Portland cement for stably curing heavy metal lead and preparation method

Abstract

The invention provides a preparation method of Portland cement for stably curing heavy metal lead. The Portland cement is prepared from the following raw materials in parts by weight: 80-100 parts of ordinary Portland cement, 5-20 parts of low-activity metakaolin, 5-10 parts of lead nitrate powder and 40-50 parts of water. The preparation method comprises the following steps: adding lead nitrate powder into water, stirring to obtain a uniform water solvent, slowly adding the uniform water solvent into a uniform mixture of cement and low-activity metakaolin, then adjusting working parameters of a rotary mixer for mixing to obtain uniform mixed slurry, and finally forming and curing according to the national standard. The Portland cement capable of stably curing the heavy metal lead can be obtained. The raw material adopts industrial solid waste low-activity metakaolin as an auxiliary cementing material, the industrial waste is reasonably utilized, the use of Portland cement is reduced, the engineering cost and energy consumption are reduced, and meanwhile, the Portland cement material with good capability of stably curing heavy metal lead is prepared by improving the internal structure.

Description

Technical Field

[0001] The present invention relates to a preparation method of a silicate cement for stably solidifying heavy metal lead, belonging to the technical fields of building materials and solid waste treatment. Background Art

[0002] With the acceleration of the industrialization process, the problem of heavy metal pollution has become increasingly severe. Among them, lead (Pb) has become a key object for prevention and control due to its strong toxicity and high bioaccumulation. If lead-containing solid wastes (such as lead battery waste, smelting slag, contaminated soil, etc.) are not properly treated, lead ions are likely to enter the environment through rain leaching, seriously threatening the ecology and human health. At present, the cement-based solidification / stabilization (S / S) technology has been widely used in the treatment of heavy metal pollution due to its low cost and simple operation. The hydration products of silicate cement (such as C-S-H gel, ettringite) can fix heavy metals through mechanisms such as physical encapsulation, ion exchange, and chemical precipitation. However, there are the following problems in the traditional silicate cement for solidifying lead: low solidification efficiency: the chemical binding ability between lead ions and cement hydration products is limited. Especially under acidic or long-term leaching conditions, lead is likely to be released from the solidified body. Research shows that the solidification rate of ordinary silicate cement for lead is usually less than 70%, which is difficult to meet strict environmental protection standards (such as TCLP, GB 5085.3); insufficient stability: the porosity of the cement matrix is high, and lead may migrate through diffusion or penetration; at the same time, lead compounds (such as Pb(OH)2, PbCO3) are prone to phase change during carbonization or wet-dry cycles, resulting in secondary release; poor material adaptability: existing technologies mostly rely on increasing the cement dosage or adding high-cost additives (such as phosphates, sulfides), but excessive cement will reduce the mechanical properties of the solidified body, while chemical agents may introduce new environmental risks. In summary, it is urgent to develop a low-cost and environmentally friendly silicate cement-based solidification method, by regulating the cement composition, introducing functional additives (such as metakaolin, etc.) and optimizing the curing conditions, to enhance the chemical fixation ability and long-term stability of lead, so as to solve the defects of the existing technologies. Summary of the Invention

[0003] Technical Problem: To solve the above technical problems, the present invention provides a preparation method of a silicate cement doped with low-activity metakaolin for stably solidifying heavy metal lead, so as to solve the problems of high cost of additives and unstable solidification effect of silicate cement for stably solidifying heavy metal lead in the existing technology.

[0004] Technical Solution: A silicate cement for stably solidifying heavy metal lead, the raw materials are calculated by mass parts, and include the following components: 80-100 parts of ordinary silicate cement, 5-20 parts of low-activity metakaolin, 5-10 parts of lead nitrate powder, and 40-50 parts of water.

[0005] The silicate cement is 42.5 grade ordinary silicate cement.

[0006] In the low-reactivity metakaolin, the SiO2 content is ≥50%, the Al2O3 content is ≥35%, and the specific surface area is ≤20000 m 2 / kg.

[0007] The preparation method of the silicate cement for stably solidifying heavy metal lead includes the following steps:

[0008] Step 1: Take ordinary Portland cement and low-reactivity metakaolin, stir and mix them evenly to obtain a uniformly mixed cementitious material;

[0009] Step 2: Add lead nitrate powder to water, stir to obtain a uniform aqueous solvent, slowly add it to the mixture in Step 1, then mix to obtain a uniformly mixed slurry, and finally form and cure according to national standards to obtain the silicate cement for stably solidifying heavy metal lead.

[0010] The stirring and mixing is carried out by a rotary mixer. When mixing in Step 2, the rotation speed of the mixer is 140 - 280 r / min, and the mixing time of the rotary mixer is 90 - 120 s.

[0011] Beneficial effects:

[0012] In the present invention, lead nitrate powder is added to water, stirred to obtain a uniform aqueous solvent, slowly added to the mixture of uniform cement and low-reactivity metakaolin, then the working parameters of the rotary mixer are adjusted for mixing to obtain a uniformly mixed slurry, and finally formed and cured according to national standards to obtain the silicate cement for stably solidifying heavy metal lead. In the present invention, the raw material uses low-reactivity metakaolin, an industrial solid waste, as an auxiliary cementitious material, reasonably utilizes industrial waste, reduces the use of Portland cement, reduces the engineering cost and energy consumption, and at the same time prepares a silicate cement material with good ability to stably solidify heavy metal lead by improving the internal structure. Description of the drawings

[0013] Figure 1 is a schematic flow chart of the preparation steps of the silicate cement of the present invention. Specific embodiments

[0014] The following further describes in detail the embodiments of the present invention with reference to the drawings and examples. The following examples are used to illustrate the present invention, but cannot be used to limit the scope of the present invention.

[0015] Example 1: As Figure 1 shown, the present invention provides a silicate cement for stably solidifying heavy metal lead, which includes the following components by weight:

[0016] 100 parts of ordinary Portland cement, 5 parts of lead nitrate powder, and 40 parts of water. The following preparation method is adopted:

[0017] (1) Wet the cement paste mixer and the tools used.

[0018] (2) Sequentially add the weighed cement and low-activity metakaolin into the mixing container of the mixer, cover the mixer container, rotate at a speed of 140 r / min, and stir for 60 S to make the mixture evenly mixed to obtain the dry mixture of the cementitious material.

[0019] (3) Add the weighed lead nitrate powder to water, stir with a glass rod for several seconds to obtain a uniform aqueous solution. Slowly add the evenly stirred aqueous solution into the mixture from the water injection port, rotate at a speed of 280 r / min, and stir for 120 S. After forming and curing, the silicate cement for stabilizing and solidifying heavy metal lead can be obtained.

[0020] Example 2, a silicate cement for stabilizing and solidifying heavy metal lead, by weight, includes the following components:

[0021] 95 parts of ordinary portland cement, 5 parts of low-activity metakaolin, 5 parts of lead nitrate powder, and 40 parts of water. The preparation method is the same as that of Example 1.

[0022] Example 3, a silicate cement for stabilizing and solidifying heavy metal lead, by weight, includes the following components:

[0023] 90 parts of ordinary portland cement, 10 parts of low-activity metakaolin, 5 parts of lead nitrate powder, and 40 parts of water. The preparation method is the same as that of Example 1.

[0024] Example 4, a silicate cement for stabilizing and solidifying heavy metal lead, by weight, includes the following components:

[0025] 80 parts of ordinary portland cement, 20 parts of low-activity metakaolin, 5 parts of lead nitrate powder, and 40 parts of water. The preparation method is the same as that of Example 1.

[0026] Comparative Example 1:

[0027] The difference from Example 1 is that 20 parts of portland cement are replaced with an equal amount of fly ash, and the others remain unchanged.

[0028] Comparative Example 2:

[0029] The difference from Example 1 is that 20 parts of portland cement are replaced with an equal amount of lead-zinc tailings, and the others remain unchanged.

[0030] Performance detection:

[0031] The properties of the neat cement paste mixtures and hardened cement pastes of the above Examples 1, 2, 3, 4 and Comparative Examples 1, 2 were tested. The leaching test was carried out with reference to "Horizontal Oscillation Method for Leaching Toxicity of Solid Wastes" (HJ 557-2009), and the results are shown in Table 1.

[0032] Table 1 Test Results

[0033]

[0034] From the results in Table 1 above, it can be seen that the indexes such as the compressive strength and flexural strength of the portland cement specimens obtained in Examples 1-4 of the present invention are relatively stable. The leaching tests of Examples 2-4 containing low-reactivity metakaolin all meet the limit value of 0.05 mg / g specified in the "Identification Standard for Hazardous Wastes", and the performance is good. Compared with Comparative Example 1, after using low-reactivity metakaolin to replace fly ash, the 28-day compressive strength, 28-day compressive strength, curing performance, etc. of the product have all been improved to a certain extent. In addition, compared with Comparative Example 2, it can be found that using low-reactivity metakaolin to replace fly ash can effectively reduce the 2+ leaching concentration.

[0035] The embodiments of the present invention are given for the purposes of illustration and description. Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A silicate cement for stably solidifying heavy metal lead, characterized in that, The raw materials, by mass parts, include the following components: 80 - 100 parts of ordinary portland cement, 5 - 20 parts of low - activity metakaolin, 5 - 10 parts of lead nitrate powder, and 40 - 50 parts of water.

2. The silicate cement for stably solidifying heavy metal lead according to claim 1, wherein: The portland cement is 42.5 - grade ordinary portland cement.

3. The silicate cement for stably solidifying heavy metal lead as claimed in claim 1, wherein: In the described low-reactivity metakaolin, the SiO2 content is ≥ 50%, the Al2O3 content is ≥ 35%, and the specific surface area is ≤ 20,000 m 2 / kg.

4. The preparation method of the silicate cement for stably solidifying heavy metal lead according to any one of claims 1 to 3, characterized in that, It includes the following steps: Step 1: Take ordinary portland cement and low - activity metakaolin, stir and mix them evenly to obtain a uniformly - mixed cementitious material. Step 2: Add lead nitrate powder into water, stir to obtain a uniform aqueous solution, slowly add it to the mixture in Step 1, then mix to obtain a uniformly - mixed slurry, and finally form and cure according to national standards to obtain the portland cement for stably solidifying heavy metal lead.

5. The preparation method of the silicate cement based on stable solidification of heavy metal lead according to claim 4, characterized in that: The stirring and mixing is carried out using a rotary mixing blender. During the mixing in Step 2, the rotational speed of the blender is 140 - 280 r / min, and the mixing time of the rotary mixing blender is 90 - 120 s.

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