Method for desilication of magnesite flotation by using a collector SAA

Abstract

A method for desilication of magnesite flotation by using a collector SAA belongs to the technical field of magnesite beneficiation and purification process, and steps are as follows: high-silicon low-grade magnesite is crushed, and ball-milled to obtain magnesite powder; at room temperature, the magnesite powder is placed in a flotation device, and deionized water is added to carry out slurry preparation; then, HCl solution is added to adjust the pH value, and stirring is carried out to obtain magnesite slurry; the collector SAA is added to the magnesite slurry, and stirring is uniformly carried out, and then one-roughing one-cleaning one-scavenging reverse flotation purification is carried out to obtain low-silicon magnesite concentrate. The application of a new collector SAA is developed, because the collector SAA has strong selective collecting property for silicon-containing minerals, the desilication process is shortened and simplified, the flotation process operation is more stable, the operation is more simple, and the collector SAA has more environmental protection compared with other chemical collectors. The ore treated by the method has low grade, and the content of SiO2 in the crude ore is high; the obtained magnesite concentrate can reach the special-grade standard of metallurgical industry.

Description

Technical Field

[0001] This invention belongs to the field of magnesite beneficiation and purification technology, specifically relating to a method for using collector SAA for magnesite flotation desilication. Background Technology

[0002] Magnesium, as one of the fundamental metallic materials for national economic and military construction, enjoys the reputation of "21st-century green engineering material." China has the world's largest reserves of magnesite ore, and the main source of magnesium metal in industrial applications is magnesite. However, with the demands of national economic and military construction, high-quality magnesite ore resources have been almost exhausted, and low-grade magnesite ore (MgO grade less than 42%), accounting for more than 60% of the total reserves, has become the main source of magnesium metal materials. Therefore, research on the efficient utilization of low-grade magnesite ore resources is in line with the national economic security, national defense security, and the development of strategic emerging industries.

[0003] Flotation is a method of separating target minerals from gangue minerals by utilizing the differences in their physical and chemical properties. Over the past decade, excessive consumption and irrational development of high-quality magnesite resources have led to the abandonment or stockpiling of large quantities of low-grade magnesite. With the booming development of industries such as refractory materials, the demand for high-grade magnesite is increasing year by year, making the efficient and comprehensive utilization of low-grade magnesite a research hotspot for mineral processing workers. Flotation is widely used in the industrial practice of purifying low-grade magnesite, possessing advantages such as mature technology, wide applicability, and high gangue mineral removal rate.

[0004] With the advancement of a sound green, low-carbon, and circular economic system, existing traditional magnesite desilication flotation reagents are increasingly inadequate for dealing with the increasingly "poor, fine, and complex" magnesite ore resources. Their low selectivity towards valuable minerals and gangue minerals leads to complex beneficiation processes, low resource utilization, high energy consumption, and high carbon emissions. Therefore, the development and research of novel, highly selective flotation purification reagents for magnesite is one of the main breakthroughs for the efficient utilization of low-grade magnesite ore resources and the establishment of green and low-carbon magnesite beneficiation processes.

[0005] In the beneficiation and purification process of magnesite, reducing the SiO2 content is crucial for improving its quality. The SiO2 in magnesite is mainly contained within the impurity mineral quartz (SiO2). Currently, dodecylamine is commonly used as a collector for separating magnesite and quartz. Analysis shows that electrostatic attraction and hydrogen bonding are the main mechanisms by which dodecylamine collectors adsorb onto mineral surfaces. However, due to the strong electronegativity and weak steric hindrance of dodecylamine, the reverse flotation separation of magnesite and quartz in its presence leads to a large amount of magnesite floating alongside silica-bearing gangue minerals, reducing the magnesite recovery rate in the concentrate. Therefore, it is imperative to develop a cationic collector with strong selectivity for quartz to improve the utilization rate of complex, low-grade magnesite resources.

[0006] SAA (octadecylamine acetate) is a highly silicon-selective surfactant, readily soluble in water, and exhibits low foaming activity. The tertiary amine salt structure of SAA enhances its selectivity; under weakly acidic conditions, it can adsorb onto the negatively charged surface of quartz, but its effect on magnesite is relatively small. Therefore, SAA can be used as a collector for reverse flotation desilication of magnesite, providing a novel collector for the desilication of low-grade magnesite. Summary of the Invention

[0007] The purpose of this invention is to provide a method for desilication of magnesite by using collector SAA. Based on the differences in floatability of magnesite and its impurity mineral quartz under different amounts of collector octadecylamine acetate (SAA), the method removes silicon minerals from magnesite, improves the quality of magnesite, and provides a new reagent for desilication of high-silicon, low-grade magnesite.

[0008] The present invention provides a method for using collector SAA in the flotation desilication of magnesite, wherein collector SAA is used in the flotation desilication process of magnesite and is used to prepare magnesite slurry.

[0009] Furthermore, the method for using collector SAA for desilication of magnesite flotation involves dissolving collector SAA in deionized water to prepare an aqueous solution of collector SAA with a molar concentration of 0.01–0.05 mol / L.

[0010] A method for using collector SAA in the flotation desilication of magnesite specifically includes the following steps:

[0011] Step 1: Grinding

[0012] High-silicon, low-grade magnesite is crushed and ball-milled to obtain magnesite powder; among which, the mass of magnesite powder with a particle size <74μm after ball milling accounts for 70-90% of the total mass.

[0013] Step 2: Prepare the paste

[0014] At room temperature, magnesite powder is placed in a flotation device, deionized water is added and stirred for 3-5 minutes to prepare the slurry; then HCl solution is added to adjust the pH value to 5-7, and stirred for 3-5 minutes to obtain magnesite slurry.

[0015] Step 3: Reverse flotation desilication

[0016] Collector SAA is added to the magnesite slurry and stirred evenly. Then, a roughing, cleaning, and scavenging reverse flotation process is carried out to purify the magnesite and obtain a low-silica magnesite concentrate.

[0017] In step 1, the high-silicon, low-grade magnesite is magnesite with a SiO2 content greater than 3%.

[0018] In step 2, the flotation equipment is a hanging tank flotation machine with a rotation speed of 1600-1900 rpm.

[0019] In step 2, the mass fraction of the HCl aqueous solution is 1-5%.

[0020] In step 2, the pH value is preferably 5.0 to 6.5.

[0021] In step 2, the mass concentration of magnesite powder in the magnesite slurry is 20-40%.

[0022] In step 3, the collector SAA is an aqueous solution of SAA with a molar concentration of 0.01 to 0.05 mol / L.

[0023] In step 3, the rotation speed of the flotation equipment for reverse flotation purification is 1700-1900 rpm, preferably 1800-1850 rpm.

[0024] In step 3, the stirring time after adding the collector is 2-5 minutes, and the flotation time for each stage of reverse flotation purification is 2-5 minutes.

[0025] In step 3, during the coarse stage, the amount of collector SAA added to the slurry is 90-120 mg / L, preferably 95-105 mg / L, according to the solid-liquid ratio.

[0026] In step 3, during the first refining stage, the amount of collector SAA added to the slurry is 45-60 mg / L, preferably 45-55 mg / L, according to the solid-liquid ratio.

[0027] In step 3, during the initial scavenging stage, the amount of collector SAA added to the slurry is 20-30 mg / L, preferably 25-30 mg / L, according to the solid-liquid ratio.

[0028] In step 3, the main components of the low-silica magnesite concentrate and the weight percentage of each component are as follows: MgO 46.5-47.5%, SiO2≤0.3%, CaO≤0.6%.

[0029] The present invention provides a method for desilication of magnesite by flotation using collector SAA. By weight percentage, the recovery rate of low-silicon magnesite concentrate is 70-85%, and the recovery rate of MgO in low-silicon magnesite concentrate is 65-75%.

[0030] Compared with existing technologies, the method provided by this invention has the following advantages:

[0031] 1. This invention develops the application of a new collector, SAA. Because the new collector SAA has strong selective collecting ability for silicon-containing minerals, it shortens and simplifies the flotation desilication process, making the flotation process more stable and easier to operate. Furthermore, the new collector SAA is more environmentally friendly compared to other chemical collectors. Ultimately, a magnesite concentrate with an MgO grade greater than 47% and a recovery rate of 65-85% can be obtained.

[0032] 2. Compared with the prior art, the method of the present invention processes ore with low grade and high SiO2 content in the raw ore; the obtained magnesite concentrate can reach the metallurgical industry special grade standard (YB321~81), that is, MgO≥47.00%, SiO2≤0.30%, CaO≤0.8%.

[0033] 3. The collector of this invention is octadecylamine acetate (SAA), a surfactant with extremely high silicon selectivity, readily soluble in water, and exhibiting low foaming properties. The tertiary amine salt structure of SAA enhances its selectivity; under weakly acidic conditions, it can adsorb onto the negatively charged quartz surface, but its effect on magnesite is relatively small. Therefore, SAA can be used as a collector for reverse flotation desilication of magnesite, providing a new collector for the desilication of low-grade magnesite. Attached Figure Description

[0034] Figure 1 In Embodiment 1 of this invention, a schematic diagram of the process flow for the flotation desilication of magnesite using collector SAA is shown.

[0035] Figure 2 In Embodiment 1 of the present invention, FTIR images of quartz and magnesite before and after the addition of SAA are shown; wherein, Figure (a) is the FTIR image of magnesite before and after the addition of SAA, and Figure (b) is the FTIR image of quartz before and after the addition of SAA. Detailed Implementation

[0036] The present invention will be further described in detail below with reference to the embodiments.

[0037] In the following examples, the high-silicon, low-grade magnesite used was the Shuidonggou magnesite mine in Kuandian County, Liaoning Province. The elemental composition of the high-silicon, low-grade magnesite was analyzed using an X-ray fluorescence spectrometer. Its main components by weight percentage were: MgO 44.81%, SiO2 3.51%, CaO 0.39%, with the balance being loss on ignition and unavoidable impurities.

[0038] The collector SAA and the pH adjuster HCl used were of analytical grade. The SAA reagent used in the experiment was dissolved and prepared with water, and all other reagents were prepared into aqueous solutions of the appropriate concentrations using deionized water.

[0039] Example 1

[0040] A method for using collector SAA in the flotation desilication of magnesite is illustrated in the following process flow diagram. Figure 1 As shown, the FTIR plots before and after the experiment are as follows: Figure 2 As shown, where, Figure 2 (a) shows the FTIR images of magnesite before and after the addition of SAA. Figure 2 (b) shows the FTIR images of quartz before and after the addition of SAA, specifically including the following steps:

[0041] High-silicon, low-grade magnesite is crushed and ball-milled to obtain magnesite powder; among which, the mass of magnesite powder with a particle size <74μm after ball milling accounts for 70% of the total mass.

[0042] Step 2: Prepare the paste

[0043] At room temperature, magnesite powder was placed in a hanging trough flotation machine, deionized water was added, and the mixture was stirred for 3 minutes at a flotation machine speed of 1750 rpm to prepare the magnesite slurry. Subsequently, a 3% (w / w) HCl aqueous solution was added to the magnesite slurry to adjust the pH value to 5.0, and the mixture was stirred for 3 minutes until the slurry was homogeneous, resulting in a magnesite slurry with a pH value of 5.0. The mass concentration of magnesite powder in the magnesite slurry was 30%.

[0044] Step 3: Reverse flotation desilication

[0045] A 0.02 mol / L aqueous solution of tertiary amine collector SAA was added to the magnesite slurry. The slurry was stirred for 3 minutes at a flotation machine speed of 1750 rpm to homogenize it. Then, a roughing-cleaning-scavenging reverse flotation process was performed to purify the slurry and obtain low-silica magnesite concentrate. The roughing stage flotation time was 4 minutes, and the amount of tertiary amine collector SAA added to the slurry was 90 mg / L according to the solid-liquid ratio. The cleaning stage flotation time was 3 minutes, and the amount of tertiary amine collector SAA added to the slurry was 45 mg / L according to the solid-liquid ratio. The scavenging stage flotation time was 3 minutes, and the amount of tertiary amine collector SAA added to the slurry was 23 mg / L according to the solid-liquid ratio.

[0046] In this embodiment, the main components of the low-silicon magnesite concentrate are 47.23% MgO, 0.25% SiO2, and 0.59% CaO by weight percentage; the recovery rate of the low-silicon magnesite concentrate is 73.2%, and the MgO recovery rate in the low-silicon magnesite concentrate is 66.25%.

[0047] Example 2

[0048] A method for using collector SAA in the flotation desilication of magnesite specifically includes the following steps:

[0049] Step 1: Grinding

[0050] High-silicon, low-grade magnesite raw material is crushed and ball-milled to obtain magnesite powder; among which, the mass of magnesite powder with a particle size <74μm after ball milling accounts for 80% of the total mass.

[0051] Step 2: Prepare the paste

[0052] At room temperature, magnesite powder was placed in a hanging trough flotation machine, deionized water was added, and the mixture was stirred for 4 minutes at a flotation machine speed of 1750 rpm to prepare the magnesite slurry. Subsequently, a 2.5% (w / w) HCl aqueous solution was added to the magnesite slurry to adjust the pH value to 5.5, and the mixture was stirred for 4 minutes until the slurry was homogeneous, resulting in a magnesite slurry with a pH value of 5.5. The mass concentration of magnesite powder in the magnesite slurry was 25%.

[0053] Step 3: Reverse flotation desilication

[0054] A 0.022 mol / L aqueous solution of tertiary amine collector SAA was added to the magnesite slurry. The slurry was stirred for 4 minutes at a flotation machine speed of 1800 rpm to homogenize it. Then, a roughing-cleaning-scavenging reverse flotation process was performed to purify the slurry and obtain low-silica magnesite concentrate. The roughing stage flotation time was 5 minutes, and the amount of tertiary amine collector SAA added to the slurry was 95 mg / L according to the solid-liquid ratio. The cleaning stage flotation time was 4 minutes, and the amount of tertiary amine collector SAA added to the slurry was 47 mg / L according to the solid-liquid ratio. The scavenging stage flotation time was 3.5 minutes, and the amount of tertiary amine collector SAA added to the slurry was 25 mg / L according to the solid-liquid ratio.

[0055] In this embodiment, the main components of the low-silicon magnesite concentrate are 47.23% MgO, 0.14% SiO2, and 0.57% CaO by weight percentage; the recovery rate of the low-silicon magnesite concentrate is 77.5%, and the MgO recovery rate in the low-silicon magnesite concentrate is 70.25%.

[0056] Example 3

[0057] A method for using collector SAA in the flotation desilication of magnesite specifically includes the following steps:

[0058] Step 1: Grinding

[0059] High-silicon, low-grade magnesite raw material is crushed and ball-milled to obtain magnesite powder; among which, the mass of magnesite powder with a particle size <74μm after ball milling accounts for 75% of the total mass.

[0060] Step 2: Prepare the paste

[0061] At room temperature, magnesite powder was placed in a hanging trough flotation machine, deionized water was added, and the mixture was stirred for 3.5 minutes at a flotation machine speed of 1850 rpm to prepare the magnesite slurry. Subsequently, a 2% (w / w) HCl aqueous solution was added to the magnesite slurry to adjust the pH value to 5.5, and the mixture was stirred for 5 minutes until the slurry was homogeneous, resulting in a magnesite slurry with a pH value of 5.5. The mass concentration of magnesite powder in the magnesite slurry was 35%.

[0062] Step 3: Reverse flotation desilication

[0063] A 0.028 mol / L aqueous solution of tertiary amine collector SAA was added to the magnesite slurry. The slurry was stirred for 5 minutes at a flotation machine speed of 1850 rpm to homogenize it. Then, a roughing-cleaning-scavenging reverse flotation process was performed to purify the slurry and obtain low-silica magnesite concentrate. The roughing stage flotation time was 5 minutes, and the amount of tertiary amine collector SAA added to the slurry was 100 mg / L according to the solid-liquid ratio. The cleaning stage flotation time was 5 minutes, and the amount of tertiary amine collector SAA added to the slurry was 55 mg / L according to the solid-liquid ratio. The scavenging stage flotation time was 4 minutes, and the amount of tertiary amine collector SAA added to the slurry was 28 mg / L according to the solid-liquid ratio.

[0064] In this embodiment, the main components of the low-silicon magnesite concentrate are 47.23% MgO, 0.22% SiO2, and 0.19% CaO by weight percentage; the recovery rate of the low-silicon magnesite concentrate is 76.2%, and the MgO recovery rate in the low-silicon magnesite concentrate is 66.25%.

[0065] Example 4

[0066] A method for using collector SAA in the flotation desilication of magnesite specifically includes the following steps:

[0067] Step 1: Grinding

[0068] High-silicon, low-grade magnesite raw material is crushed and ball-milled to obtain magnesite powder; among which, the mass of magnesite powder with a particle size <74μm after ball milling accounts for 80% of the total mass.

[0069] Step 2: Prepare the paste

[0070] At room temperature, magnesite powder was placed in a hanging trough flotation machine, deionized water was added, and the mixture was stirred for 4.5 minutes at a flotation machine speed of 1900 rpm to prepare the magnesite slurry. Subsequently, a 1.5% (w / w) HCl aqueous solution was added to the magnesite slurry to adjust the pH value to 5.8, and the mixture was stirred for 3.5 minutes until the slurry was homogeneous, resulting in a magnesite slurry with a pH value of 5.8. The mass concentration of magnesite powder in the magnesite slurry was 28%.

[0071] Step 3: Reverse flotation desilication

[0072] A 0.03 mol / L aqueous solution of tertiary amine collector SAA was added to the magnesite slurry. The slurry was stirred for 3.2 min at a flotation machine speed of 1900 rpm to homogenize it. Then, a roughing-cleaning-scavenging reverse flotation process was performed to purify the slurry and obtain low-silica magnesite concentrate. The roughing stage flotation time was 4.5 min, and the amount of tertiary amine collector SAA added to the slurry was 110 mg / L according to the solid-liquid ratio. The cleaning stage flotation time was 3.5 min, and the amount of tertiary amine collector SAA added to the slurry was 57 mg / L according to the solid-liquid ratio. The scavenging stage flotation time was 3.5 min, and the amount of tertiary amine collector SAA added to the slurry was 30 mg / L according to the solid-liquid ratio.

[0073] In this embodiment, the main components of the low-silicon magnesite concentrate are 47.35% MgO, 0.14% SiO2, and 0.20% CaO by weight percentage; the recovery rate of the low-silicon magnesite concentrate is 79.2%, and the MgO recovery rate in the low-silicon magnesite concentrate is 67.35%.

[0074] Example 5

[0075] A method for using collector SAA in the flotation desilication of magnesite specifically includes the following steps:

[0076] Step 1: Grinding

[0077] High-silicon, low-grade magnesite raw material is crushed and ball-milled to obtain magnesite powder; among which, the mass of magnesite powder with a particle size <74μm after ball milling accounts for 85% of the total mass.

[0078] Step 2: Prepare the paste

[0079] At room temperature, magnesite powder was placed in a hanging trough flotation machine, deionized water was added, and the mixture was stirred for 4.2 minutes at a flotation machine speed of 1880 rpm to prepare the magnesite slurry. Subsequently, a 1% (w / w) HCl aqueous solution was added to the magnesite slurry to adjust the pH value to 5.2, and the mixture was stirred for 3.8 minutes until the slurry was homogeneous, resulting in a magnesite slurry with a pH value of 5.2. The mass concentration of magnesite powder in the magnesite slurry was 32%.

[0080] Step 3: Reverse flotation desilication

[0081] A 0.033 mol / L aqueous solution of tertiary amine collector SAA was added to the magnesite slurry. The slurry was stirred for 4.2 min at a flotation machine speed of 1880 rpm to homogenize it. Then, a roughing-cleaning-scavenging reverse flotation process was performed to purify the slurry and obtain low-silica magnesite concentrate. The roughing stage flotation time was 3.8 min, and the amount of tertiary amine collector SAA added to the slurry was 112 mg / L according to the solid-liquid ratio. The cleaning stage flotation time was 4.6 min, and the amount of tertiary amine collector SAA added to the slurry was 57 mg / L according to the solid-liquid ratio. The scavenging stage flotation time was 3.6 min, and the amount of tertiary amine collector SAA added to the slurry was 29 mg / L according to the solid-liquid ratio.

[0082] In this embodiment, the main components of the low-silicon magnesite concentrate are 47.28% MgO, 0.25% SiO2, and 0.39% CaO by weight percentage; the recovery rate of the low-silicon magnesite concentrate is 78.3%, and the MgO recovery rate in the low-silicon magnesite concentrate is 73.69%.

[0083] Example 6

[0084] A method for desilication of magnesite by flotation using collector SAA is the same as in Example 1, except that the mass of magnesite powder with a particle size <74μm accounts for 73% of the total magnesite powder mass. The main components of the obtained low-silica magnesite concentrate, and the weight percentages of each component are as follows: MgO 47.36%, SiO2 0.21%, and CaO 0.47%; the recovery rate of the low-silica magnesite concentrate is 81.2%, and the MgO recovery rate in the low-silica magnesite concentrate is 69.25%.

[0085] Example 7

[0086] A method for desilication of magnesite by flotation using collector SAA is the same as in Example 1, except that the mass of magnesite powder with a particle size <74μm accounts for 75% of the total magnesite powder mass. The main components of the obtained low-silica magnesite concentrate, and the weight percentages of each component are as follows: MgO 47.46%, SiO2 0.20%, and CaO 0.27%; the recovery rate of the low-silica magnesite concentrate is 82.2%, and the MgO recovery rate in the low-silica magnesite concentrate is 74.26%.

Claims

1. A method for using collector SAA in the flotation desilication of magnesite, characterized in that, Specifically, the following steps are included: Step 1: Grinding High-silicon, low-grade magnesite is crushed and ball-milled to obtain magnesite powder; among which, the mass of magnesite powder with a particle size <74μm after ball milling accounts for 70-90% of the total mass; Step 2: Prepare the paste At room temperature, magnesite powder is placed in a flotation device, deionized water is added and stirred for 3-5 minutes to prepare the slurry; then HCl solution is added to adjust the pH value to 5-7, and stirred for 3-5 minutes to obtain magnesite slurry. Step 3: Reverse flotation desilication Collector SAA (octadecylamine acetate) is added to the magnesite slurry and stirred until homogeneous. Then, a roughing, cleaning, and scavenging reverse flotation process is performed to purify the magnesite and obtain a low-silica magnesite concentrate.

2. The method for using collector SAA for desilication of magnesite flotation according to claim 1, characterized in that, In step 1, the high-silicon, low-grade magnesite is magnesite with a SiO2 content greater than 3%.

3. A method for using collector SAA for desilication of magnesite flotation according to claim 1, characterized in that, In step 2, the flotation equipment is a hanging flotation machine with a rotation speed of 1600~1900 rpm; the mass fraction of the HCl aqueous solution is 1~5%; the pH value is 5.0~6.5; and the mass concentration of magnesite powder in the magnesite pulp is 20~40%.

4. A method for using collector SAA for desilication of magnesite flotation according to claim 1, characterized in that, In step 3, the collector SAA is an aqueous solution of SAA with a molar concentration of 0.01~0.05 mol / L.

5. A method for using collector SAA for desilication of magnesite flotation according to claim 1, characterized in that, In step 3, the rotation speed of the flotation equipment for reverse flotation purification is 1700~1900 rpm; the stirring time after adding the collector is 2~5 min; and the flotation time for each stage of reverse flotation purification is 2~5 min.

6. A method for using collector SAA in the flotation desilication of magnesite according to claim 5, characterized in that, The flotation equipment used for reverse flotation purification operates at a speed of 1800~1850 rpm.

7. A method for using collector SAA for desilication of magnesite flotation according to claim 1, characterized in that, In step 3, in the coarsening stage, the amount of collector SAA added to the slurry is 90~120 mg / L according to the solid-liquid ratio; in the finishing stage, the amount of collector SAA added to the slurry is 45~60 mg / L according to the solid-liquid ratio; and in the scavenging stage, the amount of collector SAA added to the slurry is 20~30 mg / L according to the solid-liquid ratio.

8. A method for using collector SAA in the flotation desilication of magnesite according to claim 7, characterized in that, In the first coarsening stage, the amount of collector SAA added to the slurry is 95~105 mg / L according to the solid-liquid ratio; in the first finishing stage, the amount of collector SAA added to the slurry is 45~55 mg / L according to the solid-liquid ratio; and in the first scavenging stage, the amount of collector SAA added to the slurry is 25~30 mg / L according to the solid-liquid ratio.

9. A method for using collector SAA in the flotation desilication of magnesite according to claim 1, characterized in that, In step 3, the main components of the low-silica magnesite concentrate and the weight percentage of each component are as follows: MgO 46.5~47.5%, SiO2≤0.3%, CaO≤0.6%.

10. A method for using collector SAA for desilication of magnesite flotation according to claim 1, characterized in that, The recovery rate of low-silica magnesite concentrate is 70-85% by weight, and the recovery rate of MgO in low-silica magnesite concentrate is 65-75%.

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