CN108190924B - A kind of preparation method that reduces magnesium hydroxide chlorine content - Google Patents

Abstract

The invention belongs to magnesium hydroxide preparation fields, are specifically put forward for the first time the method for the chlorine in cleaning magnesium hydroxide；In the present invention, the magnesium hydroxide to be processed containing chlorine impurity is carried out to the agitator treating of single-stage；Or the multi-stage countercurrent agitator treating through chlorine removal system, obtain dechlorination magnesium hydroxide；The present invention originally proposes a kind of using adverse current stirring mode of washing.The chlorinity of magnesium hydroxide can be down to 0.2% and less for 0.8% or more by the method for the present invention.

Description

A kind of preparation method that reduces magnesium hydroxide chlorine content

technical field

The invention belongs to the field of magnesium hydroxide preparation, in particular to a preparation process of low-chloride high-purity magnesium hydroxide

Background technique

China's salt lake resources are also very rich. Among them, there are 731 salt lakes with an area of more than 1km ² , and the total area of these lakes has reached 23,784km ² . Among them, the Qaidam Basin in Qinghai is rich in resources, and the potassium salt reserves in the salt lakes in this area are about The magnesium salt reserves are about 4.815 billion tons, of which 65.3% are magnesium chloride and 34.7% are magnesium sulfate. Foreign salt lake resources mainly include Sears Salt Lake and Great Salt Lake in the United States, Atacama Salt Lake in Chile, and the Dead Sea near Israel and Jordan. With the continuous advancement of science and technology, the development of salt lake resources in foreign countries is no longer satisfied with the production of a single chemical product, but is moving towards diversified and comprehensive utilization.

Qinghai Chaerhan Salt Lake is an important potash fertilizer production base in China. In the process of potash fertilizer production, a large amount of old brine enriched with magnesium chloride is produced. Taking advantage of the unique local climate conditions, it is easy to obtain low-cost and high-quality brine through salt field evaporation, concentration and crystallization. Bischofite (MgCl ₂ .6H ₂ O) solid ore is a very important salt lake magnesium resource.

my country's salt lake magnesium resources are very rich, and the production and development of salt lake magnesium resources is mainly the production and development of bischofite, a by-product of salt lake potash fertilizer. system.

The development of magnesium resources in salt lakes in my country is mainly the development of bichoromagnesite resources in Chaerhan Salt Lake. It is an old brine rich in magnesium salts discharged during the production of potash fertilizers. It is concentrated by evaporation in salt fields by utilizing the unique local natural climate conditions. A secondary magnesium resource solid mineral obtained by crystallization, which has the characteristics of high grade, low impurity content, and large resource volume. The Qaidam area is rich in hydropower, oil and other resources, which provide sufficient guarantee for the magnesium salt production plant. In addition, the "West-to-East Gas Pipeline" project currently under construction provides the most powerful support for the continuous upgrading of the magnesium processing industry. At the same time, with the active support of national policies related to the western development of the country, the land is cheap, the market is more standardized, and the system is more complete, so the development of salt lake magnesium resources has significant advantages.

Magnesium hydroxide, white, colorless crystal, belongs to hexagonal crystal system, tasteless, non-toxic and corrosive. High-purity magnesium hydroxide refers to products with a magnesium hydroxide content greater than 99%. It has a high decomposition temperature and a large heat absorption. It is an important inorganic chemical material and is widely used, mainly in flame retardants, flue gas desulfurization, wastewater treatment, etc. .

High-purity magnesium hydroxide was first enriched with hydrochloric acid in the "magnesia brick" factory, and its particle size was ground to less than 0.5mm, and then dissolved in hydrochloric acid with a concentration of 12.5-20%, after impurity removal treatment, and precipitation. High-purity magnesium hydroxide. In the world, the United States, Japan, and the United Kingdom were the first to obtain mature technologies for preparing high-purity magnesia. After that, countries such as Italy, Mexico, Norway and Greece successively prepared high-purity magnesium hydroxide.

Seawater method is mostly used in Western Europe, where the sedimentation speed and washing efficiency are the focus. Studies have shown that dolomite lime as a precipitant reacts with seawater to create the best conditions for magnesium hydroxide. When A-130 flocculant is used, the settling speed is greatly enhanced, and the device capacity is also improved accordingly.

The production scale of China's high-purity magnesium hydroxide is small and the equipment is aging, which cannot meet the market demand. In recent years, scientific research achievements of high-purity magnesium salt products have been continuously poured out, and most of them have been put into the market, but even these are far from enough to meet the needs of the domestic market, and exports are even less. Due to the small production volume, the economy of magnesium salt enterprises cannot be improved. . Therefore, the production of functional magnesium salt products is the only way for the development of magnesium salt.

Generally speaking, the production of magnesium salt in China is still in its infancy, with a single product, insufficient added value, and weak functionality. For example, flame retardant magnesium hydroxide, magnesium hydroxide for medicine, etc., can only be imported if the domestic demand is large. This situation has already attracted the attention of many domestic universities, scientific research institutes and magnesium salt enterprises. What we need to do now is to actively invest in manpower and material resources to develop new technologies and new processes to meet domestic and foreign needs, improve product grades, and occupy the international market.

In the prior art, the chlorine content of magnesium hydroxide is relatively high, but the chlorine content of magnesium hydroxide has not been paid attention to in this field.

Contents of the invention

The present invention focuses on the technical problem of the chlorine content of magnesium hydroxide for the first time, and provides a preparation method for reducing the chlorine content of magnesium hydroxide. Through the original multi-stage countercurrent stirring washing of the present invention, the chlorine content of the obtained magnesium hydroxide is obviously reduced. content.

A preparation method for reducing the chlorine content of magnesium hydroxide. The magnesium hydroxide containing chlorine impurities is subjected to single-stage agitation and washing; or multi-stage countercurrent agitation and washing of a chlorine removal system to obtain chlorine-removing magnesium hydroxide;

The dechlorination system includes multi-stage dechlorination units; each dechlorination unit is provided with an inlet and an outlet of magnesium hydroxide, and an outlet and an inlet of cleaning liquid; each dechlorination unit is connected in series through the outlet and inlet of magnesium hydroxide , wherein, the magnesium hydroxide inlet of the first stage dechlorination unit is the inlet of magnesium hydroxide to be treated, and the magnesium hydroxide outlet of the last stage dechlorination unit is the recovery outlet of magnesium hydroxide after dechlorination;

The outlet of the cleaning solution of the first-level dechlorination unit is the extraction outlet of the cleaned washing solution, and the clear liquid inlet of the last-level dechlorination unit is the inlet of clean water; the cleaning solution of the dechlorination units of other levels The outlets are connected to the cleaning liquid inlets of the respective upper-stage dechlorination units connected in series;

Magnesium hydroxide enters the dechlorination system from the magnesium hydroxide inlet of the first-stage dechlorination unit, and clear water enters the dechlorination system from the feed liquid inlet of the last stage; Stage dechlorination unit movement; cleaning liquid moves from the last stage to the first stage dechlorination unit, magnesium hydroxide and clear liquid are stirred and washed in each dechlorination unit, and the stirred and washed magnesium hydroxide is dechlorinated by the last stage The magnesium hydroxide outlet of the unit is extracted, and the cleaning liquid is extracted from the cleaning liquid outlet of the first-stage dechlorination unit.

First of all, the present invention proposes a method for cleaning the chlorine content in magnesium hydroxide for the first time. In addition, the inventors of the present invention provide a preparation method that can reduce the chlorine content of magnesium hydroxide, that is, through the chlorine removal system described in the present invention, the magnesium hydroxide is subjected to multi-stage countercurrent stirring and washing, which can Efficiently remove chlorine content in magnesium hydroxide.

In the treatment system of the present invention, in each chlorine removal unit, the outlet of the magnesium hydroxide is preferably arranged at the lower part of the chlorine removal unit; the inlet of the magnesium hydroxide is preferably arranged at the top of the chlorine removal unit. Both the inlet and the outlet of the cleaning solution are preferably arranged on the upper part of the chlorine removal unit, and the outlet and inlet of the cleaning solution are arranged at opposite positions on the upper part of the chlorine removal unit.

Each chlorine removal unit described in the present invention is also provided with a stirring device, a transfer device for transferring magnesium hydroxide to the next-stage chlorine removal unit, and a transfer device for transferring the cleaning liquid to the upper-stage chlorine removal unit.

The magnesium hydroxide to be treated enters the dechlorination system from the first-stage dechlorination unit, and the clean water enters the system from the last-stage cleaning liquid inlet; the magnesium hydroxide is first transferred in the first-stage dechlorination unit and the second-stage dechlorination unit The cleaning liquid that comes over is stirred and washed, and then the magnesium hydroxide after the first-stage stirring and washing is continuously or intermittently transferred to the second-stage dechlorination unit, and the cleaning liquid transferred from the third stage is stirred and washed. Multi-stage countercurrent stirring and washing is carried out in the treatment system; until it is extracted from the outlet of the last stage of magnesium hydroxide.

The inventors of the present invention have found that the multi-stage countercurrent agitation and washing with the inventive dechlorination system of the present invention can further improve the dechlorination effect by controlling appropriate agitation and washing parameters.

Studies have found that adjusting parameters such as the particle size (bulk density) of the magnesium hydroxide to be treated, the stirring speed of the washing process, the liquid-solid ratio, and the washing temperature can further improve the chlorine removal effect.

Preferably, the bulk density of the magnesium hydroxide to be treated is 0.8-2.0 g/ml; more preferably 1.2-1.5 g/ml. Studies have found that controlling the bulk density within an appropriate range can further improve the chlorine removal effect, and also help to further benefit the multi-stage countercurrent stirring washing described in the present invention, and help to improve the preparation effect.

In actual production, the magnesium hydroxide to be treated can be ground in advance, and the bulk density of the magnesium hydroxide to be treated can be controlled within the preferred range through the grinding time. Preferably, the magnesium hydroxide to be treated is ground before washing, and the grinding time is 5-20 minutes, more preferably 5-10 minutes.

In the process of multi-stage countercurrent stirring and washing, in each dechlorination unit, the magnesium hydroxide transferred from the upper stage and the cleaning liquid transferred from the next stage are stirred and washed; the appropriate solid-liquid ratio and stirring speed are controlled and the The residence time of each dechlorination unit can synergistically improve the chlorine removal and washing effect.

Preferably, during the stirring and washing process, the liquid-solid weight ratio of the magnesium hydroxide to the cleaning solution is 1-5:1. When the proportion of the liquid part is larger, it can help to improve the chlorine removal effect, but the higher the liquid proportion, the lower the preparation effect and the lower the filtration speed.

Further preferably, during the stirring and washing process, the liquid-solid weight ratio of the magnesium hydroxide to the cleaning solution is 2-4:1. Under the preferred liquid-solid ratio, the chlorine removal effect is good, and the production efficiency is high.

Preferably, the temperature of the stirring and washing process is 50-90°C. The study found that the dechlorination effect can be further improved when the range temperature is higher, and the dechlorination effect is decreased at lower and higher washing temperatures.

More preferably, the temperature of the stirring and washing process is 60-80°C. At this preferred temperature, the chlorine removal effect is ideal, the preparation efficiency is high, and the filtration speed is fast, which is beneficial to large-scale industrial production.

Preferably, during the stirring and washing process, the stirring speed is not lower than 50r/min. When the stirring is faster, the removal effect of chlorine is better, but if the stirring is too fast, it is not conducive to the implementation of industrial production, and the filtration speed is slow.

More preferably, during the stirring and washing process, the stirring speed is 50-250 r/min; most preferably 100-250 r/min. Under the preferred stirring speed, the production efficiency is high, and the chlorine removal effect is more ideal.

As a preference, under the agitation washing temperature, solid-to-liquid ratio, and agitation speed, the preferred agitation washing time is greater than 10 min. The longer the stirring and washing time, the further improved the dechlorination effect, but the filtration speed decreased.

More preferably, the stirring and washing time is greater than or equal to 10 minutes, and is 10-60 minutes, more preferably 30-60 minutes. Under the preferred stirring and washing time, the dechlorination effect and production effect are more ideal.

The method of the present invention is applicable to the treatment of magnesium hydroxide with any Cl- content; preferably suitable for the treatment of magnesium hydroxide with chlorine impurity content of 0.6-0.9%.

In the present invention, the cleaning solution in the single-stage washing process is clear water.

Under the parameters of the single-stage washing, the chlorine content of magnesium hydroxide can be reduced to about 0.3%, but the cleaning effect is not stable. In the present invention, by adopting the preferred multi-stage countercurrent cleaning method of the present invention, the cleaning effect of chlorine is better, and continuous cleaning can be realized. Relatively speaking, the amount of cleaning liquid used is less.

Preferably, in the chlorine removal system, the number of serial stages of the chlorine removal unit is 2-10; preferably 3-6. Under the above multi-stage washing conditions, under magnesium hydroxide with any chlorine content, the chlorine content can be obtained at about 0.2% or below.

The magnesium hydroxide to be treated in the present invention can be an existing product purchased from outside, or a product synthesized by using the prior art.

In the present invention, the magnesium hydroxide to be treated is preferably obtained by ammonia method.

As a preference, the preparation process of the magnesium hydroxide to be treated is as follows: adding the magnesium chloride solution and ammonia water dropwise to the ammonia water-ammonium chloride buffer system added with magnesium hydroxide seeds, stirring and reacting to obtain the hydrogen to be treated magnesium oxide.

The present inventor's research has found that the parameters of the preparation process of the magnesium hydroxide to be treated, such as the concentration of magnesium chloride solution, ammoniacal liquor, dropwise addition mode, dropwise addition ratio, crystal seed and the dosage of crystal seed, the stirring speed of stirring reaction, Parameters such as the reaction temperature are reasonably controlled, and the magnesium hydroxide to be treated that is more conducive to the multi-stage countercurrent agitation and washing of the present invention is obtained. Cooperating with the multi-stage counter-current agitation and washing of the present invention can further reduce the chlorine removal effect and improve the filtration performance. , improve the preparation effect and make it more suitable for industrial scale-up production.

The magnesium chloride solution may be a solution obtained by dissolving bischofite and removing impurities through a conventional impurity removal process, or may be a solution obtained in water by using an analytical grade magnesium chloride solvent.

Preferably, the molar concentration of the magnesium chloride solution is 1-4 moL/L; more preferably 2-3 moL/L.

Preferably, the concentration of ammonia water is 10-13.3 mol/L.

Preferably, the dosing ratio (molar ratio) of magnesium chloride solution to ammonia water is 1:2-1:8; more preferably 1:2-1:5; still more preferably 1:2.2-2.8.

In the present invention, the magnesium chloride solution and ammonia water are added dropwise to the reaction system at the same time, and the dechlorination effect can be further improved by controlling the stirring speed and reaction temperature, combined with the multi-stage countercurrent stirring and washing described in the present invention.

The ammonia water-ammonium chloride buffer system of the present invention is a buffer solution with a pH=9 ratio of ammonia water and ammonium chloride.

Preferably, the added amount of the magnesium hydroxide seed crystal is 10-40% of the product.

The study found that the amount of seed crystals added can affect the conversion rate of the product, and affect the filtration speed and bulk density of the product. Preferably, the added amount of the magnesium hydroxide seed crystal is 20-30%. Under the preferred addition amount of seed crystals, the conversion rate of the product is high and the filtration efficiency is high, and the obtained product can further improve the dechlorination effect by using the stirring and washing method described in the present invention.

Preferably, the stirring speed of the stirring reaction is not lower than 50r/min; more preferably 50-150r/min. When the stirring speed is increased, the filtration performance is enhanced, but as long as the solution is stirred to disperse, the filtration performance does not change much when the stirring speed is increased, indicating that the stirring speed plays a role in dispersing the magnesium hydrochloride solution to reduce the instantaneous saturation and generate precipitation. The particle size increases.

More preferably, the stirring speed of the stirring reaction is 100-150 r/min.

Preferably, the temperature of the stirring reaction process is 40-80°C.

Preferably, the stirring reaction time is 10 to 40 minutes, and at 30 minutes, the particles are the largest.

The method for reducing the chlorine content of the present invention is particularly suitable for dechlorination of magnesium hydroxide produced by the magnesium chloride ammonia method. In the process of processing magnesium hydroxide produced by the magnesium chloride ammonia method, the multi-stage countercurrent cleaning process of the present invention has more obvious advantages than single-stage washing. For example, the chlorine content can be stabilized at about 0.2%, and chlorine removal The effect is better, and the ammonia in magnesium hydroxide can be removed well.

Beneficial effect

1. The invention uniquely adopts the multi-stage countercurrent stirring washing method, which can help to significantly improve the chlorine removal effect.

2. The present invention adopts the method of agitation and washing, by studying factors such as aging temperature, aging time, liquid-solid ratio, stirring speed, etc., and creatively inventing technologies such as grinding, multi-stage countercurrent agitation, washing and aging to reduce the chloride content in the product, so as to Determine the optimal process conditions for reducing chloride.

3. The magnesium hydroxide to be treated according to the present invention can be made of bischofite as a raw material, first dissolved with pure water, filtered and purified to remove impurities to obtain high-concentration brine, and then use ammonia as a precipitating agent and adopt the brine-ammonia precipitation method Get magnesium hydroxide, study the influence of factors such as reaction temperature, reaction time, stirring speed and feeding mode and feeding speed on magnesium hydroxide particle size and filter agitation washing performance,

4. Utilize the inventive method to clean the magnesium hydroxide that chlorine magnesium ammonia method makes, multistage countercurrent washing can make dechlorination effect be controlled at 0.2% and below, also can obviously remove ammonia, maintain the granularity of the magnesium hydroxide that obtains.

Description of drawings:

Fig. 1 is the preparation flow schematic diagram of magnesium hydroxide;

Fig. 2 is a schematic diagram of washing with multi-stage agitation and countercurrent agitation.

Detailed ways

Gansu Jinmao Mining Development Co., Ltd. provides industrial grade lightly burned magnesite powder.

The magnesium chloride solution of the present invention can be obtained by the following method: take about 500g of bischofite, add 100ml of distilled water to dissolve, leave it overnight, vacuum filter, remove the insoluble matter, and put the insoluble matter into the next dissolution beaker In order to avoid waste, put the prepared saturated magnesium chloride solution into a large beaker for later use. The magnesium chloride concentration was determined to be 4.81 mol/l.

The saturated magnesium chloride solution obtained in the experiment was heated to 120°C, cooled slowly at room temperature, and then recrystallized to obtain bischofite. The content of elements in the saturated magnesium chloride produced by the two is shown in Table 1:

Table 1 The comparison of elements in saturated magnesium chloride after primary crystallization and recrystallization dissolution

It can be known from Table 1 that the bischofite obtained by recrystallization has significantly less impurity elements than that obtained by primary crystallization, and the purity has reached more than 99%. Therefore, in order to reduce the impurities in the raw material bischofite, I chose the recrystallized bischofite as the raw material for my follow-up experiments.

In this experiment, magnesium chloride solution and ammonia water are added dropwise to the ammonia water-ammonium chloride buffer system added with magnesium hydroxide seeds, and the reaction temperature and dropping speed are controlled to obtain magnesium hydroxide through reaction. Finally, the product was obtained by washing, filtering and drying.

Among the present invention, embodiment 1～7 screens the parameter of the preparation process of magnesium hydroxide: Among embodiment 1～7, except special statement, the molar concentration of the magnesium chloride that adopts is all above-mentioned 4.81mol/1 that makes; The concentration is 13.33mol/1.

Example 1

Different concentrations of _MgCl2 solutions were carried out single factor test, and _MgCl2 and ammonia solution (13.33mol/l) were added at the same time, the reaction rate of magnesium chloride and ammonia solution was 10ml/min, the stirring rate was 150r/min, and the reaction temperature was 80°C 1. After the material is added, the stirring time is continued to be 30min, and the magnesium hydroxide obtained by the reaction is shown in Table 2 as a result:

The impact of table 2 brine magnesium ion concentration on product filtration rate

From the perspective of magnesium conversion rate, when the concentration of MgCl ₂ is 3mol/l, the magnesium conversion rate is higher. At low concentration, increasing the Mg ²⁺ concentration increases the conversion rate significantly, and the filtration rate increases slightly. After exceeding 3mol/l, the conversion rate slows down, and the filtration rate and bulk density change significantly. This is because the Mg ²⁺ concentration increases. The solution appears colloidal, the stirring effect is weakened, and the diffusion of magnesium ions is affected. Therefore, the concentration of magnesium ions in brine is 3mol/l.

Example 2

During the experiment, MgCl and ammonia solution _were added at the same time, the reaction titration rate of magnesium chloride and ammonia solution was 10ml/min, the stirring rate was 150r/min, the reaction temperature was 80°C, and the stirring time was continued for 30min after the addition of the materials. Magnesium oxide, MgCl ₂ and ammonia material molar ratio are respectively 1: 2.2, 1: 2.4, 1: 2.6, 1: 2.8, and other conditions remain the same. The results are shown in Table 3:

Table 3 Material Ratio Effect on Product Filtration Speed

It can be seen from the experimental data that the increase in the amount of ammonia water is conducive to the growth of crystals, and the filtration speed and bulk density change significantly. However, after the material ratio exceeds 1:2.6, the filtration speed decreases slowly. This is because the concentration of free ammonia in the reaction is large. The instantaneous supersaturation of magnesium hydroxide increases, which is beneficial to the formation of crystal nuclei but not conducive to growth. Therefore, the ratio of ammonia to material was chosen to be 1:2.6 in the experiment.

Example 3

Add MgCl simultaneously (3mol/l) and ammoniacal solution (MgCl and ammonia material molar ratio are respectively ₁ : 2.6), magnesium chloride and ammoniacal liquor reaction rate of addition are all 10ml/min, stirring speed is 150r/min, 80 ℃ of reaction temperatures, After adding the materials, continue to stir for 30 minutes, add magnesium hydroxide with a product reaction volume of 10%-40% as crystals, and react the magnesium hydroxide obtained. The results are shown in Table 4:

Table 4 The effect of seed crystal addition on product filtration speed

When the amount of seed crystals is 10%, the filter cake is hardened and the filtration speed is slow. If it is more than 20%, the filtration speed increases slowly, and the conversion rate is the largest when 30% is added. Therefore, it is better to select magnesium hydroxide with 30% reaction amount as the crystal seed. Suitable.

Example 4

Add MgCl ₂ (3mol/1) and ammonia solution simultaneously, magnesium chloride and ammonia solution reaction rate of addition are all 10ml/min (MgCl ₂ and ammonia material molar ratio are 1: 2.6 respectively), stirring rate is 50～150r/min, reaction temperature 80°C, after adding the materials, continue to stir for 30 minutes, add magnesium hydroxide with a reaction volume of 30% of the product as a crystal, and react the obtained magnesium hydroxide. The results obtained under different stirring speeds are shown in Table 5:

The influence of table 5 stirring speed on product filtration speed

From table 5, it can be seen that other conditions are constant, the stirring speed increases, and the filtration performance strengthens, but as long as the solution is dispersed by stirring, and the stirring speed is increased, the filtration performance does not change much, indicating that the stirring speed plays a role in making magnesium hydrochloride The dispersion of the solution reduces the instantaneous saturation, and the particle size of the generated precipitate increases. So choose stirring speed 150r/min.

Example 5

Add MgCl ₂ and ammonia solution simultaneously (MgCl ₂ and ammonia material molar ratio are 1: 2.6 respectively), magnesium chloride and ammonia water reaction titration rate are all 10ml/min, stirring speed is 150r/min, add the hydroxide of 30% product reaction amount Magnesium is used as a crystal. After the material is added, the stirring time is continued at 40-80°C and 150r/min for 30 minutes. The magnesium hydroxide obtained by the reaction,

The results under different temperature conditions are shown in Table 6:

The influence of table 6 reaction temperature on product filtration speed

It can be seen from Table 6 that the higher the temperature, the faster the filtration rate, but if the temperature is too high, the utilization rate of ammonia water will decrease, and the increase in the pressure in the three-necked bottle will easily cause experimental accidents. Therefore, when the temperature reaches 80°C, the temperature should not be increased.

Example 6

The MgCl ₂ solution (concentration 3moL/L) was subjected to a single factor test, while adding MgCl ₂ and ammonia solution ((MgCl ₂ and ammonia material molar ratio were 1:2.6)), the stirring rate was 150r/min, and the reaction temperature was 80°C 1. After the material has been added, the stirring time is continued for 30min, and the magnesium hydroxide obtained by the reaction, other conditions are constant, and the reaction rate of addition is changed, and the results are shown in Table 7.

Table 7 ammoniacal liquor, magnesium chloride drop speed influence on product filtration speed

According to Table 7, it can be analyzed that: when magnesium chloride was added dropwise too fast, the amount of ammonia gas feeding was not enough, the reaction was not complete, and the particle size was very small; The instantaneous supersaturation increases, which is conducive to the formation of crystal nuclei but not conducive to growth, and the particles are also very small; when the dropping speed on both sides is equal and slow, the particle size becomes obviously larger and the filtration speed becomes faster. Therefore, it is more appropriate for magnesium chloride and ammonia water reaction titration rate to be 10ml/min.

Example 7

_MgCl2 solution (concentration 3moL/L) is carried out single factor test respectively, add _MgCl2 and ammonia solution simultaneously, ( _MgCl2 and ammonia material molar ratio are respectively 1: 2.6), magnesium chloride and ammoniacal liquor reaction titration rate are all 10ml/min , The stirring rate is 150r/min, the reaction temperature is 80°C, and the reaction time mainly affects the conversion rate of magnesium. However, when exploring the experiment, it is found that the product will be difficult to filter if the reaction time is too long, so other factors in the experiment follow the best plan of the appeal. Do, the reaction time has respectively sample 1: 10min; Sample 2: 20min; Sample 3: 30min; Sample 4: 40min; Sample 5: 50min, sample 6: 60min.

The impact of table 8 reaction time on conversion rate and filterability

It is easy to see that with the increase of time, the conversion rate of the reaction gradually increases. In the first 20 minutes, the concentration of magnesium chloride and ammonia water is high, and the combination of the two generates a large amount of magnesium ^hydroxide . Both the concentration of Mg 2+ and Mg ²⁺ decrease, the reaction becomes slow, and the crystal grows slowly. After more than 40 minutes, the conversion rate of reaction hardly changed, and the conversion rate of magnesium hydroxide decreased, because at this time, almost no product was generated and Mg(OH) ₂ would be reversely dissolved, causing the particle size to dwindle, and the solution was difficult to filter, so 30 minutes were used as optimal reaction time.

This example uses the ammonia method to prepare magnesium hydroxide. The single factor method considers the influence of different conditions on its filtration speed, finds out the process conditions with good filterability, and provides convenience for the reduction of chloride concentration in the next chapter. The conclusions are as follows:

(1) In the experiment, the concentration of magnesium ions in brine is 3.0mol/L, the mol ratio of magnesium chloride solution and ammoniacal liquor is 1: 2.6, the magnesium hydroxide that adds product amount 30% is made crystal seed, and magnesium chloride and ammoniacal liquor reaction rate of addition are all 10ml/min , the stirring speed is 150r/min, the reaction temperature is 80°C, and the stirring time after the addition of the materials is 30min, the magnesium hydroxide particle size obtained by the reaction is large, the filtration performance is good (523ml/min), and the bulk density is high (0.87g/ml ).

The chlorine content of the magnesium hydroxide that embodiment 1～7 makes is at 0.8%. The content of chloride ions therein is ignored in the prepared magnesium hydroxide, and the present invention pays attention to the problem of chlorine content in the prepared magnesium hydroxide for the first time. By adopting the following examples, aging and washing are carried out to reduce the chlorine content; in addition, the following examples, by investigating the particle size of magnesium hydroxide, the aging washing temperature, the aging washing time and the liquid-solid ratio and other factors to reduce chlorine root concentration to determine the optimal aging process conditions.

The measuring method of chlorine content of the present invention is: after the solid-liquid separation after washing, the filtrate is put forward and can be used as the mother liquor of making magnesium hydroxide, then quantitatively add water in batches to wash the filter cake, vacuum suction filtration, take a certain amount of filtrate and nitric acid each time The silver was reacted until almost no white precipitate was left. After drying, take a certain amount and weigh it to react with dilute nitric acid until it just dissolves, and measure its chloride concentration.

Example 8

The present invention is raw material (chlorine content is at 0.8%) with the magnesium hydroxide that embodiment 1 (for example adopts No. 3 experimental product) to make,

Divide the samples into 1: no grinding; 2: grinding for 5 min; 3: grinding for 10 min; 4: grinding for 15 min; 5: grinding for 20 min. Put it into a beaker with a liquid-solid mass ratio of 2:1, stir at 80°C for 40 minutes, and the results are shown in Table 9 (the content of chloride in the original product is 0.97).

The impact of table 9 grinding time on chloride radical content and filtration speed

As can be seen from Table 9, the longer the magnesium hydroxide grinding time, the smaller the chloride content, but after 10 minutes of grinding, the chloride content hardly changes, this is because the grinding reduces the particle size of the product and increases the water content. Contact area.

Example 9

The present invention takes the magnesium hydroxide that embodiment 1 (for example adopts No. 3 experimental product) to make as raw material, has investigated to have determined optimal aging process condition, adopts not to grind, and sample is put into the liquid-solid ratio and is 2: 1 in a beaker, respectively at 50°C, 60°C, 70°C, 80°C, and 90°C, and stirred for 40 minutes. The content of chloride radicals is shown in Table 10.

The influence of table 10 temperature on chlorine radical content and filtering speed

It can be seen from Table 10 that the higher the starting temperature, the lower the content of chloride radicals, and there is almost no change in the content of chloride radicals above 80°C.

As the temperature rises, the ion activity in the system increases, and the chloride radicals are more easily soluble in water; after the temperature rises, the product is easy to aggregate, the particle size becomes larger, and it is easy to wrap the chloride radicals; the suitable washing temperature is 80°C.

Example 10

The present invention takes the magnesium hydroxide that embodiment 1 (for example adopts No. 3 experimental product) to make as raw material, to determine the optimum process condition of optimum stirring speed, sample is put into the beaker that liquid-solid ratio is 2: 1 , at 80°C, reacted for 40 minutes, stirring speeds were 50r/min, 100r/min, 150r/min, 200r/min, 250r/min, and the chloride content was shown in Table 11.

The impact of table 11 stirring speed on chloride radical content and filtration speed

It can be seen from Table 11 that the greater the stirring speed, the lower the content of chlorine radicals. When the stirring speed was 50r/min, the precipitate was not stirred and the chlorine content decreased slowly.

Afterwards, the stirring speed is fast, and the chance of contact between chlorine radicals and water is increased, and the chlorine content drops rapidly, so the experimental stirring speed is selected to be 250r/min.

Example 11

The present invention is with the magnesium hydroxide that embodiment 1 (for example adopts No. 3 experimental product) to make as raw material, researches the optimal process condition of liquid-solid ratio, and liquid-solid ratio is respectively 1,2,3,4,5 5 After a sample was stirred at 80°C and 250r/min for 40 minutes, the chloride content was obtained as shown in Table 12.

The impact of table 12 liquid-solid ratio on chloride content and filtration speed

It can be seen in Table 12 that the larger the liquid-solid ratio, the chloride content is only slightly reduced. When the liquid-solid ratio is 1:1, there are more chlorine radicals. The reason may be that water is too small compared to solids. After stirring, some solids and water no contact.

Example 12

The present invention is with the magnesium hydroxide that embodiment 1 (for example adopts No. 3 experimental products) to make as raw material, researches stirring time to the best process condition of chloride root content with the sample of liquid-solid ratio 2: 1 at 80 ℃, stirring speed At 250r/min, the reaction time is 10min; 20min; 30min; 40min; 50min, the results are shown in Table 13 below.

The impact of table 13 stirring time on chloride radical content and filtration speed

According to the analysis in Table 13, the longer the stirring time, the lower the chloride content, but after 40 minutes, the change is not obvious, because the longer the stirring, the smaller the particle size of magnesium hydroxide and the more thorough dissolution of chloride. Considering the filtration situation, the best stirring time for the experiment is 40 minutes.

Single-stage washing can achieve a certain effect, but the chlorine content of the magnesium hydroxide obtained is unstable. In many cases, the chlorine content of the magnesium hydroxide after washing cannot be reduced to below 0.3%, and the process is unstable.

Example 13

As shown in the schematic diagram in Figure 2,

Pump the slurry with a solid content of 500kg/m3 in the settling tank into the No. 1 aging tank at a flow rate of 30m3/h, and at the same time, the overflow washing liquid (60m3/h) of the No. 2 aging tank also enters the No. 1 aging tank , and carry out stirring, aging, sedimentation and separation in the aging tank, the supernatant (60m3/h) is incorporated into the mother liquor de-ammonia distillation section, and the solid content of the bottom material slurry is controlled at 30kg/m3 and pumped into No. 2 aging tank At the same time, the No. 3 aging tank lotion also enters the No. 2 aging tank for stirring, aging, sedimentation and separation, and the rest are analogous. The contents of ammonium and chloride are shown in Table 14; It is 250r/min; the washing solid-liquid ratio is 1:2.

The impact of table 14 multistage countercurrent sedimentation washing ammonium chloride content

The free ammonia content in the settling tank is generally controlled at 2 kmol/m3, assuming that the free ammonia content in No. 1, 2, 3, 4, 5, and 6 aging tanks are respectively C1, C2, C3, C4, C5, and C6, then the following relationship The formula is established:

C1＝(30×2+60C2)/90＝(2+2C2)/3 (1)

C2＝(30C1+60C3)/90＝(C1+2C3)/3 (2)

C3＝(30C2+60C4)/90＝(C2+2C4)/3 (3)

C4＝(30C3+60C5)/90＝(C3+2C5)/3 (4)

C5＝(30C4+60C6)/90＝(C4+2C6)/3 (5)

C6＝30C5/90＝C5/3 (6)

C1=63C6, C2=31C6, C3=15C6, C4=7C6, C5=3C6

Substitute C1=63C6, C2=31C6 into (1) formula

63C6＝(2+2×31 C6)/3

C6=0.01575kmol/m3

That is, after washing, stirring and aging in 6 aging tanks, the content of free ammonia in the lotion dropped from 2 kmol/m3 of the raw material to 0.01575 kmol/m3. Compared with the above-mentioned ammonia washing effect, the chloride ion concentration in the settling tank was 6.254 kmol/m3 , after washing, stirring and aging in 6 aging tanks, the chloride ion concentration should be reduced to:

(6.254/2)×0.01575=0.04925kmol/m3=1.748kg/m3

Assuming that No. 6 aging tank bottom material slurry (solid content 500kg/m3) has a water content of 10% after centrifuge dehydration, then without washing, the chlorine content in the magnesium hydroxide product is: (1.5m3 * 1.748 kg/m3)/15000kg=0.01748%.

By comparing Example 13 with Examples 8-12, it is found that the multistage countercurrent washing of Example 13 has the following further advantages:

Compared with single-stage washing, the chlorine root content is between 0.25-3.2%, and the continuous multi-stage countercurrent sedimentation washing method is adopted. After the magnesium hydroxide slurry undergoes 6-stage aging, ① the chlorine root content in the product can be reduced to the lowest level Chloride content can be reduced to less than 0.2% (0.01748), and relatively stable, which is expected to completely solve the problem of unstable product quality (especially chloride content) that has always existed in the past.

② After the magnesium hydroxide slurry has been aged for 6 stages, the free ammonia content in the slurry can be reduced to 0.01575mol/L, and there will be no ammonia gas overflow when it is filtered and separated by the centrifuge, which greatly improves the operating environment of the centrifuge .

③ After the magnesium hydroxide slurry has undergone 6-stage aging, there is no need to add water for washing (or add a small amount of water) when the centrifuge is separated, and the direct dehydration can meet the product quality requirements. In this way, the processing capacity of the centrifuge is greatly increased, which can Significantly reduce energy consumption.

④ The magnesium hydroxide slurry is continuously aged by adding water, and the amount of water added for washing is small and constant, which can ensure the stability of the ammonia distilled mother liquor composition, thus ensuring the stability of the production process.

⑤ You don't have to worry about the 304 stainless steel material of the 6 centrifuges.

⑥ The newly added equipment investment cost is not much.

Claims (10)

1. a kind of preparation method for reducing magnesium hydroxide chlorinity, which is characterized in that by the hydroxide to be processed containing chlorine impurity Multi-stage countercurrent agitator treating of the magnesium through chlorine removal system, obtains dechlorination magnesium hydroxide；

The chlorine removal system includes multistage dechlorination unit；Each dechlorination unit is provided with the entrance and exit, clear of magnesium hydroxide The outlet of washing lotion and entrance；Each dechlorination unit is serially connected by the outlet and entrance of magnesium hydroxide, wherein the first order is removed The magnesium hydroxide entrance of chlorine unit is the inlet port of magnesium hydroxide to be processed, the magnesium hydroxide outlet of afterbody dechlorination unit For the extraction mouth of the magnesium hydroxide after dechlorination；

The rinse liquid outlet of the dechlorination unit of the first order is the extraction mouth of the cleaning solution after cleaning, the dechlorination unit of afterbody Clear liquid liquid entrance is the inlet port of clear water；The outlet of the cleaning solution of other dechlorination units at different levels and the upper level being respectively connected in series The filter washing water inlet connection of dechlorination unit；

Magnesium hydroxide enters the chlorine removal system by the magnesium hydroxide entrance of first order dechlorination unit, and clear water is by afterbody Feed liquid port enters chlorine removal system；Magnesium hydroxide from the first order dechlorinate unit to afterbody dechlorinate unit motion；Cleaning solution by Afterbody to the first order dechlorinate unit motion, magnesium hydroxide and clear liquid liquid agitator treating, agitator treating in each dechlorination unit Magnesium hydroxide afterwards by afterbody dechlorination unit magnesium hydroxide export extraction, cleaning solution by the first order dechlorination unit cleaning Liquid outlet extraction；

The bulk density 0.8-2.0g/ml of the magnesium hydroxide to be processed；

In each dechlorination unit, the solvent and solute weight ratio of magnesium hydroxide and cleaning solution is 1~5:1；

Speed of agitator is not less than 50r/min；

The temperature of agitator treating process is 50~90 DEG C；

The agitator treating time is not less than 10min in each dechlorination unit.

2. reducing the preparation method of magnesium hydroxide chlorinity as described in claim 1, which is characterized in that the magnesium hydroxide Outlet be arranged in dechlorination unit lower part；The top of dechlorination unit is arranged in the entrance of the magnesium hydroxide；

The entrance and exit of the cleaning solution is arranged at the top of dechlorination unit, and the outlet of the cleaning solution and entrance are set Set the relative position on dechlorination unit top.

3. reducing the preparation method of magnesium hydroxide chlorinity as described in claim 1, which is characterized in that the hydrogen to be processed The bulk density of magnesia is 1.2-1.5g/ml.

4. reducing the preparation method of magnesium hydroxide chlorinity as described in claim 1, which is characterized in that the hydrogen to be processed The chlorine impurity content of magnesia is 0.6-0.9%.

5. reducing the preparation method of magnesium hydroxide chlorinity as described in claim 1, which is characterized in that agitator treating process In, the cleaning solution of single-stage agitator treating process is clear water；

During agitator treating, magnesium hydroxide is followed by stirring and washing with cleaning solution；

Wherein, the solvent and solute weight ratio of magnesium hydroxide and cleaning solution is 2~4:1；

In each dechlorination unit, speed of agitator is 50~250r/min；

The agitator treating time is 10-60 minutes in each dechlorination unit.

6. reducing the preparation method of magnesium hydroxide chlorinity as claimed in claim 5, which is characterized in that the chlorine removal system In, the series connection series of the dechlorination unit is 3~6 grades.

7. reducing the preparation method of magnesium hydroxide chlorinity as claimed in claim 6, which is characterized in that the hydrogen to be processed Magnesia is ground in advance before washing, and milling time is 5~20min；

The temperature of agitator treating process is 60~80 DEG C.

8. the preparation method as described in any one of claims 1 to 7 for reducing magnesium hydroxide chlorinity, which is characterized in that described Magnesium hydroxide to be processed preparation process are as follows:

Magnesium chloride solution and ammonium hydroxide are added drop-wise to together in the ammonium hydroxide added with magnesium hydroxide crystal seed-chloride buffer system, stirred Reaction, is made magnesium hydroxide to be processed.

9. reducing the preparation method of magnesium hydroxide chlorinity as claimed in claim 8, which is characterized in that the magnesium chloride is molten The molar concentration of liquid is 1-4moL/L；The concentration of ammonium hydroxide is 10-13.3mol/L；Magnesium chloride solution and ammonium hydroxide add molar ratio For 1:2-1:8；

The magnesium hydroxide seed load is the 10~40% of product quality.

10. reducing the preparation method of magnesium hydroxide chlorinity as claimed in claim 8, which is characterized in that be stirred to react process Temperature be 40~80 DEG C；

The speed of agitator being stirred to react is not less than 50r/min；

Being stirred to react the time is 10~40min.