New process for replacing precious metals in cyanide solution with aluminum powder

New process for replacing precious metals in cyanide solution with aluminum powder


1893 Malden Hai Eph first proposed Useful aluminum precipitate from alkaline cyanide solutions gold.

In 1904, Muriel proposed the use of zinc to precipitate gold.

1906 vacuum deoxidation technology with zinc precipitation (Crowell)

Silver precipitated with aluminum at the Deloro smelter in 1908 (Mexico)

Canada's Nipisin Industry also has applications

First, the process advantages

1 Aluminum does not consume sodium cyanide and consumes NaOH.

3Au(CN) 2 - +AL+4OH - ——3Au+6CN - +AlO 2 - +H 2 O

2Au(CN) 2 - +Zn——2Au+Zn(CN) 4 2 -

In the same case, 0.5 mol of Zn powder is required to precipitate 1 mol of Au, and CN- in Au(CN) 2 - is eaten by Zn 2 + , while 1 mol of Al powder, 4/3 mol of NaOH is precipitated by precipitating 1 mol of Au, and 2 mol of NaCN is released.

2Al is a harmful impurity in the cyanidation leaching solution. Cu(CN) 4 3- , Pb 2 + , Zn(CN) 4 2- can cause precipitation of Cu, Zn, Pb, etc. in the gold mud by a lower reduction potential than zinc. In the middle, sewage treatment may not be carried out.

3 Aluminum is less affected by harmful ions than zinc, such as the influence of Se and Sb sulfides.


1 Previous technical requirements pH greater than 12 to ensure Al (OH) 3 + OH - - AlO 2 - + H 2 O

2 control of pH can not use lime, because 2AlO 2 - + Ca (OH) 2 - CaAl 2 O 4 + 2OH -

A calcium aluminate having a low solubility is formed, which clogs the filter and contaminates the final gold precipitate.

3 When gold is recovered from a solution containing a small amount of silver or no silver, the efficiency of aluminum is much lower than that of Zn, but when Ag is more than 50 g/m 3 , precipitation of Au and Ag is excellent.

4 Degassing is required before the precipitation.

5 The method of smelting the precipitated gold mud is different from the method of depositing the gold mud by zinc powder.

6 With Pb(AC) 2, aluminum acetate or calcium acetate is produced, which causes filtration problems.

7 The noble liquid purification plate filter press is easy to block and difficult to clean.

8 industrial trials have certain limitations

Second, industrial production practices

In order to give full play to the advantages of Al, I started industrial testing in a cyanide plant in 2002 and officially applied it to industrial production in 2004, which brought huge economic benefits to the company.

1, the choice of aluminum powder

After a lot of experiments, choose a Q325 type aluminum powder with high water solubility, fast dispersion, high activity and fineness, which is the key to the process.

2, pH value

Generally, it is required to add pH NaOH at the pH=10.5, and add NaOH to the purification liquid entering the gold mud replacement frame, so that the pH of the noble liquid before entering the gold frame is 11; because the aluminum replacement consumes NaOH.

3. Addition of Na 2 CO 3

When the pH is adjusted with lime in the cyanide mineral powder, NaCO 3 may be added to the ball mill to make Ca(OH) 2 +NaCO 3 -CaCO 3 +NaOH, and the other solution of AlO 2 - will also be Ca ( OH) of generation 2 Ca 2 + Ca (AlO 2) 2 and precipitate solution is expensive to ensure Ca 2+ minimum.

4, strengthen the purification of precious liquid

Because CaCO 3 , Ca(AlO 2 ) 2 and fine mud in the ore powder, if not cleaned, the surface of the aluminum powder will be contaminated during the replacement, which will affect the replacement efficiency and pollute the gold mud. In order to solve this contradiction, a new type of filter cloth 747 is used to cover the polyester filter non-woven blanket, and the precious liquid is purified by a plate filter press. Before filtering, a filter aid layer is coated with a filter aid. Take 100g-200g/m 2 ; at the same time, use the frame filter to outsource the 747 type cloth for secondary purification, so that the clarity is extremely high.

5. Strengthen deoxidation, increase vacuum and venting

The water jet pump is replaced by a corrosion-resistant water circulation vacuum pump. Since the circulating water is a noble liquid, the working water temperature is low, so the work of the vacuum machine is relatively stable, and the vacuum degree is high, 0.08-0.09 PMPa.

6, activator Pb (NO 3 ) 2

In order to enhance the replacement effect of aluminum powder, Pb(NO 3 ) 2 is used instead of Pb(AC) 2 , because the crystal is easy to block the gold cabinet, and the amount of PbNO 3 is generally increased by the amount of Al powder (1/10 to 1/8).

7, the smelting of gold mud

Because there is excessive aluminum powder in the gold mud, it is possible to choose a safe and reasonable smelting process. It has been proved by practice that the inorganic method is added with inorganic acid plus oxidant MnO 2 or Cl 2 to remove Cu, combined with the impurity removal operation in the Poliden process. When the Au is high in the gold mud, the inorganic acid is used to remove the impurities; when the Ag high is low, the inorganic acid is selected to remove the impurities (Pb, Zn, Al, Cu) and then the phase-transfer filtration, drying, and piercing of the anode plate are performed. Electrolytic silver.

8. The improved aluminum powder process has strong adaptability and completely replaces the Zn process, especially in the process of high silver cyanide replacement.

9. Simplify sewage treatment. It is mainly Cu(CN) 4 3- and Cu(SCN) 2 , and when Al is replaced, CN- is simultaneously released. Generally, the acidification precipitation method is used now, because the aluminum powder replaces the noble liquid, the displacement force of the aluminum powder is large, so that the Cu in the noble liquid can precipitate more, and even Zn(CN) 2 - can be replaced, which was previously unexpected. It does not affect the cyanidation process due to Cu(CN) 4 3- .

The lean liquid can be recycled. To a certain extent, SO 4 2- is too high, and Na 2 SO 4 crystals appear when the weather is cold in winter. To prevent clogging, natural freezing crystallization is selected to place a part of the poor liquid. In the open-air pool, after the Na 2 SO 4 crystallizes, the lean liquid is returned to the process, and the Na 2 SO 4 crystals are piled up.

10, gold mud composition analysis statistics

From 2006 to 2007, the main application statistics in a cyanide plant in Shandong are as follows:

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