Method for preparing chelating agent CaS from red gypsum and biochar and application of chelating agent CaS

Abstract

The invention provides a method for preparing a chelating agent CaS by using red gypsum and biochar and application of the chelating agent CaS. The preparation method comprises the following steps: respectively drying, crushing and grinding the red gypsum and tobacco waste, and sieving to obtain red gypsum powder and biomass; then pyrolyzing the biomass in a reducing atmosphere to obtain solid biochar; uniformly mixing the solid biochar and red gypsum powder, and performing pyrolysis in a reducing atmosphere, thereby obtaining the product, wherein the mass ratio of the biochar to the red gypsum powder is (0.1: 1)-(0.5: 1). The method comprises the following steps: crushing and grinding tobacco waste, pyrolyzing to prepare solid biochar, and pyrolyzing the solid biochar and red gypsum powder in a reducing atmosphere to generate a chelating agent CaS capable of forming a stable chelate with heavy metal ions, thereby achieving the purposes of fixing and stabilizing fly ash through the chelating agent CaS.

Description

Technical Field

[0001] The present invention relates to the technical field of ecological environmental protection and solid waste resource utilization, and in particular to a method for preparing a chelating agent CaS by utilizing red gypsum and biochar, and application thereof. Background Art

[0002] Nowadays, fly ash solidification and stabilization is a technology used to treat fly ash, most of which comes from waste incineration and coal-fired power plants. The technology of fly ash fixation and stabilization aims to reduce the harm of harmful substances in fly ash to the environment and human health. Nowadays, fly ash solidification mostly uses physical or chemical methods to fix or convert pollutants in fly ash into a more stable form, thereby reducing its mobility and toxicity, preventing heavy metals and other harmful substances in fly ash from leaching under the action of rainwater or groundwater to pollute soil and water bodies, and reducing the potential harm of fly ash to the environment and human health.

[0003] Among them, chelating agent, as a fly ash solidifying agent, can form stable complexes with heavy metals in fly ash, thereby significantly reducing the mobility and leaching rate of heavy metals. However, the cost of chelating agents in the prior art is relatively high, which increases the overall cost of fly ash treatment. The complexes formed by chelating agents and heavy metals are prone to dissociation under long-term environmental changes, and some chelating agents have low resource utilization rates and are difficult to degrade in the environment, which may cause secondary pollution to soil and water.

[0004] Therefore, how to prepare a chelating agent with high resource utilization, low cost, environmental friendliness and the ability to achieve efficient solidification and stability is the key to fly ash treatment technology.

[0005] In view of this, the present invention is proposed. Summary of the invention

[0006] The first purpose of the present invention is to provide a method for preparing a chelating agent CaS using red gypsum and biochar. The chelating agent CaS is prepared by using red gypsum and tobacco waste to achieve fly ash solidification and stabilization. The combination of the two to prepare a chelating agent can well achieve fly ash solidification and stabilization while realizing waste resource utilization and reducing environmental pollution. The use of waste to prepare a chelating agent reduces dependence on chemical synthesis reagents, thereby reducing the risk of secondary pollution, which is in line with the principles of green chemistry.

[0007] The second object of the present invention is to provide the use of the above-mentioned chelating agent CaS for fly ash solidification and stabilization.

[0008] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are particularly adopted: A method for preparing a chelating agent CaS by using red gypsum and biochar comprises the following steps: The red gypsum and tobacco waste are dried, crushed, ground and sieved to obtain red gypsum powder and biomass; Then, the biomass is pyrolyzed under a nitrogen atmosphere to obtain biochar; The biochar and red gypsum powder are mixed evenly and pyrolyzed in a reducing atmosphere to obtain; The mass ratio of the biochar to the red gypsum powder is (0.1:1)-(0.5:1).

[0009] Preferably, as a further specific implementation, the mass ratio of the biochar to the red gypsum powder is (0.15:1)-(0.3:1).

[0010] Preferably, as a further specific implementation, the mass ratio of the biochar to the red gypsum powder is 0.3:1.

[0011] In the present invention, after pyrolyzing tobacco waste to produce biochar, the biochar is used to reduce calcium sulfate in red gypsum to CaS chelated with fly ash, thereby providing an efficient way for resource utilization of tobacco waste and red gypsum, and the method of pyrolyzing tobacco waste can effectively degrade harmful substances in tobacco waste, thereby avoiding affecting subsequent reaction processes, and the rich organic components in tobacco waste can be decomposed to generate reducing substances after pyrolysis, and the tobacco waste after pyrolysis forms a porous structure, which increases its specific surface area and thus improves its reaction activity as a reducing agent, and the main component of red gypsum is calcium sulfate, which can be more easily reduced to CaS by biochar after pyrolysis, and the red gypsum particles after pyrolysis are finer and the specific surface area is increased, so that it is more fully in contact with biochar, thereby improving the reaction efficiency of the two.

[0012] For the present invention, the mass ratio of biochar to red gypsum is limited to a certain extent. When the mass ratio of the biochar to the red gypsum powder is (0.1:1)-(0.5:1), preferably the mass ratio of the biochar to the red gypsum powder is (0.15:1)-(0.3:1), and more preferably the mass ratio of the biochar to the red gypsum powder is 0.3:1, the effect achieved is excellent. This is because the mass ratio of red gypsum to biochar is a key parameter for preparing the chelating agent CaS, which affects the efficiency of the reaction and the quality of the product. If the amount of biochar is insufficient, the amount of reducing agent used in the reaction between the two will be insufficient to completely reduce the calcium sulfate in the red gypsum, resulting in incomplete reaction and reduced CaS yield. If the amount of biochar is too low, the reduction reaction of the two will not be complete, which may cause the product to contain unreacted calcium sulfate or other intermediates, reducing the purity of CaS. Although excessive use of biochar can ensure that the calcium sulfate in the red gypsum is fully reduced, the excess biochar residue affects the purity of the product.

[0013] Preferably, as a further specific embodiment, the reducing atmosphere is N 2 and CH 4 A mixture of.

[0014] Preferably, as a further specific embodiment, the reducing atmosphere contains N 2 With CH 4 The volume ratio is (3:1)-(17:3).

[0015] Preferably, as a further specific embodiment, the reducing atmosphere contains N 2 With CH 4 The volume ratio is 17:3.

[0016] In the present invention, the pyrolysis of red gypsum and tobacco waste needs to be carried out under a reducing atmosphere, wherein the reducing atmosphere is N 2 and CH 4 When mixed, the effect that can be achieved is excellent. This is because the mixture of nitrogen and methane can provide a stable reducing environment for the pyrolysis process of the two. Nitrogen, as an inert gas, can well isolate oxygen while preventing the raw materials from being oxidized at high temperatures and maintaining the stability of the reaction system. Methane, as a reducing gas, can be well decomposed into hydrogen and carbon at high temperatures, thereby providing additional reducing agents for the reduction of calcium sulfate, improving the reaction rate and efficiency. In addition, under the reducing atmosphere of nitrogen and methane, the selectivity of the reaction between the two is higher, which can well reduce the generation of by-products and improve the purity and yield of the product.

[0017] In the present invention, N in the reducing atmosphere 2With CH 4 The volume ratio of N is limited to a certain extent. 2 With CH 4 The volume ratio of N in the reducing atmosphere is (3:1)-(17:3). 2 With CH 4 When the volume ratio of nitrogen to methane is 17:3, the effect that can be achieved is excellent. This is because when pyrolyzing red gypsum and tobacco waste, the volume ratio of nitrogen to methane in the reducing atmosphere is a key parameter, which directly affects the efficiency of the pyrolysis reaction, product quality and energy consumption. When the proportion of methane in the reducing atmosphere is too high, the stronger the reducing atmosphere, the more conducive it is to the full reduction of calcium sulfate. However, due to the increase in the reaction rate of excessive methane, it may also cause excessive reduction and produce by-products, affecting the purity of the product; if the amount of methane is too little, the reducing atmosphere will be weak, resulting in incomplete reduction of calcium sulfate, thereby generating intermediates or causing incomplete reaction.

[0018] Preferably, as a further specific embodiment, the pyrolysis temperature is 750-950°C; Preferably, the pyrolysis temperature is 900°C.

[0019] Preferably, as a further specific implementation, when the red gypsum and tobacco waste are dried, crushed, ground and sifted, the drying temperature is 100-110° C. and the drying time is 24-26 hours.

[0020] Preferably, as a further specific implementation, when the red gypsum and tobacco waste are dried, crushed, ground and sieved, a 60-mesh sieve is used for sieving.

[0021] The present invention also provides an application of the above-mentioned chelating agent CaS for fly ash solidification and stabilization, wherein the specific application process is to mix the prepared chelating agent CaS with fly ash and cement, wherein the mass ratio of cement to fly ash is 0.3:1, the solid-liquid ratio is 0.7:1, the curing time is 28 days, the curing humidity is 95%, the curing temperature is 20°C, and then the heavy metal leaching concentration test is carried out.

[0022] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides a method for preparing a chelating agent CaS using red gypsum and biochar. The chelating agent CaS is prepared by using red gypsum and tobacco waste to achieve fly ash solidification and stabilization. The combination of the two can well achieve fly ash solidification and stabilization while realizing waste resource utilization, reducing environmental pollution, and using waste to prepare the chelating agent reduces dependence on chemical synthesis reagents, thereby reducing the risk of secondary pollution, which is in line with the principle of green chemistry. The present invention provides the application of the above-mentioned chelating agent CaS in fly ash solidification and stabilization. BRIEF DESCRIPTION OF THE DRAWINGS By reading the detailed description of the preferred embodiment below, various other advantages and benefits will become clear to those of ordinary skill in the art. The accompanying drawings are only used for the purpose of illustrating the preferred embodiment and are not considered to be limitations of the present invention. In addition, the same reference symbols are used to represent the same components throughout the accompanying drawings.

[0023] Figure 1 This is the XRD pattern of the fly ash used in the experimental example; Figure 2 This is the XRD pattern of red gypsum used in the present invention; Figure 3 This is the XRD diagram of the calcined products of red gypsum powder and biochar. DETAILED DESCRIPTION

[0024] The technical solution of the present invention will be clearly and completely described below in conjunction with specific implementation methods, but those skilled in the art will understand that the embodiments described below are part of the embodiments of the present invention, rather than all of the embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0025] In order to more clearly explain the technical solution of the present invention, it is described in the form of specific embodiments below.

[0026] Example 1 A method for preparing a chelating agent CaS by using red gypsum and biochar, the steps are as follows: First, the tobacco waste is dried in an electric constant temperature air drying oven at 100°C for 24 hours, and after drying, it is transferred to a crusher for crushing, and then passed through a 60-mesh sieve to obtain biomass; Take red gypsum, dry it in an electric constant temperature blast drying oven at 100°C for 24 hours, transfer it to an agate mortar for grinding after drying, and pass it through a 60-mesh sieve after grinding to obtain red gypsum powder; Then, the obtained biomass was added into a tubular furnace, heated to 400°C at a heating rate of 10°C / min under a nitrogen atmosphere, and then pyrolyzed at a constant temperature for 2 h to prepare biochar; Then, N 2 With CH 4 Mixing to prepare a reducing atmosphere; Then, 3 g of the obtained biochar and 30 g of red gypsum powder were mixed, and after the mixture was evenly mixed, it was put into a tubular furnace, and the reducing atmosphere was adjusted to increase the temperature to 750 °C at 10 °C / min, and then pyrolyzed at a constant temperature for 30 minutes, and the pyrolysis was completed.

[0027] Example 2 A method for preparing a chelating agent CaS by using red gypsum and biochar, the steps are as follows: First, the tobacco waste is dried in an electric constant temperature air drying oven at 110°C for 26 hours, and after drying, it is transferred to a crusher for crushing, and then passed through a 60-mesh sieve to obtain biomass; Take red gypsum, dry it in an electric constant temperature blast drying oven at 110°C for 26 hours, transfer it to an agate mortar for grinding after drying, and pass it through a 60-mesh sieve to obtain red gypsum powder; Then, the obtained biomass was added into a tubular furnace, heated to 400°C at a heating rate of 10°C / min under a nitrogen atmosphere, and then pyrolyzed at a constant temperature for 2 h to prepare biochar; Then, N 2 With CH 4 Mixing to prepare a reducing atmosphere; Then, 15 g of the obtained biochar and 30 g of red gypsum powder were mixed, and after the mixture was evenly mixed, it was put into a tubular furnace, and the reducing atmosphere was adjusted to increase the temperature to 950 °C at 10 °C / min, and then pyrolyzed at a constant temperature for 30 minutes, and the pyrolysis was completed.

[0028] Experimental Example 1 Exploration of the mass ratio between biochar and red gypsum powder The specific implementation steps are consistent with Example 1, the only difference is the quality between red gypsum and biochar, and experimental groups 1-10 are set; The mass ratio of biochar to red gypsum powder in experimental group 1 was 0.02:1, i.e., 0.2 g of biochar and 10 g of red gypsum powder; In experimental group 2, the mass ratio of biochar to red gypsum powder was 0.05:1, i.e., 0.5 g of biochar and 10 g of red gypsum powder; In experimental group 3, the mass ratio of biochar to red gypsum powder was 0.1:1, i.e., 1 g of biochar and 10 g of red gypsum powder; In experimental group 4, the mass ratio of biochar to red gypsum powder was 0.2:1, i.e., 2 g of biochar and 10 g of red gypsum powder; In experimental group 5, the mass ratio of biochar to red gypsum powder was 0.3:1, i.e., 3 g of biochar and 10 g of red gypsum powder; In experimental group 6, the mass ratio of biochar to red gypsum powder was 0.4:1, i.e., 4 g of biochar and 10 g of red gypsum powder; In experimental group 7, the mass ratio of biochar to red gypsum powder was 0.5:1, i.e., 5 g of biochar and 10 g of red gypsum powder; In experimental group 8, the mass ratio of biochar to red gypsum powder was 0.6:1, i.e., 6 g of biochar and 10 g of red gypsum powder; The mass ratio of biochar to red gypsum powder in experimental group 9 was 0.9:1, i.e., 9 g of biochar and 10 g of red gypsum powder; The mass ratio of biochar to red gypsum powder in experimental group 10 was 1:1, i.e., 10 g of biochar and 10 g of red gypsum powder; Subsequently, the chelating agent obtained in the control group and experimental groups 1-10 was added to 200g of fly ash and 60g of cement to form a block, wherein the solid-liquid ratio was 0.7:1, the curing time was 28d, the curing humidity was 95%, and the heavy metal leaching concentration test was carried out after crushing and sieving. The final table is shown in Table 1 below, wherein the XRD pattern of the fly ash used is shown in Figure 1 As shown by Figure 1 It can be seen that fly ash contains Ca(OH) 2 , CaHClO, KCl, NaCl, CaSO 4 ; The XRD pattern of the red gypsum used is as follows Figure 2 As shown in the figure, it can be seen that red gypsum contains CaSO 4 、CaSO 4 ∙0.5H 2 O, CaSO 4 ∙0.15H 2 O; The XRD patterns of red gypsum powder and biochar roasting products are shown in Figure 3 As shown in the figure, it can be seen that the roasting products of red gypsum and biochar mainly contain CaS.

[0029] Table 1

[0030] Therefore, it can be seen from the above table that, for the present invention, the mass ratio between red gypsum powder and biochar is crucial in the process of preparing the chelating agent CaS. This is because the present invention produces biochar by pyrolyzing tobacco waste and then uses biochar to reduce calcium sulfate in red gypsum to CaS that chelates fly ash, thereby providing an efficient way for the resource utilization of tobacco waste and red gypsum while effectively achieving fly ash solidification and stabilization. The inventors have found through a series of creative work that when the mass ratio of red gypsum powder to biochar is in a suitable range, the chelating agent prepared by them has excellent effect on fly ash solidification and stabilization. When the mass ratio of the biochar to the red gypsum powder is (0.1:1)-(0.5:1), preferably the mass ratio of the biochar to the red gypsum powder is (0.15:1)-(0.3:1), and more preferably the mass ratio of the biochar to the red gypsum powder is (0.15:1)-(0.3:1). When the ratio is 0.3:1, the effect that can be achieved is excellent. This is because the mass ratio of red gypsum and biochar is a key parameter for preparing the chelating agent CaS, which affects the efficiency of the reaction, the purity of the product and the amount of the final product. If the amount of biochar is insufficient, the amount of reducing agent used in the reaction process between the two will be insufficient to completely reduce the calcium sulfate in the red gypsum, resulting in incomplete reaction, reduced CaS yield, and affecting the subsequent fly ash solidification and stabilization. If the amount of biochar is too low, the reduction reaction of the two will not be complete, which may cause the product to contain unreacted calcium sulfate or other intermediates to reduce the purity of CaS. Although excessive use of biochar can ensure that the calcium sulfate in the red gypsum is fully reduced, excessive biochar may cause the reaction system to be too complicated, resulting in many side reactions, thereby affecting the yield of CaS, and excess biochar will also introduce additional impurities, which will have a negative impact on fly ash solidification to a certain extent.

[0031] Experimental Example 2 Effect of reducing atmosphere on chelating agent performance The specific implementation steps are consistent with those in Example 1, except that the reducing atmosphere is adjusted, a control group and experimental groups 11-12 are set, wherein the control group is not set with a reducing atmosphere, and the remaining steps are the same as those in Example 1; In experimental group 11, the reducing atmosphere was set to N 2 ; In Experiment 12, the reducing atmosphere was set to CH 4 ; In experimental group 13, the reducing atmosphere was set to N 2 and CH 4 The volume ratio is 1:1; In experimental group 14, the reducing atmosphere was set to N 2 and CH 4 The volume ratio is 2:1; In experimental group 15, the reducing atmosphere was set to N 2 and CH 4 The volume ratio is 3:1; In experimental group 16, the reducing atmosphere was set to N 2 and CH 4 The volume ratio is 5:1; In experimental group 17, the reducing atmosphere was set to N 2 and CH 4 The volume ratio is 10:1; In experimental group 18, the reducing atmosphere was set to N 2 and CH 4 The volume ratio of the mixture is 11:2; In experimental group 19, the reducing atmosphere was set to N 2 and CH 4 The volume ratio of the mixture is 15:3; In the experimental group 20, the reducing atmosphere was set to N 2 and CH 4 The volume ratio of the mixture is 17:3; In experimental group 21, the reducing atmosphere was set to N 2 and CH 4 The volume ratio of the mixture is 17:5; In experimental group 22, the reducing atmosphere was set to N 2 and CH 4 The volume ratio of the mixture is 20:3; Subsequently, the chelating agents obtained in the control group and experimental groups 11-22 were added to 200 g of fly ash and 60 g of cement to form a block, wherein the solid-liquid ratio was 0.7:1, the curing time was 28 days, the curing humidity was 95%, and the heavy metal leaching concentration test was carried out after crushing and screening. The final table is shown in Table 2 below.

[0032] Table 2

[0033] As can be seen from the above table, for the present invention, the selection of reducing atmosphere is very important. This is because in the preparation process of the present invention, the pyrolysis of red gypsum and tobacco waste needs to be carried out under a reducing atmosphere. When nitrogen and methane are mixed as the reducing atmosphere, the pyrolysis effect of red gypsum and tobacco waste is good, and the purity and yield of the product are high. This is because nitrogen, as an inert gas, mainly provides an oxygen-free environment for red gypsum and tobacco waste, avoiding oxidation reactions during the pyrolysis process, thereby avoiding the combustion of organic components in red gypsum and tobacco waste, and causing side reactions while reducing the yield of CaS. Methane, as a reducing gas, can further decompose at high temperature to generate hydrogen and activated carbon, thereby providing additional reducing ability during the reaction of red gypsum powder and biochar, further promoting the generation of target products, reducing the generation of by-products, and thus improving the yield and purity of the product. Therefore, through the joint action of nitrogen and methane, the generation of CaS can be further promoted while avoiding side reactions. As can be seen from the above table, the volume ratio between methane and nitrogen in the reducing atmosphere is limited. When N 2 With CH 4 The volume ratio of N in the reducing atmosphere is (3:1)-(17:3). 2 With CH 4 When the volume ratio of nitrogen to methane is 17:3, the effect that can be achieved is excellent. This is because when pyrolyzing red gypsum and tobacco waste, the volume ratio of nitrogen to methane in the reducing atmosphere is a key parameter, which directly affects the efficiency of the pyrolysis reaction, product quality and energy consumption. When the proportion of methane in the reducing atmosphere is too high, the stronger the reducing atmosphere, the more conducive it is to the full reduction of calcium sulfate. However, due to the increase in the reaction rate of excessive methane, it may also cause excessive reduction and produce by-products, affecting the purity of the product; if the amount of methane is too little, the reducing atmosphere will be weak, resulting in incomplete reduction of calcium sulfate, thereby generating intermediates or causing incomplete reaction.

[0034] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a chelating agent CaS using red gypsum and biochar, characterized in that: The following steps are involved: The red gypsum and tobacco waste are dried, crushed, ground and sieved to obtain red gypsum powder and biomass; Then, the biomass is pyrolyzed under a nitrogen atmosphere to obtain biochar; The biochar and red gypsum powder are mixed evenly and pyrolyzed in a reducing atmosphere to obtain; The mass ratio of the biochar to the red gypsum powder is (0.1:1)-(0.5:1).

2. The method for preparing chelating agent CaS by using red gypsum and biochar according to claim 1, characterized in that: The mass ratio of the biochar to the red gypsum powder is (0.15:1)-(0.3:1).

3. The method for preparing chelating agent CaS by using red gypsum and biochar according to claim 2, characterized in that: The mass ratio of the biochar to the red gypsum powder is 0.3:

1.

4. The method for preparing chelating agent CaS by using red gypsum and biochar according to claim 1, characterized in that: The reducing atmosphere is a mixture of N2 and CH4.

5. The method for preparing chelating agent CaS by using red gypsum and biochar according to claim 4, characterized in that: The volume ratio of N2 to CH4 in the reducing atmosphere is (3:1)-(17:3).

6. The method for preparing chelating agent CaS by using red gypsum and biochar according to claim 5, characterized in that: The volume ratio of N2 to CH4 in the reducing atmosphere is 17:

3.

7. The method for preparing chelating agent CaS by using red gypsum and biochar according to claim 1, characterized in that: The pyrolysis temperature is 750-950°C; Preferably, the pyrolysis temperature is 900°C.

8. The method for preparing chelating agent CaS by using red gypsum and biochar according to claim 1, characterized in that: When the red gypsum and tobacco waste are dried, crushed, ground and sieved, the drying temperature is 100-110° C. and the drying time is 24-26 hours.

9. The method for preparing chelating agent CaS by using red gypsum and biochar according to claim 1, characterized in that: When the red gypsum and tobacco waste are dried, crushed, ground and sieved, a 60-mesh sieve is used for sieving.

10. Use of the chelating agent CaS prepared by the method for preparing the chelating agent CaS by using red gypsum and biochar as described in any one of claims 1 to 9 in fly ash solidification and stabilization.

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