A method for detecting the stability of sodium gold sulfite solution

Abstract

A method for testing the stability of a sodium gold sulfite solution is described. A certain amount of the sodium gold sulfite solution is added to an alkaline solution of a desired concentration, followed by the addition of a hydrogen peroxide solution. The stability of the solution is determined by comparing the color change time and the gold foil precipitation time of the mixed solution. The method utilizes the oxidizing properties of hydrogen peroxide to destroy various ligands in the solution, then utilizes the reducing properties of hydrogen peroxide to reduce the gold in the solution. Finally, the stability of the solution is determined based on the difference in the two reaction times. This method offers advantages such as rapid testing, stable results, and simple operation.

Description

Technical Field

[0001] The invention relates to a hydrometallurgical process in the field of metallurgy, in particular to a method for determining the stability of a sodium gold sulfite solution used for cyanide-free gold plating. Background Art

[0002] Gold is a scarce strategic metal, widely used in gold jewelry, currency reserves, and high-tech industries. With the continuous development of society, gold's monetary function is declining, while its application in industrial and high-tech fields is gradually expanding. Gold has excellent conductivity, stability, toughness, and ductility in air. It is used for surface plating in a wide range of fields, including fine finishing, integrated circuits, and electronic communications. Gold plating offers excellent properties such as low contact resistance, good conductivity, ease of soldering, strong corrosion resistance, and good wear resistance. With the miniaturization and intelligentization of electronic products, the requirements for electronic device functionality and related technologies are becoming increasingly stringent. For example, high-frequency circuits have particularly high signal loss requirements. While other surface treatment technologies result in significant losses, gold plating reduces signal loss. With the advent of the 5G era, high-frequency circuits will become mainstream applications, which will undoubtedly drive large-scale demand for gold plating technology.

[0003] Common gold plating processes are mainly categorized as cyanide gold plating and cyanide-free gold plating. Cyanide gold plating is widely used in decoration, aerospace, and electronics due to its high coordination stability constant for cyanide to gold, excellent bath system stability, wide pH range during the electroplating process, and excellent adhesion and uniformity of the deposited layer. Cyanide gold plating solutions are generally divided into two categories. Alkaline cyanide gold plating solutions primarily consist of gold cyanide salts and free cyanide. These solutions exhibit strong cathodic polarization, resulting in bright, fine, and highly pure deposits, but with a certain degree of porosity. Acidic or neutral cyanide gold plating solutions, on the other hand, incorporate gold in the form of potassium aurous cyanide. Free cyanide is absent, resulting in a low cyanide content. These solutions are relatively stable, resulting in low porosity and excellent solderability. However, cyanide is highly toxic, causing many problems in operational safety, waste liquid disposal, and environmental protection, and posing potential hazards to the human body and the natural environment. Currently, the industry hopes to replace the cyanide gold plating system with a cyanide-free gold plating system.

[0004] Cyanide-free gold plating systems primarily include sulfite systems, citrate systems, thiosulfate systems, sulfite-thiosulfate composite systems, hydantoin systems, ethylenediamine systems, and thiourea systems. Currently, the sulfite system is the most widely studied and applied. Compared to the cyanide system, it offers advantages such as non-toxicity, strong dispersion, excellent coverage, high current efficiency, bright and dense coatings, fast deposition rates, and small pores. This system meets the gold plating needs of components in the electronics and communications industry and is suitable for surface gold plating of copper, nickel, and silver substrates, as well as for gold plating of cloisonné ceramic jewelry and eyeglass frames. Furthermore, it can be used in conjunction with electroplating solutions for other metals to produce jewelry with alloy coatings of varying K values.

[0005] The sulfite system usually uses sodium gold sulfite as the gold salt. Sodium gold sulfite, with the molecular formula Na3Au(SO3)2 and a molecular weight of 426.06, is a purple-red powder or a colorless transparent liquid. The compound has poor stability and is therefore usually stored in the form of a solution; it is soluble in water, slightly soluble in alcohol, and insoluble in ether. Although sodium gold sulfite is an ideal reagent to replace cyanide gold plating, the sulfite in sodium gold sulfite has a strong reducing property under alkaline conditions and is easily decomposed and precipitated into S at room temperature or under light. 2- and with Au + The formation of black gold sulfide Au2S precipitate affects product quality. Therefore, sodium gold sulfite should be stored at low temperature and away from light, or a stabilizer should be added to enhance the stability of the solution to extend the shelf life.

[0006] There are two common methods for preparing sodium gold sulfite: gold fulminate and gold hydroxide. Patent CN114164465A uses the gold fulminate method to prepare sodium gold sulfite. The process involves dissolving gold in aqua regia—adjusting the base with ammonia—gold fulminate—washing—and dissolving with sodium sulfite. While gold fulminate precipitation effectively removes chloride ions, the intermediate product, gold fulminate, is an explosive trivalent gold salt, posing a significant safety hazard. Furthermore, it continuously decomposes and produces ammonia gas during the production process, creating a poor operating environment.

[0007] Patent CN113046800A uses a direct reduction method of chloroauric acid to produce sodium gold sulfite. The process flow is "gold - gold dissolution in aqua regia - concentrated nitrate removal - sodium hydroxide neutralization - sodium sulfite complex dissolution." This process does not produce the dangerous and explosive gold fulminate intermediate. However, chloroauric acid is neutralized with sodium hydroxide and then directly complexed and dissolved, resulting in a high chloride ion content in the sodium gold sulfite solution. This severely corrodes the subsequent electroplating equipment and makes process control difficult. Patent CN105568269A improves the process for preparing sodium gold sulfite from gold hydroxide. The process flow is "gold dissolution - nitrate removal - sodium hydroxide neutralization - liquid-solid separation - washing - sodium sulfite complex dissolution - concentrated crystallization." The intermediate gold hydroxide can be washed to effectively reduce chloride ions. However, the preparation process of sodium gold sulfite uses dilute sulfuric acid to repeatedly adjust the solution pH, making the preparation process complex and the gold solution unstable, making it unsuitable for industrial production.

[0008] The above two methods for preparing sodium gold sulfite have their own advantages and disadvantages. The advantages of the gold fulminate method are high direct yield of the product, but there is an explosion risk, and the product contains ammonia. The advantage of the gold hydroxide method is that the product contains low chlorine, but the direct yield of gold is low. The sodium gold sulfite electroplating gold water prepared by these two methods is not stable enough, and gold powder is precipitated during the subsequent placement process, which is not conducive to the subsequent electroplating process. Regarding the detection method for the stability of sodium gold sulfite, enterprises usually adopt a long-term placement to observe its decomposition. This method is not only time-consuming, but also has no reference value for the subsequent use process. Based on this, the present invention provides a method for quickly detecting the stability of sodium gold sulfite solution, which has good guiding significance for the preparation process and electrolysis process of sodium gold sulfite solution.

[0009] SUMMARY OF THE INVENTION: In order to overcome the shortcomings of traditional methods for detecting the stability of sodium gold sulfite solution, the present invention proposes a method for determining the stability of sodium gold sulfite solution by oxidation method, which has significant detection effect, short time and simple operation.

[0010] To achieve the above objectives, the present invention employs a technical solution comprising: first, adding a predetermined volume of sodium gold sulfite solution to an alkaline solution of a desired concentration, then adding a predetermined volume of hydrogen peroxide solution; and comprehensively assessing the stability of the sodium gold sulfite solution by recording the time it takes for the mixed solution to change color and the time it takes for gold foil to precipitate. The essence of the present invention is to first utilize the oxidizing properties of hydrogen peroxide to destroy various ligands in the sodium gold sulfite solution, then utilize the reducing properties of hydrogen peroxide to reduce the gold in the solution. Finally, the stability of the sodium gold sulfite solution is determined based on the difference in these two reaction times. This allows for rapid stability testing of the sodium gold sulfite solution, significantly improving detection speed.

[0011] The specific process and process parameters are as follows:

[0012] First, take 1-30 ml of an alkaline solution with a concentration of 20-100 g / L and place it in a conical flask. Then add 1-5 ml of a sodium gold sulfite solution. Finally, add 1-20 ml of hydrogen peroxide of the required concentration. After thorough shaking, let it stand and observe. When the mixed solution turns purple within 20-80 minutes and the time for gold foil to precipitate is 80-120 minutes, it is determined that the sodium gold sulfite solution has good stability.

[0013] The invention is suitable for determining the stability of a sodium gold sulfite solution for cyanide-free gold plating, wherein the mass concentration of gold in the sodium gold sulfite solution is 1-100 g / L.

[0014] The alkaline solution is one or two of sodium hydroxide solution, sodium carbonate solution, potassium hydroxide solution or potassium carbonate solution, and all of them are analytically pure reagents.

[0015] The hydrogen peroxide is an analytically pure reagent, and its mass percentage is not less than 30%.

[0016] Compared with the traditional method for detecting the stability of sodium gold sulfite solution, the present invention has the following advantages: 1. The present invention adopts an oxidation-reduction method to determine the stability of the sodium gold sulfite solution, using hydrogen peroxide to first oxidize and destroy the ligand and then reduce the gold, and the stability is determined by the length of the two reaction times; 2. The present invention has the advantages of significant detection effect, short time, simple operation, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 : Schematic diagram of process flow of the present invention. DETAILED DESCRIPTION

[0018] Example 1: The gold concentration in the sodium gold sulfite solution is 60 g / L, the mass percentage of analytically pure hydrogen peroxide is not less than 30%, and the mass percentage of analytically pure sodium hydroxide is not less than 96.0%. First, 20 ml of the 60 g / L sodium hydroxide solution is placed in a conical flask, followed by 3 ml of the sodium gold sulfite solution and finally 20 ml of hydrogen peroxide. The mixture is shaken thoroughly and allowed to stand for observation. When the mixed solution turns purple within 60 minutes and the time for gold foil precipitation is 100 minutes, the stability of the sodium gold sulfite solution is determined to be good.

Claims

1. A method for testing the stability of a sodium gold sulfite solution, comprising: first, taking 1-30 ml of an alkaline solution with a concentration of 20-100 g / L and placing it in a conical flask; then adding 1-5 ml of the sodium gold sulfite solution; and finally adding 1-20 ml of hydrogen peroxide with a required concentration; shaking the mixture thoroughly, and then standing for observation. When the mixed solution turns purple within 20-80 minutes and the time for gold foil to precipitate is 80-120 minutes, the stability of the sodium gold sulfite solution is determined to be good; and the mass concentration of gold in the sodium gold sulfite solution is 1-100 g / L.

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