Method for the management of phosphogypsum

Abstract

A method for the management of phosphogypsum consists in that a reactor (2) is charged with apatite and/or phosphorite phosphogypsum and with an aqueous or ammoniacal solution of ammonium carbonate and/or bicarbonate from a pre-reactor (1), at 1: (0.1-4) ratio of phosphogypsum to the aqueous or ammoniacal solution of ammonium carbonate and/or bicarbonate, the entire contents are stirred at 10 C. to 200 C. for at least 2 minutes, CO.sub.2 being released in the course of the process is directed to the pre-reactor (1), and the post-reaction mixture is directed to a filter (3) to obtain an aqueous ammonium sulphate solution, whereas the precipitate from the filter (3) is heat-treated, followed by dissolving it in nitric acid in a reactor (5), and the resultant suspension is filtered through a filter (6) to obtain an aqueous calcium nitrate solution, and CO.sub.2 being released in the reactor (5) is recirculated to the pre-reactor (1) wherein CO.sub.2 is reacted with ammonia in an aqueous solution to obtain the aqueous or ammoniacal solution of carbonate and/or bicarbonate which is directed to the reactor (2), with the process for obtaining the aqueous or ammoniacal solution of ammonium carbonate and/or bicarbonate being conducted until the pH 7-12 of the solution is reached.

Claims

1. A method for the management of phosphogypsum, characterized in that a reactor is charged with apatite and/or phosphorite phosphogypsum and with an aqueous or ammoniacal solution of ammonium carbonate and/or bicarbonate from a pre-reactor, at 1:(0.1-4) ratio of phosphogypsum to the aqueous or ammoniacal solution of ammonium carbonate and/or bicarbonate, the entire contents are stirred at 10 C. to 200 C. for at least 2 minutes, CO.sub.2 being released in the course of the process is directed to the pre-reactor, and the post-reaction mixture is directed to a filter to obtain an aqueous ammonium sulphate solution, whereas the precipitate from the filter is heat-treated, followed by dissolving it in nitric acid in a reactor, and the resultant suspension is filtered through a filter to obtain an aqueous calcium nitrate solution, and CO.sub.2 being released in the reactor is recirculated to the pre-reactor wherein CO.sub.2 is reacted with ammonia in an aqueous solution to obtain the aqueous or ammoniacal solution of carbonate and/or bicarbonate which is directed to the reactor, with the process for obtaining the aqueous or ammoniacal solution of ammonium carbonate and/or bicarbonate being conducted until the pH 7-12 of the solution is reached.

2. The method according to claim 1, characterized in that the reactor is charged with an aqueous or ammoniacal ammonium carbonate and/or bicarbonate solution of the total concentration of 10-50% by weight from the pre-reactor.

3. The method according to claim 1, characterized in that the contents of the reactor are sonicated for from 1 minute per every 10 minutes of the duration of the process to the continuous sonication.

4. The method according to claim 1, characterized in that the precipitate from the filter is heat-treated in an oven at 40-800 C.

5. The method according to claim 1, characterized in that residual gases from the heat treatment of the precipitate from the filter are directed to the pre-reactor.

6. The method according to claim 1, characterized in that the precipitate from the filter after the heat treatment is mixed with an aqueous solution of calcium nitrate before being dissolved in the reactor.

7. The method according to claim 1, characterized in that the filtrate from the filter is directed to a mixer wherein the pH value of the filtrate is adjusted to 3-7, whereas the residual CO.sub.2 being released is introduced to the pre-reactor.

Description

EXAMPLES

(1) The FIGURE shows schematically how to carry out the method according to the invention.

Example 1

(2) The reactor 2 equipped with 200 W ultrasonic system is charged with 8 kg of ammonium carbonate and bicarbonate solution of the total concentration of 35% by weight from the pre-reactor 1 and with 8 kg of apatite phosphogypsum. The weight ratio of phosphogypsum to the ammonium carbonate and bicarbonate solution is 1 to 1. The contents are stirred vigorously using a high-speed turbine mixer. The metathesis processthe reaction of calcium sulphate contained in phosphogypsum with carbonates contained in the ammonium carbonate and bicarbonate solution to obtain calcium carbonate and an aqueous solution of ammonium sulphate, is carried out at room temperature. The temperature and pH of the reaction mixture are measured in a continuous manner. In the course of the reaction, the pH of the reaction mixture decreases from 9.8 to 8.7. The reaction is conducted for 2 hours. In the entire course of the process, ultrasound is switched on for 5 minutes and then switched off for 10 minutes. CO.sub.2 forming in the course of the reaction of ammonium bicarbonate with calcium sulphate from phosphogypsum is directed to the pre-reactor 1. When the reaction has been completed, the mixture is directed to the filter 3.

(3) The filtrate from the filter 3 containing the aqueous ammonium sulphate solution is directed to the ammonium sulphate mixer 7 wherein the pH value of the solution is adjusted to 4-6, and the residual CO.sub.2 being released is introduced to the pre-reactor 1.

(4) The aqueous ammonium sulphate solution contains:

(5) TABLE-US-00001 ammoniacal nitrogen 9% by weight, ammonium sulphate 42% by weight, sulphates 28.3% by weight.

(6) Aqueous ammonium sulphate solution is a commercial product.

(7) The precipitate from the filter 3 contains the produced calcium carbonate and small amounts of non-reacted phosphogypsum. The precipitate is subjected to a treatment aimed at obtaining an aqueous calcium nitrate solution used as a fertiliser.

(8) According to the Regulation (EC) No. 2003/2003 on fertilisers, the ammoniacal nitrogen content in an aqueous calcium nitrate solution may not exceed 1% by weight. For this purpose, the residual amounts of water and ammonia are removed from the precipitate from filter 3 by a brief calcination of the obtained calcium carbonate precipitate for 5 minutes at 300 C. in the oven 4. Then, 7 kg of the precipitate after calcination is introduced to the chalk dissolution reactor 5. The dissolution is conducted with 55% nitric acid. 7.7 kg of the acid is introduced gradually over 1 hour while stirring the suspension vigorously with a high-speed gate stirrer. After introducing the whole amount of the acid, the reaction mixture is stirred vigorously for additional 1 hour. CO.sub.2 forming in the course of the reaction is directed to the pre-reactor 1. The post-reaction mixture is separated using the filter 6.

(9) The parameters of the obtained commercial aqueous calcium nitrate solution are as follows:

(10) TABLE-US-00002 nitrate nitrogen 9.5% by weight, ammoniacal nitrogen <1% by weight, calcium nitrate 55.6% by weight, free nitric acid 0.01% by weight, calcium expressed as CaO 19% by weight, pH 4.9

(11) Carbon dioxide being released in the apparatuses 1, 5, 7 is directed by bubbling to the bottom of the pre-reactor 1 packed with Bialecki rings. 25% ammonia water is fed periodically to the pre-reactor 1. The contents are stirred by closed circuit pumping. The internal temperature of the scrubber is kept below 35 C. by cooling the jacket with cold process water, if necessary. The pre-reaction is terminated at pH 10.1. The mixture of the ammonium carbonate and bicarbonate solution obtained in the pre-reactor 1 is directed to the reactor 2.

Example 2

(12) The reactor 2, equipped with 100 W ultrasonic system is charged with 8 kg of ammonium carbonate and bicarbonate solution of the total concentration of 30% by weight from the pre-reactor 1 and with 9.6 kg of phosphorite phosphogypsum. The weight ratio of phosphogypsum to the ammonium carbonate and bicarbonate solution is 1 to 0.8. The contents are stirred vigorously using a high-speed turbine mixer. The metathesis processthe reaction of calcium sulphate contained in phosphogypsum with carbonates contained in the ammonium carbonate and bicarbonate solution to obtain calcium carbonate and an aqueous solution of ammonium sulphate, is conducted at 30 C. The temperature and pH of the reaction mixture are measured in a continuous manner. In the course of the reaction, the pH of the reaction mixture decreases from 9.6 to 8.8. The reaction is conducted for 3 hours. In the entire course of the process, ultrasound is switched on for 10 minutes and then switched off for 10 minutes. CO.sub.2 forming in the course of the reaction of ammonium bicarbonate with calcium sulphate from phosphogypsum is directed to the pre-reactor 1. When the reaction has been completed, the mixture is directed to the filter 3.

(13) The filtrate from the filter 3 containing the aqueous ammonium sulphate solution is directed to the ammonium sulphate mixer 7 wherein the pH value of the solution is adjusted to 4-6, and the residual CO.sub.2 being released is introduced to the pre-reactor 1.

(14) The aqueous ammonium sulphate solution contains:

(15) TABLE-US-00003 ammoniacal nitrogen 8.5% by weight, ammonium sulphate 40% by weight, sulphates 27% by weight.

(16) Aqueous ammonium sulphate solution is a commercial product.

(17) The precipitate from the filter 3 contains the produced calcium carbonate and small amounts of non-reacted phosphogypsum. The precipitate is subjected to a treatment aimed at obtaining an aqueous calcium nitrate solution used as a fertiliser.

(18) According to the Regulation (EC) No. 2003/2003 on fertilisers, the ammoniacal nitrogen content in an aqueous calcium nitrate solution may not exceed 1% by weight, thus the residual amounts of water and ammonia are removed from the precipitate from the filter 3 by a brief calcination of the obtained calcium carbonate precipitate for 7 minutes at 200 C. in the oven 4. Then, 8.3 kg of the precipitate after calcination is introduced to the chalk dissolution reactor 5. The dissolution is conducted with 45% nitric acid. 8.5 kg of the acid is introduced gradually over 1.5 hours while stirring the suspension vigorously with a high-speed gate stirrer. After introducing the whole amount of the acid, the reaction mixture is stirred vigorously for additional 30 minutes. CO.sub.2 forming in the course of the reaction is directed to the pre-reactor 1. The post-reaction mixture is separated using the filter 6.

(19) The parameters of the obtained commercial aqueous calcium nitrate solution are as follows:

(20) TABLE-US-00004 nitrate nitrogen 8.5% by weight, ammoniacal nitrogen <1% by weight, calcium nitrate 50% by weight, free nitric acid 0.01% by weight calcium expressed as CaO 17.1% by weight, pH 5.2

(21) Carbon dioxide being released in the apparatuses 1, 5, 7 is directed by bubbling to the bottom of the pre-reactor 1 equipped with a gate stirrer. 23% ammonia water is fed periodically to the pre-reactor 1. The contents are stirred. The internal temperature of the pre-reactor 1 is kept below 35 C. by cooling the jacket with cold process water, if necessary. The pre-reaction is terminated at pH 10. The mixture of the ammonium carbonate and bicarbonate solution obtained in the pre-reactor 1 is directed to the reactor 2.

Example 3

(22) The reactor 2 equipped with 300 W ultrasonic system is charged with 9.6 kg of ammonium carbonate and bicarbonate solution of the total concentration of 25% by weight from the pre-reactor 1, and with 4 kg of apatite phosphogypsum and 4 kg of phosphorite phosphogypsum. The weight ratio of phosphogypsum to the ammonium carbonate and bicarbonate solution is 1 to 1.2. The contents are stirred vigorously using a high-speed turbine mixer.

(23) The metathesis processthe reaction of calcium sulphate contained in phosphogypsum with carbonates contained in the ammonium carbonate and bicarbonate solution to obtain calcium carbonate and an aqueous solution of ammonium sulphate is conducted at 35 C. The temperature and pH of the reaction mixture are measured in a continuous manner. In the course of the reaction, the pH of the reaction mixture decreases from 9.7 to 8.6. The reaction is conducted for 1 hour. In the entire course of the process, ultrasound is switched on. CO.sub.2 forming in the course of the reaction of ammonium bicarbonate with calcium sulphate from phosphogypsum is directed to the pre-reactor 1. When the reaction has been completed, the mixture is directed to the filter 3.

(24) The filtrate from the filter 3 containing the aqueous ammonium sulphate solution is directed to the ammonium sulphate mixer 7 wherein the pH value of the solution is adjusted to 4-6, and the residual CO.sub.2 being released is introduced to the pre-reactor 1.

(25) The aqueous ammonium sulphate solution contains:

(26) TABLE-US-00005 ammoniacal nitrogen 8.1% by weight, ammonium sulphate 38.1% by weight, sulphates 25.7% by weight.

(27) Aqueous ammonium sulphate solution is a commercial product.

(28) The precipitate from the filter 3 contains the produced calcium carbonate and small amounts of non-reacted phosphogypsum. The precipitate is subjected to a treatment aimed at obtaining an aqueous calcium nitrate solution used as a fertiliser.

(29) According to the Regulation (EC) No. 2003/2003 on fertilisers, the ammoniacal nitrogen content in an aqueous calcium nitrate solution may not exceed 1% by weight, thus the residual amounts of water and ammonia are removed from the precipitate from the filter 3 by a brief calcination of the obtained calcium carbonate precipitate for 2 minutes at 350 C. in the oven 4. Then, 6.8 kg of the precipitate after calcination are mixed with 4 kg of the aqueous calcium nitrate solution obtained as in the Example 2 to prepare a suspension, which is introduced to the chalk dissolution reactor 5. The dissolution is conducted with 50% nitric acid. 7.2 kg of the acid is introduced gradually over 45 minutes while stirring the suspension vigorously with a high-speed gate stirrer. After introducing the whole amount of the acid, the reaction mixture is stirred vigorously for additional 30 minutes. CO.sub.2 forming in the course of the reaction is directed to the pre-reactor 1. Post-reaction mixture is separated using the filter 6.

(30) The parameters of the obtained commercial aqueous calcium nitrate solution are as follows:

(31) TABLE-US-00006 nitrate nitrogen 8.2% by weight, ammoniacal nitrogen <1% by weight, calcium nitrate 48% by weight, free nitric acid 0.02% by weight, calcium expressed as CaO 16.4% by weight, pH 5.0

(32) Carbon dioxide being released in the apparatuses 1, 5, 7 is directed by bubbling to the bottom of the pre-reactor 1 packed with Bialecki rings. 20% ammonia water is fed periodically to the pre-reactor 1. The contents are stirred by closed circuit pumping. The internal temperature of the scrubber is kept below 35 C. by cooling the jacket with cold process water, if necessary. The pre-reaction is terminated at pH 9.9. The mixture of the ammonium carbonate and bicarbonate solution obtained in the pre-reactor 1 is directed to the reactor 2.