Water chlorination method for gold extraction-high temperature chlorination volatilization leaching process

As early as 1851, Prattner proposed the use of chlorine to convert gold into gold chloride, and then extract gold chloride with water. This method was later adopted in Silla. Allen first recognized the volatilization of gold chloride. The problem of volatilization of gold chloride has led to a series of studies. In 1964, Schafer and many Soviet scholars presented valuable research, and at the end of 1970 Hag and Hill's research work at the Colorado School of Mines reached its climax. The US Bureau of Mines recently proposed various chlorides of gold, their stable zones, and based on the experiments of gold ore chlorination by Essell, Hainan, and Fisher. Generate the latest thermodynamic data for these chlorides. This section does not repeat these derivations, but rather describes the process outlined by Stuart Crossel for the Holmeske type gold ore and the design of the roasting, chlorinator and condensing systems; and the Soviet Union’s four different The results of the chlorination test of the ore and the expansion test of the Liaoning Metallurgical Research Institute.
1) Chlorination process of the Holmesk gold mine
The chlorination process is shown in the figure below. The crushed ore is fed into a fluidized roaster, and the generated SO ₂ gas is sent to a contact sulfuric acid plant. The calcined ore enters the two-stage chlorinator and is passed to the chlorinator for chlorine gas for recycling. The gas evolved from the chlorinator enters the condensation chamber where it contacts and reacts with sodium chloride to form a salt-gold chloride melt (gold has been extracted from the gas stream) which is further processed to recover gold. The chlorine gas and the spent material are cooled and washed with sulfuric acid and sent to the compressor for repressurization. A portion of the returned gas stream is taken for liquefaction so that the chlorine gas can be distilled and the spent material removed

1 roaster. When gold ore chlorination process described silicon containing moderate amount of pyrite has been drawn a simple process comprising operations including temperature and flow rate, as shown in FIG 5% iron content, roasting There is no need to replenish carbon in the process, and enough heat can be generated to achieve the ore roasting. Whether oxygen or air is used in the roasting process, or a combination of the two, it is determined by experiments that oxygen is used, because at this time, although the power consumption and investment cost are increased, the volume of the roaster can be reduced, and the SO ₂ concentration can be obtained. The gas is sent to the sulphuric acid plant, thus offsetting the additional cost of oxygen. [next]
The design of the calcination should be based on whether oxygen or air is used, taking into account the optimum calcination temperature. For the sake of convenience, it is appropriate and feasible to assume a calcination temperature of 627 ° C, but it is also possible at a lower temperature (decreased by 100 ° C). When the calcination temperature is lowered, that is, when calcined in a reactor at 527 ° C, the feedstock may be cooled and completely bare shell, but still in thermal equilibrium.
In order to accelerate the reaction of chlorine and gold, the operating pressure of the chlorinator must be increased, but the pressure of the calciner is higher than the operating pressure of the chlorinator. It is also desirable to increase the pressure of the chlorinator in order to provide S0 ₂ for the contact sulfuric acid.
2 chlorinator. This type of gripper must be designed as a two-stage or three-stage reactor, and these sections may all be placed in the same furnace shell. The most suitable operating temperature is about 350 °C. Although the flow of chlorine gas will cool the reactor and there will not be a large amount of heat of reaction, it is still necessary to cool the calcined ore feed. Since the gold-iron chloride complex will accumulate on the furnace wall and leave a large amount of gold in the furnace (these gold can only be recovered when the reactor is washed once a year or two), the chlorination reactor The lining of the refractory material should be designed as much as possible to prevent it from accumulating gold complexes at the walls. Since the conditions of these reactions are relatively moderate, corrosion problems of the refractory material do not occur.
In order to consider the balance between heat and mass, the chlorine gas flow rate is 61 cm/s, which is the lowest fluidization velocity for the solid material to achieve good agitation, and the lowest steady state gas flow. The pulsating flow of chlorine is also available, which reduces the amount of chlorine flowing into the reactor and throughout the condensation stage. In addition, the design itself is not intended to utilize all of the oxygen, but instead it is recycled by chlorine. Maintain a high pressure to ensure that the gold complex is formed at a fast reaction rate.
Experiments have shown that gold ore is directly chlorinated in the absence of any promoter, and the -200 mesh sample can be chlorinated at a rate of 3.45% per minute. Operating in the presence of ferric chloride (which increases the rate of chlorination by at least 25 times) and has a certain chlorine pressure (which increases the rate of chlorination by 13.5-18 times), the reaction kinetics appear to be quickly. It is expected that the gold mine in Holmst will be broken to -20 mesh, and the gold can be completely converted into gold chloride by staying in the chlorinator for 1 hour. However, in order to ensure a high conversion rate in a chlorinator, the reaction bed must be operated at a relatively low average bed concentration. With two stages of chlorination, the first stage can be operated at a higher gold concentration, and the final finishing stage is operated at a very low gold concentration, which allows gold to achieve a high total conversion.
This process shows that it is necessary to add a small amount of iron powder to each chlorinator. Because the equilibrium calculations show that the reaction of iron oxide with chlorine at the reaction temperature of the chlorinator does not provide the necessary amount of FeCl ₃ complex.
3 condensation system. After the formation of the gold complex in the chlorinator, the vaporous complex escapes from the reactor in its very low concentration in oxygen. Before the gold complex condenses, the dust is removed from the gas stream near the chlorinator temperature by a cyclone dust collector, and then these gases are contacted with the sodium chloride containing the melt to make the volatile gold-iron complex The compound can be converted to NaAuC1 ₄ equivalent to sodium tetrachloroferrate.
The bond strength of the NaAuC1 ₄ complex salt is sufficient to separate the gold chloride from the gas phase AuFeCl ₆ complex and, at less than 150 ° C, in the form of a liquid melt containing such a complex.
This reaction and gas cooling process is carried out in a horizontal or vertical high-speed flue having a diameter of 0.46 m and a height of 30 m. If necessary, the flue can be bent 180 ^o . This liquid salt complex can be collected at the end of the flue with a cyclone, while the gas (at a temperature of about 150 ° C) is further cooled to 80 ° C by contact with the sulfuric acid of the scrub cyclone. The oxygen is then compressed in an axial compressor and returned to the chlorination stage at 80 °C. To achieve high compression and distillation, a portion of the gas is released to prevent accumulation of spent gas. The reaction of such a gold complex with a salt may release a large amount of heat, but it is still too small to achieve thermal equilibrium, so heat transfer becomes an important factor. [next]
It is believed that the use of a salt to complex the gold-containing chloride in the gas phase is achievable and provides a more efficient method of adsorption than activated carbon to recover gold from the gas stream exiting the chlorinator. Gold or silver ore is treated by low-temperature chlorination to volatilize gold and silver in the ore to achieve the purpose of gold extraction and silver.
2) Chlorination volatilization method recovering gold from insoluble gold concentrate. Chlorination volatilization method is to heat the concentrate together with the chlorinating agent to chlorinate gold, silver, copper , lead , zinc and other metals to form volatile. Substances are sublimed and captured in soot, which is then recovered step by step from the soot by hydrometallurgy.
The chlorinating agent NaCl or CaCl ₂ is usually used in an amount of 10% to 15% by mass of the concentrate. When the raw material is a sulfide concentrate, incomplete oxidation roasting should be carried out in advance to make 3%~5% sulfur remain in the calcined sand, so as to generate a part of the chlorination catalyst to produce S ₂ Cl ₂ during the chlorination process. The ore can be chlorinated at 1 000 ° C, but when the concentrate does not contain sulfur, the chlorination temperature must not be lower than 1150 ° C. At this point the amount of chlorinating agent can be reduced to 5% of the concentrate quality. The concentrate is usually mixed with water with a mass fraction of 10%~15% NaCl to make a ball in a disc ball making machine. After drying at 150~200 °C, the powder is removed by sieving, and then chlorination is carried out in a vertical furnace. When the material used is powder (no ball), the rotary kiln can be used for chlorination. The chlorination volatilization test results of the four insoluble gold concentrates in the Soviet Union are shown in the table below.

In China, a high-temperature chlorination volatilization expansion test was carried out on the gold concentrate of a mine. Gold concentrate components: Cu 0.20%, Pb 0.29%, Zn 0.29%, Fe 32.00%, S 30.96%, Si0 ₂ 26.30%, CaO 0.48%, MgO 0.49%, A1 ₂ 0 ₃ 0.89%, Au 76.38 g/ t, Ag 41.83 g/t. Since the concentrate contains high sulfur, it is first desulfurized by boiling roasting. After calcination, the calcination was combined with 70.6% of 140-180 mesh soot, and a calcium chloride solution having a relative density of 1.29 to 1.30 was sprayed on a disc granulator to prepare pellets having a diameter of 10 to 12 mm. It is dried in a vertical drying oven to about 1% water. At this time, the pellet contains 8%-10% calcium chloride and the compressive strength is 10~15kg/t. After the sieve is removed by shaking, it is sent to the rotary kiln for chlorination. Roasting.
The rotary kiln with test capacity is 0.98 t/(m ³ ·d), the inclination of the kiln body is 1.85%, the rotation speed is 1.42 r/min, the filling coefficient of the ball in the kiln is 10.3%, and the residence time is 80 min. For heating diesel, the fuel consumption per ton of mineral balls is 250~300 kg. The temperature in the high temperature zone (chlorination zone) of the kiln is 1040~1080°C, the flue gas contains 5%~9% oxygen, and the flue gas discharge rate is 1.5~2 m/s. After roasting by chlorination, the weight loss rate of the ore ball is about 10%, and the compressive strength is 31 ~ 95 kg/t. The iron and impurities contained in the ball meet the requirements of iron making, and the pig iron can be directly smelted into the blast furnace. Dust collection uses a wet fast dust collection system consisting of a settling bucket, an impact washer, an internal spray venturi and a wet electrostatic precipitator.
The gold in the chlorinated volatile soot is all in a metallic state, and the hydrochloric acid solution is added to the magnetic ball mill , and the bleaching powder and sulfuric acid are added to the liquid to liberate the active chlorine to chlorinate the gold: [next]
2Au+Cl _{2 ^{—→}} 2AuCl

AuCl+Cl ^{- _{—→}} AuC1 ₂

AuC1 ₂ ^- +C1 ₂ —→ AuC1 ₄ ^-

Its total reaction formula is:
2Au+3Cl ₂ +2HCl —→ 2HAuCl ₄

Since the tobacco method contains more gold (12 kg/t), two leaching is used. The dust was ground to -0.15 mm (100 mesh) before leaching. The leaching conditions were as follows: solid-liquid ratio 1:2, 10% hydrochloric acid, 5% bleaching powder, 4% sulfuric acid, leaching time 4h, gold leaching rate up to 96.70%. The secondary leaching conditions were as follows: solid-liquid ratio 1:1.5, 10% hydrochloric acid, 3% bleaching powder, 4% sulfuric acid were added, and the leaching time was 4 h, and 79.80% of the residual gold was allowed to enter the solution. The total leaching rate of the two leaching golds is over 99%, and the leaching slag contains less than 100g/t of gold.
The secondary leaching slag is washed twice with a mass fraction of 2% hydrochloric acid, one washing liquid is returned for secondary leaching, and the second washing liquid is returned for one washing. The washing slag is filtered and sent to recover silver and lead. The secondary chlorinated leachate is returned for a single leaching to obtain a gold-rich leachate.
One leached gold-rich solution, reduced by sodium sulfite at a concentration of 0.7 moV/L hydrochloric acid:

2AuCl ₃ +3Na ₂ S0 ₃ +3H ₂ 0 ==== 2Au ↓ +6HC1+3Na ₂ SO ₄

The amount of sodium sulfite is 1.2 to 1.8 times the theoretical amount, usually 1.5 g per gram of gold. The reduction rate of gold is 99.9%, and the mass concentration of gold in the liquid is below 0.01 g/L. The reduced gold particles are filtered, washed twice with hydrochloric acid having a mass fraction of 1%, and washed twice with water to obtain a purity of gold greater than 98.5%, and then treated with ammonium chloride solution and dilute nitric acid to remove silver, lead, etc. Impurities, gold purity can be increased to 99.7% ~ 99.8%.
The leached gold residue is washed with an acidic saline solution having a pH of 1, and sent to recover other metals.

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