Keywords:  laterite-nickel ore   wet process refining technology   development status

 

According to geologic origin, the nickel ore could be divided into two kinds: magma type nickel sulfide ore & weathering type laterite-nickel ore, while the laterite-nickel ore reserves occupies 72% of worldwide nickel resources. In recent years, due to the leading of stainless steel industry, the nickel demand in the worldwide keeps increasing, the stainless steel output of China has reached 10 million tons in 2008, while actual output is only 5.35 million tons and one of the important reasons is the short supply of nickel.
     

At present, about 60% nickel is extracted from nickel sulfide ore while the nickel sulfide resources is reducing quickly, the quality is decreasing while the mining depth is deepening, difficulty of extracting is increasing and the cost is increasing. While the cost for investigation and extracting of laterite-nickel ore is lower, which could directly produce nickel oxide, polydymite and ferronickel, thus, high efficiently develop laterite-nickel ore resources is really urgent. In 1950s, extracting nickel from laterite-nickel ore occupied 10% of worldwide nickel production, while in 2008, this percent has reached 455 and in 2012, it is estimated to be 510 000 tons, this percent should increase to 51%。

The process of extracting nickel from laterite-nickel ore could be divided into fire process and wet process. Due to its high consumption and investment during refining process, fire process is mainly used for high quality laterite-nickel ore. However, though wet process has complicated process, long flow and high requirements on equipments, etc., compared to fire process, it has the advantages of lower consumption and high recovery rate of metal. Especially the progress of atmospheric pressure leaching and the appearance of new flow of wet process makes the center of developing & utilizing laterite-nickel ore has moved to wet process from fire process during tens years of development of wet process. 
   

 一、The categories & characteristics of worldwide laterite-nickel ore resources

  The upper of nickel oxide mineral deposit is brown iron ore laterite which is suitable for wet process treating; lower is magnesium silicic acid nickel ore ( mainly is serpentinite) which is suitable for fire process. Middle transition section is suitable for two methods. According to estimation, the reserve of laterite nickel-ore (limonite, nontronite, turface) which is suitable for wet process is more than two times than those (garnierite, humic ore ) which is suitable for fire process.
   Complying with gradual development and utilization of laterite nickel-ore resources, people has new knowledge of its function and types: one called wet process which is mainly distributes nearby equator, such as New Caledonia, Indonesia, Philippine, Papua New guinea, Caribbean Area, its grade is higher, clay is less which is easy for treatment; the other kind is dry process, which is mainly distributes in southern hemisphere area which is far away than equator, and its composition is complicate, clay content is higher which is not easy for treatment.
   Though laterite nickel-ore has several different types, but seeing from general; they have following characters:
    1、Nickel content is 1.0～3％, its grade is lower and composition is more complicated than that of Nickel sulfide ore, and it is hard to gain Nickel Ore Concentrate with higher nickel content which is over 6%, meanwhile nickel ore with lower nickel content is hard to be used for simple metallurgical process directly.
    2、Fluctuation of component content is larger, not only the change of valuable elements content such as nickel is larger, meanwhile the composition change of gangue such as SiO2、MgO、Fe2O3、Al2O3 and water is larger, even in same mineral bed, the composition of laterite ore (Ni，Co，Fe & MgO) will gradually change complying with the depth of different mineral layers.
    3、There is little cobalt, Sulfur-free, no heat value in ore.
    4、The storage of ore is larger meanwhile it is on earth’s surface which is easy for collecting and it could be operated in the open-air and it has advantage for development.

二、Development status of worldwide laterite-nickel ore

   From the mark of laterite nickel ore development of New Caledonia, metal nickel production from laterite nickel has been over 100 year’s history so far. For recent years, due to huge requirements of nickel for stainless steel industry, many countries producing nickel actively enlarge the development and utilization of laterite nickel ore.

   As we have less laterite nickel-ore resource, some large enterprises of China has caught the chances to enlarge the investment of laterite nickel-ore project of foreign countries. At present developed or been developed foreign laterite nickel ore projects are: 1) Bao-steel group and Jinchuan group invested 1 billion USD for nickel iron resource development in Philippines, 2) China Minmetals and Cuba set up nickel production with annual production of 22.5thousands t, 3) CNMC developed Myanmar nickel ore, its average grade of nickel ore is 2% which includes about 700 thousand t nickel; 4) CHINA METALLURGICAL CONSTRUCTION(GROUP)CORPORATION cooperated with Ji’en Nickel Company for nickel iron development whose average grade is about 1%; 5) China Campbell mineral company signed the contract with Myanmar Moweitang Nickel ore for cooperation, etc.  In future laterite nickel project, wet process occupies large percent, and it is estimated to be 2012, the percent of wet process nickel production of total nickel production will increase from 62% to 80%.

三、Refining technology status of wet process laterite-nickel ore

    1、Reducing roasting - ammonia leaching process (RRAL)
    Reducing roasting - ammonia leaching process (RRAL) is developed by Carson, thus it is called Caron process. Guba Nijialuo nickel plant utilizes reducing roasting – ammonia leaching process to treat Nickel laterite high-magnesium has been over half centuries, suitable for utilizing Ammonia Alkali leaching method to treat typical mineral composition which is 1.4％Ni，8％MgO，14％SiO2.  
    In order to improve the nickel drilling leaching rate, American mineral bureau developed new process of reducing roasting - ammonia leaching process and its abbreviation is USBM. The importance of this method is to add FeS2 to make the grain and utilize pure carbon monoxide for reduction.
   
    2、Sulfuric acid pressurizing acid leaching process (HPAL)
    Sulfuric acid pressurizing acid leaching process is suitable for treating brown iron ore type laterite ore including lower magnesia, the principle of pressurizing acid leaching process is as the following picture, the largest advantages of this process is the return rate of metal could reach over 90%,

      Pictures 1: The process flow of principle of pressurizing acid leaching process

This technology begins from 50s of 20^th century; first it is used for Cuba Moa Bay ore calling A-MAX-PAL technology. Since after, in 70s Australia QNI Company sets up Yabula nickel plant, acid leaching process treats laterite nickel ore in New Caledonia, Indonesia & Queensland of Australia. On second half year of 1998, Murrin of Australia, Cawse, Bulong utilizes new process of pressurizing acid leaching of laterite ore to put developing project into operation and absorb large attention. The acid pressurizing leaching technology for these three processes is similar to Cuba Mo’ao Company, just utilizing horizontal autodave to replace the vertical autodave of Mo’ao Company. However, the return program has following difference:
    1、In Cawse process, mixed metal hydroxides is precipitated from high pressure lixivium, then utilizes ammonia leaching them, and then have solvent exhaustion & electro-deposition.
    2、In Bulong process, utilizes H2S to precipitate the mixed sulfides from high pressure lixivium, and then lixiviate sulfide under aerobic conditions, then have solvent exhaustion, hydrogen reduction, tabletting, etc.
    3、In Murrin process, directly have solvent exhaustion and electro-deposition from high pressure lixivium.

The resources, annual production，achieving rate and design production of these three laterite nickel plant is shown in form 3. Seen from form 3, the process of three laterite ore HPAL project of Australia is not very satisfying, just the Cawse could reach 74% of the design production, manufacturing cost decrease from USD 4.1 to USD 1.54; the production of Murrin is 1/3 of the design production, however this conditions is reached under the situation of pushing again & again, Bulong plant is forced to be bankrupt in 2004 due to technology & fund problem.

             Form 3   Simple situations of three HAPL nickel plants of west Australia

   There are lots of problems on technology, mechanical design and cost calculation of these three projects, for example: the material chosen on equipment is not proper or the configuration is out of joint, etc. Though these three projects haven’t reaches the expected target, but the setting up of them has supplied precious experiences on the development of pressurizing acid leaching technology.
    

 3、Other flow of wet process
    Atmospheric pressure leaching (AL): it is suitable for treating laterite nickel ore including lower iron content and higher magnesia content. At present Skye resource company is researching on developing Atmospheric pressure leaching for Guatemala laterite ore development, the residual acid leached from brown ore & acid released after precipitating of rubinglimmer which will be used for the composition of humus soil ore.

Dump leaching: it is mainly suitable for humus soil ore. The abundant results showing that: utilizing dump leaching technology, the leaching rate of nickel in 3 months could reach over 75%, the leaching rate of cobalt could reach over 60%. European Nickel company is having large-scale leaching experiment in Turnkey at present and it is expected to set up first dump leaching plant extracting nickel & cobalt.  

Microwave sintering—pressurizing leaching method: to have micronwave sintering to disturb the crystal grating of mineral, then pressurize and leach under low temperature to make the iron ion be precipitated as the hematite type then strengthen the leaching and decrease the temperature and pressure of high pressure acid leaching.

Chloride segregation - ammonia leaching: Add some carbonaceous reducer and chloridizing agent (sodium chloride or calcium chloride), heat in netural or weak deoxidation atmosphere making the valuable metal volatilize from ore meanwhile reduce the surface of carbon grain to be metal grain. Then roasted product will be directly treats in ammonia leaching. Wang Chengyan utilizes this method to treat the Nickel oxide ore of Yuanjiang pin, the testing result is: the leaching rate of nickel is over 80%, while the leaching rate of cobalt is over 50%.

Bioleaching: via oxido-reduction of Microorganism makes metal dissolve effectively from low grade ore. Castro etc. has researched the bioleaching. The sample comes from Acesita mineral company, its chemical composition is 43.2％SiO2、0.09％Ni。The grinded grain size should be less than 147μm，while mineral leaching utilizes 5 kinds of auxohetertrophs. The Leaching conditions is: the weight of mineral sample should be 5kg (pre-sterilized under 121℃)，there is medium including microbe, temperature should be 30℃，the rotating rate of bottle should be 200r/min and the leaching rate of Ni is more than 80％。