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The regions of dispersion, coagulation precipitation, coagulation flotation, and redispersion were determined for aqueous bentonite-cationic surfactant and bentonite-cationic surfactant-polyacrylamide(PAA) systems. The region of coagulation flotation was markedly extended by the addition of PAA to both the lower and higher concentration regions of the cationic surfactant, hexadecyldimethylbenzylammonium chloride(HDBAC), and to the lower concentration region of bentonite. The phenomenon of coagulation flotation was investigated in detail and was applied to the removal of Co2+ ions and nuclear fission products, 144Ce and 155Eu, from an aqueous solution. The composition of the reagents for the maximum efficiency of bentonite flotation corresponded to that of the maximum efficiency of Co2+-ion flotation. The effect of the pH on the flotation efficiency was studied in particular. The maximum flotation efficiency of 96% was obtained at pH 11 for Co2+ ions, 86% at pH 9.7 for 144Ce, and 93% at pH 10.5 for 155Eu. ...

Using the Ames Salmonella-microsome system, we detected mutagenic activity in the exhaust from two kinds of 4-cycle gasoline engines of unregulated and regulated cars, and from diesel engines, as well as in the particulates from air collected in tunnels. The mutagenicity of particulates from a car equipped with a catalyst (regulated car), as compared with that from an unregulated car, was reduced very much (down to 500 from 4500 revertants/plate/m 3 in tester strain TA98). However, the mutagenicity of the ether-soluble acid and neutral fractions from the condensed water of emissions from a regulated car was still high (down to 2880 from 10 900 revertants/plate/m 3 in tester strain TA100). The mutagenic activity of emission exhaust from old diesel car engines was very high; the particulates showed 9140 and 19 600 revertants/plate/m 3 from strain TA98 incubated with an activating rat-liver S9 fraction. A small diesel engine of the type used for the generation of electric power or in farm machinery also produced exhaust with highly mutagenic particulates. The mutagenic activity of a methanol extract of particulate air pollutants collected in a highway tunnel showed 39 revertants/plate/m 3 toward strain TA98 and 87 toward strain TA100. The ether-soluble neutral fraction yielded 86 revertants/plate/m 3 from strain TA98 and 100 from strain TA100. This fraction also contained carcinogenic compounds, including benzo[ a ]pyrene, benzo[ e ]pyrene, benz[ a ]anthracene, benzo[ ghi ]perylene and chrysene. Very high mutagenic activity was detected, especially in the particulate air pollutants collected at night, in another tunnel on a superhighway: 60–88 revertants/plate/m 3 from strain TA100 for the sample collected by day, but 121–238, by night. Night traffic includes many more diesel-powered vehicles compared with gasoline-powered automobiles.