4.3. Magnetization roasting technology

22 million tons by the end of 2012 [19]. Changsha Institute of Mining and Metallurgy proposed a selective flocculation desliming-anti-flotation technology and developed a SA-2 flocculant (for the purpose of fine grain size, complex nature of igneous iron ore in Qidong iron deposit) [20]. At present, the Qidong iron deposit uses this technology to build a beneficiation plant with an annual treatment capacity of 2.8 million tons. Under the conditions of a raw ore grade of 28.36% and a grinding fineness of 0.038 mm (98%), the concentrate iron grade 62.5%, the recovery of 68% have been achieved [18–20]. There are many examples like this. Stage grinding —stage magnetic separation likely is the best process for processing fine-grained magnetite [21, 22]; for fine-grained magnetite-hematite mixed iron ore, weak magnetic—strong magnetic resurfacing—reverse flotation process can obtain the high recovery rate; that sorting fine particles hematite process mainly has strong magnetic—desliming—reverse flotation [23, 24], selective flocculation—reverse flotation [25] and strong magnetic—centrifugal beneficiation [26].

It would be subdivided into: high-pressure roller mill technology, self-grinding/semi-self-grinding technology and stirring mill technology [12]. The high-pressure roller mill technology is highly dependent on ore ultra-fine grinding equipment: high-pressure roller mill. It is a unit of low energy consumption, high handling capacity. Compared with the traditional crushing equipment, high-pressure roller mill pulverized products significantly increase the internal microcracking, ensure high content of fine-grained fraction and mineral dissociation [3, 27–30]. Domestic experts and scholars carried out a great deal of research work on the application of high-pressure roller mill technology in iron ore, and formed the crushing-preselection technology of high-pressure roller mill to maximize the crushing and minimize friction in order to reduce processing costs. Masteel company conducted this technic on low-grade iron ore (including high-pressure roller mill, wet grading, coarse magnetic separation pre-selected tail-polishing technology) in Nanshan iron ore deposit, the annual throughput of the beneficiation plant increased by 2.7 million tons, and the electricity consumption and the consumption of steel per unit ore dropped by about 30% [20]. And then, this technology has been introduced into dozens of iron ore processing plants in Hebei Province such as Sijiaying Iron Mine, Panzhihua Iron Mine in Sichuan and Dachang Iron Mine in Anhui [31]. The grain size, grinding and dissociation characteristics of lean hematite ore after being crushed by a high-pressure roller mill have been studied. Details of this technology are still locked. However, compared with the jaw crusher, the high-pressure roller mill has a high crushing ratio, high content of fine-grained, uniform particle size distribution and the Bond power index decreased by 13.96–28.23%, 0.5 mm grain iron ore monomer dissociation increased by 15.16% [13]. Compared with the conventional three-stage closed-circuit crushing process, the self-grinding/semi-autogenous grinding process has the features of simple process, low capital investment, large-scale equipment efficiency and low dust pollution. At present, China has more than 60 beneficiation plants using more than 160 selfgrinding/semi-autogenous mills. For example, Dahongshan Iron Mine of Kunming Iron and Steel Co., Ltd. has used 8.53 m 4.32 m semiautomatic milling + ball milling + ball milling (SAC) process to crush iron ore from 2006 with the processing capacity of 4 million t/a [1]. Stir mill as a fine to ultra-fine grinding equipment was gradually being applied to the fine-graining of iron mines in China [20, 32]. In 2010, Panzhihua Iron and Steel Co., Ltd. purchased three

4.2. Efficient grinding technology

16 Iron Ores and Iron Oxide Materials

In recent years, many domestic research units aim for magnetization roasting technology and equipment and carry out a large number of studies. Flash magnetization roasting technology was one of them, which was proposed by Yu and his team [34]. And then this technology was applied to the Daxigou siderite deposit, Wangjiatan magnetite deposit, and Jielong magnetite deposit, where they obtained iron grade more than 55 and 70% of recovery rate. In 2009, Lingbao plant started the pilot construction of flash magnetization roasting project of 50,000 tons per year. In 2012, the Institute of Process Engineering of Chinese Academy of Sciences built the pilot project of annual handling capacity of 100,000 tons of refractory iron ore fluidized roasting. Northeastern University put forward a complex refractory iron ore suspension roasting technology, and designed a laboratory batch suspension roaster. Using the designed roaster, restricted the air velocity, reducing gas concentration, calcination temperature and roasting time were tested on the positive flotation tailings and oolitic hematite of Anshan Iron & Steel Co., Ltd. at Dong'anshan Sintering Plant. Under the best experimental conditions, they got iron grade 56–61% and recovery rate of 78–84% [35]. According to the basic research results, Northeastern University and the Institute of Mineral Utilization of Chinese Academy of Geological Sciences and Shenyang XinBo Industrial Design Co., Ltd., designed and built a 150 kg/h complex refractory iron ore suspension roasting pilot system in Emeishan City. In September 2014, the continuous flotation test was carried out with the positive flotation tailings from the tailings of the East Anshan Sintering Factory and the magnetic separation of the tailings of the Ouzanshan Magnetic Puller tailings. The magnetized roasted products produced by this system, after magnetic separation, reached the grade of concentrate iron 63–65%, and the recovery rate of 78–83%.

#### 4.4. Deep reduction and magnetic separation technology

For those beyond conventional processing methods and magnetization roasting technology, the relevant domestic researchers put forward a deep reduction-magnetic separation technology that uses coal as an agent to reduce iron ore minerals to metallic iron below the melting temperature of ore, and then promotes the growth of metal iron particles to a certain size. Deep reduction-magnetic separation technology for the development of complex refractory iron ore provides a new way to become one of the hot topics in the field of mineral processing in recent years. Raw materials of oolitic hematite, hematite with carbonate, iron tailings, red mud, Zincbearing iron ore were tested by this technic. After the magnetic separation, the deep reduced iron powder with 85–95% Fe and more than 90% recovery rate can be obtained [36]. Deep reduction temperature is generally higher than 1000�C, iron ore reduction process is Fe2O3 ! Fe3O4 ! FeO ! Fe. The process of reduction can be divided into three stages: initial, middle and late stage. The reaction kinetics models of each stage are Avrami-Erofeev equation, chemical reaction model and three-dimensional diffusion model, respectively. The size of the iron particles in the reduced material can be detected using optical microscopic image analysis techniques. It is noteworthy that the reduction temperature and the reduction time have a significant effect on the size distribution of iron particles [21].

results show that the pre-enrichment of iron minerals in the tailings can be achieved by the reseparation, grinding-magnetic separation and the iron concentrate with grade greater than 40% can be obtained. And then, via the process of grinding—weak magnetic—strong magnetic reverse flotation process or 1 rough 1 fine 1 flotation column process sorting, reaching more than 64% of concentrate grade, the recovery rate more than 88% [38–40]. Meishan iron ore processing plant integrated tailings, strong magnetic separation tailings, phosphorus tailings on the basis of a comprehensive analysis of mineralogical characteristics of the re-separation were carried out: iron grade of 18% in the tailings can be concentrated to 56.5%. Experimental studies have shown that the nature of iron tailings in different regions vary greatly, hence iron tailings re-separation process is not the same [13]. Most of the domestic iron ore beneficiation plants use an anionic reverse flotation process to reduce silicon, and the collectors used are fatty acids. Anion reverse flotation process has the advantages of stable production, good indicators, the disadvantage is the collector preparation and the required high flotation temperature (preparation temperature is usually 50–70C, the slurry temperature is generally 35–40C). As the result floating pulp slurry needs heating treatment, which increases production costs [41]. Luo et al. [42] developed a new modified fatty acid collector, and flotation tests at 25C showed that they got grade of 65.79% with 83.01% recovery rate from the Sijiaying iron deposit. This fatty acid collector has good water solubility and collectibility at room temperature [43–46]. Aiming at the flotation of iron ore at room temperature, a series of new efficient collectors with low temperature solubility, strong catching ability and excellent selectivity have been developed in China. The efficient separation of iron ore at room temperature has been achieved for some them. However, at present these new collectors are still in the laboratory research or semi-industrial test stage, and

The Chinese Iron Ore Deposits and Ore Production http://dx.doi.org/10.5772/intechopen.76729 19

This chapter addresses the topic of iron ore types, structure of import, market analysis, financial aspects, overseas investments, etc. It also covers development of innovative beneficiation processes in China. Probably due to large national land area and multi-period orogeny, from the view of metallogeny, lots of iron deposits developed in China, and the proven total reserves of iron ores are relatively abundant, but mainly low-grade ores. For years, China's iron ore reserves are far from being able to meet the requirement of rapid development of steel industry. China is the world's largest importer of iron ore, which imports accounted for onethird of the world's total in recent decades; however, the buyer has not the final say. The strategic importance of iron ore resources in national economy not only depends on the social value and economic value created by the iron ore exploitation, but also depends on whether the requirements of the steel industry and steel downstream industry, and safety ensuring, economy and sustainability of steel and steel downstream industry. In order to improve the self-sufficiency rate of iron ore and get rid of the shackles of foreign mining giants, a great deal of research work has been carried out by relevant researchers around the efficient utilization of iron ore resources. In the process of fine iron ore beneficiation, ore crushing, roasting-magnetic separation, deep reduction, tailings re-election, low temperature collector research and devel-

the industrial application process needs to be accelerated.

5. Conclusions

opment has made achievements.

High-phosphorus oolitic hematite is an important iron ore resource in China. Due to the extremely fine grain size (less than 10 μm) and high-phosphorus content of hematite, it is difficult to effectively classify the hematite by conventional beneficiation process. However, the deep reduction-magnetic separation process can be applied to high-phosphorus oolitic hematite iron enrichment. The study found that during the deep reduction process, the phosphate minerals in the ore will be reduced to elemental phosphorus, and a considerable part of the elemental phosphorus enters the metallic iron phase, causing high content of phosphorus in the reduced iron powder [37]. In response to this problem, relevant scholars put forward two solutions: deep reduction of dephosphorization and deep reduction of phosphorus-rich [12]. For the raw ore with phosphorus content less than 0.8%, by adding dephosphorization agent (Na2CO3, Ca (OH)2, Na2SO4, etc.) the vast majority of phosphorus remains in the slag phase. This way would get the low-phosphorus deep reduced iron powder (phosphorus content ≤ 0.05%) that can be directly used in steel-making [13]. For raw ore containing more than 0.8% phosphorus, by controlling the migration of phosphorus, more than 80% of the phosphorus enters the metallic iron phase. It would get high-phosphorus deep reduced iron powder (phosphorus content ≥ 1.5%), and then use smelting dephosphorization technology to deal with high-phosphorus iron powder, and qualified molten steel at the same time get high-phosphorus steel slag, the highphosphorus steel slag can be used directly as phosphate fertilizer or acid soil improver. Presently, this technic is not yet widely used because of lacking equipment.

#### 4.5. Others

Other mineral processing and ore metallurgy technology would include the tailings reseparation technology and room temperature collector technology. [12] Due to the low grade of iron ore resources in China, an average of 1 ton of iron concentrates needs to be discharged to 2.5 tons of tailings. With the continuous increase of production capacity of mining enterprises, the discharge of iron tailings has rapidly increased and has become the largest industrial solid waste. Tailings discharge not only occupy a large amount of land, sometimes due to poor management, but also cause tailings dam break, resulting in casualties, environmental pollution, destruction of villages and towns and other serious consequences. The iron tailings usually contain a certain amount of metallic iron with a fine grain size, so the energy consumption of grinding is lower than that of raw ore. Anshan Iron and Steel Mining Company, Qidashan iron plant and Gongchangling beneficiation plant conducted flotation tailings re-separation pilot study. The

results show that the pre-enrichment of iron minerals in the tailings can be achieved by the reseparation, grinding-magnetic separation and the iron concentrate with grade greater than 40% can be obtained. And then, via the process of grinding—weak magnetic—strong magnetic reverse flotation process or 1 rough 1 fine 1 flotation column process sorting, reaching more than 64% of concentrate grade, the recovery rate more than 88% [38–40]. Meishan iron ore processing plant integrated tailings, strong magnetic separation tailings, phosphorus tailings on the basis of a comprehensive analysis of mineralogical characteristics of the re-separation were carried out: iron grade of 18% in the tailings can be concentrated to 56.5%. Experimental studies have shown that the nature of iron tailings in different regions vary greatly, hence iron tailings re-separation process is not the same [13]. Most of the domestic iron ore beneficiation plants use an anionic reverse flotation process to reduce silicon, and the collectors used are fatty acids. Anion reverse flotation process has the advantages of stable production, good indicators, the disadvantage is the collector preparation and the required high flotation temperature (preparation temperature is usually 50–70C, the slurry temperature is generally 35–40C). As the result floating pulp slurry needs heating treatment, which increases production costs [41]. Luo et al. [42] developed a new modified fatty acid collector, and flotation tests at 25C showed that they got grade of 65.79% with 83.01% recovery rate from the Sijiaying iron deposit. This fatty acid collector has good water solubility and collectibility at room temperature [43–46]. Aiming at the flotation of iron ore at room temperature, a series of new efficient collectors with low temperature solubility, strong catching ability and excellent selectivity have been developed in China. The efficient separation of iron ore at room temperature has been achieved for some them. However, at present these new collectors are still in the laboratory research or semi-industrial test stage, and the industrial application process needs to be accelerated.
