To investigate the structure and dynamics of water in mixed solutions including laponite clay particles and poly(ethylene oxide) (PEO), we measured the Raman spectra of the mixed solutions in the temperature range 283-313 K. The results show that the vibrational energies of the O-H stretching modes in the mixed solutions depend on the water content and temperature. The energy shifts of the O-H stretching modes are attributed to changes in the water structure. By applying a structural model of bulk water to the spectra in the O-H stretching region, the local structures of water in the solutions were analyzed. The result shows that the formation probability of hydrogen bonds in the solutions decreases as the water content decreases. Laponite and PEO have effects to disrupt the network structure of hydrogen bonds between water molecules. Further, it was found that laponite and PEO cause increase in the strength of hydrogen bonds of surrounding water,although the strength of the hydrogen bonds increases with the order water-laponite < water-water < water-PEO. It is concluded that water in laponite-PEO mixed solutions has a less-networked structure with strong hydrogen bonds compared with bulk water.
To comply with zinc effluent regulations, we investigated the influence of plating chemicals on zinc removal from zinc chloride solutions by coagulation with sodium hydroxide. Plating chemicals including ethylenediaminetetraacetic acid disodium salt (EDTA・2Na) , ammonium chloride, sodium citrate, triethanolamine (TEA) , sodium diphosphate, and potassium dihydrogen phosphate decrease zinc removal capabilities. The zinc removal capability in the solutions depends on the concentrations of additive compounds. Especially, the addition of EDTA・2Na and sodium diphosphate exert an important influence that is attributable to the complex forming reaction of zinc and EDTA・2Na. For the addition of 8.8 mg/L EDTA・2Na, removal of zinc from the solutions and exceeding the effluent regulation value of zinc was difficult. Furthermore, to reduce compounds interfering in wastewater, we examine emissions management. Results demonstrated that the drain of barrel processing increases the interfering compounds in wastewater. Plating chemicals disturb the zinc wastewater treatment.
Heavy metals such as zinc are widely used in plating plants for the processing of material surfaces; therefore, an adequate wastewater treatment is required afterwards to comply with wastewater regulations. However, the presence of chemicals such as degreasing agents in the wastewater generated from the plating process inhibits the formation of hydroxides, thereby making treatment of wastewater and compliance with the stipulated regulations difficult. Herein, the effects of fine bubbles on oil cleaning and wastewater treatment were investigated for developing an alternative cleaning technology to degreasing agents. The concentration of fine bubbles significantly affected the oil cleaning. The fine bubbles demonstrated remarkable cleaning of highly viscous oil, which was difficult to remove using pure water. The high cleaning effect of fine bubbles on oil was achieved because of the hydrophobic interaction of the bubbles. Furthermore, a decrease in cleaning effect was observed for samples with uneven shapes, which was attributed to the difficulty in penetration of fine bubbles in materials with irregularities. Furthermore, fine bubble cleaning exhibited better efficiency for wastewater treatment than degreaser cleaning. Therefore, fine bubble cleaning is speculated to be an excellent cleaning technology with high oil cleaning effectiveness and improved wastewater treatability.
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