CN110877914A - Method for preparing high-purity high-white calcium carbonate by mineralizing and fixing carbon dioxide with phosphogypsum - Google Patents

Abstract

The invention relates to a method for preparing high-purity and high-white calcium carbonate by using phosphogypsum as a raw material to mineralize and fix carbon dioxide. The carbon dioxide is then mineralized and fixed under pressurized conditions. On the one hand, the carbon dioxide greenhouse gas can be converted into high-quality calcium carbonate products in a very short period of time, and the huge pressure of carbon dioxide emission reduction in my country can be relieved. On the other hand, the green resource utilization of bulk industrial solid waste phosphogypsum can be realized. Storage pollution of solid waste phosphogypsum. The method of the invention can greatly improve the conversion rate and reaction rate of carbonation and the quality of product carbonation, not only the efficiency of phosphogypsum mineralization and fixing carbon dioxide is greatly increased, but also the economic benefits and industrial application prospects are also significantly improved, and the phosphogypsum is effectively promoted. Development of mineralized carbon dioxide fixation technology.

Description

A method for preparing high-purity high-white calcium carbonate by mineralizing and fixing carbon dioxide by phosphogypsum

technical field

The invention belongs to the technical field of room temperature gas emission reduction and bulk solid waste resource utilization, and particularly relates to a solid waste phosphogypsum as a raw material, which is used for reducing carbon dioxide emissions after efficient impurity removal, alleviating the greenhouse effect and producing high-quality carbonic acid. Calcium method.

Background technique

The environmental problem caused by carbon dioxide, a greenhouse gas, has become a common problem faced by the world, and has attracted more and more attention from all over the world. At present, China's CO ₂ emissions ranks first in the world, and it is difficult to change the current energy consumption structure in a short period of time. With the rapid development of China's economy, CO ₂ emissions are bound to continue to increase, and China will face a huge pressure on CO ₂ emission reduction. Therefore, a carbon dioxide emission reduction technology system with low R&D cost and low environmental risk is an urgent scientific and technological demand for my country to cope with climate change and solve my country's carbon dioxide emission problem.

The use of solid waste phosphogypsum rich in calcium resources to mineralize and fix carbon dioxide can not only convert carbon dioxide into calcium carbonate products and relieve the huge pressure of carbon dioxide emission reduction in my country, but also realize the resource utilization of solid waste phosphogypsum and alleviate the pollution of phosphogypsum. Stockpile contamination issues. However, due to the high impurity content in phosphogypsum, carbon dioxide reacts directly with phosphogypsum, not only is the phosphogypsum difficult to convert completely, but also the obtained calcium carbonate product has low purity and whiteness, and can only be used as a low value-added cement production raw material or a flue gas desulfurizer. , poor economic efficiency. We propose an efficient impurity removal method for phosphogypsum in patent CN201510029369.X, which can efficiently remove almost all impurities in phosphogypsum. Therefore, phosphogypsum removes impurities efficiently, and then demineralizes and fixes carbon dioxide, which can eliminate the influence of impurities on the conversion rate of carbonation reaction and the quality of calcium carbonate products.

The reaction process of phosphogypsum mineralization to fix carbon dioxide to prepare calcium carbonate is that phosphogypsum and carbon dioxide gas undergo carbonation reaction in an ammonia medium system to generate ammonium sulfate fertilizer and calcium carbonate products. The reaction mechanism is shown in Equation 1.

Phosphogypsum + CO ₂ + Ammonia Medium → Calcium Carbonate + Ammonium Sulfate (1)

Due to the normal pressure process conditions, the complete conversion of phosphogypsum requires a longer reaction time of more than 60 minutes. Due to the strong volatility of ammonia, a longer reaction time will inevitably increase the loss of raw material ammonia. In patents CN201410092500.2 and CN201310057123.4, a method for strengthening calcium-based solid waste mineralization and fixing carbon dioxide in ammonia medium is proposed. By appropriately increasing the reaction pressure, the dissolution and ionization of CO ₂ are strengthened, thereby significantly shortening the carbonation reaction time. , and improve the utilization rate of ammonia by inhibiting the decomposition of ammonium salts.

Another product in the process of phosphogypsum mineralization to fix _CO2 to prepare calcium carbonate is ammonium sulfate, which is currently low in price and fluctuates greatly, which makes it difficult for the direct carbonation process of phosphogypsum to achieve economic benefits. Therefore, it is necessary to improve the quality and added value of calcium carbonate produced. , to make up for the price difference caused by the lower price of ammonium sulfate, thereby reducing the overall process cost. The purified gypsum with low impurity content is obtained by using the phosphogypsum high-efficiency impurity removal method, and then the purified gypsum is used for carbonation reaction with carbon dioxide under pressurized conditions. On the one hand, high-quality calcium carbonate products can be obtained, and on the other hand, increasing the pressure can increase the reaction rate of carbonation and improve the processing capacity of fixed carbon dioxide. In addition, the conversion and reaction rate of the carbonation reaction will be further improved due to the elimination of impurities from the phosphogypsum feed end. At present, there is no literature report on the high-efficiency impurity removal of phosphogypsum, followed by mineralization and fixation of carbon dioxide under pressurized conditions, and the preparation of high-quality calcium carbonate in a short reaction time.

SUMMARY OF THE INVENTION

The purpose of the present invention is to realize carbon dioxide emission reduction and resource utilization of solid waste phosphogypsum, and provide a kind of phosphogypsum as raw material, after efficient impurity removal, mineralization and fixation of carbon dioxide under pressurized conditions, for greatly improving Quality of product carbonation and method of carbonation conversion and reaction rate.

The technical scheme of the present invention is as follows:

A method for preparing high-purity high-white calcium carbonate by using phosphogypsum as a raw material to mineralize and fix carbon dioxide provided by the invention comprises the following steps:

(1) Phosphogypsum screening pretreatment:

In order to make the impurity removal in phosphogypsum more sufficient, the phosphogypsum was subjected to 40 mesh sieve treatment;

(2) Efficient removal of impurities in phosphogypsum:

Weigh the phosphogypsum of a certain quality step (1), add it into a three-necked flask containing a certain amount of sulfuric acid solution with a mass concentration of 10 to 45%, add an organic solvent according to a certain mass ratio, and then put the three-necked flask into a constant temperature oil bath in and sealed. The reaction is carried out for 20 to 60 minutes at a stirring speed of 300 rpm and a certain reaction temperature. After the reaction, the slurry was transferred to a separatory funnel, shaken for 5 min, and left to stand for stratification. The upper layer was an organic phase containing impurities, and the lower layer was an aqueous sulfuric acid phase containing purified gypsum. The upper organic phase and the lower aqueous phase are separated, and the separated impurities and purified gypsum are obtained respectively through vacuum filtration and washing with deionized water. The obtained purified gypsum was dried in an oven at 60° C. for 12 hours to obtain a purified gypsum product with low impurity content.

(3) Pressurized carbonation of phosphogypsum and CO ₂ to prepare CaCO ₃ :

Firstly, a certain amount of deionized water is added with ammonia water with a concentration of 25%, thereby preparing a certain concentration of dilute ammonia solution; the prepared dilute ammonia water and the purified gypsum with low impurity content in step (2) are added to In the autoclave, install the autoclave and mix the purified gypsum and dilute ammonia water uniformly in the autoclave at a certain stirring speed, and set the slurry mixing and stirring time to 30min. Then carbon dioxide gas with a concentration of 99.9% was continuously introduced into the autoclave at a certain pressure, and the carbonation reaction started immediately, and the reaction residence time was set to 5-60 min. After the reaction was completed, a certain amount of sample slurry was taken out from the sampling port of the autoclave. The slurry is filtered, and the obtained filter cake is fully washed with deionized water, and then placed in an oven at 60 °C to dry to a constant quality to obtain a high-purity and high-white calcium carbonate product.

(4) Preferably, the organic solvent used in the step (2) is selected from one or more of dimethyl sulfoxide, cyclohexane, sulfonated kerosene, liquid paraffin, tributyl phosphate, gasoline, and benzene.

(5) Preferably, the mass ratio of the organic solvent used in the step (2) to the phosphogypsum is 5-0.5:1.

(6) Preferably, the reaction temperature of the step (2) for efficient impurity removal is 50-120°C.

(7) Preferably, the ratio of the dilute ammonia water in the step (3) to the purified gypsum with low impurity content in the step (2) is 4-1:1 according to a certain mass ratio.

(8) Preferably, the pressure of the carbon dioxide gas in the step (3) is 0.4-1.6 MPa.

The advantages of the method of the present invention are:

①The conversion rate is greatly increased: Through efficient impurity removal, the content of almost all impurities in phosphogypsum can be significantly reduced. When the purified gypsum with low impurity content is mineralized to fix carbon dioxide, the conversion rate can be increased from about 97% to more than 99%.

②The reaction rate is greatly improved: the pressurized carbonation reaction can greatly reduce the reaction time of carbonation from about 60 minutes to about 10 minutes.

③The quality of product calcium carbonate is greatly improved: due to the efficient removal of impurities, the purity of calcium carbonate products can be increased from about 86% to more than 99%, and the whiteness can be greatly increased from about 47% to more than 91%.

The beneficial effects of the invention are as follows: using the industrial waste phosphogypsum produced in the industrial production process of wet phosphoric acid as a raw material to obtain purified gypsum with low impurity content through an efficient impurity removal method, and then using the purified gypsum and carbon dioxide for carbonation under pressurized conditions reaction. On the one hand, it can convert carbon dioxide greenhouse gas into high-quality calcium carbonate products in a very short period of time, and relieve the huge pressure of carbon dioxide emission reduction in my country. On the other hand, it can realize the resource utilization of phosphogypsum and alleviate the solid waste phosphogypsum. stack pollution problem. The method of the invention can greatly improve the reaction rate of carbonation of phosphogypsum by increasing the pressure, thereby improving the mineralization and fixation capacity of carbon dioxide. The purity and whiteness of calcium carbonate products are significantly increased, the corresponding added value is higher, and the use is wider, which significantly improves the economical and industrial application prospects of phosphogypsum mineralization and fixed CO ₂ technology, and effectively promotes the development of phosphogypsum mineralization and fixed CO ₂ technology. .

Description of drawings

Fig. 1 is a kind of high-purity high-white calcium carbonate SEM image prepared from phosphogypsum pressurized mineralized carbon dioxide according to the present invention.

Fig. 2 is a kind of high-purity high-white calcium carbonate XRD pattern prepared from phosphogypsum pressurized mineralized carbon dioxide according to the present invention.

Detailed ways

The patent of the present invention is further described below in conjunction with the examples.

The phosphogypsum of a certain ammonium phosphate factory selected in this example has a dry content of calcium sulfate dihydrate of 92.35%, a whiteness of 50.67%, and a pH value of 2.0. The contents of impurities silicon, fluorine and phosphorus are 6.31%, 0.91% and 0.71% respectively. In addition, phosphogypsum also contains aluminum, iron, and trace amounts of magnesium, potassium, titanium, strontium, barium and other impurities.

The specific process is as follows:

(1) phosphogypsum pretreatment: take the phosphogypsum sample of 40 mesh sieves;

(2) Efficient removal of impurities in phosphogypsum:

Weigh the phosphogypsum of a certain quality step (1), join it in the there-necked flask containing the sulfuric acid solution of a certain amount of mass concentration 30%, then add the organic solvent tributyl phosphate according to the mass ratio of 2:1, then put the there-necked flask into the three-necked flask. into a constant temperature oil bath and seal. The reaction was carried out for 40 min at a stirring speed of 300 rpm and a reaction temperature of 90 °C. After the reaction, the slurry was transferred to a separatory funnel, shaken for 5 min, and left to stand for stratification. The upper layer was an organic phase containing impurities, and the lower layer was an aqueous sulfuric acid phase containing purified gypsum. The upper organic phase and the lower aqueous phase are separated, and the separated impurities and purified gypsum are obtained respectively through vacuum filtration and washing with deionized water. The obtained purified gypsum was dried in an oven at 60°C for 12 hours to obtain a purified gypsum product with low impurity content, wherein the content of main impurities silicon and phosphorus were reduced to 0.12% and 0.01% respectively, and the fluorine content was lower than the detection line.

(3) Pressurized carbonation of phosphogypsum and CO ₂ to prepare CaCO ₃ :

At first, a certain amount of deionized water is added with ammonia water with a concentration of 25%, thereby preparing a certain concentration of dilute ammonia water; Add the purified gypsum into the autoclave, install the autoclave and mix the purified gypsum and dilute ammonia water in the autoclave at a certain stirring speed, and set the slurry mixing time to 30min. Then, carbon dioxide gas with a concentration of 99.9% was continuously introduced into the autoclave at a reaction pressure of 0.8 MPa, and the carbonation reaction started immediately, and the reaction residence time was set to 15 min. After the reaction was completed, a certain amount of sample slurry was taken out from the sampling port of the autoclave. The slurry is filtered, and the obtained filter cake is fully washed with deionized water, and then placed in an oven at 60° C. to dry to constant quality to obtain a calcium carbonate product with a purity of 99.1% and a whiteness of 91.7%.

The patent of the present invention is further described above with the help of specific embodiments, but it should be understood that the specific description here should not be construed as a limitation on the essence and scope of the patent of the present invention. Various modifications made in the above-mentioned embodiments and the replacement of phosphogypsum with other gypsum raw materials belong to the scope of protection of the patent of the present invention.

Claims (1)

1. a method for preparing high-purity high-white calcium carbonate by phosphogypsum mineralization fixing carbon dioxide, comprising the following steps: (1) Phosphogypsum screening pretreatment: In order to make the impurity removal in phosphogypsum more sufficient, the phosphogypsum was subjected to 40 mesh sieve treatment; (2) Efficient removal of impurities in phosphogypsum: Weigh the phosphogypsum of a certain quality step (1), add it into a three-necked flask containing a certain amount of sulfuric acid solution with a mass concentration of 10 to 45%, add an organic solvent according to a certain mass ratio, and then put the three-necked flask into a constant temperature oil bath in and sealed. The reaction is carried out for 20 to 60 minutes at a stirring speed of 300 rpm and a certain reaction temperature. After the reaction, the slurry was transferred to a separatory funnel, shaken for 5 min, and left to stand for stratification. The upper layer was an organic phase containing impurities, and the lower layer was an aqueous sulfuric acid phase containing purified gypsum. The upper organic phase and the lower aqueous phase are separated, and the separated impurities and purified gypsum are obtained respectively through vacuum filtration and washing with deionized water. The obtained purified gypsum was dried in an oven at 60° C. for 12 hours to obtain a purified gypsum product with low impurity content. (3) Pressurized carbonation of phosphogypsum and CO ₂ to prepare CaCO ₃ : Firstly, a certain amount of deionized water is added with ammonia water with a concentration of 25%, thereby preparing a certain concentration of dilute ammonia solution; the prepared dilute ammonia water and the purified gypsum with low impurity content in step (2) are added to In the autoclave, install the autoclave and mix the purified gypsum and dilute ammonia water uniformly in the autoclave at a certain stirring speed, and set the slurry mixing and stirring time to 30min. Then carbon dioxide gas with a concentration of 99.9% was continuously introduced into the autoclave at a certain pressure, and the carbonation reaction started immediately, and the reaction residence time was set to 5-60 min. After the reaction was completed, a certain amount of sample slurry was taken out from the sampling port of the autoclave. The slurry is filtered, and the obtained filter cake is fully washed with deionized water, and then placed in an oven at 60 °C to dry to a constant quality to obtain a high-purity and high-white calcium carbonate product. (4) Preferably, the organic solvent used in the step (2) is selected from one or more of dimethyl sulfoxide, cyclohexane, sulfonated kerosene, liquid paraffin, tributyl phosphate, gasoline, and benzene. (5) Preferably, the mass ratio of the organic solvent used in the step (2) to the phosphogypsum is 5-0.5:1. (6) Preferably, the reaction temperature of the step (2) for efficient impurity removal is 50-120°C. (7) Preferably, the dilute ammonia water in step (3) and the purified gypsum with low impurity content in step (2) are in a mass ratio of 4:1 to 1:1 according to a certain mass ratio. (8) Preferably, the pressure of the carbon dioxide gas in the step (3) is 0.4-1.6 MPa.

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