Dry-grinding and dry-selecting tailings cementitious material and dry-mixed mortar and preparation method thereof

Abstract

In response to the problems of relatively low utilization rate and added value of tailings, and the high cost of using traditional cement, river sand or machine-made sand as cementitious materials and aggregates for dry-mixed mortar, the present invention provides a dry-ground and dry-selected tailings cementitious material and dry-mixed mortar and a preparation method. The dry-ground and dry-selected tailings cementitious material is composed of the following components in parts by weight: 15 to 19.5 parts of dry-ground and dry-selected tailings fine powder, 4.5 to 9 parts of fly ash, and 0.5 to 1 part of a composite activator; wherein the composite activator is composed of 0.3 to 0.6 parts of industrial by-product gypsum and 0.2 to 0.4 parts of steel slag powder. The present invention utilizes the characteristics of dry-ground and dry-selected tailings that not only have certain activity and can be supplemented with other materials to prepare cementitious materials, but can also be used as aggregates, and uses dry-ground and dry-selected tailings as the main raw material to prepare low-cost dry-mixed mortar. The present invention can not only achieve large-scale and high-value-added utilization of tailings, but also reduce the cost of preparing dry-mixed mortar.

Description

Technical Field

[0001] The invention belongs to the technical field of building materials, and particularly relates to a dry-grinded and dry-selected tailings cementitious material and dry-mixed mortar and a preparation method thereof. Background Art

[0002] Tailings are a major solid waste generated during mining operations. Currently, they are primarily used as aggregate for backfilling mined areas, but their overall utilization rate is less than 20%. The remainder is stored in tailings ponds, which not only occupies land, pollutes the environment, but also wastes resources. Dry-grinding and dry-selected tailings are more active than traditional wet-selection methods and do not require drying. Using them as active admixtures for cement and concrete is both simple and cost-effective.

[0003] Dry-mix mortar refers to a powdery or granular mixture of fine aggregate, inorganic binder, mineral admixture, and other admixtures produced by professional manufacturers and dried and screened, mixed in a certain proportion. The mixture is then added with water and stirred according to the instructions at the construction site to form a mortar mixture. Dry-mix mortar is also known as dry-mixed mortar, dry powder, etc. Compared with traditional mortar, dry-mix mortar has the advantages of stable quality and high construction efficiency. In the existing technology, dry-mix mortar binders are mainly made of cement or metallurgical slag, and the aggregates are mainly river sand, machine-made sand, etc., which are relatively expensive. With the continuous improvement of environmental protection requirements and the maturity of metallurgical slag resource utilization technology, the cost of raw materials will further increase, which will affect the development and application of traditional dry-mix mortar.

[0004] There are also some studies on dry-mix mortar in the existing technology, such as:

[0005] CN 108117356A discloses a method for preparing high-strength dry-mix mortar from industrial waste. This technology uses industrial waste dihydrate phosphogypsum, blast furnace slag, cement clinker, limestone powder, quicklime, and a coagulant in weight ratios of 30-50 parts, 35-45 parts, 4-8 parts, 6-16 parts, 2-10 parts, and 2-8 parts to form a cementitious material to prepare the high-strength dry-mix mortar. The mortar has a 28-day compressive strength of 7-30 MPa and a water retention rate of nearly 80%. However, this product requires expensive materials such as blast furnace slag and cement clinker, and the utilization ratio of the waste dihydrate phosphogypsum is low. The product also has a large number of components, a complex process, and a high cost.

[0006] CN 103922667A discloses a limestone-based machine-made sand dry-mix mortar and a preparation method thereof. This technology uses limestone-based machine-made sand as an aggregate instead of river sand, and mixes it with cement, fly ash, and fly ash in weight ratios of 70-85 parts, 10-25 parts, and 5-8 parts, respectively. 0.06-0.08 parts of a water-retaining agent are added to prepare the mortar. The mortar has a 28-day strength of approximately 20 MPa. However, this product requires the addition of 10% to 25% cement, which is relatively expensive. Furthermore, machine-made sand can only be made from limestone raw materials, and the raw material source is limited, which limits its promotion and application.

[0007] CN 102093006A discloses a fly ash dry-mix mortar. This technology directly uses fly ash as a cementitious material and prepares the mortar according to a weight ratio of 25-30 parts fly ash, 0-5 parts cement, 65-75 parts aggregate, 0.15-0.3 parts composite activator, 0.03-0.05 parts water-retaining agent, and 0.3-0.5 parts anti-cracking agent. The mortar is suitable for interior and exterior wall plastering and has a compressive strength of approximately 7 MPa. However, the fly ash utilization rate of this product is only 25% to 30%, and an anti-cracking agent needs to be added to reduce the risk of cracking. The compressive strength is low, and the mortar can only be used as a plastering material.

[0008] CN 114873961A discloses a molybdenum tailings dry-mix mortar and its application method. This technology prepares the mortar using 72-80 parts of molybdenum tailings sand, 19-25 parts of a cementitious material, 0.65-2.16 parts of a redispersible polymer latex powder, 0.17-0.31 parts of a water-retaining thickener, 0.1-0.2 parts of a water-reducing agent, 0.01-0.03 parts of an air-entraining agent, and 0.1-0.3 parts of a synergist. The mortar has a 28-day strength of 9-20 MPa. However, this product requires pre-treating the molybdenum tailings using an acid-dissolution-ammonia fluorosilicic acid method, followed by drying and calcining to produce molybdenum tailings fine powder to replace part of the cement. This process is relatively complex and the cost is relatively high.

[0009] Due to the problems existing in the dry-mix mortar products in the prior art, it is necessary to conduct further research on dry-mix mortar. Summary of the Invention

[0010] To address the relatively low utilization and added value of tailings, as well as the high cost of using traditional cement, river sand, or machine-made sand as a binder and aggregate in dry-mixed mortar, the present invention provides a dry-ground, dry-selected tailings binder and dry-mixed mortar, as well as a preparation method. This invention utilizes the properties of dry-ground, dry-selected tailings, which not only possess a certain degree of activity that can be used with other materials to prepare binders but can also be used as an aggregate, to prepare low-cost dry-mixed mortar using dry-ground, dry-selected tailings as the primary raw material. This invention not only enables large-scale, high-value-added utilization of tailings, but also reduces the cost of preparing dry-mixed mortar.

[0011] One of the technical solutions of the present invention is a dry-ground and dry-selected tailings cementitious material, which is composed of the following components in parts by weight: 15 to 19.5 parts of dry-ground and dry-selected tailings fine powder, 4.5 to 9 parts of fly ash, and 0.5 to 1 part of a composite activator;

[0012] The composite activator is composed of 0.3 to 0.6 parts of industrial by-product gypsum and 0.2 to 0.4 parts of steel slag powder.

[0013] Furthermore, in the above-mentioned dry-ground and dry-selected tailings cementitious material, the particle size of the dry-ground and dry-selected tailings powder is ≤20μm.

[0014] Furthermore, the chemical composition of the dry-ground and dry-selected tailings cementitious material and the dry-ground and dry-selected tailings fine powder includes: SiO2 60% to 70%; Al2O3 4% to 8%; CaO 3% to 6%; MgO 3% to 6%; S < 1%; and TFe 8% to 13%.

[0015] Furthermore, in the above-mentioned dry-grinding and dry-selecting tailings cementitious material, the industrial by-product gypsum includes at least one of desulfurized gypsum and fluorinated gypsum.

[0016] The second technical solution of the present invention is a dry-grinded and dry-selected tailings dry-mix mortar, which is composed of dry-grinded and dry-selected tailings, the cementitious material according to claim 1, a water reducer and a water retaining agent; the components are expressed in parts by weight, and the mixing ratio is as follows:

[0017] Dry grinding and dry selection of tailings: 70-80 parts;

[0018] Cementitious material: 20-29.5 parts;

[0019] Water reducing agent: 0-0.2 parts;

[0020] Water-retaining agent: 0-0.3 parts.

[0021] Furthermore, in the above-mentioned dry-grinded, dry-selected tailings dry-mixed mortar, the particle size gradation distribution of the dry-grinded, dry-selected tailings is, by weight percentage: particle size d<30μm accounts for 40% to 55%; 30≤d<74μm accounts for 20% to 35%; 74≤d<150μm accounts for 5% to 10%; d≥150μm accounts for 5% to 15%.

[0022] Furthermore, in the dry-grinded, dry-selected tailings dry-mixed mortar, the chemical composition of the dry-grinded, dry-selected tailings includes: SiO2 60% to 70%; Al2O3 4% to 8%; CaO 3% to 6%; MgO 3% to 6%; S < 1%; and TFe 8% to 13%.

[0023] Furthermore, the fly ash in the dry-grinded, dry-selected tailings dry-mixed mortar meets the requirements of Class I or Class II fly ash specified in the national standard "Fly ash used in cement and concrete" GB / T 1596-2017.

[0024] Furthermore, the above-mentioned dry-grinded, dry-selected tailings dry-mixed mortar, the industrial by-product gypsum is mainly composed of the following chemical components: by weight percentage, CaO 40% to 48%, SO3 35% to 45%, SiO2 3% to 7%, Al2O3 0 to 2%, MgO 0 to 2%; and the fineness (45μm sieve residue) is less than 15%.

[0025] Furthermore, in the dry-grinded, dry-selected tailings dry-mixed mortar, the steel slag is converter slag, and after grinding, the fineness (45μm sieve residue) is less than 15%, and the CaO content is not less than 40%.

[0026] Furthermore, in the above-mentioned dry-grinded, dry-selected tailings dry-mixed mortar, the water reducer is a polycarboxylic acid water reducer; and the water retaining agent is one or more of methyl cellulose, cyanoethyl cellulose, hydroxypropyl methyl cellulose, and modified starch.

[0027] The third technical solution of the present invention is a method for preparing dry-grinding, dry-selecting tailings and dry-mixed mortar, comprising the following steps:

[0028] 1) The dry-ground and dry-selected tailings are screened, and the portion with a particle size of ≤20 μm is used as tailings fine powder for use as a raw material for cementitious materials; the portion with a particle size of >20 μm is used as mortar aggregate;

[0029] 2) Mix the raw materials evenly according to the weight percentage ratio to make dry mixed mortar.

[0030] Furthermore, in the preparation method of the dry-grinded and dry-selected tailings dry-mixed mortar, a certain amount of water is added to the dry-mixed mortar to obtain a dry-mixed mortar slurry; preferably, the mass ratio of the dry-mixed mortar to water is 6 to 9:1.

[0031] Compared with the prior art, the advantages of the present invention are:

[0032] 1. The present invention utilizes the potential activity of dry-grinded and dry-selected tailings and uses the screened fine powder as raw material. However, the fine powder itself has poor activity. By mixing it with a small amount of highly active cementitious material and stimulating its activity, a cementitious material is prepared to replace cement in preparing mortar. This can be achieved by simply screening and reasonable stimulation, and the cost is low.

[0033] 2. It does not use expensive raw materials such as blast furnace slag and cement clinker. Instead, it uses solid waste as the main active material and activator, which simplifies the production process and reduces costs.

[0034] 3. Dry grinding and dry selection of tailings to screen out relatively coarse particles as aggregates, and the screened fine particles as cementitious material raw materials. The tailings solid waste utilization rate is high, avoiding storage pollution to the environment;

[0035] 4. Compared with wet-grinded tailings, dry-grinded and dry-selected tailings can save the dehydration and drying process when preparing dry-mixed mortar, and have higher activity. Not only does it have a wide source of raw materials and a simple production process, but it also has better mortar performance and lower cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 , process flow chart of the method in Example 3. DETAILED DESCRIPTION

[0037] Example 1

[0038] The dry grinding and dry separation tailings of an open-pit mine in Liaoning were used for activity tests of dry grinding and dry separation tailings of different particle sizes according to GB / T12957 "Test method for activity of industrial waste residues used in cement admixtures". The results are shown in Table 1.

[0039] Table 1. Activity of dry-grinded and dry-separated tailings of different particle sizes in an open-pit mine in Liaoning

[0040] Group 3d / MPa 7d / MPa 28d / MPa Activity Index Benchmark Group 28.8 43.9 54.7 100 D75 18.6 27.1 33.1 60.6 D60 17.2 25.5 34.5 62.8 D45 16.5 26.9 34.4 63.0 D30 18.7 28.6 36.1 66.2 D20 19.1 30.0 37.2 68.1 D10 18.2 29.0 38.1 69.3

[0041] Example 2

[0042] The dry-grinded and dry-selected tailings powder from a molybdenum mine in Hebei Province was used to conduct a cementitious material activity test according to the ratio of 19.5 parts of dry-grinded and dry-selected tailings powder, 9 parts of fly ash, 0.3 parts of desulfurization gypsum, and 0.2 parts of steel slag. The results are shown in Table 2.

[0043] Table 2. Activity results of dry grinding and dry separation tailings cementitious materials from a molybdenum mine in Hebei

[0044]

[0045] Example 3

[0046] A method for preparing dry-grinded, dry-selected tailings dry-mixed mortar is as follows:

[0047] The dry grinding and dry separation tailings from an open-pit mine in Liaoning were analyzed for particle size distribution and chemical composition. The specific results are shown in Tables 3 and 4.

[0048] Table 3. Particle size distribution of dry-grinded and dry-selected tailings from an open-pit mine in Liaoning

[0049]

[0050] Table 4 Chemical composition of dry-grinding and dry-separation tailings from an open-pit mine in Liaoning

[0051]

[0052] The mortar preparation process is as follows:

[0053] 1) The dry-ground and dry-selected tailings are sent to a high-frequency screen for screening. The tailings with a particle size greater than 20 μm are used as aggregate, and the tailings powder with a particle size ≤ 20 μm is used as raw material for preparing cementitious materials;

[0054] 2) The fly ash from the open pit power plant was tested for particle size distribution, activity, and microscopic morphology and found to meet the requirements for Class II fly ash;

[0055] 3) After drying, 0.3 kg of the desulfurization gypsum from the open-pit mine power plant and 0.2 kg of steel slag were respectively fed into a ball mill and ground to a fineness (45 μm sieve residue) of 10%. After grinding and homogenization, a composite activator was prepared. The chemical composition analysis of the desulfurization gypsum and steel slag is shown in Table 5;

[0056] 4) preparing a cementitious material by taking 15 kg, 8.5 kg and 0.5 kg of tailings fine powder, fly ash and composite activator respectively;

[0057] 5) Take 24 kg, 76.6 kg, 0.2 kg and 0.2 kg of cementitious material, tailings aggregate, water reducer and water retaining agent respectively, and mix them evenly to form dry-mix mortar;

[0058] 6) preparing a dry-mix mortar slurry by mixing dry mortar material and water in a weight ratio of 8:1;

[0059] After testing, the obtained dry-mixed mortar had a consistency of 78mm, a 2h consistency loss rate of 17.3%, and a water retention rate of 89.7%; the compressive strength after 28d of standard curing reached 29.2MPa.

[0060] Table 5 Chemical composition of steel slag and desulfurized gypsum used in this example

[0061]

[0062] Example 4

[0063] A method for preparing dry-grinded, dry-selected tailings dry-mixed mortar is as follows:

[0064] The dry grinding and dry separation tailings of a molybdenum mine in Hebei Province were collected. The particle size analysis and chemical composition are shown in Table 6 and Table 7 respectively.

[0065] Table 6. Particle size distribution of dry-grinded and dry-separated tailings from a molybdenum mine in Hebei

[0066]

[0067] Table 7 Chemical composition of dry grinding and dry separation tailings from a molybdenum mine in Hebei

[0068]

[0069] The mortar preparation process is as follows:

[0070] 1) The dry-ground and dry-selected molybdenum ore tailings are sent to a high-frequency screen for screening. The tailings with a particle size greater than 20 μm are used as aggregate, and the tailings powder with a particle size less than 20 μm is used as a raw material for preparing cementitious materials;

[0071] 2) Purchased power plant fly ash, desulfurization gypsum, and steel slag powder, of which the fly ash is Class I fly ash, the desulfurization gypsum has a fineness of 9.4% and a measured SO3 content of 36.12%, and the steel slag powder has a fineness of 10.6% and a CaO content of 45.6%;

[0072] 3) Take 0.4 kg of desulfurized gypsum and 0.3 kg of steel slag powder respectively to prepare a composite activator;

[0073] 4) preparing a cementitious material by taking 16 kg of tailings fine powder, 6.3 kg of fly ash, and 0.7 kg of a composite activator, respectively;

[0074] 5) Take 23 kg, 76.7 kg, 0.1 kg and 0.2 kg of cementitious material, tailings aggregate, water reducer and water retaining agent respectively, and mix them evenly to form dry-mix mortar;

[0075] 6) preparing a dry-mix mortar slurry by mixing dry-mix mortar and water in a weight ratio of 7:1;

[0076] After testing, the dry-mixed mortar has a consistency of 76mm, a 2h consistency loss rate of 18.1%, and a water retention rate of 86.5%; the compressive strength after 28d of standard curing reaches 31.6MPa.

[0077] Example 5

[0078] A method for preparing dry-grinded, dry-selected tailings dry-mixed mortar is the same as that in Example 3, except that:

[0079] 3) Take 0.6 kg of desulfurized gypsum and 0.4 kg of steel slag powder respectively to prepare a composite activator;

[0080] 4) Prepare a cementitious material by taking 19.5 kg of tailings fine powder, 9 kg of fly ash, and 1 kg of composite activator, respectively;

[0081] 5) Take 29.5 kg of cementitious material and 70 kg of tailings aggregate respectively and mix them evenly to make dry-mix mortar;

[0082] 6) Prepare dry mortar slurry by mixing mortar dry material and water in a weight ratio of 6:1.

[0083] Example 6

[0084] A method for preparing dry-grinded, dry-selected tailings dry-mixed mortar is the same as that in Example 3, except that:

[0085] 3) Take 0.3 kg of desulfurized gypsum and 0.2 kg of steel slag powder respectively to prepare a composite activator;

[0086] 4) Prepare a cementitious material by taking 15 kg, 4.5 kg, and 0.5 kg of tailings fine powder, fly ash, and composite activator, respectively;

[0087] 5) Take 20 kg, 80 kg, 0.15 kg and 0.3 kg of cementitious material, tailings aggregate, water reducer and water retaining agent respectively, and mix them evenly to make dry-mix mortar;

[0088] 6) Prepare dry mortar slurry by mixing mortar dry material and water in a weight ratio of 9:1.

Claims

1. A dry grinding and dry separation tailings cementitious material, characterized in that: The invention is composed of the following components in parts by weight: 15-19.5 parts of dry-ground and dry-selected tailings fine powder, 4.5-9 parts of fly ash, and 0.5-1 part of a composite activator; The composite activator is composed of 0.3-0.6 parts of industrial by-product gypsum and 0.2-0.4 parts of steel slag powder; The particle size of dry grinding and dry separation tailings powder is ≤20μm; The chemical composition of dry-grinded and dry-selected tailings powder includes: SiO2 60%~70%; Al2O3 4%~8%; CaO 3%~6%; MgO 3%~6%; S <1%; TFe 8%~13%.

2. The dry grinding and dry separation tailings cementitious material according to claim 1, characterized in that: The industrial by-product gypsum includes at least one of desulfurized gypsum and fluorinated gypsum.

3. A dry grinding and dry separation tailings dry mixed mortar, characterized in that: The invention is composed of dry-grinded and dry-selected tailings, the cementitious material according to claim 1, a water reducer and a water retaining agent; the components are calculated in parts by weight and the mixing ratio is as follows: Dry grinding and dry selection of tailings: 70~80 parts; Cementitious material: 20~29.5 parts; Water reducing agent: 0~0.2 parts; Water-retaining agent: 0~0.3 parts.

4. The dry-grinding and dry-selecting tailings dry-mix mortar according to claim 3, characterized in that: The particle size distribution of dry grinding and dry selection tailings is calculated by weight percentage: particle size d<30μm accounts for 40%~55%; 30≤d<74μm accounts for 20%~35%; 74≤d<150μm accounts for 5%~10%; d≥150μm accounts for 5%~15%.

5. The dry-grinding and dry-selecting tailings dry-mix mortar according to claim 3, characterized in that: The chemical composition of dry grinding and dry separation tailings includes: SiO2 60%~70%; Al2O3 4%~8%; CaO 3%~6%; MgO 3%~6%; S <1%; TFe 8%~13%; The fly ash meets the requirements of Class I or Class II fly ash specified in the national standard "Fly ash for cement and concrete" GB / T 1596-2017; Industrial by-product gypsum is mainly composed of the following chemical components: by weight, CaO 40%~48%, SO3 35%~45%, SiO2 3%~7%, Al2O3 0~2%, MgO 0~2%; and the fineness is 45μm sieve residue <15%; The steel slag is converter slag, which has a 45μm sieve residue of less than 15% after grinding and a CaO content of not less than 40%; The water reducer is a polycarboxylic acid water reducer; The water-retaining agent is one or more of methyl cellulose, cyanoethyl cellulose, hydroxypropyl methyl cellulose and modified starch.

6. The method for preparing dry-grinded and dry-selected tailings dry-mixed mortar according to claim 3, characterized in that: The steps include: 1) The dry-ground and dry-selected tailings are screened, and the part with a particle size of ≤20μm is used as tailings fine powder and used as cementitious material raw material; the part with a particle size of >20μm is used as mortar aggregate; 2) Mix all the raw materials evenly according to the weight percentage ratio to make dry-mix mortar.

7. The method for preparing dry-grinded and dry-selected tailings dry-mixed mortar according to claim 6, characterized in that: After adding a certain amount of water to the dry-mixed mortar, dry-mixed mortar slurry is obtained.

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