CN1301215C - Technological process of preparing potassium nitrate and magnesium chloride - Google Patents

Abstract

The present invention discloses a technological process of preparing potassium nitrate and magnesium chloride. Powdery magnesite is added in nitric acid solution for a reaction; then, potassium chloride and returned coarse potassium nitrate are added and dissolved; an additive is added; after the operation of sedimentation with temperature preservation, filtration, cooling crystallization, centrifugal separation and dryness on the solution, agricultural potassium nitrate is obtained; after being mixed, mother solution I and mother solution III are concentrated by evaporation and crystallized by cooling for separating magnesium chloride hexahydrate crystals; after mother solution II is crystallized by cooling and centrifugally separated, the coarse potassium nitrate and the mother solution III are obtained. The present invention has the advantages of simple technology, convenient operation, energy saving, consumption reduction, full closed circulation of the whole technology, and no three waste.

Description

A kind of process for preparing potassium nitrate and magnesium chloride

1. Technical field:

The invention relates to a nitric acid conversion method for preparing potassium nitrate, in particular to the technical field of preparing potassium nitrate by using nitric acid, potassium chloride and magnesite as raw materials and producing magnesium chloride by-product.

2. Background technology:

Due to the scarcity of natural potassium nitrate resources on the earth, while the demand for potassium nitrate continues to grow, the technology of producing potassium nitrate has attracted widespread attention. Usually, people use potassium chloride and nitrate as raw materials to convert nitric acid. Potassium, among numerous technical routes of potassium nitrate production, the method of directly producing potassium nitrate with nitric acid as raw material has always been paid attention to by various countries.

In November 1963, Southwest Potash Company of the United States successfully developed a potassium nitrate production method that directly decomposed potassium chloride with nitric acid and produced chlorine by-product. restricted. At present, the law has gradually lost its competitiveness in the international arena.

In July 1969, Israel Haifa Company successfully developed potassium nitrate extraction method under low temperature conditions to produce potassium nitrate with potassium nitrate chloride. The package is used to decompose phosphate rock), the process is complex, the investment is huge, and the production cost is relatively high.

In 1990, AST Corporation of the United States developed the ISEP process. Potassium chloride and nitric acid solutions were used to enter an ISEP rotary ion exchange contactor equipped with ion exchange resins to continuously produce potassium nitrate solutions and hydrochloric acid solutions. The disadvantage is that the concentration of the product solution is Still low, high energy consumption, inconvenient storage and transportation of by-product hydrochloric acid.

Chinese patent ZL95115710.8 has proposed a kind of method with nitric acid, potassium chloride and magnesium oxide as raw material to produce potassium nitrate, although process is simple, investment is few. However, the process fails to achieve closed-circuit production, and the solution needs to be frozen to minus 10-15°C, which requires high energy consumption. At the same time, magnesium chloride is not recovered, and the magnesium chloride solution can only be discharged as waste, polluting the environment, and the utilization rate of raw materials is low.

3. Contents of the invention:

The purpose of the present invention is to provide a kind of technology that can overcome above-mentioned technological deficiency, and technology is simple, easy to operate, energy-conserving and consumption-reducing, can realize the technological process full-closed cycle production, the processing method of producing potassium nitrate and magnesium chloride without three wastes generation.

The main contents and technical features of the present invention are: under the condition of stirring, adding magnesite to the nitric acid solution with a concentration of 15-45%, controlling the reaction temperature to be 70-90°C, adjusting the pH value of the solution to 6.5-7, and then Add potassium chloride and crude potassium nitrate under constant stirring, and keep the reaction temperature at 100-115°C; then add potassium hydroxide or calcium hydroxide to the reactor, adjust the pH value of the solution to about 6.5, and then add calcium chloride or chlorine Dilute barium and keep the solution temperature at about 100°C for 6-8 hours and then filter; cool the filtered solution to 0°C-30°C to crystallize potassium nitrate, obtain potassium nitrate after centrifugation and drying, and separate potassium nitrate The solution is the mother liquor I, and the mother liquor I is evaporated and concentrated to a water content of about 45-60%, and then cooled to 50-80° C. to crystallize and separate to obtain magnesium chloride hexahydrate crystals; the solution after separating the magnesium chloride hexahydrate crystals is mother liquor II, and Cool the mother liquor II to 0-20°C, crystallize and centrifuge to obtain crude potassium nitrate, return the crude potassium nitrate to participate in the circulation reaction with potassium chloride, and the solution after separating the crude potassium nitrate is the mother liquor III, and return the mother liquor III together with the mother liquor I recycle.

The content of the present invention is described in detail below:

Take potassium chloride, nitric acid, magnesite (MgO) as raw material reaction to produce the total chemical reaction equation of potassium nitrate and magnesium chloride as follows:

…………(1)

Magnesite is obtained by calcining and decomposing magnesite at a temperature of 800-850 degrees. The main component is magnesium oxide. my country's magnesite is very rich, and most of it is concentrated in the three northeastern provinces and Shandong province.

In the nitric acid solution, slowly add powdered magnesite, stir continuously to dissolve, the nitric acid and magnesite react to generate Mg(NO ₃ ) ₂ , and release a lot of heat at the same time.

Then add potassium chloride and stir continuously to dissolve. In order to convert more potassium ions in the solution into potassium nitrate crystals, the Mg(NO ₃ ) ₂ in the solution is usually excessive. Because magnesite and potassium chloride contain certain impurities, in order to obtain high-quality potassium nitrate and magnesium chloride, the impurities in the solution must be removed. The solubility decreased significantly, so a large number of potassium nitrate crystals were precipitated. The mother liquor I for separating potassium nitrate crystals mainly contains MgCl ₂ in addition to a small amount of KNO ₃ .

Since the solubility of magnesium chloride varies little with temperature, the mother liquor I can be evaporated and concentrated to a certain concentration, and then the concentrated solution is cooled to 50-80°C to crystallize magnesium chloride hexahydrate crystals, and centrifuged at 50-80°C Magnesium chloride hexahydrate crystals.

Cool the mother liquor II from which magnesium chloride hexahydrate crystals are separated to 0-20°C, then potassium nitrate crystals will be crystallized, and the precipitated potassium nitrate crystals will contain a certain amount of magnesium salt, so the obtained potassium nitrate is called crude potassium nitrate. The crude potassium nitrate is returned and added to the magnesium nitrate solution together with potassium chloride to participate in the reaction. The mother liquor III after separating the crude potassium nitrate returns to participate in the circulation reaction together with the mother liquor I.

The specific process is as follows:

1. Neutralization reaction: In the reactor, first add nitric acid solution, and under constant stirring, add an appropriate amount of water according to the concentration of the nitric acid solution to adjust the concentration of the nitric acid solution to be 15% to 45%. Under the condition of continuous stirring, add magnesite to the nitric acid solution, and control the feeding speed so that the reaction temperature is 70-90°C. Adjust the pH value of the solution to 6.5-7, and react to prepare a magnesium nitrate solution.

2. Dissolution reaction: in the reactor, continue to add potassium chloride to the magnesium nitrate solution, the addition ratio (molar ratio) is, potassium chloride: nitric acid=1: (1～1.5), constantly stirring and dissolving, and simultaneously adding back The crude potassium nitrate is continuously stirred and dissolved, the amount of crude potassium nitrate added does not exceed the amount of potassium chloride, and the reaction temperature is kept at 100-115°C.

3. Impurity removal treatment: Add a certain amount of potassium hydroxide or calcium hydroxide to the reactor to adjust the pH value of the solution so that the pH value of the solution is around 6.5, remove iron ions in the solution, and improve the whiteness of the product. Add calcium chloride or barium chloride to remove sulfate radicals in the solution. In order to speed up the sedimentation rate of calcium sulfate, the temperature of the solution must be kept at about 100°C. Keep the solution warm and settling for 6-8 hours, and then send it to a filter press to filter to remove impurities.

4. Potassium nitrate separation and drying: the solution after filtering to remove impurities is sent to a cooling crystallizer to cool to 0°C to 30°C, and the solution crystallizes to precipitate a large amount of potassium nitrate crystals. The potassium nitrate feed liquid is sent to a centrifuge for centrifugation to obtain potassium nitrate. When the centrifuge is centrifuged, the potassium nitrate crystals are washed with a small amount of clear water, and the mother liquor I is sent to the evaporator; the separated potassium nitrate is sent to a drier to dry and become agricultural potassium nitrate.

5. Separation of magnesium chloride: mix the mother liquor I with the returned mother liquor III, then evaporate and concentrate to a concentration of about 45-60% water content, then cool the concentrated solution to 50-80°C, and crystallize MgCl ₂ ·6H ₂ O crystals, Centrifuge or filter the feed liquid to obtain magnesium chloride hexahydrate crystals. When separating, wash the magnesium chloride hexahydrate crystal with a small amount of clear water, and the solution after separating the magnesium chloride body crystal is mother liquor II.

6. Separation of crude potassium nitrate: Cool the mother liquor II from the separated magnesium chloride hexahydrate crystals to 0-20°C in the cooling crystallizer, then crystallize and precipitate potassium nitrate crystals containing a small amount of magnesium salt, so the obtained potassium nitrate is called crude potassium nitrate . The crude potassium nitrate feed liquid is sent to a centrifuge for centrifugation to obtain crude potassium nitrate, and the crude potassium nitrate is returned to participate in the circulation reaction together with potassium chloride. The mother liquor III that separates crude potassium nitrate returns and circulates with mother liquor I.

The main equipment required by the process of the present invention are reactors, filters, cooling crystallizers, evaporators, dryers, centrifuges, pumps and the like.

The present invention has the following advantages:

1. At present, the main method of producing potassium nitrate in my country is to use ammonium nitrate and potassium chloride as raw materials, using double decomposition process and ion exchange process. Due to the strict control of the country on ammonium nitrate, which is a hazardous explosive, the price of ammonium nitrate is tight High, transportation is also restricted, seriously restricting the production of potassium nitrate. And the present invention adopts nitric acid, potassium chloride and magnesite as raw materials to produce agricultural potassium nitrate and magnesium chloride hexahydrate, not only the sources of raw materials are very wide, but also the price is low, and the cost of raw materials is significantly reduced, which provides a good way for the production of potassium nitrate Raw material route.

2. According to the different characteristics of the solubility of potassium nitrate and magnesium chloride, the present invention realizes the separation of potassium nitrate and magnesium chloride through cooling, evaporation and other technological operations, and the crystallization rate of the product is high, and the potassium ions in the solution are converted into the crystallization of potassium nitrate crystals The rate can reach 95%. Moreover, the quality of the products potassium nitrate and magnesium chloride hexahydrate meets the requirements. Potassium nitrate contains _K2O4 4.0-44.5% (dry basis), N 13.5-13.65 (dry basis), C 10.3-1.5%, water-insoluble matter 0.50-0.85%, and water repellent 0.2-1.0%. Magnesium chloride hexahydrate contains 43.0-45.5% of MgCl ₂ , which meets the national standard of GB8453-87.

3. The whole process of the present invention is produced in a fully closed closed-circuit cycle. All mother liquor and crude potassium nitrate are circulated to participate in the reaction, and are finally converted into products. Therefore, raw materials can be completely converted into products, and the utilization rate of raw materials is high. Based on the production of 1 ton of agricultural potassium nitrate, the consumption quota is 0.66 tons of nitric acid (converted into 100%), 0.77 tons of potassium chloride (KCl≥98%), and 0.26 tons of magnesite (MgO≥85%). Magnesium chloride hydrochloride is 0.9 tons, and the production cost is low.

4. The present invention adopts adding potassium hydroxide and calcium chloride to react with ferric ions and sulfate ions in the solution, and removes ferric ions, sulfate radicals and other impurities in the solution by sedimentation and filtration, thereby improving the quality of the product and white package Spend. At the same time, due to the impurity removal treatment, the quality of raw materials used in the present invention is not limited, and poor raw materials can also be used for production.

5. The whole process of the present invention is fully enclosed and closed-circuit cycle production, the process operation is safe, simple and convenient, without any "three wastes" produced, and without any pollution to the environment. It is beneficial to realize the continuous operation of the production device.

6. The by-product magnesium chloride produced by the present invention is a very important chemical raw material, which is widely used in metallurgy, building materials, textiles, food, medicine, refractory materials and other industries, and is also used for deicing and snow removal on roads.

4. Description of drawings:

Fig. 1 is a block diagram of the process flow of the present invention.

5. Implementation method:

As can be seen from Fig. 1, the process flow of the present invention is: first add nitric acid solution in the reactor, then add powdery magnesite, constantly stir and dissolve, then add potassium chloride and thick potassium nitrate, constantly stir and dissolve, then add hydrogen Potassium oxide and other additives, the solution is kept warm and settled; then the solution is sent to a filter to filter and remove impurities, and then sent to a cooling crystallizer to cool and crystallize the solution to precipitate potassium nitrate, and then sent to a centrifuge for centrifugal separation to obtain potassium nitrate, and the separated potassium nitrate was sent to the dryer for drying That is agricultural potassium nitrate; the mother liquor I and the returned mother liquor III are sent to the evaporator for mixing, after evaporation and concentration, then cooled and crystallized to precipitate magnesium chloride crystals, and then sent to a centrifuge (or filter press) for separation to obtain crystalline magnesium chloride, and the mother liquor II is sent to be cooled and crystallized The crude potassium nitrate crystals containing a small amount of magnesium salt are separated out by cooling and crystallizing in the reactor, and the crude potassium nitrate and mother liquor III are obtained after being sent to the centrifuge for centrifugation, and the crude potassium nitrate returns to the reactor to participate in recycling with potassium chloride; the mother liquor III returns to the evaporator and Mother liquor I is mixed and recycled.

Embodiment 1: in the nitric acid solution of 100 kilograms of 33%, gradually slowly add powdery magnesite (MgO≥85%. Free CaO≤2%, loss on ignition≤8%. Following quality is all the same), constantly stirring reaction , keep the reaction temperature at 90° C., and adjust the pH value of the solution to 6.5. Then add 40 kilograms of potassium chloride (KCl≥98%, the following mass is the same), stir and dissolve continuously, keep the reaction temperature at 115° C., add a small amount of potassium hydroxide solution and an appropriate amount of calcium chloride, and adjust the pH value of the solution to 6.5. Keep the temperature at 100°C, let the solution settle for 6 hours, filter the solution to remove impurities, then cool the solution down to 5°C, obtain potassium nitrate by centrifugation, wash potassium nitrate crystals with a small amount of water, separate potassium nitrate and send it to a dryer for drying , to obtain 50.5 kg of potassium nitrate for agricultural use, containing 44.5% of K ₂ O (dry basis), 13.5% of N (dry basis), 10.3% of C, 0.50% of water-insoluble matter, and 0.2% of water content. After the separated mother liquor I was evaporated and concentrated to a water content of 45%, cooled to 80°C, magnesium chloride hexahydrate was crystallized, and the isolated magnesium chloride hexahydrate contained 45.2% MgCl ₂ . Separate the mother liquor II and continue cooling to 0°C, crystallize crude potassium nitrate, and separate the crude potassium nitrate and mother liquor III.

Embodiment 2: In 90 kilograms of 45% nitric acid solution, add powdery magnesite, continuously stir and react, keep the reaction temperature at 70° C., and adjust the pH value of the solution to 7. Then add 35 kilograms of potassium chloride, stir and dissolve continuously, then add the crude potassium nitrate obtained in Example 1, stir and dissolve, keep the reaction temperature at 100° C., add a small amount of calcium hydroxide, and adjust the pH value of the solution to 6.5. Keep the temperature at 100°C, let the solution settle for 8 hours, filter the solution to remove impurities, then cool the solution down to 25°C, obtain potassium nitrate by centrifugation, wash potassium nitrate crystals with a small amount of water, separate potassium nitrate and send it to a dryer for drying , to obtain agricultural potassium nitrate, containing K ₂ O 44.3% (dry basis), N 13.65% (dry basis), C 10.5%, water insoluble 0.56%, moisture 0.25%. The separated mother liquor I was mixed with the mother liquor III obtained in Example 1, evaporated and concentrated to a water content of 50%, cooled to 70°C, and magnesium chloride hexahydrate was crystallized, and the isolated magnesium chloride hexahydrate contained 43.8% MgCl ₂ . Separate the mother liquor II and continue cooling to 15°C, and crystallize crude potassium nitrate. Separate crude potassium nitrate and mother liquor III.

Embodiment 3: In 260 kilograms of 15% nitric acid solution, add powdery magnesite, continuously stir and react, keep the reaction temperature at 90° C., and adjust the pH value of the solution to 7. Then add 40 kilograms of Potassium Chloride, continue stirring and dissolving, then add the crude potassium nitrate obtained in Example 2, stir and dissolve, keep the reaction temperature at 100° C., add a small amount of potassium hydroxide solution, and adjust the pH value of the solution to 6.5. Keep the temperature at 100°C, let the solution settle for 8 hours, filter the solution to remove impurities, then cool the solution down to 0°C, centrifuge to obtain potassium nitrate, separate the potassium nitrate and send it to a dryer for drying to obtain agricultural potassium nitrate, containing K ₂ O 44.6% (dry basis), N 13.6% (dry basis), Cl 0.2%, water insoluble 0.46%, water 0.22%. The isolated mother liquor I was mixed with the mother liquor III obtained in Example 2, evaporated and concentrated to a water content of 60%, cooled to 50°C, and magnesium chloride hexahydrate was crystallized, and the isolated magnesium chloride hexahydrate contained 45.0% MgCl ₂ . Separate the mother liquor II and continue to cool to 5 ° C, and crystallize crude potassium nitrate. Separate crude potassium nitrate and mother liquor III.

Claims (1)

1, a kind of processing method of producing saltpetre and magnesium chloride is characterized in that may further comprise the steps:

1. under agitation condition, add magnesia in 15～45% salpeter solutions, control reaction temperature is 70～90 ℃, adjusts pH value of solution value to 6.5～7;

2. add Repone K again in solution, the Repone K of adding and the mol ratio of nitric acid are 1: (1～1.5), add the thick saltpetre that is no more than the Repone K amount again, continuous stirring and dissolving, keeping temperature of reaction is 100～115 ℃;

3. in solution, add potassium hydroxide or calcium hydroxide, about regulator solution pH value to 6.5, add calcium chloride again and keep solution temperature at 6～8 hours after-filtration of 100 ℃ of left and right sides sedimentations;

4. the solution after will filtering gets saltpetre after being cooled to 0 ℃～30 ℃ crystallizations, centrifugation, drying, and the solution behind the separation saltpetre is mother liquor I;

5. with mother liquor I with after the mother liquor III that returns mixes, evaporation concentration is 45～60% concentration to water content, be cooled to 50～80 ℃ of crystallizations again, separate the magnesium chloride hexahydrate crystal, the solution that separates behind the magnesium chloride hexahydrate crystal is mother liquor II;

6. mother liquor II is cooled to 0～20 ℃ again, crystallization, centrifugation get thick saltpetre, participate in circulating reaction with Repone K in returning thick saltpetre 2., separate that solution is mother liquor III behind the thick saltpetre, and mother liquor III returns with mother liquor I and recycles.

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