Prepare aqua regia, nitric acid (63%): hydrochloric acid (33%) = 1: 5 or so; Heating aqua regia to about 85℃ and stirring to dissolve sponge gold in aqua regia; Filtering, and washing filter residues; The filtrate was reduced with sodium sulfite aqueous solution to form gold powder. The gold powder was washed, filtered, dried and cast into gold ingots. With proper operation, 99.99% gold can be obtained.

Introduction:

Pure gold refers to 24K gold, which means its gold content is 100%. But there is no 24K gold in the world. Therefore, if there is gold marked "24K gold" or "pure gold" on the market, it is not true.

The content of pure gold in decorative gold is called "gold position", which is Karat in English, so it is called K gold. Generally speaking, pure gold is called 24K, which means the theoretical gold content is 100%.

In China, 18K is generally used for inlaying jewelry, so the fastness of inlaying jewelry is relatively high. K gold refers to the alloy of gold mixed with other metals. Kai is the unit of measurement of K gold, which divides pure gold into 24 parts.

According to the gold content in jewelry, it is divided into different kinds of gold, so 24K refers to pure gold. For example, the gold content of 18K is 18/24=75.0%. Because the gold content of 18K is 75.0%, it is also called 750.