Progress in research and practice of magnesium reduction in Jinchuan nickel-copper concentrate

Jinchuan is a serpentine ore polymetallic sulfide ore. In order to solve the problem of magnesium reduction in flotation concentrates, many experts and scholars have conducted long-term research, and made some progress in the grinding and flotation process, acid flotation, and magnesium reduction agents.

Jinchuan Nonferrous Metals Co., Ltd. is the largest nickel producer in China, and its nickel production accounts for more than 80% of the national production. Its ore is a serpentine polymetallic sulfide ore. There are four mining areas. The nickel reserves in a mining area account for 16.36%. The mine was put into operation in the mid-1960s, and the annual output is still over 1 million tons. The ore in this mining area is a sponge-like iron -like structure, followed by a semi-sponge, iron-like, and variegated structure. The main metallic minerals: pyrite, purple-sulfur nickel ore, copper ore and a small amount of yellow pyrrhotite, pentlandite, marcasite, chalcopyrite ink; after this dressing ore, concentrate produced Due to the high content of MgO, the concentrate has been used as a raw material for the ore-heating furnace. The second mining area is the largest, nickel reserves account for 75.39%, and the second mine has 351 ore bodies. The No. 1 ore body reserves account for 57.8% of the four mines. The No. 2 ore body accounts for 17.08%, and the remaining 349 ore bodies account for only 0.51. %. The mining area has been mined since 1983. It has been the mixed ore of No.1 and No.2 ore bodies. In 1996, the ore body volume of No. 2 was reduced to 25%. In 1997, the ore-bearing capacity of No. 2 ore body basically disappeared. At present, the second mining area has an annual mining capacity of more than 3 million tons. The rich ore in the second mining area is a sponge crystal iron structure, and the lean ore is a dip-like structure. The main metal minerals are: pyrrhotite, pentlandite, chalcopyrite, pyrite, stellite ore, sulphide ore, sulphur sinter, magentor, magnetite, chrome spinel Etc; the main gangue minerals are olivine, serpentine, pyroxene, tremolite , carbonate, talc , chlorite, mica and so on. Nickel pyrite, chalcopyrite, and pyrrhotite are unevenly embedded in coarse and fine particles, and are densely symbiotic with each other. The ore serpentine alteration degree of the ore area in a mining area is greater than that of the second mining area, and the ore of the No. 1 ore body in the second mining area is greater than that of the No. 2 ore body ^{[1–3 ]} .

For a long time, magnesium reduction in flotation concentrates is a problem, especially since the flash furnace was put into production. The flash smelting technology is advanced, which is about 25% more energy-efficient than the electric furnace. The flue gas SO and high concentration are easy to produce acid. At the same time, the flash furnace has the advantages of large capacity and small environmental pollution compared with the electric furnace, but the quality of the concentrate is good. The requirements are also higher. The MgO content in the concentrate must be less than 6.5% ^[4] . to this end. Many universities, research institutes and on-site engineering and technical personnel in China have done a lot of work and made a lot of progress. Because the ore serpentine petrochemical in a mining area is too serious, and the nickel mineral is mainly purple sulphur nickel iron ore, if the MgO content in the concentrate is reduced to below 6.5%, the nickel recovery rate will be greatly reduced, which is more for nickel resources. A poor country is unrealistic, therefore. After the flotation of the ore in a mining area, the concentrate is still smelted in a hot-melt furnace. In recent years, the reduction of magnesium in ore dressing has mainly targeted the ore in the second mining area.

I. Test and research on the grinding and floating process

The grinding and floating process has been studied by many units for a long time. It is believed to combine the characteristics of Jinchuan ore. It is better to use the stage grinding process than the centralized grinding-flotation process ^{[5-10 ]} . In this way, the coarse-grained nickel sulfide mineral and the copper sulfide mineral can be recovered in advance to prevent the overgrown causing the slime cover and the like to affect the recovery of the mineral.

(a)) Flash flotation

Flash flotation is a fast-growing flotation technology for the rapid recovery of coarse-grained useful minerals. In the middle of the grinding circuit, the slurry after grinding by the ball mill enters the cyclone grading, and the grit takes into the flash float. The machine is selected to preferentially float the metal ore with coarse grain size and good floatability in the ore, so as to achieve early harvest and overcharge, and the flash flotation tailings return to the ball mill. The significant advantage is that it can reduce the slime cover caused by over-grinding, which can improve the metal recovery rate and reduce the cyclic load of the grinding circuit ^[11] . In 1999, Jinchuan Company conducted a flash flotation industrial test and achieved good results ^[12] . The total recovery rates of nickel and copper were 1.32% and 0.75% higher than those without flash flotation. Due to the coarser grain size of the concentrate produced by the flash flotation machine, the content of -0.074mm in the concentrate is 32% lower than that of the flash-free flotation machine, which in turn reduces the cost of concentrate dewatering. However, flash flotation can only reduce the coarse-grained minerals that have been dissociated as early as possible, reduce the loss of useful minerals, and can not greatly improve the quality of concentrates ^[12] . Because the useful mineral inlay size of Jinchuan Copper-Nickel Sulfide ore is uneven, the useful minerals in the fine-grained fraction must also be recovered. However, the fine-grained part must be re-ground to achieve the dissociation of useful minerals and gangue minerals. However, at this time, the slurry muddy phenomenon caused by the fragile serpentine is difficult to avoid, in order to recover this part of the fine Granular grade useful minerals, some serpentines will inevitably float together into the concentrate; therefore, in order to improve the recovery of nickel and copper ore, it is difficult to greatly increase the Ni and cu grades in the final flotation concentrate and greatly reduce MgO. content. Industrial practice shows that the recovery rate of ore dressing is closely related to the Ni, cu grade and MgO content in the concentrate, and it is necessary to reduce the MgO content of the concentrate by 1%. The Ni recovery rate is lost by 1.5% or more.

(2) Stage grinding and coarse concentrate regrind process

In view of the rich ore in the second mining area, many units have carried out small-scale test and industrial test research on the grinding process of one grinding or two grinding and two coarse concentrate refining processes, and have achieved good selection indicators. Under the premise of ensuring the nickel concentrate grade > 7% and the nickel recovery rate in the concentrate > 88%. Concentrate the MgO content can be reduced to 6.5% or less ^{[6-10, 13, 14].} Experimental study ^{[3, 15, 16]} two separate coarse concentrate regrinding process of two mill was also carried out for a mine ore, also achieved good sorting index. In the process of refining the coarse concentrate, the rough concentrate selected by the rough selection is actually a continuous body of useful minerals, which can greatly reduce the influence of serpentine mud on the flotation caused by over-grinding, and then Improve the quality of the final concentrate. However, since the coarse concentrate must be reground, a qualified final concentrate can be selected. This not only causes more process equipment, higher energy consumption, but also leads to finer final concentrate size. It is difficult to dewater concentrates, and the water content after pressure filtration is more than 13%. It is difficult to treat such high-concentration concentrates by airflow drying in front of the flash furnace, so so far. The coarse concentrate regrind process has not been used in industrial production ^[2] .

(3) Two product plans

Because there are more pyrrhotite in the nickel-copper ore in Jinchuan No. 2 Mine, it limits the further improvement of nickel grade in the concentrate (under the premise of ensuring nickel recovery rate) and further reduction of MgO content in the concentrate. Some ore dressing scholars believe that only a low-nickel pyrrhotite concentrate can be obtained from a mixed concentrate to obtain a nickel-copper concentrate with a higher nickel grade and a lower MgO content. To this end, a pilot study of the two product schemes was carried out ^[17] . The results show that under natural pH conditions, two final concentrates – nickel-copper concentrate and maghemite concentrate – can be obtained using a simpler process. The nickel grade in nickel-copper concentrates is over 11%. The MgO content is reduced to less than 5%, and the nickel recovery rate is over 80%; the nickel grade in the pyrrhotite concentrate is about 1%, and the MgO content is above 11%. The nickel recovery rate is about l0%. Compared with a product scheme, the nickel grade in nickel-copper concentrate is greatly improved, the MgO content is significantly reduced, and the total recovery rate of nickel is improved; however, no cost-effective treatment of maghemite concentrate has been found. Therefore, the two product solutions have not yet been applied in production practice. Some people ^{[5] have} also proposed appropriate distribution of concentrates to produce two nickel-copper concentrates, low-magnesium and high-nickel concentrates for flash furnace smelting. High-magnesium and low-nickel concentrate power supply furnace smelting. However, its process flow and pharmaceutical system are complex. Moreover, the total recovery rate of nickel has not been greatly improved, and thus it has not been used in production practice.

Second, acid flotation

Flotation medium is an important factor affecting flotation. Many units have conducted comparative flotation experiments on acidic, neutral and alkaline media conditions. The results show that the recovery rate of copper and nickel is the highest in the flotation index of acidic medium. The second is the medium, the lowest of the neutral medium ^[18] . The main feature of acid flotation is: in the acidic medium, the surface of the secondary nickel sulfide mineral, the purple iron sulphide ore formed during the oxidation and oxidation process can be dissolved to make the purple sulfur nickel iron ore. At the same time, the surface of the pentlandite and nickel-bearing pyrrhotite can be cleaned in time to prevent its surface oxidation and improve its floatability. The recovery of copper in Jinchuan nickel-copper ore dressing is much better than that of nickel. The low recovery rate is mainly due to the low floatability of the copper-copper ore, and the low floatability of the copper-copper ore is mainly due to the fact that the brucite layer in the copper-copper ore is softer than the copper-iron sulfide layer. In the case of ore, the copper-copper ore is easily hydrophilic along the brucite layer, and the brucite layer on the surface of the copper-copper ore is dissolved in the acidic medium to expose the surface of the copper-iron sulfide and thereby activate the flotation of the copper-copper ore. ; cobalt ores, gold, silver and platinum group elements and the like can also be surfaced with increasing amounts of copper and nickel to improve the recovery rate of minerals ^[19]. However, since the Jinchuan ore is an ultrabasic rock type ore, the alteration is severe and the ore itself is alkaline; and the Jinchuan mine uses a cementation filling mining method to make the filling material more or less mixed into the ore, and the filling alkali is more alkaline. Strong planing; therefore acid consumption of acid flotation is very large, and the addition of acid is likely to cause corrosion of equipment. Therefore, although the acid flotation index is good, it has not been applied in production practice. The plant has been used for flotation under natural pH medium (pH=8, 5~9.5).

Third, magnesium tablets

In order to solve the problem of magnesium reduction in concentrates, Jinchuan Company and many universities and research institutes have carried out many years of research and research, and carried out experimental research on various process conditions and pharmaceutical systems, and made significant progress. Most researchers take ^{[3, 6, 8, 18} ], CMC, phosphorus, sodium hexametaphosphate, sodium silicate can be effectively suppressed in a serpentine gangue minerals magnesium-based, small-scale tests are good indicators, However, in industrial production, magnesium reduction measures are difficult to achieve due to various factors.

According to reports ^[21] , the combination inhibitor EP has a good inhibitory effect on serpentine, and the single mineral test and the actual ore test have achieved good results.

The Northwest Institute of Mining and Metallurgy has carried out a large number of research work on new magnesium inhibitors. Among them, JCD magnesium-reducing new medicine is composed of T-1140 inorganic salt, 29# organic polymer and 0# neutral oil. It has activating effect on pentlandite and nickel-bearing pyrrhotite; 29# agent is a calcium-magnesium inhibitor, and T-1140 has a strong inhibitory effect on serpentine; 0# oil is T-1140 and 29 #药的辅助剂, which acts to eliminate stickiness, blistering and assist in magnesium reduction ^[9] . The new JCD drug was completed in March 1992 and the industrial test was completed in June of the same year ^[14] . The test indicators are shown in Table 1 ^[9] . The site has been in use ever since, and it is the most successful combination of magnesium inhibitors in industrial practice. However, it has also been found in industrial production that the MgO content in concentrates fluctuates greatly due to unstable chemical properties, fluctuations in ore properties, and the like.

Electrochemical flotation is the frontier flotation process of current beneficiation technology . If it can be successfully applied to production practice, it can better solve the problem of low ore dressing efficiency caused by the complex and variable nature of the selected materials. During the "Ninth Five-Year Plan" period, some units have conducted potential-controlled flotation experiments. The main contents include: flotation process optimization; automatic detection of electronically controlled flotation process parameters; computer online control. The laboratory test results are ideal. Under the premise that the Ni recovery rate is greater than 90%, the MgO content in the concentrate is less than 6.5%. However, on-site industrial tests have not been successful.

According to the industrial grade of the Jinchuan ore body, 0.3% to 0.99% of nickel is a poor ore, and nickel containing ≥1% is a rich ore. It is still "poor and poor". However, more than 1 million tons of nickel metal is hidden in the lean ore and covers the top of the rich ore body. In order to reduce the mining cost and expand the available nickel resources, it is imperative to develop and utilize the lean ore. However, the nature of lean ore is different from that of rich ore. The ore-poor ore Ni (0.55%) and Cu (0.35%) are less than half of the rich ore (Nil.6%, Cu0, 83%), and the lean ore MgO content (28%) is better than Rich ore (22%) high. The ore-poor beneficiation is more difficult than the rich ore. Many units have carried out the “Ninth Five-Year” scientific and technological research on the lean ore dressing process, and have made great progress. However, under the condition of ensuring that the MgO content in the concentrate is less than 7%, the nickel recovery rate Can only reach about 75% lead. If the nickel recovery rate is to be further increased, it is difficult to ensure that the MgO content in the concentrate is less than 7%.

Fourth, the conclusion

Due to the special nature of Jinchuan nickel ore, the ore contains low sulfur. The content of pyrrhotite is relatively small, which is difficult to reduce the magnesium oxide content of nickel concentrate. Because the gangue minerals are high in serpentine and easy to float; at the same time, the nature of Jinchuan ore fluctuates greatly, and the ore properties of different mining areas vary greatly, which brings great difficulty to magnesium in concentrate. Even if the flotation uses a special magnesium-lowering agent such as JCD to treat its easily selected ore zone ore, it can only reduce the MgO content in the concentrate by 0.6% to 1% while ensuring higher recovery rate ^[2]. . From the results of field production practice in recent years. For the easy-to-treat ore area, the Ni recovery rate can reach about 86%, the Ni grade in the concentrate is about 7%, and the MgO content in the concentrate is about 6.8%; it is more difficult for the original ore grade to be lower and the MgO higher. The ore of a mine in the treatment area has not been overcome due to the joint research of many units for many years. The MgO content in the concentrate is still around 10%. It cannot be smelted in an advanced flash furnace and can only be sent to an electric furnace for smelting. However, electric furnaces have high energy consumption, high production costs, serious pollution, and backward technology. The nickel concentrate flash smelting system was completed and put into operation in 1992. It has advanced technology, low energy consumption, low pollution, low production cost and large production capacity. This can completely replace the electric furnace, but the flash furnace has strict requirements on the quality of the concentrate (Ni>6.5%, MgO<6.5%). If the MgO content is high, not only the Ni yield of the smelting is low, but the cost rises. The slag viscosity is too large, causing nodules in the furnace, corroding the furnace body, and creating a leaking furnace. After many years of efforts by the smelting workers, Jinchuan's flash furnace can relax the MgO content of the concentrate into ≤7%. But even so. Magnesium ore dressing is still an urgent problem in Jinchuan beneficiation; and with the further depletion of ore, the MgO content in the ore is further increased, and the physical ore dressing is used to reduce the MgO content in the smelting furnace material to meet the difficulty of the flash furnace. It is getting bigger and bigger, and it is difficult to make a major breakthrough in the near future. Therefore, it is necessary to carry out other non-physical beneficiation methods for the study of magnesium reduction in concentrates. In order to overcome this major problem that affects the economic benefits of Jinchuan Company and restricts the overall adjustment of the company's industrial structure and product structure.

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