Pyrite cinder comprehensive recovery series iron red product technology

Industrial waste slag is pyrite sulfur iron ore during the production of sulfuric acid produced. China is a large country producing sulfuric acid, and its output has leapt to the third place in the world. Among them, the amount of acid produced by pyrite is about 80% of the total. In general, 0.8 to 0.9 t of slag is produced per 1 t of sulfuric acid produced.

At present, China's chemical and metallurgical sulfuric acid system to produce an annual cinder nearly 20 million t, except for a small amount of iron, chemicals and building materials industry, the vast majority have not yet been discharged stockpiling or use. The long-term storage of slag not only occupies a large amount of land, but also causes harmful components in the slag to enter the atmosphere, soil and water bodies due to weathering and raining, which not only seriously pollutes the environment, but also wastes valuable iron resources. According to reports, in order to control pollution and comprehensive utilization of valuable components in the slag, Japan, the United States and Germany and other developed countries have achieved slag utilization rates of 75% to 80%, 80% to 85% and about 100%, respectively. Up to 10% to 20%, especially in the context of China's steel production is the world's first and iron ore is heavily dependent on imports from abroad, research on the comprehensive utilization of slag has been one of the hot topics in the pyrite industry. .

In the 1950s, China carried out research and exploration on slag and comprehensive utilization, such as brick making; comprehensive recovery of valuable metals such as gold, silver , copper , zinc , lead and iron; organic waste iron or aluminum complex was used directly in the production of flocculating agents, water treatment agent, ferric oxyhydroxide; recovering the direct reduction of iron ore and iron is used as the cold-forming EAF; also for preparing iron oxide yellow And iron oxide red and so on.

In this paper, a typical pyrite cinder is taken as the research object, and the purpose of effective recovery of iron oxide is as follows. Based on the principle of low cost, low pollution and high benefit, the classification and reverse flotation-chemical treatment are determined through in-depth research and optimization. In addition to the impurity-ultrafine-flash-drying-oxidation roasting process, a number of key technologies are integrated, and the whole process test and subsequent industrial application have achieved satisfactory results. The expert appraisal opinion is “the project is mature, advanced and reliable. It is the first in China and the international advanced level. All products are in line with the requirements of relevant industries and have broad market prospects, which can bring good economic, environmental and social benefits. It is recommended to expand production as soon as possible. After the industrialization of the results, significant economic, environmental and social benefits have been achieved.

I. Analysis of physicochemical and structural characteristics of slag

(1) Physical characteristics

The main physical indexes of the slag are: density 4.5g/cm ³ , bulk density 1.9t/m ³ , surface electrical conductivity -13.1mV, pH=5.4, plasticity 13.7～23.9, plasticity index 9.9, uniform consistency moisture content 17.2%.

(2) Main components and phase composition

The main components of the slag are iron oxide (expressed as TFe), SiO ₂ , Al ₂ O ₃ and Pb, etc., and the elemental analysis results are shown in Table 1. The main mineral composition of the slag is shown in Table 2.

Table 1 Chemical multi-element analysis results of calcined raw materials (mass fraction) /%

Note: The unit is g/t.

Table 2 Main mineral composition of calcined slag (mass fraction) /%

(3) Particle composition and distribution of main elements

The slag was sieved and analyzed, and the contents of TFe, Si, and S were analyzed. The results are shown in Table 3. From Table 3, the content of sulfuric acid slag-0.074mm is greater than 90%, SiO ₂ is significantly higher in the coarse particle size, and Fe is relatively enriched in the fine particle size.

Table 3 sieve water analysis results

(4) Occurrence state and mineral process characteristics of iron in slag

The results of phase analysis show that the iron in the slag mainly exists in the form of hematite, maghemite and magnetite. The iron in several forms accounts for more than 95% of the total iron of the slag.

The measurement results show that the iron monomer dissociation degree in the slag is above 85%. The continuous forms of iron minerals and gangue minerals in the slag are mainly contiguous or mutually wrapped. The iron mineral particles generally have an irregular round shape, a circular shape, and the like, and the particles are loose and porous or even form large cavities.

Second, process test research and results

(1) Iron red recycling and deep processing process

In order to maintain the loose and active characteristics of the iron oxide structure in the slag, the iron oxide is recovered by a mineral processing method. However, since the symbiotic relationship between iron oxide and impurity minerals is very complicated, it is wrapped and contiguous with each other. Only when the particle size is 5-10 μm, the monomer dissociation degree of iron oxide minerals is over 95%, which means that it must be adopted. Special technology can effectively separate iron oxide and impurity components, obtain iron red products of different quality and use, and then adopt corresponding deep processing technology according to different application requirements. After detailed conditional test research, the principle process of determining iron red recycling and deep processing of products is shown in Figure 1.

Figure 1 Process of recovery of iron red from sulfuric acid slag

(II) Main process conditions and test results

1. Pre-selection treatment process Mineralogy research shows that in the coarse-grained grade (+0.074mm), iron oxide is mainly encapsulated by impurity minerals, and the total iron content is low, in order to reduce the dosage of chemicals and reduce the production cost. Screening and roughing.

After the pulping, the pH of the pulp is low (pH=3 or so), which not only causes serious corrosion to the equipment, but also affects the separation effect of iron oxide and impurities due to the presence of soluble salts, and increases the production cost. Therefore, the film must be treated before removal to remove soluble impurities.

As described above, only when the average particle size reaches 5 to 10 μm, the iron oxide can obtain sufficient monomer dissociation. To this end, the slag is finely ground before being selected to have an average particle size lower than the critical particle size (10 μm) of the conventional flotation material to satisfy the effective separation of the iron oxide from the impurity mineral.

2, flotation decarbonization, sulfur test sulfuric acid slag has a small amount of carbon, sulfur, carbon is mainly in the form of carbonaceous rock, sulfur is mainly composed of unburned residual residual pyrite and part of sublimed sulfur, this part of impurities It directly affects the quality of iron red, and also affects the next step of flotation desiliconization, so it needs to be floated first. It is worth mentioning that in the process of flotation removal of carbon and sulfur, some of the easily floatable silicon-containing minerals float up with carbon and sulfur, which is beneficial to the removal of iron red.

The best butyl xanthate sulfur coal flotation conditions experimentally determined, ^# 2 oil, kerosene and the amount of time the carbon sulfur flotation whole process test results shown in Table 4.

Table 4 Test results of carbon and sulfur flotation

It can be seen from the results in Table 4 that the whole flotation effect is ideal, and the removal rates of SiO ₂ , S, C and other impurities reach 37.95%, 80.17%, and 78.41%, respectively, especially the removal of some easily floating silicon-containing gangue. The next step is to lay the foundation for the removal of impurities.

3. Floating silicon test The content of SiO _{2 in} iron red ore is still high, and it is difficult to obtain the ideal beneficiation index by conventional flotation method and medicament. After the multi-agent program research and comparison, the self-developed high-performance modifiers SAF-1, XTD-6 and high-efficiency floating silicon collector SCH-9 were combined to carry out reverse flotation of silicon. After the condition test, the optimum dosage of NaOH, SAF-1, XTD-6 and SCH-9 and the suitable roughing time of floating silicon were finally determined. The whole process test of flotation silicon was carried out. The results are shown in Table 5.

Table 5 Full-flow test results of floating silicon rough sweep

4. The whole process test of the slag recovery series of iron oxide red products passed the scheme and condition test of recovering the series of iron oxide red from sulfuric acid slag, and determined the recovery process and main process parameters. Based on this, the series of recovery from sulfuric acid slag was carried out. The whole process test of iron oxide red product, the test process is shown in Figure 2, and the results are shown in Table 6.

Figure 2 Process flow of slag recovery iron oxide red

Table 6 Test results of complete process of recovery of iron oxide red from slag

After the condition test, the iron red product was further processed, and the final calcination temperature was 600 ° C and the calcination time was 45 min.

(3) Product inspection

The iron oxide red products recovered from the slag were inspected. The chemical element analysis results of each product are shown in Table 7, and the particle size test results are shown in Table 8.

Table 7 Results of chemical multi-element analysis of iron red products (1) (mass fraction) /%

Table 7 Results of chemical multi-element analysis of iron red products (2) (mass fraction) /%

Table 8 Results of particle size measurement of iron red products

The inspection results of iron red products show that the iron red five-grade product recovered from the slag by flotation reaches the quality standard of iron oxide red pigment in the national roasting method, and the fourth-grade product meets the quality standard of iron red in the ceramic industry. The grades also meet the requirements of relevant enterprises to produce high-grade permanent magnet oxidants.

(4) Secondary slag utilization and wastewater treatment and reuse

The slag and S and C flotation foams before the flotation process are pumped into the tailings pond of the selected plant or used as building materials additives. The process wastewater produced by flotation operation is in good condition and is recycled. The wastewater produced by the surface treatment process (soft red iron production) has a low pH value and contains a certain concentration of toxic and harmful substances. After the "lime-basic aluminum chloride" method, the concentration of each pollutant can reach Relevant emission standards, all treated wastewater is reused as slag water for the drying system.

(5) Application of results and industrialization effects

In the early 21st century, this technology was used to build a recycling iron red production line with an annual processing capacity of about 20,000 tons of sulfuric acid slag in a group company. In the past few years, products have been introduced into the market for enterprises in different industries. For example, a paint factory in Hunan and other enterprises use iron red five-grade products to produce iron red antirust paint; a ceramic company in Guangdong uses iron red four-grade products to produce ceramic black color materials; a factory in Sichuan and other enterprises use iron red three-grade products to produce Yong Magnetic materials, etc. Especially in recent years, the supply of products has been in short supply, resulting in significant economic, environmental and social benefits.

Third, the conclusion

(1) The use of sulfuric acid slag for disposal is a treasure, and comprehensive recovery of iron red has broad prospects.

(2) The slag contains major impurities such as SiO ₂ , CaO, Al ₂ O ₃ , S, C, etc., and its mineral and iron minerals have a symbiotic relationship. After using special techniques and chemicals, high-quality iron-red products can be obtained.

(3) The industrialization project implemented by applying the results was included in the 2002 national high-tech industrialization new material demonstration project. It has a good demonstration role and important promotion and application value for controlling the pollution of sulfuric acid slag in China, improving the utilization rate of mineral resources, transforming and upgrading traditional industries, ensuring the sustainable development of enterprises and social stability.