I. Introduction

With the opening of gold market opening and Shanghai Gold Exchange (hereinafter referred to as the Shanghai Stock Exchange), the gold refining, gold bullion standard is increasingly becoming China's gold production enterprises to improve economic efficiency and to market a stepping stone. In order to improve the level of refining, some domestic enterprises such as Zhongjin Gold Co., Ltd. Gold Refining Plant, Shandong Gold Group Co., Ltd. Jiaojia Refinery and other enterprises will not hesitate to introduce the world's leading level of Polish Poliden's refining technology to improve product competition. Some companies such as Zijin Mining Group Co., Ltd. and Zhejiang Yuchang Gold Mine Co., Ltd. are based on their own technology development. Through the integration of various process technologies, they also produce gold alloy ingots that fully meet the requirements of the Shanghai Stock Exchange. . This paper mainly introduces the unique gold electrolysis process of the Suichang Gold Mine and the processing technology and operation skills of the lkg standard gold ingot casting process.

Second, the gold refining process

High-purity gold and even Au99.99 production processes mainly include chemical methods and gold electrolysis. Chemical refining has the advantages of less investment and less metal backlog, but it also has its insurmountable shortcomings, that is, due to the influence of the amount of silver in the chlorinated liquid and the adsorption of the reduced gold powder, impurities such as silver and iron are high. Although the operation requirements of a company are quite fine, the pass rate of Au99.99 is only 60%. The quality of the products produced by the company is shown in Table 1.

Table 1 Gold ingot quality analysis table %

In the use of electrolysis, most companies use AC and DC superposition power supplies. It is understood that in the Au99.99 brand of domestic gold enterprises, the impurity content (%): Ag 0.0015 ~ 0.01, Cu 0.0003 ~ 0.003, Pb 0.0002 ~ 0.0021, Fe 0.0002 ~ 0.0036, Bi 0.0001 ~ 0.002, Sb 0.000l ~ 0.001 .

The gold electrolysis refining of Zhejiang Suichang Gold Mine Co., Ltd. began in 1998 with the use of asymmetric AC power. The main advantage of this power supply is that it has strong adaptability to raw materials, high quality of electric gold, and good resistance to gold anode plates containing 92% to 98% of Au, 0.8% to 3.6% of Ag, and 0.43% to 5.41% of Pb. Passivation, after a period of exploration of the process, determined the better process conditions, the quality of the gold is generally above 99.997%, the chemical composition of the gold ingots cast with the gold is not only better than the requirements of the national standard Au-l Also, the Au99.995 grade requirement in American ASTMB562-95 is shown in Table 2.

Table 2 Gold chemical composition comparison table %

Third, burning and shaping process

In 2002, Zhejiang Yuchang Gold Mine Co., Ltd., in line with the requirements of the designated production enterprises of the Shanghai Stock Exchange, did not meet the requirements of the designated production enterprises of the Shanghai Stock Exchange, and jointly used the technology of Zichang Gold Mine Co., Ltd. to use the Zijin brand. Participate in market competition. After years of exploration in production practice, a set of casting and shaping processes for producing lkg standard gold ingots was concluded.

(1) Main principles

Using the high temperature of oxy-acetylene flame, the same batch of electric gold is cut, rough-melted, refined, cast, etc., interspersed for sampling, primary and secondary weights, and finally the weight is lkg+(≥20) Mg, intrinsic quality, appearance size, appearance, gold ingots that fully meet the requirements of the Shanghai Stock Exchange's Au99.99 brand.

(2) Operation process

The operation process is shown in Figure 1.

Figure 1 Casting and shaping process operation flow

(3) Main operation process

1, cutting

Since the weight of each piece of gold is different, the purpose of cutting is to divide the gold of more than 1kg into pieces of gold of 0.9-1.0kg, and at the same time, the molten metal is poured into beads, and the obtained gold beads are used for primary and secondary weights. .

2, one weight

After cutting, the gold and gold beads are weighted once on the electronic balance by the weight of each piece of lkg+(3~5)g.

3, rough sampling

There are two purposes for rough melting: one is the sampling requirement, because the metal is sampled after being thoroughly mixed in the molten state, and the sample is highly representative. The second is the process of rough melting - one casting - secondary weighting - fine melting - secondary casting. The standard gold ingot produced has a low weight deviation rate and a high pass rate. However, if the electric gold is directly used for the melting and casting, the weight deviation is large. This is because the surface of the gold is rough, and particles are splashed during the melting process, causing weight deviation.

Sampling is carried out when the rough melt is turned on. The sampler is made of high-temperature-resistant high-purity graphite rod. After the same batch of gold is sampled, the crude sample is collected for water quenching. After sampling, a layer of floating matter will appear on the surface of the melt, which may be caused by the introduction of high melting point oxides in high purity graphite. Just add the amount of AR grade borax in the previous casting, it can be removed. Otherwise, a grayish white oxide film is formed on the surface of the ingot to affect the appearance of the ingot.

4, secondary weight, fine melting, secondary casting

In order to ensure that the weight of the refined ingot is in lkg+(≥20)mg without causing excessive loss of the enterprise's interests, the weight of the second heavy weight is generally selected at 1kg+(40-80)mg.

The appearance quality, physical specifications and weight of the gold ingot are reflected in the finishing and secondary casting processes. Therefore, the key to the production of fine melting and secondary casting lkg standard gold ingots. According to our long-term exploration of the operation, the following factors are considered to be the main cause of defects in the lkg gold ingot (see Table 3), and measures for prevention or resolution are proposed.

Table 3 The reason why the appearance of gold ingot does not meet the requirements and preventive measures