Formation Of Ferronickel Nugget And The Intensifying Method By Coal Based Reduction Of Nickel Laterite With The Condition Of High Melting Point Slag System

Stainless steel has a widespread application in military, industry and agriculture because of its corrosion resistance. With the economic development, China has be the first in the production and consumption of stainless steel after 2001. In recent decade, the great rapid increase of stainless steel in China has led to a great demand for nickel. Nickel is usually extracted from two distinct ore types: nickel sulphide deposits and nickel laterite. With the continuous depletion of sulfide nickel deposits and high grade laterite ore, the development and utilization of low grade nickel laterite get more and more attention. Compared with other pyrometallurgical processes, direct reduction-gravity or magnetic separation process has advantages in reducing cost and utilization of nickel resource. However, direct reduction- gravity or magnetic still has some problems in the current studies, including low enrichment efficiency of nickel from laterite at low temperature, high levels of additives cause environment pollution and equipment corrosion, slag bond with refractory material at high temperature. Therefore, in order to improve nickel enrichment efficiency and avoid slag bonding with refractory material, it is important to improve the current process.The study is a key research project supported by National Natural Science Foundation(No. 51234010). This paper focuses on the formation of ferronickel and the sodium sulfate strengthen reduction and separation and the growth mechanism of ferronickel grain under the high melting point nickel laterite slag system. Several conclusions were shown as follow:① The nickel laterite used in the paper contains high Si and Mg. And the nickel and iron grade are 1.814% and 17.87% respectively. The main mineral phase of the nickel laterite are lizardite, hematite, antigorite and gismondine.② The temperature point of the laterite pellet can be increased by adding silica. During the experiment of reducing laterite with high carbon, magnetic separation efficiency can be improved by elevating reduction temperature within a certain range, and the content of Ni and Fe in concentrate after magnetic separation increased with the increasing of temperature. At the same temperature, the content of Ni and Fe in concentrate first increased and then decreased with the increasing of reduction time. In this study, reduction time shouldn’t be over 90 min, and the content of Ni and Fe in concentrate after magnetic separation reached 5.63% and 71.82% when temperature is 1500 ℃, reduction time is 90 min and C/O is 1.2. The content of Ni in concentrate after magnetic separation can be enriched by reducing laterite with high carbon, but the enrichment efficiency is low.③ During the experiment of reducing laterite with low carbon, the temperature point of laterite pellet increased, the melting degree of laterite pellet lessened and the content of Ni and Fe in concentrate after magnetic separation increased with the increasing of Si O2/(Si O2+Al2O3+Mg O). When Si O2/(Si O2+Al2O3+Mg O) is 75%, pellet can keep ball shape and bigger ferronickel grain generated. In addition, the content of Ni and Fe in ferronickel grain reached up to 8.82% and 86.94% respectively. And the content of Ni and Fe in ferronickel were 8.33% and 84.71%, the recovery ratio of Ni and Fe in ferronickel were 75.70% and 77.97% when Si O2/(Si O2+Al2O3+Mg O) is 75%, C/O is 1.0.④ Sodium sulfate has a good effect in strengthening laterite reduction and separating ferronickel from slag. Meanwhile, slag didn’t bond with crucible by adding sodium sulfate in pellet. With the sodium sulfate increased from 0% to 2%, the content of Ni in concentrate after magnetic separation increased from 2.37% to 8.35%, and the recovery ratio of Ni increased from 56.80% to 82.48% when reduction temperature is 1400 ℃, reduction time is 60 min, C/O is 0.8. And when reduction temperature is 1420 ℃, the content of Ni in concentrate after magnetic separation increased from 3.21% to 8.72%, and the recovery ratio of Ni increased from 56.82% to 85.57%, keeping adding sodium sulfate in pellet to 8% can get ferronickel grain with 9.7% nickel grade.⑤ The growth behavior of ferronickel grain was investigated using Hillert model, the results show that the average size of ferronickel grain increases rapidly at 30 min to 60 min, then it increases slowly at 90 min to 120 min at 1400 ℃. The growth index and growth rate constant of ferronickel grain are 1.5361 and 2.136 μm2?min-1 respectively when roasted at 1400 ℃ for 30 min to 120 min, and the relationship between the average size of ferronickel grain and time is d =exp(0.6510 ln t +0.49406). Increasing temperature can improve the ferronickel grain growth. The apparent activation energy of ferronickel grain growth is 128.70 k J/mol when roasted at 1200 ℃ to 1400 ℃ for 60 min, and the relationship between the average size of ferronickel grain and temperature is d =exp(-10077.4 / T +9.2874). The apparent activation energy of ferronickel grain growth can be decreased and the average size of ferronickel grain can be increased by adding sulfur in pellet. With the sulfur addition increases from 0% to 8%, the apparent activation energy of ferronickel grain growth decreases from 129.42 k J/mol to 110.47 k J/mol when roasted at 1200 ℃ for 60 min.