Ferrous sulfate-based cement high-temperature-resistant chromium reducing agent

Abstract

The invention discloses a ferrous sulfate-based high-temperature-resistant chromium reducing agent. The high-temperature-resistant chromium reducing agent is prepared from the following raw materials: a main reducing agent, an auxiliary chromium reducing agent, an antioxidant and a moisture-proof dispersing agent, the main chromium reducing agent is ferrous sulfate; the auxiliary reducing agent is one or a mixture of more than two of antimony trioxide, antimony potassium tartrate, manganese sulfate, stannous sulfate and thiourea dioxide; the antioxidant is one or a mixture of two of methanol and ethanol; the moisture-proof dispersing agent is one or a mixture of more than two of slag powder, fly ash and pozzolanic powder. A certain proportion of the chromium-reducing agent is doped into cement at the temperature of less than or equal to 130 DEG C, and after heat preservation for 7 days, the content of hexavalent chromium in the cement is obviously reduced compared with that of cement without the chromium-reducing agent.

Description

Technical Field

[0001] The present invention relates to a method for reducing water-soluble hexavalent chromium in the field of cement and preparing a high-temperature resistant chromium-reducing product based on ferrous sulfate. Background Art

[0002] Water-soluble hexavalent chromium in cement is a harmful substance to the human body and the environment. As a commonly used chromium-reducing agent, ferrous sulfate is sourced from industrial by-products. Due to its low price, high chromium-reducing efficiency and other advantages, it is widely used in cement enterprises. However, during the application process, affected by factors such as the temperature of the clinker, the heat generated by the hot air and the collision of steel balls, the temperature of the cement leaving the mill and entering the warehouse is high, usually between 90°C and 130°C. After the cement leaves the mill, affected by the speed of sales, it needs to be stored in a cement warehouse at this temperature for several hours to one or two months. In such a high-temperature environment, ferrous sulfate is easily oxidized to ferric sulfate, and the chromium-reducing effect is greatly reduced. Summary of the Invention

[0003] Aiming at the defects or deficiencies of the prior art, the present invention provides a high-temperature resistant chromium-reducing agent based on ferrous sulfate.

[0004] To this end, the raw materials for preparing the high-temperature resistant chromium-reducing agent of the present invention include a main reducing agent, an auxiliary chromium-reducing agent, an antioxidant and a moisture-proof dispersant;

[0005] The main chromium-reducing agent is ferrous sulfate; the auxiliary reducing agent is one or more of antimony trioxide, potassium antimonyl tartrate, manganese sulfate, stannous sulfate, thiourea dioxide;

[0006] The antioxidant is a mixture of one or two of methanol and ethanol;

[0007] The moisture-proof dispersant is a mixture of one or more of slag powder, fly ash and pozzolanic powder.

[0008] An optional solution is that the main reducing agent is 60 - 70 parts by mass, the antioxidant is 10 - 20 parts by mass, the moisture-proof dispersant is 20 - 30 parts by mass, and the mass fraction of the auxiliary reducing agent is less than or equal to 10 parts by mass.

[0009] An optional solution is that the preparation method of the chromium-reducing agent includes: mixing the raw materials and drying them under the condition of 100°C to 200°C.

[0010] The present invention also provides a corresponding ferrous sulfate-based cement, and the above high-temperature resistant chromium-reducing agent is added to the ferrous sulfate-based cement. Optionally, the added mass percentage of the high-temperature resistant chromium-reducing agent is 0.05% - 0.5%.

[0011] The present invention uses ferrous sulfate as the main reducing agent, admixes auxiliary reducing agents, antioxidants, and moisture-proof dispersion carriers, and prepares a high-temperature resistant chromium-reducing agent for cement by compounding. By improving the antioxidant ability of the chromium-reducing agent, changing the charge distribution and reaction activity on the surface of the reducing agent particles, and forming a protective layer on the surface of reducing agents such as ferrous sulfate, the chromium-reducing agent entering the cement silo together with the cement can still have good chromium-reducing ability when kept in cement at 130 °C for 7 - 14 days, thereby achieving excellent and stable chromium-reducing effects in cement production applications and having broad market prospects.

[0012] When 0.1% of the chromium-reducing agent of the present invention is incorporated into cement at ≤130 °C and stored at this temperature for 7 days, the content of hexavalent chromium in the cement is reduced by 10 - 15 ppm compared with the cement without adding the chromium-reducing agent. It meets the requirement in the group standard T / CCAS - 009 - 2019 "Reducing Agents for Water-Soluble Chromium (Ⅵ) in Cement" of the China Cement Association that the dosage of the reducing agent used for reducing 1 mg / kg of water-soluble chromium (Ⅵ) per ton of cement, and the powder dosage ≤150 g / t.

[0013] In addition, for the cement added with the chromium-reducing agent of the present invention at a temperature ≤130 °C, compared with the initial chromium content when just added, the content of hexavalent chromium shows no significant increase at 7 days and 14 days. To prevent the oxidation of hydrated ferrous sulfate with the extension of high-temperature time, multiple reducing agents are used in combination in this formula, and the effect is better and more lasting. For the cement added with the reducing agent, within 90 days, the reproducibility limit of the detection results of the content of water-soluble chromium (Ⅵ) in the cement meets the requirements of GB31893 "Limit and Determination Method of Water-Soluble Chromium (Ⅵ) in Cement".

[0014] In addition, after adding the chromium-reducing agent of the present invention, the properties of the cement such as strength, setting time, soundness, and durability all meet the technical index requirements specified in T / CCAS - 009 - 2019. Specific Embodiments

[0015] Unless otherwise specified, the scientific and technical terms in this article are understood according to the knowledge of those of ordinary skill in the relevant fields.

[0016] The following combines specific embodiments to further describe the specific embodiments of the present invention. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention. All raw materials used in the present invention are commercially available products. In the preferred solution, the particle size of each raw material is less than 2 mm. The particle size of the raw materials used in the following embodiments is all less than 2 mm.

[0017] The fly ash used in the following examples meets the physical and chemical property requirements of fly ash for use as active cementitious materials in "Fly Ash Used in Cement and Concrete" (GB / T 1596-2017). The ground granulated blast-furnace slag powder used meets the technical requirements of S95 ground granulated blast-furnace slag powder in "Ground Granulated Blast-Furnace Slag Powder Used in Cement, Mortar and Concrete" (GB / T 18046). The pozzolanic material powder used shall meet the technical requirements of "Pozzolanic Blending Materials Used in Cement" (GB / T 2847). The specific pozzolanic material used is calcined coal gangue.

[0018] Example:

[0019] The preparation method of the chromium-reducing agent in each example is as follows: First, mix the main reducing agent (A), auxiliary reducing agent (B) and moisture-proof dispersant (D) well; then add the antioxidant (C) and mix thoroughly, and then put it into an oven at 150 ± 10 °C for drying. The mass ratios of the components in each example and comparative example are shown in Table 1.

[0020] Table 1 Preparation ratio (mass ratio) of ferrous sulfate-based cement high-temperature resistant chromium-reducing agent

[0021]

[0022] To verify the effects of the chromium-reducing agents in Table 1, ferrous sulfate-based P.O42.5 cement with excessive hexavalent chromium was ground, and the initial hexavalent chromium content was 22.79 mg / kg. This sample was divided into 8 parts, 1 part was blank cement, and the other 7 samples were successively added with 0.10% of the above-mentioned comparative examples and example chromium-reducing agents and mixed thoroughly. After being kept warm in an oven at 130 °C for 7 days and 14 days, the hexavalent chromium content at 7 days and 14 days was detected according to "Limit and Determination Method of Water-Soluble Chromium (VI) in Cement" (GB 31893-2015), and the Cr 6+ reduction effect was calculated according to the formula in Appendix A.5 of T / CCAS009-2019. The reduction effect (Rn) of the reducing agent is calculated according to Equation (Equation 1), and the result is accurate to 0.1 g / [t·(mg / kg):

[0023] R n = W3 / W1 - W2 (Equation 1)

[0024] (In Equation 1): R n represents the reduction effect, with the unit of grams per ton·milligrams per kilogram {g / [t·(mg / kg)};

[0025] W3 represents the water-soluble chromium (VI) reducing agent, that is, the dosage of the chromium-reducing agent of the present invention in cement, with the unit of grams per ton (g / t);

[0026] W1 represents the blank water-soluble chromium (VI) content, with the unit of milligrams per kilogram (mg / kg);

[0027] W2 represents the water-soluble chromium (VI) content in the reducing agent, with the unit of milligram per kilogram (mg / kg).

[0028] Table 2 Reduction effect of ferrous sulfate-based cement high-temperature chromium-reducing agent

[0029]

[0030] According to T / CCAS-009-2019 "Reducing Agent for Water-soluble Chromium (VI) in Cement", although this standard does not stipulate the maximum dosage of the chromium-reducing agent in cement, it requires the manufacturer to label the main components, technical indicators, recommended dosage (the recommended dosage of common products ranges from 0.05% to 0.5%), etc. on the product manual, and the reduction effect of water-soluble hexavalent chromium in cement should be less than the limit of 150 g·t (mg / kg). However, this regulation does not limit the storage temperature of cement. Many chromium-reducing agents can generally meet this requirement in normal-temperature tests, but when added to the cement silo during large-scale production, the chromium reduction effect will be greatly reduced at high temperatures (about 90°C to 130°C). To focus on the actual production, the present invention considered evaluating the reduction effect of the chromium-reducing agent at high temperatures from the beginning of the experiment.

[0031] As can be seen from Table 2, compared with the blank cement (the detected hexavalent chromium is 22.79 mg / kg at 7 days and 22.50 mg / kg at 14 days), among the cements added with the chromium-reducing agent, the samples of Examples 1-5 can still meet the high-temperature reduction effect when kept at 130°C until 14 days. For the comparative example 1 using only ferrous sulfate heptahydrate as the chromium-reducing agent, the hexavalent chromium is hardly reduced; the chromium-reducing agent of Example 1 with the addition of the auxiliary reducing agent antimony trioxide has the best effect. At a fixed dosage of 0.1%, in the cement silo at 130°C, the amount of reducing agent required per ton of cement to reduce 1 mg / kg of water-soluble (VI) is 44.6 g at 7 days and 48.4 g at 14 days.

[0032] Further in accordance with the requirements of T / CCAS-009-2019, the two chromium reducing agents used in the representative Examples 1 and 4, which have good effects in the examples, are added in an amount of 0.10% to a unified test small mill of Φ500×500, and ground together with cement clinker and gypsum (the mass ratio of clinker to gypsum is 95:5) to prepare small-mill cement. The prepared small-milled blank cement without the chromium reducing agent of the present invention and the cements respectively added with the chromium reducing agent of the present invention were tested for water-soluble hexavalent chromium reduction effect and stability according to GB 31893-2015 "Limit and determination method of water-soluble chromium (VI) in cement" and T / CCAS-009-2019 "Water-soluble chromium (VI) reducing agent in cement". The standard consistency, setting time and stability were tested according to GB / T1346 "Test method for water consumption, setting time and stability of cement standard consistency (ISO method)". The mortar fluidity and mortar strength were tested according to GB / T17671 "Test method for strength of cement mortar". Chloride ion detection was carried out according to GB / T176 "Cement chemical analysis method", and shrinkage test was carried out according to JC / T603 "Cement mortar shrinkage test method". The specific test results are shown in Table 3.

[0033] After the initial hexavalent chromium content was detected, the three samples were sealed and placed for 90 days, and the water-soluble chromium (VI) content in the cement was measured to meet the requirement of reproducibility of the test results ≥ 95% within 90 days.

[0034] Table 3 Performance test of blank cement and cement with high temperature resistant chromium reducing agent

[0035]

[0036] The results in Table 3 show that, through the comparison of various physical properties of the blank sample and the chromium-reducing sample, adding 0.1% of the chromium-reducing agent sample will not have an adverse effect on the cement performance. Table 4 shows the specific comparison results of the chromium-reducing agent used in Example 1. As shown in Table 4, the stability, standard consistency water consumption, setting time, boiling stability, cement mortar fluidity, cement mortar compressive strength, mortar shrinkage rate and chloride ion index in the table are the comparison results of Example 1 and the blank cement.

[0037] Table 4 Comparison results of blank cement and cement with high temperature resistant chromium reducing agent

[0038]

[0039] The content of the present invention is not limited to the embodiments listed, and any equivalent changes made to the technical solution of the present invention by ordinary technicians in this field after reading the specification of the present invention are covered by the claims of the present invention.

Claims

1. A ferrous sulfate-based high-temperature resistant chromium-reducing agent, characterized in that, The raw materials for preparing the high-temperature resistant chromium-reducing agent include a main reducing agent, an auxiliary chromium-reducing agent, an antioxidant, and a moisture-proof dispersant; The main chromium-reducing agent is ferrous sulfate; the auxiliary reducing agent is one or a mixture of two or more of antimony trioxide, potassium antimonyl tartrate, manganese sulfate, stannous sulfate, and thiourea dioxide; The antioxidant is one or a mixture of two substances of methanol and ethanol; The moisture-proof dispersant is one or a mixture of two or more of slag powder, fly ash, and pozzolanic powder.

2. The ferrous sulfate-based high-temperature resistant chromium-reducing agent according to claim 1, wherein The main reducing agent is 60-70 parts by mass, the antioxidant is 10-20 parts by mass, the moisture-proof dispersant is 20-30 parts by mass, and the mass fraction of the auxiliary reducing agent is less than or equal to 10 parts by mass.

3. The ferrous sulfate-based high-temperature resistant chromium-reducing agent according to claim 1, characterized in that, The preparation method of the chromium-reducing agent includes: mixing the raw materials and drying them under the condition of 100°C to 200°C.

4. A ferrous sulfate-based cement, characterized in that, The high-temperature resistant chromium-reducing agent described in claim 1 is added to the ferrous sulfate-based cement.

5. The ferrous sulfate-based cement according to claim 4, wherein The added mass percentage of the high-temperature resistant chromium-reducing agent is 0.05% to 0.5%.

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