Banking material, processing method of dewatered cake

Abstract

To provide, while contributing to reduction of an environmental load, a banking material capable of effectively utilizing dewatered cakes generated in a line stone cleaning process, and a processing method of the dewatered cakes.SOLUTION: A lime stone cleaning process including the gravel and the dewatered cake generated from the limestone cleaning process include a sprinkling process for the limestone, a separation process to separate sludge from the wastewater generated by the sprinkling process, and a dewatering process to dewater the sludge through filtration. The dewatered cake contains calcium carbonate derived from limestone, and a proportion of the dewatered cake in the mixture of 100 pts.mass of gravel and the dewatered cake is characterized by being 23 pts.mass or more and 40 pts.mass or less.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for treating embankment material and dewatered cake. [Background technology]

[0002] Limestone is one of Japan's major resources, and is mined in various parts of the country. However, the washing process in the limestone manufacturing process generates a large amount of industrial waste, known as dehydrated cake. Summary of the Invention [Problem to be solved by the invention]

[0003] The cost and environmental impact of disposing of the large amount of dehydrated cake generated during the washing process in the limestone manufacturing process have been considered problems, but there have been no reports on how to dispose of it.

[0004] An object of the present invention is to provide a method for treating embankment material and dehydrated cake that can effectively utilize the dehydrated cake generated in the limestone washing process while contributing to reducing the environmental burden. [Means for solving the problem]

[0005] The embankment material according to the present invention is Gravel and Dehydrated cake generated in the limestone washing process and The limestone washing step includes: A process of watering the limestone; A separation process for separating sludge from the wastewater generated by the watering process; A dewatering step of dewatering the sludge by filtration, The dehydrated cake contains calcium carbonate derived from limestone, The ratio of the dehydrated cake to 100 parts by mass of a mixture of the gravel and the dehydrated cake is 23 parts by mass or more and 40 parts by mass or less.

[0006] The banking material having the above-mentioned structure can effectively utilize the dehydrated cake, which is an industrial waste, thereby contributing to reducing the environmental load.

[0007] In the embankment material, The maximum dry density measured by the compaction test (JIS A 1210) is 2.15 g / cm 3 More than 2.8g / cm 3 The following is the result.

[0008] The embankment material having the above-mentioned configuration improves the stability of the constructed embankment against collapse.

[0009] In the embankment material, The optimum moisture content measured by the compaction test (JIS A 1210) is 5% or more and 10% or less.

[0010] The embankment material having the above-mentioned configuration can ensure the load-bearing capacity of the constructed embankment.

[0011] In the embankment material, The percentage of gravel in the embankment material measured by grain size test (JIS A 1204) is between 55% and 65%. The sand content of the embankment material measured by the grain size test (JIS A 1204) is 20% or more and 30% or less, The proportion of fine particles in the embankment material as measured by the particle size test (JIS A 1204) is between 10% and 20%.

[0012] The embankment material having the above-mentioned configuration can suppress subsidence and changes in the constructed embankment.

[0013] The method for treating dehydrated cake according to the present invention comprises the steps of: The limestone washing process is carried out, The limestone washing step includes: A process of watering the limestone; A separation process for separating sludge from the wastewater generated by the watering process; A dehydration step of dehydrating the sludge by filtration. A mixing step is carried out to obtain a fill material by mixing the gravel with the dehydrated cake generated in the limestone washing step; The dehydrated cake contains calcium carbonate derived from limestone, The ratio of the dehydrated cake to 100 parts by mass of a mixture of the gravel and the dehydrated cake is 23 parts by mass or more and 40 parts by mass or less.

[0014] According to the above method, the dehydrated cake can be effectively utilized as an embankment material. Effect of the Invention

[0015] According to the present invention, there are provided a method for treating embankment material and dehydrated cake that can effectively utilize the dehydrated cake generated in the limestone washing process while contributing to reducing the environmental burden. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 shows a flow diagram of a method for treating dewatered cake according to one embodiment. [Diagram 2] FIG. 2 shows a plan view of the entire test yard as viewed from above in the embodiment. [Diagram 3] FIG. 3 shows the measurement results of the surface settlement of the test embankment in Example 1. [Figure 4] FIG. 4 shows the measurement results of the amount of surface settlement of the test embankment in Comparative Example 1. [Diagram 5] FIG. 5 shows the measurement results of the amount of surface settlement of the test embankment in Comparative Example 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Hereinafter, one embodiment of the embankment material according to the present invention will be described. The fill material comprises gravel and dewatered cake generated from the limestone washing process. As the gravel, gravel deposited on the riverbed can be suitably used. In one embodiment, gravel from the riverbed of the Niyodo River or Mononobe River in Kochi Prefecture can be used. The limestone used in the limestone washing step is mined in various parts of Japan. In one embodiment, limestone mined in the Tosayama mine or the Shirakidani mine in Kochi Prefecture can be used, and the dehydrated cake generated when the limestone is used in the limestone washing step can be used.

[0018] The limestone washing step is a step associated with the limestone manufacturing step of refining raw limestone. As shown in Fig. 1, some steps of the limestone manufacturing step overlap with the limestone washing step. Although Fig. 1 also shows the limestone manufacturing step, the limestone washing step is not essential for the limestone washing step according to the present invention.

[0019] The limestone washing step and the limestone production step include a water spraying step for washing the limestone rough, in which the limestone rough is washed by spraying water onto the limestone rough with a shower while moving the limestone rough with a vibrating screen. The vibrating screen is equipped with a transport member, and the washed limestone rough moves on the transport member. The transport member is also equipped with a sieve, and the rough is sieved by size by vibration. Rough stones 30 mm or larger move downstream on the transport member as they are. Rough stones 2.5 mm or larger but smaller than 30 mm fall through the sieve of the vibrating screen and are separated. Limestone rough or soil attached to limestone rough that is 2.5 mm or smaller in size is discharged from the vibrating screen as the first drainage together with the sprayed water. The washed raw limestone having a size of 30 mm or more and the raw limestone having a size of 2.5 mm or more but less than 30 mm are then refined into limestone.

[0020] The limestone washing step includes a step of separating sludge from the first wastewater generated by the water spraying step. Specifically, the limestone washing step includes a first separation step of separating the first wastewater into a second wastewater and a solid matter, and a second separation step of separating the second wastewater into a supernatant and a sludge, which are carried out successively.

[0021] A screw conveyor is used in the first separation step. A screw conveyor is a device that has a shaft inside a cylindrical pipe with spiral blades attached around the shaft, and transports the materials to be treated by rotating the shaft and the blades. The solid matter contained in the first wastewater moves downstream in the screw conveyor as the blade rotates. On the other hand, the liquid contained in the first wastewater (the second wastewater) does not move with the solid matter even when the blade rotates, but moves downward due to gravity. This separates the solid matter from the second wastewater from the first wastewater. The solid matter is then dried to become sand. The sand can be used for aggregates and other purposes.

[0022] In the second separation step, the second wastewater is separated by sedimentation into suspended contaminants (the sludge) contained in the second wastewater and a supernatant. Specifically, the second wastewater is stored in a water tank and allowed to stand, causing the sludge to settle to the bottom of the tank. In this case, multiple inclined plates may be provided in the water tank. By providing multiple inclined plates in the water tank, the settling efficiency can be increased. The sludge that has settled to the bottom of the tank is gently stirred to prevent solidification, and then separated from the supernatant and taken out. Meanwhile, the supernatant is discharged from the tank by overflowing, and is then reused as water to wash the limestone again in the watering process.

[0023] The limestone washing step includes a step of dewatering the sludge by filtration (hereinafter, referred to as a "dewatering step"). Specifically, the sludge is dewatered by filter filtration. In one embodiment, a method of installing a filter on the entire bottom surface of the water tank used in the second separation step can be adopted. That is, the dewatering step can be carried out by capturing the sludge that has settled on the upper surface of the filter with the filter and moving the supernatant in the water tank to the lower surface of the filter through the filter. When moving the supernatant to the lower surface of the filter, the dewatering step can be carried out by sucking it from the lower surface of the filter using a vacuum pump. The sludge becomes the dehydrated cake by being dehydrated. A certain percentage of moisture remains in the dehydrated cake immediately after the dehydration step. Therefore, in order to further dry the dehydrated cake, it may be naturally dried by piling it up outdoors. Piling up outdoors means piling things up outdoors.

[0024] In general sedimentation separation, if the precipitation of suspended turbid matter is not sufficiently expressed and sufficient separation cannot be achieved, an arbitrary flocculant may be used. By using a flocculant, it is possible to promote the precipitation of suspended turbid matter and improve the separation performance from the supernatant. In this embodiment, the flocculant may or may not be used in the second separation step. If the flocculant is not used, the flocculant is prevented from being mixed into the embankment material as an impurity, and therefore the performance of the embankment material can be prevented from being deteriorated.

[0025] In the second separation step, in addition to the flocculant, slaked lime can be added to improve the dewatering efficiency in the dewatering step. When the viscosity of the second wastewater is low, the addition of slaked lime is very effective in improving the dewatering efficiency. In this embodiment, the slaked lime may or may not be used in the second fractionation step.

[0026] By carrying out the water spraying step and the separation step, the size of the treated object is reduced, so that the dehydrated cake finally produced in the limestone washing step is obtained as a very fine-grained product. The lower limit of the particle size of the dehydrated cake that is 95% (w / w) or more is not particularly limited, but is preferably 1 μm or more. The upper limit of the particle size of the dehydrated cake that is 95% (w / w) or more is 100 μm or less, preferably 75 μm or less, and more preferably 50 μm or less. As described above, by using the dehydrated cake having a fine particle size as the embankment material, it is possible to prepare an embankment material having a particle size distribution that satisfies suitable conditions.

[0027] The main component of the dehydrated cake is soil particles. On the other hand, the main component of limestone is calcium carbonate. Therefore, the dehydrated cake obtained in the limestone washing process contains calcium carbonate that is dissolved and scraped off from the limestone surface during the washing process. In addition, the moisture remaining in the dehydrated cake immediately after the dehydration process also contains calcium carbonate, and calcium carbonate is further precipitated in the dehydrated cake during the process of evaporation of the moisture by open-air stacking. As mentioned above, the main component of limestone is calcium carbonate, but the details of the components of limestone mined in Japan vary slightly depending on the region where it is mined. The precipitated calcium carbonate strengthens the binding force between the sand particles in the embankment material, improving the interlocking between the sand particles and enhancing friction. Embankments constructed using such embankment materials can exhibit stable strength.

[0028] The banking material according to this embodiment is obtained by carrying out a mixing step of mixing the gravel with the dehydrated cake generated in the limestone washing step. The lower limit of the ratio of the dehydrated cake to 100 parts by mass of the mixture of the gravel and the dehydrated cake is 23 parts by mass or more, preferably 24 parts by mass or more, and more preferably 25 parts by mass or more. The upper limit of the ratio of the dehydrated cake to 100 parts by mass of the mixture of the gravel and the dehydrated cake is 40 parts by mass or less, preferably 35 parts by mass or less, and more preferably 30 parts by mass or less.

[0029] The mixture of gravel and the dewatered cake may include optional additives, for example, the mixture may include optional additives such as quicklime, hydrated lime, etc.

[0030] The lower limit of the maximum dry density measured by the compaction test (JIS A 1210) of the embankment material according to this embodiment is 2.15 g / cm 3 More preferably, it is 2.17 g / cm 3 More preferably, it is 2.19 g / cm 3 The upper limit of the maximum dry density measured by the compaction test (JIS A 1210) is 2.8 g / cm 3 is preferably 2.5 g / cm or less. 3 More preferably, it is 2.3 g / cm or less. 3 The following is the result. It is known that the higher the maximum dry density, the wider the particle size distribution of the embankment material, and the higher the energy required to compact the embankment material (hereinafter referred to as "compaction energy"). In other words, the lower the compaction energy, the less energy is required to compact the embankment material when constructing the embankment, making it impossible to construct an embankment with stable strength. Conversely, when the compaction energy is high, the embankment can be compacted with sufficient energy, making it possible to construct an embankment with stable strength. Therefore, since the maximum dry density is within the above range, the particle size distribution of the embankment material satisfies suitable conditions and the embankment material can be compacted under optimal conditions, so that embankments constructed using such embankment material can exhibit stable strength.

[0031] The lower limit of the optimum moisture content measured by the compaction test (JIS A 1210) is 5% or more, preferably 6% or more, and more preferably 6.5% or more. The upper limit of the optimum moisture content measured by the compaction test (JIS A 1210) is 10% or less, preferably 8% or less, and more preferably 7.5% or less. By having the optimum water content within the above range, it becomes possible to construct stronger embankments.

[0032] The maximum dry density and optimum moisture content of embankment material can be determined using Method B of JIS A1210:2020 "Test method for soil compaction by tamping."

[0033] The lower limit of the gravel content in the embankment material measured by the particle size test (JIS A 1204) according to this embodiment is 55% or more, preferably 57% or more, and more preferably 59% or more. The upper limit of the gravel content in the embankment material measured by the particle size test (JIS A 1204) is 65% or less, preferably 63% or less, and more preferably 61% or less.

[0034] The lower limit of the sand content in the embankment material measured by the grain size test (JIS A 1204) is 20% or more, preferably 21% or more, and more preferably 23% or more. The upper limit of the sand content in the embankment material measured by the grain size test (JIS A 1204) is 30% or less, preferably 28% or less, and more preferably 26% or less.

[0035] The lower limit of the fine fraction in the embankment material measured by the particle size test (JIS A 1204) is 10% or more, preferably 12% or more, and more preferably 14% or more. The upper limit of the fine fraction in the embankment material measured by the particle size test (JIS A 1204) is 20% or less, preferably 18% or less, and more preferably 16% or less. By having the proportions of gravel, sand, and fine particles contained in the embankment material fall within the above ranges, the particle size distribution of the embankment material satisfies favorable conditions, and embankments constructed using such embankment materials are able to exhibit stable strength.

[0036] The grain size of fill material (gravel, sand, fine grain) can be determined according to JIS A1204:2020 "Soil grain size testing method."

[0037] The lower limit of the average water content of the embankment material according to the present embodiment measured by the field density test (JIS A 1214) is 1% or more, preferably 1.5% or more, and more preferably 2% or more. The upper limit of the average water content measured by the field density test (JIS A 1214) is 10% or less, preferably 7% or less, and more preferably 5% or less.

[0038] The lower limit of the degree of compaction measured by the field density test (JIS A 1214) is 85% or more, preferably 90% or more, and more preferably 95% or more. The upper limit of the degree of compaction measured by the field density test (JIS A 1214) is not particularly limited, but is preferably 99.9% or less.

[0039] The lower limit of the average dry density measured by the on-site density test (JIS A 1214) is 2.00 g / cm 3 More preferably, it is 2.05 g / cm 3 More preferably, it is 2.10 g / cm 3 The upper limit of the average dry density measured by the on-site density test (JIS A 1214) is 2.50 g / cm 3 or less, preferably 2.45 g / cm 3 More preferably, it is 2.40 g / cm 3 The following is the result.

[0040] The average moisture content, degree of compaction, and average dry density of fill material can be determined using JIS A1214:2013 "Soil density testing method using sand replacement method." EXAMPLES

[0041] The present invention will now be described in more detail with reference to examples, but the present invention is not limited to these.

[0042] Example 1 Raw limestone extracted from the Shirakidani mine in Kochi Prefecture was subjected to a water spraying process, a first fractionation process, a second fractionation process, and a dehydration process to obtain a dehydrated cake. Fill material A was prepared by mixing 25 parts by mass of the dehydrated cake with 75 parts by mass of gravel excavated from the Niyodo River in Kochi Prefecture. Before carrying out the test embankment, the foundation was compacted and the ground was leveled. Then, as shown in Figure 2, embankment material A was unrolled and test yard 10 was constructed. The unrolled thickness was 30 cm. The soil was further compacted by rolling it several times using a vibrating roller (3t). The number of times of compaction was 2, 4, 6, 8, and 10 times. The height of the embankment after unrolling was used as the standard, and the amount of surface settlement was evaluated at four points, 12a to 12d, in Figure 2. After that, the compaction density was measured at the three compaction density measurement points 11 in Figure 2, and a field density test (JIS A 1214) was conducted. Separately, a compaction test (JIS A 1210) and a grain size test (JIS A 1204) were conducted on embankment material A.

[0043] Comparative Example 1 The test was carried out in the same manner as in Example 1, except that embankment material B consisting of 100 parts by mass of gravel was used instead of embankment material A.

[0044] Comparative Example 2 The test was conducted in the same manner as in Example 1, except that instead of embankment material A, embankment material C was used, which was prepared by mixing 75 parts by mass of gravel, 22.5 parts by mass of dehydrated cake generated in the limestone washing process, and 2.5 parts by mass of slaked lime.

[0045] The test and evaluation results are shown in Table 1 and Figs.

[0046] [Table 1]

[0047] 3 to 5, the difference in the amount of surface settlement at each measurement position in Example 1 is smaller than that in other comparative examples. In other words, the embankment in Example 1 has no difference in strength at each measurement position, has uniform strength overall, and is excellent in stability as an embankment.

[0048] From Table 1, it can be seen that the embankment material A of Example 1 has a higher maximum dry density and a wider particle size distribution based on the content of each particle than the embankment materials of the other comparative examples. By adding an appropriate amount of the dehydrated cake, the particle size distribution becomes more favorable than the other comparative examples, and as a result, it can be seen that it also contributes to improving the functionality of the embankment. [Explanation of symbols]

[0049] 1: limestone washing process, 2: limestone manufacturing process, 10: test yard, 11: compaction density measurement point, 12a: surface subsidence measurement point, 12b: surface subsidence measurement point, 12c: surface subsidence measurement point, 12d: surface subsidence measurement point

Claims

1. Gravel and Dehydrated cake generated in the limestone washing process and The limestone washing step includes: A process of watering the limestone; A separation process for separating sludge from the wastewater generated by the watering process; A dewatering step of dewatering the sludge by filtration, The dehydrated cake contains calcium carbonate derived from limestone, A banking material, characterized in that the ratio of the dehydrated cake to 100 parts by mass of the mixture of the gravel and the dehydrated cake is 23 parts by mass or more and 40 parts by mass or less.

2. The maximum dry density measured by the compaction test (JIS A 1210) is 2.15 g / cm 3 2.8g / cm or more 3 2. The embankment material according to claim 1, characterized in that:

3. 2. The embankment material according to claim 1, characterized in that the optimum moisture content measured by the compaction test (JIS A 1210) is 5% or more and 10% or less.

4. The ratio of gravel in the embankment material measured by the grain size test (JIS A 1204) is 55% or more and 65% or less, The proportion of sand in the embankment material measured by the grain size test (JIS A 1204) is 20% or more and 30% or less, 3. The embankment material according to claim 1, wherein the proportion of fine particles in the embankment material measured by the particle size test (JIS A 1204) is 10% or more and 20% or less.

5. The limestone washing process is carried out. The limestone washing step includes: A process of watering the limestone; A separation process for separating sludge from the wastewater generated by the watering process; A dehydration step of dehydrating the sludge by filtration. A mixing step is carried out to obtain a fill material by mixing the gravel with the dehydrated cake generated in the limestone washing step; The dehydrated cake contains calcium carbonate derived from limestone, A method for treating dehydrated cake, wherein a ratio of the dehydrated cake to 100 parts by mass of a mixture of the gravel and the dehydrated cake is 23 parts by mass or more and 40 parts by mass or less.

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