One of the procedures to handle liquid radioactive waste is by filtration process. To do this process, suitable filter should be used because of radioactive nature of the waste. Ceramic filter is one of the suitable filters that could be used for this purpose. This paper will discuss about producing ceramic filter from local clay and test its performance. Performance of the filter is given by its flux, compressive strength, Decontamination Factor (DF) and adsorption efficiency. The results show that there are almost no effects of casting pressure on both flux and compressive strength of ceramic filter, but zeolite addition produces different effect. The higher concentration of zeolite will decrease the filter flux and increase filter compressive strength. The optimal composition from this research is 70% w/o clay-25% w/o zeolite-5% w/o charcoal. It has adsorption efficiency (60.36) and Decontamination Factor (2.52). Besides, Sr concentration after filtration is still higher than environmental standard for Sr-90 and more studies are still needed.
Liquid radioactive wastes vary in solution composition and the radionuclide they contain. They came from spent fuel reprocessing, reactor coolant, drain, and laundry waste water. Liquid wastes should be treatment for radioactive material removal or volume reduction as coagulation-sedimentation, filtration, evaporation, and ion exchange [
For serious nuclear accident, application of Micro Electro Mechanical Systems (MEMS) inertial impactor filter has been studied. It can filtrate and collect 1 - 3 microns aerosol particles without changing filter paper because MEMS can significantly reduce the flow resistance in filtering process. This technique uses particle inertia for separating and collecting, so based on this effect, MEMS inertial impactor model’s geometry is designed into a T tube with flat nozzle inlet and entrance width is far less than its length [
Ceramic is available for wide application such as filter, membrane catalytic substrate and structural panel. They have low thermal expansion and thermal conductivity, high permeability and chemical inertness. Ceramic made from several materials include silicon carbide, alumina, glasses, cordierite as well as solid waste [
Ceramic water filter could be manufactured from local clay and sawdust. This filter was low cost but efficient for treatment drinking water in developing country. But most of available ceramic filters were not produced to treat heavy metal like zinc, nickel, manganese, lead, chromium and copper. So calcium silicate can mixed in its forming step and will act like tobermorite, to trap and absorb heavy metal in its pore [
Except for filtration, porous medium was also used for Magnetohydrodynamic (MHD) application. MHD is a combination between magneto (magnetic), hydro (liquid) and dynamic (movement of particles) in which magnetic field induces current flows in a dynamic fluid and creates forces on the fluid. There is a wide application of MHD through a porous channel such as diffusion technology, transpiration cooling, hemodialysis processes, and flow control in nuclear reactor. Some research shows that volume fraction of nanoparticles has affected MHD stagnation point flow, heat and mass transfer as well as entropy generation [
Heat and mass transfer through porous medium also has a great interest in many researchers in past decades. Implementing porous media such as metal foam in compact electronic cooling became popular due to their high heat transfer area per unit volume, energy absorbent, high temperature tolerance as well as high mechanical strength. Mohammadian et al. [
The fluid flows in porous medium are important applications in engineering such as filtration and purification process. Equation of fluid flows inside channel in porous medium is a set of non-linear Differential Equation. Homotopy Pertubation Method (HPM) is one of the novel methods for solving non-linear differential equation which is used by various researchers. Seyf and Mousevi [
Indonesia has abundant amount of ceramic’s raw material like local clay and zeolite. Zeolite is also known as an absorbent. It has good capability and selectivity as well as low cost. Zeolite’s selectivity resulted from their structure: aluminosilicate framework, exchangeable cations and zeolitic water. The aluminosilicate framework will define the crystalline structure. These crystalline structures are important in their sorption capability due to dimensions and locations of the channels through which molecule diffuses into the inter-crystalline free volume. Natural zeolites are also considered for radioactive waste treatment due to their high cation-exchange capacities and selectivity for Cs, Ba and Sr [
Ceramic filter material that was used in this research were clay from Godean (western part of Yogyakarta city), zeolite from Gunung Kidul (southern part of Yogyakarta city) and charcoal powder made from kesambi wood (Schleichera oleosa). Clay consists of Si 24.8% w/o, Al 10.71% w/o and Mg 0.136% w/o, was used as ceramic base material. It has molecular formula Al2O3∙2SiO2∙2H2O. Charcoal contains 85% - 98% w/o carbon. Charcoalin ceramic composition was used as pore maker. During thermal decomposition, charcoal powder was removed into carbon monoxides and carbon dioxide gases. After thermal decomposition process, the pores were created in the material [
The preparations of clay, charcoal and zeolite were done separately. Clay was sliced into chips and dried. The dried clay then ground and reheated in oven with temperature 50˚C to avoid granulation during sieving. Zeolite was ground, sifts using 200 mesh sieve and activated chemically using HF 1% solution, then neutralized and dried using oven. Charcoal was dried, ground and sifts using 200 meshsieve.
Ceramic filter was produced by mixing zeolite-charcoal and clay. There were four different weight compositions with the variations in the amount of charcoal-zeolite. The composition was(in % w/o) clay 70%-zeolite 0%-charcoal 30%, clay 70%-zeolite 5%-charcoal 25%, clay 70%-zeolite 10%-charcoal 20%, clay 70%-zeolite 20%-charcoal 10%, clay 70%-zeolite 25%-charcoal 5%.
Each composition was pressed with casting pressing variations: 5.73 MPa, 7.01 MPa, 8.28 MPa and 9.55 MPa. After casting, filter was air dried and heated in furnace until it reach 1000˚C and was hold for 4 hours then it was cooled inside furnace to room temperature. Flux testing using water and pressure testing were done to ceramic filter. The optimal composition result from these tests then soaked in Sr(NO3)2 solution to simulate liquid waste that contains radioactive Sr-90 for radioactive filtering capacity test.
Components | Compositions (%) |
---|---|
SiO2 | 64.74 - 66.59 |
Al2O3 | 13.89 - 14.17 |
CaO | 1.64 - 2.81 |
Fe2O3 | 0.96 - 1.64 |
MgO | 0.60 - 0.94 |
Na2O | 1.23 - 1.47 |
K2O | 0.95 - 1.27 |
MnO | 0.16 - 0.18 |
H2O | 2.22 - 2.61 |
The parameters in this research are flux, porosity percentage, compressive strength, Decontamination Factor (DF) and adsorption efficiency.
Flux (J) was determined using the following formula
where V is volume of solution, A is surface area and t is flowing time.
Compressive strength (σ) is formulated as
where F is force and A is surface area
Porosity percentage, %P is known by its water adsorption power, and was measured using formula as
where mb = weight of wet sample, mk = weight of dry sample
Decontamination factor (DF) is ratio between pre-treatment liquid waste activity (A0) and post-treatment one (AF). Post-treatment activity means that liquid activity after being processed.
Filter performance, such as flux, affected by density and size of filter’s pores. Organic burn-out material will combust in high temperature heating and leaving cavities in fired clay. These cavities made water flow easily through it compared to pores in clay so flow rate per area will increase [
Casting Pressure (MPa) | Flux (L/m2∙jam) | ||||
---|---|---|---|---|---|
Zeolite 0%-Charcoal 30% | Zeolite 5%-Charcoal 25% | Zeolite 10%-charcoal 20% | Zeolite 20%-charcoal 10% | Zeolite 25%-Charcoal 5% | |
5.73 | 8.24 ± 0.19 | 14.91 ± 0.11 | 14.37 ± 0.16 | 6.36 ± 0.13 | 6.61 ± 0.26 |
7.01 | 7.22 ± 0.00 | 21.82 ± 1.38 | 15.58 ± 0.02 | 5.83 ± 0.48 | 8.23 ± 0.13 |
8.28 | 8.34 ± 0.00 | 20.13 ± 0.91 | 16.71 ± 0.20 | 7.07 ± 0.85 | 6.22 ± 0.30 |
9.55 | 6.89 ± 0.02 | 14.57 ± 0.16 | 15.27 ± 0.69 | 5.80 ± 0.28 | 6.10 ± 0.05 |
Casting Pressure (MPa) | Porosity (%) | ||||
---|---|---|---|---|---|
Zeolite 0%-Charcoal 30% | Zeolite 5%-Charcoal 25% | Zeolite 10%-charcoal 20% | Zeolite 20%-charcoal 10% | Zeolite 25%-Charcoal 5% | |
5.73 | 40.59 ± 1.22 | 49.04 ± 0.10 | 41.48 ± 1.38 | 38.13 ± 0.11 | 30.41 ± 0.13 |
7.01 | 42.41 ± 0.05 | 46.56 ± 0.13 | 43.31 ± 0.14 | 37.78 ± 0.15 | 35.42 ± 0.87 |
8.28 | 42.99 ± 0.36 | 49.98 ± 0.29 | 48.27 ± 0.96 | 37.25 ± 0.50 | 31.66 ± 1.58 |
9.55 | 39.99 ± 0.99 | 47.77 ± 0.04 | 45.60 ± 0.46 | 39.55 ± 1.77 | 29.92 ± 0.79 |
know that casting pressure variation has no effect on porosity but zeolite content in filter composition has. When zeolite content is increased and the charcoal powder as a pore-maker decreased. At high temperature, charcoal powder is burned into gas and made porous material, so if proportion of charcoal powder decreased, the percent of porosity would decrease [
Porosity decrease means filter will have small pores. In pores perspectives, small pores size increases friction between fluid and porous structure, so permeability of porous medium will decrease and lead to increasing pressure drop along the channel. Lower permeability of porous material due to decreasing in Darcy number, prevents penetrating of the fluid therefore less amount of flow enters the channel and lower velocity is attained [
casting pressure.
Increasing zeolite composition will increase compressive strength. Zeolite has a SiO4 or AlO4 tetrahedral structure with cages and cavities as secondary structures due to different arrangement of tetrahedral structures [
The less pores will make filter stronger. From
Casting Pressure (MPa) | Compressive Strength (MPa) | ||||
---|---|---|---|---|---|
Zeolite 0%-Charcoal 30% | Zeolite 5%-Charcoal 25% | Zeolite 10%-charcoal 20% | Zeolite 20%-charcoal 10% | Zeolite 25%-Charcoal 5% | |
5.73 | 18.30 ± 1.32 | 24.78 ± 0.14 | 59.07 ± 5.91 | 138.45 ± 42.50 | 200.91 ± 11.42 |
7.01 | 11.93 ± 2.58 | 24.53 ± 0.80 | 51.65 ± 7.27 | 165.82 ± 6.81 | 160.00 ± 4.37 |
8.28 | 11.61 ± 0.03 | 26.16 ± 3.92 | 50.05 ± 9.10 | 127.28 ± 22.57 | 170.53 ± 10.14 |
9.55 | 11.33 ± 0.52 | 29.03 ± 1.10 | 37.60 ± 5.92 | 166.3 ± 0.38 | 209.27 ± 44.40 |
Flux test result shows that filter with 25 % w/o zeolite content, which is formed using 7.01 MPa casting pressure, has good enough flux capability. It also has the lowest porosity value. Compressive strength shows that filter with 25% w/o zeolite content has the highest value. For radioactive filtering capacity test, we use the optimal value of filter composition forming. The filter composition optimal value is based on flux value and compressive strength value. Filter should have high compressive strength but also the fluid can easily passes through it. So the optimal composition result from flux test and compressive strength test is clay 70%-zeolite 25% and charcoal 5%. Then filter formed using this composition is soaked in Sr-90 waste simulation using Sr(NO3)2 solution for filtering capacity test. The initial concentration of Sr solution is 65 ppm. The radioactive filtering capacity test result shown is
This filter made from 70% w/o clay-25% w/o zeolite-5% w/o charcoal shows the value of adsorption efficiency is 60.36 and Decontamination Factor (FD) is 2.52. The FD value resulted from this filter is lower than FD ultrafiltration using Polyethersulfone (PES), Polysulfone (PS) and Surface Modified (SMM) Membranes which have value between 35 - 230 [
Filter made from | Sr concentration (ppm) before filtration process | Sr concentration (ppm) after filtration process | Adsorption efficiency (%) | Decontamination Factor |
---|---|---|---|---|
70% w/o clay-25% w/o zeolite-5% w/o charcoal | 65 | 25.77 | 60.36 | 2.52 |
did not measure filter pore size but Mopoung et al. [
The Sr concentration after filtration is 25.77 ppm which is equal to 3.54 Ci/l(1.3 × 1011 Bq/l). This value is still higher than environmental standard for Sr-90 (4 × 103 Bq/l) [
The research explores local material which is potential as ceramic filter to handle liquid radioactive waste. The research aim is to find an optimal composition of local clay-zeolite-charcoal and casting pressure that have high mechanical strength and good capability for adsorbing Sr component but also have high flux that flows through it. Ceramic filter was made from Clay from Godean, Zeolite from Gunung Kidul and Kesambi Charcoal powder with various mixed composition and casting pressure.
The results show that there are almost no effects of casting pressure on both flux and compressive strength of ceramic filter, but zeolite addition has. The higher concentration of zeolite will decrease the filter flux and increase filter compressive strength. The optimal composition from this research is 70% w/o clay-25% w/o zeo- lite-5% w/o charcoal. It has adsorption efficiency (60.36) and Decontamination Factor (2.52). Besides, Sr concentration after filtration is still higher than environmental standard for Sr-90 and more studies are still needed.
In addition to liquid radioactive waste treatment purposes, ceramic filter produced from this research is also potential for drinking water treatment, but more studies in this purpose are still needed.
The authors gratefully acknowledge the support of the Department of Nuclear Engineering and Engineering Physics, Universitas Gadjah Mada.
Widya Rosita,Ferdiansjah ,Antonius Wisnu Yogha Pamungkas,Tri Joko Prihatin, (2016) Indonesia’s Local Material Effect in Clay-Based Ceramic Filter Fabrication as an Alternative for Liquid Radioactive Waste Processing Material. Materials Sciences and Applications,07,371-379. doi: 10.4236/msa.2016.77033