Amphiphilic block copolymers as dual flocculation-flotation agents for rapid solid–liquid separation of radioactive wastes

The potential of poly(acrylic acid)-b-poly(n-butyl acrylate) as a dual flocculant-collector in combined flotation-sedimentation dewatering operations was investigated. The amphiphilic block copolymers were synthesised with consistent hydrophilic chain lengths and varying hydrophobic chain lengths. Various techniques were employed to analyse polymer behaviour at the air–water interface, being interfacial surface tension and dilational viscoelasticity. Polymer adsorption onto Mg(OH)2 was determined differentially using UV–Vis spectroscopy. Floc structures were determined using static light scattering, and flocculation-flotation performance was analysed using settling tests and flotation cell material balances. Results showed that longer hydrophobic chains were less surface-active, reducing foamability and water entrainment. The unimer-micellar adsorption transition points were identified through viscoelastic properties and particle adsorption studies. A distinct change in floc density and structure was observed for the largest molecular weight copolymer when the dosed concentration increased into the micellar adsorption region, suggesting a pseudo-bridging flocculation mechanism. Settling rates were significantly higher for particles flocculated with the larger molecular weight polymer, correlating to their larger aggregate sizes, especially over the micellar transition point. The largest molecular weight block copolymer demonstrated superior collection efficiency compared to the traditional surfactant, sodium dodecylsulfate (SDS), below its micellar adsorption transition point. However, beyond this point, the lack of exposed hydrophobic blocks hindered the hydrophobisation of Mg(OH)2 particles, reducing collection efficiency. Comparing flotation cell particle size distributions, it was suggested that recovery may be hydrodynamically hindered by the largest floc sizes, though recovery was observed for particles in the order of < 600 μm

Cardiac metastases

We report a case of esophageal cancer with symptomatic metastases to the heart; the patient was treated with short-course radiotherapy with good symptomatic relief. We reviewed the current literature regarding the epidemiology, clinical presentation, diagnostic tools, treatment modalities, and the prognosis of cardiac metastases. In this report we summarize the most recent autopsy studies (published between 1975 and 2007), in which we found an autopsy incidence of cardiac metastases of 2.3% among the general population, while the incidence among autopsies of cancer patients was 7.1%. Therefore, we share the opinion with others that there has been an increase in the incidence of cardiac metastases among cancer patients diagnosed after 1970, in comparison with the reported incidences in older series before 1970 (7.1% vs 3.8%; Kruskal-Wallis rank test; P = 0.039). Special attention was given to the role of radiotherapy in the management of cardiac metastases