The effects of hydrolysable metal salts on the flotation of potato starch with anionic surfactant, sodium dodecylsulfate, were investigated. It was presented that negatively charged starch surface was activated by the hydrolysable metal salts of Al(III), Fe(III), Cu(II) and Ni(II). The pH range in which the activation was observed ranged from the precipitation pH of each metal hydroxide to the isoelectric point, IEP, of each hydroxide precipitate. SEM images indicated that starch particles were covered with hydroxide precipitate above the precipitation pH. The results of adsorption test and micro electrophoresis indicated that the effect of adsorbed hydroxy complex was not sufficient to reverse the negative charge of starch surface. These results suggested that in the anionic flotation of starch it was not hydroxy complexes but hydroxide precipitates that acted as an activating species which modified the starch particle surface.
Flotation experiments of potato starch particle with several collectors; sodium dodecylsulfate and sodium oleate as anionic collectors, sorbitan monolaurate as a nonionic collector and dodecylammonium and dodecyltrimethylammonium salts as cationic collectors, were carried out. With anionic and nonionic collectors, good floatability was not observed, whereas the starch particles were successfully recovered with cationic collectors. The results indicated that the surface hydrophilic/hydrophobic property of the starch particle could be modified with cationic collectors.The result of microelectrophoretic measurement showed that the surface of the starch particle is negatively charged in water, and therefore, cationic collector adsorbs electrostatically onto the starch particle. The results of adsorption experiment showed that neutral amine molecules adsorbed onto the starch surface and/or absorbed into the starch particle. It was suggested that capillary condensation or similar phenomena stripped neutral molecules from the water phase.
Establishing economic treatment technology for safe disposal of photo-processing waste (PW) has most recently become an urgent environmental concern. This paper describes a new biological treatment process for PW using sulfur-oxidizing bacteria (SOB) in conjunction with activated carbon (AC). Batch-type acclimation and adsorption experiments using SOB/PAC, SOB/PNAC, and SOB reactor type systems demonstrated that AC effectively adsorbs the toxic/refractory compounds which inhibit thiosulfate oxidization of SOB in PW. Thus, to further clarify the effect of AC, we performed a long-term (≈ 160 d) continuous-treatment experiment on 4- to 8-times dilution of PW using a SOB/GAC system which simulated a typical wastewater treatment system based on an aerobic activated sludge process that primarily uses acclimated SOB. The thiosulfate load and hydraulic retention time (HRT) were fixed during treatment such that they ranged from 0.8-3.7 kg S2O32-/l/d and 7.7-1.9 d, respectively. As expected, continuous treatment led to breakthrough of the adsorption effect of GAC. Renewing the GAC and continuing treatment for about 10 d demonstrated good treatment effectiveness.
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