RU2279404C1 - Magnesium oxide production process - Google Patents

Abstract

FIELD: production of inorganic compounds.

SUBSTANCE: invention relates to technology of processing non-conventional types of mineral raw materials to produce magnesium oxide therefrom. Process of producing magnesium oxide from magnesium-containing raw material comprises crushing and treatment with sulfuric acid at elevated temperature, purification of thus obtained magnesium sulfate suspension to remove metallic impurities, undestroyed raw material, and silica gel by neutralizing substance-assisted precipitation, filtration-mediated separation of precipitate, precipitation of magnesium hydroxide from filtrate, filtration-mediated separation of magnesium hydroxide, and decomposition thereof into magnesium oxide. Crushing of magnesium-containing raw material is effected to achieve fraction not exceeding 0.5 mm, treatment with sulfuric acid is effected at 60-70^°C, neutralizing substance utilized is 20-30% lime milk or 20-30% soda solution and suspension of magnesium sulfate is treated with neutralizing substance is effected to achieve pH 7.0-8.0, precipitation of magnesium hydroxide from filtrate is performed with 20-30% soda solution, to which burnt magnesia is added in amount 2.0-8.0% of the total content of magnesium oxide in magnesium sulfate solution. Filtrate obtained after separation of magnesium hydroxide is used to precipitate magnesium hydroxide.

EFFECT: improved environmental aspect of production and increased economical efficiency of process.

4 tbl, 5 ex

Description

The present invention relates to a technology for processing non-traditional types of mineral raw materials, in particular for the production of magnesium oxide from it.

A known method of producing magnesium oxide from magnesium-containing raw materials, including grinding it to a particle size of not more than 0.5 mm, dissolving in sulfuric acid, cooling the resulting mixture to a crystallization temperature, washing the crystallized mixture with such a volume of water so that the concentration of magnesium sulfate in the solution is 290- 330 g / l, separation of the insoluble residue from the obtained sulfate solution, sequential purification of the obtained filtrate from impurity metals by precipitation at a temperature of 30-40 ° C in the form of hydroxides with using a 40-50% sodium hydroxide solution, treating the resulting solution with an alkaline agent, separating the magnesium hydroxide precipitate, heat treatment it in two stages and washing the target product with water after the second heat treatment stage (US Pat. RF 2209780, class C 02 F 5/02 published on 08.19.03).

The disadvantage of this method is its low economic efficiency, namely:

1) The cooling of 5.5 kg of the suspension obtained by dissolving 1 kg of serpentinite in 40% sulfuric acid to a crystallization temperature (5 ° C) without using a refrigeration unit is very difficult, and in the process of continuous multi-ton production it is practically impossible;

2) During the leaching of finely ground serpentine (particle size less than 0.5 mm) and neutralization of sulfate solutions with a 40-50% NaOH solution, suspensions are formed containing precipitates in the form of silicic acid gels and Fe ³⁺ , Al ³⁺ , Cr hydroxides ³⁺ and others. Due to clogging of the pores of the filter cloth with fine particles of sediment, the filtration rate of such suspensions is extremely low and ineffective. To increase their filtration rate, it is necessary to introduce substances into such suspensions that would contribute to the formation of dense, easily filtered precipitates.

The closest in technical essence and the achieved result is a method of producing magnesium oxide from magnesium-containing raw materials, comprising treating the latter with sulfuric acid at a temperature of 90-100 ° C with a concentration of 10-50%, purification of the resulting solution of magnesium sulfate from metal impurities by alkali precipitation at pH 8 , 0-8.5, separation of the precipitate formed by filtration and precipitation of magnesium hydroxide from the filtrate, followed by its thermal decomposition to magnesium oxide (US Pat. RF No. 2038301 class. C 01 F 5/06, publ. 06/27/95).

The disadvantages of this method include:

1) Difficulties in filtering gel-like precipitates of silicic acid and hydroxides of impurity metals;

2) The process of decomposition of finely ground serpentine ores with a 50% solution of sulfuric acid at 90-100 ° C is accompanied by the rapid release of SO ₃ vapors, which significantly worsens the environmental situation in production facilities.

The objective of the invention is to improve the ecology of production and increase the economic efficiency of the method.

The problem is solved by the method of producing magnesium oxide from magnesium-containing raw materials, including grinding and processing it with sulfuric acid at elevated temperatures, purification of the obtained suspension of magnesium sulfate from metal impurities, undecomposed raw materials and silica gel by precipitation with a neutralizing substance, separation of the precipitate by filtration, precipitation of magnesium hydroxide from the filtrate , separation by filtration, followed by decomposition to magnesium oxide. The magnesium-containing raw material is crushed to a fraction not exceeding 0.5 mm, its treatment with sulfuric acid is carried out at a temperature of 60-70 ° C, lime milk with a concentration of 20-30 wt.% Or 20-30 wt.% Soda solution is used as a neutralizing substance and they purify the suspension of magnesium sulfate to pH 7.0-8.0, the precipitation of magnesium hydroxide from the filtrate is carried out with 20-30 wt.% soda solution with the addition of burnt magnesia in an amount of 2.0-8.0 wt.% of the total oxide content magnesium in a solution of magnesium sulfate. The filtrate obtained after separation of the precipitate of magnesium hydroxide is directed to the precipitation of magnesium hydroxide.

Tables 1-3 show the chemical, x-ray phase and fractional composition of the crushed ore, in table 4 - the chemical composition and quality of the obtained magnesium oxide (periclase).

Example 1

1 kg of serpentine ore of the composition wt.% (See table 2) (particle size -0.4 ± 0.071 mm = 94.7%) is placed in a reactor with a jacket and stirrer, pour 43% sulfuric acid solution and at a temperature 70 ° C and continuous stirring for 2 hours, leaching is carried out.

The leaching process proceeds according to the following reactions:

MgO + H ₂ SO ₄ → MgSO ₄ + H ₂ O

Cr ₂ O ₃ + 3H ₂ SO ₄ → Cr ₂ (SO ₄ ) ₃ + 3H ₂ O

Fe ₂ O ₃ + 3H ₂ SO ₄ → Fe ₂ (SO ₄ ) ₃ + 3H ₂ O, etc.

Next, a 20% aqueous solution of milk of lime is introduced into the resulting suspension, neutralized to a pH of 4.0-4.5, a 37% solution of hydrogen peroxide is added to convert ferrous to ferric iron according to the reactions:

2FeO + H ₂ O ₂ = Fe ₂ O ₃ + H ₂ O

Fe ²⁺ + H ₂ O ₂ → Fe ³⁺

(Fe (OH) ₂ precipitates at pH 7-8; Fe (OH) ₃ - at pH 1-2)

Then continue the neutralization with a solution of Ca (OH) ₂ to a pH of 7.5. After maturing gypsum crystals for 1 hour and setting the precipitate, a suspension containing metal impurities, undecomposed raw materials and silica gel is filtered at 70 ° C on a vacuum filter with a filtration rate of 21 l / min · m ²

The precipitate is sent for further processing, and the filtrate with a pH of 7.5 and a volume of 5.64 l, containing 53.15 g / l MgO, is loaded into a vessel with a 30% soda solution, 24 g (8%) of burnt magnesia are added and neutralized at pH 12. After a 2-hour maturation of the precipitate, the suspension is filtered at 70 ° C with a filtration rate of 15 l / min · m ² . The precipitate is washed three times from Na ₂ O by repulpation to a content of sodium oxide in the precipitate of 0.43%, dried to a moisture content of 1.5% at 350 ° C, heat treated at 850 ° C and cooled. The chemical composition is given in table 4

The filtrate contains MgO = 0.86 g / L and Na ₂ O = 40.0 g / L.

Example 2. 1 kg of serpentine ore (particle size - 0.4 ± 0.071 mm = 94.7 wt.%) Is placed in a reactor with a jacket and stirrer, pour 43% solution of sulfuric acid and at a temperature of 70 ° C with continuous stirring leaching is carried out for 2 hours. Next, a 25% aqueous solution of milk of lime is introduced into the suspension with a pH of 1.2, neutralized to a pH of 4.0-4.5, a 37% solution of hydrogen peroxide is added and neutralization with a Ca (OH) ₂ solution is continued to pH 7, 5. After the gypsum crystals have matured for 1 hour and the sediment has set, the suspension containing metal impurities, undecomposed raw materials and silica gel is filtered at 70 ° C on a vacuum filter with a filtration rate of 21 l / min · m ² . The precipitate is sent for further processing, and the filtrate with a pH of 7.5 and a volume of 5.64 l, containing 53.15 g / l MgO (300 g), is loaded into a vessel with a 30% soda solution, 15 g, t. e. 5% of the total MgO content in the filtrate of "active" burnt magnesia and neutralized at pH 12.0. After 2 hours of aging of the precipitate of magnesium hydroxide, the suspension is filtered at 70 ° C with a filtration rate of 15 l / min · m ² . The precipitate is washed three times from Na ₂ O by repulpation to a content of sodium oxide in the precipitate of 0.43%, dried to a moisture content of 1.5% at 350 ° C, heat treated at 850 ° C and cooled.

The chemical composition of the finished product, see table 4. The filtrate containing MgO = 0.86 g / l and Na ₂ O = 40.0 g / l, reused to obtain magnesium hydroxide.

The use of milk of lime to neutralize the suspension after leaching with a concentration of Ca (OH) _{2 of} less than 20% and more than 30% is technologically impractical, because (respectively):

1) the duration of neutralization and maturation of CaSO ₄ · 2H ₂ O crystals increases up to 3 hours;

2) due to the delamination of the solution of milk of lime, it is significantly more difficult to load it into the reactor.

The introduction of 1% burnt magnesia into a neutralized solution leads to a loss of magnesium sulfate during the filtration of 6.3 g / l MgO.

The addition of more than 8.0 wt.% Burnt magnesia is not economically feasible, since the concentration of MgO in the exhaust filtrate does not significantly decrease.

Example 3

The same as in example 1, but the neutralization of the acid suspension after leaching from pH 1.2 to pH 7.0 is carried out with a 30% soda solution. After 3 hours of aging, the suspension is filtered at 70 ° C with a filtration rate of 28 l / min · m ² . The filtrate obtained after the precipitation of magnesium hydroxide is directed to the precipitation of magnesium hydroxide from a solution of magnesium sulfate.

Example 4. The same as in example 1, but in a suspension with a pH of 1.2 injected with a 30% aqueous solution of milk of lime. In this case, the filtrate volume will be 4.7 liters. The concentration of MgO in the filtrate is 63.82 g / l or 300 g of MgO. The filtrate obtained after the precipitation of magnesium hydroxide is directed to the precipitation of magnesium hydroxide from a solution of magnesium sulfate.

Example 5

The same as in example 1, but the neutralization of the magnesium sulfate solution is carried out with the addition of the filtrate obtained after the previous precipitation of magnesium hydroxide. The quality of the obtained product is the same as in example 1, and the processes of neutralization and filtration proceed more intensively and economic efficiency is significantly higher.

Thus, it can be seen from the above examples that the proposed method is high-tech, cost-effective, simple, environmentally friendly and waste-free, allows you to use unlimited reserves of natural and technogenic raw materials and substantially satisfy the need of Russian enterprises for high-purity magnesium oxide.

This method has been tested on an industrial scale in the processing of 200 tons of Bashkir serpentinite.

Table 1 Fractional composition of crushed ore Particles in size, mm Content, wt.% +0.5 No +0.4 0.5 +0.1 36.0 +0.071 58.2 -0.071 5.3 TOTAL 100.0 table 2 The chemical composition of the crushed ore, wt.% MgO Cr ₂ About ₃ Fe ₂ About ₃ A ₂ O ₃ SiO ₂ Cao ppp 33.5 1,63 5.67 1,1 33.5 1,08 23.52 Table 3 Mineralogical composition, wt.% Serpentine Chromicotitis Olivine (forsterite) CaCO ₃ ppp 71,4 3.3 8.2 1.93 15.17 Table 4 The chemical composition of magnesium oxide (periclase), wt.% MgO SiO ₂ Al ₂ O ₃ SO ₃ Cao Fe ₂ O ₃ Na ₂ O MnO ppp 97.0 0.0015 0,0008 0.0011 0.24 0.0081 1,2 0,0485 1,5

Periclase quality indicators:

Iodine number (activity) = 120.0 mg equiv J / 100 g MgO.

Bulk density = 0.11 g / cm ³ .

Claims (1)

A method of producing magnesium oxide from magnesium-containing raw materials, including grinding and processing it with sulfuric acid at elevated temperatures, purification of the resulting suspension of magnesium sulfate from metal impurities, undecomposed raw materials and silica gel by precipitation with a neutralizing agent, separation of the precipitate by filtration, precipitation of magnesium hydroxide from the filtrate, separation of hydroxide magnesium by filtration, followed by its decomposition to magnesium oxide, characterized in that the magnesium-containing raw materials are crushed to a fraction not exceeding 0, 5 mm, its treatment with sulfuric acid is carried out at a temperature of 60-70 ° C, 20-30 wt.% - milk of lime or 20-30 wt.% - a solution of soda is used as a neutralizing substance and they are used to clean the suspension of magnesium sulfate to pH 7.0-8.0, precipitation of magnesium hydroxide from the filtrate is carried out with a 20-30 wt.% solution of soda with the addition of burnt magnesia in an amount of 2.0-8.0 wt.% of the total content of magnesium oxide in a solution of magnesium sulfate while the filtrate obtained after the separation of magnesium hydroxide is directed to the precipitation of magnesium hydroxide.