FR3109542A1 - A manufacturing process and application of the soil conditioner made from solid waste - Google Patents

Abstract

The invention relates to the field of soil conditioner, and relates in particular to a soil conditioner made from solid waste, its manufacturing process and its application. The raw materials for preparing said soil conditioner include: granite powder, marble powder, sludge and additive; The manufacturing process includes the following steps: grinding raw materials (granite, marble and mud) into fine powder; mix the granite powder, marble powder, mud powder with the additive, add water until a homogeneous mixture is obtained; dry this mixture to obtain the mixture; turn the mixture on to a high temperature and allow it to cool and dry, to obtain the finished soil conditioner product. Said soil conditioner takes advantage of components in residual stones, such as silicon oxide, aluminum oxide, iron oxide and calcium oxide, as well as rich components in sewage sludge , such as P2O5, potassium oxide and magnesium oxide. Under the heat treatment, the components turn into crystals with less defect, such as aluminosilicates. This has the effect of increasing the specific surface and forming a microporous surface structure, in order to achieve the decontamination of soils polluted by heavy metals.

Description

A manufacturing process and application of the soil conditioner made from solid waste

The invention relates to the field of soil conditioner, and relates in particular to a soil conditioner made from solid waste, its manufacturing process and its application.

With the development of the economy, natural stone products are increasingly appreciated by consumers. During the rapid development of the industry, pollution from waste generated during stone shaping, grinding and polishing is getting more serious every day. According to reports, to make 30 m² of stone slabs, about 1 ton of stone powder and residue is generated. China alone can produce over 9 million tons of stone powder waste every year. The particle size of the stone powder is relatively small, the powder can be easily diffused by wind or rain, which may cause secondary pollution of the environment. Therefore, there is an urgent need to develop new ways to realize the recycling of waste stone powder.

In China, the expansion of industrialization and urbanization generates an enormous amount of wastewater every day. Since the implementation of the Water Pollution Prevention and Treatment Plan of Action in 2015, the Chinese government has participated vigorously in the fight against water pollution. Until the end of 2018, China's urban sewage treatment capacity of 167 million m ³ / day, the total amount of treated wastewater was 51.9 billion m ³ / day (Press on ecology and environment of China, 2018). When treating wastewater, the production of sewage sludge in large quantities is inevitable. As a by-product of wastewater treatment, sewage sludge contains various pollutants, such as organic pollutants such as POPs (abbreviation of the English term "persistent organic pollutant") and inorganic pollutants such as metal compounds. heavy. These pollutants impose severe restrictions on the recycling of sewage sludge.

According to the analysis of 9.02 million soil samples taken from soil tests from 2005 to 2011, the pH of 40% of cultivated land in China is less than 6.5, of which 22.85 million mu of land crops have a pH below 4.5 and 226 million mu of cropland have a pH below 5.5. Soil acidification is severe, which directly affects agricultural production. Acidic soils are often accompanied by heavy metal pollution. According to the Report of investigation of soil pollution in China published in 2014, soil general situation of China is not optimistic. 16.1% of the soils exceeded the limit value. Pollution in southern China is more serious than that in the north. The problem is especially acute in areas such as the Yangtze Delta, the Pearl River Delta and the former industrial base in the Northeast. In southwest and south-central China, heavy metals greatly exceed accepted limit standards.

Conventional techniques for treating soils polluted with heavy metals have limitations: They do not apply to large-scale heavy metal pollution of soils. Therefore, the development of an economical, efficient and easy to produce soil conditioner is of significant importance for the remediation of soils polluted by large-scale heavy metals.

Silicon is an essential nutrient for plants. Nitrogen, phosphorus, potassium and silicon are the four main nutrients that plants need. Among them, silicon has a strong influence on the yield of rice and cane crops. Soils contain large amounts of silicon, but most of it exists as crystalline in silicates. The content of plant-available silicon, such as orthosilicic acid, is relatively low. According to surveys, silicon deficiency in soils is severe in southern China, especially in areas where rice cultivation is critical. Silicon deficiency in soils is a direct constraint on food production.

In view of the aforementioned problems, the object of the invention is to provide a soil conditioner made from solid waste, its manufacturing process and its application. This involves transforming the phase and structure of raw materials by the technique of alkaline calcination through scientific control of the contents of the elements, in order to produce a soil conditioner with a porous structure. It is a soil conditioner made from natural minerals that contains significant amounts of the secondary element (silicon, calcium) and an additional amount of phosphorus, potassium and magnesium.

The technological content of the invention is described in the following:

The object of the invention is to provide a soil conditioner made from solid waste, the raw materials of which include: granite powder, marble powder, sludge and additive.

The proportion of granite powder, marble powder, mud and additive is 1: (0.5-1.5): (0.5-1.5): (0.1-0.5) .

Said additive comprises one or more of these: calcium hydroxide, sodium hydroxide, potassium hydroxide, calcium carbonate and sodium carbonate.

The effective silicon content in the assimilable state in said soil conditioner is equal to or greater than 20%. The phosphorus content is equal to or greater than 1%. Previous pot trials have shown that said soil conditioner product can effectively increase biomass in crops, as well as improve soil and protect plants from heavy metals in soils;

The invention uses as raw materials the residual stone powder generated during the shaping of stones and the sewage sludge from water treatment plants. During this process, the additive and the calcination heat treatment make it possible to transform _{crystalline SiO 2} into silicon in the assimilable state: Ca ₂ SiO ₄ , Ca ₂ SiO ₄ , Na ₂ SiO ₃ , Na ₂ Al ₂ O ₃ ; thus transforming the phosphorus in the sewage sludge into CaNaPO ₄ , Ca ₃ (PO ₄ ) ₂ , Ca ₄ Mg ₅ (PO ₄ ) ₆ . This helps improve nutrient availability and increase soil fertility.

The invention provides a method of manufacturing the soil conditioner made from solid waste, the manufacturing process of which comprises the following steps: grinding raw materials (granite, marble and mud) into fine powder; mix the granite powder, marble powder, mud powder with the additive, add water until a homogeneous mixture is obtained; dry this mixture to obtain the mixture; turn the mixture on to a high temperature and allow it to cool and dry, to obtain the finished soil conditioner product.

The grinding of raw materials is carried out by electromagnetic crushing. The crushed raw materials are filtered through the 100-200 mesh sieves, in order to reduce the particle size to less than 0.1mm;

High temperature thermal activation is used to heat and activate the mixture. To do this, the calcination temperature is 500-100 ° C, the heating time is 0.5-3h, and the temperature rise rate is 10-40 ° C / min;

The drying temperature is maintained between 80 ° C and 100 ° C throughout the process, so that the moisture content of the mixture is less than 6%;

Said cooling is achieved quickly by quenching in water. When quenching the melt with water, the finer the water quench and the faster the cooling, the higher the solubility of citric acid in the product.

Said mixture is filtered through the 60-100 mesh sieves after grinding, to obtain the product.

Said process is first used to mix granite powder, marble powder and dried sludge; under the effect of the additive, components like silicon, calcium and phosphorus are activated and harmful elements are fixed, so that the mixture turns into a soil conditioner. First, during heat treatment, organic pollutants in sewage sludge are destroyed at high temperature and lose their harmfulness. Second, the melting point of the materials being reduced by the additives, the materials are in the molten state. Traces of heavy metals are enveloped in minerals in residual form, which prevents them from being released into the environment, reduces the toxicity of materials without aggravating soil pollution. The resulting soil conditioner contains crystals with less defect, such as aluminum silicate and calcium silicate. In the crystal structure of aluminosilicates there is a large amount of cations and oxygen vacancies; In calcium silicate, the silicon-oxygen tetrahedron forms a stable structure, the calcium of which can be replaced by the heavy metal cation in order to generate stable metal silicates. During the chemical reaction, the iron oxide in the sludge is transformed into α-Fe ₂ O ₃ , the specific surface area increases, which also helps to absorb some of the heavy metals.

The invention provides a soil conditioner made from solid waste which is used to decontaminate soils polluted with heavy metals. Adding said soil conditioner in soils at a mass fraction of 0.5-1% can reduce the effective content of heavy metals like Cu, Pb, Zn, Cd in soils, lower heavy metal content in plants significantly, as well as promoting plant growth.

The beneficial effects of the invention are as follows:

The soil conditioner provided by the invention takes advantage of the components in the residual stones, such as silicon oxide, aluminum oxide, iron oxide and calcium oxide, as well as the rich components in sewage sludge, such as P ₂ O ₅ , potassium oxide and magnesium oxide. Under the heat treatment, the components turn into crystals with less defect, such as alumino-silicate. This has the effect of increasing the specific surface and forming a microporous surface structure, in order to achieve the decontamination of soils polluted by heavy metals. The crystals generated bear few defects, such as aluminum silicate and calcium silicate; the cation exchange capacity is high, which allows heavy metals to be absorbed into the microporous structure. After a long period of aging, the heavy metals inside the crystals are fixed as a stable substance, thus reducing the harmfulness of heavy metals in soils and the risk of leaching again.

The soil conditioner proposed by the invention has a silicon content which can be assimilated by plants equal to or greater than 20% and contains essential elements for plants such as calcium, phosphorus, potassium and magnesium. The product has a low alkalinity which can improve acidic soils while providing plants with the nutrients of silicon, calcium, phosphorus, potassium and magnesium. It helps to significantly increase crop yield, improve soil fertility, reduce heavy metal content in plants, and protect plants against heavy metals;

In conclusion, the manufacturing process of the soil conditioner proposed by the invention uses raw materials from many sources, easy to obtain and at low cost; The formula and technique are easy to master; It takes advantage of the residual stone powder generated during the shaping of stones and the sewage sludge from water treatment plants, in order to transform waste into an energy resource, to reduce material costs and to fight against pollution. through waste recycling. Adding the additive can reduce the activation temperature and shorten the activation time. This easy-to-learn, low-cost process is advantageous for promotion and large-scale use. The market outlook is very promising.

Detailed description of embodiments of the invention

In what follows, the invention will be described in more detail with reference to specific embodiments. It should be noted that the embodiments described below only serve to explain the invention, and that the invention is not limited to the various embodiments described. On reading the invention, one skilled in the art can make other modifications of an equivalent nature without departing from the scope of the invention and it is intended to claim all such modifications as being within the scope of the claims of the invention. invention.

Unless otherwise indicated, all raw materials and reagents used in the invention are conventional products available on the market.

In the example embodiment, the residual stone powder comes from Yunfu City in Guangdong Province; the sewage sludge comes from a water treatment plant in the city of Canton with a particle size of less than 0.1mm. The analysis of the chemical composition of granite powder and marble powder in tail stone powder as well as sewage sludge is presented below:

Table 1 Composition of granite powder (wt%)

SiO ₂ Al ₂ O ₃ MgO K ₂ O Fe ₂ O ₃ CaO 66.81% 8.43% 7.31 5.46% 4.02% 3.24%

Table 2 Composition of marble powder (wt%)

CaO Al ₂ O ₃ MgO SiO ₂ Fe ₂ O ₃ 56.37% 0.21% 0.13 0.12 0.10

Table 3 Composition of sludge (wt% dried sludge)

SiO ₂ Fe ₂ O ₃ Al ₂ O ₃ CaO P ₂ O ₅ K ₂ O MgO 23.71 9.74 8.13 12.51 5.28 1.63 0.97

Example 1

A soil conditioner made from solid waste:

1) Mixing of materials: Granite powder, marble powder and sludge are crushed using the electromagnetic mill to obtain a 100-200 mesh powder. This involves mixing the granite powder, marble powder, mud powder and additive in a proportion of 10: 5: 5: 1, adding water until a homogeneous mixture is obtained, and then dry it at 80 ° C to obtain the mixture;

2) High temperature thermal activation: This involves placing the mixture in the muffle furnace preheated to 500 ° C for a calcination which lasts 0.5 hours, the temperature of which is rising at 10 ° C / min. . Heating activates the mixture;

3) Water Quench: The activated mixture is quenched in cold water for rapid cooling.

4) Drying: After rapid cooling, the mixture is dried and ground into 60-100 mesh powder to obtain the soil conditioner product. Tests have shown that the effective silicon content is 20.92%.

Example 2

A soil conditioner made from solid waste:

1) Mixing of materials: Granite powder, marble powder and sludge are crushed using the electromagnetic mill to obtain a 100-200 mesh powder. This involves mixing the granite powder, marble powder, mud powder and additive in the proportion of 10:10: 10: 3, adding water until a homogeneous mixture is obtained, and then dry it at 90 ℃ to obtain the mixture;

2) High temperature thermal activation: This involves placing the mixture in the muffle furnace preheated to 800 ° C for a calcination that lasts 2 hours, with a temperature rise rate of 25 ° C / min. Heating activates the mixture;

3) Water Quench: The activated mixture is quenched in cold water for rapid cooling.

4) Drying: After rapid cooling, the mixture is dried and ground into 60-100 mesh powder to obtain the soil conditioner product. Tests have shown that the effective silicon content is 20.21%.

Example of realization 3

A soil conditioner made from solid waste:

1) Mixing of materials: Granite powder, marble powder and sludge are crushed using the electromagnetic mill to obtain a 100-200 mesh powder. This involves mixing the granite powder, the marble powder, the mud powder and the additive in the proportion of 10:15:15: 5, adding water until a homogeneous mixture is obtained, and then dry it at 100 ℃ to obtain the mixture;

2) High temperature thermal activation: This involves placing the mixture in the muffle furnace preheated to 1000 ℃ for a calcination that lasts 3 hours, with a temperature rise rate of 40 ℃ / min. Heating activates the mixture;

3) Water Quench: The activated mixture is quenched in cold water for rapid cooling.

4) Drying: After rapid cooling, the mixture is dried and ground into 60-100 mesh powder to obtain the soil conditioner product. Tests have shown that the effective silicon content is 21.68%.

Test example 1

This example takes soil from the top layer (0-25cm) near the Dabaoshan Mine in Shaoguan City, Guangdong Province, allows it to air dry and removes impurities, and passes this soil through a 2 mm mesh sieve after grinding;

According to the measurement, the pH value of the soil is 4.28 (water: soil = 2.5: 1), the organic carbon content is 19.06g / kg, the fast-acting nitrogen 33.25mg / kg , the fast-acting phosphorus 8.38 mg / kg, the fast-acting potassium 79.67 mg / kg, and the content in the assimilable state of silicon is 15.33 mg / kg. According to the DTPA extraction method (abbreviation of the English term “Diethylenetriaminepentaacetic acid”), the Cu in the assimilable state is 54.13 mg / kg, the Pb in the assimilable state is 142.98 mg / kg, the Zn in the assimilable state is 19.57 mg / kg and the Cd in the assimilable state is 0.19 mg / kg;

In this example, it is a question of adding the solutions of copper nitrate, lead nitrate, zinc nitrate and cadmium nitrate, and mixing them sufficiently in order to increase the concentration of Cu, Pb, Zn and Cd to l. assimilable state. It takes 15 days for this mixture to reach equilibrium, and for it to be allowed to air dry. According to the measurement, the concentrations of Cu, Pb, Zn and Cd in the assimilable state are respectively 188.84mg / kg, 518.98mg / kg, 291.24mg / kg and 3.14mg / kg. The mixture is stored under natural conditions for future use;

To compare, we must take 4 groups of soils polluted by heavy metals, three of which are mixed respectively with 1% of the soil conditioners prepared in implementation examples 1-3 (Experimental groups 1-3), while the last is used control group (without adding soil conditioner). After 15 days of waiting, a new measurement of the heavy metal content is carried out on these 4 groups of soils. The results are shown in the tables below.

Table 4 Variation in the content of heavy metals in the assimilable state in soils

The content of heavy metals in the assimilable state in soils Control group Experimental group 1 Experimental group 2 Experimental group 3 The average content of the experimental group Reduction rate% The Cu content in the assimilable state (mg / kg) 188.84 123.54 121.80 119.73 121.69 35.56 The Pb content in the assimilable state (mg / kg) 518.98 387.13 389.21 382.95 386.43 25.54 The Zn content in the assimilable state (mg / kg) 291.24 143.98 145.73 142.60 144.10 50.52 The Cd content in the assimilable state (mg / kg) 3.14 2.90 2.89 2.93 2.91 7.32

From Table 4, it is evident that in the soils treated with the soil conditioner in Embodiments 1-3, the Cu content in the assimilable state experienced an average reduction of 35.56%; the Pb content in the assimilable state experiences an average reduction of 25.54%; the Zn content in the assimilable state has an average reduction of 7.32%; the pH value of the soil increases from 4.28 to 6.45, the silicon content in the assimilable state increases from 15.33 mg / kg to 202.39 mg / kg. The quality of the soil is significantly improved. It is clear that the soil conditioner manufactured in said exemplary embodiments has a significant effect on soil improvement.

Test example 2

This example takes soil from the top layer (0-25cm) in cultivated fields near the Fankou Lead Zinc Mine in Shaoguan City, Guangdong Province. This involves letting the soil air dry and remove impurities, and then pass it through a 2mm mesh sieve after grinding;

According to the measurement, the pH value of the soil is 4.71, the fast-acting nitrogen 87.6mg / kg, the fast-acting phosphorus 28.9mg / kg, the fast-acting potassium 71.7 mg / kg, the total copper content is 173.7 mg / kg, the total lead content is 211.3 mg / kg, the total zinc content is 279.4 mg / kg, and the total cadmium content is 0.19 mg / kg;

This exemplary embodiment concerns 7 groups of pots (25cm in diameter, 30cm in height), with 5kg of soil in each pot. In these 7 groups of jars, it is necessary to put respectively 1% of the soil conditioners prepared in the examples of realization 1-3 (D1-D3), the granite powder (D4), the marble powder (D5), the powder of dried sludge (D6), while the last group of pots serves as the control group (CK). Said treatment is repeated 3 times for each pot. Chives are planted in these pots after waiting 10 days.

After 20 days of chive cultivation, soil samples must be taken to analyze the assimilable levels of heavy metals, namely Pb, Cd, Zn and Cu; At the same time, it is necessary to collect samples of chives to analyze the change in concentration of heavy metals in the plants. The results are shown in Tables 5 and 6.

Table 5 Variation of the heavy metal content in the soil of the pots

Heavy metals in soils CK D1 D2 D3 D4 D5 D6 Pb content in the assimilable state (mg / kg) 5.51 3.37 3.60 3.29 5.52 5.48 6.14 Pb reduction rate in the assimilable state% - 38.84 34.66 40.29 -0.18 0.54 0.57 Cd content in the assimilable state (mg / kg) 1.33 1.07 1.13 1.01 1.34 1.31 1.57 Cd reduction rate in assimilable state% - 19.55 15.04 24.06 -0.75 1.50 1.53 Zn content in the assimilable state (mg / kg) 13.07 8.81 8.79 8.52 13.01 12.87 13.23 Zn reduction rate in the assimilable state% - 32.59 32.75 34.81 0.46 1.53 7.59 Cu content in the assimilable state (mg / kg) 3.92 2.07 2.11 1.98 3.91 3.88 3. 96 Cu reduction rate to assimilable state% - 47.19 46.17 49.49 0.26 1.02 0.77

Table 6 Variation of the heavy metal content in chives

CK D1 D2 D3 D4 D5 D6 Pb in total (mg / kg) 0.471 0.296 0.291 0.288 0.470 0.462 0.473 Reduction rate% - 37.15 38.22 38.85 0.21 1.91 -0.002 Cd in total (mg / kg) 0.061 0.043 0.046 0.040 0.062 0.060 0.060 Reduction rate% - 29.51 24.59 34.43 -1.64 1.64 1.64 Zn in total (mg / kg) 9.197 6.532 6.537 6.523 9.194 9.191 9.198 Reduction rate% - 28.98 28.92 29.07 0.03 0.07 - Cu in total (mg / kg) 2,598 1,976 1,981 1,932 2,599 2,574 2,562 Reduction rate% - 23.94 23.75 25.64 -0.04 0.92 -0.001

From Table 5, it is evident that the assimilable contents of Pb, Cd, Zn and Cu in the soils of the pots containing the soil conditioner all showed reductions, the greatest reduction of which was caused by the soil conditioner manufactured in Embodiment Example 3: the drops in Pb, Cd, Zn and Cu in the assimilable state respectively reach 0.29%, 24.06%, 34.81% and 49.49%;

From Table 6, it is evident that the products in the 3 exemplary embodiments, when mixed in the soils, can all effectively reduce the content of heavy metals, such as Pb, Cd, Zn and Cu, in plants (the heavy metal content in the plants after treatment is significantly lower than in the control group). However, groups that only use granite powder, marble powder and dried sludge powder show no results. It is clear that the soil conditioner manufactured by the invention has the function and effect of improving soil and protecting plants from heavy metals.

Claims (9)

A soil conditioner made from solid waste, characterized in that the raw materials for preparing said soil conditioner include: granite powder, marble powder, sludge and additive. The soil conditioner made from solid waste according to claim 1, characterized in that the ratio of granite powder, marble powder, sludge and additive is 1: (0.5-1.5) : (0.5-1.5): (0.1-0.5). The soil conditioner made from solid waste according to claim 1, characterized in that the additive comprises one or more of these: calcium hydroxide, sodium hydroxide, potassium hydroxide, calcium carbonate and sodium carbonate . The soil conditioner made from solid waste according to claim 1, characterized in that the effective assimilable silicon content in the soil conditioner is 20% or more, and the effective potassium content is equal. or greater than 1%. The manufacturing process of the soil conditioner made from solid waste according to any of claims 1 to 4, characterized in that the manufacturing process comprises the following steps: grinding raw materials (granite, marble and mud) fine powder; mix the granite powder, marble powder, mud powder with the additive, add water until a homogeneous mixture is obtained; dry this mixture to obtain the mixture; turn the mixture on to a high temperature and allow it to cool and dry, to obtain the finished soil conditioner product. The manufacturing method of the soil conditioner made from solid waste according to claim 5, characterized in that the crushing of the raw materials is carried out by electromagnetic crushing, and the crushed raw materials are filtered through the 100-200 mesh sieves, in order to reduce the particle size to less than 0.1mm. The method of manufacturing the soil conditioner made from solid waste according to claim 5, characterized in that high temperature thermal activation serves to heat and activate the mixture, for this the calcination temperature is 500- 100 ° C, the heating time is 0.5-3h, and the temperature rise rate is 10-40 ° C / min. The method of manufacturing the soil conditioner made from solid waste according to claim 5, characterized in that the drying temperature is maintained between 80 ° C and 100 ° C throughout the process, so that the moisture content of the mixture is less than 6%. Use of the soil conditioner made from solid waste according to any one of claims 1 to 4 for decontaminating soils polluted with heavy metals.