bath performance and produce commercially acceptable films. The drawback is that it disappears.

If ferrocyanide is present in excess in the bath, additional steps are required to consciously add and remove contaminating metal ions to precipitate this excess ferrocyanide. Therefore, the method described in the previous HC U.S. patent requires precise analysis of contaminant ions in the bath and precise addition of precipitants, which is cumbersome and time-consuming. And requires a long line. Moreover, the precipitate of 7erocyanide is collared and requires special treatment when discarded.

A method has also been proposed in which a contaminated trivalent chromium electrolyte is electrolytically purified by electrolyzing a bath for a long period of time and allowing the contaminated metal ions to coexist on the sorted surface. The %L Wl n H method is somewhat effective in reducing contaminating copper ions, but is not very effective in removing nickel and zinc ions, and only has a partial moving bed for iron removal.

A method of precipitating heavy metals from a plating washing solution using dithiocarbamic acid and making pi (alkaline) has also been proposed for some time.

According to the discoveries constituting the present invention, it is possible to remove chromium ions from a trivalent chromium plating solution without substantially removing chromium ions, which are present at a concentration of about 50 times or more than the contaminating gold ions present in the bath. Selected dithiocarbamate compounds have been discovered that can be utilized in the purification of aqueous acidic trivalent chromium plating baths because they preferentially react with the contaminating gold ions they contain to form a precipitate. Moreover, although such trivalent chromium plating solutions often contain metals such as vanadium as preferred components to provide a controlled reduction in the formation of hexavalent chromium ions, such selective dithiocarbamate additives are It is surprising that vanadium is not substantially removed even after 7 hours of use. In addition, trivalent chrono plating solution is usually about 1.5
211 on the acidic side of the range from about 5 to 5, which is significantly lower than the alkaline pH previously proposed for treatment of plating rinse water.

An unanticipated result of the present invention is that
This can be further evidenced by the fact that certain dithiocarbamates, such as dithiocarbamates, do not give satisfactory results. Similarly, dimethylglyoxin, a compound known as a precipitant for nickel ions, is not effective in sufficiently precipitating contaminated nickel ions from trivalent ROM baths, and furthermore, the precipitate formed has a gelatinous appearance and may cause damage to the storage tank walls and structures. It sticks to the surface of the strip, creating an undesirable film and contaminating the filter equipment. Similarly, for example, sodium thiocarbonate (Na
2O2g) and sodium thiocyanide (NaSCN
When sulfide-containing compounds such as 1.) are added to a trivalent chromium bath, they significantly degrade the chromium film and turn the low current density recesses dark blue or black, significantly impairing the coating ability of the bath.

The benefits and medicinal properties of the present invention can be achieved by using dimethyldithiocarbamate and diethyldithiocarbamate and mixtures thereof as zero formulations in trivalent chromium plating solutions, in which undesirable contaminating ions and Since a preferential reaction occurs selectively to form a crystalline precipitate, it can be easily separated using a conventional d3 filtration device. Since dimethyldithiocarbamic acid and diethyl-dithiocarbamic acid are unstable, it is economical and preferable to add them to the bath as bath-soluble alkali metal and ammonium salts such as sodium salts. This additive is preferably introduced in the form of a concentrated aqueous solution and dispersed in the plating solution. The amount of additive added during the MH process depends on the amount of contaminant metal ions in the liquid. Therefore, the density of contaminant ions is reduced to a level at which the performance of the plating solution is restored by using an amount added that is calculated to remove at least a sufficient amount of such contaminant metal ions. A typical concentration of precipitant relative to the concentration of contaminant metal ions is approximately 8 j l
g/l.

Other advantages and inventive steps of the invention will become apparent from the description of the preferred embodiments given in conjunction with the inventive IT embodiments.

The purification process of the present invention involves the use of 3
valent chromium ions and a complexing agent for maintaining the chromium ions in the liquid, the formate ions having a concentration such that the molar ratio of complexing agent to chromium ions is from about 1:1 to about 3:1; acetate ion or a mixture thereof, a conductive salt such as an alkali metal salt or an alkaline earth metal salt, and an amount of hydrochloric acid, sulfuric acid, or less than or equal to about 3 ooy/7 to provide the necessary conductivity. It is particularly effective for purifying trivalent chromium plating solutions containing strong acids such as

Such conductive salts include fluoroboric acid and its alkali metal, alkaline earth metal and bath soluble ammonium salts. As an optional ingredient.

The trivalent chromium plating solution further contains ammonium ions in an amount such that the molar ratio of total ammonium ions to chromium ions is about 2=1 to about 11:1, and the amount of ammonium ions to halide ions is about 0.8:1. It is advantageous to contain halide ions, including chloride and bromide ions, in amounts such that the molar ratio is between about 1O:1. U.S. 1F Application No. 21) No. 5,406 (November 10, 1980)
The vanadium ion, which is a Lujouna type gold AN source agent, is also about 0.015 to about 6.31/l.
Advantageously, it is contained in a concentration of .

Additionally, it has been found to be particularly preferred to optionally include boric acid as a buffer, from about 0.15 moles up to the limit of solubility in the bath. Also about 0.05 to about 11
Wetting agents of the type commonly used during nickelization and hexavalent chromium plating tEi- may also be preferably used. Trivalent chromium plating solution is also available. P(1
It contains 9 hydrogen ions to make it acidic with a pH of about 2.5 to about 5.5.

U.S. Patent No. 3,954,574 - U.S. Patent No. 4,107,0
No. 04; No. 4,169,022 and $4,196
The benefits of the present invention can also be achieved using this refining agent for trivalent chromium plating solutions of the type described generally and specifically in Vr-, No. 063.

During normal plating production using such a trivalent chromium plating solution, there are problems such as bringing in the plating solution, dissolving it from the container containing the plating solution or the surface of the tank, dissolving the gold-plated surface of the article to be plated, and removing the surface of the rack from the protruding part of the rack. The plating solution becomes seriously contaminated due to contamination from water and chemicals used for dissolution, replenishment, and make-up. As a result, the concentration of undesirable contaminating metal ions such as nickel ions, zinc ions, iron ions, copper ions, and lead ions has increased significantly, and experiments have shown that nickel ions of about 150 ppm or more are harmful. This results in damage to the chrome film. Approximately 5
00 ppm, iron ions in the lower bite are preferred as they tend to promote the precipitation of chromium films.

Above about 1000 ppm (15//l) it is generally harmful to chromium coatings. Similarly, about 15pp
Copper ions above +n and zinc ions above about 10 ppm are also harmful. When multiple such metal ions are present, the harmful effects of each ion are synergistic9, with low concentrations of these ions damaging the chromium film; This is evidenced by the appearance of blemishes and blemishes.

In the present invention, dimethyl ditheocarbamate and/or
Additionally, a sufficient amount of L-diethyldithiocarbamate as an aqueous concentrated solution of an alkali metal and ammonium salt, preferably a sodium salt, is added to the contaminated trivalent chromium plating solution to precipitate at least a portion of the contaminated gold ions to a satisfactory level of the solution. The concentration of contaminant metal ions is reduced to a level that restores performance. In contrast to the toxic precipitate produced by ferrocyanide, this non-toxic precipitate can be easily disposed of using conventional disposal techniques. Unlike the case of ferrocyanide precipitants, excessive use of the refining agent of the present invention does not affect the quality of the chromium plating film.

Also, after treatment, 93. Any unreacted refining agent in the distillate will be progressively decomposed and/or removed during electrolysis of the plating solution during normal plating operations.

The fffi agent is preferably not in the form of a dry, soluble powder, but in the form of a concentrated, bath-soluble aqueous solution, which is added to the bath with stirring to ensure uniform dispersion. This liquid scale liquid generally contains about 30 parts of purifying agent.
14 is about 8, preferably 9 or higher to improve storage stability. When using industrial grade dimethyl dithiocarbamate or diethyl didiocarbame-I, it is usually best to purify it using carbon film or other methods.

This improves the performance of the plating bath after the final treatment.
It removes undesirable side reaction impurities that may give.

The purifying agent of the present invention is effective over a wide range of purposes. General jC is about 2 to about 5.5 for trivalent chromium plating solution.
, typically operating at a PH of from about 3 to about 4. The refining agents of this invention can be used effectively within these ranges as well as at a pH as low as about 1.5.

Next, the present invention will be explained in detail by way of examples. These are merely for illustrative purposes and the invention is not limited thereto.

Example 1 A hostile 31illi chromium aqueous test plating solution was prepared with the following composition; Ingredients Concentration Cr''' 24.2g/7 Nli, COOH44, Og/l NaBF4 55.(19/I NH4Cl 150,09/1 ) f3BO35
7, I El/1 voso4i, o y7 as a wet fishing agent” 2. Occ/1 “Wetting agent is 0
．． 1344g/l) IJumsulfosuccinic acid dihegycyl ester and 0.244! /l of 2-ethyl-1-
Consists of a sodium sulfate derivative of hexanol.

Iron ion concentration of about 0.3121171, about 0.0321
Tapping solutions contaminated with iron, hook and nickel ions were prepared by adding the respective sulfates to give a concentration of nickel ions of about 0.110 Ii/l and a concentration of nickel ions of about 0.110 Ii/l. . The above plating solution II contains contaminant ions! Sodium diegoldithiocarbamate trihydrate was added to the solution at 75"F (23"C) at rJ1 of approximately 3.2.

About 1 (stirred for 1 minute, then left to stand for 2 hours).

The liquid was then separated through a carbon filter and analyzed for metal contaminants. The analysis result is iron ion concentration 0.168
cI/l ; m i: t7 concentration io, o121/l i Nickel ion concentration was 0.042 (i/l. Therefore, about 46.2% of iron ions; about 620% of copper ions.
1, Example 2 The trivalent chromium test plating solution described in Example 1, 4 (l
Contaminant metal salts are added to Ome to reduce the iron ion concentration to 0.
3121171, nickel ion concentration 0.120g
7t, copper ion concentration 0.080! /l. This plating solution containing contaminated metal ions contains 3.5 g/l.
(7) Sodium diethyldithiocarbamate trihydrate was added and the melt joint was stirred at about 3.120'li' (49°C) for about 1.5 hours. Then about 2 hours, 75'y
After incubating at 23° C. for 1 hour, the mixture was separated through a carbon filter. Analysis of f liquid [according to iron ion concentration approximately $0.
07277/l, nickel ion concentration is approximately 0.01
0.9/I! However, the copper ion concentration was significantly reduced. Therefore, approximately 77% of iron ions and 91.7% of nickel ions were removed, and virtually 100% of copper ions were removed.

Example 3 - Is the essence according to the present invention? For the purpose of evaluating the influence on the effectiveness of one agent, the same test plating solution as described in Example 2, containing the same level of fouling metals, was prepared by adding ammonium hydroxide to approx. I made it.

The solution was then treated in the same manner as in Example 2. According to the analysis results of the P solution, iron ions decreased to approximately 0.0129/V, and nickel ions and copper ions were concentrated at 7° Negrizhiru. Therefore, approximately 96.2% of the iron ions were removed and virtually 100% of the nickel and copper ions were removed -C. The results of Example 3 show that this additive was used in Example 2 at about p
This shows that rJ(4 is more effective than i(2).

Example 4 The trivalent ROM ion concentration is 21.7 g/J, υ, the ammonium formate f1 degree is about 51.0II//, and the boric acid concentration is about 50.8! A trivalent chromium test plating solution having a composition similar to that described in Example 1 was prepared, except that the remaining part was the same as that described in Example J. The - of the plating solution was adjusted to approximately 3.5, but the contaminant ion concentration was approximately 0.298 g/l for iron ions, approximately 0.188 g/l for nickel ions, and approximately 0.04711 g/l for zinc ions. It was l.

Current density: 45 ASF (4.8 A/Dm),
Plating for 10 minutes using a conventional Watt-type bright nickel plating bath at a bath temperature of 145°F (63°C) produces approximately θ,3
A specimen with a mil (0,0762**) thick bright nickel plating was rinsed with water and then tested at a cathodic current density of 10 OASF in the contaminated trivalent chromium plating solution described above.
(10,7A/Dm2), i(5℃75'li'(
Plating was carried out for 3 minutes at 23°C. The chrome skin pA exhibited a rainbow color in the intermediate current density region and black streaks in the eddy current density region. This chromium film contained a large amount of contaminant metals and was considered to be rejected from a commercial standpoint.

Next, while continuously agitating the contaminated trivalent chromium plating solution, 3,89/l of sodium diethyl ditheocarbamate was added and treated at 75'F (23°C) for 1 hour. After filtration with a carbon filter, residual metal contamination ions in the p liquid were analyzed. Iron ions are approximately 0.164Ii/J, nickel ions are negative, and zinc ion rust is 0.0004g//. I found out. Therefore, about 45% of iron ions, about 100% of nickel ions, and about 99% of zinc ions were removed.

Nickel plated specimens of the type described above were plated in the treated filtrate under the same conditions as applied to the untreated solution. A shiny chrome film was formed over the entire surface and had a uniform appearance.

This plating film was of commercially acceptable quality. This plating test further indicated that the presence of excess sodium diethyldithiocarbamate in the solution after processing did not adversely affect the performance of the trivalent chromium plating solution.

This example shows that the present invention is effective for regenerating a trivalent chromium plating bath that is contaminated with metal ions and exhibits commercially unacceptable performance, and that a satisfactory chromium film can be obtained. It is clear that the contaminated bath can be regenerated to give

EXAMPLE 5 A trial treatment of 4,000 gallons (15 KI) of an industrial trivalent chromium plating solution having the same composition as shown in Example 1 was conducted. The presence of iron ions, nickel ions and reducing agents in the samples before and after treatment was reduced by 1ull of ions and nickel contaminating ions.
Nadium ions were analyzed.

Before treatment (1/l) After treatment (g/l') Fe
1.310 1.00ONi
O,5010,351 V 00238 0.238 Purification process is about 350g of sodium diethyldithiocarbamate
The electrolysis was stopped and the additive solution was added while filtering. A dark precipitate formed immediately upon addition, but surprisingly, this precipitate This resulted in a decrease in the back pressure without increasing it.Removal of this precipitate was therefore extremely easy, and the performance of the liquid was restored within about an hour after treatment, resulting in a commercially acceptable film. Analysis of the precipitate recovered by filtration revealed that it contained approximately 66,3 mol of iron diethyldithiocarbamate, and 33.3 mol of nickel diethyldithiocarbamate. This additive was found to selectively extract only contaminant metal ions, as vanadium and chromium were not extracted at all.A similar test using a ferrocyanide additive showed that vanadium and chromium were not extracted at all in the trivalent chromium plating solution. It has been found that significant amounts of both chromium and vanadium, which are useful components of carbon dioxide, are removed.

Widely different results without departing from the spirit and scope of this invention! Since it is obvious that the i-aspect can be ovalized, this invention is not limited to the attached frame.
There are no limitations to the particular implementation thereof.

1 person

Claims (6)

[Claims] (1) A method for purifying an aqueous trivalent chromo-plating solution containing a lethal amount of contaminating metal ions, the method comprising: purifying aqueous trivalent chromoplating solution containing a lethal amount of contaminating metal ions from the group consisting of dimethyldithiocarbamate ion, diethyldithiocarbamate ion/and mixtures thereof; Addition of a selected soluble and compatible purification agent in sufficient quantity to uniformly disperse and precipitate at least a portion of the contaminant metal ions to a level that restores satisfactory performance of the plating solution. A method for producing fiT, which comprises the steps of reducing the amount of precipitate and then removing the precipitate from the plating solution. (2) Scope No. 1 of the patent application, characterized in that dimethyldithiocarbamelt ion and diethyldithiocarbamate ion are added in the form of alkali gold salts and ammonium salts which are soluble and compatible with the plating solution. The method described in section. (3) Claim 1 characterized in that dimethyldithiocarbamate ion and diethyldithiocarbamate ion are added as their natriue salts.
The method described in section. (4) The method according to claim 1, wherein dimethyldithiocarbamate ion and diethyldithiocarbamate ion are added in the form of an aqueous solution. (5) The method according to claim 1, wherein the precipitate is removed by filtration. 6. The method of claim 1, wherein the 'a formulation is added at a weight ratio of purification agent to contaminant metal ions of about 8:1.