Study on Extraction of High Purity Magnesium Oxide from Low Grade Magnesite

Abstrac:. The carbonization soakingof low2grade granularmagnesite is studied Themineralproperty and light baking performance ofmagnesite, the digestingprocessofMgO aswell as the technologicalparametersof carbonization soaking are investigated With the carbonization soaking of magnesite, high2grade MgO has been obtained, which contains 99% ofMgO..

China's magnesium ore resources are very rich, and the process of producing light magnesium carbonate by carbonization is divided into two types according to the nature of ore: dolomite carbonization and magnesite carbonization. The production process of dolomite carbonization is mature, but due to the high calcium content in the carbonization leaching process, the production of high purity products is limited. With the continuous development of smelting technology, metallurgical process many special operations tend to use high-purity magnesia to greatly improve the life of the refractory products, reduce production costs. At the same time, due to the large number of high-grade magnesite exports, the comprehensive utilization of magnesium resources has become increasingly prominent. To this end, the author used low-grade magnesite ore to carry out carbonization extraction of high-purity magnesium oxide (w _MgO greater than 99%) process research. In the test, the ore properties and light burning properties of magnesite, the process of magnesium oxide digestion and the process conditions and parameters of carbonization leaching were studied, and high-purity magnesia was produced from the obtained high-purity basic magnesium carbonate.

I. Ore properties research and process

The mineral composition of the sample is relatively simple, main minerals magnesite and dolomite, minor minerals talc, chlorite; trace minerals are quartz, brown iron pyrite, apatite and the like. MgO is mainly present in the ore as a basic form of independent minerals in ore mineral magnesite and gangue mineral dolomite, talc and chlorite. CaO exists in minerals in two forms: one is in the form of a basic composition that forms an independent mineral, such as dolomite, apatite, and the other is present in the magnesite crystal in the form of fine inclusions of dolomite. SiO _{2 is} also present in two forms of gangue minerals such as quartz, talc, chlorite, tremolite , and stellite, and the other is in the form of fine mechanical inclusions of quartz and silicate minerals. In the ore crystal.

The results of particle size analysis showed that w _SiO2 and w _Al2O3 were slightly higher in the fine fraction (-150 mesh). w _MgO , w _CaO , wFe ₂ O ₃ did not change much in each particle size, and was similar to the multi-element chemical analysis results. The chemical analysis results are shown in Table 1. The test process flow is shown in Figure 1.

Second, test results and analysis

(1) Calcination test

Natural magnesite does not directly interact with carbon dioxide during carbonization. Carbonic acid only reacts with active magnesium oxide. Therefore, the ore needs to be lightly burned in high-temperature equipment to cause magnesite to escape carbon dioxide and produce active oxidation. magnesium. The calcination reaction is as follows:

Magnesite (about 50% for W _MgCO3 ) Light burning material (W _MgO greater than 90%) + CO ₂ ↑ (1)

In order to make the magnesium oxide easy to digest and carbonize, the sample was subjected to differential thermal analysis. The differential thermal analysis showed that the initial thermal decomposition temperature of MgCO ₃ in the sample was 666 °C. According to the weight loss curve, it can be seen that it is above 700 °C. Since the activity of lightly burned magnesia is related to the calcination temperature and time, the temperature is controlled between 700 and 850 ° C, and the calcination conditions are tested in different holding times. Figure 2 shows the effect of temperature and time on magnesite burning. The results show that the burning of magnesite increases with increasing temperature and time. In order to ensure that the light burning material is not burnt, but does not burn, and has high activity, the optimum calcination temperature should be controlled at 800 ° C, and the calcination time is 1.5 h.

(two) digestion test

The production practice of many manufacturers shows that in the process of producing light magnesium carbonate by dolomite, after dolomite calcination, about 30% of CaO in the ore reacts with water to form Ca(OH) ₂ , and the ore is naturally cracked, w _MgO is 20 % also easily reacts with water to form Mg(OH) ₂ , thus eliminating the need for a fine grinding process. From the perspective of energy conservation, the experiment is to crush the magnesite to a smaller particle size and then carry out calcination and digestion tests to explore the optimal process conditions of the digestion process. The chemical reaction of the digestion process is as follows:

MgO+H ₂ O→Mg(OH) ₂ (2)

The process of converting magnesium oxide in light burned material into magnesium hydroxide in aqueous solution is related to factors such as reaction concentration, temperature and time, and is related to particle size. The digested sample of this test is a light burned powder of less than 2 mm.

1, digestion concentration

The sample was placed in water at 80 ° C, stirred for 4 min, and filtered to analyze the effect of different concentrations on the digestibility. It is known from the test results that the concentration of the digestive process is large and the conversion rate is low. When the concentration is less than 20%, the digestibility does not change much, so the decontamination concentration is 20% and the following test is carried out.

2, digestion time

Since the digestibility of the concentration test was low, the agitation time test was enhanced under the conditions of a digestion temperature of °C and a concentration of 80%. The effect of time changes on digestibility is shown in Figure 3. The curve in Figure 3 shows that the increase in digestion time has a significant effect on the digestibility. The digestion time is over 12 minutes and the digestibility has reached 98%.

3, digestion temperature

The effect of temperature on the digestion results is shown in Figure 4 under conditions where the test concentration and time are relatively stable. It can be seen from Fig. 4 that the process of converting magnesium oxide into magnesium hydroxide is controlled by chemical reaction, and the reaction temperature is increased, the reaction speed can be accelerated, and the digestion temperature is increased, and the influence on the digestion process is extremely obvious. The appropriate digestion temperature should be controlled above 80 °C.

(3) Carbonization leaching test

The conversion of magnesium hydroxide to magnesium bicarbonate is carried out under the conditions of specific concentration and temperature by using an appropriate amount of carbon dioxide as a leaching agent, and different times and pressures have a great influence on the leaching results. Its chemical reaction formula is as follows

Mg(OH) ₂ +CO ₂ +H ₂ O→Mg(HCO ₃ ) ₂ +H ₂ O (3)

Drawing on the work done in the previous period, the carbonized leaching test was carried out on the digested sample under normal temperature and normal pressure conditions. The n _MgO of the tower liquid was 18.62g / L, and the c _CO2 was 33%. The slurry was periodically filtered during the leaching process. , analysis of W _{MgO in} magnesium bicarbonate solution, the test results are shown in Figure 5. The lower curve in Figure 5 shows that the sample has a larger particle size and a longer carbonization time. After 90 min, the conversion of magnesium oxide was not significantly increased, and the n _{MgO in the} slurry was 7.8 g/L. For this reason, the concentration of magnesium oxide in the column liquid was lowered under the condition that the above leaching process conditions were relatively stable. It can be seen from the upper curve in Fig. 5 that the conversion rate increases greatly with the decrease of the concentration of magnesium oxide in the column liquid. When the carbonization reaction reaches 90 min, the conversion rate of MgO reaches 84.01%, and the recovery rate is 80.97%.

(4) Thermal hydrolysis test

The carbonization leaching process achieves the transfer of the target component from the solid phase to the liquid phase. The solid residue is separated, the residue is filtered off, and the filtrate (heavy magnesium water) is heated to convert magnesium hydrogencarbonate to form basic magnesium carbonate. The chemical reaction formula is as follows:

5Mg(HCO ₃ ) ₂ →4Mg(OH) ₂ ·Mg(OH ₂ )·4 H ₂ O+6 CO ₂ ↑ (4)

According to the above formula, the effect of the thermal hydrolysis time on the magnesium oxide content in the mother liquor (waste magnesium water) was tested while the filtrate was warmed to the boiling temperature. The test results show that the concentration of magnesium oxide in the mother liquor decreases with time. After more than 5 minutes, the n _MgO in the mother liquor is 0.18 g / L, so the thermal hydrolysis process is controlled to heat the filtrate to boiling temperature and continue to keep warm for 5 min. The multi-element chemical analysis and magnesium oxide recovery rate of the basic magnesium carbonate product after filtration and drying are shown in Table 2.

Third, the conclusion

(1) The low-grade magnesite ore fines are treated by the carbonization leaching process, and the high-purity light magnesium carbonate with a w _MgO of 99.31% when the ignition is zero is obtained. The recovery rate of magnesium oxide was 80.97%. After the sintering process, a high-purity sintered magnesite having a magnesium oxide content of 99.21% and a bulk density of 3.38 g/cm can be obtained.

(2) The content of calcium oxide in the light magnesium carbonate produced by the atmospheric pressure carbon dioxide leaching process is slightly higher than that of the final product of the previous pressure test.

(3) Since the grinding process is not used in the carbonization leaching process of magnesite, the particle size of the sample is large, so the conversion rate and recovery rate of magnesium oxide are not satisfactory. When the particle size became smaller, the conversion index of magnesium oxide in the leachate was very satisfactory.

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