Preparation method of coal gangue composite adsorbent for treating hexavalent chromium-containing wastewater

Abstract

The invention discloses a preparation method of a coal gangue composite adsorbent for treating wastewater containing hexavalent chromium, and belongs to the technical field of wastewater treatment.The preparation method comprises the steps that the surface of coal gangue is washed with deionized water, and the washed coal gangue, calcium-containing salt and chloride are dried in a drying oven; respectively sieving the dried coal gangue, calcium-containing salt and chloride for later use; mixing the sieved coal gangue with calcium-containing salt according to a certain proportion, then adding a certain mass fraction of sieved chloride, and mixing again; carrying out vacuum calcination on the mixed coal gangue, calcium-containing salt and chloride by using a muffle furnace under the condition that the temperature is increased from room temperature to target temperature; and cooling the mixture subjected to vacuum calcination, grinding and crushing to obtain the coal gangue composite adsorbent. According to the method, the waste coal gangue can be fully recycled, the purpose of treating waste with waste is achieved, and the prepared coal gangue composite adsorbent product is low in cost.

Description

Technical Field

[0001] The present invention relates to the technical field of wastewater treatment, and in particular to a preparation method of a coal gangue composite adsorbent for treating wastewater containing hexavalent chromium. Background Art

[0002] Chromium is an element widely used in industrial production, and hexavalent chromium (Cr(VI)) is highly toxic, causing serious harm to the environment and human health. Wastewater containing Cr(VI) mainly comes from industrial activities such as electroplating, leather making and metal finishing. At present, methods for treating wastewater containing Cr(VI) include chemical reduction method, ion exchange method, reverse osmosis method, precipitation method, adsorption method and biological method, etc., but these methods all have some limitations, such as high cost, low efficiency, and a large amount of waste to be treated, etc.

[0003] Coal gangue is an important residue generated during coal mining and coal washing processes, accounting for about 10 - 15% of the raw coal output. The disorderly stacking of coal gangue not only occupies a large amount of land resources, but also pollutes the surrounding environment. However, coal gangue has a large surface area, and functional groups such as -OH and -COOH exist on the surface, providing a large number of active sites for adsorption. It can be used as a raw material to prepare a composite adsorbent for removing pollutants in wastewater. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a preparation method of a coal gangue composite adsorbent for treating wastewater containing hexavalent chromium. The coal gangue composite adsorbent prepared by mixing coal gangue, calcium salt and chloride in a certain proportion and calcining has good adsorption performance for wastewater containing Cr(VI), with obvious removal effect, simple preparation method, easy process control, full resource utilization of waste coal gangue, and low cost of the obtained product.

[0005] To solve the above technical problem, the technical solution adopted by the present invention is:

[0006] A preparation method of a coal gangue composite adsorbent for treating wastewater containing hexavalent chromium, comprising the following steps:

[0007] Step 1, rinse the surface of the coal gangue with deionized water, and dry the washed coal gangue, calcium salt and chloride in an oven respectively;

[0008] Step 2, sieve the dried coal gangue, calcium salt and chloride respectively and reserve for use;

[0009] Step 3, mix the sieved coal gangue and calcium salt in a certain proportion, and then add a certain mass fraction of the sieved chloride and mix again;

[0010] Step 4: Vacuum calcine the mixed coal gangue, calcium salt and chloride in a muffle furnace from room temperature to the target temperature.

[0011] Step 5: Grind and pulverize the mixture after vacuum calcination to obtain the coal gangue composite adsorbent.

[0012] A further improvement of the technical solution of the present invention is that: the calcium salt is limestone or calcium chloride.

[0013] A further improvement of the technical solution of the present invention is that: the chloride is aluminum chloride or zinc chloride.

[0014] A further improvement of the technical solution of the present invention is that: in the step, the drying time is 20 - 48 h.

[0015] A further improvement of the technical solution of the present invention is that: in step 2, the mesh number of sieving is 100 - 400 meshes.

[0016] A further improvement of the technical solution of the present invention is that: in step 3, the mixing ratio of the coal gangue to the calcium salt is 1:1 - 1:5.

[0017] A further improvement of the technical solution of the present invention is that: in step 3, the mass fraction of the added chloride is 5% - 25%.

[0018] A further improvement of the technical solution of the present invention is that: in step 4, the target temperature of the vacuum calcination is 400°C - 800°C.

[0019] A further improvement of the technical solution of the present invention is that: in step 4, during the vacuum calcination, when heating from room temperature to the target temperature, it is divided into two stages. The first stage is heating from room temperature to 280°C with a heating rate of 1°C / min; the second stage is heating from 280°C to the target temperature with a heating rate of 2°C / min.

[0020] A further improvement of the technical solution of the present invention is that: in step 4, after reaching the target temperature during the vacuum calcination, the calcination time is 60 - 260 min.

[0021] Due to the adoption of the above technical solution, the technical progress achieved by the present invention is:

[0022] 1. The coal gangue composite adsorbent prepared by mixing and calcining coal gangue, calcium salt and chloride in a certain proportion in the present invention has good adsorption performance for Cr(VI)-containing wastewater, with obvious removal effect, simple preparation method, easy process control, fully resource-utilizes waste coal gangue, and the obtained product has a low cost.

[0023] 2. The coal gangue composite adsorbent prepared by the present invention has good adsorption performance for Cr(VI) in Cr(VI)-containing wastewater. This is mainly because the specific surface area of the coal gangue composite adsorbent is significantly increased, there are more adsorption active sites for Cr(VI), the chemical stability is improved, and the negative zeta potential improves the adsorption efficiency through electrostatic attraction and reduction of aggregation. It can be further used in the field of wastewater purification with good effects and is convenient for popularization and application.

[0024] 3. The coal gangue composite adsorbent of the present invention is prepared by using the waste coal gangue from coal mining as raw material, adding limestone and aluminum chloride and then calcining. The measured specific surface area is much larger than that of the raw coal gangue. Its particle surface is rough, increasing the specific surface area of the particles and the contact opportunity between the coal gangue and the adsorbent, increasing the available binding sites of the coal gangue with the adsorbate, and greatly improving the adsorption effect of the coal gangue composite adsorbent on Cr(VI).

[0025] 4. It can be detected that the coal gangue composite adsorbent prepared by the present invention contains components such as silicate minerals, kaolinite, quartz and dolomite, and at the same time, there are also Al-O groups, calcium content, and the presence of various functional groups such as fatty ethers and amino acids. The negative charge on the surface of the coal gangue composite adsorbent enables it to generate electrostatic attraction with the positively charged Cr(VI) ions, thereby improving the adsorption efficiency.

[0026] 5. The present invention uses coal gangue as the main raw material of the adsorbent, which is a sustainable waste management and resource utilization method. It can convert waste into valuable environmental remediation materials, achieving the goal of "treating waste with waste", realizing the resource utilization of solid waste, and reducing the environmental pollution caused by coal gangue. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings;

[0028] Figure 1 It is the SEM diagram of coal gangue and coal gangue composite adsorbent in Example 1 of the present invention;

[0029] Figure 2 It is the X-ray diffraction pattern of the coal gangue composite adsorbent prepared in Example 1 of the present invention;

[0030] Figure 3 It is the effect diagram of the coal gangue composite adsorbent prepared in Example 3 of the present invention adsorbing Cr(VI) in Cr(VI)-containing wastewater with different pH values;

[0031] Figure 4 It is the effect diagram of the coal gangue composite adsorbent prepared in Example 3 of the present invention for adsorbing Cr(VI) in wastewater containing Cr(VI) at different concentrations;

[0032] Figure 5 It is the infrared spectrogram of the coal gangue composite adsorbent prepared in Example 4 of the present invention;

[0033] Figure 6 It is the ζ-potential detection and analysis diagram of the coal gangue composite adsorbent prepared in Example 5 of the present invention. Detailed implementation manners

[0034] It should be noted that the terms "including" and "having" and any variations thereof in the description and claims of the present invention and the above-mentioned drawings are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device that includes a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or are inherent to these processes, methods, products or devices.

[0035] The present invention will be further described in detail below with reference to the drawings and embodiments:

[0036] In the following embodiments, unless otherwise specified, the reagents used are all commercially available reagents. Unless otherwise specified, the following experimental methods and detection methods are all existing experimental methods and detection methods.

[0037] Example 1

[0038] A preparation method of a coal gangue composite adsorbent for treating wastewater containing hexavalent chromium includes the following steps:

[0039] Step 1, rinse the surface of the coal gangue with deionized water, and dry the washed coal gangue, calcium salt and chloride in an oven for 24 hours to reduce the water content;

[0040] Step 2, pass the dried coal gangue, limestone and zinc chloride through a 300-mesh sieve and reserve them for use;

[0041] Step 3, mix the sieved coal gangue and limestone in a ratio of 2:3, and then add 15% by mass of the sieved zinc chloride and mix again;

[0042] Step 4, use a muffle furnace to heat the mixed coal gangue, limestone and zinc chloride from room temperature to 400°C for vacuum calcination; carry out vacuum calcination at 400°C for 60 min;

[0043] When heating from room temperature to 280 °C, the heating rate is 1 °C / min; when heating from 280 °C to 400 °C, the heating rate is 2 °C / min.

[0044] Step 5: After the mixture after vacuum calcination is cooled, it can be ground and pulverized to obtain the coal gangue composite adsorbent.

[0045] Compare the SEM image of the coal gangue composite adsorbent prepared in this example with the SEM image of pure coal gangue. As Figure 1 shown, it is proved that for the coal gangue composite adsorbent after calcination with the addition of limestone and zinc chloride, compared with pure coal gangue, its surface structure has changed. The high-temperature calcination removes the volatile components in the coal gangue, increasing the specific surface area of the coal gangue. During the preparation process, the limestone added reacts with zinc chloride to form small and uniform calcium zincate particles, which can act as adhesives between the coal gangue particles. And it makes the surface of the coal gangue composite agent particles rough, increasing the specific surface area of the particles and the contact opportunity between the coal gangue and the adsorbent, increasing the sites available for the coal gangue to bind with the adsorbate, and greatly improving the adsorption effect of the coal gangue composite adsorbent on Cr(VI).

[0046] Perform X-ray diffraction on the coal gangue composite adsorbent prepared in this example. As Figure 2 shown, it is proved that the stable substances in the coal gangue composite adsorbent are activated after high-temperature roasting, including silicate minerals belonging to the orthorhombic system, kaolinite belonging to the triclinic system, quartz and dolomite belonging to the trigonal system, etc.

[0047] Example 2

[0048] A preparation method of a coal gangue composite adsorbent for treating hexavalent chromium-containing wastewater, comprising the following steps:

[0049] Step 1: Rinse the surface of the coal gangue with deionized water, and dry the washed coal gangue, calcium chloride and aluminum chloride in an oven for 36 hours to reduce the water content;

[0050] Step 2: Pass the dried coal gangue, calcium chloride and aluminum chloride through a 200-mesh sieve and reserve for use;

[0051] Step 3: Mix the sieved coal gangue and calcium chloride in a ratio of 1:1, and then add 5% by mass of the sieved aluminum chloride and mix again;

[0052] Step 4: Use a muffle furnace to heat the mixed coal gangue, calcium chloride and aluminum chloride from room temperature to 500 °C for vacuum calcination; perform vacuum calcination at 500 °C for 110 min;

[0053] When heating from room temperature to 280 °C, the heating rate is 1 °C / min; when heating from 280 °C to 500 °C, the heating rate is 2 °C / min.

[0054] Step 5: After the mixture after vacuum calcination is cooled, it is ground and pulverized to obtain the coal gangue composite adsorbent.

[0055] Example 3

[0056] A preparation method of a coal gangue composite adsorbent for treating hexavalent chromium-containing wastewater, comprising the following steps:

[0057] Step 1: Rinse the surface of the coal gangue with deionized water, and dry the washed coal gangue, limestone and aluminum chloride in an oven for 48 hours to reduce the water content;

[0058] Step 2: The dried coal gangue, limestone and aluminum chloride are respectively sieved through a 200-mesh sieve and reserved for use;

[0059] Step 3: Mix the sieved coal gangue and limestone in a ratio of 3:2, and then add 10% by mass of the sieved aluminum chloride and mix again;

[0060] Step 4: Use a muffle furnace to heat the mixed coal gangue, limestone and aluminum chloride from room temperature to 600 °C for vacuum calcination; vacuum calcine at 600 °C for 160 min;

[0061] When heating from room temperature to 280 °C, the heating rate is 1 °C / min; when heating from 280 °C to 600 °C, the heating rate is 2 °C / min.

[0062] Step 5: After the mixture after vacuum calcination is cooled, it is ground and pulverized to obtain the coal gangue composite adsorbent.

[0063] Using the coal gangue composite adsorbent prepared in this example to treat Cr(VI)-containing wastewater, the effect of adsorbing Cr(VI) in Cr(VI)-containing wastewater with different pH values is as Figure 3 shown

[0064] Using the coal gangue composite adsorbent prepared in this example to treat Cr(VI)-containing wastewater, the effect of adsorbing Cr(VI) in Cr(VI)-containing wastewater with different concentrations is as Figure 4 shown.

[0065] Example 4

[0066] A preparation method of a coal gangue composite adsorbent for treating hexavalent chromium-containing wastewater, comprising the following steps:

[0067] Step 1: Rinse the surface of the coal gangue with deionized water, and then dry the washed coal gangue, calcium chloride, and aluminum chloride in an oven for 30 hours to reduce the water content.

[0068] Step 2: Pass the dried coal gangue, calcium chloride, and aluminum chloride through a 200-mesh sieve and reserve them for use.

[0069] Step 3: Mix the sieved coal gangue and calcium chloride in a ratio of 1:4, and then add 20% by mass of the sieved aluminum chloride and mix again.

[0070] Step 4: Use a muffle furnace to heat the mixed coal gangue, calcium chloride, and aluminum chloride from room temperature to 700 °C for vacuum calcination; carry out vacuum calcination at 700 °C for 210 min.

[0071] When heating from room temperature to 280 °C, the heating rate is 1 °C / min; when heating from 280 °C to 600 °C, the heating rate is 2 °C / min.

[0072] Step 5: After the mixture after vacuum calcination is cooled, grind and crush it to obtain the coal gangue composite adsorbent.

[0073] Perform infrared spectroscopy detection on the coal gangue composite adsorbent prepared in this example, as Figure 5 shown, which proves that in addition to preserving the ore components of the coal gangue, the coal gangue composite adsorbent also has Al-O groups, calcium content, and the presence of various functional groups such as aliphatic ethers and amino acids.

[0074] Example 5

[0075] A preparation method of a coal gangue composite adsorbent for treating hexavalent chromium-containing wastewater, comprising the following steps:

[0076] Step 1: Rinse the surface of the coal gangue with deionized water, and then dry the washed coal gangue, limestone, and aluminum chloride in an oven for 28 hours to reduce the water content.

[0077] Step 2: Pass the dried coal gangue, limestone, and aluminum chloride through a 200-mesh sieve and reserve them for use.

[0078] Step 3: Mix the sieved coal gangue and limestone in a ratio of 1:5, and then add 25% by mass of the sieved aluminum chloride and mix again.

[0079] Step 4: Use a muffle furnace to heat the mixed coal gangue, calcium chloride, and aluminum chloride from room temperature to 800 °C for vacuum calcination; carry out vacuum calcination at 800 °C for 260 min.

[0080] When heating from room temperature to 280 °C, the heating rate is 1 °C / min; when heating from 280 °C to 600 °C, the heating rate is 2 °C / min.

[0081] Step 5: After the mixture after vacuum calcination is cooled, it can be ground to obtain the coal gangue composite adsorbent.

[0082] The ζ potential of the coal gangue composite adsorbent prepared in this example was detected and analyzed. As Figure 6 shown, it was proved that the particles of the coal gangue composite adsorbent carried negative charges, the Zeta potential was -56.84 mV, and the mobility was -4.433e-004 cm2 / Vs. The measured value of the conductivity of the particles was 0.0056 mS / cm. The negative zeta potential of the coal gangue composite adsorbent had an important influence on its adsorption efficiency for Cr(VI). The negative charges on the surface of the adsorbent generated electrostatic attraction between the adsorbent and the positively charged Cr(VI) ions, thereby improving the adsorption efficiency.

[0083] The removal efficiencies of the coal gangue composite adsorbents prepared in Examples 1-5 for Cr(VI) were detected respectively:

[0084] The same dosage of the coal gangue composite adsorbents prepared in Examples 1-5 was taken respectively and added to 50 mL of the solution containing Cr(VI). The pH value of the solution was adjusted to be the same. After the mixture was oscillated for a certain time and then centrifuged, the absorbance values of the supernatant were detected respectively, and then compared with the simulated wastewater without adsorption, and the removal efficiency of Cr(VI) was calculated, as shown in Table 1 below:

[0085] Table 1 Removal effect table of the coal gangue composite adsorbent

[0086]

[0087] As can be seen from Table 1, the coal gangue composite adsorbent prepared by the method of the present invention had good removal rates for Cr(VI) in the wastewater containing Cr(VI). The coal gangue composite adsorbent prepared in Example 3 had the best removal effect on Cr(VI) in the wastewater containing Cr(VI). From Figure 3 , Figure 4 it can be seen that under different pH values and different concentrations of the wastewater containing Cr(VI), the adsorption effects of the coal gangue composite adsorbent prepared by the method of the present invention on Cr(VI) were different. When in use, it can be adjusted according to the specific situation of the actual wastewater containing Cr(VI).

[0088] In addition, the upper and lower limit values and interval values of the process parameters (such as temperature, time, ratio, mass fraction, etc.) of the present invention can all achieve the present invention, and the examples are not listed one by one here.

[0089] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A preparation method of a coal gangue composite adsorbent for treating hexavalent chromium-containing wastewater, characterized in that, It includes the following steps: Step 1: Rinse the surface of coal gangue with deionized water, and then dry the washed coal gangue, calcium salt and chloride in an oven respectively. Step 2: Sieve the dried coal gangue, calcium salt and chloride respectively for standby. Step 3: Mix the sieved coal gangue and calcium salt in a certain proportion, and then add a certain mass fraction of the sieved chloride and mix again. Step 4: Use a muffle furnace to conduct vacuum calcination on the mixed coal gangue, calcium salt and chloride under the condition of raising the temperature from room temperature to the target temperature. Step 5: After the mixture after vacuum calcination is cooled, grind and crush it to obtain the coal gangue composite adsorbent.

2. The preparation method of a coal gangue composite adsorbent for treating hexavalent chromium-containing wastewater according to claim 1, characterized in that, The calcium salt is limestone or calcium chloride.

3. The preparation method of a coal gangue composite adsorbent for treating hexavalent chromium-containing wastewater according to claim 1, characterized in that, The chloride is aluminum chloride or zinc chloride.

4. The preparation method of a coal gangue composite adsorbent for treating hexavalent chromium-containing wastewater according to claim 1, characterized in that, In the step, the drying time is 20 - 48h.

5. The preparation method of a coal gangue composite adsorbent for treating hexavalent chromium-containing wastewater according to claim 1, characterized in that, In Step 2, the mesh number of sieving is 100 - 400 meshes.

6. The preparation method of a coal gangue composite adsorbent for treating hexavalent chromium-containing wastewater according to claim 1, wherein, In Step 3, the mixing ratio of the coal gangue and the calcium salt is 1:1 - 1:

5.

7. The preparation method of a coal gangue composite adsorbent for treating hexavalent chromium-containing wastewater according to claim 1, characterized in that, In Step 3, the mass fraction of the added chloride is 5% - 25%.

8. The preparation method of a coal gangue composite adsorbent for treating hexavalent chromium-containing wastewater according to claim 1, characterized in that, In Step 4, the target temperature of the vacuum calcination is 400°C - 800°C.

9. The preparation method of a coal gangue composite adsorbent for treating hexavalent chromium-containing wastewater according to claim 1, wherein, In Step 4, during the vacuum calcination, when heating from room temperature to the target temperature, it is divided into two stages. The first stage is to heat from room temperature to 280°C at a heating rate of 1°C / min; the second stage is to heat from 280°C to the target temperature at a heating rate of 2°C / min.

10. The preparation method of a coal gangue composite adsorbent for treating hexavalent chromium-containing wastewater according to claim 1, characterized in that, In Step 4, after reaching the target temperature during the vacuum calcination, the calcination time is 60 - 260min.

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