Method for detoxifying chromium slag by using high sulfur coal

Abstract

The present invention discloses a method for detoxifying chromium slag by using high sulfur coal. The method includes: sieving chromium slag into coarse-grained chromium slag and fine-grained chromium slag, air-drying and crushing both the coarse-grained chromium slag and the fine-grained chromium slag; separately mixing the crushed coarse-grained chromium slag and fine-grained chromium slag with the crushed high sulfur coal uniformly; adjusting pH values of a coarse-grained slag mixture and a fine-grained slag mixture to 8.0-11.0 and moisture content thereof to 12%-18%; conducting reduction on the treated coarse-grained slag mixture and fine-grained slag mixture, where the reduction temperature of the fine-grained slag mixture is 500-700° C., the reduction time of the fine-grained slag mixture is 10-30 min, the reduction temperature of the coarse-grained slag mixture is 800-1000° C., the reduction time of the coarse-grained slag mixture is 10-30 min; after the reduction, conducting water quenching, and discharging the product.

Claims

1. A method for detoxifying chromium slag by using high sulfur coal, specifically comprising the following steps: (1) sieving chromium slag into coarse-grained chromium slag and fine-grained chromium slag, wherein a grain size of the coarse-grained chromium slag is greater than or equal to 10 meshes, and a grain size of the fine-grained chromium slag is less than 10 meshes; air-drying and crushing both the coarse-grained chromium slag and the fine-grained chromium slag; and air-drying and crushing high sulfur coal; (2) separately mixing the crushed coarse-grained chromium slag and fine-grained chromium slag in step (1) with the high sulfur coal uniformly, to obtain a coarse-grained slag mixture and a fine-grained slag mixture; (3) adjusting pH values of the coarse-grained slag mixture and the fine-grained slag mixture in step (2) to 8.0-11.0 and moisture content thereof to 12%-18% by spraying water or an acid solution; (4) separately conducting stirring and reduction on the treated coarse-grained slag mixture and fine-grained slag mixture in step (3) in a rotary kiln, wherein the reduction temperature of the fine-grained slag mixture is 500-700° C., the reduction time of the fine-grained slag mixture is 10-30 min, the reduction temperature of the coarse-grained slag mixture is 800-1000° C., and the reduction time of the coarse-grained slag mixture is 10-30 min; and (5) mixing reduced coarse-grained slag mixture and fine-grained slag mixture in step (4), conducting water quenching for cooling the slag mixture to below 300° C., and discharging the product.

2. The method for detoxifying chromium slag by using high sulfur coal according to claim 1, wherein the coarse-grained chromium slag, the fine-grained chromium slag, and the high sulfur coal in step (1) are air-dried at normal temperature for more than 24 h, and the coarse-grained chromium slag, the fine-grained chromium slag, and the high sulfur coal are all crushed until they can pass through a sieve of 20 meshes.

3. The method for detoxifying chromium slag by using high sulfur coal according to claim 1, wherein in step (2), the mass fractions of chromium slag in the coarse-grained slag mixture and the fine-grained slag mixture are 85%-95%, and the mass fraction of high sulfur coal is 5%-15%.

4. The method for detoxifying chromium slag by using high sulfur coal according to claim 1, wherein the acid solution in step (3) is a dilute H.sub.2SO.sub.4 solution or a FeSO.sub.4 solution.

5. The method for detoxifying chromium slag by using high sulfur coal according to claim 1, wherein the rotary kiln in step (4) is internally provided with a helical stirring device; the helical stirring device comprises a helical blade (1) and a rotary rod (2); the rotary rod (2) traverses the rotary kiln; and the helical blade (1) is arranged on the rotary rod (2).

6. The method for detoxifying chromium slag by using high sulfur coal according to claim 1, wherein a solvent for the water quenching in step (5) is water or a FeSO.sub.4 solution, and the mass fraction of the FeSO.sub.4 solution is 1%-5%.

Description

DRAWINGS

(1) FIG. 1 is a schematic diagram (front view) of a helical stirring structure of a rotary kiln according to Embodiment 1 of the present invention;

(2) FIG. 2 is a schematic diagram (left view) of the helical stirring structure of the rotary kiln according to Embodiment 1 of the present invention;

(3) FIG. 3 is an SEM image of chromium slag according to Embodiment 1 of the present invention;

(4) FIG. 4 is an SEM image of detoxified chromium slag according to Embodiment 1 of the present invention; and

(5) FIG. 5 is an SEM image of detoxified chromium slag according to Embodiment 2 of the present invention.

(6) In the figures, 1-helical blade, 2-rotary rod, and 3-outer wall of a rotary kiln.

DETAILED DESCRIPTION

(7) The following embodiments are intended to describe the present invention but are not intended to limit the scope of the present invention.

Embodiment 1

(8) A method for detoxifying chromium slag by using high sulfur coal is provided, specifically including the following steps:

(9) (1) material preparation: sieving chromium slag into coarse-grained chromium slag (greater than or equal to 10 meshes) and fine-grained chromium slag (less than 10 meshes), air-drying both the coarse-grained chromium slag and the fine-grained chromium slag at normal temperature for 24 h, and crushing both the coarse-grained chromium slag and the fine-grained chromium slag until they can pass through a sieve of 20 meshes; and air-drying high sulfur coal at normal temperature for 24 h, and crushing the high sulfur coal until it can pass through the sieve of 20 meshes;

(10) (2) mixing: separately mixing the coarse-grained chromium slag and the fine-grained chromium slag in step (1) with the high sulfur coal uniformly, to obtain a coarse-grained slag mixture and a fine-grained slag mixture, where the mass fractions of chromium slag in the coarse-grained slag mixture and the fine-grained slag mixture are both 95%, and the mass fraction of the high sulfur coal is 5%;

(11) (3) adjustment of pH values and moisture content: adjusting pH values of the coarse-grained slag mixture and the fine-grained slag mixture to 11.0 and moisture content of the slag mixture to 12% by spraying water;

(12) (4) reduction: in a rotary kiln, separately conducting reduction on the coarse-grained slag mixture and the fine-grained slag mixture whose pH values are adjusted in step (3), where the reduction temperature of the fine-grained slag mixture is 600° C., the reduction time of the fine-grained slag mixture is 30 min, the reduction temperature of the coarse-grained slag mixture is 800° C., and the reduction time of the coarse-grained slag mixture is 20 min; the rotary kiln is internally provided with a helical stirring device; as shown in FIG. 1 and FIG. 2, the helical stirring device includes a helical blade 1 and a rotary rod 2, the rotary rod 2 traverses the rotary kiln, the helical blade 1 is arranged on the rotary rod 2, and the helical blade 1 and the rotary rod 2 are closed in the rotary kiln by an outer wall 3 of the rotary kiln; and helical stirring is conducted to make the chromium slag and the high sulfur coal fully mixed in the reduction process and make reducing gases: carbon monoxide and sulfur dioxide generated by the combustion of the high sulfur coal be in full contact, so as to improve the reduction efficiency of the process and expand the treatment scale of the process; and

(13) (5) cooling: mixing reduced coarse-grained slag mixture and fine-grained slag mixture in step (4), conducting water quenching with water for cooling the slag mixture to below 300° C., and discharging the product.

(14) FIG. 3 is an SEM image of the chromium slag according to this embodiment. It can be seen from this figure that, chromium slag grains that have not been detoxified are relatively coarse, and has a relatively loose microstructure.

(15) FIG. 4 is an SEM image of detoxified chromium slag according to this embodiment. It can be seen from this figure that, detoxified chromium slag grains are relatively fine and in denser distribution because an original mineral structure containing hexavalent chromium is decomposed during the reaction.

(16) Through measurement, it can be learned that a leaching value of hexavalent chromium in the discharged chromium slag is 0.02 mg/L, and sulfur dioxide in exhaust gas is less than 200 mg/m.sup.3. After the detoxified chromium slag is naturally stockpiled for 30 days, the measured leaching value of hexavalent chromium is 0.05 mg/L, which is far lower than an environmental protection requirement of the process for detoxifying chromium slag.

Embodiment 2

(17) A method for detoxifying chromium slag by using high sulfur coal is provided, specifically including the following steps:

(18) (1) material preparation: sieving chromium slag into coarse-grained chromium slag (greater than or equal to 10 meshes) and fine-grained chromium slag (less than 10 meshes), air-drying both the coarse-grained chromium slag and the fine-grained chromium slag at normal temperature for 24 h, and crushing both the coarse-grained chromium slag and the fine-grained chromium slag until they can pass through a sieve of 20 meshes; and drying high sulfur coal at normal temperature for 24 h, and crushing the high sulfur coal until it can pass through the sieve of 20 meshes;

(19) (2) mixing: separately mixing the coarse-grained chromium slag and the fine-grained chromium slag in step (1) with the high sulfur coal uniformly, to obtain a coarse-grained slag mixture and a fine-grained slag mixture, where the mass fractions of chromium slag in the coarse-grained slag mixture and the fine-grained slag mixture are both 85%, and the mass fraction of the high sulfur coal is 15%;

(20) (3) adjustment of pH values and moisture content: adjusting pH values of the coarse-grained slag mixture and the fine-grained slag mixture to 10 and moisture content of the slag mixture to 15% by spraying a FeSO.sub.4 solution with a mass fraction of 5%.sub.;

(21) (4) reduction: in a rotary kiln, separately conducting reduction on the coarse-grained slag mixture and the fine-grained slag mixture whose pH values are adjusted in step (3), where the reduction temperature of the fine-grained slag mixture is 700° C., the reduction time of the fine-grained slag mixture is 25 min, the reduction temperature of the coarse-grained slag mixture is 900° C., and the reduction time of the coarse-grained slag mixture is 30 min; the rotary kiln is internally provided with a helical stirring device; the helical stirring device is the same as that in Embodiment 1; and helical stirring is conducted to make the chromium slag and the high sulfur coal fully mixed in the reduction process and make reducing gases: carbon monoxide and sulfur dioxide generated by the combustion of the high sulfur coal be in full contact, so as to improve the reduction efficiency of the process and expand the treatment scale of the process; and

(22) (5) cooling: mixing reduced coarse-grained slag mixture and fine-grained slag mixture in step (4), conducting water quenching with a ferrous sulfate solution with a mass fraction of 1% for cooling the slag mixture to below 300° C., and discharging the product.

(23) FIG. 5 is an SEM image of detoxified chromium slag according to this embodiment. It can be seen from this figure that, the detoxified chromium slag has denser distribution and a finer grain size due to the higher reduction temperature. This indicates that higher temperature leads to more thorough decomposition of a mineral containing hexavalent chromium in the chromium slag, which also facilitates detoxification of the chromium slag.

(24) Through measurement, it can be learned that a leaching value of hexavalent chromium in the discharged chromium slag is 0.01 mg/L, and sulfur dioxide in exhaust gas is less than 200 mg/m.sup.3. After the detoxified chromium slag is naturally stockpiled for 30 days, the measured leaching value of hexavalent chromium is 0.02 mg/L, which is far lower than an environmental protection requirement of the process for detoxifying chromium slag.

Embodiment 3

(25) A method for detoxifying chromium slag by using high sulfur coal is provided, specifically including the following steps:

(26) (1) material preparation: sieving chromium slag into coarse-grained chromium slag (greater than or equal to 10 meshes) and fine-grained chromium slag (less than 10 meshes), air-drying both the coarse-grained chromium slag and the fine-grained chromium slag at normal temperature for 28 h, and crushing both the coarse-grained chromium slag and the fine-grained chromium slag until they can pass through a sieve of 20 meshes; and air-drying high sulfur coal at normal temperature for 24 h, and crushing the high sulfur coal until it can pass through the sieve of 20 meshes;

(27) (2) mixing: separately mixing the coarse-grained chromium slag and the fine-grained chromium slag in step (1) with the high sulfur coal uniformly, to obtain a coarse-grained slag mixture and a fine-grained slag mixture, where the mass fractions of chromium slag in the coarse-grained slag mixture and the fine-grained slag mixture are both 90%, and the mass fraction of the high sulfur coal is 10%;

(28) (3) adjustment of pH values and moisture content: adjusting pH values of the coarse-grained slag mixture and the fine-grained slag mixture to 8.0 and moisture content of the slag mixture to 18% by spraying a H.sub.2SO.sub.4 solution with a mass fraction of 5%.sub.;

(29) (4) reduction: in a rotary kiln, separately conducting reduction on the coarse-grained slag mixture and the fine-grained slag mixture whose pH values are adjusted in step (3), where the reduction temperature of the fine-grained slag mixture is 500° C., the reduction time of the fine-grained slag mixture is 10 min, the reduction temperature of the coarse-grained slag mixture is 1000° C., and the reduction time of the coarse-grained slag mixture is 10 min; the rotary kiln is internally provided with a helical stirring device; the helical stirring device is the same as that in Embodiment 1; and helical stirring is conducted to make the chromium slag and the high sulfur coal fully mixed in the reduction process and make reducing gases: carbon monoxide and sulfur dioxide generated by the combustion of the high sulfur coal be in full contact, so as to improve the reduction efficiency of the process and expand the treatment scale of the process; and

(30) (5) cooling: mixing reduced coarse-grained slag mixture and fine-grained slag mixture in step (4), conducting water quenching with a FeSO.sub.4 solution with a mass fraction of 5% for cooling the slag mixture to below 300° C., and discharging the product.

(31) Through measurement, it can be learned that a leaching value of hexavalent chromium in the discharged chromium slag cannot be detected, and sulfur dioxide in exhaust gas is less than 200 mg/m.sup.3. After the detoxified chromium slag is naturally stockpiled for 30 days, the measured leaching value of hexavalent chromium is 0.01 mg/L, which is far lower than an environmental protection requirement of the process for detoxifying chromium slag.

Embodiment 4

(32) A method for detoxifying chromium slag by using high sulfur coal is provided, specifically including the following steps:

(33) (1) material preparation: sieving chromium slag into coarse-grained chromium slag (greater than or equal to 10 meshes) and fine-grained chromium slag (less than 10 meshes), air-drying both the coarse-grained chromium slag and the fine-grained chromium slag at normal temperature for 30 h, and crushing both the coarse-grained chromium slag and the fine-grained chromium slag until they can pass through a sieve of 20 meshes; and air-drying high sulfur coal at normal temperature for 24 h, and crushing the high sulfur coal until it can pass through the sieve of 20 meshes;

(34) (2) mixing: separately mixing the coarse-grained chromium slag and the fine-grained chromium slag in step (1) with the high sulfur coal uniformly, to obtain a coarse-grained slag mixture and a fine-grained slag mixture, where the mass fractions of chromium slag in the coarse-grained slag mixture and the fine-grained slag mixture are both 90%, and the mass fraction of the high sulfur coal is 10%;

(35) (3) adjustment of pH values and moisture content: adjusting pH values of the coarse-grained slag mixture and the fine-grained slag mixture to 9 and moisture content of the slag mixture to 16% by spraying a FeSO.sub.4 solution with a mass fraction of 5%.sub.;

(36) (4) reduction: in a rotary kiln, separately conducting reduction on the coarse-grained slag mixture and the fine-grained slag mixture whose pH values are adjusted in step (3), where the reduction temperature of the fine-grained slag mixture is 650° C., the reduction time of the fine-grained slag mixture is 15 min, the reduction temperature of the coarse-grained slag mixture is 850° C., and the reduction time of the coarse-grained slag mixture is 25 min; the rotary kiln is internally provided with a helical stirring device; the helical stirring device is the same as that in Embodiment 1; and helical stirring is conducted to make the chromium slag and the high sulfur coal fully mixed in the reduction process and make reducing gases: carbon monoxide and sulfur dioxide generated by the combustion of the high sulfur coal be in full contact, so as to improve the reduction efficiency of the process and expand the treatment scale of the process; and

(37) (5) cooling: mixing reduced coarse-grained slag mixture and fine-grained slag mixture in step (4), conducting water quenching with a FeSO.sub.4 solution with a mass fraction of 3% for cooling the slag mixture to below 300° C., and discharging the product.

(38) Through measurement, it can be learned that a leaching value of hexavalent chromium in the discharged chromium slag cannot be detected, and sulfur dioxide in exhaust gas is less than 200 mg/m.sup.3. After the detoxified chromium slag is naturally stockpiled for 30 days, the measured leaching value of hexavalent chromium is 0.02 mg/L, which is far lower than an environmental protection requirement of the process for detoxifying chromium slag.

(39) The foregoing descriptions are only preferred implementation manners of the present disclosure. It should be noted that for a person of ordinary skill in the art, several improvements and modifications may further be made without departing from the principle of the present disclosure. These improvements and modifications should also be deemed as falling within the protection scope of the present disclosure.