Development of World Laterite Nickel Resources and Progress of Hydrometallurgical Technology

According to geological genesis, there are two main types of nickel deposits: magmatic nickel sulfide or weathered laterite nickel, of which laterite nickel ore reserves account for 72% of global nickel resources. In recent years, due to the stainless steel industry, the demand for nickel in the world is rising. In 2008, China's stainless steel production capacity reached 10 million tons, while the actual output was only 5.35 million tons. The shortage of nickel supply is one of the important reasons.

At present, about 60% of nickel is extracted from sulfide ore, while the sulfide ore resources are drastically reduced, the grade is reduced, the mining depth is increased, the mining difficulty is increased, and the cost is increased. Laterite nickel ore resources have the advantages of low exploration and mining costs, and can directly produce products such as nickel oxide, nickel antimony and nickel iron . Therefore, it is very urgent to efficiently develop laterite nickel ore resources. In the 1950s, the extraction of nickel from lateritic nickel ore metals accounted for only 10% of the world nickel content; by 2008, this proportion reached 45%, about 5l million t by 2012, that proportion will grow to 5l%.

Nickel production from laterite nickel ore can be simply divided into fire and wet processes. Due to the high energy consumption and high cost in the smelting process, the fire process is mainly used to treat high-grade laterite nickel ore. Although the wet process has problems such as complicated process, long process, and high requirements on equipment, it has the advantages of low energy consumption and high metal recovery rate compared with the fire method. Especially in the decades since the development of the wet process, the advancement of pressure leaching technology and the emergence of new wet process have turned the development of the laterite nickel mine from the fire method to the wet method.

I. Classification and characteristics of the world laterite nickel ore resources The upper part of the nickel oxide deposit is a brown iron type laterite ore, which is suitable for the wet process; the lower part is a magnesia silicate mineral (mainly serpentine), suitable for the fire process. deal with. The intermediate transition section is suitable for both methods. It is estimated that the laterite nickel ore reserves (limonite, nontronite, montmorillonite) suitable for wet treatment are more than twice as suitable for the fire method (silica-magnesium-nickel ore, humus) .

With the continuous development and utilization of laterite nickel ore resources, people have a new understanding of their utilization properties and types: one is called “wet type” and is mainly distributed in the near equatorial region, such as New Caledonia, Indonesia. The Philippines, Papua New Guinea and the Caribbean have higher grades, less clay and are easier to handle. One type is called “dry”, mainly distributed in the southern hemisphere continent far from the equator, with complex composition and high clay content. Not easy to handle.

Although laterite nickel ore has different types, they generally have the following characteristics:

(1) 1.0-3% nickel, the grade is lower and the composition is much more complicated than the nickel sulfide ore. It is difficult to obtain a higher (6% or more) nickel concentrate by beneficiation , and it is difficult to use the nickel directly too low. The metallurgical process is enriched.

(2) The composition content fluctuates greatly, not only the content of valuable elements such as nickel varies greatly, but also the gangue components such as SiO ₂ , MgO, Fe ₂ O ₃ , Al ₂ O ₃ and water fluctuate greatly, even in the same deposit. The composition of laterite ore (Ni, Co, Fe, MgO, etc.) also varies with the depth of different layers.

(3) There is only a small amount of cobalt associated with the ore, no sulfur, no calorific value.

(4) The ore reserves are large, and they are deposited on the surface, easy to harvest, and can be operated in the open air, with superior conditions for development.

Second, the development status of the world laterite nickel ore

With the development of the red clay mine in New Caledonia as a symbol, the production of metallic nickel from laterite mines has been more than 100 years old. In recent years, due to the huge demand for nickel in the stainless steel industry, many large nickel-producing countries have actively increased the development and utilization of laterite mines. More influential are the Coral Bay project started in 2005 by Sumitomo/Mitsui Corporation of the Philippines; the Inoco project officially launched by Inco in New Mexico in 2007, with an estimated annual production of 54,000 tons of nickel; in addition, in Australia, Indonesia, The development of some nickel ore resources in countries such as Brazil is also being implemented and studied, as detailed in Table 1.

Table 1 Major Laterite Nickel Projects under construction abroad

Due to the small amount of laterite nickel ore resources in China, some large domestic enterprises have taken the opportunity to increase investment in foreign laterite nickel ore projects. The foreign laterite nickel ore projects that have been or are currently underway include: (1) Baosteel Group and Jinchuan Group have jointly invested 100 million US dollars in the development of nickel mineral resources in the Philippines, and the partner of the Philippines is Philnico, the owner of the mine. (2) China Minmetals Corporation and Cuba cooperate to build a production plant with an annual output of 22,500 tons of nickel in Moa, of which Chinese companies hold 49%; (3) China Nonferrous Mining Group develops Dagongshan nickel mine in Myanmar, the mine The average grade of nickel is 2%, and the amount of nickel metal is about 700,000 tons. (4) China Metallurgical Construction Group cooperates with Jien Nickel Co., Ltd. to develop the Ramu Nickel Mine in Papua New Guinea. The average grade of nickel in the mine is about l. (5) China Jinbao Mining Co., Ltd. and the Myanmar Ministry of Mines have signed a cooperative exploration and feasibility study agreement for the Mochoitang nickel mine in Myanmar. In the future red earth mine project, the wet process project will occupy a large proportion. It is expected that by 2012, the proportion of nickel produced by wet process to total nickel production will increase from the current 62% to 80%.

3. Status of hydrometallurgical technology of laterite nickel ore

(1) Reduction roasting-ammonia leaching process (RRAL)

The reduction roasting-ammonia leaching process was invented by Professor Caron, so it is also called the Caron process. Nickel reduction roasting古巴尼加罗Plant - Treatment ammonia leaching high magnesium laterite oxide has reached half a century, this typical composition suitable for ore leaching method of treating ammonia-soda was 1.4% Ni, 8% MgO, 14 % SiO2. The basic process is that the ore having a particle size of less than 74 μm is placed in a multi-hearth furnace for reduction roasting. The nickel and cobalt in the laterite ore are substantially in the form of ferrite, and after reduction and calcination, nickel and cobalt are converted into a metal or an alloy. The calcination is leached with ammonia-ammonium carbonate mixed solution, treated by a thickener, overflowed into a rich liquid, purified and evaporated to produce a nickel carbonate slurry, which is dried and calcined in a rotary kiln to obtain a nickel oxide product and magnetically selected. The method selects iron concentrate from the leaching residue. For this reason, in the reduction and calcination, it is necessary to sufficiently reduce the nickel and cobalt combined with iron, and to prevent excessive reduction of iron. In the 1970s, China assisted the Albanian Al Bassan Iron and Steel Joint Enterprise Project, firstly completing the research on the reduction of nickel-cobalt-leaching slag magnetic separation-iron concentrate steelmaking from laterite reduction and roasting-ammonia leaching in the world. Applied to industrial production.

In order to improve the leaching rate of nickel diamond, the US Bureau of Minerals has developed a new process for the reduction roasting-ammonia leaching process for laterite ore, referred to as the USBM method. The main point of this method is the addition of pyrite (FeS2) for granulation before reduction roasting, and the use of pure carbon monoxide for reduction. The leachate uses Lix64-N as an extractant to separate cobalt and nickel. The whole system is closed loop, which effectively utilizes resources. According to reports, when this method is used to treat laterite ore containing 1% nickel and 0.2% cobalt, the recovery rates of nickel and cobalt are 90% and 85%, respectively. When processing low-grade laterite ore containing 0.53% nickel and 0.06% cobalt, the recovery of cobalt can reach 76%. Compared with the original ammonia leaching process, the recovery rate of nickel and cobalt is greatly improved, and the energy consumption of the process is reduced.

Outokumpu-Lurgi is developing a process for calcination and fluidized bed pre-reduction of limonite or humus ore, which is used in the subsequent Caron process.

In terms of product process, the reduction roasting-ammonia leaching process produces sintered nickel oxide (99%), nickel, nickel or nickel. The process flow and products of typical manufacturers are listed in Table 2.

Table 2 Typical manufacturers and products of reduction roasting-ammonia leaching process

(2) Sulfuric acid pressurization acid leaching process (HPAL)

The sulfuric acid pressure acid leaching process is suitable for the treatment of limonite-type laterite ore containing low magnesium oxide. The principle of pressurized acid leaching is shown in Figure 1. The biggest advantage of this process is that the recovery rate of metal can reach more than 90%. The principle process of the pressure acid leaching method is shown in Figure 1. The technology began in the 1950s and was first used in the Moa Bay mine in Cuba, called A-MAX-PAL technology. Since then, in the 1970s, Australia's QNI Corporation built the Yabula nickel plant, acid-leaching red clay-type nickel mines in New Caledonia, Indonesia and Queensland, Australia. In the second half of 1998, Australia's Murrin Murrin, Cawse and Bulong developed a laterite mining development project using pressurized acid leaching technology, which caused great concern. The acid pressure leaching technology in these three processes is similar to that used in Cuba Moo's production, except that the vertical autoclave has replaced the Moo company's vertical autoclave. However, the recycling step has the following differences:

Figure 1 Flow chart of pressurized acid leaching

1. In the Cawse process, the mixed hydroxide is precipitated from the high pressure leaching solution, and then leached with ammonia, followed by solvent extraction and electrowinning.

2. In the Bulong process, the mixed sulfide is precipitated from the high pressure leaching solution by H2S, and then the sulfide is leached under aerobic conditions, followed by solvent extraction, hydrogen reduction, tableting and the like.

3. In the Murrin process, the high pressure leaching solution is directly subjected to solvent extraction and electrowinning.

The resources, annual production, yield and design capacity of the three laterite nickel plants are listed in Table 3. As can be seen from Table 3, the process of the three red clay mines in Australia is not very satisfactory. Only Cawse has reached 74% of the design capacity, and the production cost has dropped from 4.1 USD/lb nickel to 1.54 USD/lb nickel. Murrin Murrin was one-third of the design and was reached after the original plan was pushed forward. The Bulong plant was forced to enter bankruptcy liquidation in 2004 due to technical and financial problems.

Table 3 Profile of three HPL nickel plants in Western Australia

These three projects have many problems in technology, mechanical design and cost calculation, such as improper equipment selection and dislocation. Although these three projects did not achieve the desired goals, their establishment provided valuable experience for the development of pressurized acid leaching technology in the future.

Since about 70% of the laterite resources are of limonite type, the high-pressure acid leaching technology has received the greatest attention and has been technically improved. Since 1998, several major companies, including BHPB, Brazil's state-owned mining company (CVRD), and Canada's Falcon bridge, have conducted technology development projects. Both BHPB and CVRD tend to use new processes to produce mixed sulfides or hydroxides. Inco uses a two-step solvent extraction method in which nickel is transferred from a sulfuric acid medium to a hydrochloric acid medium, and then the solution is hydrolyzed at a high temperature to obtain a nickel oxide product and hydrochloric acid, which can be recycled.

SGS Lakefileld has developed a high-pressure acid leaching scheme characterized by the addition of elemental sulfur and oxygen to the autoclave to produce sulfuric acid in situ. This makes it unnecessary to preheat the slurry before it enters the autoclave, thereby significantly saving equipment costs.

(3) Other wet process

Atmospheric pressure leaching (AL): Suitable for treating lateritic nickel ore with low iron content and high magnesium content. At present, Skye Resources is researching the atmospheric pressure leaching method for the development of the Guatemala laterite deposit, which uses the residual acid after leaching of limonite and the acid released by precipitation in the form of goethite for leaching a large amount of humus Share.

Heap leaching: mainly suitable for humus soil. A large number of research results show that with heap leaching technology, the leaching rate of nickel can reach more than 75% within 3 months, and the leaching rate of cobalt can reach more than 60%. European Nickel is currently conducting a large-scale dip test in Turkey and is expected to build the world's first plant to extract nickel and cobalt using heap leaching technology.

Microwave sintering-pressure leaching method: the laterite ore is subjected to microwave sintering to destroy the mineral crystal lattice, and then subjected to pressure leaching at a low temperature to precipitate iron ions in the form of hematite to achieve enhanced leaching, lowering the high-pressure acid leaching temperature and The purpose of stress.

Chlorination Segregation-Ammonia Leaching: Adding a certain amount of carbonaceous reducing agent and chlorinating agent (sodium chloride or calcium chloride) to the ore, heating in a neutral or weak reducing atmosphere to make valuable metals from ore The chlorination volatilizes and simultaneously reduces to metal particles on the surface of the carbon particles. The calcination is followed by direct ammonia leaching. Wang Chengyan used this method to treat the Yuanjiang lean nickel oxide ore. The experimental results are as follows: the nickel leaching rate is greater than 80%, and the cobalt leaching rate is greater than 50%.

Bioleaching: The metal is efficiently dissolved from low grade ore by microbial catalyzed oxidation-reduction. Castro et al. studied the leaching of nickel from silicon-magnesium-nickel ore by heterotrophic microorganisms. The ore sample was taken from Acesita Mining Company of Brazil with a chemical composition of 43.2% SiO2 and 0.09% Ni. Grinding to a particle size of 147 μm or less, five heterotrophic microorganisms were used for leaching. The leaching conditions were as follows: the ore sample weighed 5 g (pre-sterilized at 12 l ° C), the microbial-containing medium 1000 mL, the temperature 30 ° C, the shake flask rate 200 r / min, and the Ni leaching rate was greater than 80%.

4. Prospects for hydrometallurgical technology of laterite nickel ore

The traditional pressurized acid leaching process has received more and more attention. In the new laterite nickel ore project in the next few years, this method accounts for a large proportion. This is because pressurized acid leaching is technically and economically superior to fire and ammonia leaching. However, this technology also has many problems, such as large investment in disposable equipment; it is only suitable for handling brown iron-type ore with low magnesium content, and has requirements for the grade of ore; the same liquid waste, polluting the environment, etc., these problems have been limited The development of the process. While perfecting the pressurized acid leaching technology, people are also constantly developing new laterite nickel ore wet processes, such as atmospheric pressure leaching and bioleaching. These new processes have received much attention in recent years, and they have the following advantages compared to pressurized acid leaching processes:

(1) Atmospheric leaching and bioleaching techniques can treat laterite nickel ore with higher magnesium content, which are suitable for processing low grade ore.

(2) Atmospheric leaching and bioleaching can be carried out under normal temperature and normal pressure conditions, with low equipment requirements, simple process and convenient operation, so the investment is low and the production cost is low.

(3) Pressurized acid leaching method has many solid-liquid wastes and pollutes the environment. New processes such as bioleaching do not produce SO ₂ gas, and the resulting solid-liquid waste is environmentally acceptable and environmentally friendly.

However, these new processes are still immature, and there are still some technical problems, such as the difficulty of separation of leachate in atmospheric leaching, and the problem that organic acids cannot be circulated by bioleaching. From the current reports, atmospheric pressure and bioleaching techniques are used to treat laterite nickel. The leaching rate of nickel and cobalt in the mine is generally lower than that of pressurized acid leaching. Although there are many problems, it is believed that through continuous improvement of technology, it will eventually be solved. Atmospheric leaching and bioleaching will have good development prospects.

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