Synchronous red mud dealkalization method for soil

Abstract

The invention relates to an aluminum oxide industrial waste residue treatment technology, in particular to a red mud synchronous dealkalization soil treatment method. According to the method, citric acid and calcium nitrate are adopted as treating agents to cooperatively treat the red mud, the sodium content requirement of planting soil is taken as the standard, the red mud is dealkalized to reduce the sodium content, meanwhile, the granularity of the dealkalized red mud is improved, the organic matter content of the dealkalized red mud is increased, and then the dealkalized red mud and normal soil are mixed in proportion to form the dealkalized red mud soil. The physicochemical indexes of the dealkalized red mud soil are as follows: the volume weight is 1.18-1.26 g / cm < 3 >, the organic matter content is 10.6-12.3%, the pH value is 7.2-7.35, the EC is 0.492-0.562 ms / cm, and the specific surface area is 51.49-59.80 m < 2 > / g. The dealkalized red mud soil obtained through the synergistic treatment of the citric acid and the calcium nitrate completely meets the physicochemical properties of the soil and the planting requirements of plants.

Description

Technical Field

[0001] The invention relates to alumina industrial waste residue treatment technology, and in particular to a red mud synchronous dealkalization soil conversion method. Background Art

[0002] Red mud is a kind of strong alkaline industrial solid waste generated in the production process of alumina industry. The comprehensive utilization rate of red mud in my country is only about 10%, and the accumulated stockpile has reached 1.6 billion tons. Its strong alkalinity, fine particles and complex mineral phase composition make it difficult to use on a large scale. When it is piled in the open air, it will cause land salinization, pollute surface water and groundwater, and pose a serious threat to the surrounding environment. How to use red mud on a large scale has become a key issue of concern to the world's alumina industry.

[0003] Currently, the main ways to utilize red mud include the extraction of valuable metals such as Fe, Al, Cs, and Ti; the preparation of red mud-based building materials; as an adsorbent and modifier for acidic pollution; and the preparation of red mud-based catalysts. However, none of the above methods can effectively utilize red mud on a large scale.

[0004] The soilification of red mud is expected to become a way to utilize red mud on a large scale. There are three main types of research on the soilification methods of red mud at present, namely, topsoil covering, biological improvement, and substrate improvement. The topsoil covering method is to cover the surface of the red mud with normal soil and cooperate with planting to achieve the soilification of red mud. However, since the red mud has not been de-alkalized, the surface soil will become salinized over time, seriously affecting the growth of plants on it. Biological improvement is to directly plant plants or add microorganisms on the red mud, and use the organic acids and organic matter produced by biological metabolism to improve the red mud. However, due to the high alkalinity and extreme physical properties of red mud, the activity of plants or microorganisms is poor and the survival rate is low, which greatly affects the improvement effect of this method on red mud.

[0005] The matrix improvement method is a method that has been studied more. It is mainly based on the dealkalization of red mud. Commonly used modifiers include acid, salt (gypsum, brine), etc. Studies have shown that the use of waste acid or acidic waste gas to improve red mud will introduce new impurities or heavy metals, which will have an adverse effect on plants and the water and soil environment; the use of inorganic acid to treat red mud, on the one hand, the dealkalized red mud is highly acidic, and on the other hand, a large amount of wastewater will be produced to cause secondary pollution; low-concentration salt solutions have a poor improvement effect on red mud, while high-concentration salt solutions will cause the red mud to become compacted and salinized after improvement. The matrix improvement method mainly deals with the dealkalization of red mud, and does not consider the changes in the physical and chemical indicators of the red mud after dealkalization. The physical and chemical indicators of the dealkalized red mud obtained by this method are very different from the physical and chemical indicators of the soil for planting plants (pH value, organic matter content, bulk density, porosity, specific surface area, etc.), especially the difference in organic matter content is the most prominent, which requires further treatment.

[0006] Therefore, in view of the problems existing in the current large-scale utilization methods of red mud, it is urgently necessary to develop a method for the simultaneous dealkalization of red mud into soil, which can reduce the alkali content of red mud while improving the physical and chemical properties of red mud (increasing organic matter content, increasing bulk density, optimizing porosity, and increasing specific surface area), effectively promoting the soilization of red mud, and achieving the purpose of large-scale utilization of red mud. Summary of the invention

[0007] The object of the present invention is to provide a method for synchronously de-alkalizing red mud into soil, that is, using citric acid and calcium nitrate as treatment agents to synergistically treat red mud, taking the sodium content requirement of planting soil as the standard, de-alkalizing red mud to reduce the sodium content, and at the same time, improving the particle size of the de-alkalized red mud and increasing the organic matter content of the de-alkalized red mud, and then mixing the de-alkalized red mud with normal soil in a certain proportion to form de-alkalized red mud soil.

[0008] A method for synchronously dealkalizing red mud into soil comprises the following steps: adding red mud into a dealkalizing solution having a molar ratio of calcium nitrate to citric acid of 1 to 3:1 and stirring the solution, wherein the volume / mass liquid-to-solid ratio is 3 to 6:1; heating the solution in a constant temperature water bath at 20 to 80°C; washing and filtering the dealkalizing red mud, and uniformly mixing the dealkalizing red mud with normal soil at a mass ratio of 1 to 7:1 to obtain dealkalizing red mud soil.

[0009] A method for synchronously dealkalizing red mud into soil, comprising the following steps: (1) Grinding the red mud into powder that can pass through a sieve of 50 mesh or more; (2) drying the crushed red mud in step (1) at 80° C. to 100° C. for 5 to 16 hours; (3) preparing a citric acid solution with a concentration of 0.2 to 0.4 mol / L, and adding calcium nitrate to the citric acid solution to prepare a dealkalizing solution with a molar ratio of calcium nitrate to citric acid of 1 to 3:1; (4) placing the dealkalization solution of step (3) in a constant temperature water bath and heating it at a temperature of 20 to 80° C., then adding the red mud of step (2) into the constant temperature dealkalization solution, with a volume / mass liquid-to-solid ratio of 3 to 6:1, a stirring speed of 300 to 600 rad / min, and a reaction time of 2 h to 4 h; (5) filtering the red mud after the reaction in step (4) while hot, and washing it with deionized water for 1 to 3 times to obtain dealkalized red mud; (6) crushing the dealkalized red mud from step (5) through a sieve with a mesh size smaller than 20; (7) Crush normal soil through a sieve with a mesh size of less than 20; (8) The de-alkali red mud sieved in step (6) and the normal soil sieved in step (7) are uniformly mixed in a mass ratio of 1 to 7:1 to obtain de-alkali red mud soil.

[0010] The filtrate from step (5) is returned to step (3) for reuse.

[0011] The physical and chemical indicators of the de-alkali red mud soil are: bulk density: 1.18-1.26 g / cm 3 , organic matter content: 10.6-12.3%, pH: 7.2-7.35, EC: 0.492-0.562 ms / cm, specific surface area: 51.49-59.80m 2 / g.

[0012] According to 60g / m 3 The alfalfa seeds were sown on the de-alkali red mud soil obtained above, watered every day, and the germination rate was recorded after 10 days. The wet weight, dry weight and average plant height of the plants were measured after 30 days. The planting effect was shown in Table 1. Figure 1 .

[0013] The present invention adopts citric acid and calcium nitrate as red mud treatment agents, and realizes the improvement of red mud particle size and the increase of red mud organic matter while de-alkalizing red mud, solves the problem of poor physical and chemical indicators such as small particle size and low organic matter content of de-alkalized red mud by the current matrix improvement method, thereby achieving the purpose of large-scale soil utilization of red mud. The interaction between citric acid and calcium nitrate will produce a stable calcium citrate complex, enhance the ionization strength of citric acid, increase the hydrogen ion concentration in the solution, reduce the amount of organic acid, solve the problem of weak acidity and large amount of organic acid, and is conducive to de-alkalization, which can effectively reduce the pH of red mud. At the same time, citric acid is an organic acid that can increase the organic matter content of de-alkalized red mud; in addition to promoting citric acid to release hydrogen ions for de-alkalization, calcium ions themselves can also replace sodium in red mud, which has a superimposed de-alkalization effect; in addition, calcium ions can reduce the electric potential on the surface of red mud particles, promote the mutual aggregation between red mud particles, increase the particle size of de-alkalized red mud, and effectively improve the physical properties of red mud. At the same time, calcium nitrate is also the main component of agricultural quick-acting nitrogen fertilizer, which can improve the nutrients of de-alkalized red mud.

[0014] In summary, the present invention uses citric acid and calcium nitrate to synergistically dealkalize red mud, and simultaneously obtains dealkalized red mud with a sodium content that meets the requirements of planting soil, a better particle size and a higher organic matter content. The dealkalized red mud is mixed with normal soil to obtain dealkalized red mud soil with good planting effect, which provides strong technical support for the large-scale utilization of red mud soil. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 These are planting effect diagrams of original red mud, normal soil and embodiments. DETAILED DESCRIPTION

[0016] The measuring methods of various physical and chemical properties of the embodiments of the present invention are as follows: There is no national standard for the pH detection method of red mud. The present invention refers to the potentiometric method for measuring soil pH (HJ-962-2018); the conductivity is measured according to the method in "Electrode Method for Determining Soil Conductivity" (HJ 802-2016); the bulk density is measured according to the method in "Soil Testing Part 4: Determination of Soil Bulk Density" (NY / T 1121.-2006). Organic matter is measured according to the method in "Determination of Organic Matter in Solid Waste by Ignition Loss Method" (HJ 761-2015); ICP is used to measure the sodium content of red mud after dealkalization.

[0017] The results of using de-alkali red mud soil for potted planting show that the growth of potted plants in de-alkali red mud soil is comparable to that in normal soil (suitable for planting soil). Figure 1 .

[0018] Embodiment 1: (1) Grinding the red mud into powder that can pass through a sieve of 50 mesh or more; (2) drying the crushed red mud in step (1) at 90° C. for 10 hours; (3) preparing a citric acid solution with a concentration of 0.4 mol / L, and adding calcium nitrate to the citric acid solution to prepare a dealkalizing solution with a molar ratio of calcium nitrate to citric acid of 3:1; (4) placing the dealkalization solution of step (3) in a constant temperature water bath and heating the temperature to 25° C., adding the red mud of step (2) into the dealkalization solution after the temperature is constant, the liquid-solid ratio (volume: mass) is 3:1, the stirring speed is 300 rad / min, and the reaction time is 4 h; (5) filtering the red mud after the reaction in step (4) while hot, and washing it three times with deionized water to obtain dealkalized red mud; (6) crushing the dealkalized red mud from step (5) through a sieve with a mesh size of less than 20; (7) Pass normal soil through a sieve with a mesh size of less than 20; (8) The de-alkali red mud sieved in step (6) and the normal soil sieved in step (7) were uniformly mixed in a mass ratio of 5:3 to obtain 400 g of de-alkali red mud soil.

[0019] According to 60g / m 3 The sowing amount was 2.5, and alfalfa seeds were sown in the de-alkali red mud soil. Water was applied every day. The germination rate was recorded after 10 days. The wet weight, dry weight and average plant height of the plants were measured after 30 days. The planting effect was shown in Table 1. Figure 1 .

[0020] Embodiment 2: (1) Grinding the red mud into powder that can pass through a sieve of 50 mesh or more; (2) drying the crushed red mud in step (1) at 90° C. for 10 hours; (3) preparing a citric acid solution with a concentration of 0.2 mol / L, and adding calcium nitrate to the citric acid solution to prepare a dealkalizing solution with a molar ratio of calcium nitrate to citric acid of 1:1; (4) placing the dealkalization solution of step (3) in a constant temperature water bath and heating the temperature to 80° C., adding the red mud of step (2) into the dealkalization solution after the temperature is constant, the liquid-solid ratio (volume: mass) is 6:1, the stirring speed is 600 rad / min, and the reaction time is 3 h; (5) filtering the red mud after the reaction in step (4) while hot, and washing it three times with deionized water to obtain dealkalized red mud; (6) crushing the dealkalized red mud from step (5) through a sieve with a mesh size smaller than 20; (7) Pass normal soil through a sieve with a mesh size of less than 20; (8) The de-alkali red mud sieved in step (6) and the normal soil sieved in step (7) were uniformly mixed in a mass ratio of 3:1 to obtain 400 g of de-alkali red mud soil.

[0021] According to 60g / m 3 The sowing amount was 2.5, and alfalfa seeds were sown in the de-alkali red mud soil. Water was applied every day. The germination rate was recorded after 10 days. The wet weight, dry weight and average plant height of the plants were measured after 30 days. The planting effect was shown in Table 1. Figure 1 .

[0022] Embodiment 3: (1) Grinding the red mud into powder that can pass through a sieve of 50 mesh or more; (2) drying the crushed red mud in step (1) at 90° C. for 10 hours; (3) preparing a citric acid solution with a concentration of 0.3 mol / L, and adding calcium nitrate to the citric acid solution to prepare a dealkalizing solution with a molar ratio of calcium nitrate to citric acid of 2:1; (4) placing the dealkalization solution of step (3) in a constant temperature water bath and heating the temperature to 50° C., adding the red mud of step (2) to the dealkalization solution after the temperature is constant, the liquid-solid ratio (volume: mass) is 5:1, the stirring speed is 500 rad / min, and the reaction time is 2 h; (5) filtering the red mud after the reaction in step (4) while hot, and washing it three times with deionized water to obtain dealkalized red mud; (6) crushing the dealkalized red mud from step (5) through a sieve with a mesh size smaller than 20; (7) Pass normal soil through a sieve with a mesh size of less than 20; (8) The de-alkali red mud sieved in step (6) and the normal soil sieved in step (7) were uniformly mixed at a mass ratio of 7:1 to obtain 400 g of de-alkali red mud soil.

[0023] According to 60g / m 3The sowing amount was 2.5, and alfalfa seeds were sown in the de-alkali red mud soil. Water was applied every day. The germination rate was recorded after 10 days. The wet weight, dry weight and average plant height of the plants were measured after 30 days. The planting effect was shown in Table 1. Figure 1 .

[0024] Comparative Example 1 (original red mud): (1) Pass the original red mud through a sieve with a mesh size of less than 20; (2) Take 400 g of raw red mud with a sieve smaller than 20 mesh; According to 60g / m 3 The sowing amount was 2.5, and alfalfa seeds were sown in the original red mud. Water was applied every day. The germination rate was recorded after 10 days. The wet weight, dry weight and average plant height of the plants were measured after 30 days. The planting effect was shown in Table 1. Figure 1 .

[0025] Comparative Example 2 (Normal Soil): (1) Pass normal soil through a sieve with a mesh size of less than 20; (2) Take 400g of normal soil that is smaller than 20 mesh sieve; According to 60g / m 3 The sowing amount was 2.5, and alfalfa seeds were sown in normal soil. Water was applied every day. The germination rate was recorded after 10 days. The wet weight, dry weight, and average plant height of the plants were measured after 30 days. The planting effect was shown in Table 1. Figure 1 .

[0026] The physicochemical properties of the samples of Comparative Example 1, Comparative Example 2 and Examples are shown in Table 1.

[0027] Table 1 Physical and chemical properties of samples from different cases Case <![CDATA[Unit weight g / cm 3 > Organic matter content% pH ECms / cm <![CDATA[Specific surface area m 2 / g]]> Example 1 1.18 10.6 7.2 0.492 51.49 Example 2 1.25 11.8 7.24 0.511 55.12 Example 3 1.26 12.3 7.35 0.562 59.80 Comparative Example 1 0.94 0.7 9.89 0.748 16.86 Comparative Example 2 1.36 7.357 6.48 0.101 41.52

[0028] The germination rate of comparative example 1, comparative example 2 and embodiment after 10 days of planting and the growth status of plants after 30 days of planting are shown in Table 2 and Figure 1 .

[0029] Table 2 Plant growth in different cases Indicator Case Wet weight / g (30 days) Dry weight / g (30 days) Plant / cm (30 days) Germination rate% (10 days) Example 1 0.4178 0.0388 3.46 88 Example 2 0.4547 0.0447 5.12 87 Example 3 0.4858 0.0589 5.45 92 Comparative Example 1 none none none 8 Comparative Example 2 0.4308 0.0432 4.05 94

[0030] It can be seen from Table 1 that the physical and chemical properties of the dealkalized red mud soil of the embodiment are significantly different from those of Comparative Example 1 (original red mud), and are closer to those of Comparative Example 2 (normal soil). Figure 1 It can be seen that the germination rate and growth of plants planted in the de-alkali red mud soil in the examples are good, which are comparable to those in Comparative Example 2 (normal soil), and Example 3 has the best effect. This shows that the de-alkali red mud soil obtained by synergistically treating red mud with citric acid and calcium nitrate fully meets the physical and chemical properties of the soil and the requirements for plant planting.

Claims

1. A method for synchronously de-alkalizing red mud into soil, characterized in that: The red mud is added into a dealkalizing solution having a molar ratio of calcium nitrate to citric acid of 1 to 3:1 and stirred, with a volume / mass liquid-to-solid ratio of 3 to 6:1, and heated in a constant temperature water bath at 20 to 80°C, and the dealkalizing red mud obtained by washing and filtering is uniformly mixed with normal soil at a mass ratio of 1 to 7:1 to obtain dealkalizing red mud soil.

2. A method for synchronously de-alkalizing red mud into soil, characterized in that: The following steps are involved: (1) Grinding the red mud into powder that can pass through a sieve of 50 mesh or more; (2) drying the crushed red mud in step (1) at 80° C. to 100° C. for 5 to 16 hours; (3) preparing a citric acid solution with a concentration of 0.2 to 0.4 mol / L, and adding calcium nitrate to the citric acid solution to prepare a dealkalizing solution with a molar ratio of calcium nitrate to citric acid of 1 to 3:1; (4) placing the dealkalization solution of step (3) in a constant temperature water bath and heating it at a temperature of 20 to 80° C., then adding the red mud of step (2) into the constant temperature dealkalization solution, with a volume / mass liquid-to-solid ratio of 3 to 6:1, a stirring speed of 300 to 600 rad / min, and a reaction time of 2 h to 4 h; (5) filtering the red mud after the reaction in step (4) while hot, and washing it with deionized water for 1 to 3 times to obtain dealkalized red mud; (6) crushing the dealkalized red mud from step (5) through a sieve with a mesh size smaller than 20; (7) Crush normal soil through a sieve with a mesh size of less than 20; (8) The de-alkali red mud sieved in step (6) and the normal soil sieved in step (7) are uniformly mixed in a mass ratio of 1 to 7:1 to obtain de-alkali red mud soil.

3. The method for synchronous dealkalization of red mud into soil according to claim 2, characterized in that: The filtrate from step (5) is returned to step (3) for reuse.

4. The method for synchronous dealkalization of red mud into soil according to claim 2, characterized in that: The physical and chemical indicators of the de-alkali red mud soil are: bulk density: 1.18-1.26 g / cm 3 , organic matter content: 10.6-12.3%, pH: 7.2-7.35, EC: 0.492-0.562 ms / cm, specific surface area: 51.49-59.80m 2 / g.

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