Carbon-Containing Pellets with Laterite Nickel Ore(3)
Source: internal company
Fig1: Effect of water content on the strength of briquetts. Fig2: Effect of bentonite content on the strength of briquetts.
3. Effect of water content on the strength of briquetts
Laterite nickel ore is added with CaO with a mass fraction of 10%, anthracite with a particle size of 75-150 µ m is added according to the carbon-oxygen atom ratio Nc/No=1. 3, and water with different mass is added without binder to prepare carbon-containing pellets. The influence of water addition on pellet strength is shown in the figure. Moisture can play a lubricating role in the mixture, and the friction force between particles is reduced, so that the material is piled up densely, and the plasticity of the mixture can be increased, so that it is easier to form balls. Proper moisture can also reduce the friction between the ball pressing material and the mold wall. If the moisture in the mixture is too high, excessive moisture will be pressurized out, which will lead to difficult demoulding and thus affect the ball forming rate. In addition, excessive moisture will increase the pressure in the subsequent drying process, and after drying, there will be a large number of voids in the pellets, resulting in a decrease in the strength of the pellets. Therefore, proper moisture selection is very important to the ball pressing process.
As can be seen from the figure1, with the increase of moisture in the mixture, the liquid filling rate between the particles increases, which gradually increases the bonding force between the particles of the material and improves the compressive strength of the pellets. When the moisture content is 18%, the compressive strength will reach the maximum of 192N. If the water content continues to increase, excessive water content will form a water film, which will hinder the direct contact between particles, thus reducing the molecular adhesion between particles, and the compressive strength of pellets will show a downward trend. When the mass fraction of water added to the pellets is 14%-20%, the falling strength of the pellets increases with the increase of water added. Based on the above data, it is known that the optimal water addition fraction for laterite nickel ore pelletizing under this process condition is 18%.
4. Effect of bentonite binder on the strength of pellets
Laterite nickel ore is added with 10% CaO by mass fraction, and anthracite with particle size of 75-150 µ m is added according to carbon-oxygen atomic ratio Nc/No=1. 3. Adding bentonite with different qualities and adding a certain amount of water to make carbon-containing pellets. As shown in the figure, the influence of different bentonite addition amount on pellet strength is shown. In the process of ball pressing, the binder can evenly wrap or adhere to the surface of mineral particles, reduce the friction between material particles and between the material and the mold wall, thus increasing the plasticity of the material, making the material have better ball forming property, and reducing the agglomeration cracking caused by uneven density distribution and elastic aftereffect. In the process of pressing the ball, the binder molecules can penetrate into the cracks on the surface of the particles and the cracks between the particles, increasing the contact area between the particles, thus enabling the molecular force to be better transmitted and the strength of the briquette to be improved. The main mineral component of bentonite is montmorillonite, which has a layered structure and a large surface area. The crystal layers can absorb a large amount of water and obviously increase the distance between crystal layers after absorbing water. The layers of bentonite can slide relatively, and the water-absorbing and swollen bentonite fine particles can play a role of infiltration and filling between ore particles. However, each layer is composed of negatively charged silicone oxide compounds. When the mixture is added to press the ball, the interface between bentonite and liquid phase has higher electric potential and large surface energy, which can increase the bonding force at the interface of ore particles to improve the strength of the ball.
With the increase of bentonite content, the bonding between the granules of the pellets becomes more compact, and the compressive strength and falling strength of the pellets are obviously improved. When the mass of binder in the pellets is 2%, the compressive strength and falling strength of the pellets reach the maximum respectively. With the further increase of bentonite content, the compressive strength and falling strength of the pellets decrease slightly. The main reason may be that the gap between the particles is continuously narrowing during the ball pressing process, and some binder is extruded out, thus losing the bonding effect on the particles.
5.1 Laterite nickel ore contains higher kaolinite, and kaolinite belongs to clay mineral, so it has greater plasticity. The bonding force between molecules can be fully exerted in the ball pressing process, so that the laterite mineral powder is easy to form balls, and the mineral powder has a certain particle size composition, irregular particle shape, rough surface, and the particles can fully fit in the briquetting process, thus improving the briquette strength.
5.2 Whether bituminous coal or anthracite coal, when the particle size is small, the strength of laterite nickel ore cold consolidated pellets will be adversely affected. The compressive strength and falling strength of the pellets decrease with the increase of pulverized coal addition, and the strength of the pellets added with anthracite is higher than that of the pellets added with bituminous coal. If pulverized coal with larger particle size is added, pulverized coal can play a skeleton role in the mixture. With the gradual increase of coal blending amount, the skeleton role of pulverized coal has a greater favorable influence on the strength of pellets, thus improving the strength of pellets. However, when the dosage of pulverized coal exceeds a certain value, the pellet strength shows a downward trend.
5.3 Moisture can play a lubricating role in the mixture. It can reduce the friction force between particles, make the materials compact, increase the plasticity of the mixture, and make the ball forming rate higher. With the increase of moisture content in the mixture, the compressive strength of the pellets gradually increases. When the moisture content is 18%, the compressive strength of the pellets reaches the maximum value of 192N. However, if the moisture content continues to increase, the pelletizing rate of mineral powder will decrease and the compressive strength will decrease. The water content of the pellets is in the range of 14%-20%, and the falling strength of the pellets increases with the increase of water content.
5.4 With the increase of binder bentonite addition, the bonding between the pellets becomes closer, and the compression resistance and falling strength of the pellets are obviously improved. When the mass fraction of bentonite is 2%, the compressive strength and falling strength of the pellets reach the maximum respectively. However, with the further increase of bentonite dosage, the compressive strength and falling strength of pellets will decrease.