MINERAL SOIL CONDITIONER PRODUCED BY COAL ASH AND PREPARATION METHOD THEREOF

Abstract

The present invention discloses a mineral soil conditioner produced by coal ash and a preparation method thereof. The preparation method includes: (1) mixing coal ash with a heteroacid to form a mixture, stirring and filtering the mixture under the action of ultrasound to obtain a refined coal ash and a filtrate; (2) mixing the refined coal ash obtained in the step (1) with a calcium-based compound and a potassium-based compound well, performing drying with the residual heat of tail gas of a kiln after granulation; (3) performing calcination and activation continuously after granulation and drying in the step (2), then cooling, and processing by ball milling and molding to obtain a novel mineral soil conditioner. The present invention achieves the efficient utilization of a fuel coal by-product, namely, coal ash in agriculture and reduces the heavy metal content in coal ash and environmental contamination caused thereby.

Claims

1. A method for producing a mineral soil conditioner with coal ash, comprising the following steps: (1) mixing coal ash with a heteroacid to form a mixture, stirring and filtering the mixture under the action of ultrasound to obtain a refined coal ash and a filtrate; (2) mixing the refined coal ash obtained in the step (1) with a calcium-based compound and a potassium-based compound well, then performing drying after granulation; and (3) performing calcination and activation after granulation and drying, then cooling, and processing by ball milling or molding to obtain the mineral soil conditioner.

2. The method according to claim 1, wherein in the step (1), the heteroacid is a mixed acid of any two or more of humic acid, hydrochloric acid, hydrofluoric acid, sulfuric acid, nitric acid, perchloric acid, citric acid, formic acid, acetic acid or tartaric acid, and each acid has a concentration of 0.1-1 mol/L; a solid-liquid mixing ratio of the coal ash to the heteroacid is 1:0.1-1:10 g/mL; and the ultrasound time is 1-30 min.

3. The method according to claim 1, wherein the method further comprises a step of adding a sodium sulfide solution to the filtrate obtained in the step (1), then filtering after tempering and stirring, wherein, the sodium sulfide solution has a concentration of 0.1-5 mol/L, and pH=4.0-9.5 after tempering.

4. The method according to claim 1, wherein in the step (1), the stirring rate is 50-200 r/min and the stirring time is 10-120 min.

5. The method according to claim 1, wherein in the step (2), the calcium-based compound is a mixture of two or more of CaCO.sub.3, Ca(OH).sub.2, CaCl.sub.2 or CaMg[CO.sub.3].sub.2; the potassium-based compound is KOH, KCl, K.sub.2SO.sub.4 or K.sub.2CO.sub.3; in the step (2), a filter residue obtained after filtering in the step (1), the calcium-based compound and the potassium-based compound have the following mixing mass fractions: 10%-70% filter residue obtained after filtering in the step (1), 10%-70% calcium-based compound and 10%-70% potassium-based compound.

6. The method according to claim 1, wherein in the step (2), before granulation, water is added until a water content reaches 5-6%, then the granulation begins, the particle size is 0.3-5.5 cm and the drying time is 30-300 min.

7. The method according to claim 1, wherein in the step (3), the method comprises: activating for 30-60 min and performing calcination at 800-1050° C., then taking out and cooling to room temperature, and ball milling into a powdery mineral soil conditioner; or after cooling to room temperature, continuously adding 5-8 wt % water for disk granulation into a particle mineral soil conditioner, wherein the soil conditioner has a particle size of 0.3-5.5 cm.

8. The method according to claim 3, wherein the filtrate obtained after adding the sodium sulfide solution and filtering can be recycled for the second time; the heteroacid is supplemented to recover the concentration of the heteroacid in the step (1); stirring and filtering under the action of ultrasound in the step (1) are continuously performed, thus extracting heavy metals to obtain a refined coal ash.

9. The method according to claim 3, wherein a filter residue containing heavy metals obtained after being precipitated by sodium sulfide and filtered is washed at least for 3 times, and then subjected to landfill treatment, wherein a water content in the filter residue is limited to 40 wt % or below.

10. The mineral soil conditioner prepared by the method of claim 1, wherein the mineral soil conditioner has a water content less than 2 wt %; citric acid-soluble silicon dioxide has a content of 15 wt % or above; citric acid-soluble calcium oxide has a content of 25 wt % above; citric acid-soluble potassium oxide has a content of 4 wt % above; citric acid-soluble magnesium oxide has a content of 2 wt % above; total active ingredients in the nutrient are not less than 80 wt %; and the pH value is 9-12.

Description

BRIEF DESCRIPTION OF DRAWINGS

Description of Drawings

[0028] FIG. 1 is a schematic diagram showing a technical process of a mineral soil conditioner produced by coal ash in an example.

DESCRIPTION OF EMBODIMENTS

Embodiments of the Invention

[0029] The technical solution of the present invention will be further described in detail with reference to detailed examples and accompanying drawings, but the protection scope and embodiments of the present invention are not limited thereto.

[0030] FIG. 1 shows a schematic diagram showing a technical process of a mineral soil conditioner produced by coal ash in an example; the specific process flow is as follows:

[0031] Various acid pickling solutions are prepared, including humic acid, hydrochloric acid, sulfuric acid, nitric acid, perchloric acid, citric acid, formic acid, acetic acid, tartaric acid, and the like with a mixing concentration of 0.1-10 mol/L; the acid pickling solutions and coal ash are mixed, stirred and filtered to dissolve out and separate a heavy metal in coal ash, thus being up to the limit standard value of the heavy metal in agricultural coal ash. After separating the heavy metal, a filtrate containing the heavy metal and the coal ash after being removed the heavy metal, namely, refined coal ash are obtained. A sodium sulfide solution is added to the obtained filtrate containing the heavy metal to precipitate the heavy metal, and the heavy metal is filtered to obtain a filtrate; a portion of 3-6% (consumption) of heteroacid is supplemented to the filtrate for reuse; a filter residue containing the heavy metal sulfide may be used as hazardous solid wastes for disposal; a calcium-based compound and a potassium-based compound are added to the refined coal ash to be mixed well, dried, granulated, activated, cooled, broken and packaged, thus finally obtaining the mineral soil conditioner.

[0032] Coal ash is utilized to produce the mineral soil conditioner produced according to the process flow of FIG. 1.

Example 1

[0033] A certain thermal power plant in Inner Mongolia had an annual output of 1 million tons of coal ash, of which, silicon dioxide had a content of 57.67 wt %, potassium oxide had a content of 0.42 wt %, aluminium oxide had a content of being up to 17.32 wt %, calcium oxide had a content of 2.15 wt %, and ferric oxide had a content of 1.35 wt %; the heavy metal content was as follows: Pb had a content of 121.73 mg/kg, Cd had a content of 2.15 mg/kg, Hg had a content of 0.74 mg/kg, and Cu had a content of 7.97 mg/kg.

[0034] The operation process was as follows:

[0035] (1) Coal ash was mixed with a mixed acid of humic acid, hydrochloric acid, sulfuric acid, nitric acid and perchloric acid having a concentration of 0.2 mol/L according to a solid/liquid ratio of 1:1 g/mL, and subjected to ultrasound treatment for 20 min, then stirred for 55 min by a stirrer at 85 r/min to be mixed evenly, and then filtered; the removal rate of heavy metals in the obtained coal ash was respectively: 67% Pb, 86% Cd, 66% Hg and 87% Cu.

[0036] (2) A sodium sulfide solution having a concentration of 0.15 mol/L was added to the filtrate filtered in the step (1), and the PH=5.5 after tempering. The product obtained in the above step was stirred for 85 min by a stirrer at 150 r/min and then filtered; the sulfide heavy metal residues were washed with fresh water for 3 times; the precipitation rate of Pb, Cd, Hg and Cu in the filtrate was up to 90% or above; the filtrate after being removed the heavy metals was supplemented with the heteroacid to recover the concentration of the heteroacid in the step (1) for recycling.

[0037] (3) Calcium carbonate, calcium hydroxide and potassium hydroxide were added to the filter residue of the refined coal ash filtered in the step (1); the mixing mass ratio was as follows: 45% filter residue obtained after suction filtration in the step (1), 25% calcium carbonate, 20% calcium hydroxide and 10% potassium hydroxide; after being stirred evenly, the above materials were dried for 70 min with a tail gas of a kiln; the dried sample was calcinated for 30 min at 900° C., and cooled to room temperature, then broken and sieved with 100 meshes to obtain a soil conditioner rich in mineral elements.

[0038] It can be seen from the detection of a third party that in the produced soil conditioner, there are 84.35 wt % total mineral nutrients, including 15.34 wt % available silicon dioxide, 26.87 wt % available calcium oxide, 5.82 wt % available magnesium oxide, 4.75 wt % available potassium oxide, and 2.74 wt % available sodium oxide; the pH value is 10.5; the produced soil conditioner is a soil conditioner containing multiple mineral nutrients.

Example 2

[0039] A certain thermal power plant in Liaoning province had an annual output of 1.6 million tons of coal ash, of which, silicon dioxide had a content of 52.67 wt %, aluminium oxide had a content of being up to 21.76 wt %, potassium oxide had a content of 0.72 wt %, calcium oxide had a content of 3.15 wt %, and ferric oxide had a content of 3.57 wt %; the heavy metal content was as follows: Pb had a content of 101.30 mg/kg, Cd had a content of 1.71 mg/kg, Hg had a content of 0.78 mg/kg, and Cu had a content of 19.48 mg/kg.

[0040] The operation process was as follows:

[0041] (1) Coal ash was mixed with a mixed acid of humic acid, hydrochloric acid, sulfuric acid, hydrofluoric acid, nitric acid and perchloric acid having a concentration of 0.57 mol/L according to a solid/liquid ratio of 1:2.5 g/mL, and subjected to ultrasound treatment for 15 min, then stirred for 60 min by a stirrer at 150 r/min to be mixed evenly, and then filtered; the removal rate of heavy metals in the obtained coal ash was respectively: 78% Pb, 82% Cd, 49% Hg and 70% Cu.

[0042] (2) A sodium sulfide solution having a concentration of 0.25 mol/L was added to the filtrate filtered in the step (1), and a tempering solution was controlled to pH=6.7; then stirred for 25 min by a stirrer at 90 r/min and then filtered; the sulfide heavy metal residues were washed with fresh water for 3 times; the precipitation rate of Pb, Cd, Hg and Cu in the filtrate was up to 92% or above; the filtrate after being removed the heavy metals was supplemented with the heteroacid to recover the concentration of the heteroacid in the step (1) for recycling.

[0043] (3) Calcium chloride, dolomite and potassium carbonate were added to the filter residue of the refined coal ash filtered in the step (1); the mixing mass ratio was as follows: 35% filter residue obtained after suction filtration in the step (1), 35% calcium chloride, 20% dolomite and 10% potassium carbonate; after being stirred evenly, the above materials were dried for 45 min at 105° C.; the dried sample was calcinated for 2 h at 870° C., and cooled to room temperature, then broken and sieved with 100 meshes to obtain a soil conditioner rich in mineral elements.

[0044] It can be seen from the detection of a third party that in the produced soil conditioner, there are 82.01 wt % total mineral nutrients, including 17.98 wt % available silicon dioxide, 31.09 wt % available calcium oxide, 6.16 wt % available magnesium oxide, and 6.21 wt % available potassium oxide; the pH value is 11.1; the produced soil conditioner is a soil conditioner containing multiple mineral nutrients.

Example 3

[0045] A certain thermal power plant in Hebei province had an annual output of 3 million tons of coal ash, of which, silicon dioxide had a content of 46.67 wt %, aluminium oxide had a content of being up to 15 wt %, potassium oxide had a content of 0.92 wt %, calcium oxide had a content of 6.15 wt %, and ferric oxide had a content of 2.71 wt %; the heavy metal content was as follows: Pb had a content of 71.73 mg/kg, Cd had a content of 1.13 mg/kg, Hg had a content of 1.07 mg/kg, and Cu had a content of 38.02 mg/kg.

[0046] The operation process was as follows:

[0047] (1) Coal ash was mixed with a mixed acid of humic acid, hydrochloric acid, sulfuric acid, hydrofluoric acid, acid and perchloric acid having a concentration of 0.9 mol/L according to a solid/liquid ratio of 1:5 g/mL, and subjected to ultrasound treatment for 27 min, then stirred for 115 min by a stirrer at 195 r/min to be mixed evenly, and then filtered; the removal rate of heavy metals in the obtained coal ash was respectively: 72% Pb, 73% Cd, 73% Hg and 79% Cu.

[0048] (2) A sodium sulfide solution having a concentration of 2 mol/L was added to the filtrate filtered in the step (1), and a tempering solution was controlled to pH=7.2; then stirred for 45 min by a stirrer at 77 r/min and then filtered; the sulfide heavy metal residues were washed with fresh water for 3 times; the precipitation rate of Pb, Cd, Hg and Cu in the filtrate was up to 91% or above; then landfill treatment was performed, and a water content in the filter residue was limited to 40 wt % or below; the filtrate after being removed the heavy metals was supplemented with the heteroacid to recover the concentration of the heteroacid in the step (1) for recycling.

[0049] (3) Calcium carbonate, magnesium hydroxide and potassium sulfate were added to the filter residue of the refined coal ash filtered in the step (1); the mixing mass ratio was as follows: 45% filter residue obtained after suction filtration in the step (1), 25% calcium carbonate, 16% magnesium hydroxide and 14% potassium sulfate; after being stirred evenly, the above materials were dried for 50 min at 105° C. with a tail gas of a kiln; the dried sample was calcinated for 30 min at 1000° C., and cooled to room temperature, then broken and sieved with 100 meshes to obtain a soil conditioner rich in mineral elements.

[0050] It can be seen from the detection of a third party that in the produced soil conditioner, there are 82.93 wt % total mineral nutrients, including 17.46 wt % available silicon dioxide, 31.04 wt % available calcium oxide, 8.12 wt % available magnesium oxide, 5.18 wt % available potassium oxide, and 1.94 wt % available sodium oxide; the pH value is 11.8; the produced soil conditioner is a soil conditioner containing multiple mineral nutrients.

[0051] The above examples are preferred embodiments of the present invention, and merely illustrative of the present invention, but not construed as limiting the present invention. Moreover, any alteration, replacement, combination, simplification, modification and the like made by a person skilled in the art without departing from the spirit and principle of the present invention shall be equivalent substitution mode, and shall fall within the protection scope of the present invention.