WO2015051482A1

WO2015051482A1 - Method for manufacturing sheet monodisperse nano-magnesium hydroxide by using magnesite

Info

Publication number: WO2015051482A1
Application number: PCT/CN2013/001222
Authority: WO
Inventors: 白丽梅; 姜玉芝; 李萌; 朱一民; 郭爱红; 聂一苗; 张勇; 邢智博
Original assignee: 河北联合大学
Priority date: 2013-10-11
Filing date: 2013-10-11
Publication date: 2015-04-16
Also published as: ZA201602515B; CN104968605B; CN104968605A

Abstract

A method for manufacturing sheet monodisperse nano-magnesium hydroxide by using magnesite as a material. Specifically, magnesite is calcined to generate magnesian powder having components with different activities; the magnesian powder is made into a solution with a concentration and the solution is stirred, and then the solution is added into an acidification attrition mill to carry out attrition and acidification; the magnesian powder is purified by controlling an amount of the magnesian powder, an amount of hydrochloric acid and an acidification reaction condition; and sheet nano-magnesium hydroxide is prepared by controlling the activity, the particle size and the hydration condition of the magnesia, a hydrated magnesium hydroxide precursor. Hydrochloric acid, water, and an additive can be recycled, which is friendly to the environment and needs low cost. The technology can activate an existing magnesite resource, so as to achieve high value-added processing and utilization of the resource.

Description

Method for preparing sheet-like monodisperse nanometer magnesium hydroxide from magnesite

The invention relates to a method for deep processing of magnesite and preparing sheet-like monodisperse nanometer magnesium hydroxide, belonging to the technical field of mineral processing.

BACKGROUND ART A magnesium hydroxide material used as a flame retardant has a dual function of flame retardancy and smoke suppression. However, the addition amount generally needs to reach 40% or more in order to obtain the desired flame retardant effect. Therefore, the amount of magnesium hydroxide is increased without affecting the mechanical properties of the material, and the magnesium hydroxide is required to have a fine particle size, high purity, and surface polarity. The small shape is uniform and easy to add to the material. To this end, most of the previous studies used normal temperature synthesis, hydrothermal treatment and surface modification to produce flame retardant magnesium hydroxide in a three-step process. This makes the production process of magnesium hydroxide more complicated and the production cost is high, so that it is difficult to industrialize. Many researchers focus on soluble magnesium salts and sodium hydroxide or books

A base such as liquid ammonia is reacted, and nano magnesium hydroxide is prepared by controlling the reaction conditions. The acid-base neutralization reaction is used in the preparation process, which consumes a large amount of acid and alkali and is seriously polluted by the environment. If the reaction process has additives, the additive cannot be reused.

The magnesia ore is calcined to prepare active magnesium oxide, and the active magnesium oxide is hydrated to prepare flame retardant hydrogenated magnesium. The process is simple and the investment is low. However, the purity of magnesite is relatively high, and the purity of magnesite is generally above 96%. If the magnesite contains iron, it will seriously affect the color of magnesium hydroxide and reduce the quality of the product. Secondly, the prepared Magnesium hydroxide has a coarse particle size and no fixed morphology, and can only reach the micron level. Therefore, this process can only use high-quality magnesite as raw material to prepare lower quality flame retardant magnesium hydroxide.

) Summary of the content:

With the continuous extraction of magnesite resources in China, high-quality magnesite resources will be less and less, but the demand for high-performance monodisperse nano-magnesium hydroxide is increasing. To this end, the present invention has been directed to the provision of a sheet-like monodisperse nanometer magnesium hydroxide using low-quality magnesite using a low-cost, non-polluting, environmentally friendly method.

The method for preparing sheet-like monodisperse nanometer magnesium hydroxide using magnesite according to the invention comprises the following steps:

(1) Magnesite calcination water-soluble: Magnesite ore is calcined to obtain magnesia powder, the calcined magnesia powder is added to a stirred tank, a certain amount of water is added to the stirred tank, and the magnesia powder is formulated into a mass percentage. The slurry with a concentration of 60% is stirred for about 0.3 min;

(2) Magnesium oxide powder liquid grinding and acidification: Transfer the stirred magnesium oxide powder slurry to an acidified stirring mill for grinding. After grinding for 2 minutes, hydrochloric acid is added to the acidified stirring mill to acidify the magnesium oxide powder, and the acidification time is Lmin, the magnesium oxide powder slurry is added to the acidified stirring mill from the bottom end, hydrochloric acid is added to the acidified stirring mill from the middle, and the acidified slurry is discharged from the upper end of the acidizing stirring mill, and the unsatisfactory magnesium oxide powder particles which are ground and acidified fall into the gravity. The grinding zone of the acidified stirring mill is further subjected to grinding and acidizing treatment to realize acidification of the side edge;

(3) Magnesium oxide powder slurry acidification and impurity removal: In the acidification process, hydrochloric acid is added to the acidification stirring mill. The mass percentage of the specification is 20%~23%. The volume ratio of the mass of the magnesia powder to the hydrochloric acid during acidification is lg: 5.0 m lg: 5.8 ml, and the acidified slurry is filtered to obtain a filtrate and a residue, during the acidification process. Excessive magnesium oxide powder, impurities such as iron, manganese, calcium and excess magnesium oxide powder enter the solid residue;

(4) Preparation of active magnesium oxide: The filtrate is vacuum crystallized to obtain crystals of magnesium chloride hexahydrate, calcined at a low temperature of magnesium chloride hexahydrate, calcination temperature is 470 ° C ~ 490 ° C, calcination time is lh ~ 1.5 h, calcined to obtain active magnesium oxide, Hydrogen chloride gas and water vapor;

(5) Recycling of the filter residue: The filter residue is returned to the agitation tank for re-grinding and acidification. When the ratio of the circulation amount of the magnesium oxide powder to the newly added amount, that is, the cycle load reaches 100% to 120%, the cycle is terminated, and the discharged residue is discharged. Acidification was carried out by adding hydrochloric acid, and the pH of the acidification was controlled to 5 to 6, after acidification, filtration was carried out, the residue was discarded, and the filtrate was vacuum-crystallized together with the filtrate in the step (4).

(6) Preparation of flaky monodisperse nanometer magnesium hydroxide: The active magnesium oxide and the adjusting agent dextrin are slowly added to the hydration reaction emulsification tank for hydration reaction, and the volume concentration of the dextrin in the hydration reaction solution is 〗〖mg/L 〜2mg L The liquid-solid ratio of active magnesium oxide to water in hydration reaction is 30:1~40: 1, the hydration reaction temperature is 75°C~85°C, the hydration reaction stirring speed is 3800 r/min~4000r/min, hydration reaction After 2 h, the solution was filtered to obtain a magnesium hydroxide cake and a filtrate, and the cake was dried at a low temperature to obtain a sheet-like monodisperse nano magnesium hydroxide.

According to the above scheme, the magnesite in the step (1) is broken to 9 mm or less, and the magnesite is calcined after the crushing, the calcination temperature is 630 ° C, and the calcination time is 3 hours.

According to the above scheme, the vacuum crystallization in step (4) has a vacuum of 0.05 Mpa to 0.1 Mpa, a crystallization temperature of 75 ° C to 90 ° C, and a crystallization time of 5 h to 6 h.

According to the above scheme, the hydrogen chloride gas and the water vapor in the step (4) are passed through a condenser, and a certain amount of cooling water is added to obtain hydrochloric acid having a mass percentage of 20% to 23%, and the obtained hydrochloric acid is returned to the step of claim 1 ( 2) Reuse in an acidified stirred mill.

According to the above scheme, the filtrate in the step (6) is returned to the hydration reaction emulsification tank in this step.

The invention firstly determines the suitable calcination conditions of the magnesite according to the difference of the decomposition temperature and the decomposition speed of each mineral, effectively increases the difference of activity between the components, and increases the reaction speed and acidification rate of the magnesium salt and hydrochloric acid; According to the difference between the reactivity of each component in the magnesium oxide powder after calcination and the acid, the iron, manganese, calcium and other insoluble impurities in the magnesium oxide powder are removed by controlling the amount of the magnesium oxide powder and hydrochloric acid and the acidification reaction conditions. If the coarse particles are not effectively acidified during the reaction, they will fall into the grinding zone by gravity and then grind, realizing the dynamic acidification process of acidification while grinding, thus effectively reducing the grinding energy consumption, reducing the acidification time and strengthening. The acidification efficiency can also increase the difference in activity of each component after calcination.

The activity and appearance of the active magnesium oxide precursor magnesium oxide are controlled by controlling the crystallization condition of the magnesium chloride hexahydrate solution and the calcination temperature of the magnesium chloride hexahydrate crystal, thereby shortening the hydration time of the active magnesium oxide and enhancing the conversion rate of the active magnesium oxide. The particle size and morphology of the nanometer magnesium hydroxide were controlled by controlling the hydration conditions and the type and amount of the adjusting agent, and finally, a nano-sheet-shaped barium hydroxide product having a uniform particle size and morphology was prepared. In the process for synthesizing magnesium hydroxide from the magnesite, not only hydrochloric acid, water and heat energy can be recycled, but even additives which do not act on the surface of the magnesium hydroxide can be recycled, which is environmentally friendly and low in cost. This process can revitalize existing magnesite resources and achieve high value-added conversion of resources.

BRIEF DESCRIPTION OF THE DRAWINGS: BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a technical roadmap of the present invention.

Figure 2 Example 1 SEM photograph of a magnesium hydroxide product prepared using the method of the present invention. Figure 3 Example 1 XRD pattern of a magnesium hydroxide product prepared using the process of the present invention. Figure 4 Example 2 SEM photograph of a magnesium hydroxide product prepared using the method of the present invention. Figure 5 Example 2 XRD pattern of a magnesium hydroxide product prepared using the process of the present invention. Figure 6 Example 3 SEM photograph of a magnesium hydroxide product prepared using the method of the present invention. Figure 7 Example 3 XRD pattern of a magnesium hydroxide product prepared using the process of the present invention. BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below with reference to FIG. 1 and an embodiment:

detailed description:

Example 1

First step: Magnesite calcination water soluble

The magnesite is crushed to below 9 mm, crushed and calcined, calcination temperature is 630 ° C, calcination time is 3 hours, magnesium oxide powder is obtained, 28 g of magnesium oxide powder is weighed, added to a stirred tank, and 18 ml is added to the stirring tank. The water was stirred for 0.3 min.

Step 2: Magnesium oxide powder slurry grinding and acidification

The stirred magnesium oxide powder slurry is transferred to an acidified stirring mill for grinding. After grinding for 2 minutes, hydrochloric acid is added to the acidified stirring mill to acidify the magnesium oxide powder, the acidification time is lmin, and the magnesium oxide powder slurry is acidified from the bottom end. In the stirring mill, hydrochloric acid was added from the middle to the acidified stirring mill, and the acidified slurry was discharged from the upper end of the acidizing stirring mill.

The third step: the magnesium oxide powder slurry acidification and impurity removal

In the acidification process, 162ml of 20% hydrochloric acid by weight is added from the middle to acidify the magnesium oxide powder. This process requires insufficient hydrochloric acid, excessive magnesium oxide powder, brownish red precipitate in the slurry, and the upper end of the acidified stirring mill. The slurry is filtered to obtain a filtrate and a residue, impurities such as iron, manganese, calcium, and excess magnesium oxide powder are introduced into the solid residue, and the filtrate is a magnesium chloride solution after the impurity removal.

The fourth step: preparation of active magnesium oxide

The filtrate is placed in a vacuum drying oven for crystallization, the degree of vacuum is 0.05 Mpa, the evaporation crystallization temperature is 90 ° C, and the crystals are evaporated and evaporated for 5 hours to obtain crystals of magnesium chloride hexahydrate, and then the obtained crystals of magnesium chloride hexahydrate are placed in a calcining furnace for calcination and calcination. The temperature was 470 ° C and the calcination time was 1.5 h. After calcination, active magnesium oxide was obtained, and hydrogen chloride gas and water vapor generated were passed through an acid-resistant condensation dust collector, and 100 ml of water was added to obtain hydrochloric acid having a mass percentage of 20% by weight.

Step 5: Cycle acidification of filter residue

Returning the filter residue in the third step to the agitation tank in the first step, and re-grinding and acidifying into the acidification agitating mill. When the circulation load of the magnesium oxide powder and the newly added amount reaches 100%, the cycle is terminated and discharged. The residue is placed in a stirred tank and acidified by adding hydrochloric acid. The pH of the acidification is controlled at 5.4. After acidification, the mixture is filtered, the residue is discarded, and the filtrate is returned to the fourth step to carry out evaporative crystallization to obtain crystals of magnesium chloride hexahydrate.

Step 6: Hydration of magnesium hydroxide In the specification, the active magnesium oxide and the adjusting agent dextrin are slowly added to the emulsification tank for hydration reaction, the volume concentration of the dextrin in the hydration reaction solution is 1 mg/L, and the liquid-solid ratio of the active magnesium oxide to water in the hydration reaction is 30:1. The hydration reaction temperature is 75 ° C, the hydration reaction stirring speed is 4000 r / min, and after hydration reaction for 2 h, the solution is filtered to obtain magnesium hydroxide filter cake and filtrate, and the filtrate is returned to the hydration reaction emulsification tank, and the filter cake is dried at a low temperature to obtain a tablet. Monodisperse nanometer magnesium hydroxide.

The monodisperse nanometer magnesium hydroxide was prepared to have a purity of 99.34%.

Example 2

First step: Magnesite calcination

The same as the first step of Example 1.

Step 2: Magnesium oxide powder slurry grinding and acidification

The same as the second step of the embodiment 1.

In the acidification process, 140ml of hydrochloric acid with a mass concentration of 23% is added from the middle to acidify the magnesium oxide powder. This process requires insufficient hydrochloric acid, excessive magnesium oxide powder, brownish red precipitate in the slurry, and the upper end of the acidified stirring mill. The slurry is filtered to obtain a filtrate and a residue, impurities such as iron, manganese, calcium, and excess magnesium oxide powder are introduced into the solid residue, and the filtrate is a magnesium chloride solution after the impurity removal.

The fourth step: preparation of active magnesium oxide

The filtrate is placed in a vacuum drying oven for crystallization, the degree of vacuum is 0.1 Mpa, the evaporation crystallization temperature is 75 ° C, and the evaporation crystallization is 5.5 h to obtain crystals of magnesium chloride hexahydrate, and then the obtained crystals of magnesium chloride hexahydrate are placed in a calciner for calcination. The calcination temperature is 480 ° C, the calcination time is 1.5 h, the activated magnesium oxide is obtained after calcination, the hydrogen chloride gas and water vapor produced are passed through an acid-resistant condensation dust collector, and 77 ml of water is added to obtain a hydrochloric acid having a mass concentration of 23%. .

Step 5: Cycle acidification of filter residue

Returning the filter residue in the third step to the agitation tank in the first step, and re-grinding and acidifying into the acidification agitating mill. When the circulation load of the magnesium oxide powder and the newly added amount reaches a cycle load of 110%, the cycle is terminated and discharged. The residue is placed in a stirred tank and acidified by adding hydrochloric acid. The pH of the acidification is controlled at 5.2. After acidification, the mixture is filtered, the residue is discarded, and the filtrate is returned to the fourth step to carry out evaporative crystallization to obtain crystals of magnesium chloride hexahydrate.

Step 6: Hydration of magnesium hydroxide

The active magnesium oxide and the adjusting agent dextrin are slowly added to the emulsification tank for hydration reaction, the volume concentration of the dextrin in the hydration reaction solution is 1.5 mg L, and the liquid-solid ratio of the active magnesium oxide to water in the hydration reaction is 35:1, hydration The reaction temperature is 80° (the hydration reaction stirring speed is 3800r/min, and after hydration reaction for 2h, the solution is filtered to obtain magnesium hydroxide filter cake and filtrate, and the filtrate is returned to the hydration reaction emulsification tank, and the filter cake is dried at a low temperature to obtain a sheet shape. Monodisperse nanometer magnesium hydroxide.

The monodisperse nanometer magnesium hydroxide was prepared to have a purity of 99.12%. Example 3 First step: Magnesite calcination

The same as the first step of Example 1.

Step 2: Magnesium oxide powder slurry grinding and acidification

The same as the second step of the embodiment 1.

In the acidification process, 149 ml of hydrochloric acid with a mass concentration of 21.5% was added from the middle to acidify the magnesium oxide powder. This process requires insufficient hydrochloric acid, excessive magnesium oxide powder, brownish red precipitate in the slurry, and the upper end of the acidified stirring mill. The slurry is filtered to obtain a filtrate and a residue, impurities such as iron, manganese, calcium, and excess magnesium oxide powder are introduced into the solid residue, and the filtrate is a magnesium chloride solution after the impurity removal.

The fourth step: preparation of active magnesium oxide

The filtrate was placed in a vacuum drying oven for crystallization, the degree of vacuum was 0.08 MPa, and the evaporation crystallization temperature was 80 ° C.

Book

Evaporation and crystallization for 5h to obtain crystals of magnesium chloride hexahydrate, and then the obtained crystals of magnesium chloride hexahydrate are calcined in a calcining furnace, calcination temperature is 490 ° C, calcination time is lh, calcination to obtain active magnesium oxide, hydrogen chloride gas and water produced The vapor was passed through an acid-resistant condensing dust collector, and 88 ml of water was added to obtain a hydrochloric acid having a mass percentage of 21.5%.

Step 5: Cycle acidification of filter residue

Returning the filter residue in the third step to the agitation tank in the first step, and re-grinding and acidifying into the acidification agitating mill. When the cycle load of the magnesium oxide powder and the newly added amount reaches 120%, the cycle is terminated and discharged. The filter residue is placed in a stirred tank and acidified by adding hydrochloric acid. The pH value during acidification is controlled at 6. After acidification, filtration is carried out, the filter residue is discarded, and the filtrate is returned to the fourth step to carry out evaporative crystallization to obtain crystals of magnesium chloride hexahydrate.

Step 6: Hydration of magnesium hydroxide

The active magnesium oxide and the adjusting agent dextrin are slowly added to the emulsification tank for hydration reaction, the volume concentration of the dextrin in the hydration reaction solution is 1.3 mg/L, and the liquid-solid ratio of the active magnesium oxide to water in the hydration reaction is 35:1. The hydration reaction temperature is 85 ° C, the hydration reaction stirring speed is 3900 r / min, and after hydration reaction for 2 h, the solution is filtered to obtain magnesium hydroxide filter cake and filtrate, and the filtrate is returned to the hydration reaction emulsification tank, and the filter cake is dried at a low temperature to obtain a tablet. Monodisperse nanometer magnesium hydroxide.

The purity of the sheet-like monodisperse nano magnesium hydroxide was 99.28%.

Claims

claims

1. A method for preparing flaky monodisperse nanometer magnesium hydroxide from magnesite. The method is carried out as follows:

(1) Magnesite calcined water-soluble: Calculate magnesite to obtain magnesium oxide powder, add the calcined magnesium oxide powder to the stirring tank, add a certain amount of water to the stirring tank, and prepare the magnesium oxide powder to a mass percentage The concentration is

60% slurry, stir for about 0.3 minutes;

(2) Grinding and acidification of magnesium oxide powder slurry: Transfer the stirred magnesium oxide powder slurry to an acidifying stirring mill for grinding. After grinding for 2 minutes, add hydrochloric acid to the acidizing stirring mill to acidify the magnesium oxide powder. The acidification time is lmi The magnesium oxide powder slurry is added to the acidifying stirring mill from the bottom end, and the hydrochloric acid is added to the acidifying stirring mill from the middle. The acidified slurry is discharged from the upper end of the acidizing stirring mill. The magnesium oxide powder particles that fail to be ground and acidified fall into the acidifying mill due to gravity. The grinding area of the stirring mill is then subjected to grinding and acidification treatment to achieve grinding and acidification at the same time;

(3) Acidification and impurity removal of magnesium oxide powder slurry: During the acidification process, the mass percentage concentration of hydrochloric acid added to the acidification stirring mill is 20%~23%. The volume ratio of the mass of magnesium oxide powder to the added hydrochloric acid during acidification is 1 g. : 5.0 mMg: 5.8ml, filter the acidified slurry to obtain the filtrate and filter residue. During the acidification process, excess magnesium oxide powder is used, causing impurities such as iron, manganese, calcium and excess magnesium oxide powder to enter the solid filter residue;

(4) Preparation of activated magnesium oxide: The filtrate is vacuum crystallized to obtain magnesium chloride hexahydrate crystals, and magnesium chloride hexahydrate is calcined at low temperature. The calcining temperature is 470°C to 490°C, and the calcining time is 1h to 1.5h. After calcining, active magnesium oxide and hydrogen chloride are obtained. Gases and water vapor;

(5) Circular acidification of the filter residue: The filter residue is returned to the stirring tank for re-grinding and acidification. When the ratio of the circulating amount of magnesium oxide powder to the newly added amount, that is, when the circulating load reaches 100%~120%, the cycle is terminated and the filter residue is discharged. Add hydrochloric acid and then perform acidification. The pH value of the acidification is controlled at 5 to 6. After acidification, filtering is performed, the filter residue is discarded, and the filtrate is subjected to vacuum crystallization together with the filtrate in step (4).

(6) Preparation of flaky monodisperse nanometer magnesium hydroxide: Slowly add active magnesium oxide and regulator dextrin into the hydration reaction emulsification tank to perform hydration reaction. The volume concentration of dextrin in the hydration reaction solution is 1mg/L ~2mg/L , the liquid-to-solid ratio of activated magnesium oxide and water in the hydration reaction is 30:1 40:1, the hydration reaction temperature is 75°C-85°C, the hydration reaction stirring speed is 3000 r/min~4000r/min, and the hydration reaction is 2 hours Afterwards, the solution is filtered to obtain a magnesium hydroxide filter cake and filtrate, and the filter cake is dried at low temperature to obtain flaky monodisperse nanometer magnesium hydroxide.

2. A method for preparing flaky monodisperse nanometer magnesium hydroxide from magnesite according to claim 1, characterized in that: the magnesite in step (1) of claim 1 is crushed to less than 9 mm, and after crushing Magnesite is calcined, the calcining temperature is 630°C, and the calcining time is 3 hours.

3. A method for preparing flaky monodisperse nanometer magnesium hydroxide from magnesite according to claim 1, characterized in that: the vacuum crystallization in step (4) of claim 1 has a vacuum degree of 0.05Mpa ~ 0.1 MPa, the crystallization temperature is 75°C~90°C, and the crystallization time is 5h~6h.

4. A method for preparing flaky monodisperse nanometer magnesium hydroxide from magnesite according to claim 1, characterized in that: the hydrogen chloride gas and water vapor in step (4) of claim 1 pass through a condenser and are added A certain amount of cooling water is used to obtain hydrochloric acid with a mass concentration of 20% to 23%, and the obtained hydrochloric acid is returned to the acidifying stirring mill in step (2) of claim 1 for reuse.

5. A method for preparing flaky monodisperse nanometer magnesium hydroxide from magnesite according to claim 1, characterized in that: the filtrate in step (6) of claim 1 is returned to the hydration reaction emulsification tank in this step .