Extraction method of dicyandiamide waste residue

Abstract

The present invention provides a method for extracting dicyandiamide waste residue, belonging to the field of treatment of dicyandiamide waste residue. The extraction method is as follows: after taking the dicyandiamide waste residue to make a slurry, it is enriched by magnetic separation, and the effluent is collected. Then, it is treated by introducing carbon dioxide. After the obtained dicyandiamide waste residue slurry is washed in multiple stages, a primary washing filtrate and multiple filter cakes are obtained; after the pH value of the primary washing filtrate is adjusted to 8.8 - 9.2 with ammonia water, low-pressure evaporation concentration and polymerization of monocyanamide are carried out at 70 - 75 °C. The obtained high-concentration dicyandiamide solution is crystallized and filtered to obtain the dicyandiamide product; the multiple filter cakes are dissolved with hydrochloric acid and filtered to obtain a filtrate and a carbon product; after adding chitosan to the filtrate, ammonium carbonate is added to make a spherical calcium carbonate product. By using the extraction method of dicyandiamide waste residue of the present invention, dicyandiamide, carbon and calcium carbonate in the dicyandiamide waste residue can be effectively extracted and made into corresponding products for recycling.

Description

Technical Field

[0001] The present invention relates to the field of dicyandiamide waste residue treatment, and particularly to a method for extracting dicyandiamide from waste residue. Background Art

[0002] All along, as industrial waste residue, if dicyandiamide waste residue is exposed in the yard, due to the property that dicyandiamide is soluble in water, it adheres to the surface of the waste residue, and rainwater will wash the residual dicyandiamide into groundwater and rivers, causing water pollution. In the process of producing dicyandiamide products, the first problem to be solved is the high content of dicyandiamide in the dicyandiamide waste residue. In the process of industrial production, the higher the content of dicyandiamide in the waste residue, the greater the difficulty in treating the waste; when the content of dicyandiamide in the waste residue is extremely low, the waste residue can be used as a raw material for producing special cement to recycle the waste. However, at present, the waste residue contains a high content of dicyandiamide, so that the waste residue cannot be recycled.

[0003] In addition to dicyandiamide, the dicyandiamide waste residue mainly contains a large amount of calcium carbonate and a small amount of iron oxide, magnesium carbonate, carbon, calcium hydroxide, silicon dioxide and other substances. If these components can be comprehensively utilized, it is not only beneficial to the treatment of dicyandiamide waste residue and environmental protection, but also can recycle the components in the dicyandiamide waste residue, which helps enterprises improve their economic benefits. Summary of the Invention

[0004] In view of the above problems, the present invention provides a method for extracting dicyandiamide from waste residue.

[0005] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] A method for extracting dicyandiamide from waste residue, comprising the following steps:

[0007] S1. Pulping

[0008] After taking the dicyandiamide waste residue to make a slurry, it is magnetically separated and enriched, the effluent is collected, and then carbon dioxide is introduced for treatment to obtain a dicyandiamide waste residue slurry.

[0009] S2. Multi-stage washing

[0010] After the dicyandiamide waste residue slurry is multi-stage washed, a primary washing filtrate and multi-stage filter cakes are obtained.

[0011] S3. Product recovery

[0012] After the pH value of the primary washing filtrate is adjusted to 8.8 - 9.2 with ammonia water, low-pressure evaporation concentration and monocyanamide polymerization are carried out at 70 - 75 °C, and the obtained high-concentration dicyandiamide solution is crystallized and filtered to obtain dicyandiamide products;

[0013] The multi-stage filter cakes are dissolved with hydrochloric acid and filtered to obtain a filtrate and carbon products.

[0014] After adding chitosan to the filtrate, ammonium carbonate is added to produce spherical calcium carbonate products.

[0015] Furthermore, in step S1, the magnetic separation intensity for magnetic separation enrichment is 180 - 200 mT.

[0016] Furthermore, in step S2, the multi - stage washing includes the following steps:

[0017] Take the dicyandiamide waste residue slurry, after washing it through a primary cyclone and dewatering it with a primary vacuum belt filter, a primary filter cake and a primary washing filtrate are obtained;

[0018] After the primary filter cake is pulped with the tertiary washing filtrate, and then washed through a secondary cyclone and dewatered with a secondary vacuum belt filter, a secondary filter cake and a secondary washing filtrate are obtained; among them, the secondary washing filtrate is used as washing water to pulp the dicyandiamide waste residue in step S1;

[0019] After the secondary filter cake is pulped, and then washed through a tertiary cyclone and dewatered with a tertiary vacuum belt filter, a tertiary filter cake and a tertiary washing filtrate are obtained; among them, the tertiary washing filtrate is used as washing water to pulp the primary filter cake; the tertiary filter cake is the multi - stage filter cake.

[0020] Furthermore, in step S3, during the low - pressure evaporation concentration and the melamine polymerization process, after the evaporated steam is condensed, the obtained condensed water after evaporation is used as washing water to pulp the secondary filter cake.

[0021] Furthermore, in step S3, the concentration of the dicyandiamide solution is 12 - 14 wt%.

[0022] Furthermore, in step S3, before adding ammonium carbonate after adding chitosan, the concentration of chitosan in the obtained solution is 6 - 8 g / L.

[0023] Furthermore, in step S3, during the addition of ammonium carbonate, the temperature of the obtained system is 50 - 55 °C.

[0024] Furthermore, in step S3, during the addition of ammonium carbonate, the obtained system is stirred at a stirring speed of 400 - 450 r / min.

[0025] Furthermore, in step S3, ammonium carbonate uses an ammonium carbonate aqueous solution with a concentration of 18 - 22 wt%.

[0026] Furthermore, in step S1, the solid content in the slurry made from the dicyandiamide waste residue is 20 - 25 wt%.

[0027] The beneficial effects of the extraction method of the dicyandiamide waste residue of the present invention are:

[0028] By designing a reasonable process route, after removing iron oxide and part of magnesium carbonate from dicyandiamide waste residue through magnetic separation, carbon dioxide is introduced to convert calcium hydroxide in the dicyandiamide waste residue into calcium carbonate, and then through multi-stage washing, a primary washing filtrate containing a relatively high concentration of dicyandiamide and monocyanamide and a tertiary filter cake are obtained; after controlling the specific pH value of the primary washing filtrate with ammonia water, low-pressure evaporation concentration and monocyanamide polymerization are carried out to obtain dicyandiamide products, and by controlling the system at a specific pH value and the temperature of low-pressure evaporation concentration with ammonia water, the purity and recovery rate of dicyandiamide products can be effectively improved;

[0029] Meanwhile, after the tertiary filter cake is dissolved in hydrochloric acid and filtered to obtain carbon products, a specific amount of chitosan is added to the filtrate, and using chitosan and magnesium chloride contained in the filtrate as crystal form control agents together, calcium chloride is controlled to be converted into spherical calcium carbonate products under the action of ammonium carbonate;

[0030] Using the extraction method of dicyandiamide waste residue of the present invention, dicyandiamide, carbon and calcium carbonate in the dicyandiamide waste residue can be effectively extracted and made into corresponding products for recycling;

[0031] By controlling the specific pH value of the primary washing filtrate with ammonia water in the present invention, it is not only beneficial to the polymerization of monocyanamide to form dicyandiamide, but also can inhibit the decomposition of dicyandiamide to produce ammonia during the heating concentration process, thereby further improving the recovery rate of dicyandiamide;

[0032] The present invention adopts a countercurrent washing method to wash and dehydrate the dicyandiamide waste residue, which can effectively recover dicyandiamide and monocyanamide in the dicyandiamide waste residue, and at the same time reduce the concentrations of residual dicyandiamide and monocyanamide in the dicyandiamide waste residue;

[0033] The present invention uses the method of negative pressure evaporation. By controlling a specific temperature, the moisture in the system can be evaporated, and at the same time, the polymerization of monocyanamide is promoted, further improving the recovery rate of dicyandiamide. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is the process flow chart of Embodiment 1 of the present invention;

[0035] Figure 2 is the structural characterization diagram of the calcium carbonate product prepared in Embodiment 1 of the present invention;

[0036] Figure 3 is the structural characterization diagram of the calcium carbonate product prepared in Comparative Example 1 of the present invention;

[0037] Figure 4 is the structural characterization diagram of the calcium carbonate product prepared in Comparative Example 2 of the present invention;

[0038] Figure 5 is the structural characterization diagram of the calcium carbonate product prepared in Comparative Example 3 of the present invention

[0039] Figure 6 It is the structural characterization diagram of the calcium carbonate product prepared in Comparative Example 4 of the present invention. Specific embodiments

[0040] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Many specific details are set forth in the following description in order to fully understand the present invention, but the present invention can also be implemented in other ways different from those described herein. Those skilled in the art can make similar generalizations without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

[0041] Example 1 A method for extracting dicyandiamide waste residue

[0042] This example is a method for extracting dicyandiamide waste residue, as Figure 1 shown, specifically including the following steps carried out in sequence:

[0043] S1. Pulping

[0044] Take the dicyandiamide waste residue and add it to the first-stage washing tank, add the filtrate of the second-stage washing, stir and wash in the first-stage washing tank to make pulp, and make a slurry with a solid content of 20-25 wt% (the solid content of the slurry in this example is 25 wt%), so that dicyandiamide and monocyanamide in the dicyandiamide waste residue are fully dissolved in water;

[0045] Turn on the exciting current, adjust the magnetic separation intensity of the magnetic separator to 180-200 mT (the magnetic separation intensity in this example is 200 mT), start injecting the slurry for magnetic separation, and collect the effluent after the slurry is magnetically separated once;

[0046] By setting a specific magnetic separation intensity, metal substances such as iron oxide and part of magnesium carbonate in the dicyandiamide waste residue are removed and it is ensured that calcium elements and dicyandiamide are not adsorbed, so as to reduce the difficulty of subsequent treatment and improve the purity of the recovered dicyandiamide product and calcium carbonate product. At the same time, since only part of magnesium carbonate is adsorbed, the remaining magnesium carbonate in the slurry will be converted into magnesium chloride during the subsequent preparation of the calcium carbonate product, and cooperate with chitosan as a crystal form control agent to control the formation of spherical calcium carbonate products.

[0047] The effluent enters the aeration tank, and carbon dioxide is introduced for aeration treatment for 10-15 minutes to convert the excess calcium hydroxide in the system into calcium carbonate, further improving the purity of the recovered dicyandiamide and calcium carbonate, and making a dicyandiamide waste residue slurry;

[0048] S2. Multi-stage washing

[0049] The dicyandiamide waste residue slurry is pumped into a first-stage hydrocyclone for washing by a first-stage transfer pump. The overflow liquid flowing out from the top of the first-stage hydrocyclone directly returns to the aeration tank and is cyclically pumped into the first-stage hydrocyclone. The dicyandiamide residue slurry at the bottom of the hydrocyclone is dewatered by a first-stage vacuum belt filter to obtain a first-stage filter cake and a first-stage washing filtrate; the dicyandiamide content in the first-stage filter cake is only 20-25 wt% of that in the dicyandiamide waste residue slurry.

[0050] The first-stage filter cake is transported by a belt conveyor to a second-stage washing tank for stirring, washing, and pulping. The third-stage washing filtrate is used as washing water to prepare a second-stage slurry, which helps to wash the dicyandiamide and monocyanamide in the first-stage filter cake into the water to a greater extent.

[0051] The prepared second-stage slurry is pumped into a second-stage hydrocyclone for washing by a second-stage slurry supply pump. The overflow liquid at the top of the third-stage hydrocyclone returns to the second-stage washing tank. The thick slurry at the bottom of the second-stage hydrocyclone is dewatered by a second-stage vacuum belt filter to obtain a second-stage filter cake and a second-stage washing filtrate; among them, the concentrations of dicyandiamide and monocyanamide in the second-stage washing tank are slightly higher. The source of dicyandiamide in the second-stage washing tank is the dicyandiamide carried by the free water in the first-stage filter cake and the dicyandiamide carried by the third-stage washing filtrate; the dicyandiamide content in the second-stage filter cake is only 20-25% of the concentration of the second-stage slurry.

[0052] The dicyandiamide concentration in the second-stage washing filtrate is relatively high, and it returns to the first-stage washing tank as washing water for pulping.

[0053] The second-stage filter cake is transported by a belt conveyor to a third-stage washing tank for stirring, washing, and pulping. The condensed water after evaporation is used as washing water to prepare a third-stage slurry, which helps to wash the dicyandiamide and monocyanamide in the dicyandiamide waste residue into the water to the maximum extent, while ensuring the minimum amount of dicyandiamide in the waste residue.

[0054] The prepared third-stage slurry is pumped into a third-stage hydrocyclone for washing by a third-stage slurry supply pump. The overflow liquid at the top of the third-stage hydrocyclone directly returns to the third-stage washing tank. The thick slurry at the bottom of the third-stage hydrocyclone directly enters the third-stage vacuum belt filter for dewatering to obtain a third-stage filter cake and a third-stage washing filtrate.

[0055] The sources of dicyandiamide and monocyanamide contained in the third-stage washing filtrate are only the dicyandiamide and monocyanamide carried by the free water in the second-stage filter cake. Therefore, the concentrations of dicyandiamide and monocyanamide contained in the third-stage washing filtrate are the lowest, and it returns to the second-stage washing tank as washing water for pulping.

[0056] S3. Product recovery

[0057] The filtrate from the primary washing is pumped into the recovery tank using a recovery pump. Ammonia water with a concentration of 30 wt% is added to adjust the pH value to 8.8 - 9.2 (in this example, the pH value is adjusted to 9.0). It is then pumped into the low-pressure evaporation system through a feed pump and maintained at 70 - 75 °C for low-pressure evaporation concentration and cyanamide polymerization (in this example, the maintained temperature is 72 °C). Utilizing heat and a negative pressure environment, the water in the primary washing filtrate is evaporated, and heat and an alkaline environment are used to further polymerize the cyanamide in the primary washing filtrate to form dicyandiamide, thereby obtaining a dicyandiamide solution with a concentration of 13 wt%. After the evaporated steam is condensed, the condensed water after evaporation is returned to the tertiary washing tank as washing water for pulping.

[0058] The high-concentration dicyandiamide solution is cooled to below 5 °C and crystallized for more than 2 h (in this example, the crystallization temperature is 0 °C and the time is 3 h). It is then filtered and dried to obtain a dicyandiamide product with a purity of 98.76% and a recovery rate of 96.59% (recovery rate = weight of dicyandiamide product ÷ theoretical weight of dicyandiamide in dicyandiamide waste residue × 100%).

[0059] The tertiary filter cake is transported to the pulping tank by a belt conveyor, and 20 wt% hydrochloric acid is added and stirred to dissolve and pulp it. After all the calcium carbonate is converted into calcium chloride (when no bubbles are generated, calcium carbonate is completely converted into calcium chloride, stop adding hydrochloric acid, and at the same time, a small amount of magnesium carbonate in the tertiary filter cake is converted into magnesium chloride), it is filtered to obtain a filtrate and a carbon product (the carbon product contains a small amount of silicon dioxide).

[0060] The filtrate is transported to the product tank by a liquid transfer pump, and chitosan is added. The concentration of chitosan in the resulting solution is 6 - 8 g / L (in this example, the concentration of chitosan in the solution is 7 g / L). It is stirred and dissolved. Using the small amount of magnesium chloride and chitosan contained in the filtrate as crystal form control agents, it is heated to 50 - 55 °C (in this example, the temperature after heating is 52 °C), and an aqueous ammonium carbonate solution with a concentration of 18 - 22 wt% is added dropwise (in this example, the concentration of the aqueous ammonium carbonate solution is 20 wt%). Continue to stir at 50 - 55 °C, and the stirring speed is 400 - 450 r / min (in this example, the stirring speed is 420 r / min). Control the generation of spherical calcium carbonate precipitate. When no more precipitate is generated after dropping, stop adding the aqueous ammonium carbonate solution. Continue to stir for 10 min, then cool down, filter, wash, and dry to obtain spherical calcium carbonate products with a whiteness of 95.1. The structural characterization diagram is shown in Figure 2 。

[0061] Extraction method of dicyandiamide waste residue in Examples 2 - 6

[0062] Examples 2 - 6 are respectively an extraction method of dicyandiamide waste residue. Their steps are basically the same as those of Example 1, except for the different raw material dosages and process parameters. For details, see Table 1:

[0063] Table 1 List of Process Parameters in Examples 2 - 6

[0064]

[0065]

[0066] The content of other parts in Examples 2 - 6 is the same as that in Example 1.

[0067] Experimental Example 1 Comparative Test on the Extraction Method of Dicyandiamide Waste Residue

[0068] Comparative Examples 1 - 9 are comparative tests on the extraction method of dicyandiamide waste residue in Example 1, with the only differences being:

[0069] In step S1 of Comparative Example 1, the magnetic separation intensity is 150 mT. The purity of the obtained dicyandiamide product is 97.42%, the recovery rate is 95.87%, the whiteness of the obtained calcium carbonate product is 93.1, and its structural characterization diagram is shown in Figure 3 , and regular spheres cannot be formed.

[0070] In step S1 of Comparative Example 2, the magnetic separation intensity is 250 mT. The purity of the obtained dicyandiamide product is 97.42%, the recovery rate is 95.87%, the whiteness of the obtained calcium carbonate product is 93.1, and its structural characterization diagram is shown in Figure 4 , and regular spheres cannot be formed.

[0071] After adding chitosan in step S3 of Comparative Example 3, the concentration of chitosan in the obtained solution is 2 g / L, the whiteness of the obtained calcium carbonate product is 93.7, and its structural characterization diagram is shown in Figure 5 , and regular spheres cannot be formed.

[0072] After adding chitosan in step S3 of Comparative Example 4, the concentration of chitosan in the obtained solution is 15 g / L, the whiteness of the obtained calcium carbonate product is 92.6, and its structural characterization diagram is shown in Figure 6 , and regular spheres cannot be formed.

[0073] In Comparative Example 5, no carbon dioxide aeration is carried out in step S1, and the magnetic separation effluent is directly used as the dicyandiamide waste residue slurry for subsequent treatment. The purity of the obtained dicyandiamide product is 94.17%, the recovery rate is 94.66%, and the whiteness of the obtained calcium carbonate product is 93.4.

[0074] In Comparative Example 6, the multi - stage washing process of the dicyandiamide waste residue slurry in step S2 includes the following steps:

[0075] After the dicyandiamide waste residue slurry is stirred and washed at the first stage, it is filtered by a first - stage filter press to obtain a first - stage filter cake and a first - stage washing filtrate.

[0076] The primary filter cake uses the filtrate of three-stage washing as washing water to prepare the secondary slurry. After stirring and washing in the secondary stage, it is filtered by a secondary filter press to obtain the secondary filter cake and the secondary washing filtrate;

[0077] The secondary filter cake uses the condensed water after evaporation as washing water to prepare the tertiary slurry. After stirring and washing in the tertiary stage, it is filtered by a tertiary filter press to obtain the tertiary filter cake and the tertiary washing filtrate;

[0078] Other technological processes are consistent with those in Example 1. The purity of the dicyandiamide product obtained is 92.15%, the recovery rate is 87.56%, and the whiteness of the calcium carbonate product obtained is 91.7.

[0079] In Step S3 of Comparative Example 7, the primary washing filtrate is directly fed into the low-pressure evaporation system for low-pressure evaporation concentration and cyanamide polymerization without adjusting the pH value with ammonia water. The purity of the dicyandiamide product finally obtained is 82.75%, the recovery rate is 86.24%, and the whiteness of the calcium carbonate product obtained is 94.6.

[0080] In Step S3 of Comparative Example 8, 30 wt% ammonia water is added to the primary washing filtrate to adjust the pH value to 10.0, and then it is fed into the low-pressure evaporation system for low-pressure evaporation concentration and cyanamide polymerization. The purity of the dicyandiamide product finally obtained is 87.64%, the recovery rate is 89.52%, and the whiteness of the calcium carbonate product obtained is 95.0.

[0081] In Step S3 of Comparative Example 9, the temperature of low-pressure evaporation concentration and cyanamide polymerization is 50 °C. The purity of the dicyandiamide product obtained is 87.64%, the recovery rate is 72.93%, and the whiteness of the calcium carbonate product obtained is 94.7.

[0082] Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

Claims

1. A method for extracting dicyandiamide waste residue, characterized in that, The extraction method includes the following steps: S1. Pulping After making dicyandiamide waste residue into slurry, it is enriched by magnetic separation, the effluent is collected, and then carbon dioxide is introduced for treatment to obtain dicyandiamide waste residue slurry; the magnetic separation intensity for magnetic separation enrichment is 180 - 200 mT S2. Multi - stage washing After the dicyandiamide waste residue slurry is subjected to multi - stage washing, a primary washing filtrate and multi - stage filter cakes are obtained; the multi - stage washing includes the following steps: Take the dicyandiamide waste residue slurry, wash it through a primary cyclone and dehydrate it with a primary vacuum belt filter to obtain a primary filter cake and a primary washing filtrate; The primary filter cake is made into slurry with the tertiary washing filtrate, then washed through a secondary cyclone and dehydrated with a secondary vacuum belt filter to obtain a secondary filter cake and a secondary washing filtrate; among them, the secondary washing filtrate is used as washing water to pulp the dicyandiamide waste residue in step S1; After the secondary filter cake is made into slurry, it is washed through a tertiary cyclone and dehydrated with a tertiary vacuum belt filter to obtain a tertiary filter cake and a tertiary washing filtrate; among them, the tertiary washing filtrate is used as washing water to pulp the primary filter cake; the tertiary filter cake is the multi - stage filter cake; S3. Product recovery After the pH value of the primary washing filtrate is adjusted to 8.8 - 9.2 with ammonia water, low - pressure evaporation concentration and cyanamide polymerization are carried out at 70 - 75 °C. The obtained high - concentration dicyandiamide solution is crystallized and filtered to obtain dicyandiamide products; The multi - stage filter cakes are dissolved with hydrochloric acid and filtered to obtain a filtrate and carbon products; During low - pressure evaporation concentration and cyanamide polymerization, the steam evaporated is condensed, and the obtained condensed water after evaporation is used as washing water to pulp the secondary filter cake; Chitosan with a concentration of 6 - 8 g / L is added to the filtrate, and then ammonium carbonate is added to make spherical calcium carbonate products.

2. The extraction method of dicyandiamide waste residue according to claim 1, wherein, In step S3, the concentration of the dicyandiamide solution is 12 - 14 wt%.

3. The extraction method of dicyandiamide waste residue according to claim 1, characterized in that, In step S3, during the addition of ammonium carbonate, the temperature of the obtained system is 50 - 55 °C.

4. The extraction method of dicyandiamide waste residue according to claim 1, characterized in that, In step S3, during the addition of ammonium carbonate, the obtained system is stirred at a stirring speed of 400 - 450 r / min.

5. The extraction method of dicyandiamide waste residue according to claim 1, characterized in that, In step S3, ammonium carbonate is an ammonium carbonate aqueous solution with a concentration of 18 - 22 wt%.

6. The extraction method of dicyandiamide waste residue according to claim 1, wherein, In step S1, the solid content in the slurry made from dicyandiamide waste residue is 20 - 25 wt%.

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