A method for removing heavy metal ions in desulfurization sludge and a leaching agent

Abstract

The present application relates to sludge remediation technical field, especially to a kind of removal method and leaching agent of heavy metal ion in desulfurization sludge.The present application provides a kind of heavy metal ion leaching agent in desulfurization sludge, including the following weight parts of raw material and water mixture: amino acid 3-5 parts;Inorganic salt 2-4 parts;And erythritol 1-2 parts.The leaching agent prepared by amino acid, inorganic salt and erythritol as raw material can repair mercury, chromium complex pollution desulfurization sludge, efficiently remove heavy metals in desulfurization sludge, reduce its secondary pollution risk, realize resource utilization.The leaching agent of the present application can be used at room temperature, without using other equipment to heat it.The preparation method of the present application is simple, raw material is easy to obtain, and the price is low, can remove mercury and chromium in mercury, chromium complex pollution desulfurization sludge Mercury element and chromium element, has good application prospect.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of sludge remediation, in particular to a method for removing heavy metal ions in desulfurization sludge and a leaching agent. BACKGROUND

[0002] At present, the power supply is still mainly based on thermal power, which accounts for more than 60% of the total power generation. In the flue gas pollution control of coal-fired power plants, the proportion of wet desulfurization technology accounts for 85% of the total desulfurization technology. Limestone-gypsum is the most common method of wet desulfurization technology. This method significantly reduces sulfur dioxide in flue gas of coal-fired power plants, but requires regular discharge of desulfurization wastewater. A large amount of desulfurization sludge is generated during the treatment process. The pollution problem of desulfurization sludge has attracted the attention and concern of the state, so the desulfurization system waste containing high-concentration heavy metal pollutants needs to be handled carefully and strictly to reduce its harm to the social and ecological environment.

[0003] The existing desulfurization sludge treatment methods include chemical leaching, physical method and biological method. Among them, the chemical leaching method has the advantages of fast effect and good removal effect compared with the physical method and the biological method, and is currently the most commonly used removal method for removing heavy metals in desulfurization sludge. The leaching agent can not only remove heavy metals in the sludge, but also further recover and utilize heavy metals. The leaching agent is mainly divided into four categories: inorganic leaching agent, artificial chelating agent, natural organic acid and biological surfactant. The inorganic leaching agent is represented by hydrochloric acid, supplemented by some chloride salts. Due to the strong acidity of hydrochloric acid, the soil physicochemical properties and micro-aggregate structure are completely destroyed while the heavy metals are washed out. The leached soil has no value and cannot be widely applied. The artificial chelating agent is represented by EDTA (ethylenediaminetetraacetic acid), which also has very good effect in washing out heavy metals. The reason is that EDTA has very strong ability to complex metal ions and the formed complex is very stable. However, EDTA and most artificial chelating agents are toxic, and as the main component of the leaching agent, they will enter the ecological cycle system and cause secondary pollution. Biological surfactants are active substances produced by biological metabolism, which have degradability and ultra-low surface tension. They can rely on ultra-low surface tension to make heavy metals from soil colloids into solution. However, not all biological surfactants have the ability to leach heavy metal contaminated soil, and their absorption capacity for heavy metals is lower than that of inorganic acids and artificial chelating agents. SUMMARY

[0004] In view of this, the present application provides a method for removing heavy metal ions in desulfurization sludge and a leaching agent. The raw materials of the leaching agent are widely available and low in price, and can efficiently remove heavy metal ions in desulfurization sludge.

[0005] To solve the above technical problems, the embodiments of the present application adopt the following technical solutions:

[0006] In a first aspect, the present application provides a heavy metal ion leaching agent for desulfurization sludge, which is prepared by mixing the following raw materials with water:

[0007] amino acid 3-5 parts;

[0008] inorganic salt 2-4 parts; and

[0009] erythritol 1-2 parts.

[0010] The amino acid and the inorganic salt are both common leaching agents for removing heavy metal ions in desulfurization sludge. However, the removal effects of both on mercury ions and chromium ions in desulfurization sludge are not ideal. The inventor finds that adding a proper amount of erythritol to the amino acid and inorganic salt leaching agent can improve the removal effect of the amino acid and inorganic salt leaching agent on mercury ions and chromium ions in desulfurization sludge, and also has a good removal effect on other heavy metal ions. Erythritol has good biodegradability, and can gather and wrap heavy metal ions, enhance the mobility of heavy metal ions, reduce the surface tension of desulfurization sludge and water, and make it easier to migrate from desulfurization sludge, so as to produce a good synergistic effect with the amino acid and the inorganic salt. Moreover, erythritol exists widely in nature, and is easier to obtain as a raw material.

[0011] In the present application, the weight fractions of the amino acid, the inorganic salt and the erythritol are also critical. If too much amino acid and inorganic salt are added to the leaching agent, the combination of heavy metal ions and the leaching agent has basically reached saturation, and the concentration of the amino acid and the inorganic salt will not increase the leaching effect any more, and will also cause the reaction product to block the gaps in the desulfurization sludge, thereby leading to a decrease in the removal effect. If too little amino acid and inorganic salt are added to the leaching agent, the removal effect of heavy metal ions will not be obvious. If too little erythritol is added to the leaching agent, the concentration of erythritol will be lower than the critical micelle concentration, the number of micelles formed will decrease, and the removal effect will not be ideal. When the concentration of erythritol is greater than the critical micelle concentration, the contact opportunities of erythritol and heavy metal ions will increase, and the removal effect will gradually increase. However, when the concentration of erythritol reaches a certain value, the combination of erythritol and heavy metal ions basically reaches saturation, and the concentration of erythritol will not improve the removal effect of heavy metal ions.

[0012] Preferably, the amino acid is selected from one or more of glutamine, hydroxyproline or arginine, and / or the inorganic salt is selected from one or more of sodium thiosulfate, ammonium bisulfite or potassium iodide.

[0013] In the present application, the amino acid is not limited to one or more of glutamine, hydroxyproline and arginine, and other amino acids that can remove heavy metal ions in desulfurization sludge can also be used. The inorganic salt is not limited to one or more of sodium thiosulfate, ammonium bisulfite and potassium iodide, and other inorganic salts that can remove heavy metal ions in desulfurization sludge can also be used.

[0014] Preferably, the weight ratio of the total weight of the amino acid, the inorganic salt and the erythritol to the weight of water is 1:100-500.

[0015] Preferably, the leaching agent is prepared by mixing 4-5 parts by weight of the amino acid, 2-3 parts by weight of the inorganic salt and 1-2 parts by weight of the erythritol with 700-1000 parts by weight of water.

[0016] Preferably, the leaching agent is prepared by mixing 4-5 parts by weight of the amino acid, 2-3 parts by weight of the inorganic salt and 1-2 parts by weight of the erythritol with 700-1000 parts by weight of water.

[0017] In the second aspect, the embodiments of the present application also provide a method for removing heavy metal ions in desulfurization sludge, which comprises the step of leaching the desulfurization sludge to be treated with the leaching agent.

[0018] Preferably, the method comprises the steps of drying and crushing the desulfurization sludge to be treated,

[0019] The crushed desulfurization sludge is mixed with the leaching agent and stirred, and then is allowed to stand, and the leaching agent is filtered out, so as to obtain the desulfurization sludge from which the heavy metal ions are removed; or the crushed desulfurization sludge is leached with the leaching agent.

[0020] In the present application, the desulfurization sludge needs to be dried and crushed before being leached with the leaching agent. This is because the mechanical dewatering can obtain sludge with a solid content of 20%-30%, which is also called sludge cake. The moisture content of the sludge cake is still high, and the sludge cake has fluid properties and high viscosity, and the disposal difficulty and cost are still high, so it is necessary to further reduce the amount. The main purpose of sludge drying is to reduce the amount, that is, to remove the water in the sludge by technical means before treatment, so as to prepare for the later treatment. Crushing the dried desulfurization sludge can change the desulfurization sludge into granules or powders, so as to increase the specific surface area of the desulfurization sludge and further improve the leaching effect of the leaching agent on the desulfurization sludge.

[0021] In the present application, the drying method can be that the desulfurization sludge is placed in a 60℃ oven for drying treatment for 24h. The drying method, temperature and time are not limited to the above-mentioned method, as long as the desulfurization sludge is dried. The crushing method can be grinding and sieving. The crushing method is not limited to the above-mentioned method, as long as the desulfurization sludge is changed into granules or powders.

[0022] Preferably, the metal ions at least include mercury and chromium, and further include cadmium.

[0023] Preferably, the solid-liquid ratio of the leaching agent and the desulfurization sludge after drying is 10-15 ml / g, and / or the rotating speed of the stirring is 1000-1500 r / min.

[0024] Compared with the prior art, the present application has the following beneficial effects:

[0025] The leaching agent prepared from amino acids, inorganic salts and erythritol can repair the desulfurization sludge with mercury and chromium complex pollution, efficiently remove heavy metals in the desulfurization sludge, reduce the risk of secondary pollution, and realize resource utilization. The leaching agent of the present application can be used at room temperature without heating by other equipment. The preparation method of the present application is simple, the raw materials are easy to obtain, and the price is low. The leaching agent can remove mercury and chromium elements in the desulfurization sludge with mercury and chromium complex pollution, and has a good application prospect. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical scheme and advantages of the present application clearer, the present application will be further described in detail below in combination with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the present application.

[0027] The desulfurization sludge is a residue formed by desulfurization wastewater with high suspended solids. The main components of the desulfurization sludge include ash, gypsum, chloride ions and heavy metals. Among them, the content of desulfurization gypsum (CaSO4·2H2O) is generally 90%-95%.

[0028] The desulfurization sludge has the characteristics of high salt content and difficulty in dewatering. During the crystallization of desulfurization gypsum, a certain amount of water is left in the gypsum crystal, causing the water content of the gypsum to increase. Ca2Cl is left between the gypsum grains and the grains, blocking the channel of free water between the crystals. In addition, the gypsum lattice is distorted, generating more crystal nuclei, making it difficult for the gypsum to dewater, so the desulfurization sludge has a high water content, high viscosity and large volume. The desulfurization sludge is very unstable, containing water, coal ash, unreacted calcium carbonate, aluminum oxide and silicon oxide, etc. The desulfurization sludge contains heavy metals such as Hg, As, Cd, Cr, Pb, Ni, Zn and Cu. If not treated, it will seriously pollute the environment.

[0029] The present application is mainly aimed at the treatment of desulfurization sludge produced in the wet desulfurization process of coal-fired power plants. The desulfurization sludge contains various heavy metal ions.

[0030] The desulfurization sludge in the following examples and comparative examples is taken from the sludge after desulfurization of a certain coal-fired power plant in Shijiazhuang. Among them, the detection method of heavy metal ion content in the sludge is determined according to the "Sludge Test Method for Municipal Sewage Treatment Plant" (CJ / T 221-2005), and the inductively coupled plasma emission spectrometry method is used after atmospheric digestion. It is determined that the heavy metal content in the sludge after wet desulfurization is: mercury ion 52.9 mg / kg, chromium ion 580.6 mg / kg, and cadmium ion 1.1 mg / kg.

[0031] The desulfurization sludge heavy metal ion leaching agent provided by the present application is mixed by 3-5 parts by weight of amino acid, 2-4 parts by weight of inorganic salt and 1-2 parts by weight of erythritol and water. The inorganic salt is selected from one or more of sodium thiosulfate, ammonium bisulfite or potassium iodide, which is environmentally friendly, cheap and easy to obtain; the amino acid can acidify the desulfurization sludge, easily dissolve the heavy metals, and is more conducive to the removal of metal ions in the leaching process; erythritol is often used as a sweetener, and has good biodegradability. In this application, erythritol has the functions of ion exchange and hydrophilic group, which is conducive to enhancing the fluidity of heavy metal ions, reducing the interfacial tension between the desulfurization sludge and water, and making it easier to migrate out of the desulfurization sludge, especially for the removal rate of mercury and chromium in the desulfurization sludge.

[0032] The amino acid in the present application can be selected from one or more of glutamine, hydroxyproline or arginine. Preferably, the amino acid can be any two of glutamine, hydroxyproline or arginine. The present application does not have a special limitation on the amount of any two of the amino acids, for example, the weight ratio can be 0.5-5:1, and the present application is not limited thereto.

[0033] The inorganic salt in the present application can be selected from one or more of sodium thiosulfate, ammonium bisulfite or potassium iodide. Preferably, the inorganic salt can be any two of sodium thiosulfate, ammonium bisulfite or potassium iodide. The present application does not have a special limitation on the amount of any two of the inorganic salts, for example, the weight ratio can be 0.1-5:1, and the present application is not limited thereto.

[0034] The following specific examples illustrate the scheme of the present application.

[0035] Example 1

[0036] The present application provides a kind of desulfurization sludge heavy metal ion leaching agent, and the raw materials including as follows are weighed: 3kg hydroxyproline, 2kg ammonium bisulfite and 1kg erythritol, after mixing, 600kg water is added, stirring, and the leaching agent is obtained.

[0037] Examples 2-7

[0038] The preparation method of the eluent provided in Embodiments 2-7 is the same as in the embodiments, wherein the components and their proportions are shown in Table 1.

[0039] Table 1 Raw materials and weights in the eluents of Embodiments 2-7

[0040]

[0041] Comparative Examples 1-9

[0042] In order to investigate the effect of erythritol in the embodiments, other-component eluents were also prepared, wherein the components and their proportions are shown in Table 2.

[0043] Table 2 Raw materials and weights in the eluents of Comparative Examples 1-9

[0044]

[0045] Test Example

[0046] The effect of removing heavy metal ions in desulfurization sludge by the eluents of each embodiment and comparative example was tested.

[0047] First, the desulfurization sludge was dried in an oven at 60°C for 24 h, then crushed (ground) to a particle size of 1-20 cm and passed through a 100-mesh sieve for standby;

[0048] Then, the eluents of each embodiment and comparative example were mixed with the sieved desulfurization sludge, stirred, and sufficiently eluted and evenly distributed, and then the desulfurization sludge that was sufficiently eluted and evenly distributed was left to stand for solid-liquid separation, the eluent was removed by filtration, and the remaining residue desulfurization sludge was the repaired desulfurization sludge.

[0049] The solid-liquid ratio of the eluent to the desulfurization sludge, the stirring speed, and the stirring time in each embodiment and comparative example are shown in Table 3:

[0050] Table 3 Solid-liquid ratio, stirring speed, and stirring time in the elution process of each embodiment and comparative example

[0051]

[0052] The heavy metal ion content of the repaired desulfurization sludge of each embodiment and comparative example was detected, and the heavy metal removal rate (%) was calculated according to the formula: (heavy metal content in the desulfurization sludge before repair - heavy metal content in the desulfurization sludge after repair) / heavy metal content in the desulfurization sludge before repair x 100%, and the results are shown in Table 4.

[0053] Table 4 Heavy metal ion content and removal rate in the repaired sludge of the embodiments and comparative examples

[0054]

[0055] Test the influence of non-broken desulfurization sludge after drying on the leaching agent

[0056] After the desulfurization sludge is placed in a drying oven at 60 DEG C for drying treatment for 24 hours, the leaching agent obtained in Example 1 is mixed with the desulfurization sludge at a solid-liquid ratio of 10 ml / g, and the mixture is stirred at a stirring speed of 1000 r / min for 30 min to fully leach and uniformly wash the desulfurization sludge, and then the fully leached and uniformly washed desulfurization sludge is allowed to stand for solid-liquid separation, the leaching liquid is removed by filtration, and the remaining residual desulfurization sludge is the repaired desulfurization sludge.

[0057] The heavy metal ion content of the repaired sludge is detected, the mercury ion content is 18.36 mg / kg, the chromium ion content is 137.62 mg / kg, and the cadmium ion content is 0.49 mg / kg.

[0058] According to the heavy metal removal rate (%) of the desulfurization sludge = (the heavy metal content in the desulfurization sludge before repair - the heavy metal content in the desulfurization sludge after repair) / the heavy metal content in the desulfurization sludge before repair x 100%, the removal effect of the leaching agent in the examples and the comparative examples is calculated, the removal rate of mercury ions is 65.3%, the removal rate of chromium ions is 76.3%, and the removal rate of cadmium ions is 55.5%.

[0059] It can be seen from the above test that breaking (grinding and sieving) the dried sludge can promote the removal effect of the leaching agent on the heavy metal ions in the desulfurization sludge.

[0060] The above only describes the preferred embodiments of the present application and should not be used to limit the present application, and any modification, equivalent replacement or improvement made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A heavy metal ion eluent for desulfurization sludge, characterized by, The eluent is mainly composed of the following raw materials and water: Amino acid 3-5 parts; Inorganic salt 2-4 parts; and Erythritol 1-2 parts.

2. The heavy metal ion leaching agent for desulfurization sludge according to claim 1, characterized by, The eluent is composed of 4-5 parts of amino acid, 2-3 parts of inorganic salt and 1-2 parts of erythritol and 700-1000 parts of water.

3. The eluent for heavy metal ions in desulfurization sludge according to claim 1, characterized by, The eluent is composed of 4-5 parts of hydroxyproline, 2-3 parts of ammonium bisulfite and 1-2 parts of erythritol and 700-1000 parts of water.

4. The heavy metal ion leaching agent for desulfurization sludge according to claim 1 or 2, characterized by, The amino acid is selected from one or more of glutamine, hydroxyproline or arginine; and / or, The inorganic salt is selected from one or more of sodium thiosulfate, ammonium bisulfite or potassium iodide.

5. The eluent for heavy metal ions in desulfurization sludge according to any one of claims 1 to 3, characterized by, The total weight of the amino acid, inorganic salt and erythritol is 1:100-500 compared with the weight of water.

6. A method for removing heavy metal ions from desulfurization sludge, characterized by, The eluent of any one of claims 1-5 is used to elute the desulfurization sludge to be treated.

7. The method for removing heavy metal ions from desulfurization sludge according to claim 6, characterized by, The method comprises the following steps: The desulfurization sludge to be treated is dried and crushed; The crushed desulfurization sludge is mixed with the eluent, stirred, then left to stand, the eluent is filtered off, and the desulfurization sludge with metal ions removed is obtained; or the crushed desulfurization sludge is eluted with the eluent.

8. The method for removing heavy metal ions from desulfurization sludge according to claim 7, characterized by, The metal ions at least include mercury and chromium.

9. The method of removing heavy metal ions from desulfurization sludge according to claim 8, characterized by, The metal ions also include cadmium.

10. The method for removing heavy metal ions from desulfurization sludge according to claim 7, characterized by, The solid-liquid ratio of the eluent and the dried desulfurization sludge is 10-15 ml / g, and / or the stirring speed is 1000-1500 r / min.

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