A method for resource utilization of chromium-containing sludge

Abstract

A method for the resource utilization of chromium-containing sludge involves conditioning, decomposition, and roasting of the sludge. During roasting, a non-oxidizing atmosphere is introduced for protection, ensuring that chromium (Cr) is enriched in the residue in a non-toxic, non-volatile, low-valence state, thus producing high-value-added calcium-chromium sand. Simultaneously, sulfur-containing flue gas is collected during roasting to produce sulfuric acid or sodium sulfite, preventing sulfur diffusion and air pollution. This significantly reduces hazardous solid waste emissions from related production processes and lowers hazardous waste disposal costs. This method achieves both the harmless treatment of chromium-containing sludge and the comprehensive resource utilization of chromium, calcium, and sulfur within the sludge.

Description

Technical Field

[0001] This invention belongs to the field of industrial hazardous solid waste treatment technology, and particularly relates to a method for the resource utilization of chromium-containing sludge. Background Technology

[0002] Chromium-containing sludge is a type of solid hazardous waste generated by industries such as steel and non-ferrous metals. Its composition varies significantly depending on the raw materials and production processes. For example, wastewater from the chromate passivation process in the cold rolling mill of steel plants generates a large amount of chromium-containing sludge after treatment. Its main components are calcium sulfite, calcium sulfate, and chromium compounds. The carcinogenic heavy metal chromium (Cr) in the sludge is readily soluble and reaches a content of 1-20%, thus classifying it as hazardous waste. After being pressed into cakes, the moisture content of chromium-containing sludge is generally 50-60%, and the Cr content is 0.5-20%. Furthermore, chromium-containing sludge also contains small amounts of elements such as Zn, Pt, and F, making it unsuitable for recycling in metallurgical production and direct application in the production of building materials such as glass, thus becoming a burden for steel and electroplating companies.

[0003] Chromium (Cr) in chromium-containing sludge is a valuable mineral resource and a scarce mineral in China, with over 80% of its annual consumption relying on imports. Chromium has a wide range of applications. In the building materials industry, it is used as a colorant in glass, ceramics, artificial stone, and coatings, and also as a nucleating agent for microcrystalline glass. In the metallurgical industry, chromium is a major raw material for the production of stainless steel and chromium-containing alloys. Calcium oxide is a major component of many silicate building materials and is also an important metallurgical auxiliary material.

[0004] There are many technologies for treating chromium-containing sludge, including solidification and stabilization landfill, acid leaching, ammonia leaching, high-temperature alkaline roasting leaching, and microbial methods to enrich and recover chromium, and sludge can be diluted and used as a raw material for cement and ceramics. However, these technologies all have problems such as high treatment costs, incomplete harmless treatment, large flue gas treatment volume, and secondary heavy metal pollution.

[0005] Currently, steel and non-ferrous metal companies typically outsource the disposal of chromium-containing sludge, resulting in high disposal costs. The environmentally friendly and resource-based disposal of chromium-containing sludge is a crucial technical challenge that these companies urgently need to address for achieving zero solid waste emissions. If chromium-containing sludge can be utilized in an environmentally friendly and resource-based manner, it will help reduce hazardous waste treatment costs for companies and protect the ecological environment. Summary of the Invention

[0006] The purpose of this invention is to provide a method for the resource utilization of chromium-containing sludge. Using chromium-containing sludge as the main raw material, the method enriches the chromium in the residue in a harmless, low-valence state, fully utilizing the Cr and Ca elements in the chromium-containing sludge to prepare high-value-added calcium-chromium sand. This achieves the harmless treatment and resource utilization of chromium-containing sludge, turning waste into treasure. The generated calcium-chromium sand can be used as a raw material in the production of stainless steel, chromium alloys, ceramics, colored glass, artificial stone, microcrystalline glass, coatings, etc. Simultaneously, during the treatment process, the sulfur element in the chromium-containing sludge is decomposed and released for use in the production of acid or sodium sulfite, avoiding the diffusion of sulfur and the formation of air pollution, significantly reducing the emission of hazardous solid waste in related production processes, and lowering hazardous waste disposal costs.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows:

[0008] A method for the resource utilization of chromium-containing sludge includes the following steps:

[0009] 1) Pretreatment of chromium-containing sludge

[0010] The chromium-containing sludge was dried and broken into sludge powder.

[0011] 2) Preparation of batch materials

[0012] The sludge powder and conditioning material are mixed evenly and then granulated to form a chromium-containing sludge compound; the weight ratio of the conditioning material to the sludge powder is 1:0.8-50.

[0013] The conditioning material comprises, by weight percentage: SiO2: 55-95%, Al2O3: 1-30%, CaF2: 0-1%, B2O3: 0-2%, Na2O: 0.2-5%, K2O: 0.1-1%, P2O5: 0.1-2%, Fe2O3: 0.05-15%;

[0014] 3) Roasting

[0015] Chromium-containing sludge batches are roasted under a non-oxidizing atmosphere to form calcium-chromium sand. The roasting temperature is 890–1150℃ and the roasting time is 30–70 min. Sulfur-containing flue gas is collected during the roasting process.

[0016] 4) Cooling, packaging, and warehousing.

[0017] Preferably, in step 1), the drying temperature is 110-180℃ and the drying time is 10-60 min.

[0018] Preferably, in step 1), the sludge powder has a particle size of 100-200 mesh.

[0019] Preferably, in step 2), the particle size D of the chromium-containing sludge batch material is... 50 The thickness is 0.1–5 mm.

[0020] Preferably, in step 3), the non-oxidizing atmosphere is one or more of nitrogen, helium, hydrogen, and argon.

[0021] Preferably, the sulfur-containing flue gas collected during the roasting process in step 3) is prepared into sulfuric acid or sodium sulfite.

[0022] Preferably, in step 4), the residual heat in the calcium chromium sand is recovered during the cooling process.

[0023] The melting temperature of the calcium chromium sand described in this invention is 1180–1350°C.

[0024] Furthermore, calcium chromium sand is prepared in multiple batches according to the method described above. The calcium chromium sand obtained is sent to the corresponding silos according to the different chromium contents. Then, calcium chromium sand is taken out from different silos according to the preset ratio and mixed and homogenized to obtain calcium chromium sand with the required chromium content.

[0025] Preferably, the number of hoppers is 3 to 10.

[0026] In the method of this invention, after the chromium-containing sludge is mixed and conditioned with the conditioning material, the addition of low-melting-point fluxing agents such as Na2O, K2O, and B2O3 to the conditioning material during the subsequent roasting and cooling process can significantly reduce the decomposition temperature of sulfur-containing compounds in the chromium-containing sludge. At the same time, the introduction of a non-oxidizing atmosphere during the roasting process can prevent calcium sulfite from being oxidized to calcium sulfate, thus avoiding an increase in the decomposition temperature. This allows the sulfur-containing compounds in the chromium-containing sludge to be completely decomposed in a lower temperature range of 890–1150°C, reducing equipment investment and energy consumption in the treatment process, thereby reducing production costs.

[0027] The non-oxidizing atmosphere introduced during roasting ensures that the chromium element in the chromium-containing sludge remains in a non-toxic, non-volatile, low-valence state in the calcium chromium sand, producing high-value-added calcium chromium sand. Simultaneously, the flue gas generated from the decomposition of sulfur compounds during roasting is collected and used to produce sulfuric acid or sodium sulfite. The resulting sodium sulfite is recycled for the treatment of chromium-containing wastewater within the plant, ensuring its rational utilization and preventing the diffusion of sulfur and its contribution to air pollution. This method achieves the harmless treatment of chromium-containing sludge while comprehensively utilizing the chromium, calcium, and sulfur elements within it, significantly reducing the emission of hazardous solid waste during related production processes and lowering hazardous waste disposal costs.

[0028] To obtain calcium chromium sand with different chromium contents and improve the product's value, calcium chromium sand can be prepared in multiple batches according to the method described in this invention. The resulting calcium chromium sand is fed into corresponding silos according to its different chromium contents. Then, calcium chromium sand is taken out from different silos according to a preset ratio, mixed, and homogenized to obtain calcium chromium sand with stable composition. The improved composition and performance stability of calcium chromium sand is beneficial to product application and market promotion, further improving its technical and economic efficiency.

[0029] This invention incorporates low-melting-point fluxing agents such as Na2O, K2O, and B2O3, which lowers the melting temperature of calcium chromium ore to 1180–1350°C. Furthermore, the composition is stable, melting energy consumption is low, and added value is high. It can be used as a raw material for the production of stainless steel, chromium alloys, green glass, microcrystalline glass, ceramic glazes, coatings, etc., and has good economic value and promising prospects for widespread application.

[0030] The beneficial effects of this invention are:

[0031] 1. This invention involves conditioning and roasting chromium-containing sludge, introducing a non-oxidizing atmosphere during the roasting process to ensure that the Cr element in the chromium-containing sludge is retained in the residue in a non-toxic, non-volatile, low-valence state. This fully utilizes the Cr and Ca elements in the chromium-containing sludge to prepare calcium chromium sand with high added value, achieving the harmless treatment and resource utilization of chromium-containing sludge, turning chromium-containing sludge into a valuable resource, significantly reducing the emission of hazardous solid waste in related production processes, and lowering the cost of hazardous waste disposal.

[0032] 2. In the treatment process of chromium-containing sludge of the present invention, after the chromium-containing sludge is mixed with the conditioning material, low-melting-point combined fluxes such as Na2O, K2O, and B2O3 are added to the conditioning material. At the same time, a non-oxidizing atmosphere is introduced for protection during the roasting process, which can prevent calcium sulfite from being oxidized to calcium sulfate and thus avoid increasing the decomposition temperature. This reduces the decomposition temperature of sulfur-containing compounds in the chromium-containing sludge, reduces equipment investment and energy consumption in the treatment process, thereby reducing production costs.

[0033] 3. During the roasting process, sulfur-containing compounds are completely decomposed, and the resulting sulfur-containing flue gas can be used to produce sulfuric acid or sodium sulfite. The sodium sulfite produced is recycled for the treatment of chromium-containing wastewater in the plant. This achieves the harmless treatment of chromium-containing sludge while avoiding the diffusion of sulfur elements and the formation of air pollution, thus making full use of the resource value of chromium-containing sludge.

[0034] 4. Prepare calcium chromium sand in multiple batches according to the method of the present invention. The obtained calcium chromium sand is homogenized according to the different chromium contents to obtain calcium chromium sand with the required chromium content, thereby improving the product's use value.

[0035] 5. The calcium chromium sand prepared by this invention has stable composition, low melting temperature, and high added value. It can be used as a raw material for the production of stainless steel, chromium alloys, green glass, microcrystalline glass, ceramic glazes, coatings, etc., and has good economic value and promising application prospects. Attached Figure Description

[0036] Figure 1 This is a process flow diagram of an embodiment of the present invention. Detailed Implementation

[0037] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0038] See Figure 1 The method for resource utilization of chromium-containing sludge according to the present invention includes the following steps:

[0039] 1) Pretreatment of chromium-containing sludge

[0040] The chromium-containing sludge was dried and broken into sludge powder.

[0041] 2) Preparation of batch materials

[0042] The sludge powder and conditioning material are mixed evenly and then granulated to form a chromium-containing sludge compound; the weight ratio of the conditioning material to the sludge powder is 1:0.8-50.

[0043] The conditioning material comprises, by weight percentage: SiO2: 55-95%, Al2O3: 1-30%, CaF2: 0-1%, B2O3: 0-2%, Na2O: 0.2-5%, K2O: 0.1-1%, P2O5: 0.1-2%, Fe2O3: 0.05-15%;

[0044] 3) Roasting

[0045] Chromium-containing sludge batches are roasted under a non-oxidizing atmosphere to form calcium-chromium sand. The roasting temperature is 890–1150℃ and the roasting time is 30–70 min. Sulfur-containing flue gas is collected during the roasting process.

[0046] 4) Cooling.

[0047] Preferably, in step 1), the drying temperature is 110-180℃ and the drying time is 10-60 min.

[0048] Preferably, in step 1), the sludge powder has a particle size of 100-200 mesh.

[0049] Preferably, in step 2), the particle size D of the chromium-containing sludge batch material is... 50 The thickness is 0.1–5 mm.

[0050] Preferably, the sulfur-containing flue gas collected during the roasting process in step 3) is prepared into sulfuric acid or sodium sulfite.

[0051] Preferably, in step 4), the residual heat in the calcium chromium sand is recovered during the cooling process.

[0052] Furthermore, calcium chromium sand is prepared in multiple batches according to the method described above. The calcium chromium sand obtained is sent to the corresponding silos according to the different chromium contents. Then, calcium chromium sand is taken out from different silos according to the preset ratio and mixed and homogenized to obtain calcium chromium sand with the required chromium content.

[0053] Preferably, the number of hoppers is 3 to 10.

[0054] The composition of the conditioning materials in this embodiment of the invention is shown in Table 1; the process parameters in this embodiment of the invention are shown in Table 2.

[0055] The calcium chromium sand prepared in this embodiment of the invention has a melting temperature of 1180–1350℃. This calcium chromium sand can be used as a raw material for the production of stainless steel, chromium-containing alloys, green glass, and microcrystalline glass, and has good economic value and promising prospects for widespread application.

[0056]

[0057]

Claims

1. A method for the resource utilization of chromium-containing sludge, characterized in that, Includes the following steps: 1) Pretreatment of chromium-containing sludge The chromium-containing sludge was dried and broken into sludge powder. 2) Preparation of batch materials The sludge powder and conditioning material are mixed evenly and then granulated to form a chromium-containing sludge compound; the weight ratio of the conditioning material to the sludge powder is 1:0.8-50. The conditioning material comprises, by weight percentage: SiO2: 55-95%, Al2O3: 1-30%, CaF2: 0-1%, B2O3: 0-2%, Na2O: 0.2-5%, K2O: 0.1-1%, P2O5: 0.1-2%, Fe2O3: 0.05-15%; 3) Roasting Chromium-containing sludge batches are roasted under a non-oxidizing atmosphere to form calcium-chromium sand. The roasting temperature is 890–1150℃ and the roasting time is 30–70 min. Sulfur-containing flue gas is collected during the roasting process. 4) Cooling, packaging, and warehousing.

2. The method for resource utilization of chromium-containing sludge as described in claim 1, characterized in that, In step 1), the drying temperature is 110-180℃ and the drying time is 10-60 minutes.

3. The method for resource utilization of chromium-containing sludge as described in claim 1, characterized in that, In step 1), the sludge powder has a particle size of 100-200 mesh.

4. The method for resource utilization of chromium-containing sludge as described in claim 1, characterized in that, In step 2), the particle size D of the chromium-containing sludge batch material is... 50 The thickness is 0.1–5 mm.

5. The method for resource utilization of chromium-containing sludge as described in claim 1, characterized in that, In step 3), the non-oxidizing atmosphere is one or more of nitrogen, argon, helium, and hydrogen.

6. The method for resource utilization of chromium-containing sludge as described in claim 1, characterized in that, The sulfur-containing flue gas collected during the roasting process in step 3) is prepared into sulfuric acid or sodium sulfite.

7. The method for resource utilization of chromium-containing sludge as described in claim 1, characterized in that, In step 4), the residual heat in the calcium chromium sand is recovered during the cooling process.

8. The method for resource utilization of chromium-containing sludge as described in claim 1, characterized in that, Calcium chromium sand is prepared in multiple batches according to the method described above. The calcium chromium sand is sent to the corresponding silo according to the different chromium contents. Then, calcium chromium sand is taken out from different silos according to the preset ratio and mixed and homogenized to obtain calcium chromium sand with the required chromium content.

9. The method for resource utilization of chromium-containing sludge as described in claim 8, characterized in that, The number of silos is 3 to 10.

10. The method for resource utilization of chromium-containing sludge as described in any one of claims 1 to 9, characterized in that, The melting temperature of the obtained calcium chromium sand is 1180–1350℃.

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