2 Century BC began iron-displacement method of recovering copper from the pit water containing copper sulfate, to Song, i.e. accounted for leaching copper producing 15% to 20% of the copper production. 1968 Arizona Ran Jia Shi (Ranches) pioneered the solvent extraction of copper, has opened a new chapter in the copper industry, resulting in a modern hydrometallurgical copper industry. So far, modern wet copper smelting has become an independent industrial system, and its development speed is much higher than the development speed of the overall copper industry, mainly from low-grade ore, such as oxidized ore, stripped off-balance sheet ore, flotation tailings. The copper is recovered, and these materials are the raw materials that are difficult to use in pyrometallurgical smelting. With the gradual depletion of copper resources and the improvement of copper hydrometallurgical technology, the raw materials of copper hydrometallurgy are constantly changing and expanding. Sulfuric acid is the most widely used and widely used leaching agent in wet copper smelting. It can leach copper from acidic and low-alkaline copper ore. It is not suitable for copper ore with high content of alkaline gangue. On the one hand, high acid consumption leads to high production cost. On the other hand, the calcium sulfate formed by the reaction will adhere to the surface of the ore to reduce the reaction rate, prolong the copper leaching period, and even hinder copper leaching. The ammonia-ammonium salt leaching system is an important leaching medium system in hydrometallurgy. Foreign countries such as the Anaconda Copper Company and the Escondida mine in Chile conducted semi-industrial and industrial tests on copper sulfide concentrates using ammonia-ammonium salt leaching media. Yunnan Dongchuan Mining Bureau and Beijing Research Institute of Mining and Metallurgy have conducted research on the Tangdan Copper Mine for more than ten years and conducted industrial tests. Aiming at the problem of copper extraction from high-alkaline low-grade copper oxide ore, the industrial test results of high-alkaline gangue low-grade copper oxide copper extraction in ammonia-ammonium salt system were introduced, and the process and economic analysis were carried out. The results showed that ammonia leaching - The extraction-electrowinning process is feasible, and the cathode copper mass can reach 99.99%. First, the nature of the ore The ore is a soil-shaped copper oxide ore, and the ore mine accounts for more than 90%. The lump ore is severely weathered and brittle. The ore is brownish yellow and has clear blue malachite particles after washing with water. The results of multi-element analysis and copper phase analysis of ore are shown in Tables 1 and 2, respectively. Table 1 Results of multi-element chemical analysis of ore Note: Au, Ag content unit is g / t. Table 2 Copper phase analysis results of ore % From Table 1, the ore containing up to 33.78% calcium oxide, magnesium oxide, calcium oxide to the total amount of 34.94%, overbased metal ore. The ore is high in silver and can be recycled. In addition, the ore also contains a certain amount of antimony . It can be seen from Table 2 that the copper in the copper oxide minerals is 97.12%, and the ore type is a high oxidation rate copper oxide ore, wherein the free copper oxide accounts for 73.44%. 2. Theoretical analysis of ammonia leaching of copper oxide ore and determination of process flow The ammonia-ammonium salt system is an important hydrometallurgical leaching system. Metal ions such as copper, cobalt and nickel can form a stable ammonia complex compound and dissolve in the ammonia-ammonium salt solution. Since copper ions form a stable coordination compound Cu(NH 3 ) n 2+ (n=1 to 4) in the ammonia solution, the solubility is large. An ammonium salt such as ammonium sulfate or ammonium hydrogencarbonate is added to the solution to buffer the pH of the solution and prevent the hydrolysis reaction of copper. Copper in a basic carbonate mineral such as malachite and copper oxide is dissolved in an ammonia solution by forming a complex, and the reaction equation is as follows: The copper in the copper oxide ore is contacted with the ammonia-ammonium salt of the leaching medium to form soluble copper ammine ions into the solution to complete the dissolution and leaching of the copper. Using a solvent extraction technique, the copper and the impurities in the solution system are separated and enriched, and sent to the electrowinning system to obtain a cathode copper containing more than 99.99% of copper. The process flow is shown in Figure 1. Figure 1 Process Third, industrial test results (1) Raw ore and broken The ore is mainly composed of earthy powder ore and contains a small amount of massive ore-like block. The ore is sieved twice and broken twice to ensure that the ore entering the ball mill has a particle size of less than 2 mm. The first screening of the ore uses a vibrating screen. The lump ore larger than 100 mm on the sieve enters the jaw crusher , then enters the double-roll crusher, and the discharge enters the ball mill storage bin; the first sieves the ore into the 5 mm vibration. Screening and sieving products directly enter the ball mill storage bin, and the multi-roller crusher is larger than 5 mm. The crushing system discharge size is 100% to -2 mm, meeting the design requirements. In the industrial test operation, due to the high proportion of fine ore, the crushing system is in intermittent operation, which reduces energy consumption and reduces the cost of crushing. (2) Grinding process The slurry concentration and grinding fineness are directly related to the grinding quality and grinding cost, and affect the subsequent leaching quality. In terms of grinding cost, the grinding time is short, the unit processing capacity is high, the energy consumption per unit ore is low, the ball mill utilization rate is high, and the unit wear is small; for leaching, the finer the ore particle size, the higher the useful mineral exposure degree, and The contact probability and contact area of ​​the leaching medium increase, the leaching rate increases, and the leaching time is shortened. The concentration of pulp is the main factor affecting the treatment volume. The concentration of pulp is high, and the grinding time can be increased to obtain a good grinding fineness; the concentration of pulp is low, the treatment volume is small, and the efficiency of stirring and leaching equipment is reduced. See Table 3 for the concentration of grinding slurry, treatment volume and particle size distribution in industrial test operation. Table 3 Typical distribution of slurry concentration, treatment volume and particle size After a period of industrial test operation, it is determined that the grinding index is 34% to 36% of the slurry concentration, the grinding fineness -200 mesh accounts for 85%, and the treatment volume is 75 to 80 t/d. (3) Stirring and leaching The agitation leaching is a kind of enhanced leaching relative to heap leaching and percolation leaching, and the leaching time is short and the leaching rate is high. Factors affecting the agitation leaching process include chemical reaction dissolution rate, concentration and amount of leaching agent, liquid-solid ratio, leaching temperature, ore particle size, stirring strength, and leaching time. In the industrial test, the leaching rate of the mixing time of 2.5 h and 3.0 h is not much different, and the leaching rate is only increased by 4 to 5 percentage points. The stirring time is finally determined to be 2.5 h in consideration of the processing capacity of the equipment. The specification of the mixing drum is φ2500mm×2500mm. The stirring input power was 0.4 kW/m 3 . The operation is intermittent. At the end of the leaching, the leaching solution contains 6-7 g/L of copper, the leaching slag contains 0.5% to 0.6% of copper, and the leaching rate is over 70%. (4) Ways of adding medicines The concentration and amount of leaching agent is one of the main factors affecting the leaching rate. The leaching rate is accelerated as the initial concentration of the leaching agent increases. The ammonia-ammonium salt dissolves copper in the copper ore to be selective, and in addition to malachite, in combination with copper oxide, it can dissolve free copper oxide in all copper oxide minerals. After the concentration of ammonia reaches a certain value, increasing the ammonia concentration has little effect on increasing the copper leaching rate, while the ammonia volatilization and consumption increase. The main role of ammonium bicarbonate in the leaching process is to adjust the pH and maintain a certain ammonia environment. 1. Addition of ammonium bicarbonate In industrial trials, the addition of a medicament is divided into two phases. In the initial experimental stage, ammonium bicarbonate was added in a large amount, the amount of addition was 180 to 190 kg/t, and the concentration in the solution was 1.02 mol/L. In practice, it is found that the dissolution of ammonium bicarbonate is slow, and because of the small density, it is easy to float on the liquid surface, delaying the reaction time. In order to improve the utilization rate of the mixing tank, ammonium bicarbonate and pulp are added at the same time, that is, the amount of pulp in the mixing tank. When the depth reaches 0.5 m and the agitation is working normally (ie, the slurry floods the agitating paddle), ammonium bicarbonate is added. The addition speed is 10~12 kg/min, which ensures that the amount of ammonium bicarbonate required when the slurry is full is also added. After half a month of industrial test operation, the concentration of NH 4 + ions in the liquid gradually increased, and the amount of ammonium bicarbonate was gradually reduced. When the concentration of NH 4 + ions in the solution system was 1.9 moI/L, it was not added. 2, the addition of ammonia Ammonia water under normal temperature and pressure has strong volatility and irritancy, and requires high storage, transportation, handling and use conditions. The ammonia leaching process must be carried out under sealed conditions to reduce ammonia consumption and achieve clean production. The amount of ammonia added and the rate of addition are the main factors affecting the leaching effect. In the industrial test, in order to obtain the best leaching rate and leaching rate, the nozzle for adding ammonia is inserted into the surface of the slurry for 1.5 m, and the ammonia addition time is 30 to 45 minutes. This reduces the evaporation and re-dissolution of ammonia, which can be contacted and reacted with minerals in time. The amount of ammonia added is calculated as a multiple of the theoretical amount of copper. Too much addition will result in high residual ammonia concentration, large volatilization loss, and poor operating environment. Insufficient addition will result in high copper content in the leaching tailings, resulting in low metal recovery. At the beginning of the industrial test, the added agent was added according to the test data, and after a period of operation, it was added according to the industrial test data. The relationship between the amount of chemicals added in production and the copper leaching rate is shown in Table 4. Table 4 Relationship between dosage of chemical agent and copper leaching rate (5) Solid-liquid separation Solid-liquid separation is an important process in the leaching-extraction-electrowinning copper process. The solids content of the leaching solution subsequent extraction of hazard is great, the extraction process increases the amount of flocs and increase the consumption of extractant and kerosene, deterioration of electrolyte entrained, trigger a chain of problems, can cause serious production. 1. Original design situation. The original design was a solid-liquid separation using a horizontal belt vacuum filter. The leaching slurry is pumped to the intermediate storage tank by a slurry pump, and is filtered by a horizontal vacuum belt filter. In order to prevent a small amount of turbidity entrainment, the supernatant was filtered into a 150m 3 volume grit chamber for further natural sedimentation and separation, and then clarified by two clarifiers with a volume of 600m 3 before entering the extraction system. Since the solution system contains high turbidity and turbidity, the filtrate from the horizontal vacuum belt filter does not meet the requirements, and the solid-liquid separation is modified. 2. Transformation. According to the characteristics of the natural sedimentation speed of the leaching slurry, two thick boxes with a volume of 30 m 3 and two plate and frame filter presses with a filter area of ​​100 m 2 are added. The leaching slurry pump is sent to the two dense boxes connected in series to form preliminary sedimentation separation. The bottom stream is discharged to the slurry washing tank, and the remaining liquid is added to the slurry to be washed, pumped to the plate and frame filter press for filtration, and the filtrate enters the grit chamber. The slag is sent to the slag yard for storage. The supernatant from the thick box flows into the grit chamber, the sump, etc., and is further clarified for extraction by copper in the extraction plant. After the thick box is added, the underflow can also be filtered by the horizontal vacuum belt filter, and the original design of the filtration and washing is realized at the same time, and the processing capacity of the plate and frame filter press is alleviated. After the transformation, the mud content of the grit chamber is (5~10)×10 -6 , which satisfies the requirements of extraction. (6) Extraction - Electrowinning Separation and extraction of copper in ammonia solution In the past, an intermediate product, copper oxide, was obtained by a steaming ammonia process, and metal copper was also required to enter the smelting process. The method directly uses extraction-electrowinning to obtain a high-purity copper metal product. Compared with the extraction-electrowinning process of sulfuric acid leaching, the use conditions of ammonia are limited, the ammonia solution extraction-electrolysis application is relatively small, and the special effect extractant type is also small. Commonly used extractants for extracting copper from ammonia solutions are the CIX Group's LIX series and Cytec's Acorga series of extractants. They are all chelated extractants. This industrial test uses the LIX 84-1 extractant in the LIX series, which is a mixture of water-insoluble 2-hydroxy-5-mercaptoacetophenone oxime and high flash point kerosene in a certain ratio. The extraction process was a 2-stage extraction, a 1-stage wash, and a 1-stage stripping; the extraction was compared to 1:1 (O/A) and the stripping was 2:1 (O/A). The dilute sulfuric acid washing liquid was 2:1 (O/A). In the industrial test, the feed liquid contains 2 to 2.5 g/L of copper and the raffinate contains 0.1 to 0.2 g/L of copper. The extracted organic phase is 3% to 5% LIX84-1+ kerosene for lamp (volume percentage). The acidity of the washing liquid is controlled between pH=1 and 1.5, and the washing liquid is periodically discharged to ensure that the washing liquid does not cause ammonium ion enrichment. The current density of the electrowinning is 150-200 A/(m 2 ·h), the cell voltage is 1.8-2.1 V, and the circulation rate of the electrolyte is 50 L/(m 2 ·h); the pole spacing of the same name is 80 mm. The electrowinning cycle is 7-8d, and the produced electrowinning copper product Cu≥99.99%, which meets the high purity cathode copper product quality standard. Fourth, economic analysis Through industrial test production, the production index unit consumption and direct cost are compared with the conventional acid leaching direct cost. Table 5 Production indicator unit consumption and direct production cost Note: The acid immersion indicator uses other manufacturer data. As can be seen from Table 5, the direct production cost of this type of ore is lower than acid leaching. The cost of using liquid ammonia will also decrease. The ammonia content in the commercially available ammonia water is only 25%. It is a small expense to transport 1t of ammonia to transport 3t of water. In addition, ammonia is highly volatile and has a large loss during handling, transportation and use. The equipment used for ball milling, agitation leaching, and solid-liquid separation consumes a large amount of energy, which is an additional cost compared to conventional acid leaching. The acid consumption of alkaline gangue is very large, and the ore acid consumption test is above 40t/t. During the industrial test period, the market spot price of the first-stage cathode copper is far greater than 60 000 yuan / t, so the economic benefit of the ammonia-leaching-extraction-electrowinning copper extraction process of the high-alkaline low-grade copper oxide ore is remarkable. Good market competitiveness. V. Conclusion The test results show that it is feasible to treat the high-alkaline copper oxide ore by ammonia leaching-extraction-electrowinning process, which has significant economic benefits and is a necessary supplement to the low-grade copper oxide hydrometallurgical technology. Ammonia leaching is carried out under normal temperature and pressure, and the process is simple and easy to industrialize. During the ammonia leaching process, impurities such as Mg, Al, Fe, Si, Ca, Mn in the ore do not enter the leachate, which simplifies the cleaning process and is beneficial to improve the quality of the cathode copper. Copper is extracted from the copper-containing ammonia solution by using LIX84-1. The extraction stage is configured with two-stage extraction, one-stage washing, and one-stage stripping. The organic phase entrainment and co-extraction can be fully washed through the washing section. Ammonia ensures the quality of the cathode copper and the product meets the high purity cathode copper quality standard.
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