Abstract: As an important secondary resource, nickel metallurgical slag contains valuable metals such as iron, nickel and copper. With the increasing demand for nickel, more and more nickel slag is discharged. If it cannot be used rationally, it will not only waste resources, but also pollute the environment. In this paper, the present situation of resource utilization of nickel metallurgical slag is analyzed, and the direction of further resource utilization is discussed.

Key words: nickel metallurgical slag; Resource utilization; Precious metals; building material

With the increasing demand for non-ferrous metals in China, the amount of non-ferrous metallurgical slag is increasing year by year. Because these smelting wastes are not properly utilized, they not only occupy a lot of land resources, but also pose a potential threat to the environment, which is not conducive to sustainable development. Therefore, the resource utilization of nonferrous metallurgical slag is of great significance. China is the country with the largest consumption of nickel resources in the world. Every time 1t nickel is produced, about 6~ 16t slag is needed. The nickel metallurgical slag heap in Jinchuan Group alone is as high as 40 million tons, with an annual increase of about 2 million tons [1-3]. The composition of nickel slag varies greatly due to different ore types and smelting processes. Taking the phase composition of Jinchuan nickel flash slag as an example, it is mainly composed of iron oxide, silicon oxide, calcium oxide and magnesium oxide. The slag contains about 40% iron element and a certain amount of non-ferrous metal elements such as nickel, copper and cobalt. Iron mainly exists in the form of fayalite, and olivine is filled with amorphous glass and mechanically mixed with large particles of nickel and sulfur [4]. The treatment of nickel slag has become an important process in nickel smelting. How to recover and reuse these secondary resources correctly and effectively, make the nickel smelting process go smoothly, and solve the problems of slag discharge, land occupation and environmental pollution have become the main problems of developing circular economy in nickel metallurgy. This paper summarizes the present situation of resource utilization of nickel slag. The main research of reuse includes: extracting valuable metals, using them as filling materials, making glass-ceramics and producing building materials [5-7].

1. Status of resource utilization of nickel slag

1. 1 extraction of valuable metals

Winnie [8] and others used coke as reducing agent to extract valuable iron from water-quenched nickel slag in flash furnace by melting reduction method, and discussed the effects of different basicity, reduction temperature and reduction time on iron extraction rate. The results show that the reduction rate of iron can reach 96.32% by controlling slag 65438 000 g, Cao 34.7g, Cao 4.04g, coke 8.5g, melting temperature 65438 0500℃ and reduction time 65438±080min. Wang Shuang [9] and others made nickel slag, calcium oxide and coke powder into carbon-containing pellets, which were deeply reduced to recover valuable metals such as iron, nickel and copper. The results show that alkalinity has an effect on the recovery rate of valuable metals. Properly increasing alkalinity can promote the growth of metal phase, change the morphology and structure, and be beneficial to subsequent separation. If the alkalinity is too high, impurities will be produced in the metal phase. When the alkalinity is determined as 1.0, the recovery rates of iron, copper and nickel are 965438 respectively. Iron in nickel slag exists in the form of metallic iron after deep reduction, while nickel and copper mainly exist in the form of solid solution with iron. Lu Xuefeng [10] et al. used a self-made small DC electric arc furnace to recover silicon-calcium alloy from nickel slag, and used coke and reducing agent to control the ratio of nickel slag, quicklime and reducing agent to obtain the corresponding silicon-calcium alloy. Xiao Jingbo [1 1] and others recovered iron, nickel and magnesium from nickel slag. During the experiment, nickel slag was crushed and leached with acid, and oxidant and pH control agent were added to the acid leaching solution to generate iron precipitate, which was separated and reacted with sulfuric acid to generate ferric sulfate solution. After refining, high purity iron precipitate was obtained by oxidation precipitation method. Adding sulfide into iron precipitation solution to generate nickel sulfide precipitate, separating, washing and drying to obtain nickel concentrate; Additive LN was added to the nickel extract to remove impurities, and refined magnesium sulfate solution reacted with ammonia water to prepare magnesium hydroxide products.

1.2 production of filling materials

The technology of using nickel slag as underground filling material is mature, which not only solves the problem of recycling nickel slag, but also reduces the filling cost, cement consumption and environmental pollution in cement production. At present, the key to using water-quenched slag as filling material is to excite active slag, which can be divided into mechanical excitation and chemical excitation. Traditional mechanical excitation adopts ordinary mechanical ball milling for physical refinement, and high-energy ball milling can rapidly refine slag, increase specific surface area, increase hydration reaction surface and improve physical and chemical activity of materials. After high-energy ball milling, the compressive strength of nickel slag will be significantly improved. Chemical excitation is to use the chemical reaction between activator and slag to generate substances with hydraulic gelling properties to improve the activity of slag. Sulfate and carbonate are mainly used as activators. Yang Zhiqiang [12] et al. made an experimental study with mechanical activation and chemical activation.

The results show that the optimum specific surface areas of mechanically activated nickel slag, desulfurized gypsum, carbide slag and cement clinker are 620, 200, 200 and 300 m2/kg respectively. Chemical activation is mainly based on desulfurization gypsum and carbide slag, supplemented by sodium sulfate and cement clinker. The strength of nickel slag filling body is the highest when the proportion of the first two is the same and each accounts for 5% of the total. Adding 3% sodium sulfate and 2% cement clinker can improve the excitation effect; The filling slurry with 0. 156% PC superplasticizer, binder-sand ratio of 1∶4 and slurry concentration of 79% can completely meet the strength requirements of the filling body in the mine, and can be used instead of cement for handover filling mining in Jinchuan Mine. Gao [13] and others used water-quenched secondary nickel slag to prepare mine filling materials, and used desulfurization gypsum and carbide slag to generate a large number of hydration products, with high filling strength. The results show that the ratio of desulfurization paste to carbide slag is 1∶ 1, and then mixed with a small amount of sodium sulfate and cement clinker to prepare composite activator, which has good excitation effect.

1.3 manufacturing high value-added glass

Glass-ceramics and foam glass are both high value-added glasses. Glass-ceramics have the dual characteristics of glass and ceramics, with higher brightness and stronger toughness than glass. Foam glass has the advantages of non-combustion, non-deformation, stable thermal performance, high mechanical strength and easy processing. Wang Yali [14] and others studied the preparation of glass-ceramics by melting iron-making slag with nickel slag. Through homogenization → clarification → pouring → crystallization → annealing → grinding → polishing, the glass-ceramics meeting the national standards for architectural decoration were prepared, and the optimum raw material ratio was determined. Feng Zhenzhe [15] and others used nickel slag and waste glass as main raw materials, and added sodium carbonate as foaming agent to burn foam glass. The effects of sodium carbonate addition, foaming temperature and holding time on the quality of foamed glass were discussed. The results show that the total porosity at 870℃ is 85.66438+0h when the mass fraction of nickel slag and waste glass is 20% and 80% respectively, and 5%~7% of sodium carbonate foaming agent, 2% of boric acid foam stabilizer and 2% of borax cosolvent are added.

1.4 production of building materials

The main components of nickel slag are silica, alumina and iron oxide. Using nickel slag to produce portland cement can partially replace clay and iron powder and reduce energy consumption. A small amount of nickel, copper, cobalt and other elements in nickel slag has a positive effect on reducing the lowest liquid melting point and viscosity of clinker, improving its burnability and promoting the formation of clinker minerals. Wu Yang [16] and others used nickel slag instead of iron powder to prepare road portland cement. Through reasonable proportion, road portland cement clinker with C3S, C2S and C4AF as main minerals was prepared, and its strength, mineral composition, safety and other properties met the requirements of national standards. The optimum conditions are as follows: the doping amount (mass fraction) of nickel slag is 10%, and the calcination temperature is 1370℃. Wang Shunxiang [17] and others discussed the influence of different fineness and content of nickel slag on the hydration characteristics of portland cement. The results show that with the increase of nickel slag content, the setting time of cement paste is prolonged, the exothermic reaction of hydration is reduced, and the compressive strength and flexural strength of hardened cement mortar are improved. On the contrary, with the increase of nickel slag fineness, the above influence can be improved, which is beneficial to the structural densification of hardened cement paste. Nickel slag can be used as concrete admixture and aggregate to improve the strength of concrete. Moreover, the nickel slag has compact structure, high metal content and a lot of olivine, which makes the nickel slag have high hardness, thus improving the wear resistance of concrete mixed with nickel slag. Li Hao [18] and others studied the influence of the content of nickel slag sand on the wear resistance of concrete. When nickel slag powder, fly ash and nickel slag sand are mixed into concrete at the same time, the wear resistance of concrete is the best when the dosage is 10%, 10% and 40% respectively. Ding Tianting [19] and others studied the influence of nickel slag content on the compressive strength of concrete. When the content of nickel slag is 20%, the compressive strength of concrete is the largest, and when the content of nickel slag is 50%, the compressive strength of concrete is the smallest.

2. Development trend

Low utilization rate of resources, shortage of resources and unreasonable industrial structure have become strategic problems that restrict China's economic and social development. According to the present situation of mineral resources in China, the main metal contained in nickel slag is iron, so iron should be extracted as the main resource for resource utilization, which can not only alleviate the pressure of iron ore resources in China, but also be conducive to sustainable development and increase enterprise benefits. The secondary slag after iron extraction can also be used to prepare building materials such as glass-ceramics and filler materials, and nickel slag resources are fully utilized.

3. Conclusion

As an important secondary resource, nickel slag contains valuable elements such as iron, nickel, cobalt and copper. Moreover, the economy of simply extracting valuable metals is limited, and there is the problem of secondary slag discarding. Simple treatment of non-metallic resources causes waste of valuable metal elements; Therefore, it is more beneficial to the efficient and ecological utilization of nickel slag to extract valuable metals from nonmetallic resources and then treat the secondary slag.

refer to

Zhang Yanyun. Thermodynamic Study on Enriching Iron Resources in Nickel Slag by Melting Oxidation [D]. Lanzhou: Lanzhou University of Technology, 20 18.

Li,,, et al. Comprehensive utilization of nickel metallurgical slag [J]. China Metallurgy, 2017,27 (8):1-5.

Li Xiaoming, Shen Miao, Wang Yi, et al. Analysis on the present situation and development trend of nickel slag resource utilization [J]. Material Guide, 2017,31(5):100-105.

, Yang,,, et al. Analysis of mineral characteristics of Jinchuan nickel slag process [J]. Comprehensive utilization of minerals, 20 18 (1): 82-85.

Xie Geng. Study on multi-component comprehensive utilization of Jinchuan nickel slag [D]. Shaanxi: xi University of Architecture and Technology, 20 15.

Guo Yaguang, Zhu Rong, Pei Zhongye, et al. Kinetics of extracting iron from nickel slag by melting reduction [J]. China Nonferrous Metallurgy, 2017,46 (5): 75-80.

;