Ammonia leaching of copper sulfide ammonia leaching of copper sulfide ore same root sulfur required in order to become soluble copper salt, the oxidizing agent used is air or oxygen. Since the potential for further oxidation of sulfur to a high oxidation state in an alkaline solution is much lower than in an acidic medium, sulfur is easily oxidized to a product of a high oxidation state, mainly sulfate, and elemental sulfur cannot be obtained. Taking leaching chalcopyrite as an example, the total reaction can be written as: The leaching mechanism consists of a copper ore and pyrite with different potentials in solution. The unstable cuprous ion in the Cu 2 S lattice of the chalcopyrite is dissolved in the solution, and at the same time, an electron on it is conducted to the potential. Higher pyrite, where oxygen is reduced in the solution to form OH - . The dissolved Cu 2+ and NH 3 form an ammonia complex ion. The copper of the chalcopyrite is gradually dissolved, and passes through Cu 1.96 S, Cu 1.8 S, and Cu 1.7 S in many intermediate state copper-sulfur compounds, eventually becoming copper blue CuS. Because the molar volume of CuS is smaller than that of Cu 2 S, the ore particles shrink in volume while leaching copper, and cracks and pores are continuously generated, providing diffusion channels for reactants and products. Under sufficient oxygen supply, the leaching speed can reach 1% copper per minute. The overall reaction equation can be expressed as follows: [next] Bicycle Air Pump,Bicycle Hand Pump,Bicycle Mini Pump,Bike Pump Xingtai Yiming Bicycle Co., Ltd , https://www.ymbicycleparts.com
1 1
CuFeS 2 +4——O 2 +6NH 3 +(n+1 )H 2 O ==== Cu(NH 3 ) 4 2+ + ——Fe 2 O 3 ·nH 2 O+2NH 4 + +2SO 4 2-
4 2
It can be seen from the reaction:
(1) Since the oxidation state of sulfur is from 2 to +6, 2 mol of 0 2 is consumed per mole of sulfur.
(2) The oxygen consumed by the oxidation of iron is only 1/16 of that of sulfur. The formation of hydrated iron oxide can separate iron from the solution, but the precipitation may form a film that coats the surface of the ore and affects further reactions. For iron-free minerals such as chalcopyrite, the process is much simpler.
(3) Sufficient NH 3 is required to form a complex with the leached copper ions and neutralize the generated acid.
The overall reaction is thermodynamically very advantageous, but the rate of reaction depends on the kinetic factors. Due to the large amount of oxygen consumption, the kinetic control step is often the rate of oxygen supply, especially the rate of diffusion of oxygen from the solution to the reaction zone in the ore. The results of the experimental study indicate that:
(1) The mill is finely ground, which reduces the diffusion route of the reactants and products, and is advantageous for leaching, and generally needs to be ground up to 200 mesh.
(2) The molar ratio of NH 3 in the leachate to the expected leached copper is between 5 and 6.5, and NH 4 + is generally 2 mol / L. NH 4 + NH 3 and the composition of the buffer system, the pH value rises slow, prevent hydrolysis of metal ions.
(3) an increase in agitation, dissolved oxygen is not only conducive to, diffusion, and, in strong erosion, can be hydrated iron oxide particles off the surface of the mine.
(4) Increasing the partial pressure of oxygen is conducive to increasing the solubility of oxygen. However, the partial pressure of oxygen has a significant effect on the leaching speed before 0.6 MPa, and after that, the effect is weakened.
(5) Increasing the reaction temperature can increase the reaction rate, but after 120 ° C, the effect is gentle.
The latter two conditions are already under pressure and warm leaching, and are carried out in a pressurized reactor with high investment and operating costs. Although there are many studies on copper mine pressure leaching, current industrial applications are limited to the treatment of scrap alloys, nickel matte or complex concentrates, and copper is only one of them.
The recovery of copper in the ammonia solution is carried out by steaming ammonia precipitation to warm the copper-containing ammonia solution, and the ammonia is distilled off. If the leachate is composed of NH 3 -NH 4 + -CO 3 2- , CO 2 is also distilled off with NH 3 . As the concentration of free ammonia in the solution decreases, the copper-ammonium complex gradually dissociates, and the free copper ion hydrolyzes to form a hydrated oxide and a basic salt, which is dissolved into a solution by using sulfuric acid, and the electrowinning can obtain high-quality copper.
Ammonium sulfate in the solution cannot be distilled off, and can be evaporated and crystallized as a product for sale. It is also possible to add lime to the solution to cause causticization, further distill off the ammonia, and the resulting gypsum is discarded.
Hydrogen reduction Hydrogen reduction of copper ammonia solution can directly produce copper powder. However, before the reduction, the temperature is raised to a high temperature of 240 ° C, and the sulfur compound having an oxidation state of less than 6 in the solution is sufficiently oxidized to sulfate. Otherwise, the sulfur content of the product copper powder will be high. The NH 3 /Cu ratio before reduction should be adjusted to about 2. The hydrogen reduction is carried out at 170 to 205 ° C under a pressure of 4 MPa, and the resulting copper powder is spherical. The addition of polyamine is advantageous for the dispersion of copper powder and prevention of crusting. If there are metal ions such as nickel, cobalt , and zinc coexisting in the solution, they are not reduced when the copper is reduced, and thus can be recovered after separating the copper powder.
Abbott Process Anaconda's Arbiter process uses a closed container for ammonia leaching at 75-80 ° C, 48-55 kPa oxygen partial pressure. The material is mainly copper ore and sulfur. Arsenic copper ore. After leaching for 3~4h, the copper leaching rate is about 80%. Extending the leaching time can increase the copper leaching rate, but it is not conducive to the recovery of the latter silver . The leachate is subjected to extraction-electrolysis after stripping. Copper has been tested for precipitation with sulfur dioxide. The copper flotation in the leach residue is recovered, the total copper yield is 96%~97%, and the total yield of silver is 90%. [next]
This process was produced on a 91t/d scale for many years and was shut down due to the discontinuation of Anaconda. Part of the sulfur in this process mineral is oxidized to sulfate and leached. In order to remove the sulfate, lime is added to the causticized ammonia, which is often a problem.
Ammonia leaching process according to Scone Scone Dida Dida process according to Chile (Escondida) is used by the mining company BHP Minerals laboratory in Nevada developed [1]. If the sulphide is to be oxidized when leaching the sulphide ore, the oxygen consumption is large, and ammonium sulfate or calcium sulfate which is not used is generated. The Iskandida mine is a chalcopyrite, some of which are easily leached under conditions of air oxidation. Moreover, almost no sulfur is oxidized and dissolved. Thus, there is no need to exclude sulfate.
The process is as shown in the figure below. Leaching with ammonia-ammonium sulfate can leach 40%~50% of copper in the ore. The solution is extracted - stripped and purified, and then electrowinned. The leaching slag is subjected to flotation to enrich the unleached copper minerals, and is sent to a fire smelting plant. 
1
Cu 2 S+——O 2 +2NH 3 +2NH 4 + ==== Cu(NH 3 ) 4 2+ +CuS+H 2 O
2
It can be seen that in this reaction, since oxygen is used only for the cuprous oxide salt without oxidizing sulfur, the compound having no sulfur is eluted.
The influence of various factors on the diffuse
NH 3 +NH 4 +
The size of the ore particles has a greater influence on the initial velocity. Add ammonia to the leaching 50% copper, so that —————— is constant, when the ratio reaches 2.5 left Cu 2+
The right leaching speed is very fast. The temperature has little effect and the leaching can be carried out at room temperature or around 40 °C. Tests have shown that the supply of air during the leaching process is critical, and good gas supply conditions can increase the reaction rate. Excessive gas supply, although increasing the copper leaching rate, significantly increased sulfate in the leachate, indicating that some of the sulfur was oxidized.
A pilot plant with a daily processing capacity of 600 kg of ore was subjected to a six-month test and showed that only 0.6% of the sulfur was oxidized.
The leachate contains 32g/L of copper, and the zinc in the impurities is higher, reaching 50~70mg/L, and the others are very low. 75% kerosene LIX54- organic phase was extracted level, 0 / A = 1 ~ 1.2 . The organic phase load copper can reach 30g/L, and the washing liquid is recycled by using the 1 or 2 stage ammonia washing.
Level 1 stripping, O/A = 0.8.
The plant design and operation process was finally adopted by the Iskandida mine, and a production plant with an annual processing capacity of 500,000 tons of ore and 80,000 tons of copper was designed and built. The plant was commissioned in November 1994. Electrolytic copper contains 99.9999% copper. However, due to serious technical and economic problems, the plant has been discontinued. Recently, it has been reported that after four months of operation, there is a problem of stripping difficulties and two interphase entrainment problems. The study found that it is related to the reaction of LIX54 ketone with ammonia to form ketimine [2] .
references:
1.Queneau PB, Gruber R WJ Metals, 1997, Oct: 34
2. Kordosky, GA, Proc. ISEC 2002, Ed. Sole KC et al., South Africa Institute of Mining and Metallurgy, Johannesburg, 2002, 360-365