A method for dehydrating sludge by using red mud instead of coagulant

Abstract

The present invention discloses a method for dehydrating sludge by using red mud instead of a coagulant. The method comprises the following steps: A. diluting dehydrated red mud with a solid content of 40-60% produced by the alumina industry to a solid content of 3% to 10% with water, and stirring for 5 to 15 minutes to obtain a red mud coagulant; B. mixing the red mud coagulant with sludge with a solid content of 10 to 13% to condition the sludge; C. adding an anionic polyacrylamide flocculant to the sludge conditioned by the red mud coagulant; the flocculant is added in two steps, and after mixing, the mixture is fed into a flocculation sedimentation tank for flocculation, precipitation, and concentration; D. dehydrating the flocculated, precipitated, and concentrated sludge by filter pressing to obtain dehydrated sludge. The present invention can improve the resource utilization rate of red mud, reduce the amount of coagulant and flocculant used, and improve the flocculation and sedimentation performance of the sludge, the dehydration performance, and the physical and chemical properties of the dehydrated product.

Description

Technical Field

[0001] The invention belongs to the technical field of red mud and sludge treatment and disposal in the weathered alumina industry, and particularly relates to a sludge dehydration method using red mud instead of a coagulant aid. Background Art

[0002] Aluminum is the non-ferrous metal with the largest output, but bauxite mining and smelting will bring about a large number of ecological and environmental problems, such as the disposal of red mud and ore slime, the lack of sufficient soil to fill bauxite goafs, and the fragmentation of landforms and landscapes.

[0003] Red mud and mineral slime are solid wastes generated after bauxite ore washing and aluminum extraction in the alumina industry. Their composition originates from weathered residual slope sediments from the parent rock in mining areas. Washing mud has a chemical composition similar to that of soils from sloping farmland surrounding goafs, but its physical properties, such as particle size, structure, and moisture content, have changed. After undergoing a series of alumina extraction processes, red mud undergoes significant changes in salinity and alkalinity, significantly reducing its aluminum content. Its other chemical compositions are also largely similar to those of soils from sloping farmland surrounding goafs.

[0004] In line with the natural law of "where you come from, where you return", soil treatment of mineral mud and red mud has become the most effective way to dispose of bulk solid waste in the alumina industry. It can also repair the landscape ecology and mine "scars" damaged by mining, and restore the original soil properties and land resource properties of mineral mud and red mud.

[0005] Washing sludge typically has a moisture content of 85% to 90%, primarily composed of clay and silt particles less than 50μm in size, with a zeta potential of less than -20mv. The interparticle repulsion is greater than the attraction, making it hydrophilic, with a high specific resistance and difficult to dewater. Therefore, prior to mechanical dewatering, the sludge is typically conditioned with the addition of lime coagulants and anionic polyacrylamide flocculants to modify the surface properties of the sludge particles and disrupt their colloidal structure, thereby improving their dewatering performance. The coagulants and coagulants used in existing sludge dewatering processes are expensive, and the addition of dry lime powder increases the amount of sludge to be disposed of, significantly impacting the engineering and economic viability of sludge treatment and disposal, becoming the primary bottleneck in sludge treatment and disposal in the alumina industry. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for dewatering sludge by using red mud instead of coagulant. The method of the present invention uses the saline-alkali substances, chemically active components and fine viscosity of red mud as sludge flocculation and coagulant to replace the currently commonly used lime powder coagulant to condition the sludge, reduce the amount of exogenous coagulant used in the alumina industry, improve the flocculation and sedimentation performance, dewatering performance and physical and chemical properties of the dehydrated products of the sludge, reduce the cost of coagulant and flocculant agents for sludge treatment and disposal, reduce the increase in sludge disposal caused by the addition of lime, and improve the resource utilization rate of red mud.

[0007] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0008] The method for dehydrating sludge by using red mud instead of a coagulant aid comprises the following steps:

[0009] A. Dilute the dehydrated red mud with a solid content of 40-60% discharged from alumina production with water to a solid content of 3% to 10%, and stir for 5 to 15 minutes to obtain a red mud coagulant aid;

[0010] B. Using the red mud coagulant prepared in step A to condition the ore mud with a solid content of 10-13%; the ratio of the red mud coagulant to the ore mud is as follows: dry weight of red mud coagulant: dry weight of ore mud = 4-8:92-96;

[0011] C. Add anionic polyacrylamide flocculant with a molecular weight of 12 million to 18 million to the sludge conditioned with red mud coagulant aid. The total dosage of the anionic polyacrylamide flocculant is 20 to 45 g per ton of dry weight of the sludge. The addition method is to add the flocculant in two steps, first adding 50% to 80% of the anionic polyacrylamide; after stirring and mixing evenly, add the remaining anionic polyacrylamide for the second time, further mix and mix, and then enter the flocculation sedimentation tank for flocculation, coagulation and concentration of the sludge;

[0012] D. The concentrated sludge in the flocculation sedimentation tank is dehydrated by filter pressing to obtain dehydrated sludge.

[0013] The anionic polyacrylamide flocculant in step C is added in two steps:

[0014] For the first time, 50% to 80% anionic polyacrylamide is added to the red mud coagulant conditioning sludge, and stirred in the pipeline mixer for 1 to 2 minutes; then the remaining anionic polyacrylamide is added for the second time at the end of the sludge conveying pipeline, and further mixed for 1 to 2 minutes through the folded plate mixing gallery, and then the water is dropped into the flocculation sedimentation tank.

[0015] The method for flocculation sedimentation in the flocculation sedimentation tank comprises the following steps:

[0016] After adding anionic polyacrylamide flocculant, the red mud-assisted coagulation and sludge flocculation mixture enters the flocculation sedimentation tank through the central pipe of the flocculation sedimentation tank and settles in the flocculation sedimentation tank for 0.75 to 1.5 hours. After the mud and water are separated in the flocculation sedimentation tank, the sludge is concentrated in the mud hopper of the flocculation sedimentation tank.

[0017] The present invention has the following advantages:

[0018] The method of the present invention fully utilizes the saline-alkali substances, chemically active components and fine viscosity characteristics of red mud, a large amount of solid waste generated by the alumina industry, as a sludge flocculation and coagulant, replacing the currently commonly used lime powder coagulant to condition the sludge. It can reduce the amount of coagulant used, improve the flocculation and sedimentation performance, dehydration performance and physical and chemical properties of the dehydrated products of the sludge, reduce the cost of coagulants and flocculants for sludge treatment and disposal, reduce the increase in sludge caused by the addition of lime, and at the same time promote the resource utilization of red mud, a solid waste of the alumina industry, and improve the resource utilization rate of red mud. DETAILED DESCRIPTION

[0019] In order to facilitate a better understanding of the present invention, the following examples are provided for illustration. These examples belong to the protection scope of the present invention, but do not limit the protection scope of the present invention. Example 1

[0020] The method for dehydrating sludge by using red mud instead of a coagulant aid comprises the following steps:

[0021] A. Dilute the dehydrated red mud with a solid content of 40% discharged from alumina production with water to a solid content of 3% and stir for 7 minutes to obtain a red mud coagulant aid;

[0022] B. Use the red mud coagulant prepared in step A to condition the sludge with a solid content of 10%. The ratio of red mud coagulant to sludge is as follows: dry weight of red mud coagulant: dry weight of sludge = 5; 95;

[0023] C. Add anionic polyacrylamide flocculant with a molecular weight of 13-15 million to the sludge conditioned with red mud coagulant. The total dosage of anionic polyacrylamide flocculant is 28g per ton of dry weight of sludge. The addition method is to add 75% anionic polyacrylamide in two steps. After stirring and mixing, the remaining 25% anionic polyacrylamide is added in a second step. After further mixing, the sludge is then placed in a flocculation sedimentation tank for flocculation, coagulation, and concentration. After the addition of anionic polyacrylamide flocculant, the red mud coagulant conditioned sludge enters the flocculation sedimentation tank through the central pipe and settles in the flocculation sedimentation tank for 1 hour. After the mud and water are separated in the flocculation sedimentation tank, the sludge is concentrated in the sludge hopper of the flocculation sedimentation tank.

[0024] D. The concentrated sludge in the flocculation sedimentation tank is dehydrated by filter pressing to obtain dehydrated sludge. Example 2

[0025] The method for dehydrating sludge by using red mud instead of a coagulant aid comprises the following steps:

[0026] A. Dehydrated red mud with a solid content of 60% discharged from alumina production was diluted with water to a solid content of 10%, and stirred for 15 minutes to obtain a red mud coagulant aid;

[0027] B. Use the red mud coagulant prepared in step A to condition the sludge with a solid content of 13%. The ratio of red mud coagulant to sludge is as follows: dry weight of red mud coagulant: dry weight of sludge = 8; 92;

[0028] C. Add an anionic polyacrylamide flocculant with a molecular weight of 16-18 million to the sludge conditioned with red mud coagulant. The total dosage is 22g per ton of dry weight of the sludge. The addition is done in two steps: first, add 55% of the anionic polyacrylamide; after stirring and mixing, add the remaining 45% of the anionic polyacrylamide for a second time. After further mixing, the sludge enters the flocculation sedimentation tank for flocculation, coagulation, and concentration. After the addition of the anionic polyacrylamide flocculant, the red mud conditioned sludge enters the flocculation sedimentation tank through the central pipe and settles in the flocculation sedimentation tank for 1.5 hours. After the sludge and water are separated in the flocculation sedimentation tank, the sludge is concentrated in the sludge hopper of the flocculation sedimentation tank.

[0029] D. The concentrated sludge in the flocculation sedimentation tank is dehydrated by filter pressing to obtain dehydrated sludge. Example 3

[0030] The method for dehydrating sludge by using red mud instead of a coagulant aid comprises the following steps:

[0031] A. Dehydrated red mud with a solid content of 50% discharged from alumina production was diluted with water to a solid content of 7%, and stirred for 11 minutes to obtain a red mud coagulant aid;

[0032] B. The red mud coagulant prepared in step A is used to condition the ore mud with a solid content of 11%. The ratio of the red mud coagulant to the ore mud is as follows: dry weight of red mud coagulant: dry weight of ore mud = 6; 94;

[0033] C. Add anionic polyacrylamide flocculant with a molecular weight of 15-16 million to the sludge conditioned with red mud coagulant. The total dosage is 25g per ton of dry weight of sludge. The addition is done in two steps. First, add 65% of the anionic polyacrylamide to the sludge conditioned with red mud coagulant aid and stir in a pipeline mixer for 1.5 minutes. Then, add the remaining 35% of the anionic polyacrylamide at the end of the sludge conveying pipeline. Mix further for 1.5 minutes through a folded plate mixing gallery before flowing into the flocculation sedimentation tank. The sludge then enters the flocculation sedimentation tank for flocculation, coagulation, and concentration. After the addition of the anionic polyacrylamide flocculant, the sludge conditioned with red mud coagulant aid enters the flocculation sedimentation tank through the central pipe and settles in the flocculation sedimentation tank for 1.25 hours. After the sludge and water are separated in the flocculation sedimentation tank, the sludge is concentrated in the sludge hopper of the flocculation sedimentation tank.

[0034] D. The concentrated sludge in the flocculation sedimentation tank is dehydrated by filter pressing to obtain dehydrated sludge. Example 4

[0035] The method for dehydrating sludge by using red mud instead of a coagulant aid comprises the following steps:

[0036] A. Dehydrated red mud with a solid content of 55% discharged from alumina production was diluted with water to a solid content of 8%, and stirred for 13 minutes to obtain a red mud coagulant aid;

[0037] B. Use the red mud coagulant prepared in step A to condition the sludge with a solid content of 12%. The ratio of red mud coagulant to sludge is as follows: dry weight of red mud coagulant: dry weight of sludge = 5; 95;

[0038] C. Add anionic polyacrylamide flocculant with a molecular weight of 14-15 million to the sludge conditioned with red mud coagulant. The total dosage is 32g per ton of dry weight of sludge. The addition is done in two steps. The first step is to add 60% of the anionic polyacrylamide to the sludge conditioned with red mud coagulant and stir it in a pipeline mixer for 1.2 minutes. The second step is to add the remaining 40% of the anionic polyacrylamide at the end of the sludge conveying pipeline. The sludge is further mixed for 1.8 minutes in a folded plate mixing gallery before entering the flocculation sedimentation tank. After the addition of the anionic polyacrylamide flocculant, the sludge is fed into the flocculation sedimentation tank through the central pipe and settles for 0.9 hours. After the sludge and water are separated in the flocculation sedimentation tank, the sludge is concentrated in the sludge hopper of the flocculation sedimentation tank.

[0039] D. The concentrated sludge in the flocculation sedimentation tank is dehydrated by filter pressing to obtain dehydrated sludge.

[0040] experiment

[0041] Compared with the original one-time addition process, adding 80-120g lime powder / t of ore mud and 60-70g APAM / ton of ore mud to aid flocculation sludge dehydration process, the current process does not require the addition of lime powder, and the APAM dosage is reduced to 25-35g / ton of dry ore mud. The daily dry lime powder dosage is reduced by 1t and the mud increment with a moisture content of 40% is reduced by 1.7. The daily anionic polyacrylamide dosage is reduced by 300-350kg. The single operation time of the original plate and frame filter press to dehydrate the ore mud to a moisture content of 40% is reduced by more than 12 minutes, the total energy consumption of the ore mud dehydration workshop is reduced by 3.5%, and the red mud generated by the alumina industry is utilized as a resource.

[0042] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for dehydrating sludge by using red mud instead of a coagulant aid, characterized in that: The following steps are involved: A. Dilute the dehydrated red mud with a solid content of 40-60% discharged from alumina production with water to a solid content of 3% to 10%, and stir for 5 to 15 minutes to obtain a red mud coagulant aid; B. Using the red mud coagulant prepared in step A to condition the ore mud with a solid content of 10-13%; the ratio of the red mud coagulant to the ore mud is as follows: dry weight of red mud coagulant: dry weight of ore mud = 4-8:92-96; C. Add anionic polyacrylamide flocculant with a molecular weight of 1.2 million to 1.8 million to the sludge conditioned with red mud coagulant aid. The total dosage of the anionic polyacrylamide flocculant is 20 to 45 g per ton of dry weight of the sludge. The addition method is to add the flocculant in two steps, first adding 50% to 80% of the anionic polyacrylamide; after stirring and mixing evenly, add the remaining anionic polyacrylamide for the second time, further mix and mix, and then enter the flocculation sedimentation tank for flocculation, coagulation and concentration of the sludge; The method for adding the anionic polyacrylamide flocculant in step C is specifically as follows: For the first time, 50% to 80% of anionic polyacrylamide is added to the red mud coagulant conditioned sludge, and stirred in a pipeline mixer for 1 to 2 minutes; then the remaining anionic polyacrylamide is added for the second time at the end of the sludge conveying pipeline, and further mixed for 1 to 2 minutes through the folded plate mixing gallery, and then the water is poured into the flocculation sedimentation tank; D. The concentrated sludge in the flocculation sedimentation tank is dehydrated by filter pressing to obtain dehydrated sludge.

2. The method for dehydrating sludge by using red mud instead of a coagulant aid according to claim 1, characterized in that: The method for flocculation sedimentation in the flocculation sedimentation tank comprises the following steps: After adding anionic polyacrylamide flocculant, the red mud coagulation conditioning sludge enters the flocculation sedimentation tank from the central pipe of the flocculation sedimentation tank, settles in the flocculation sedimentation tank for 0.75 to 1.5 hours, and is concentrated in the mud hopper of the flocculation sedimentation tank after mud and water separation in the flocculation sedimentation tank.