Abstract
Flotation using cationic surfactants has been investigated as a rapid separation technique to dewater clinoptilolite ion exchange resins, for the decontamination of radioactive cesium ions (Cs+) from nuclear waste effluent. Initial kinetic and equilibrium adsorption studies of cesium, suggested the large surface area to volume ratio of the fine zeolite contributed to fast adsorption kinetics and high capacities (qc = 158.3 mg/g). Adsorption of ethylhexadecyldimethylammonium bromide (EHDa-Br) and cetylpyridinium chloride (CPC) surfactant collectors onto both clean and 5 ppm Cs+ contaminated clinoptilolite was then measured, where distribution coefficients (Kd) as high as 10,000 mL/g were evident with moderate concentrations CPC. Measurements of particle sizes confirmed that adsorption of surfactant monolayers did not lead to significant aggregation of the clinoptilolite, while < 8% of the 5 ppm contaminated cesium was remobilised. Importantly for flotation, both the recovery efficiency and dewatering ratios were measured across various surfactant concentrations. Optimum conditions were found with 0.5 mM of CPC and addition of 30 μL of MIBC frother, giving a recovery of ∼90% and a water reduction ratio > 4, highlighting the great viability of flotation to separate and concentrate the contaminated powder in the froth phase.
Highlights
Cesium-137 (137Cs) is a beta-emitting radioisotope, which is ob tained from the fission of uranium-235 and other isotopes in nuclear activities
This study examined the use of cationic surfactants to enhance the flotation of cesium contaminated powdered clinoptilolite, as an alter native to gravitational separation or the use of large resins in elution columns
The co-adsorption of ethylhexadecyldimethylammonium bromide (EHDa-Br) and cetylpyridinium chloride (CPC) surfactants onto both clean and 5 ppm Csþ contaminated clinoptilolite was measured, using surface tension measurements modelled with a Langmuir isotherm
Summary
Cesium-137 (137Cs) is a beta-emitting radioisotope, which is ob tained from the fission of uranium-235 and other isotopes in nuclear activities. In terms of its application in nuclear related fields, ion flotation and combined co-precipitation methods have been used to remove radioisotopes of cesium, strontium and cobalt, while fine particle flotation has been used for the separation of soils and as part of nuclear wastewater treatment processes (Aziz and Beheir, 1995; Charewicz et al, 2001; De Haro-Del Rio et al, 2015; Micheau et al, 2015; Ortiz-Oliveros and Flores-Espinosa, 2019; Ortiz-Oliveros et al, 2012; Shakir et al, 1993, 2007) It has been demonstrated recently as a viable technique for the separation of cesium contaminated colloidal clays (Zhang et al, 2017, 2019a). The flotation recovery of the contaminated cli noptilolite is optimised by varying both collector concentration and through the addition of MIBC frother, where importantly, both flotation removal and dewatering ratio are measured
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