CN100411988C - Calcium removal and purification method for industrial potassium chloride - Google Patents

Abstract

The invention discloses a calcium removal and purification method for industrial potassium chloride, which belongs to the field of inorganic chemical technology. The present invention proposes a method for decalcification and purification of industrial potassium chloride, which adopts the phase conversion method to remove calcium sulfate impurities in industrial potassium chloride step by step, first in a saturated chlorination process containing solid potassium chloride and solid calcium sulfate Calcium remover A is added to the potassium suspension solution to convert the calcium sulfate in the suspension solution into calcium precipitates with lower solubility but easily soluble in acids or complexes, so that sulfate ions enter the water and are removed by filtration; The obtained solid is added to the newly prepared saturated potassium chloride solution, and calcium remover B is added to selectively dissolve the calcium precipitate, so that calcium enters the solution and is removed by filtration, thereby achieving the purpose of calcium removal. The calcium removal process proposed by the present invention can reduce the calcium content in industrial potassium chloride from 2.0 to 15% to less than 1%, and the main content of potassium chloride is greater than 99%. The calcium removal method proposed by the present invention is also suitable for removing calcium sulfate impurities from other inorganic salt systems.

Description

Calcium removal and purification method for industrial potassium chloride

technical field

The invention relates to a new technology for removing calcium sulfate impurities from industrial potassium chloride, which belongs to the field of inorganic chemical technology.

Background technique

my country is a big agricultural country, and it is also a country seriously short of potassium fertilizer resources. In order to meet the needs of agricultural development, the country spends a large amount of foreign exchange to import potassium fertilizer from Israel and other countries every year (Wang Xu, Overview of the World Potash Fertilizer Market, Agricultural Materials Science and Technology, 2004, 1 , 36-37). Most of my country's potassium resources are concentrated in Chaerhan Salt Lake in Qinghai, with 145 million tons of potassium chloride on the table, accounting for 97% of the country's proven reserves (Tu Huaikui, On the distribution characteristics and development prospects of potassium resources in western China, Gansu Geology Journal, 2002, 1, 69-75). For this reason, the state invested a huge amount of money (2.585 billion yuan) to establish a potassium chloride production line with an annual output of 1 million tons in Qinghai Salt Lake, which was put into operation in the summer of 2004 and reached the standard, which greatly alleviated the current situation of domestic potash shortage.

The project uses the natural brine collected from the salt field to dry carnallite, and then uses the reverse flotation-cold crystallization process to prepare potassium chloride. In the reverse flotation-cold crystallization process, the sodium chloride entrained in carnallite is first removed by flotation reagents, and then magnesium chloride is selectively dissolved by adding water, and potassium chloride product is obtained after centrifugal separation and drying. This project cleverly solved the separation problem of sodium chloride and potassium chloride by using flotation technology, and opened up a new way for the large-scale utilization of potassium resources in salt lakes. In the above process, potassium chloride is always in a saturated state and mostly exists in solid form. Present problem is: the brine that adopts from salt lake generally all contains more calcium sulfate impurity, and calcium content has the tendency that increases gradually, utilizes existing technology to still can't effectively remove, causes the calcium sulfate impurity content in the industrial potassium chloride to be always on the rise. The scope of 2.0～15% remains high, and the purity of potassium chloride product is mostly lower than 95%, and it is difficult to compete with imported high-purity products (potassium chloride content greater than 98%) on quality and price. Therefore, the problem of calcium removal and purification of industrial potassium chloride has become a major technical problem that needs to be solved urgently.

In the field of inorganic chemical industry, calcium removal from products is a relatively common technical problem, but most of the calcium in the systems involved exists in a soluble form. People generally adopt the method of adding a precipitating agent (such as sulfate, carbonate, oxalate, etc. to precipitate the calcium in the solution in the form of precipitation, and then remove it through solid-liquid separation (Cheng Fangqin, Li Hua, Tianyuanchun, salt lake brine purification and impurity removal) Experimental research on Shanxi University Journal (Natural Science Edition), 2004, 274(387-391)); Yuan Rongzheng, Chen Xi, Zhu Liping, Zhang Fangjun, Process control of mixed acid nitrate phosphate fertilizer decalcification process, Phosphate Fertilizer and Compound Fertilizer, 2001, 16 (6), 41-43). If calcium exists in an insoluble solid state (such as calcium sulfate, calcium carbonate) and the main product is insoluble in acid, adding inorganic acid (hydrochloric acid, nitric acid) can also effectively remove calcium impurities (Yin Zhong, Zhao Xiaodong, Calcium sulfate in hydrochloric acid and chlorination Solubility in aqueous sodium solution, Oilfield Chemistry, 1994, 11(4), 345-347). But for the potassium chloride-calcium sulfate system involved in the present invention, potassium chloride is very soluble in water, and the chemical properties of calcium sulfate are very stable, and it is difficult to dissolve in water under normal temperature conditions, and the solubility in acid/alkali It is also very limited, resulting in a significant increase in the difficulty of decalcification, and it is difficult to directly apply the existing decalcification methods. The coarse separation of potassium chloride and calcium sulfate can also be realized to a certain extent by utilizing the difference in specific gravity between potassium chloride and calcium sulfate, but it is difficult to reduce the content of calcium sulfate to below 2%. Therefore, how to effectively remove calcium sulfate impurities from potassium chloride has become an unsolved technical problem at home and abroad, and is also the key to restricting the quality of my country's industrial potassium chloride.

Contents of the invention

The purpose of this invention is to provide a new method that can remove calcium sulfate from potassium chloride, without changing the existing production process and process conditions, it can be achieved by adding cheap and easy-to-obtain calcium-removing reagents step by step. Ideal decalcification effect. Using the method of the invention can reduce the content of calcium sulfate in industrial potassium chloride from 2 to 15% to less than 1%, and the content of potassium chloride is greater than 99%. The invention provides a practical new method for the decalcification and purification of the existing industrial potassium chloride in my country, and the technology can also be used for removing calcium sulfate impurities from other soluble inorganic salt systems.

Technical scheme of the present invention is as follows:

A method for decalcifying and purifying industrial potassium chloride, characterized in that: the method adopts a phase transformation method to remove calcium sulfate impurities in industrial potassium chloride step by step, firstly, in the environment containing solid potassium chloride and solid calcium sulfate Add calcium remover A to the saturated potassium chloride suspension solution to convert the calcium sulfate in the suspension solution into calcium precipitates with lower solubility but easily soluble in acids or complexes, so that sulfate ions enter the water and pass through the filtration method Remove; then add the filtered solid to the newly prepared saturated potassium chloride solution, add calcium remover B to selectively dissolve the calcium precipitate, make the calcium enter the solution and remove it by filtration, thereby achieving the purpose of calcium removal;

The decalcifying agent A is an inorganic soluble carbonate or soluble oxalate, wherein the weight ratio of the decalcifying agent A to calcium sulfate in the suspension solution is 0.75-2:1;

The decalcifying agent B is hydrochloric acid or nitric acid, or a complexing agent that can complex with calcium to accelerate the dissolution of calcium precipitates, wherein the weight ratio of decalcifying agent B to calcium sulfate in the suspension solution is 0.5-3 : 1.

In the present invention, the inorganic soluble carbonate is preferably potassium carbonate, sodium carbonate, ammonium carbonate or ammonium bicarbonate.

In the present invention, the soluble oxalate is preferably sodium oxalate, potassium oxalate or ammonium oxalate.

In the present invention, the complexing agent capable of complexing with calcium and accelerating the dissolution of calcium precipitates is preferably ammonium chloride and ethylenediaminetetraacetic acid.

The calcium-removing reagents used in the new technology for decalcification and purification proposed by the present invention are cheap and easy-to-obtain conventional chemical products. When adopting the technology of the present invention to process potassium chloride, the reagent cost required for every 1 percent reduction of calcium sulfate content in per ton of potassium chloride is less than 30 yuan, and its selling price can be increased by 60 yuan for every 1 percent reduction of calcium sulfate content Above, the economic benefits are very significant. The calcium removal method proposed by the present invention is also suitable for removing calcium sulfate from other soluble inorganic salts. Similar work has not been reported at home and abroad.

Detailed ways

The present invention is realized through the following technical scheme of phase transformation-step-by-step removal: first, use carbonate or oxalate to carry out phase transformation, so that calcium sulfate is converted into calcium carbonate or calcium oxalate, and the sulfate radical enters the solution and is removed by filtration , and then add an appropriate amount of acid or complexing agent to selectively dissolve calcium salts in a saturated potassium chloride system containing calcium carbonate or calcium oxalate, so that calcium ions enter the solution and are removed by filtration. The operation steps are carried out in the following order:

(1) get the saturated potassium chloride suspension solution of industrial potassium chloride production site as experimental raw material, and solid potassium chloride content is 20～60% in the raw material, and solid calcium sulfate content is 2～15%;

(2) Add decalcifying agent A (preferably inorganic soluble carbonate or soluble oxalate) to the above system, wherein the weight ratio of decalcifying agent A to calcium sulfate is 0.75～2:1, stir for 1.0 hour to dissolve Calcium sulfate is converted to calcium carbonate or calcium oxalate;

(3) filter and remove sulfate radical in the solution;

(4) Disperse the filter cake in newly prepared saturated potassium chloride solution, then add decalcifying agent B (preferably hydrochloric acid, nitric acid, ammonium chloride, ethylenediaminetetraacetic acid), the weight ratio of decalcifying agent B to calcium sulfate The ratio is 0.5～3:1, stirring at room temperature for 0.5 hours can completely dissolve the calcium salt;

(5) filter and remove calcium ions in the solution, then dry at 105°C for 4 hours to obtain a product with a calcium sulfate content of less than 1% and a potassium chloride purity greater than 99%.

Specific examples are as follows:

Example 1

Adopt 100kg to be taken from the saturated potassium chloride suspension that contains 20% solid potassium chloride and 2% solid calcium sulfate from the production site of potassium chloride as experimental raw material, add 0.8kg salt of wormwood in the raw material, stir (150 rev/mins) Filter after 30 minutes; add the filter cake to 100 liters of saturated potassium chloride solution, stir (150 rpm) for 10 minutes, add 1.0 kg of 20% hydrochloric acid, continue stirring (150 rpm) for 30 minutes, and filter. The filter cake was dried at 105°C for 4 hours to obtain a potassium chloride product with a potassium chloride content of 99.8% and a calcium sulfate content of 0.2%.

Example 2

The saturated potassium chloride suspension that adopts 100kg to get from potassium chloride production site and contain 60% solid potassium chloride and 15% solid calcium sulfate is experimental raw material, adds 9kg sodium carbonate in raw material, stirs (150 revs/min) 30 Filter after 10 minutes; filter cake is added 100 liters of saturated potassium chloride solutions, stir (150 rev/min) and add 5.0kg 20% hydrochloric acid after 10 minutes, continue to stir (150 rev/min) 30 minutes, filter. The filter cake was dried at 105°C for 4 hours to obtain a potassium chloride product with a potassium chloride content of 99.0% and a calcium sulfate content of 1.0%.

Example 3

Adopt 100kg to be taken from the saturated potassium chloride suspension that contains 40% solid potassium chloride and 5% solid calcium sulfate from the production site of potassium chloride as experimental raw material, add 1.5kg ammonium carbonate in the raw material, stir (150 rev/mins) Filter after 30 minutes; add the filter cake to 100 liters of saturated potassium chloride solution, stir (150 rpm) for 10 minutes, add 5kg20% nitric acid, continue stirring (150 rpm) for 30 minutes, and filter. The filter cake was dried at 105°C for 4 hours to obtain a potassium chloride product with a potassium chloride content of 99.2% and a calcium sulfate content of 0.8%.

Example 4

Adopt 100kg to be taken from the saturated potassium chloride suspension that contains 40% solid potassium chloride and 10% solid calcium sulfate from the production site of potassium chloride as experimental raw material, add 3.5kg ammonium bicarbonate in raw material, stir (150 rev/mins) ) filter after 30 minutes; filter cake was added 100 liters of saturated potassium chloride solution, stirred (150 revs/min) and added 6.0kg 20% hydrochloric acid after 10 minutes, continued to stir (150 revs/min) 30 minutes, filtered. The filter cake was dried at 105°C for 4 hours to obtain a potassium chloride product with a potassium chloride content of 99.4% and a calcium sulfate content of 0.6%.

Example 5

Adopt 100kg to be taken from the saturated potassium chloride suspension that contains 40% solid potassium chloride and 5% solid calcium sulfate from the production site of potassium chloride as experimental raw material, add 2.5kg potassium oxalate in the raw material, stir (150 rpm) Filter after 30 minutes; add filter cake to 100 liters of saturated potassium chloride solution, add 5kg 20% nitric acid after stirring (150 rpm) for 10 minutes, continue stirring (150 rpm) for 30 minutes, and filter. The filter cake was dried at 105°C for 4 hours to obtain a potassium chloride product with a potassium chloride content of 99.5% and a calcium sulfate content of 0.5%.

Example 6

Adopt 100kg to be taken from the saturated potassium chloride suspension that contains 40% solid potassium chloride and 5% solid calcium sulfate from the production site of potassium chloride as experimental raw material, add 2.5kg sodium oxalate in the raw material, stir (150 rpm) Filter after 30 minutes; add the filter cake to 100 liters of saturated potassium chloride solution, stir (150 rpm) for 10 minutes, add 1 kg of ethylenediaminetetraacetic acid (EDTA), continue stirring (150 rpm) for 30 minutes, and filter . The filter cake was dried at 105°C for 4 hours to obtain a potassium chloride product with a potassium chloride content of 99.3% and a calcium sulfate content of 0.7%.

Example 7

Adopt 100kg to be taken from the saturated potassium chloride suspension that contains 40% solid potassium chloride and 5% solid calcium sulfate from the production site of potassium chloride as experimental raw material, add 2.5kg ammonium oxalate in the raw material, stir (150 rpm) Filter after 30 minutes; add the filter cake to 100 liters of saturated potassium chloride solution, stir (150 rpm) for 10 minutes, add 1 kg of ammonium chloride, continue stirring (150 rpm) for 30 minutes, and filter. The filter cake was dried at 105°C for 4 hours to obtain a potassium chloride product with a potassium chloride content of 99.1% and a calcium sulfate content of 0.9%.

Claims (7)

1. A method for decalcification and purification of industrial potassium chloride is characterized in that: the method adopts the phase conversion method to remove the calcium sulfate impurity in industrial potassium chloride step by step, at first containing solid potassium chloride and solid sulfuric acid Calcium remover A is added to the saturated potassium chloride suspension solution of calcium, and the calcium sulfate in the suspension solution is converted into calcium precipitates with lower solubility but easily soluble in acids or complexes, so that sulfate ions enter the water and pass through Remove by filtration; then add the filtered solid to the newly prepared saturated potassium chloride solution, add calcium remover B to selectively dissolve the calcium precipitate, let the calcium enter the solution and remove it by filtration, thereby achieving the purpose of calcium removal; Wherein the weight ratio of decalcifying agent A and calcium sulfate in the suspension solution is 0.4: 1, and described decalcification agent A adopts potassium carbonate; The weight ratio of decalcification agent B and calcium sulfate in the suspension solution is 0.1: 1. The calcium remover B uses hydrochloric acid. 2. A method for decalcification and purification of industrial potassium chloride is characterized in that: the method adopts the phase conversion method to remove the calcium sulfate impurity step by step in industrial potassium chloride, at first containing solid potassium chloride and solid sulfuric acid Calcium remover A is added to the saturated potassium chloride suspension solution of calcium, and the calcium sulfate in the suspension solution is converted into calcium precipitates with lower solubility but easily soluble in acids or complexes, so that sulfate ions enter the water and pass through Remove by filtration; then add the filtered solid to the newly prepared saturated potassium chloride solution, add calcium remover B to selectively dissolve the calcium precipitate, let the calcium enter the solution and remove it by filtration, thereby achieving the purpose of calcium removal; Wherein the weight ratio of decalcifying agent A and calcium sulfate in the suspension solution is 0.6: 1, and the described decalcification agent A adopts sodium carbonate; the weight ratio of decalcifying agent B and calcium sulfate in the suspension solution is 1: 15. The calcium remover B uses hydrochloric acid. 3. A method for decalcification and purification of industrial potassium chloride is characterized in that: the method adopts the phase conversion method to remove the calcium sulfate impurity in industrial potassium chloride step by step, at first containing solid potassium chloride and solid sulfuric acid Calcium remover A is added to the saturated potassium chloride suspension solution of calcium, and the calcium sulfate in the suspension solution is converted into calcium precipitates with lower solubility but easily soluble in acids or complexes, so that sulfate ions enter the water and pass through Remove by filtration; then add the filtered solid to the newly prepared saturated potassium chloride solution, add calcium remover B to selectively dissolve the calcium precipitate, let the calcium enter the solution and remove it by filtration, thereby achieving the purpose of calcium removal; Wherein the weight ratio of decalcifying agent A to calcium sulfate in the suspension solution is 0.3:1, and described decalcifying agent A adopts ammonium carbonate; wherein the weight ratio of decalcifying agent B to calcium sulfate in the suspension solution is 0.2 : 1, the described calcium remover B adopts nitric acid. 4. A method for decalcification and purification of industrial potassium chloride is characterized in that: the method adopts the phase conversion method to remove the calcium sulfate impurity in industrial potassium chloride step by step, at first containing solid potassium chloride and solid sulfuric acid Calcium remover A is added to the saturated potassium chloride suspension solution of calcium, and the calcium sulfate in the suspension solution is converted into calcium precipitates with lower solubility but easily soluble in acids or complexes, so that sulfate ions enter the water and pass through Remove by filtration; then add the filtered solid to the newly prepared saturated potassium chloride solution, add calcium remover B to selectively dissolve the calcium precipitate, let the calcium enter the solution and remove it by filtration, thereby achieving the purpose of calcium removal; Wherein the weight ratio of decalcifying agent A to calcium sulfate in the suspension solution is 0.35: 1, and the described decalcifying agent A adopts ammonium bicarbonate; the weight ratio of decalcifying agent B to calcium sulfate in the suspension solution is 0.12 : 1, the described calcium remover B adopts hydrochloric acid. 5. A method for decalcification and purification of industrial potassium chloride is characterized in that: the method adopts the phase conversion method to remove the calcium sulfate impurity in industrial potassium chloride step by step, at first containing solid potassium chloride and solid sulfuric acid Calcium remover A is added to the saturated potassium chloride suspension solution of calcium, and the calcium sulfate in the suspension solution is converted into calcium precipitates with lower solubility but easily soluble in acids or complexes, so that sulfate ions enter the water and pass through Remove by filtration; then add the filtered solid to the newly prepared saturated potassium chloride solution, add calcium remover B to selectively dissolve the calcium precipitate, let the calcium enter the solution and remove it by filtration, thereby achieving the purpose of calcium removal; Wherein the weight ratio of decalcifying agent A and calcium sulfate in the suspension solution is 0.5: 1, and described decalcification agent A adopts potassium oxalate; The weight ratio of decalcifying agent B and calcium sulfate in the suspension solution is 0.2: 1. The decalcifying agent B uses nitric acid. 6. A method for decalcification and purification of industrial potassium chloride is characterized in that: the method adopts the phase conversion method to remove the calcium sulfate impurity in industrial potassium chloride step by step, at first containing solid potassium chloride and solid sulfuric acid Calcium remover A is added to the saturated potassium chloride suspension solution of calcium, and the calcium sulfate in the suspension solution is converted into calcium precipitates with lower solubility but easily soluble in acids or complexes, so that sulfate ions enter the water and pass through Remove by filtration; then add the filtered solid to the newly prepared saturated potassium chloride solution, add calcium remover B to selectively dissolve the calcium precipitate, let the calcium enter the solution and remove it by filtration, thereby achieving the purpose of calcium removal; Wherein the weight ratio of decalcifying agent A and calcium sulfate in the suspension solution is 0.5: 1, and described decalcification agent A adopts sodium oxalate; The weight ratio of decalcifying agent B and calcium sulfate in the suspension solution is 0.2: 1. The decalcifying agent B uses ethylenediaminetetraacetic acid. 7. A method for decalcification and purification of industrial potassium chloride is characterized in that: the method adopts the phase conversion method to remove the calcium sulfate impurity in industrial potassium chloride step by step, at first containing solid potassium chloride and solid sulfuric acid Calcium remover A is added to the saturated potassium chloride suspension solution of calcium, and the calcium sulfate in the suspension solution is converted into calcium precipitates with lower solubility but easily soluble in acids or complexes, so that sulfate ions enter the water and pass through Remove by filtration; then add the filtered solid to the newly prepared saturated potassium chloride solution, add calcium remover B to selectively dissolve the calcium precipitate, let the calcium enter the solution and remove it by filtration, thereby achieving the purpose of calcium removal; Wherein the weight ratio of decalcifying agent A and calcium sulfate in the suspension solution is 0.5: 1, and described decalcifying agent A adopts ammonium oxalate; The weight ratio of decalcifying agent B and calcium sulfate in the suspension solution is 0.2: 1; the decalcifier B uses ammonium chloride.