Compound stabilizer for efficiently stabilizing lead in waste incineration fly ash

Abstract

The invention belongs to the technical field of lead-containing solid waste environmental pollution prevention and control, and particularly relates to a compound stabilizer for efficiently stabilizing lead in waste incineration fly ash, and the stabilizer comprises sodium dimethyl dithiocarbamate and urea in a mass ratio of 1.5-2.5. The urea and the sodium dimethyl dithiocarbamate are compounded according to a specific proportion, so that the urea and the sodium dimethyl dithiocarbamate generate a synergistic effect in the process of stabilizing the heavy metal Pb, the heavy metal Pb in the solid waste is compounded and chelated, in a stability performance evaluation experiment, after the solid waste fly ash is treated by the compound stabilizer, the leaching concentration of the heavy metal Pb is remarkably reduced, and the leaching efficiency of the heavy metal Pb is remarkably improved. And compared with a commercial stabilizer, the content is reduced by 2.55 times. In addition, due to the fact that urea replaces part of organic reagents in the preparation process, the use amount of CS2 is reduced, compared with a commercial stabilizer, the novel compound stabilizer is reduced to 5000 yuan / ton from 6500 yuan / ton, the cost is saved by 10% or above, and meanwhile the toxicity of the stabilizer is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of environmental pollution prevention and control of lead-containing solid waste, and specifically relates to a composite stabilizer for efficiently stabilizing lead in waste incineration fly ash. Background Art

[0002] Lead, as a heavy metal element widely present in nature, is toxic and persistent. It can be enriched in organisms through the food chain, causing serious impacts on the ecological environment and human health. Generally, lead pollution from natural sources does not have a significant impact on the ecological environment and human health. In contrast, lead pollution from human sources is more serious and widespread. With the rapid development of economic construction, the amount of solid waste discharged from various industrial activities and urban life has also increased year by year. Many of these solid wastes contain a large amount of heavy metal lead, such as smelting slag and tailings discharged from non-ferrous metal production processes, sludge discharged from sewage treatment plants, contaminated soil, and fly ash from domestic waste incineration plants. These solid wastes stored in the environment not only occupy a large amount of land space, but also the heavy metal Pb contained therein will leach and migrate into the environment with the effects of surface runoff erosion, rainwater leaching, weathering, etc., and ultimately endanger the ecological environment and human health. Therefore, the use of solidification / stabilization technology to prevent heavy metal pollution caused by lead-containing solid waste has become a research hotspot in the current field of environmental governance. The concept of heavy metal stabilization technology is to use physical, chemical or biological methods to transform the heavy metals in solid waste into less soluble, mobile or less toxic forms, prevent them from migrating and spreading in the environment, and thus reduce the environmental risks of heavy metals in solid waste. Considering the huge output and stockpile of various types of hazardous solid waste in my country, chemical stabilization technology has more prospects for large-scale application because of its advantages of no or little waste volume increase, environmental safety and cost-effectiveness.

[0003] The chemical agents used for general chemical stabilization are divided into two categories: inorganic agents and organic chelating agents. Inorganic agents include lime, phosphoric acid, phosphates, sodium sulfide, etc. Although inorganic agents have a relatively good stabilization effect on heavy metal Pb, the stabilization effect is poor in strong acidic and alkaline environments, and the stabilized heavy metal Pb is easily leached from the environment again. Dithiocarbamates and their derivatives (DTC) in organic chelating agents are currently the most studied and have the best performance at home and abroad. The basic synthesis method is to graft the -CS2 group to the amino group of the polymer chain. Due to the influence of C=S, the special outer electron structure of the S element on the thiol group can effectively combine with the metal elements in the transition zone, thereby achieving the purpose of forming a chelate with the heavy metal Pb and stabilizing it. Therefore, sodium dimethyldithiocarbamate has become the main component of commercial stabilizers on the market. However, due to the high price of polyamine compounds, the excessive toxicity of CS2, and the lack of long-term stability of heavy metal chelation, the large-scale promotion and application of DTC stabilizers are limited.

[0004] The disclosed patent "A method for preparing a heavy metal ion capture agent" (patent number CN103466775A) is obtained by mixing urea with an amine compound and then modifying it with dithiocarbamate. The urea-based dithiocarbamate heavy metal stabilizer has a certain effect of stabilizing Pb, but it still has defects such as insufficient stability, high stabilizer dosage, and high toxicity of the agent. On this basis, the disclosed patent "A composite heavy metal capture agent and its preparation method" (patent number CN105417667B) uses an inorganic anion surfactant and the above-mentioned heavy metal stabilizer to mix and mix, and the synergistic effect of inorganic anions and DTC improves the stability of heavy metals to a certain extent. However, the composite heavy metal stabilizer still has defects such as high CS2 dosage, high toxicity of the agent, and high stabilizer dosage. Through the study of solid waste fly ash from a waste incineration plant in Chengdu, it was found that the existing DTC stabilizer and urea can be used to chelate the composite of Pb in the solid waste, which effectively improves the stability. At the same time, because urea replaced some organic reagents and the amount of CS2 used was reduced, the toxicity and cost of the stabilizer were reduced. Based on this, a new type of compound stabilizer with lower cost, better stability and more environmental friendliness was developed. Summary of the invention

[0005] The purpose of the present invention is to provide a new type of compound stabilizer for the treatment of lead-containing solid waste, which improves the stability rate of heavy metal lead while overcoming the high production cost of traditional commercial stabilizers. At the same time, the mechanism of the effect of significantly improving the stability of lead in solid waste after compounding urea with DTC is clearly explained.

[0006] The object of the present invention is achieved through the following technical scheme: a composite stabilizer for efficiently stabilizing lead in waste incineration fly ash, comprising sodium dimethyldithiocarbamate and urea in a mass ratio of 1:1.5-2.5.

[0007] Furthermore, the sodium dimethyldithiocarbamate is a ready-made solution containing sodium dimethyldithiocarbamate, which optimizes the reaction conditions, reduces by-products and preparation costs, and the ready-made method includes:

[0008] Prepare a sodium hydroxide aqueous solution, then add dimethylamine solution in sequence, slowly add CS2 dropwise under temperature control, react for 100min to 120min, and obtain a solution of sodium dimethyldithiocarbamate without by-products.

[0009] Furthermore, the concentration range of the sodium hydroxide aqueous solution is 11% to 13%; the concentration range of the dimethylamine solution is 38-40%.

[0010] Furthermore, in the solution containing sodium dimethyldithiocarbamate, the weight ratio of each component is: 1-2 dimethylamine, 3-4 sodium dimethyldithiocarbamate, 11-19 carbon disulfide, 10-16 sodium hydroxide, and 46-51 distilled water.

[0011] Furthermore, the sodium dimethyldithiocarbamate and urea are compounded by physical blending.

[0012] Furthermore, the physical blending method is stirring for 10 min to 20 min.

[0013] The beneficial effects of the present invention are as follows: the environmental pollution problem caused by lead-containing solid waste is becoming increasingly serious, and chemical stabilizers with more large-scale application prospects have their own shortcomings. The present invention uses a specific ratio of urea and sodium dimethyldithiocarbamate to produce a synergistic effect in the process of stabilizing heavy metal Pb, and realizes the composite chelation of heavy metal Pb in solid waste. In the evaluation experiment of "Solid Waste Leaching Toxicity Leaching Method Acetic Acid Buffer Solution Method" (HJ / T300-2007) with a dosage of 2wt%, after the new composite stabilizer treats solid waste fly ash, the leaching concentration of heavy metal Pb is significantly reduced, and its leaching toxicity is reduced by 2.55 times compared with commercial stabilizers. The new composite stabilizer not only has better stability, but also because urea replaces part of the organic reagents and the amount of CS2 used in the preparation process, the new composite stabilizer is reduced from 6500 yuan / ton to 5000 yuan / ton compared with commercial stabilizers, saving more than 10% of the cost while reducing the toxicity of the stabilizer. Based on this, a composite stabilizer for efficiently stabilizing lead in waste incineration fly ash is provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1The leaching of heavy metal Pb from fly ash stabilized by the new compound stabilizer at different compounding ratios;

[0015] Figure 2 The leaching of heavy metal Pb from fly ash stabilized by the new composite stabilizer at different dosages;

[0016] Figure 3 The leaching of heavy metal Pb from fly ash stabilized by the new composite stabilizer at different pH values;

[0017] Figure 4 Morphological analysis of the stabilization mechanism of the new compound stabilizer;

[0018] Figure 5 The full XPS spectrum of the stabilization mechanism of the new compound stabilizer;

[0019] Figure 6 XPS (N1) of the stabilization mechanism of the new composite stabilizer S ) Spectrum;

[0020] Figure 7 XPS (Pb4 f ) Spectrum;

[0021] Figure 8 This is a SEM microscopic morphology characterization of the stabilization mechanism of the new compound stabilizer. DETAILED DESCRIPTION

[0022] The technical solution of the present invention is further described in detail below in conjunction with the accompanying drawings, but the protection scope of the present invention is not limited to the following.

[0023] Example 1 Preparation of a novel composite stabilizer

[0024] According to the compounding ratio of sodium dimethyldithiocarbamate (EC) to urea (Urea) of 4:1, 2:1, 1:1, 1:2, and 1:4, stabilizers were prepared respectively. The specific methods are as follows:

[0025] (1) Preparation of a solution containing sodium dimethyldithiocarbamate

[0026] Prepare 100 mL of an aqueous solution with a 12% sodium hydroxide content as the mother liquor, transfer it to a three-necked flask, and add 38 mL of 40% dimethylamine at room temperature.

[0027] Add 30 mL of CS2 and slowly add dropwise at 25°C.

[0028] After adding CS2, maintain the temperature at 25°C and react for 100 to 120 minutes.

[0029] (2) Preparation of stabilizers in different proportions

[0030] According to the mass of sodium dimethyldithiocarbamate in the solution, urea of ​​different mass ratios was mixed respectively. After mixing, the mixture was stirred for 15 minutes until fully dissolved to obtain stabilizers with different compound ratios. Analysis confirmed that the active ingredients of the new compound stabilizer were only EC and Urea.

[0031] Example 2 Screening of optimal stabilization conditions for heavy metal Pb in fly ash from waste incineration plants using a new type of composite stabilizer

[0032] In order to obtain the optimal stabilization conditions, the fly ash from the waste incineration plant was stabilized using the present invention at different compounding ratios, different dosages, and pH values, and the stabilized fly ash was evaluated for leaching toxicity according to the "Solid Waste Leaching Toxicity Leaching Method Acetate Buffer Solution Method" (HJ / T300-2007).

[0033] Firstly, the optimal compounding ratio of the new compound stabilizer was determined. At a dosage of 2wt%, the new compound stabilizer with compounding ratios of sodium dimethyldithiocarbamate (EC) and urea (Urea) of 4:1, 2:1, 1:1, 1:2, and 1:4 was selected to stabilize solid waste fly ash. The experimental results are as follows: Figure 1 As shown. Among the various compounding ratios, when the compounding ratio of EC to Urea is 1:2 (NEC), the stabilization rate of heavy metal Pb in solid waste fly ash is the highest. While meeting the pollution control standard for municipal solid waste landfills (GB 16889-2008), the leaching concentration of heavy metal Pb is reduced by 2.55 times compared with commercial stabilizers, indicating that when the compounding ratio of EC to Urea is 1:2 (NEC), the new compound stabilizer has the best stabilization effect on heavy metal Pb in fly ash. Therefore, NEC was used to stabilize solid waste fly ash at different dosages, and the leaching results are shown in Figure 2 As shown in the figure, with the addition of NEC, the leaching concentration of heavy metal Pb in fly ash drops sharply; when more than 2wt% NEC is added for stabilization, its leaching concentration is far below the national standard and the decreasing trend slows down, so it is preferred to use NEC at a dosage of 2wt%. At the same time, the stability performance of NEC, EC+Urea (1 / 1) and EC at different dosages was also compared. The results showed that the stability performance of the former two for heavy metal Pb in fly ash was significantly higher than that of EC with a single component, while the stability performance of EC+Urea (1 / 1 / ) was slightly lower than that of NEC. The performance difference among the three further shows that the compound ratio of EC and Urea in NEC is critical and is an important reason for its excellent stability performance.

[0034] Under different pH leaching conditions ( Figure 3), the leaching concentration of heavy metal Pb in the untreated fly ash exceeds the national standard in the entire pH range. After the fly ash is treated with 2wt% EC, the migration of heavy metal Pb can be effectively restricted in the pH range of 3-12, but due to the dissolution of soluble ions formed by amphoteric metals in strong acid and alkaline environments, the leaching concentration of heavy metal Pb is still higher than the national standard. Compared with EC with a single component, the fly ash stabilized with 2wt% NEC shows better stability in the pH range of 3-12. Although its leaching concentration will increase to a certain extent when pH is <3, >12, its leaching concentration of heavy metal Pb meets the national standard in the entire pH range.

[0035] Example 3 Stabilization mechanism of Pb in fly ash from waste incineration plants using a new composite stabilizer

[0036] In order to reveal the stabilization mechanism of the new compound stabilizer on Pb in fly ash from waste incineration plants, the Pb morphology analysis, XPS photoelectron spectroscopy and scanning electron microscopy were used to analyze the Pb morphology and appearance.

[0037] First, Pb speciation analysis ( Figure 4 ), the results showed that the fly ash before and after stabilization showed a trend of transformation of heavy metal Pb from unstable state to stable state, among which the most stable state was generated by NEC transformation. NEC effectively inhibited the leaching of heavy metal Pb from fly ash by converting all exchangeable states, a large amount of carbonate-bound states, and part of the iron-manganese oxidation states of heavy metal Pb in fly ash into relatively stable organic-bound states and residual states.

[0038] Secondly, XPS analysis of fly ash revealed that the XPS full spectrum ( Figure 5 ) are mainly composed of C, O, N, Na, K, Ca, etc., and Pb4 f The peak intensity is weaker than that of other elements, and with the increase of the stability of the added stabilizer, Pb4 f The peak gradually weakened and disappeared, among which the fly ash Pb4 f The peak weakened most significantly. S ) Figure 6 ) Comparative analysis found that the fly ash N1 before and after EC stabilization S There is no obvious peak in the spectrum, and the fly ash stabilized by NEC is more stable than that stabilized by Urea alone. S The peak position shift decreased by 0.5 eV, which indicates that Urea in NEC cooperates with EC to participate in the coordination stabilization of heavy metal Pb in fly ash and plays an electron-withdrawing effect in the entire heavy metal chelate formed. In addition, because NEC has better stabilization performance than EC, it can effectively stabilize Pb4 f Spectrum( Figure 7 ) in NEC, Pb 2+ , Pb 4+ The peak area is smaller than that of EC, and both Pb 2+ , Pb 4+ The peak position of the fly ash after NEC stabilization is completely opposite to that of the untreated fly ash. 2+ , Pb 4+ The binding energy of the fly ash after EC stabilization is larger and the electron cloud density decreases. 2+ , Pb 4+ The binding energy of the electron cloud is smaller and the electron cloud density is larger. S ) spectrum analysis results; Urea plays an electron-withdrawing effect in the entire heavy metal chelate formed, and the mechanism of chelate formation between NEC and heavy metals in fly ash is obtained: EC and Urea synergistically participate in the coordination of heavy metals in fly ash, and due to the strong electron-donating effect of organic sulfide and the electron-withdrawing effect of Urea carbonyl, an electron cloud deviation path is formed from organic sulfide (=S) to heavy metal, and heavy metal to Urea (NC=0), which reduces the electron cloud density on the heavy metal Pb and forms a heavy metal chelate with more uniform electron cloud distribution and stronger stability.

[0039] Finally, since the leaching behavior of heavy metal Pb in fly ash is closely related to its specific surface area, and the specific surface area of ​​fly ash particles depends on factors such as particle size, surface morphology and pore size, the microscopic morphology of fly ash was observed by SEM. Figure 8 It can be seen that the untreated fly ash particles are generally finer, and the particle shapes are different, the surface is uneven, and there are many tiny holes. The fly ash stabilized with 2wt% EC promotes the aggregation of particles in the fly ash due to the formation of heavy metal chelates, resulting in uniform agglomerated particles, but the particles are still loosely bound and have larger pores. The fly ash stabilized with 2wt% EC+Urea (1 / 1) not only has obvious agglomerated particles, but also the porosity between the agglomerated particles becomes smaller, the particle surface becomes dense, and the edges and corners become blurred. And with the addition of 2wt% NEC, which reaches the optimal ratio of EC and Urea, more ligands participate in the coordination and chelation of heavy metal Pb, so that the pores between the agglomerated particles in the fly ash disappear, and together form large spherical particles with smooth surfaces, so that the heavy metal Pb is more firmly bound in the crystal phase of the fly ash and is difficult to leach.

[0040] Combining the results of three characterization methods, the mechanism of the new composite stabilizer in stabilizing Pd in ​​waste incineration fly ash is as follows: EC and Urea in NEC synergistically participate in the stabilization of heavy metal Pb in fly ash, and through an electron cloud deviation path, improve the electron cloud distribution while increasing the number of coordination, generating more organically bound states and residual states, firmly wrapping the heavy metal Pb in the spherical large-particle crystal phase with a smooth surface, making it difficult to leach out.

[0041] The above is only a preferred embodiment of the present invention. It should be understood that the present invention is not limited to the form disclosed herein, and should not be regarded as excluding other embodiments, but can be used in various other combinations, modifications and environments, and can be modified within the scope of the concept described herein through the above teachings or the technology or knowledge of the relevant field. The changes and modifications made by those skilled in the art shall not deviate from the spirit and scope of the present invention, and shall be within the scope of protection of the claims attached to the present invention.

Claims

1. A composite stabilizer for efficiently stabilizing lead in waste incineration fly ash, characterized in that: The invention comprises sodium dimethyldithiocarbamate and urea in a mass ratio of 1:1.5 to 2.

5.

2. The composite stabilizer for efficiently stabilizing lead in waste incineration fly ash according to claim 1, characterized in that: The sodium dimethyldithiocarbamate is a freshly prepared solution containing sodium dimethyldithiocarbamate, and the freshly prepared method includes: Prepare a sodium hydroxide aqueous solution, then add a dimethylamine solution in sequence, slowly add CS2 dropwise, and react for 100 to 120 minutes to obtain a solution containing sodium dimethyldithiocarbamate.

3. A composite stabilizer for efficiently stabilizing lead in waste incineration fly ash according to claim 2, characterized in that: The concentration range of the sodium hydroxide aqueous solution is 11% to 13%; the concentration range of the dimethylamine solution is 38-40%.

4. The composite stabilizer for efficiently stabilizing lead in waste incineration fly ash according to claim 2, characterized in that: In the solution containing sodium dimethyldithiocarbamate, the weight proportions of the components are: 1-2 of dimethylamine, 3-4 of sodium dimethyldithiocarbamate, 11-19 of carbon disulfide, 10-16 of sodium hydroxide, and 46-51 of distilled water.

5. A composite stabilizer for efficiently stabilizing lead in waste incineration fly ash according to claim 2, characterized in that: The sodium dimethyldithiocarbamate and urea are compounded by physical blending.

6. A composite stabilizer for efficiently stabilizing lead in waste incineration fly ash according to claim 2, characterized in that: The physical blending method is stirring for 10 min to 20 min.

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