Description:DESCRIPTION:
Field of the invention:
[0001] The present disclosure generally relates to the technical field of and in specific relates a dual geosynthetic clay liner (GCL) system for phosphogypsum pond baselining that utilizes GCL in place of compacted clay liner (CCL).
Background of the invention:
[0002] Phosphogypsum stockpiles without proper measures have contaminated subsoil and groundwater in the past. Recent regulations in some countries prohibit dumping phosphogypsum directly on land due to its contamination and leaching potential. The standardised board recommends a composite baseliner system for phosphogypsum disposal, with a lower layer of compacted clay or compacted amended soil at least 60 cm thick. The upper layer of the composite liner system is a mechanically compacted and neutralized phosphogypsum layer placed above a drainage layer.
[0003] In some locations, suitable clay may not be available for the lower layer of the composite baselining system. In these cases, transporting clay from distant locations can be time-consuming and expensive. This research proposes an alternative to the recommended compacted clay liner for the lower layer of the composite liner system, which is a viable option in cases where locally sourced suitable clay is not readily available.
[0004] Low-permeability barriers can be used in many different places to prevent contact between a dangerous or potentially dangerous material and the environment around it. The word "containment" means keeping something in a certain place, such as to prevent it from coming into contact with the environment around it. The substance being contained can be a dangerous or mostly harmless liquid or solid.
[0005] Non-limiting settings in which it can be desirable to provide containment of a substance include, for example, retention of contaminated fluids within landfills, retention ponds, mining sites, and hazardous materials repositories such as those housing heavy metals, fly ash, coal ash, radioactive waste, and mining waste. Fluid containment within non-contaminated or substantially non-contaminated sources such as, for example, livestock ponds, decorative ponds, reservoirs, and like holding locations can also be highly desirable.
[0006] Existing composite liner systems are typically used in landfill covers and waste disposal sites. They consist of multiple layers of different materials, each of which serves a different purpose. The compacted clay liner is typically used as the lower layer in the composite liner system. Hydraulic conductivity is a measure of how easily water can flow through a material. A high hydraulic conductivity means that water can flow through the material easily. Compacted clay liners have a relatively high hydraulic conductivity, which means that they are not as effective at preventing water from infiltrating through them. This can be a problem for applications such as landfill covers, where it is important to prevent leachate from contaminating the surrounding environment.
[0007] Further, Compacted clay liners are thick and heavy, and they require a lot of space to install. This can be a problem for applications where space is limited. Compacted clay liners are susceptible to damage during handling and installation. If a clay liner is damaged, it can be difficult to repair. This can create pathways for water to infiltrate the liner and contaminate the surrounding environment.
[0008] Therefore, there is a need for a dual geosynthetic clay liner (GCL) system for phosphogypsum pond baselining that utilizes GCL in place of compacted clay liner (CCL). There is also a need for a dual GCL system that provides effective permeability when exposed to neutralized phosphogypsum over time. There is also a need for a cost-effective GCL system that requires less skilled labour for installation, and has a self-healing capacity when damaged during handling and installation.
Objectives of the invention:
[0009] The primary objective of the invention is to provide a dual geosynthetic clay liner (GCL) system for phosphogypsum pond baselining that utilizes GCL in place of compacted clay liner (CCL).
[0010] The other objective of the invention is to install a dual GCL system that provides effective permeability when exposed to neutralized phosphogypsum over time.
[0011] The other objective of the invention is to provide a cost-effective dual GCL system that aids the phosphate-based fertilizer industry in establishing baselining systems.
[0012] Another objective of the invention is to provide a dual GCL system that requires less skilled labour for installation.
[0013] The other objective of the invention is to provide a dual geosynthetic clay liner system with at least two geosynthetic clay liners (GCLs) that occupies less space compared to CCL.
[0014] Yet another objective of the invention is to provide a dual GCL system that has a self-healing capacity when damaged during handling and installation.
[0015] Another objective of the invention is to provide a dual geosynthetic clay liner system with significantly lower hydraulic conductivity.
Summary of the invention:
[0016] The present disclosure proposes a dual geosynthetic clay liner system for phosphogypsum pond baselining. The following presents a simplified summary in order to provide a basic understanding of some aspects of the claimed subject matter. This summary is not an extensive overview. It is not intended to identify key/critical elements or to delineate the scope of the claimed subject matter. Its sole purpose is to present some concepts in a simplified form as a prelude to the more detailed description that is presented later.
[0017] In order to overcome the above deficiencies of the prior art, the present disclosure is to solve the technical problem to provide a dual geosynthetic clay liner (GCL) system for phosphogypsum pond baselining that utilizes GCL in place of compacted clay liner (CCL).
[0018] According to an aspect, the invention provides a method for utilizing geosynthetic clay liners in phosphogypsum ponds for dual geosynthetic clay liner systems. At first, at least two geosynthetic clay liners (GCLs) are installed above the subsoil. The two GCLs are placed at the lowest level of the dual geosynthetic clay liner system, specifically for phosphogypsum pond applications.
[0019] Next, a geomembrane is layered over the two GCLs. Later, a drainage layer is placed over the geomembrane. In specific, the geomembrane is a high-density polyethylene (HDPE) geomembrane. The drainage layer with high-density polyethylene (HDPE) perforated pipe is placed over the geomembrane. Further, the drainage layer is surrounded by silty sand drainage material with seepage connected to the surge pond.
[0020] Next, a compacted phosphogypsum layer is disposed over the drainage layer. In specific, the compacted phosphogypsum layer is a mechanically compacted phosphogypsum that is neutralized with 50% of fly ash and 1.6% of lime. Thereby, a dual geosynthetic clay liner system is obtained.
[0021] According to another aspect, the invention provides the two GCLs have thicknesses ranging between about 12 mm to 14 mm. Each GCL has thicknesses ranging between about 5 mm to 7 mm. The geomembrane has thicknesses equal to or greater than 1.5 mm. The compacted phosphogypsum layer has thicknesses of at least 500 mm with permeability of nearly 10-4 cm/s.
[0022] Further, objects and advantages of the present invention will be apparent from a study of the following portion of the specification, the claims, and the attached drawings.
Detailed description of drawings:
[0023] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate an embodiment of the invention, and, together with the description, explain the principles of the invention.
[0024] FIG. 1 illustrates a schematic diagram of a dual geosynthetic clay liner system, in accordance to an exemplary embodiment of the invention.
[0025] FIG. 2 illustrates a flowchart of a method for utilizing geosynthetic clay liners in phosphogypsum ponds for dual geosynthetic clay liner system, in accordance to an exemplary embodiment of the invention.
Detailed invention disclosure:
[0026] Various embodiments of the present invention will be described in reference to the accompanying drawings. Wherever possible, same or similar reference numerals are used in the drawings and the description to refer to the same or like parts or steps.
[0027] The present disclosure has been made with a view towards solving the problem with the prior art described above, and it is an object of the present invention to provide a dual geosynthetic clay liner (GCL) system for phosphogypsum pond baselining that utilizes GCL in place of compacted clay liner (CCL).
[0028] According to an exemplary embodiment of the invention, FIG. 1 refers to a schematic diagram of a dual geosynthetic clay liner system. The dual geosynthetic clay liner system is formed above the subsoil 112. The dual geosynthetic clay liner system comprises a compacted phosphogypsum layer 104, a drainage layer 106, a geomembrane 108, and at least two geosynthetic clay liners (GCLs) 100.
[0029] Phosphogypsum waste 102 is a by-product of the wet process of phosphoric acid production. The phosphogypsum waste 102 is a fine, white powder that is rich in calcium sulphate. The phosphogypsum waste 102 is disposed over the compacted phosphogypsum layer 104 of the dual geosynthetic clay liner system. The two GCLs 100 are used in the dual geosynthetic clay liner system for phosphogypsum ponds. The two GCLs 100 aid to prevent the phosphogypsum from leaching into the subsoil and groundwater.
[0030] In one embodiment, the two GCLs 100 have thicknesses ranging between about 12 mm to 14 mm. The geomembrane 108 has thicknesses equal to or greater than 1.5 mm. The compacted phosphogypsum layer 104 has thicknesses of at least 500 mm with permeability of nearly 10-4 cm/s.
[0031] In one embodiment, the compacted phosphogypsum layer 104 is a layer of phosphogypsum that is compacted and neutralized to reduce its acidity. This is done by mixing the phosphogypsum with lime and fly ash.
[0032] According to another exemplary embodiment of the invention, FIG. 2 refers to a flowchart 200 of a method for utilizing geosynthetic clay liners in phosphogypsum ponds for dual geosynthetic clay liner system. At step 202, the two GCLs 100 are installed above the subsoil 112. The two GCLs 100 are placed at the lowest level of the dual geosynthetic clay liner systems, specifically for phosphogypsum pond applications. Each GCL has thicknesses ranging between about 5 mm to 7 mm. In specific, Each GCL has thicknesses of 6.8 mm.
[0033] At step 204, the geomembrane 108 is layered over the two GCLs 100. Later, the drainage layer 106 is placed over the geomembrane 108. In specific, the geomembrane 108 is a high-density polyethylene (HDPE) geomembrane. The drainage layer 106 with high-density polyethylene (HDPE) perforated pipe is placed over the geomembrane 108. Further, the drainage layer 106 is surrounded by silty sand drainage material with seepage connected to the surge pond.
[0034] At step 206, the compacted phosphogypsum layer 104 is disposed over the drainage layer 106. In specific, the compacted phosphogypsum layer 104 is a mechanically compacted phosphogypsum that is neutralized with 50% of fly ash and 1.6% of lime.
[0035] According to another exemplary embodiment of the invention, single GCL is saturated in a large-cell triaxial test apparatus under specific pressure conditions, in accordance with ASTM D 6766-20a standards. Next, the saturated GCL is placed in a permeameter and exposed to the geomembrane 108 to facilitate potential cation exchange processes. Next, coefficient of permeability of the GCL is determined using variable head permeability tests on GCL samples exposed for different durations.
[0036] The values of the coefficient of permeability of exposed GCL after 4, 7, 14 and 28 days are listed in table 1.
[0037] Table 1:
No of days of exposure Coefficient of permeability (m/s)
0 3.8 x 10-12
4 8.0 x 10-9
7 8.25 x 10-9
14 8.3 x 10-9
28 8.31 x 10-9

[0038] From table 1 it is evident that the permeability of the single GCL samples increased after 96 hours of exposure to phosphogypsum, because the sodium cations in the bentonite are replaced by calcium cations from the phosphogypsum. The single GCL samples fails to achieve the standard requirement due the increase in the permeability value.
[0039] In order to achieve effective permeability value based on standard requirement another layer of GCL is added. The permeability of the two GCLs 100 are then exposed to them to the geomembrane 108. In one embodiment, the two GCLs 100 are installed in the base of the phosphogypsum pond, when the permeability of a single GCL exceeds the standard requirements. Finally, oedometer tests are conducted on the dual GCL system to determine the effective permeability.
[0040] For instance, table 2 depicts values of the coefficient of permeability of the two GCLs 100 exposed to geomembrane 108.
[0041] Table 2:
No of days of exposure Coefficient of permeability (m/s)
0 3.8 x 10-12
4 1.42 x 10-11
7 1.48 x 10-11
14 1.48 x 10-11
28 1.48 x 10-11

[0042] From Table 2, it is observed that there is no significant increase in effective permeability (k = 1 .48 x 10-11 m/s) when two GCLs 100 are laid. The dual GCL system of two GCLs met the permeability requirement of lower layer of the composite lining system.
[0043] The equivalency of GCL with respect to conventional compacted clay liner is further verified in terms of permittivity (Permeability across the layer). Permittivity = k/z, where k is the permeability and z is the thickness of the layer. From the calculations, it is found that the permittivity of two GCLs 100 is 1.08 x 10-9 s-1• which is less than the permittivity of compacted clay liner that is 1.67 x10-9 s-1.
[0044] The two GCLs 100 have a lower hydraulic conductivity (k) than CCLs. This means that two GCLs 100 are less permeable to water, which makes them more effective at preventing leachate from contaminating groundwater. The typical hydraulic conductivity of a GCL is k < 10-10 m/s, while the hydraulic conductivity of a CCL can be 10-100 times higher. GCLs are thin, lightweight materials that can be easily rolled out and placed in place. CCLs, on the other hand, are thick and heavy materials that require specialized equipment to install.
[0045] The efficiency of a GCL depends on the hydraulic conductivity of sodium bentonite, which is the sealing material in two GCLs 100. Sodium bentonite is a type of clay that is very effective at absorbing water and swelling. When sodium bentonite swells, it creates a tight seal that prevents liquids from passing through.
[0046] Table 3:
Characteristic GCL CCL
Hydraulic conductivity k < 10-10 m/s 10-100 times higher than GCL
Ease of installation Easy to roll out and place in place Requires specialized equipment to install
Effectiveness at preventing leachate contamination More effective Less effective

[0047] Table 3 depicts key advantages of two GCLs 100 over CCLs.
[0048] Numerous advantages of the present disclosure may be apparent from the discussion above. In accordance with the present disclosure, a dual geosynthetic clay liner (GCL) system is disclosed for phosphogypsum pond baselining that utilizes GCL in place of compacted clay liner (CCL).
[0049] The dual geosynthetic clay liner system provides effective permeability when exposed to neutralized phosphogypsum over time. The cost-effective dual geosynthetic clay liner system aids the phosphate-based fertilizer industry in establishing baselining systems. The dual geosynthetic clay liner system requires less skilled labour for installation.
[0050] The dual geosynthetic clay liner system with the two GCLs that occupies less space compared to CCL. The dual geosynthetic clay liner system has a self-healing capacity when damaged during handling and installation. The dual geosynthetic clay liner system has significantly lower hydraulic conductivity.
[0051] It will readily be apparent that numerous modifications and alterations can be made to the processes described in the foregoing examples without departing from the principles underlying the invention, and all such modifications and alterations are intended to be embraced by this application.
, Claims:CLAIMS:
I / We Claim:
1. A method for arrangement of a dual geosynthetic clay liner system for phosphogypsum pond baselining, comprising:
installing at least two geosynthetic clay liners (GCLs) (100) above subsoil (112);
laying a geomembrane (108) over the at least two GCLs (100), thereby placing a drainage layer (106) over the geomembrane (108); and
disposing a compacted phosphogypsum layer (104) over the drainage layer (106),
whereby the at least two GCLs (100) is placed at a lowest level of the dual geosynthetic clay liner system, specifically for phosphogypsum pond applications.
2. The method as claimed in claim 1, wherein the at least two GCLs (100) have a thicknesses varies between 12 mm to 14 mm.
3. The method as claimed in claim 1, wherein each GCL have a thicknesses varies between 5 mm to 7 mm.
4. The method as claimed in claim 1, wherein the geomembrane (108) is a high-density polyethylene (HDPE) geomembrane.
5. The method as claimed in claim 1, wherein the geomembrane (108) have a thicknesses equal to or greater than 1.5 mm.
6. The method as claimed in claim 1, wherein the drainage layer (106) with a high-density polyethylene (HDPE) perforated pipe is placed over the geomembrane (108).
7. The method as claimed in claim 1, wherein the drainage layer (106) is surrounded by a silty sand drainage material with seepage connected to surge pond.
8. The method as claimed in claim 1, wherein the compacted phosphogypsum layer (104) is a mechanically compacted phosphogypsum that is neutralized with 50% of fly ash and 1.6% of lime.
9. The method as claimed in claim 1, wherein the compacted phosphogypsum layer (104) have a thicknesses of at least 500 mm with a permeability nearly 10-4 cm/s.