A passivator for heavy metal composite contaminated soil and a preparation method thereof

Abstract

The present application belongs to the technical field of soil heavy metal remediation, and particularly relates to a passivator for heavy metal composite contaminated soil and a preparation method thereof. In order to effectively reduce the composite heavy metal pollution in soil, 1-3 parts of sand washing sludge, 1-3 parts of straw and 1-3 parts of calcium dihydrogen phosphate are compounded to obtain the heavy metal composite contaminated soil passivator. The use of the passivator of the present application reduces the effective cadmium content in the contaminated soil by 96.89%-98.27%, reduces the effective copper content by 96.9%-98.7%, reduces the effective zinc content by 82.13%-88.86%, and reduces the effective chromium content by 34.22%-86.14%, and the heavy metal passivation effect is obvious. The present application can be used for the remediation of heavy metal composite contaminated acid and neutral soil, and does not cause secondary pollution, has a wide application prospect in the field of farmland and mine remediation, and promotes the comprehensive utilization of resources and reduces the risk of environmental pollution.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of soil heavy metal remediation, and particularly relates to a passivator for heavy metal composite contaminated soil and a preparation method thereof. BACKGROUND

[0002] The information disclosed in this Background section is for the purpose of increasing the understanding of the background of the application without admitting that such information forms any part of prior art.

[0003] The sources of heavy metals in soil are mainly as follows: one is natural source, which is due to the elements in rocks and minerals being released in the soil after weathering; the other is human factors, mainly including atmospheric deposition, discharge of wastewater in the process of urban industrialization, discharge of household garbage and industrial solid waste, sewage irrigation, sludge application, use of mulch, fertilizers and pesticides, and various agricultural activities. Heavy metal pollution can destroy the structure and function of soil, affect the growth of crops, and cause crop yield reduction or even absolute loss. The grain polluted by heavy metals in China amounts to 12 million tons per year, resulting in a grain yield reduction of more than 10 million tons, and the total economic loss of about 20 billion yuan. Heavy metals can endanger human life and health through direct exposure and food chain accumulation. Remediation of farmland soil contaminated by heavy metals is an important measure to ensure the safety of agricultural products and human health.

[0004] The commonly used methods for treating soil heavy metal pollution include physical, chemical and biological methods. At present, the remediation of farmland soil contaminated by heavy metals mainly focuses on chemical passivation. Heavy metal passivators are divided into inorganic and organic categories. The inorganic category mainly includes alkaline substances, phosphate substances, clay minerals and industrial waste residues, which can fix heavy metals by increasing soil pH, adsorption or complexation. The organic category mainly includes organic waste, biochar and organic acids, which can form insoluble metal-organic complexes with heavy metals through complex adsorption, not only having good effect on heavy metal passivation, but also improving soil fertility.

[0005] Sand washing sludge is a solid waste generated in the production process of machine-made sand. The research and development of sand washing sludge comprehensive utilization technology is of great significance to improve the comprehensive utilization level of building material mine resources, reduce environmental pollution risk and promote green mine construction. The main component of sand washing sludge generated in the production of limestone sand and gravel aggregate is limestone powder, which can increase the soil pH, make the heavy metals form hydroxide and carbonate precipitate, and thus reduce their bioavailability. Although the application of sand washing sludge alone has a certain passivation effect on soil heavy metals, long-term and large-scale application of sand washing sludge can cause soil compaction. SUMMARY

[0006] In order to solve the problems of the prior art, the present application aims to provide a passivator for heavy metal composite contaminated soil and a preparation method thereof.

[0007] In order to achieve the above-mentioned purpose, the present application is realized by the following technical scheme:

[0008] In the first aspect, the present application provides a passivator for heavy metal composite contaminated soil, comprising the following components in parts by weight: 1-3 parts of sand washing sludge, 1-3 parts of straw, and 1-3 parts of calcium dihydrogen phosphate.

[0009] In the second aspect, the present application provides a preparation method of the passivator for heavy metal composite contaminated soil according to the first aspect, comprising the following steps:

[0010] S1, after the sand washing sludge is naturally dried, it is ground and sieved;

[0011] S2, the straw is washed, dried, crushed, and sieved;

[0012] S3, the sand washing sludge, the straw, and the calcium dihydrogen phosphate are mixed.

[0013] In the third aspect, the present application provides an application of the passivator for heavy metal composite contaminated soil according to the first aspect in passivating heavy metals in soil.

[0014] In the fourth aspect, the present application provides a passivation method of heavy metal composite contaminated soil, wherein the passivator for heavy metal composite contaminated soil according to the first aspect is mixed uniformly with heavy metal contaminated soil, and deionized water is added for culture.

[0015] The above-mentioned one or more technical solutions of the present application have the following beneficial effects:

[0016] In the present application, the sand washing sludge is used to improve the pH of soil, the straw is added to improve the soil structure and enhance the passivation effect, and the phosphate provided by the calcium dihydrogen phosphate is used to form phosphate precipitates and co-precipitates with heavy metals, so as to achieve the purpose of synergistic passivation and prevent the sand washing sludge from causing soil compaction.

[0017] The sand washing sludge and the straw used in the present application are both waste materials, and the passivator has low manufacturing cost and can also solve the problem of waste material treatment and recycling.

[0018] The passivator can be used for repairing acid and neutral soil with heavy metal complex pollution, has excellent adsorption performance on Cd, Cu, Zn and Cr, does not cause secondary pollution in the process of treating soil, has wide application prospect in the field of farmland and mine repair, and promotes comprehensive utilization of resources and reduces environmental pollution risk. DETAILED DESCRIPTION

[0019] In a first typical embodiment of the present application, a passivator for soil with heavy metal complex pollution comprises the following components in parts by weight: 1-3 parts of sand washing sludge, 1-3 parts of straw, and 1-3 parts of calcium dihydrogen phosphate.

[0020] The sand washing sludge produced in the production of limestone sand and gravel aggregate mainly contains limestone powder, which can increase the pH of the soil, make the heavy metals form hydroxide and carbonate to reduce their bioavailability. The straw is mainly composed of cellulose, hemicellulose and lignin, and the functional groups such as hydroxyl, carboxyl and amino in the straw can form ionic bonds or covalent bonds with the adsorbed heavy metal ions to achieve the purpose of adsorbing metal ions. Calcium dihydrogen phosphate as a phosphate not only can passivate heavy metals in the soil, but also can improve soil fertility and promote plant growth. By using sand washing sludge, straw and calcium dihydrogen phosphate together, the soil hardening caused by sand washing sludge can be prevented, and the heavy metal passivation effect can be improved.

[0021] In one or more embodiments of this embodiment, the sand washing sludge is a filter cake obtained after primary sedimentation, coagulation sedimentation and filter pressing of sand washing wastewater in the production of limestone sand and gravel aggregate.

[0022] In a second typical embodiment of the present application, a preparation method of the passivator for soil with heavy metal complex pollution as described in the first typical embodiment comprises the following steps:

[0023] S1, dry the sand washing sludge naturally, grind and sieve;

[0024] S2, wash, dry, crush and sieve the straw;

[0025] S3, mix the sand washing sludge, straw and calcium dihydrogen phosphate.

[0026] In one or more embodiments of this embodiment, in step S1, the sand washing sludge is sieved through a 90-110 mesh sieve.

[0027] In one or more embodiments of this embodiment, in step S2, the drying temperature is 35-45 DEG C and the drying time is 18-30 h.

[0028] In one or more embodiments of this embodiment, in step S2, the straw is sieved through a 50-70 mesh sieve.

[0029] The third typical embodiment of the present application is the application of the passivation agent for heavy metal composite contaminated soil as described in the first typical embodiment in passivating heavy metals in soil.

[0030] The fourth typical embodiment of the present application is a passivation method for heavy metal composite contaminated soil, which mixes the passivation agent for heavy metal composite contaminated soil as described in the first typical embodiment with heavy metal contaminated soil uniformly and adds deionized water for culture.

[0031] In one or more embodiments of this embodiment, the passivation agent is added in an amount of 2-4% of the mass of the heavy metal contaminated soil.

[0032] In one or more embodiments of this embodiment, deionized water is added to make the water content of the heavy metal contaminated soil 75-85% of the maximum field water holding capacity, and water is supplemented and stirred uniformly during the culture process by weighing method.

[0033] In order to enable those skilled in the art to more clearly understand the technical solutions of the present application, the technical solutions of the present application will be described in detail below with specific examples and comparative examples.

[0034] In the following examples, the sand washing sludge is obtained from a stone company, which is a filter cake obtained after sand washing wastewater is subjected to primary sedimentation, coagulation sedimentation and filter pressing; corn straw; Ca(H2PO4)2; HNO3; HCl; CdCl2·2.5H2O; CuCl2·2H2O; ZnCl2; K2Cr2O7; C 14 H 23 N3O 10 ; C6H 15 NO3; CaCl2·2H2O, all of which are analytical pure.

[0035] Example 1

[0036] The passivation agent in this embodiment includes 1 part of sand washing sludge, 1 part of corn straw and 3 parts of calcium dihydrogen phosphate by mass fraction.

[0037] The sand washing sludge and corn straw are prepared by the following steps:

[0038] Sand washing sludge: natural drying, grinding, and passing through a 100-mesh sieve.

[0039] Corn straw: wash the surface stains of corn straw with deionized water, dry in an oven at 40°C for 24h, and then grind the dried corn straw with a high-speed grinder, pass through a 60-mesh sieve to obtain corn straw powder.

[0040] Example 2

[0041] The passivator in this example comprises 2 parts of sand washing sludge, 1 part of corn straw and 2 parts of calcium dihydrogen phosphate by mass fraction.

[0042] The sand washing sludge and corn straw are prepared as in Example 1.

[0043] Example 3

[0044] The passivator in this example comprises 1 part of sand washing sludge, 3 parts of corn straw and 1 part of calcium dihydrogen phosphate by mass fraction.

[0045] The sand washing sludge and corn straw are prepared as in Example 1.

[0046] Example 4

[0047] The passivator in this example comprises 2 parts of sand washing sludge, 1 part of corn straw and 2 parts of calcium dihydrogen phosphate by mass fraction.

[0048] The sand washing sludge and corn straw are prepared as in Example 1.

[0049] Example 5

[0050] The passivator in this example comprises 2 parts of sand washing sludge, 2 parts of corn straw and 1 part of calcium dihydrogen phosphate by mass fraction.

[0051] The sand washing sludge and corn straw are prepared as in Example 1.

[0052] Example 6

[0053] The passivator in this example comprises 3 parts of sand washing sludge, 1 part of corn straw and 1 part of calcium dihydrogen phosphate by mass fraction.

[0054] The sand washing sludge and corn straw are prepared as in Example 1.

[0055] Comparative Example 1

[0056] The passivator in this example comprises 1 part of sand washing sludge and 3 parts of calcium dihydrogen phosphate by mass fraction.

[0057] The sand washing sludge is prepared as in Example 1.

[0058] Comparative Example 2

[0059] The passivator in this example comprises 1 part of sand washing sludge and 1 part of corn straw by mass fraction.

[0060] The sand washing sludge and corn straw are prepared as in Example 1.

[0061] Experimental Example 1

[0062] The experimental soil is a red soil in Yingtan, Jiangxi Province, and the basic physicochemical properties of the soil are shown in Table 1.

[0063] Table 1 Basic physicochemical properties of soil

[0064]

[0065] The passivators prepared in Examples 1-6 and Comparative Examples 1-2 were added to heavy metal contaminated soil to verify the passivation effect of the passivators on heavy metals in the soil. The specific test method is as follows:

[0066] (I) Soil treatment

[0067] 230 g of artificially simulated contaminated soil was accurately weighed in a plastic box, and the corresponding passivators of Examples 1-6 and Comparative Example 1 were added and mixed with the soil, the addition amount of each example passivator was 3% of the mass of the soil, the addition amount of the passivator of Comparative Example 1 was 4% of the mass of the soil, and the addition amount of the passivator of Comparative Example 2 was 2% of the mass of the soil, each treatment was repeated three times, and the soil without adding the passivator was used as a control. After adding the passivator, a certain amount of deionized water was added to each plastic box at regular intervals to keep the soil moisture at 80% of the maximum field water holding capacity, mixed well, and cultured in a constant temperature incubator for 30 days before analysis and determination.

[0068] (II) Determination method

[0069] CaCl2 extraction method was used to evaluate the availability of heavy metals in soil samples. 1.0 g of air-dried soil sample and 10 mL of 0.01 mol / L CaCl2 extractant were added to a centrifuge tube, then placed horizontally in a constant temperature oscillator (25℃), extracted at 180 rpm for 2 h, centrifuged at 4000 rpm for 10 min, took the supernatant, passed through a 0.45 μm cellulose acetate membrane, and diluted and acidified with 1% HNO3, and the CaCl2 extractable Cd, Cu, Zn, Cr content was determined by atomic absorption spectrophotometer (Shimadzu AA-7000F / G). The determination results are shown in Table 2.

[0070] Table 2 Available heavy metal content in soil after treatment with various passivators (mg / kg)

[0071]

[0072] As can be seen from Table 2, the passivation rate of the heavy metal in the soil heavy metal passivator prepared by the application is about 34.22%-98.7%, the effective cadmium content is reduced by 96.89%-98.27%, the effective copper content is reduced by 96.9%-98.7%, the effective zinc content is reduced by 82.13%-88.86%, and the effective chromium content is reduced by 34.22%-86.14%. The passivator can be used for repairing the acid and neutral heavy metal contaminated soil, and has a broad application prospect in the field of farmland and mine repair. In the comparative example 1, the addition of the sand washing sludge increases the pH of the soil, which is not conducive to the adsorption and reduction of Cr(Ⅵ), and H2PO4 - , HPO4 2- , PO4 3- compete with Cr(Ⅵ) for the adsorption sites, so that the content of the effective Cr is higher than that of the control group. The passivation effect of the comparative example 1 on Zn is better than that of the examples 1-6 because the addition amount of the passivator is 4%, which is higher than the addition amount of the passivator in the examples 1-6 (3%). The passivation effect of the comparative example 2 on Zn is better than that of the examples 1-6 because the sand sludge and the straw have a better passivation effect on Zn than the calcium dihydrogen phosphate, and in the case that the calcium dihydrogen phosphate is not added, increasing the amount of the sand sludge and the straw can also achieve a good Zn passivation effect.

[0073] The above only describes the preferred embodiments of the application and is not used to limit the application. For those skilled in the art, the application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the application shall be included in the protection scope of the application.

Claims

1. A passivating agent for heavy metal complex contaminated soil, characterized by comprising: The components include the following weight parts: 1-3 parts of sand washing sludge, 1-3 parts of corn straw, and 1-3 parts of calcium dihydrogen phosphate; The passivator is used for repairing acid and neutral soil with Cd, Cu, Zn, and Cr heavy metal composite pollution; The sand washing sludge is the filter press mud obtained after primary sedimentation, coagulation sedimentation, and filter pressing of sand washing wastewater in limestone sand production; The corn straw is washed with deionized water to remove surface stains, dried in an oven at 40 DEG C for 24 hours, and then ground into powder with a high-speed grinder and sieved through a 60-mesh sieve.

2. A method for preparing the passivating agent for heavy metal complex contaminated soil according to claim 1, characterized in that, The method comprises the following steps: S1, drying the sand washing sludge naturally and grinding and sieving it; S2, washing, drying, and grinding the straw and sieving it; S3, mixing the sand washing sludge, the straw, and the calcium dihydrogen phosphate.

3. The production method according to claim 2, wherein In step S1, the sand washing sludge is sieved through a 90-110 mesh sieve.

4. The production method according to claim 2, wherein In step S2, the drying temperature is 35-45 DEG C, and the drying time is 18-30 hours.

5. The production method according to claim 2, wherein In step S2, the straw is sieved through a 50-70 mesh sieve.

6. The use of the passivator for heavy metal composite contaminated soil in claim 1 in passivating heavy metals in soil.

7. A method for passivating a soil contaminated with heavy metals, characterized in that, The passivator for heavy metal composite contaminated soil in claim 1 is mixed with heavy metal contaminated soil and deionized water is added for culture.

8. The passivation method according to claim 7, characterized in that, The amount of the passivator added is 2-4% of the mass of the heavy metal contaminated soil.

9. The passivation method according to claim 7, wherein Deionized water is added to make the water content of the heavy metal contaminated soil 75-85% of the maximum field water holding capacity, and water is added and stirred evenly during the culture process by weighing.

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