WO2024164985A1 - Method for enhancing weathering of coal gangue to form soil by using medium and low temperature waste heat - Google Patents

Abstract

A method for enhancing weathering of coal gangue to form soil by using medium and low temperature waste heat. The method is implemented by means of the following steps: (1) hot water or water at a natural temperature is introduced into a coal gangue pile for leaching and the coal gangue pile is then baked with flue gas, coal gangue mineral particles undergo water absorption and thermal expansion, and silicate minerals are dissolved out and reconstructed; (2) after hot water treatment, the coal gangue is allowed for standing, the water is discharged, the coal gangue is cooled, oxygen enters mineral gaps, the mineral particles undergo water loss, cooling, and shrinkage, sulfide minerals are oxidized, and the particles are crushed to expose activated crystal faces; (3) steps 1 and 2 are repeated until the mineral particles are pulverized and weakened, and the coal gangue particle size is reconstructed; and (4) the fine sand content in the coal gangue is increased, the capacities of preservation of soil moisture and preservation of soil fertility are enhanced, and the treatment is completed. The method promotes coal gangue pulverization and weakening by using medium and low temperature waste heat which is difficult to be used by coal production enterprises, to accelerate weathering of coal gangue to form soil, thereby realizing resource recycling of coal gangue.

Description

A method for enhancing weathering of coal gangue into soil using medium and low temperature waste heat

This application claims the priority of the Chinese patent application filed with the China Patent Office on February 9, 2023, with application number CN202310090127.6 and invention name “A method for enhancing the weathering of coal gangue into soil using medium and low temperature waste heat”, the entire contents of which are incorporated by reference in this application.

Technical Field

The invention belongs to the technical field of solid waste treatment, and specifically relates to a method for utilizing medium- and low-temperature waste heat to intensify the weathering of coal gangue into soil.

Background Art

A large amount of coal gangue is discharged during the coal production process. The traditional treatment method is stockpiling and building materials production. There are problems of land occupation and small consumption capacity. It is urgent to explore new ways to recycle and utilize coal gangue. Silicate minerals, clay minerals, sulfide minerals and their weathering products are the main components of coal gangue and the main components of soil. Therefore, coal gangue has the mineralogical basis for weathering into soil. Strengthening the environmental disturbance of coal gangue and accelerating its weathering process are conducive to the large-scale consumption of coal gangue stockpiles and reducing enterprise production costs.

Coal production enterprises have a large amount of medium and low temperature waste heat (50-300℃) that is difficult to utilize. Using it for mineral weathering is beneficial to strengthening the dry-wet and cold-hot alternating cycles of coal gangue, promoting the pulverization and weakening of coal gangue, and forming medium and fine sand, so as to enhance the moisture retention and fertilizer storage capacity of the processed products and make them suitable for plant settlement.

The patent with application number CN202110340511.8 discloses a dry-wet cycle soil sample disintegration evolution law tester and test method. This method belongs to the field of soil detection, has a small absorption capacity, and the processing object is soil samples, which is significantly different from this method.

Patent application number CN201911180273.8 discloses a simulation device for the weathering and oxidation of sulfide minerals under alternating dry and wet conditions. This method has a small absorption capacity and is only suitable for mineral mixtures with high sulfur content.

Patent application number CN201310631993.8 discloses a method for improving sandy land suitable for areas with severe wind erosion and water erosion. The method has a complex process, requires the addition of a large amount of exogenous substances, and is difficult to operate in practice.

Patent application number CN202210718617.1 discloses an experimental device and method for simulating the dry-wet cycle process of rock and soil samples in a natural environment. This method is an experimental device and is difficult to use in the field of solid waste treatment.

Summary of the invention

Aiming at the difficulty in recycling low-temperature waste heat in the treatment and disposal of coal gangue and coal production enterprises, the present invention proposes a method for enhancing the weathering of coal gangue into soil by utilizing medium- and low-temperature waste heat.

Principle of the invention:

Coal gangue is a sedimentary rock. Its main minerals are silicate minerals, clay minerals, sulfide minerals and their weathering products. It is similar to the main composition of soil and has a mineralogical basis for weathering and soil formation. The main difficulty in its ecological utilization lies in its large particle size and difficulty in retaining moisture and fertilizer. Therefore, strengthening the dissolution and reconstruction of coal gangue minerals and increasing the fine sand content are prerequisites for its soilification.

Step 1: Under leaching conditions, the metal cations such as K ⁺ and Ca2 ⁺ contained in the interlayers of silicate minerals (feldspar, mica) are dissolved and transformed into clay minerals, and the particle size decreases; clay minerals (illite, vermiculite, kaolinite, etc.) absorb water and expand when heated, and cracks appear in the mineral particles, which not only produce new crystal faces to continue the reaction, but also cause the particle strength to decrease and become easy to pulverize;

Step 2: As the water drains away, oxygen comes into contact with sulfide minerals through mineral cracks or fissures, forming sulfate radicals, which increase in volume and promote the development of mineral particle cracks. At the same time, sulfate radicals help to form secondary mineral gels such as polysulfate iron and aluminum to enhance particle agglomeration and air permeability. As the water content decreases and the temperature drops, the mineral particles shrink.

Step 3: The gangue is treated with dry-wet and hot-cold cycles. Microcracks gradually develop into large cracks or sections. Minerals are continuously dissolved and reconstructed, and broken. The clay and fine sand content increases, and the moisture retention and fertilizer storage capacity of the gangue is enhanced.

Step 4: Clay fine sand significantly affects the water holding rate of coal gangue. When the water holding rate is above 10%, the conditions for plant growth are initially met.

The present invention is achieved through the following technical solutions:

(1) Hot water or natural water temperature is introduced into the gangue pile for leaching and then baked with flue gas. The gangue mineral particles absorb water and heat and expand, and the silicate minerals are dissolved and reconstructed.

(2) After hot water treatment, the gangue is left to stand, the water is discharged and cooled, oxygen enters the mineral gaps, the mineral particles lose water, cool and shrink, the sulfide minerals are oxidized, and the particles break up to expose the activated crystal surface;

(3) Repeating steps (1) and (2) until the mineral particles are pulverized and weakened, the strength of the mineral particles decreases under the dry-wet and cold-hot alternating treatments, the minerals are dissolved and reconstructed, and clay minerals and floccules of iron and sulfur are formed;

(4) The fine sand content of coal gangue increases by 5-20%, the ability to retain moisture and store fertilizer is enhanced, and the treatment is completed.

Preferably, in step (1), the gangue pile is smoke-baked using medium-low temperature flue gas of 50 to 300°C.

Preferably, the present invention subjects the gangue pile to dry-wet and hot-cold alternating cycles, wherein during the hot-cold alternation, the gangue temperature difference is 30-270°C, and further the gangue temperature difference is 20-300°C; the gangue leaching time with water is 4-72h, and further the leaching time with water is 12-72h; the standing drainage time is 24-48h, the cycle number is 10-100 times, and further the cycle number is 30-50 times.

Preferably, the dry-wet and cold-hot alternating cycles of the gangue pile are performed by leaching with hot water followed by draining and cooling.

Preferably, the gangue pile is subjected to dry-wet and hot-cold alternating cycles, and then the gangue is heated by high-temperature flue gas after being leached by water in a natural environment. If flue gas is used for heating, the flue gas temperature is between 100 and 300°C, and the flue gas heating time is 12 to 36 hours.

Preferably, the main minerals of the coal gangue are silicate minerals, clay minerals and carbonate minerals, the sum of the contents of the three is above 60%, and the quartz content is less than 35%.

Preferably, the laying thickness of the gangue pile is 5 to 50 cm, and further, the laying thickness is 5 to 30 cm; the particle size of the gangue is less than 40 mm, and further, the particle size of the gangue is less than 30 mm.

Preferably, the amount of water added in step (1) is such that the solid-liquid ratio of the leached water to the coal gangue is 0.1 to 5:1. Furthermore, the solid-liquid ratio of the leached water to the coal gangue is 0.5 to 2:1.

Preferably, the fine sand refers to coal gangue particles with a particle size of ≤2 mm.

Preferably, the treatment is considered complete when the fine sand content increases by more than 10%.

Compared with the related art, the present invention has the following advantages:

(1) The present invention can process coal gangue in large quantities, sustainably and at low cost.

(2) The present invention effectively utilizes the medium and low temperature waste heat that is difficult to utilize in coal production enterprises.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a flow chart of the enhanced weathering mechanism of coal gangue of the present invention.

DETAILED DESCRIPTION

The present invention is further described below in conjunction with the embodiments, but the present invention is not limited in any way. Any changes or substitutions made based on the teachings of the present invention belong to the protection scope of the present invention.

Embodiment 1:

(1) Hot water is introduced into the gangue pile, and the hot water is boiling water. The gangue mineral particles absorb water and heat to expand, and the silicate minerals are dissolved and reconstructed. The main minerals of the gangue are silicate minerals, clay minerals, and carbonate minerals, and the sum of the three contents is 65%, and the quartz content is less than 35%. The thickness of the gangue pile is 5 cm; the particle size of the gangue is less than 40 mm. The amount of water added is such that the solid-liquid ratio of the leached water to the gangue is 5:1.

(2) After hot water treatment, the gangue is left to stand, the water is discharged and cooled, oxygen enters the mineral gaps, the mineral particles lose water, cool and shrink, the sulfide minerals are oxidized, and the particles break up to expose the activated crystal surface;

The gangue pile is subjected to dry-wet and cold-hot alternating cycles. The dry-wet and cold-hot alternating cycles of the gangue pile are hot water leaching followed by draining and cooling. The temperature difference of the cold-hot alternating gangue is about 80°C. The gangue water leaching time 24h; standing and draining time is 24h, and the number of cycles is 20 times.

(3) Repeat steps (1) and (2) until the mineral particles are pulverized and weakened. The strength of the mineral particles decreases under the alternating treatment of dry and wet and cold and hot. The minerals are dissolved and reconstructed to form floccules of clay minerals and iron and sulfur.

(4) The fine sand content of coal gangue is increased, the ability to retain moisture and fertilizer is enhanced, and the treatment is completed.

Embodiment 2:

(1) Hot water is introduced into the gangue pile, and the hot water is boiling water. The gangue mineral particles absorb water and heat to expand, and silicate minerals are dissolved and reconstructed. Preferably, the main minerals of the gangue are silicate minerals, clay minerals, and carbonate minerals, the sum of the three contents is 70%, and the quartz content is less than 35%. The thickness of the gangue pile is 30 cm; the particle size of the gangue is less than 30 mm. The amount of water added is such that the solid-liquid ratio of leached water to gangue is 2:1.

(2) After hot water treatment, the gangue is left to stand, the water is discharged and cooled, oxygen enters the mineral gaps, the mineral particles lose water, cool and shrink, the sulfide minerals are oxidized, and the particles break up to expose the activated crystal surface;

The gangue pile is subjected to dry-wet and cold-hot alternating cycles, in which hot water leaching is followed by draining and cooling, and the temperature difference of the alternating hot and cold gangue is about 75°C; the gangue leaching time is 60 hours; the standing drainage time is 48 hours, and the number of cycles is 50 times.

(3) Repeat steps (1) and (2) until the mineral particles are pulverized and weakened. The strength of the mineral particles decreases under the alternating treatment of dry and wet and cold and hot. The minerals are dissolved and reconstructed to form floccules of clay minerals and iron and sulfur.

(4) The fine sand content of coal gangue is increased, the ability to retain moisture and fertilizer is enhanced, and the treatment is completed.

Embodiment 3:

(1) The gangue pile is leached with tap water and then baked with flue gas. The gangue mineral particles absorb water and heat to expand, and the silicate minerals are dissolved and reconstructed. The gangue pile is smoke-baked with medium-low temperature flue gas of 50 to 300°C. The main minerals of the gangue are silicate minerals, clay minerals, and carbonate minerals, the sum of which is more than 60%, and the quartz content is less than 35%. The laying thickness of the gangue pile is 25 cm; the particle size of the gangue is less than 35 mm. The solid-liquid ratio of leached water to gangue is 0.5:1.

(2) After treatment, the gangue is left to stand, the water is discharged and cooled, oxygen enters the mineral gaps, the mineral particles lose water, cool and shrink, the sulfide minerals are oxidized, and the particles break up to expose the activated crystal surface;

The gangue pile undergoes dry-wet and cold-hot alternating cycles. The gangue pile undergoes dry-wet and cold-hot alternating cycles. The gangue is heated by high-temperature flue gas after leaching by water in the natural environment. The flue gas heating time is 12 hours. During the treatment process, the temperature difference of the gangue is about 250℃; the gangue leaching time is 4 hours; the standing draining time is 24 hours, and the number of cycles is 20 times.

(3) Repeat steps (1) and (2) until the mineral particles are pulverized and weakened. The strength of the mineral particles decreases under the alternating treatment of dry and wet and cold and hot. The minerals are dissolved and reconstructed to form floccules of clay minerals and iron and sulfur.

(4) The fine sand content of coal gangue increased by 15%, the ability to retain moisture and fertilizer was enhanced, and the treatment was completed.

Embodiment 4:

(1) The gangue pile is leached with tap water and then baked with flue gas. The gangue mineral particles absorb water and heat to expand, and the silicate minerals are dissolved and reconstructed. The gangue pile is smoke-baked with medium-low temperature flue gas of 100 to 300°C. The main minerals of the gangue are silicate minerals, clay minerals, and carbonate minerals. The sum of the contents of the three is more than 60%, and the quartz content is less than 35%. The laying thickness of the gangue pile is 30cm; the particle size of the gangue is less than 20mm. The amount of water added is such that the solid-liquid ratio of the leached water to the gangue is 1:1.

(2) After hot water treatment, the gangue is left to stand, the water is discharged and cooled, oxygen enters the mineral gaps, the mineral particles lose water, cool and shrink, the sulfide minerals are oxidized, and the particles break up to expose the activated crystal surface;

The gangue pile undergoes dry-wet and cold-hot alternating cycles. The dry-wet and cold-hot alternating cycles of the gangue pile are heated by high-temperature flue gas after leaching with water in the natural environment. The flue gas heating time is 36 hours. During the treatment process, the temperature difference of the gangue is 30-270℃; the gangue leaching time is 12 hours; the standing draining time is 24 hours, and the number of cycles is 40 times.

(3) Repeat steps (1) and (2) until the mineral particles are pulverized and weakened. The strength of the mineral particles decreases under the alternating treatment of dry and wet and cold and hot. The minerals are dissolved and reconstructed to form floccules of clay minerals and iron and sulfur.

(4) The fine sand content of coal gangue increases by 20%, the ability to retain moisture and store fertilizer is enhanced, and the treatment is completed.

Example 5: (Heating and adding water/dehydration and cooling)

(1) Gangue was leached with hot water at 60°C for 8 hours. The temperature of the gangue rose to 55°C, the ambient temperature was 16°C, and the temperature difference was 39°C. The thickness of the gangue pile was 35 cm, and the solid-liquid ratio of the leaching solution to the gangue was 1:1. The content of silicate minerals, clay minerals, and carbonate minerals in the gangue was 87%, and the particle size of the mixture was mainly 10-25 mm. Under the leaching state, the volume of clay minerals such as illite, vermiculite, and kaolinite contained in the particles expanded by 5-20%, cracks occurred at the junction of different minerals, and fresh interfaces were generated. Metal cations such as feldspar and mica dissolved and transformed into clay minerals.

(2) The gangue is left to stand for 24 hours, the water is drained out, the temperature drops to about 16°C, the clay minerals lose water, cool and shrink, the illite, vermiculite, kaolinite, etc. are damaged due to expansion and contraction, cracks appear on the surface, and oxygen passes through the mineral gaps and cracks and comes into contact with sulfide minerals, forming Fe3 ⁺ , Al3 ⁺ and sulfate.

(3) After 45 cycles of treatment, the strength of the coal gangue decreased significantly, the primary silicate minerals were transformed into secondary clay minerals in large quantities, and the pulverized fine sand agglomerated again.

(4) The clay and fine sand content in the coal gangue increased by 12% to 16%, and the water holding rate was 14%. After the treatment was completed, the pioneer plants for mine reclamation, such as ryegrass and alfalfa, could grow normally.

Table 1 Changes in particle size and water holding capacity of coal gangue before and after hot water leaching treatment

Example 6: (Natural water temperature leaching/smoke heating and drying)

(1) The gangue was leached using natural water at a temperature of 15°C. The solid-liquid ratio of the leaching solution to the gangue was 3:1. The treatment time was 12 h. The thickness of the gangue pile was 30 cm. The content of silicate minerals, clay minerals, and carbonate minerals in the gangue was 74%, and the particle size of the mixture was mainly 5 to 30 mm. Under the leaching state, the volume of clay minerals such as illite, vermiculite, and kaolinite contained in the particles expanded by 5 to 20%, cracks occurred at the junction of different minerals, and fresh interfaces were generated. Metal cations such as feldspar and mica dissolved and transformed into clay minerals.

(2) The gangue is left to stand for 24 hours, the water is drained out, and the gangue is heated and dried using flue gas at 180°C. The baking time is 24 hours, and the temperature difference between the hot and cold parts of the gangue is 165°C. This is one cycle. Clay minerals lose water and shrink rapidly. Illite, vermiculite, kaolinite, etc. are damaged due to expansion and contraction, and cracks appear on the surface. Oxygen passes through the mineral gaps and cracks and comes into contact with sulfide minerals to form Fe ³⁺ , Al ³⁺ and sulfate.

(3) After 55 cycles of treatment, the strength of the coal gangue decreased significantly, the primary silicate minerals were transformed into secondary clay minerals in large quantities, and the pulverized fine sand agglomerated again.

(4) The clay and fine sand content in the coal gangue increased by 18% to 29%, and the water holding rate was 24.3%. After the treatment was completed, the pioneer plants for mine reclamation, such as ryegrass and alfalfa, could grow normally.

Table 2 Changes in particle size and water holding rate of coal gangue before and after natural leaching and flue gas drying

Although the above embodiment describes the present invention in detail, it is only a part of the embodiments of the present invention rather than all the embodiments. People can also obtain other embodiments based on this embodiment without creativity, and these embodiments all fall within the protection scope of the present invention.

Claims (11)

A method for enhancing weathering of coal gangue into soil by using medium and low temperature waste heat, characterized by the following steps: (1) Adding water and heating the gangue pile causes the gangue mineral particles to absorb water and heat and expand, causing silicate minerals to dissolve and reconstruct; (2) the gangue treated in step (1) is allowed to stand, drain, and cool, so that the mineral particles lose water, cool, and shrink, oxygen enters the mineral gaps, sulfide minerals are oxidized, and the particles are broken to expose activated crystal faces; (3) Repeat steps (1) and (2) until the mineral particles are pulverized and weakened. The strength of the mineral particles decreases under the dry-wet and cold-hot alternating cycle treatment, and the minerals are dissolved and reconstructed to form clay minerals and floccules of iron and sulfur. The treatment is completed when the fine sand content in the coal gangue increases by 5-20%. The method according to claim 1 is characterized in that the adding of water and heating of the gangue pile in step (1) is to introduce hot water or natural environment water into the gangue pile for leaching and then bake it with flue gas. The method according to claim 2 is characterized in that the flue gas baking is to use medium-low temperature flue gas of 50 to 300°C to bake the coal gangue pile. The method according to claim 1 is characterized in that in the dry-wet and cold-hot alternating cycle treatment, the temperature difference of the coal gangue is 20 to 300°C when alternating between cold and hot; the number of cycles of the dry-wet and cold-hot alternating cycle treatment is 10 to 100 times. The method according to claim 2 is characterized in that the dry-wet and cold-hot alternating cycle treatment can be hot water leaching followed by draining and cooling, or it can be natural environment water leaching followed by heating the coal gangue with high-temperature flue gas. If flue gas heating is used, the flue gas temperature is between 100 and 300°C, and the flue gas heating time is 12 to 36 hours. The method according to claim 2, characterized in that the leaching time is 4 to 72 hours. The method according to claim 1, characterized in that the standing time is 12 to 48 hours. The method according to claim 1 is characterized in that the sum of the contents of silicate minerals, clay minerals and carbonate minerals in the coal gangue is above 60%, and the quartz content is less than 35%. The method according to claim 1 is characterized in that the gangue pile in step (1) is laid with a thickness of 5 to 50 cm and a particle size of the gangue is less than 40 mm. The method according to claim 2 is characterized in that the amount of water added for leaching in step (1) is such that the solid-liquid ratio of leaching water to coal gangue is 0.1 to 5:1. The method according to claim 1 is characterized in that the fine sand in step (3) is coal gangue particles with a particle size of ≤2 mm.