Treatment method for resource recycling of hexavalent chromium-containing residues

Abstract

A treatment method for resource recycling of hexavalent chromium-containing residues is provided. This method comprises steps as follows: 1) adding water to the hexavalent chromium-containing residues and mixing uniformly; 2) adding mineralizers to a solution obtained in step 1) and stirring sufficiently to obtain a mixed liquid; and the mineralizers are sodium chlorate, sodium perchlorate and hydrochloric acid; 3) treating the mixed liquid by a hydrothermal method or direct heating; 4) after the heating treatment, naturally cooling a solid-liquid mixture to room temperature for holding; 5) separating solid residues and a chromium-containing supernatant, and washing filtered residues with water and then drying; and 6) recycling a chromium-containing solution for returning to a work section, or for a treatment of recycling chromium.

Claims

1. A treatment method for resource recycling of hexavalent chromium-containing residues, characterized in that, the treatment method comprises steps as follows: 1) adding water to the hexavalent chromium-containing residues and mixing uniformly; 2) adding mineralizers to a solution obtained in step 1) and stirring sufficiently to obtain a mixed liquid; and the mineralizers are sodium chlorate, sodium perchlorate and hydrochloric acid; 3) treating the mixed liquid obtained in step 2) by a hydrothermal method or direct heating; 4) naturally cooling a solid-liquid mixture obtained in step 3) to room temperature for holding; 5) separating solid residues and a chromium-containing supernatant solution, and washing the separated solid residues with water and then drying; and 6) recycling the chromium-containing supernatant solution for returning to a work section, or for a treatment of recycling chromium.

2. The treatment method for resource recycling of hexavalent chromium-containing residues according to claim 1, wherein a w/w solid-to-liquid ratio after water is added to the hexavalent chromium-containing residues in step 1) is 1:0.5-1:10.

3. The treatment method for resource recycling of hexavalent chromium-containing residues according to claim 1, wherein sodium chlorate in step 2) in the mixed liquid has a concentration of 0.1 mol/L-1 mol/L.

4. The treatment method for resource recycling of hexavalent chromium-containing residues according to claim 1, wherein sodium perchlorate in step 2) in the mixed liquid has a concentration of 0.1 mol/L-1 mol/L.

5. The treatment method for resource recycling of hexavalent chromium-containing residues according to claim 1, wherein the mixed liquid in step 2) has a pH value of 0.5-5.

6. The treatment method for resource recycling of hexavalent chromium-containing residues according to claim 1, wherein a temperature of the hydrothermal method or direct heating in step 3) is controlled between 30 C. and 250 C.

7. The treatment method for resource recycling of hexavalent chromium-containing residues according to claim 1, wherein a time for treating the mixed liquid in step 3) is 2 to 12 hours.

8. The treatment method for resource recycling of hexavalent chromium-containing residues according to claim 1, wherein a time for naturally cooling the solid-liquid mixture in step 4) is 0.5 to 48 hours.

9. The treatment method for resource recycling of hexavalent chromium-containing residues according to claim 1, wherein the treatment of recycling chromium in step 6) has specific steps as follows: adding a reductant to the chromium-containing solution, with hexavalent chromium in the solution being reduced to trivalent chromium, then adding a precipitant NaOH to generate precipitate of Cr(OH)3, and finally calcining the precipitate of Cr(OH)3 into Cr2O3.

Description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

(1) The present invention is further described in connection with embodiments, but the implementations of the present invention are not limited by these.

Embodiment 1

(2) 1) 0.5 ton of hexavalent chromium-containing residues were added to a hydrothermal kettle, then water was added until a solid-to-liquid ratio was 1:1 (w/w), with sufficient stirring, and sodium chlorate, sodium perchlorate and hydrochloric acid were added, and a concentration of sodium chlorate in the system was adjusted to 0.5 mol/L, a concentration of sodium perchlorate was 1 mol/L and a pH value was 0.5. A temperature was set at 100 C. and a time for heat preservation was 2 hours.

(3) 2) 2 hours later, heating was stopped and the system was cooled naturally to room temperature and held for 24 hours.

(4) 3) After the holding, a supernatant solution containing hexavalent chromium was poured out. Residues which had been subjected to the hydrothermal treatment and holding were subjected to centrifugal washing and dewatering. Filtered residues were dried to obtain white solids or white and yellowish solids.

(5) 4) The chromium-containing solution was reused in the production, or collected in a waste water treatment station to perform restore, recycle and purification treatments. Reductants (such as sodium sulfide and sodium bisulfite) and precipitants (NaOH) were added to reduce the dissolved hexavalent chromium into trivalent chromium, and to generate precipitates of Cr(OH).sub.3, and the treated water could reach the national standard of drainage. During the whole process, water could be recycled in the system.

(6) 5) Final products were residues mainly containing calcium sulfate and chromic mud mainly containing Cr(OH).sub.3, respectively. The residues of calcium sulfate could be used as raw materials in industries such as rubber, plastics, fertilizer, pesticides, paint, textile and papermaking. The chromic mud could be calcined to Cr.sub.2O.sub.3 to realize recycling of chromium.

(7) A concentration of the leached hexavalent chromium from the original chromium-containing residues in this embodiment was 265 mg/L, and a concentration of the leached hexavalent chromium from the treated chromium-containing residues was 1.31 mg/L.

Embodiment 2

(8) 1 ton of hexavalent chromium-containing residues were added to the hydrothermal kettle, then water was added until the solid-to-liquid ratio was 1:2 (w/w), with sufficient stirring, and sodium chlorate, sodium perchlorate and hydrochloric acid were added. The concentration of sodium chlorate in the system was adjusted to 1 mol/L, the concentration of sodium perchlorate was 0.5 mol/L and hydrochloric acid was added until the pH value was 5, with sufficient stirring, and the hydrothermal kettle was turned off. The temperature was set at 140 C. and the time for heat preservation was 5 hours. After the heating was stopped, the system was held for 48 hours. Other process was the same as that in the Embodiment 1.

(9) The concentration of the leached hexavalent chromium from the original chromium-containing residues in this embodiment was 252 mg/L, and the concentration of the leached hexavalent chromium from the treated chromium-containing residues was 0.92 mg/L.

Embodiment 3

(10) 1 ton of hexavalent chromium-containing residues were added to the hydrothermal kettle, then water was added until the solid-to-liquid ratio was 1:5 (w/w), with sufficient stirring, and sodium chlorate, sodium perchlorate and hydrochloric acid were added. The concentration of sodium chlorate in the system was adjusted to 1 mol/L, the concentration of sodium perchlorate was 1 mol/L and hydrochloric acid was added until the pH value was 0.5, with sufficient stirring, and the hydrothermal kettle was turned off. The temperature was set at 30 C. and the time for heat preservation was 12 hours. After the heating was stopped, the system was held for 0.5 hour. Other process was the same as that in the Embodiment 1.

(11) The concentration of the leached hexavalent chromium from the original chromium-containing residues in this embodiment was 269 mg/L, and the concentration of the leached hexavalent chromium from the treated chromium-containing residues was 0.72 mg/L.

Embodiment 4

(12) 1.5 tons of hexavalent chromium-containing residues were added to the hydrothermal kettle, then water was added until the solid-to-liquid ratio was 1:10 (w/w), with sufficient stirring, and sodium chlorate, sodium perchlorate and hydrochloric acid were added. The concentration of sodium chlorate in the system was adjusted to 0.5 mol/L, the concentration of sodium perchlorate was 0.1 mol/L and the pH value was 4, with sufficient stirring, and the hydrothermal kettle was turned off. The temperature was set at 240 C. and the time for heat preservation was 2 hours. After the heating was stopped, the system was held for 24 hours. Other process was the same as that in the Embodiment 1.

(13) The concentration of the leached hexavalent chromium from the original chromium-containing residues in this embodiment was 274 mg/L, and the concentration of the leached hexavalent chromium from the treated chromium-containing residues was 0.86 mg/L.

Embodiment 5

(14) 2 tons of hexavalent chromium-containing residues were added to the hydrothermal kettle, then water was added until the solid-to-liquid ratio was 1:0.5 (w/w), with sufficient stirring, and sodium chlorate, sodium perchlorate and hydrochloric acid were added. The concentration of sodium chlorate in the system was adjusted to 0.1 mol/L, the concentration of sodium perchlorate was 0.5 mol/L and the pH value was 2, with sufficient stirring, and the hydrothermal kettle was turned off. The temperature was set at 80 C. and the time for heat preservation was 12 hours. After the heating was stopped, the system was held for 24 hours. Other process was the same as that in the Embodiment 1.

(15) The concentration of the leached hexavalent chromium from the original chromium-containing residues in this embodiment was 278 mg/L, and the concentration of the leached hexavalent chromium from the treated chromium-containing residues was 0.91 mg/L.

(16) The shorter the time for holding after the hydrothermal treatment or direct heating treatment, the smaller particles of the treated residues and the stronger re-adsorption ability to hexavalent chromium, and thus water that the washing demands will be more, resulting in a more difficult recycle. On the contrary, the longer the time for holding, the bigger particle size of the treated residues, and thus water for washing will be less, resulting in more convenient recycling of residues. However, if the time for holding is too long, the treated residues will turn yellowish which influences a treatment effect of the residues.

(17) Similarly, technical solutions given according to the protection scope defined by the claims and the description may also give a plurality of embodiments which belong to the protection scope of the present invention.