China's zinc metal reserves account for 1/4 of the world's total reserves, ranking second in the world. At the same time, China is also a major zinc producer. In 2002, the output of zinc metal reached 2,005,800 tons, ranking second in the world, and its export volume was second only to Canada, reaching 49,600 tons. 
   With the development of the national economy, the demand for zinc metal is also increasing, and there is an urgent need to develop and utilize complex and difficult zinc resources. Some of containing lead, zinc, sulfur, iron, or zinc, copper, tin, iron, sulfur, zinc and tin mines Zinc Mine in various degrees sphalerite containing iron, for example, manufacturers of Guangxi, river three lead-zinc , Huangshaping, Panjiachong, Yejiwei lead-zinc mine in Hunan, Hezhang lead-zinc mine in Guizhou, Xitieshan lead-zinc mine in Qinghai, Xilin lead-zinc mine in Heilongjiang, Fangniugou, Jilin, cattle and lead-zinc mine , Guangdong's Houpoyu lead-zinc mine, Yunnan's Dulong zinc-tin ore and antimony lead-zinc mine. The iron sphalerite of these mines generally contains 8% to 12% iron, and some have as high as 26%. 
   The reserves of zinc metal in Yunnan are more than 20 million tons, ranking first in the country. The zinc metal reserves of iron sphalerite are 7 million tons, accounting for 1/3 of the zinc metal reserves in Yunnan. The iron zinc mine of Dulong is close to Yunnan. 40%, the concentration is concentrated, and its pure iron sphalerite single mineral contains up to 20% or more of iron. 
In addition, rare metals such as indium , silver and cadmium are often associated with iron sphalerite. Taking indium as an example, China is the world's number one in terms of reserves, and Yunnan is the first in the country. The Dulong mining area has 3 968 t of indium reserves, accounting for 85% of Yunnan's 4,668 t reserves, which is the first in Yunnan. In addition to indium, the mine is also associated with silver, gallium , antimony , cadmium, cobalt and large reserves of sulfur and Arsenic, etc. Therefore, the development and utilization of iron sphalerite has attracted more and more people's attention.
1. Relationship between iron content of iron sphalerite and its color and beneficiation characteristics
1.1 Relationship between iron content of iron sphalerite and its color
Iron sphalerite (Zn×Fe(1-x)S) is one of the three zinc sulfide minerals currently found (the other two are sphalerite and wurtzite). When sphalerite contains more than 6% iron, it is called iron sphalerite; when it contains 12% iron, it is called high-speed sphalerite; when the iron content is more than 18%, it can be called super-high-speed sphalerite. 
With the increase of iron ion content in the crystal lattice, the iron sphalerite becomes darker and darker. When the iron ion content reaches about 20%, it becomes black or dark brown. The iron sphalerite of the general high-temperature thermothermal deposit has higher iron content and dark brown color; the iron sphalerite of the medium-temperature hydrothermal deposit contains less iron, which is brown or light brown; the iron flash zinc of the low-temperature hydrothermal deposit Mines contain less iron and are generally yellow. 
According to the genesis of the deposit, the general iron sphalerite does not contain antimony, while indium, silver, cadmium, gallium and the like are enriched in the iron sphalerite. The situation of Dulong shows a great consistency with this. 
1.2 Relationship between iron content of iron sphalerite and ore dressing characteristics
The zinc atom on the zinc blende crystal lattice is replaced by Fe 3+ , which makes the valence and charge state unbalanced, and causes 2 Zn 2+ to become Zn + , which reduces the hole concentration, increases the electron density, and makes the zinc flash. The ore becomes an N-type semiconductor mineral iron sphalerite, which affects its floatability, adsorption, redox state and interface electrochemical reaction. Due to the increase of electron density, the iron sphalerite forms a strong repellency to the xanthogen anion, which is not conducive to the adsorption of the collector . Therefore, the floatability of the iron sphalerite is lower than that of the sphalerite. The higher the iron content, the more the lattice parameter increases and the crystal surface energy decreases, the greater the change in ionic bond, semiconductivity, etc. in the crystal lattice, and the worse the floatability. 
The types of iron sphalerite in different mines are different, the iron content is different, the floatability and the difficulty of selection are inconsistent. The iron content of iron sphalerite, in addition to affecting its floatability, also affects its magnetic strength. The magnetic strength of iron sphalerite is directly proportional to the iron content, and the higher the iron content, the stronger the magnetic properties. Generally, when the magnetic induction intensity of magnetic separation is 0.2 to 0.3 t, the iron sphalerite can enter the magnetic product. Therefore, in some cases, the zinc concentrate is magnetically selected in order to improve the zinc concentrate grade, and part of the iron-bearing sphalerite having a high iron content is removed. In the ore dressing test of the Yinniugou lead-zinc mine, the iron sphalerite contains 6.81%~ 15.09% iron (average iron content 10.61%), and the magnetic separation of the obtained zinc concentrate containing 43.86% zinc can be sorted. Some iron-bearing zinc sphalerite and other magnetic materials are found. The zinc grade of zinc concentrate reaches 47.75%, which is 3.89 percentage points higher, and the recovery rate of zinc operation is 98.8%. [next]
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2. Flotation process of iron sphalerite
For the flotation of polymetallic sulfide ore containing iron sphalerite, there are generally three process structures to choose from, namely, mixed flotation, preferential flotation, and the like. 
Mixed flotation includes full blend flotation and partial blend flotation. Full-mix flotation is the first full flotation of copper, lead, zinc, sulfur, and then sorted into a single concentrate. Partially mixed flotation is the first copper-lead mixed flotation, and then sulfur is selected; or copper-lead is preferred, followed by zinc-sulfur mixed flotation, followed by separation and flotation. The selection index often depends on the superiority of zinc and sulfur separation. Inferior level. 
Priority flotation is the first flotation process of flotation of copper and lead, followed by zinc, and finally sulfur. From the point of view of the flotation process, preferential flotation is more advantageous than mixed flotation. When flotation is preferred, the fresh pyrite on the surface can be effectively suppressed after grinding. In the case of mixed flotation, the zinc mineral and the pyrite surface are adsorbed with a collector and an activator. In the case of zinc-sulfur separation flotation, if the pyrite is to be well inhibited, the collector of the surface must be removed. This is more difficult than suppressing the surface of fresh pyrite. Therefore, preferential flotation is more conducive to the separation of zinc and iron sulfide minerals than mixed flotation. In many cases, the essence of iron sphalerite flotation is the separation of iron sphalerite from pyrite or pyrrhotite. 
However, in actual production, it is necessary to decide which process to take based on the specific ore properties. The fine-grained zinc minerals cannot be recovered and lost to the tailings; the increase of the amount of collectors is strong, and some of the highly floatable pyrites are floating, causing the malignancy of pyrite in the zinc circuit. The cycle affects the separation of zinc and sulfur; moreover, the full priority flotation process can only be used in acidic media and cannot recover sulfur in alkaline media. 
A lead-zinc ore in the northwest contains 4.03% lead, 7.45% zinc and 19.30% sulfur. The zinc mineral is mainly iron sphalerite, which contains 8.4%~ 26.2% (average 11.3%). The zinc-sulfur preferential flotation and zinc-sulfur mixed flotation process were used to compare the separation of iron sphalerite and iron sulfide minerals. It was found that the zinc beneficiation index obtained by preferential flotation was superior to the mixed flotation index.
3. Relationship between floatability and particle size of iron sphalerite
The floatability of iron sphalerite has a great relationship with its particle size. We studied the floatability of single minerals of Dulong iron sphalerite of different grades. The flotation time was 12 min without any flotation reagent. The test results are shown in Table 2. It can be seen from Table 2 that the iron sphalerite is too coarse or too fine in particle size, and its floatability is very poor. 
3.1 Hazards of coarse-grained iron sphalerite 
The iron sphalerite particle size is too thick, mainly in the following three aspects. 
(1) In addition to causing the loss of zinc and indium (such as the original loss of Guangxi Dachang Chehe Concentrator in the zinc-sulfur mixed tailings, 90.91% of the zinc metal concentrated in the 0.25 mm fraction), the iron sphalerite granularity Too thick will also make the zinc-sulfur mixed use abnormal operation with low concentration and large dose. Most of the excess xanthate and No. 2 oil used in the mixed selection will separate into the zinc-sulfur separation operation with the foam, resulting in the separation foam being quite sticky. The difference in flotation performance between iron sphalerite and pyrrhotite is destroyed, which makes it difficult to separate zinc and sulfur. The gangue mineral is also contaminated by foam and enters the zinc concentrate. 
(2) Due to the close proximity of the density of the sulfide ore to the cassiterite, the coarse-grained sulfide ore is mixed with the fine-grained sillimanite after the subsequent re-election operation, which makes the shaker unclear and cannot intercept the cassiterite concentrate. The recovery rate of cassiterite. Dulong's cassiterite recovery rate is less than 40%. (3) The coarse particles are easy to precipitate and accumulate in the flotation tank, so that the flotation operation cannot be performed normally, or even the motor is burned out, so the water quantity and the flotation concentration have to be increased, which in turn leads to production costs such as dosage and water volume. A substantial increase. The Chehe Plant only has zinc-sulfur mixed-mix and zinc-sulfur separation operations. The amount of oil No. 2 is up to 400 g/t, sulfuric acid is 4 000 g/t, xanthate is 290 g/t; if the mineral particle size is reduced to -0.25 mm, yellow The amount of medicine can be reduced to 100 g/t, the oil of No. 2 can be reduced to 100 g/t, the sulfuric acid can be reduced to 1 000 g/t, and the pharmaceutical cost can be saved at least 2 million yuan. 
3.2 The importance of improving the classification efficiency At present, the spiral classifiers used in many concentrating plants cannot meet the requirements of grading of polymetallic sulphide ore. Because the spiral classifier is mainly classified by density, the particle size is a relatively minor factor, and the sulphide ore is mostly Heavy minerals are difficult to classify according to their respective particle sizes in a spiral classifier. The yield of greater than 0.25 mm in the overflow of the large-scale spiral classifier accounted for 15.68%, and the yield of less than 0.25 mm in the sand returning sand accounted for 61.37%, resulting in under-grinding and over-grinding of the sulfide ore. Therefore, it is very important to use high-efficiency grading equipment such as high-frequency fine screen to improve classification efficiency.
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