Method for purifying alloyed gold

Abstract

The invention provides a method for purifying alloyed gold, which comprises the following process steps of: (1) removing impurities by nitric acid, namely tabletting alloyed gold, feeding the alloyed gold into a reaction kettle, adding nitric acid according to the molar ratio of HNO3 to Ag of (6-10): 1, reacting, filtering to obtain gold slag, washing the gold slag by nitric acid, and entering an aqua regia gold dissolving stage; (2) dissolving gold with aqua regia: adding aqua regia into the gold residues obtained in the step (1) according to the molar ratio of HNO3 to Au being (5-10): 1, filtering after reaction, leaching filter residues with aqua regia again, and enabling gold-rich filtrate to enter a reduction process; and (3) reduction is conducted, specifically, a reducing agent is added into the gold-rich filtrate according to the H2C2O4 / Au molar ratio of (3-6): 1, the reducing agent is a mixture of oxalic acid and sodium tripolyphosphate, the mass ratio of oxalic acid to sodium tripolyphosphate is (95-100): 1, the temperature ranges from 40 DEG C to 80 DEG C, the reaction time ranges from 3 h to 6 h, and filtering, washing, drying, melting and ingot casting are conducted after the reaction. Through the novel reducing agent, the two steps of saltpeter removing and filtering can be omitted in the whole technological process, the direct gold recovery rate is high, the gold powder purity reaches 99.99%, secondary purification is not needed, the technological process is shortened, and operation is easy.

Description

Technical Field

[0001] The invention belongs to the technical field of hydrometallurgy, and in particular relates to a method for purifying alloy gold. Background Art

[0002] Precious metal refining usually adopts aqua regia gold dissolving chemical method, gold electrolysis method, gold extraction method and chlorination gold separation purification method, etc., which are mainly promoted and applied by different companies due to their advantages: less environmental pollution, short refining cycle, and ability to recover a variety of precious metals. The aqua regia gold dissolving method is widely used by domestic gold refining companies for its safety, mature technology and high efficiency. Compared with other methods, the aqua regia chemical refining method is a relatively mature process purification method that has been tested in long-term practice. Moreover, after a long period of development and exploration, the process of aqua regia gold dissolving method has been greatly improved, and the equipment has also undergone several upgrades. At present, this method has great advantages in product color, automatic control of the operation process, waste gas treatment, simple and easy treatment of wastewater components, and product recovery.

[0003] The aqua regia gold dissolution method mainly adopts the following process flow: acid leaching to remove impurities, aqua regia dissolution, nitrate removal, primary filtration, primary reduction, secondary filtration, secondary reduction, tertiary filtration, soaking, washing, rinsing, drying, etc. Although the aqua regia gold dissolution method is relatively mature, the operation process is relatively cumbersome. For example, nitrate removal must be carried out after aqua regia gold dissolution. Urea is usually added to convert the free nitric acid in the gold-containing aqua regia into gas overflow system to prevent excessive nitric acid from causing incomplete gold reduction or gold powder re-dissolution; the urea usually added in this process is excessive. On the one hand, excessive urea will affect the subsequent gold reduction, and on the other hand, it will cause part of the gold to be adsorbed on the surface of urea, resulting in a low direct gold recovery rate. Reduction usually uses reducing agents such as oxalic acid, sulfur dioxide, sodium sulfite or ferrous ions. When these agents are used for reduction, in the later stage of the reduction reaction, with the decrease of the solution electrode potential and the concentration of chloroauric acid, the excessive addition of reducing agents, and the change of the activation energy of the reaction, some impurity metals enter the reduced gold powder, resulting in the formation of some metal impurities that precipitate and mix with the gold powder, including platinum, palladium, selenium, tellurium, copper, nickel, etc., causing the quality of the gold powder to fail to meet the requirement of 99.99%. In order to make the gold powder reach the requirement of 99.99%, one method is to cast the coarse gold powder into an anode for electrolysis, and another method is to chlorinate the gold powder first, and then use sulfur dioxide for two-stage reduction under high acidity conditions. The first stage produces 99.99% gold powder, and the gold powder produced in the second stage is returned to chlorination. In summary, the aqua regia gold dissolution method has problems such as long process flow, low direct yield, and high impurity content of gold powder. Summary of the invention

[0004] In order to solve the above problems, the present invention provides a method for purifying alloy gold.

[0005] The technical solution of the present invention is achieved as follows: a method for purifying gold alloy, which comprises the following process steps:

[0006] (1) Nitric acid removal: The gold alloy is pressed into tablets and then sent to the reactor. 3 Add nitric acid at a molar ratio of 6 to 10:1, at a temperature of 25 to 100°C, and a reaction time of 2 to 4 hours. Impurities such as Ag, Cu, Pb, and Fe in the gold alloy react with nitric acid to form nitrates. After the reaction, the gold residue is filtered to obtain gold residue. After the gold residue is washed with nitric acid, it enters the aqua regia gold dissolution stage;

[0007] (2) Gold dissolution in aqua regia: The gold residue obtained in step (1) was heated to 400 °C with HNO 3 Aqua regia is added at a molar ratio of 5 to 10:1, the temperature is 60 to 90°C, the reaction time is 2 to 4 hours, and the reaction is filtered after the reaction. The filter residue is leached with aqua regia again, and the gold-rich filtrate enters the reduction process. The main chemical reactions that occur are as follows:

[0008] Au+HNO3+4HCl=H[AuCl4]+NO↑+2H2O;

[0009] (3) Reduction: The gold-rich filtrate is heated to 400 °C. 2 C 2 O 4 A reducing agent is added at a molar ratio of 3 to 6:1, wherein the reducing agent is a mixture of oxalic acid and sodium tripolyphosphate, and the mass ratio of the two is 95 to 100:1. The temperature is 40 to 80°C, and the reaction time is 3 to 6 hours. After the reaction, the mixture is filtered, washed, dried, melted, and cast into ingots. The main chemical reactions that occur are as follows:

[0010] 2HNO3(dilute)+3H2C2O4=6CO2↑+4H2O+2NO↑

[0011] 2HNO3(concentrated)+H2C2O4=2CO2↑+2H2O+2NO2↑

[0012] 2H[AuCl4]+3H2C2O4=2Au↓+8HCl+6CO2↑;

[0013] Preferably, the alloy gold mainly comprises Au: 50% to 99%, Ag: 0.1% to 30%, Cu: 0.1% to 10%, Pb: 0.1% to 10%, Fe: 0.1% to 5%, and Bi: 0.1% to 5%.

[0014] The beneficial effects of the present invention are as follows: the present invention uses a new type of reducing agent, and the two steps of driving out nitrate and filtering can be reduced in the entire process flow, the gold direct recovery rate is high, the gold powder purity reaches 99.99%, the gold purity is high, no further purification is required, the process flow is shortened, and the operation is simple.

[0015] Oxalic acid is a common reducing agent, and sodium tripolyphosphate is often used as a moisture retainer, quality improver, pH regulator, and metal chelator. Using oxalic acid alone to reduce the gold-rich solution will produce gold powder with high impurity content. Sodium tripolyphosphate itself has no reducing properties and cannot reduce gold; but when oxalic acid and sodium tripolyphosphate are mixed, they can change the redox state of some metal ions and give full play to the synergistic effect. After oxalic acid is added, the reducing property of oxalic acid to reduce gold ions is improved, while the reducing property of oxalic acid to reduce other metal ions is reduced, resulting in high purity gold powder. DETAILED DESCRIPTION

[0016] For better understanding and implementation, a method for purifying gold is described in detail below:

[0017] Embodiment 1:

[0018] The main components of alloy gold are: Au: 50.11%, Ag: 30.00%, Cu: 8.27%, Pb: 7.32%, Fe: 4.14%, Bi: 0.14%.

[0019] Nitric acid impurity removal: The gold alloy is pressed into tablets and then sent to the reactor. 3 Nitric acid is added at a molar ratio of 6 to 1 for Ag / Ag, the temperature is 25°C, the reaction time is 2h, and the impurities such as Ag, Cu, Pb, Fe in the gold alloy react with nitric acid to generate nitrates. After the reaction, the gold residue is filtered to obtain gold residue. After the gold residue is washed with nitric acid, it enters the aqua regia gold dissolution stage.

[0020] Aqua regia gold dissolution: The gold residue obtained is added with HNO 3 Aqua regia was added at a molar ratio of 5:1, the temperature was 60°C, the reaction time was 2h, and the reaction was filtered after the reaction. The filter residue was leached with aqua regia again, and the gold-rich filtrate entered the reduction process.

[0021] Reduction: The gold-rich filtrate was heated to 40 ℃ and then heated to 30 ℃ for 2 h. 2 C 2 O 4 / Au molar ratio of 3:1, add reducing agent, oxalic acid and sodium tripolyphosphate mass ratio of 95:1, slowly add reducing agent until no more gas is generated, temperature 40 ° C, reaction time 3h, after reaction, filter, wash, dry, melt, ingot. Comparative Example 1:

[0022] Compared with Example 1, sodium tripolyphosphate was not added and other conditions were the same.

[0023] Embodiment 2:

[0024] The main components of alloy gold are: Au: 78.21%, Ag: 12.32%, Cu: 4.12%, Pb: 2.14%, Fe: 1.38%, Bi: 1.74%.

[0025] Nitric acid impurity removal: The gold alloy is pressed into tablets and then sent to the reactor. 3 Nitric acid is added at a molar ratio of 8:1, the temperature is 100°C, and the reaction time is 4h. Impurities such as Ag, Cu, Pb, Fe in the gold alloy react with nitric acid to generate nitrates. After the reaction, the gold residue is filtered to obtain gold residue. After the gold residue is washed with nitric acid, it enters the aqua regia gold dissolution stage.

[0026] Aqua regia gold dissolution: The gold residue obtained is heated to HNO 3 Aqua regia was added at a molar ratio of 7:1, the temperature was 90°C, the reaction time was 4h, and the reaction was filtered after the reaction. The filter residue was leached with aqua regia again, and the gold-rich filtrate entered the reduction process.

[0027] Reduction: The gold-rich filtrate was heated to 40 ℃ and then heated to 30 ℃ for 2 h. 2 C 2 O 4 / Au molar ratio of 4:1, add reducing agent, the mass ratio of oxalic acid to sodium tripolyphosphate is 100:1, slowly add reducing agent until no gas is generated, temperature is 80°C, reaction time is 6h, filter, wash, dry, melt and cast after reaction.

[0028] Comparative Example 2:

[0029] Compared with Example 2, no sodium tripolyphosphate was added, and other conditions were the same.

[0030] Embodiment 3:

[0031] The main components of alloy gold are: Au: 98.01%, Ag: 0.12%, Cu: 0.14%, Pb: 0.14%, Fe: 0.15%, Bi: 1.40%.

[0032] Nitric acid impurity removal: The gold alloy is pressed into tablets and then sent to the reactor. 3 Nitric acid is added at a molar ratio of 10:1, the temperature is 80°C, and the reaction time is 3h. Impurities such as Ag, Cu, Pb, Fe in the gold alloy react with nitric acid to generate nitrates. After the reaction, the gold residue is filtered to obtain gold residue. After the gold residue is washed with nitric acid, it enters the aqua regia gold dissolution stage.

[0033] Aqua regia gold dissolution: The gold residue obtained is heated to HNO 3 Aqua regia was added at a molar ratio of 10:1 for Au / Au, the temperature was 70°C, the reaction time was 3h, and the reaction was filtered after the reaction. The filter residue was leached with aqua regia again, and the gold-rich filtrate entered the reduction process.

[0034] Reduction: The gold-rich filtrate was heated to 40 ℃ and then heated to 30 ℃ for 2 h. 2 C 2 O 4 / Au molar ratio of 6:1, add reducing agent, oxalic acid and sodium tripolyphosphate mass ratio of 97:1, slowly add reducing agent until no gas is generated, temperature 60 ° C, reaction time 4h, after reaction, filter, wash, dry, melt, ingot. Comparative Example 3:

[0035] Compared with Example 3, sodium tripolyphosphate was not added and other conditions were the same.

[0036] name Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Au direct yield % 99.24 99.34 99.18 98.24 98.15 98.51 Gold ingot purity% 99.99 99.99 99.99 98.12 98.24 98.13

[0037] It can be seen from the results of the embodiments and comparative examples that after adding an appropriate amount of sodium tripolyphosphate to the reducing agent oxalic acid, the direct recovery rate of gold reached more than 99%, and the purity of the gold ingots reached 99.99%, which meets the national standard GB / T 4134-2021 1# gold ingot standard.

Claims

1. A method for purifying alloy gold, characterized in that The process steps include: (1) Nitric acid impurity removal: After the gold alloy is pressed into tablets, it is sent to a reactor, and nitric acid is added at a HNO3 / Ag molar ratio of 6 to 10:

1. The temperature is 25 to 100°C and the reaction time is 2 to 4 hours. The impurities such as Ag, Cu, Pb, and Fe in the gold alloy react with nitric acid to form nitrates. After the reaction, the gold residue is filtered to obtain gold residue. After the gold residue is washed with nitric acid, it enters the aqua regia gold dissolution stage; (2) Gold dissolution in aqua regia: The gold residue obtained in step (1) is added with aqua regia at a HNO3 / Au molar ratio of 5 to 10:1, the temperature is 60 to 90°C, the reaction time is 2 to 4 hours, and the reaction is filtered after the reaction. The residue is leached with aqua regia again, and the gold-rich filtrate enters the reduction process. The main chemical reactions that occur are as follows: Au+HNO3+4HCl=H[AuCl4]+NO↑+2H2O; (3) Reduction: The gold-rich filtrate is added with a reducing agent according to a H2C2O4 / Au molar ratio of 3 to 6:

1. The reducing agent is a mixture of oxalic acid and sodium tripolyphosphate, and the mass ratio of the two is 95 to 100:

1. The temperature is 40 to 80°C, and the reaction time is 3 to 6 hours. After the reaction, the mixture is filtered, washed, dried, melted, and cast into ingots. The main chemical reactions that occur are as follows: 2HNO3(dilute)+3H2C2O4=6CO2↑+4H2O+2NO↑ 2HNO3(concentrated)+H2C2O4=2CO2↑+2H2O+2NO2↑ 2H[AuCl4]+3H2C2O4=2Au↓+8HCl+6CO2↑.

2. A method for purifying gold alloy as claimed in claim 1, characterized in that The alloy gold mainly comprises Au: 50%-99%, Ag: 0.1%-30%, Cu: 0.1%-10%, Pb: 0.1%-10%, Fe: 0.1%-5%, and Bi: 0.1%-5%.