Cesium removal from aqueous solution using nanocomposite material

Removal of pollutants from industrial wastewater has become one of the most important issues recently for the increase in industrial activities, especially for heavy metals and radionuclides.Radioactive wastes containing radionuclides have been considered as the most hazardous environmnetal pollutants. In recent years, with the development of nuclear technology and industry, much radioactive waste is released into water, which leads to a direct threat to human health. The main factors why they are so hazardous are containing long half-life radionuclides, high fission yields, high mobility of radionuclides in the atmosphere and easiliy joining the metabolism of living beings. Radioactive wastes are generated from nuclear power plants operation and their accidents, radioisotop production laboratories, nuclear fuel recyciling processes and univercities radiochemistry laboratories. Among the most common radionuclides are Cs-137 and Sr-60. Because of this, removal of these two radionuclides is very important. Nowadays, many different methods have been applied to remove Cs(+1) and Sr (+2) ions from aquaeous radioactive wastes. Most important methods are ion exchange, precipitation, adsorption, solvent extraction elctrochemical and membran processes. Among them, adsorption is most preferred method because of low cost, thermal stability, resistance toward ionization radiation and compatible with the final form of waste. The role of dead biomasses in the removal of heavy metal toxic ions received an increased attention during recent past as due to its fairly good exchange capacity, large abundance, and also cost effectiveness. However, scanty reports appeared for the possible application of dead biomasses in the removal of radiotoxic ions particularly the radiocesium and radiostrontium. Recently, several low cost biosorbents have been used to remove heavy metals in investigations. Biosorbent used in this study is rice husk which is a agricultural residue. An innovative technology that has gained attention is the use of magnetic materials to solve environmental problems, such as accelerating the coagulation of sewage, removing radionuclides from milk, adsorption of organic dyes and oil spill remediation. The advance in magnetic nanoparticles (MNP) has made it possible to utilize several advantages of using nanosized sorbent without typical difficulty associated with separation of nanoparticles from solution. MNP can be easily separated from the treated solution by simple application of either a permanent or electro magnet. Their uses have been proven very successful, particularly in the field of bio-nanotechnology, where MNP functionalized with various functional groups have been used in the isolation and purifications of DNAs, proteins, or drug delivery. Magnetic nanoparticles have also been used for treatment and recovery of several heavy metals and radioactive nuclides such as uranium and plutonium. These magnetic materials show the following features: (i) they combine the adsorption properties of adsorbent such as activated carbon or clay with the magnetic properties of iron oxides. (ii) they can be used to remove different types of contaminants for example metals or organics from water, (iii) they can be removed from the medium by a simple magnetic seperation process. Nanocomposite particules usually need to be seperated by high performance centrifugations, this is the most important challenge with nanocomposites because this process is time consuming and expensive but using magnetic separation to seperate nanocomposites from medium is easy, fast, efficient and simple. Recently, when the literature studies were investigated, many type of adsorbent and technique were used to remove Cs and Sr from aquaeous waste solutions. In this study, an agricultural residue rice husk was heated to form its ash then it combined with iron oxide to synthesis nonocomposite material which was used to remove Cs and Sr from aquaeus waste solutions. Using batch method, adsorption parameters such as pH, temperature, adsorbent mass, contact time and shaking rate and initial Cs concentration were determined. After determination of optimum parameters, in existance of Sr, Cs adsorption capacity has been determined. Cs and Sr ions concentrations in supernatant were determined using flame atomic absorption spectrometer equipped with hallow cathode lamp of Cs and Sr as a radiation source and air/acetylene burner for atomization. After SEM-EDX analysis, we concluded that particul shape of RHA-Fe3O4 adsorbent is not regular. The surface area is almost twice larger then Rice Husk's surface area after rice husk was treated with Fe3O4 to compose RHA- Fe3O4. The surface area of RHA- Fe2O3 is 156.34 m2/g. From XRF analysis, it can be seen that RHA- Fe3O4 is composed of Fe, Si, S, Sb and Sn elements. Their percentage amounts are 71.50, 18.93, 9.42, 0.08 ve 0.06 respectively. To synthesize magnetic nanoparticle adsorbent, after rice husk washed with double-distilled water to remove dusk and soil, it stored in 0.1 M HCl solution for 76 hours then washed three times to remove chloride ions and dried at 105 oC for 2 hours. Dried rice husk was burn in a crucible at 800 oC for 5 hours in an oven to obtain rice husk ash. After these process, 10 mL 2M FeSO4.7H2O and 40 mL 1M FeCl3 solution were added to 400 mL beaker, heated up to 70 oC then 3.3 g rice husk ash was added into this solution while stirring. To precipitate iron oxide, 100 mL 5M NaOH solution was added drop by drop. To understand that the composite is magnetic or not, an electro magnet was brought closer to beaker and composite in beaker was coagulated on the electro magnet side of the beaker. Precipitate was washed distilled-deionized water and filtered with blue banded filter paper. Synthesized black coloured magnetic composite was dried in an oven at 80 oC for 2 hours. Dried magnetic composite was grinded into powder form. The effect of different variables such as pH, initial concentration, shaking time, adsorbent mass and temperature was studied. Optimum parameters we concluded as pH:6, 30 ppm initial concentration, 30 minutes shaking time, 0.010 g adsorbent mass and 25oC temperature. Maximum adsorption capacity was found 28,82 mg Cs/g RHA-Fe3O4. The equilibrium sorption data were described by the Langmuir and Freundlich isotherm models and the results could fit more with Langmuir model with correlation coefficient 0.943. From literature studies, it can be seen that cesium adsorption capacities change between 0.011 mg Cs/g adsorbent and 1965 mg Cs/g adsorbent. Magnetic nanocomposite rice husk ash shows higher adsorption capacity from polyacrylonitrile-zeolite nanocomposite, hexacyanoferrate-polymer composite, wallnut-shell, bentonite supported polymer and magnetic zeolite nanocomposite adsorbent.