A method for inhibiting the retarding of lead-zinc cement

Abstract

The present invention belongs to the field of building materials, and more particularly, relates to a method for inhibiting the retarded setting of lead-zinc cement. Calcium hydroxide is mixed into the lead-zinc cement, and the hydroxide ions released during the hydration process co-precipitate with lead and zinc ions, thereby inhibiting the retarded setting effect. Compared with the prior art, the present invention solves the problem that lead and zinc ions inhibit cement hydration, causing retarded setting, which in turn affects the mechanical properties of cement-based materials. By adding calcium hydroxide, the solubility product of lead hydroxide and zinc hydroxide formed by the reaction of hydroxide ions with lead and zinc ions is lower than that of calcium hydroxide, thereby inhibiting the retarded setting effect of zinc and lead ions.

Description

Technical Field

[0001] The invention belongs to the field of building materials, and in particular relates to a method for inhibiting the retarding of lead-zinc cement. Background Art

[0002] With the acceleration of industrialization, the demand for lead and zinc continues to increase year by year. Simultaneously, the discharge and accumulation of lead-zinc tailings are also increasing. The long-term storage of lead-zinc tailings not only consumes valuable land resources but also causes environmental pollution and even poses a threat to human life and health. Therefore, the rational disposal of lead-zinc tailings has become a research focus.

[0003] Cement, with its high demand and annual production, has the potential to absorb large quantities of lead-zinc tailings. Discarded lead-zinc tailings can be used in the production of admixtures and as a supplementary binder for cement-based materials. The use of lead-zinc tailings in cement-based materials not only recycles lead-zinc tailings but also reduces cement production costs and carbon emissions.

[0004] Currently, the main technical difficulty in using lead-zinc tailings in cement-based materials is that lead and zinc inhibit cement hydration, reducing the early strength of cement-based materials and posing a safety hazard. Therefore, how to inhibit the retarding effect of lead-zinc compounds on cement hydration has become an urgent issue.

[0005] Patent CN1962523A discloses a method for consolidating heavy metal zinc in cement-based materials and inhibiting its retarding effect. Patent CN1994594A discloses a method for resource utilization of lead-containing solid waste. Sulfides are added to deactivate the activity of zinc and lead ions, respectively. However, the sulfides formed by the reactions are harmful to the environment and human health and require further treatment. Furthermore, the high cost of sulfides increases the cost of the treatment methods. Furthermore, the introduction of sulfides may lead to an increase in the sulfoaluminate phase in the hydration products, affecting the mechanical properties and durability of the cement-based materials, resulting in the prepared cement-based materials failing to meet the required performance requirements.

[0006] Therefore, it is necessary to propose an environmentally friendly and human-safe method to inhibit the retarding phenomenon of lead-zinc cement. Summary of the Invention

[0007] The present invention aims to address at least one of the aforementioned issues by providing a method for inhibiting the retarding effect of lead-zinc cement. This method addresses the problem that lead and zinc ions inhibit cement hydration, causing retarding, and thus affecting the mechanical properties of cement-based materials. By adding calcium hydroxide, the solubility product of lead hydroxide and zinc hydroxide, formed by the reaction of hydroxide ions with lead and zinc ions, is lower than that of calcium hydroxide, thereby inhibiting the retarding effect of zinc and lead ions.

[0008] The purpose of the present invention is achieved through the following technical solutions:

[0009] A method for inhibiting the retarding of lead-zinc cement comprises firstly mixing calcium hydroxide into the lead-zinc cement, and then releasing hydroxide ions during the hydration process to co-precipitate with lead ions and zinc ions, thereby inhibiting the retarding effect.

[0010] Preferably, the lead and zinc content in the lead-zinc cement does not exceed 1% by mass.

[0011] Preferably, the lead and zinc mass content is the sum of the lead content and the zinc content.

[0012] Preferably, when the lead content by mass is lower than 1% of the zinc content by mass, the lead-zinc content by mass is the zinc content; when the zinc content by mass is lower than 1% of the lead content by mass, the lead-zinc content by mass is the lead content.

[0013] Preferably, the added amount of calcium hydroxide is at least 2.5-5 times the mass content of lead and zinc.

[0014] Preferably, when the lead-zinc cement contains metal ions other than lead ions and zinc ions, and the solubility product of the hydroxide formed by the metal ions and hydroxide ions is less than that of lead hydroxide or zinc hydroxide, the amount of calcium hydroxide added is increased excessively according to the content of the metal ions.

[0015] Preferably, the calcium hydroxide is industrial grade calcium hydroxide.

[0016] Preferably, the calcium hydroxide is dry-mixed with lead-zinc cement to prepare the cement-based material.

[0017] Preferably, the dry mixing is carried out in a dry powder mixer for 3 hours.

[0018] Preferably, the lead-zinc cement is lead-zinc-containing Portland cement.

[0019] The working principle of the present invention is:

[0020] By adding industrial calcium hydroxide to cement containing lead and zinc ions, hydroxide ions combine with lead and zinc ions during the hydration process to form lead hydroxide and zinc hydroxide precipitates, thereby suppressing the effects of lead and zinc ions on cement hydration. Because the solubility product constants of lead and zinc hydroxides are much lower than those of calcium hydroxide, hydroxide ions will preferentially precipitate with lead and zinc ions.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1. The present invention effectively inhibits the retarding effect of lead and zinc on cement hydration, and promotes the application of solid waste containing lead and zinc in building materials.

[0023] 2. Calcium hydroxide is used to inhibit the retarding of lead and zinc. Calcium hydroxide has a wide range of uses in industry, is widely available, and is inexpensive. Therefore, the present invention has high economic practicality and effectively controls costs.

[0024] 3. Calcium hydroxide is mixed with cement using a dry mix method, which ensures that the inhibitory effect of calcium hydroxide is maximized while being easy to implement.

[0025] 4. Calcium hydroxide is used instead of calcium oxide as the retarding inhibitor to avoid the violent heat release of calcium oxide when it comes into contact with water.

[0026] 5. The zinc hydroxide and lead hydroxide produced by the reaction are more environmentally friendly and harmless than the corresponding sulfide salts, and no sulfoaluminate will be produced during the preparation of cement-based materials, which will not affect the mechanical properties and durability of cement-based materials, and fully overcome the defects of zinc sulfide and lead sulfide that require further treatment. DETAILED DESCRIPTION

[0027] The present invention will be described in detail below with reference to specific embodiments, but the present invention is by no means limited thereto.

[0028] In the following examples, unless otherwise specified, the reagents used may be conventional commercially available products, and the methods used may be well-known means in the art.

[0029] Example 1

[0030] The cement used was standard cement (P.I.42.5 grade Portland cement), analytically pure lead nitrate, and industrial-grade calcium hydroxide. The cement and lead nitrate (1% by weight of the cement) were first mixed in a blender for 3 hours. The lead-containing cement was then mixed in a blender for 3 hours with calcium hydroxide (5% by weight of the cement). The resulting cementitious materials were then mixed with water in a cement slurry mixer, achieving a water-cement ratio of 0.5.

[0031] The setting time of the pure slurry is tested in accordance with the national standard GB / T1346-2011.

[0032] Prepare the slurry as described above. The freshly mixed slurry was quickly poured into a 2 mm × 2 mm × 2 mm mold. Six specimens were prepared for each age. The specimens were then sealed and cured under standard curing conditions for 24 hours before demolding. The demolded specimens were then sealed and cured under standard curing conditions for 3 and 7 days. After curing to the specified age, the compressive strength of the slurry specimens was tested using a press at a loading rate of 500 N / s.

[0033] The sample containing calcium hydroxide was recorded as T1.

[0034] Comparative Example 1

[0035] Cement paste test blocks without calcium hydroxide were prepared in the same manner as above and tested for compressive strength as a control group.

[0036] The control group without calcium hydroxide was recorded as R1.

[0037] The effects of calcium hydroxide on the setting time and mechanical properties of lead-containing cement are shown in Tables 1 and 2, respectively.

[0038] Table 1 Effect of calcium hydroxide on setting time of leaded Portland cement (min)

[0039]

[0040] Table 2 Effect of calcium hydroxide on the compressive strength (MPa) of leaded silicate cement

[0041]

[0042] The results of setting time and compressive strength tests show that calcium hydroxide effectively inhibits the retarding effect of lead. Adding 5% of the cement mass of calcium hydroxide shortened the initial setting time by 71.3% and increased the 3-day compressive strength by 60.4%.

[0043] Example 2

[0044] Compared with Example 1, most of the contents are the same, except that 1% of the mass of cement in lead nitrate in Example 1 is replaced by 1% of the mass of cement (analytical pure Zn(NO3)2·6H2O, where 1% is the mass fraction after deducting bound water).

[0045] The sample containing calcium hydroxide was recorded as T2.

[0046] Comparative Example 2

[0047] Cement paste test blocks without calcium hydroxide were prepared in the same manner as above and tested for compressive strength as a control group.

[0048] The control group without calcium hydroxide was recorded as R2.

[0049] The effects of calcium hydroxide on the setting time and mechanical properties of zinc-containing cement are shown in Table 3 and Table 4, respectively.

[0050] Table 3 Effect of calcium hydroxide on setting time (min) of zinc-containing Portland cement

[0051]

[0052] Table 4 Effect of calcium hydroxide on compressive strength (MPa) of zinc-containing Portland cement

[0053]

[0054] The results of setting time and compressive strength tests show that calcium hydroxide effectively inhibits the retarding effect of zinc. Adding 5% of the cement mass of calcium hydroxide shortened the initial setting time by 80.7% and increased the 3-day compressive strength by 50.4%.

[0055] Example 3

[0056] Compared with Example 1, most of the contents are the same, except that the 1% lead nitrate by mass of cement in Example 1 is replaced by 0.5% lead nitrate by mass of cement and 0.5% zinc nitrate by mass of cement (analytical pure Zn(NO3)2·6H2O, where 0.5% is the mass fraction after deducting bound water).

[0057] The sample containing calcium hydroxide was recorded as T3.

[0058] Comparative Example 3

[0059] Cement paste test blocks without calcium hydroxide were prepared in the same manner as above and tested for compressive strength as a control group.

[0060] The control group without calcium hydroxide was designated as R3.

[0061] The effects of calcium hydroxide on the setting time and mechanical properties of lead-zinc cement are shown in Table 5 and Table 6, respectively.

[0062] Table 5 Effect of calcium hydroxide on setting time (min) of lead-zinc silicate cement

[0063]

[0064] Table 6 Effect of calcium hydroxide on compressive strength (MPa) of lead-zinc silicate cement

[0065]

[0066] Based on the test results of setting time and compressive strength, it can be seen that calcium hydroxide has a good inhibitory effect on the retarding effect of lead and zinc. After adding 5% of the cement mass of calcium hydroxide, the initial setting time is shortened by 79.5% and the 3d compressive strength is increased by 55.1%.

[0067] The above description of the embodiments is intended to facilitate understanding and use of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above-described embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention, without departing from the scope of the present invention, should be within the scope of protection of the present invention.

Claims

1. A method for inhibiting the slow setting of lead-zinc cement, characterized in that: Calcium hydroxide is added to lead-zinc cement to release hydroxide ions during hydration, which co-precipitate with lead and zinc ions, thereby inhibiting the retarding effect. The amount of calcium hydroxide added is 2.5-5 times the mass content of lead and zinc; and, when the lead-zinc cement contains metal ions other than lead ions and zinc ions, and the solubility product of the hydroxide formed by the metal ions and hydroxide ions is less than that of lead hydroxide or zinc hydroxide, the amount of calcium hydroxide added is increased in excess according to the content of the metal ions; The calcium hydroxide and the lead-zinc cement are dry-mixed to form a cement-based material, and the dry mixing is carried out by stirring in a dry powder mixer for 3 hours.

2. The method for inhibiting slow setting of lead-zinc cement according to claim 1, characterized in that: The lead and zinc content in the lead-zinc cement does not exceed 1% by mass.

3. The method for inhibiting slow setting of lead-zinc cement according to claim 2, characterized in that: When the lead content by mass is lower than 1% of the zinc content by mass, the lead-zinc content by mass is the zinc content; when the zinc content by mass is lower than 1% of the lead content by mass, the lead-zinc content by mass is the lead content.

4. The method for inhibiting slow setting of lead-zinc cement according to claim 1, characterized in that: The calcium hydroxide is industrial grade calcium hydroxide.

5. The method for inhibiting slow setting of lead-zinc cement according to claim 1, characterized in that: The lead-zinc cement is lead-zinc-containing silicate cement.

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