Gold Refinery Machine

Why do we need to refine gold? -Gold Refinery Machine

Gold has a certain purity. Purification is to further purify gold ornaments or nuggets. Pure gold is auratus, and its color changes with the type and amount of impurities in it. For example, silver and platinum will make the color of gold lighter, and copper will make the color of gold darker. When gold is broken into powder or ground into gold foil, its color can be cyan purple, red, purple and even dark brown to black.

Mature gold is the gold that is smelted and purified from raw gold. It is generally of high purity and fine density, and can be directly used in industrial production. Common are gold bars, pieces, ingots and various kinds of jewelry, utensils, gold coins and industrial gold wire, sheet, plate, etc. The higher the purity, the higher the market value.

In industry, the following two methods are usually used to purify gold: Aqua Regia and gold electrolysis. We will introduce these two technologies for you.

Aqua Regia Refining

Applicable metal: low purity gold

Advantage: simple the process, low technology investment, high gold recovery rate.

Notice: During the Aqua Regia Refining process, some harmful gases(mainly Sulfide waste gas)will be produced due to chemical reaction. So it shall be approved by the local environmental protection bureau before using.

It is to dissolve impure gold (such as crude gold, alloy, gold containing fertilizer, etc.) with aqua regia to form chloroauric acid. Sodium bisulfite is used as reducing agent to reduce chloroauric acid into gold powder precipitation, and then purification, washing, drying and finally adding flux are added to melt at high temperature to obtain pure gold with golden yellow color and purity above 99%.

Aqua regia: mixed acid of 1 part of concentrated nitric acid and 3 parts of concentrated hydrochloric acid.

3HCl(aq)+HNO3(aq)→2H2O(l)+NOCl(g)+Cl2(l)

Gold Refinery Technical Methods:

1.Dissolve the impure gold in the acid resistant reactor, add Aqua Regia 3 times the weight of the metal under ventilation condition. After the violent reaction, heat and evaporate to about 1 / 5 of the original volume to make the gold completely dissolved. Then add concentrated Hydrochloric acid to drive away the free Nitric acid until there is no red brown gas. Take it down and cool it, acidify it with 5% Hydrochloric acid, filter and remove the insoluble impurities, and the remaining Chloroauric acid solution Dilute with distilled water to about 50-100g / L of gold and make the pH value of 1-2.

2.Reduction: heat the chloroauric acid solution to 30-40 degrees, while stirring, quickly add 150 g / L sodium bisulfite solution until all gold is reduced to gold powder precipitation, and then leave the solution to be colorless and transparent before filtration.

3.Some impurities, such as iron compounds, may be adsorbed in the gold powder precipitate obtained by purification and filtration, which must be removed to improve the purity of gold powder. Add 15% hydrochloric acid into the gold powder, heat, stir and boil for 5 minutes, then carefully pour out the acid solution, such as 3-5 times, until it does not appear yellow.

4.Washing and drying: repeatedly wash the purified gold powder with distilled water for many times until the solution is neutral and the pH value becomes 7. Then stand, filter and dry to obtain pure gold powder

5.Smelting: put the pure gold powder together with appropriate amount of soda ash, borax and other chemical pure solvents into the crucible, and melt at 1200 ℃ for 2-3 times to obtain pure gold with the color of golden yellow and purity of more than 99%.

Supply Scope:

  1. Nitric acid high level tank
  2. Hydrochloric acid high level tank
  3. High level tank
  4. Impurity removal kettle
  5. Dissolving kettle
  6. Reduction kettle
  7. Mist separator
  8. Impurity removal filter disc
  9. Gold solution filter plate
  10. Reducing solution filter plate
  11. Precision filter
  12. Support platform
  13. Vacuum unit
  14. refrigerator
  15. Pipe fittings
  16. Power Distribution Cabinet
Aqua Regia Refining

Gold Electrolysis System

Applicable metal: 22karts gold and above

Advantage: Environmentally friendly, no chemical gas produced. Easy operation, Low production cos, thigh recovery rate. The product quality is stable and can reach 99.99%.

Notice: The plating solution needs to be changed in time. Slow speed, long working time and more power consumption.

The electrolysis of gold can be carried out in the solution of gold chloride and gold cyanide. For the sake of safety, almost all the countries in the world adopt the gold chloride electrolysis method proposed by E. Wohlwill in 1874, so it is called the wolville method. This method is carried out in the electrolyte with high current density and high concentration of gold trichloride. With the process going on, the coarse gold anode is dissolved, and the electrolytic pure gold is precipitated from the anode.

Wollwell method is to load crude gold anode and pure gold anode into the electrolytic cell of gold chloride solution. After the current is applied, the gold and impurities in the anode are dissolved, and pure gold is precipitated at the cathode. Therefore, it can be considered that the electrolysis process is carried out in the electrochemical system of Au (cathode) | HAuCl4, HC1, H20, impurity | Au, impurity (anode).

Advantage:

1. Electrolytic gold purification equipment Can gain high quality gold through, which can reach the gold ingot standard of au99.99 (grade I) of international market, and can also produce gold ingots with 99.999% purity according to special needs.

2. Low production cost: about 0.006usd / g  gold.

3. Using high current density electrolysis technology, 1000A / m2, high production efficiency, electrolysis cycle of 22h.

4. Less production cost, 5kg / D Gold electrolytic charging electrolyte 12-13l, containing 120-150g / L gold, occupying a maximum of 2kg gold.

5. Transparent closed hood, good working environment, easy to operate, beautiful and generous, the whole set of equipment covers an area of about 5m2.

6. The flue gas condensing device comes with the full Electrolytic gold purification equipment. Because the gold electrolysis process needs high temperature (60-70 ℃), the flue gas condensing device can condense the refluxing and volatilizing electrolyte to avoid the loss of gold.

7. The main body of the equipment is made of high-performance polypropylene, and the cathode and anode conductive parts are made of titanium clad copper, which has excellent conductivity.

Connection diagram of gold electrolysis equipment

Connection diagram of gold electrolysis equipment

I.Put pressed gold into the titanium bucket of the Gold Dissolution Wind Cabinet, then add nitric acid and hydrochloric acid, and dissolve them into electrolyte.

II.Melt the gold (≥95% content) with gold melting furnace, and then pour it into the prepared anode mould to make anode bullion.

III.Hang the anode bullion in the electrolytic tank, and then pour the electrolyte into the electrolytic tank for electrolysis. The electrolysis time is generally 20 hours.

IV.After electrolysis, take out the bullion for cleaning, then dry it, put it into the gold melting machine for melting, and finally cast ingot.

V.The electrolyte needs to be replaced after one month of use. You need to add anhydrous sodium sulfite to the Reduction Wind Cabinet for Spongy gold reduction. (equivalent to reducing the gold in the electrolyte)

Suggestion:

The workshop is better equipped with a Smoke Spray Tower. It can collect the waste gas produced in all processes. Then after treatment, the waste gas will be discharged out of the workshop, so as to provide a good operating environment for the workshop.

Specific operation

The gold refinery and purification process of crude gold is as follows: crude gold → crushing → nitric acid impurity removal → anode plate casting → electrolysis → washing → drying → ingot casting

1.Crush

Due to the different sizes of raw gold, if the raw gold is directly put into the reactor for treatment, it is difficult to dissolve the larger gold particles. Therefore, we design to crush the coarse gold first, or use the granulator to make the gold beads with uniform size.

Crush

Granulating machine

2.Impurity removal by nitric acid

Put the crude gold powder into the impurity removal reactor, and nitric acid is added. Nitric acid can dissolve iron, copper, lead, zinc and other base metals and silver, while gold does not react with nitric acid and is not dissolved, thus separating gold from impurities;

REACTOR

REACTOR

3.Cast anode plate

After washing and drying the gold powder after impurity removal treatment, the anode plate is melted and cast by intermediate frequency furnace;

intermediate frequency furnace

Intermediate frequency furnace 

4.Electrolysis

Pour the molten crude gold into the anode mould to make anode plate. For electrolysis. The electrolyte is composed of aqua regia gold dissolving solution. The environment for making the solution needs to be set according to the different requirements of customers. It can be completed in a complete set of gold dissolving titanium kettle or in glassware equipped with electric furnace.

Gold electrolyzer

Gold electrolyzere

5.Wash

After electrolysis, collect the gold precipitated from the cathode and wash.

wash

Abacus

6.Dry

Dry the pure gold plate which is washed to neutral in the oven.

dry

Oven

7.Cast ingot

After drying the pure gold plate, cast the gold according to the different requirements of customers, different specifications.

cast ingot

Bullion casting machine

Recovery of waste electrolyte:

When the electrolyte is electrolyzed for many times, the impurity ions in the electrolyte will exceed the standard, which will affect the quality of electrolytic cathode gold. Therefore, it is necessary to replace the electrolyte after many times of use to ensure the quality of gold powder.

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