Low-grade calcium bentonite-based drying agent and preparation method thereof

Abstract

The invention discloses a low-grade calcium bentonite-based drying agent and a preparation method thereof. The preparation method comprises the following steps: pretreating raw materials: finely crushing calcium bentonite raw ore into calcium bentonite powder; semi-dry sodium modification: finely crushed calcium bentonite powder and a sodium carbonate solution are mixed in proportion; feeding the mixed material into a twin-screw extruder for continuous extrusion forming to form a strip-shaped material; and drying and post-processing: drying the strip-shaped material, crushing the strip-shaped material into particles, and screening to obtain the low-grade calcium bentonite-based drying agent product. And moisture absorption rate evaluation: putting the low-grade calcium bentonite-based drying agent product into a standard constant-temperature and constant-humidity curing box for standing, measuring the weight of bentonite before and after moisture absorption, and calculating the moisture absorption rate. The process is high in integration level and simple in flow, and the production period is shortened by more than 40%; after the low-grade calcium bentonite is extruded and sodium-modified by a semi-dry method, the moisture absorption rate of the product in an RH 80% environment can exceed 50%; and the green manufacturing trend is met, no waste water is generated, and low-carbon emission is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of desiccant preparation, and particularly relates to a low-grade calcium-based bentonite-based desiccant and a preparation method thereof. Background Art

[0002] Environmental protection regulations globally are increasingly strict on traditional desiccants. Silica gel desiccants need to be prepared using hazardous chemicals (sulfuric acid, sodium silicate), with VOC emissions generated during the production process, and have the defects of high cost and non-renewability. Bentonite-based desiccants, on the other hand, use natural minerals as raw materials, are non-toxic and biodegradable, and conform to the development trend of green chemistry.

[0003] Calcium-based bentonite accounts for more than 70% of China's reserves. Due to the high impurity content and weak interlayer Ca 2 + exchange capacity in low-grade calcium soil ore, the moisture absorption rate of the directly prepared desiccant is only 1 / 3 of that of sodium-based bentonite, and it is difficult to directly utilize low-grade ore. Existing technologies improve the performance through purification, sodium modification, and organic intercalation, but face problems of process complexity and environmental protection.

[0004] The prior art CN111573685A proposed "a method for efficiently and environmentally friendly preparing organic bentonite using calcium-based bentonite raw soil", adopting an "integration process of sodium modification - organic modification - extraction and purification": mixing calcium-based bentonite raw soil with sodium chloride solution for sodium modification (pH = 3 - 4, stirring at 30°C for 8 h), adding cetyltrimethylammonium chloride (CTAC) for organic intercalation (reacting at 80°C for 4 h), and using cyclohexane to extract and separate organic bentonite, with a solvent recovery rate > 90%; although this method can synchronously complete sodium modification and organic modification, it requires the use of high-purity CTAC (cost accounting for 45%), and the Cl- concentration in the wastewater > 5000 mg / L, with a relatively high cost. The prior art CN104548889A proposed "a method for preparing bentonite desiccant", directly using low-grade calcium-based bentonite (montmorillonite 60%) as the raw material, mixing the original ore after crushing with polyacrylamide (0.2 - 0.6%) for granulation, and naturally drying after extrusion molding (pressure 1 - 5 MPa); this method omits the purification step, reducing the cost by 30%, but the moisture absorption rate is only 35 - 40% (RH = 80%), and the particle strength is low (crushing rate > 15%).

[0005] In general, the existing technology has a low raw material utilization rate, and the montmorillonite content needs to be increased to more than 80% through wet purification (such as centrifugal separation), resulting in the low-grade calcium-based bentonite cannot be directly utilized; the process is complex and energy-consuming, and the traditional process needs to complete the sodium modification (such as sodium carbonate treatment) and granulation steps in steps, involving multiple stages of high temperature; product performance is limited, and the moisture absorption rate of the desiccant prepared by the existing technology is generally lower than 50% (under ambient humidity of 80%); the process chain is long and requires multi-stage treatment (purification → sodium modification → organic modification → granulation); it is highly dependent on organic modifiers; and it is difficult to treat wet process wastewater.

[0006] Therefore, in view of the above problems, the present invention provides a low-grade calcium-based bentonite-based desiccant and a preparation method thereof, a method for high-value utilization of low-grade calcium-based bentonite based on mechanochemical effect, through a semi-dry extrusion sodium-based coordinated granulation process, without the need for montmorillonite enrichment pretreatment and the intervention of an organic modifier, the prepared desiccant has a balanced moisture absorption rate of >50% under the conditions of 25°C and a relative humidity of 80%, breaking through the bottleneck of the industrial application of the moisture absorption performance of low-grade calcium-based soil. Summary of the invention

[0007] The purpose of the present invention is to provide a low-grade calcium-based bentonite-based desiccant and a preparation method thereof, which realizes a desiccant with a balanced moisture absorption rate of more than 50% at 25°C and a relative humidity of 80% through a semi-dry extrusion sodium-based coordinated granulation process without the need for montmorillonite enrichment pretreatment and the intervention of an organic modifier.

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

[0009] A method for preparing a low-grade calcium-based bentonite-based desiccant comprises the following steps:

[0010] (1) Raw material pretreatment: Calcium-based bentonite ore is selected, crushed by a jaw crusher, and then crushed by a roll crusher into calcium-based bentonite powder;

[0011] (2) Semi-dry sodium modification: finely crushed calcium-based bentonite powder and sodium carbonate solution are mixed in proportion; the mixed material is sent to a twin-screw extruder for continuous extrusion molding to form a strip material;

[0012] (3) Drying and post-treatment: drying the strip material in a hot air circulation drying oven, crushing it into particles by a hammer crusher, and obtaining the low-grade calcium-based bentonite-based desiccant product after screening;

[0013] (4) Evaluation of moisture absorption rate: Place the low-grade calcium-based bentonite-based desiccant product in a standard constant temperature and humidity curing box, let it stand, measure the weight of the bentonite before and after moisture absorption, and calculate the moisture absorption rate.

[0014] Preferably, in step (1), the content of montmorillonite in the original calcium-based bentonite ore is determined by XRD quantitative analysis to be less than 70%, and then the calcium-based bentonite powder with a particle size of ≤4 mm is finely crushed by a pair-roll crusher.

[0015] Preferably, in step (2), the finely crushed calcium-based bentonite powder is mixed with a sodium carbonate solution at a solid-liquid ratio of 1:0.25 - 0.30; the addition amount of solid sodium carbonate in the sodium carbonate solution is 1.0 - 3.0% of the dry basis mass of the calcium-based bentonite.

[0016] Preferably, in step (2), the screw speed of the twin-screw extruder is 40 - 60 rpm; continuous extrusion molding is carried out under an extrusion pressure of 8 - 12 MPa to form a strip-shaped material with a diameter of 3 - 5 mm.

[0017] Preferably, in step (3), the strip-shaped material is placed in a hot air circulation drying oven and dried at 100 - 105°C until the moisture content is ≤3%; then it is crushed by a hammer crusher into particles with a mesh size of 20 - 40.

[0018] Preferably, in step (4), the standard constant temperature and humidity curing box is set with an environmental temperature of 23 - 27°C and an environmental humidity of 40% or 80%, and left standing for 12 - 24 h to measure the weight of the bentonite before and after moisture absorption.

[0019] This application also claims to protect a low-grade calcium-based bentonite-based desiccant prepared by using the above preparation method of the low-grade calcium-based bentonite-based desiccant.

[0020] Due to the application of the above technical solutions, the present invention has the following beneficial effects compared with the prior art:

[0021] 1. The process of the present invention has a high degree of integration and a simple process. Through twin-screw extrusion, sodium modification and physical granulation are completed synchronously, omitting multiple processes such as "wet sodiumization - dehydration - secondary granulation" in the traditional process, and the production cycle is shortened by more than 40%;

[0022] 2. The present invention makes efficient use of low-grade resources. For low-grade calcium-based bentonite with a montmorillonite content of <70%, through semi-dry extrusion sodiumization, the moisture absorption rate of the optimized product can exceed 50% in an environment with RH80%;

[0023] 3. The present invention adopts a semi-dry process, and no organic components or binders need to be added throughout the process, avoiding the problems of high water consumption and organic pollutant residues in the traditional wet process, conforming to the trend of green manufacturing, having no waste water and low carbon emissions. Description of the Drawings

[0024] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the accompanying drawings required for the description of the specific embodiments or the prior art. Obviously, some of the following drawings are embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0025] Figure 1 is the process flow chart of Embodiment 1 of the present invention. Specific embodiments

[0026] For a clearer understanding of the technical features, objectives, and effects of the present invention, the specific implementation methods will now be described in detail.

[0027] The present invention will be further described below in conjunction with embodiments, but the present invention is not limited to the following embodiments. The implementation conditions used in the embodiments can be further adjusted according to different requirements of specific uses. The implementation conditions not specified are conventional conditions in this industry. The technical features involved in each embodiment of the present invention can be combined with each other as long as they do not conflict with each other.

[0028] Embodiment 1

[0029] See attached Figure 1 , this embodiment provides a preparation method of a low-grade calcium-based bentonite-based desiccant, including the following steps:

[0030] (1) Raw material pretreatment: Select calcium-based bentonite ore. Through XRD quantitative analysis, the montmorillonite content is determined to be <70%. After coarse crushing by a jaw crusher, it is further finely crushed by a pair-roll crusher into calcium-based bentonite powder with a particle size ≤ 4 mm.

[0031] (2) Semi-dry sodium modification: Mix the finely crushed calcium-based bentonite powder with sodium carbonate solution at a solid-liquid ratio of 1:0.28; the addition amount of sodium carbonate solid in the sodium carbonate solution is 1.0% of the dry basis mass of calcium-based bentonite; Feed the mixed material into a twin-screw extruder, the screw speed of the twin-screw extruder is 50 rpm, and continuous extrusion molding is carried out under an extrusion pressure of 10 MPa to form a strip-shaped material with a diameter of 4 mm.

[0032] (3) Drying and post-treatment: Place the strip-shaped material in a hot air circulation drying oven and dry it at 105 °C until the moisture content ≤ 3%. Then, it is crushed into 20-40 mesh particles by a hammer crusher, and the low-grade calcium-based bentonite-based desiccant product is obtained after screening.

[0033] (4) Moisture absorption rate evaluation: Place the low-grade calcium-based bentonite-based desiccant product in a standard constant temperature and humidity curing box, set the environmental temperature to 25 °C, and set the environmental humidity to 40% and 80% respectively. Let it stand for 24 hours respectively, measure the weight of the bentonite before and after moisture absorption, and calculate the moisture absorption rate;

[0034] In this example, it was measured that: standing for 24 hours in an environment of 25 °C and RH = 40%, the moisture absorption rate: 7.9%; standing for 24 hours in an environment of 25 °C and RH = 80%, the moisture absorption rate: 12.8%.

[0035] Example 2

[0036] This example provides a preparation method of a low-grade calcium-based bentonite-based desiccant, which includes the following steps:

[0037] (1) Raw material pretreatment: Select calcium-based bentonite ore, determine that the montmorillonite content is <70% through XRD quantitative analysis, coarsely crush it with a jaw crusher, and then finely crush it into calcium-based bentonite powder with a particle size ≤ 4 mm using a pair-roll crusher;

[0038] (2) Semi-dry sodium modification: Mix the finely crushed calcium-based bentonite powder with sodium carbonate solution at a solid-liquid ratio of 1:0.28; the addition amount of sodium carbonate solid in the sodium carbonate solution is 2.0% of the dry basis mass of calcium-based bentonite; Feed the mixed material into a twin-screw extruder, the screw speed of the twin-screw extruder is 50 rpm, and continuously extrude and form at an extrusion pressure of 10 MPa to form a strip-shaped material with a diameter of 4 mm;

[0039] (3) Drying and post-treatment: Place the strip-shaped material in a hot air circulation drying oven and dry it at 105 °C until the moisture content ≤ 3%, and then crush it into 20-40 mesh particles with a hammer crusher, and obtain the low-grade calcium-based bentonite-based desiccant product after screening;

[0040] (4) Moisture absorption rate evaluation: Place the low-grade calcium-based bentonite-based desiccant product in a standard constant temperature and humidity curing box, set the environmental temperature to 25 °C, and set the environmental humidity to 40% and 80% respectively. Let it stand for 24 hours respectively, measure the weight of the bentonite before and after moisture absorption, and calculate the moisture absorption rate;

[0041] In this example, it was measured that: standing for 24 hours in an environment of 25 °C and RH = 40%, the moisture absorption rate: 48.8%; standing for 24 hours in an environment of 25 °C and RH = 80%, the moisture absorption rate: 54%.

[0042] Example 3

[0043] This example provides a preparation method of a low-grade calcium-based bentonite-based desiccant, which includes the following steps:

[0044] (1) Raw material pretreatment: Select calcium-based bentonite ore. Determine the montmorillonite content < 70% through XRD quantitative analysis. Coarsely crush it with a jaw crusher, and then finely crush it into calcium-based bentonite powder with a particle size ≤ 4 mm using a pair-roller crusher;

[0045] (2) Semi-dry sodium modification: Mix the finely crushed calcium-based bentonite powder with sodium carbonate solution at a solid-liquid ratio of 1:0.28; the addition amount of sodium carbonate solid in the sodium carbonate solution is 3.0% of the dry basis mass of calcium-based bentonite; Feed the mixed material into a twin-screw extruder, the screw speed of the twin-screw extruder is 50 rpm, and continuously extrude and form it under an extrusion pressure of 10 MPa to form a strip-shaped material with a diameter of 4 mm;

[0046] (3) Drying and post-treatment: Place the strip-shaped material in a hot air circulation drying oven and dry it at 105 °C until the moisture content ≤ 3%. Then crush it into 20-40 mesh particles with a hammer crusher, and obtain the low-grade calcium-based bentonite-based desiccant product after screening;

[0047] (4) Evaluation of moisture absorption rate: Put the low-grade calcium-based bentonite-based desiccant product into a standard constant temperature and humidity curing box, set the environmental temperature to 25 °C, and set the environmental humidity to 40% and 80% respectively. Let it stand for 24 h respectively, measure the weight of bentonite before and after moisture absorption, and calculate the moisture absorption rate;

[0048] It is measured in this example that: when standing for 24 h in an environment of 25 °C and RH = 40%, the moisture absorption rate is 46%; when standing for 24 h in an environment of 25 °C and RH = 80%, the moisture absorption rate is 51%.

[0049] Comparative Example 1

[0050] This comparative example is based on the above Example 1, and the same parts as the above Example 1 will not be elaborated.

[0051] In this comparative example, the addition amount of sodium carbonate: 0%;

[0052] It is measured in this comparative example that: when standing for 24 h in an environment of 25 °C and RH = 40%, the moisture absorption rate is 6%; when standing for 24 h in an environment of 25 °C and RH = 80%, the moisture absorption rate is 10.3%.

[0053] List the test results of the moisture absorption rate of the low-grade calcium-based bentonite-based desiccant products prepared in the above examples and comparative examples in Table 1.

[0054] Table 1

[0055]

[0056] It can be seen from the above table that the equilibrium moisture absorption rate of the low-grade calcium-based bentonite-based desiccant prepared by the present invention is > 50% under the conditions of 25 °C and relative humidity of 80%.

[0057] In summary, the process of the present invention has a high degree of process integration and a simple process. The sodium modification and physical granulation are completed synchronously by twin-screw extrusion, omitting multiple processes such as "wet sodium modification - dehydration - secondary granulation" in the traditional process, and the production cycle is shortened by more than 40%; the present invention efficiently utilizes low-grade resources. For low-grade calcium-based bentonite with a montmorillonite content of <70%, through semi-dry extrusion sodium modification, the moisture absorption rate of the optimized product can exceed 50% in an environment of RH80%; the present invention adopts a semi-dry process and does not require the addition of organic components or binders throughout the process, avoiding the problems of high water consumption and residual organic pollutants in the traditional wet process, conforming to the trend of green manufacturing, having no waste water and low carbon emissions.

[0058] The above embodiments only represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the appended claims.

Claims

1. A preparation method of a low-grade calcium-based bentonite-based desiccant, characterized in that, It includes the following steps: (1) Raw material pretreatment: Select the calcium-based bentonite ore, crush it roughly by a jaw crusher, and then finely crush it into calcium-based bentonite powder by a pair-roll crusher; (2) Semi-dry sodium modification: Mix the finely crushed calcium-based bentonite powder with sodium carbonate solution in proportion; Feed the mixed material into a twin-screw extruder for continuous extrusion molding to form a strip-shaped material; (3) Drying and post-treatment: Place the strip-shaped material in a hot air circulation drying oven for drying, and then crush it into particles by a hammer crusher, and obtain the low-grade calcium-based bentonite-based desiccant product after screening; (4) Evaluation of moisture absorption rate: Put the low-grade calcium-based bentonite-based desiccant product into a standard constant temperature and humidity curing box, let it stand still, measure the weight of bentonite before and after moisture absorption, and calculate the moisture absorption rate.

2. The preparation method of a low-grade calcium-based bentonite-based desiccant according to claim 1, wherein, In step (1), the montmorillonite content of the calcium-based bentonite ore is determined by XRD quantitative analysis to be <70%, and then it is finely crushed into calcium-based bentonite powder with a particle size ≤ 4 mm by a pair-roll crusher.

3. The preparation method of a low-grade calcium-based bentonite-based desiccant as described in claim 1, characterized in that, In step (2), the finely crushed calcium-based bentonite powder is mixed with sodium carbonate solution according to a solid-liquid ratio of 1:0.25 - 0.30; The addition amount of sodium carbonate solid in the sodium carbonate solution is 1.0 - 3.0% of the dry basis mass of calcium-based bentonite.

4. The preparation method of a low-grade calcium-based bentonite-based desiccant according to claim 1, characterized in that, In step (2), the screw speed of the twin-screw extruder is 40 - 60 rpm; Continuous extrusion molding is carried out under an extrusion pressure of 8 - 12 MPa to form a strip-shaped material with a diameter of 3 - 5 mm.

5. The preparation method of a low-grade calcium-based bentonite-based desiccant according to claim 1, characterized in that, In step (3), the strip-shaped material is placed in a hot air circulation drying oven and dried at 100 - 105 °C until the moisture content ≤ 3%; Then it is crushed into particles with a mesh size of 20 - 40 by a hammer crusher.

6. The preparation method of a low-grade calcium-based bentonite-based desiccant according to claim 1, characterized in that, In step (4), the standard constant temperature and humidity curing box is set with an environmental temperature of 23 - 27 °C, an environmental humidity of 40% or 80%, and left standing for 12 - 24 h, and the weight of bentonite before and after moisture absorption is measured.

7. A low-grade calcium-based bentonite-based desiccant, characterized in that, It is prepared by using the preparation method of the low-grade calcium-based bentonite-based desiccant according to any one of claims 1 - 6.

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