Use chrome ore dressing waste as refractory raw material

Magnesium feedstock expensive, forcing it to find new sources, including finding process characteristics. The Jinpel chrome ore beneficiation waste belongs to this new source. Chemical analysis, petrographic analysis, X-ray analysis, and weight change analysis were used to study the waste before and after calcination, and some performance indexes were determined according to the existing methods.

The chemical composition of the non-burned waste is listed in Table 1. The ratio of MgO to SiO ₂ fluctuates between 1..03 and 1.37. It is worth noting that the burning loss is very large (13.47% to 16.77%), which requires pre-calcination whether it is in the production of the furnace powder or in the production of refractory materials.

Table 1 Chemical composition of chrome ore dressing waste

The high refractoriness of high-quality silicate magnesia, (1730 ~ 1780 ° C), indicates that the use of waste in the production of refractory materials is promising.

From the appearance of the waste sample before firing, it is light green and light gray, homogeneous and dense.

Microscopic studies have shown that the sample has a network structure unique to serpentine or serpentinized pure peridotite , and is formed by a dense mesh of 3MgO·2SiO ₂ ·2H ₂ 0 serpentine light green scaly fibrous material. (mainly fiber variant - fiber serpentine) composition. 2 (MgO, FeO) SiO ₂ olivine colorless and angular non-homogeneous particles having a size of 0.06 to 0.24 mm are unevenly distributed on the nodes of the net. Olivine refractive index: Ng = 1.680 ~ 1.690, Np = 1.640 ~ 1.650. Around the olivine particles, often see finely divided ferric hydroxide (goethite type) opaque film. When the opaque magnetite meets the transparent brown chrome-containing spinel (Mg, Fe ²⁺ )O(Cr,Fe ³⁺ ,Al) ₂ O ₃ , it has a rare coarser octahedron and a size of 0.08. An angular form of ～0.32 mm exists.

The approximate mineral composition (volume ratio) of the waste: 80% to 85% of serpentine, 10% to 15% of olivine, 3% to 5% of magnetite containing iron hydroxide, and 2% of chrome-containing spinel 3%.

The x-ray phase analysis of the total sample of the original waste also showed that the main substance was serpentine (fibrous serpentine, a small amount of serpentine), there were not many olivines, and trace amounts of chrome spinel and Goethite.

The thermogravimetric analysis of the waste (Fig. 1) shows that there are three basic thermal effects unique to serpentine. The endothermic effect at 70 °C is related to the adsorption of adsorbed water; at 620 °C: the mineral structure is destroyed, while the OH ^- group is excluded, and the x-ray amorphous forsterite and eclogite are formed from the decomposition products. The exothermic effect at 770 °C is caused by the crystallization of the newly formed mineral phase.

Fig.1 Thermal spectrum of raw ore waste from chrome ore dressing

The endothermic effect at 180 ° C and 375 ° C is related to the presence of finely divided goethite. At 180 ° C, water at an intermediate position between the adsorbed water and the structural water is discharged. At 375 ° C, goethite (α-FeOH) undergoes dehydration and its conversion to α-Fe ₂ O ₃ . The second endothermic enthalpy of the polymorphic transformation of α-Fe ₂ O ₃ to ρ-Fe ₂ O ₃ occurs simultaneously with the endothermic effect of serpentinite at 770 °C.

There are four maximum weight loss stages on the thermogravimetric analysis curve: 3.5% at 20-150, 3% at 180-380 °C, 11.75% at 380-770 °C, and 0.25% at 770-1000 °C.

Data on the variation of certain performance indicators for waste are listed in Tables 2 and 3. The data in the table indicates that the reduction in ignition is reduced as the firing temperature increases.

Table 2 Some performance of chrome ore dressing waste

Table 3 Foreign refractory materials

In the heating process of the waste sample, like normal serpentinite, dehydration starts at 200-300 °C and ends at 900 °C. These processes cause the material to be loose, and the porosity reaches a maximum at 700-900 ° C. When the temperature is higher, the serpentine is dense and the porosity is lowered, and the porosity reaches a minimum at 1300-1400 ° C. When the temperature is around 1500 °C, serpentinite may expand due to increased density.

X-ray phase analysis showed that the sample was amorphized strongly after firing at 7OO °C. There is a forsterite line on the diffraction pattern, which confirms the data of the thermogram. The reflection is weak, the image is blurred, and the structure is incomplete. The parameters of the square lattice: a = 0.4760 nm, b = 1.0201 nm, and c = 0.5992 nm. There are also traces of rich body, serpentine, β-Fe ₂ O ₃ , H ₂ O, chrome-containing spinel and other phases. The sample after firing at 1400 ° C was a light red, light gray angular sintered sintered piece. Under the microscope, these fragments were mainly composed of colorless and angular equiaxed particles and forsterite flaky crystals with a size of 0.04 to 0.3 mm. Most of these crystals were not bonded to each other with a glass bond film (Table 4). That is, direct combination. The forsterite index of refraction is standard.

Table 4 Phase composition of waste samples after calcination

In the fine-grained forsterite material, a-MgSiO ₃ oblique enstatite small column crystal and octahedral crystal with a size of 0.004 to 0.02 mm bonded by a light green-light brown glass film are unevenly distributed; Circular equiaxed particles of Mg Fe ₂ O ₄ iron ore having a size of less than 3 to 15 mm are rarely seen.

A small number of angular particles of chrome-containing spinel having a slightly transparent size of 0.02 to 0.12 mm are unevenly distributed in the sample. Most of the pores are irregular equiaxed shapes having a size of 0.02 to 0.3 mm, and occasionally a curved longitudinal crack having a width of 0.02 to 0.05 mm.

The sample after firing at 1500 ° C is different from the sample fired at 1400 ° C, and has a darker color and a large porosity. From the microscope, they are very similar to the samples after firing at 1400 ° C, but the difference is that the refractive index of forsterite is slightly higher (Ng = 1.695, Np = 1.660 ± 0.003), which proves the presence of isomorphous FeO impurities. . Very small closed pores (3 μm or less in diameter) are often observed in ordinary circular equiaxed forsterite crystals. In addition, the difference is that the maficite crystals are slightly larger (below 25 μm), and there are opaque magnesia magnetite (Mg, Fe) Fe ₂ O ₄ tree crystals on the surface of the forsterite particles and a few oblique Emerald stone and glass.

On the Πayrnt silicon and Ξpnen weight change analyzers in Hungary, the thermal analysis curves (Fig. 2) of the samples fired at 1400 °C and 1500 °C obtained at a heating rate of 10/min are similar, indicating that the samples are hot. Inert.

The x-ray phase analysis of the scrap after firing at 1500 ° C also indicates that the forsterite crystal is the main component. The velvet of this phase is strong, sharp and clear. Lattice parameters: a = 0.477 nm; b = 1.020 nm, c = 0.5992 nm. In addition to the above phases, there are a small number of perilla pyroxene (Mg, Fe) ₂ Si ₂ O ₆ and magnetite in the sample, and a trace amount of dicalcium silicate.

Figure 2 Thermal spectrum of waste after firing at 1400 °C

The results of the study show that the performance of chrome ore dressing waste is as follows:

As mentioned earlier, serpentine is the main mineral phase of unburned waste. In the calcination of serpentine, the following reactions are mainly produced:

3MgO·2Si0 ₂ ·2H ₂ 0→2MgO·SiO ₂ +MgO·SiO ₂ +H ₂ 0 (1)

(forsterite) (oblique stone)

The exothermic effect on the thermogram of serpentinite at 770 ° C and greater than 770 ° C is the result of lattice reorganization to produce forsterite. As mentioned above, the forsterite curve was first observed at 700 ° C, and a large amount of forsterite was formed at a temperature of 1150 ° C and higher, which confirmed the lithofacies study.

As the temperature increases, the iron oxide (1) contained in serpentine and olivine is oxidized (about 800 ° C), at which time the olivine decomposes and partially forms metasilicate (pyroxene), which may also be precipitated. Not much silica (glass).

The iron oxide (2) formed at a temperature above 1200 °C is partially converted into magnetite, which in turn reacts with the precipitated forsterite to produce or enstatite and mafic ore:

2Mg0·Si0 ₂ +Fe ₂ O ₃ →MgO·SiO ₂ +MgO·Fe ₂ O ₃ (2)

The olivine reacts with iron oxide (3) to form a solid solution of divalent iron in the enstatite and mafic iron:

2(Mg,Fe)O·SiO ₂ +Fe ₂ O ₃ →(Mg,Fe)O·SiO ₂ +(Mg,Fe)O·Fe ₂ O ₃ (3)

Forsterite also reacts with magnetite and precipitates olivine and solid solution of mafic iron:

2MgO·SiO ₂ +Fe ₃ O ₄ →2(Mg,Fe)O·SiO ₂ +(Mg,Fe)O·Fe ₂ O (4)

The original chrome-containing spinel reacts with the scrap magnesium silicate component to form a solid solution.

Serpentine dehydration, oxidation of iron oxide (2), formation of solid solution, the performance of individual variants of beneficiation waste is different, and there are different properties depending on the degree of serpentine petrochemical and iron oxide content.

The change in the properties of the waste seen during calcination involves the recrystallization of iron oxide in the olivine particles and the formation of particulate silicate crystals (forsterite) in the serpentine segment when they are densely packed during heating. The magnesia produced during the action (at 1450 ° C) decomposes the silicate particles, which causes a slight increase in the porosity. The silicate is strongly recrystallized (1450 ~ 1500 ° C), which has an adverse effect on the sintering of the product.

The optimum burning temperature of chrome ore dressing waste should be 1400 ~ 1450 °C. At this temperature, the iron oxide has been greatly oxidized and recrystallized, while the degree of crystallization of the silicate is not large.

The research carried out shows that the main performance of the Kempel chrome ore dressing waste is similar to that of high quality silicate magnesia, which determines the possible range of use, especially for the production of furnace mix, forsterite fire resistance. material.

in conclusion

A comprehensive study was conducted on the performance of the Kemper chrome ore dressing waste and its firing pair. Studies have shown that the mineral composition of the waste is serpentine and chrome-containing spinel with a small content.

The performance of the waste at the time of firing is the same as that observed with serpentinite. According to performance indicators, Jinpel chrome ore dressing waste can be used as a raw material for magnesium silicate in the refractory industry.

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