The removal efficiency of heavy metals from offshore muds is enhanced in the presence of generated chlorine gas (Cl2). The tests showed a high removal efficiency of heavy metals at the anode end of cores after 24 hour...The removal efficiency of heavy metals from offshore muds is enhanced in the presence of generated chlorine gas (Cl2). The tests showed a high removal efficiency of heavy metals at the anode end of cores after 24 hours of EK application. In the initial tests, high electrokinetic flow potential was achieved;however, high levels of chlorine gas were produced in the high-salinity environments. The process was improved by controlling and maintaining a certain fraction of the chlorine gas (Cl2) in place. The pH was controlled by the chlorine gas maintained in-situ and transported from the anode to cathode. The transports of four heavy metals were evaluated in this study. The chlorine gas can have two impacts on the transport of metals in the system. One is to oxidize the metal ions to a higher oxidation state and the second is to form chloride complexes, which have higher mobility in the system. Determination of oxidation state and the subsequent metal chloride complex are left for future research.展开更多
Hazardous waste dechlorination reduces the potential of creating dioxins during the incineration process. To investigate the salt effect on waste dechlorination, molten hydroxides with a low melting temperature were u...Hazardous waste dechlorination reduces the potential of creating dioxins during the incineration process. To investigate the salt effect on waste dechlorination, molten hydroxides with a low melting temperature were utilized for the pre-dechlorination and decomposition of chlorine-containing organic wastes(COWs) including trichlorobenzene(TCB),perchloroethylene, hexachlorobenzene and chlordane. The results showed that a eutectic mixture of caustic sodium and potassium hydroxides(41 wt.% NaOH and 59 wt.% KOH) led to a low melting point below 300°C and a relatively high chlorine retention efficiency(CRE) with TCB as a representative COWs. The amounts of hydroxides, reaction time, and temperature all had notable influence on CRE. When the mass ratio of hydroxides to TCB reached 30:1,approximately 98.1% of the TCB was destroyed within 2.5 hr at 300°C with CRE of 71.6%.According to the residue analysis, the shapes of reaction residues were irregular with particles becoming swollen and porous. The benzene ring and C–Cl bonds disappeared, while carboxyl groups formed in the residues. The stripped chlorine was retained and condensed to form chloride salts, and the relative abundance of the chloride ions associated with the mass of TCB in residues increased from 0 to 75.0% within the 2.5 hr reaction time. The observed concentration of dioxins in residues was 5.6 ngTEQ/kg. A reaction pathway and possible additional reactions that occur in this dechlorination system were proposed. Oxidizing agents may attack TCB and facilitate hydrogenation/dechlorination reactions, making this process a promising and environmentally friendly approach for chlorine-containing organic waste treatment.展开更多
文摘The removal efficiency of heavy metals from offshore muds is enhanced in the presence of generated chlorine gas (Cl2). The tests showed a high removal efficiency of heavy metals at the anode end of cores after 24 hours of EK application. In the initial tests, high electrokinetic flow potential was achieved;however, high levels of chlorine gas were produced in the high-salinity environments. The process was improved by controlling and maintaining a certain fraction of the chlorine gas (Cl2) in place. The pH was controlled by the chlorine gas maintained in-situ and transported from the anode to cathode. The transports of four heavy metals were evaluated in this study. The chlorine gas can have two impacts on the transport of metals in the system. One is to oxidize the metal ions to a higher oxidation state and the second is to form chloride complexes, which have higher mobility in the system. Determination of oxidation state and the subsequent metal chloride complex are left for future research.
基金supported by the National Natural Science Foundation of China(No.21677112)the Science and Technology Program of Ministry of Housing and Urban–Rural Development(No.2015-K7-021)
文摘Hazardous waste dechlorination reduces the potential of creating dioxins during the incineration process. To investigate the salt effect on waste dechlorination, molten hydroxides with a low melting temperature were utilized for the pre-dechlorination and decomposition of chlorine-containing organic wastes(COWs) including trichlorobenzene(TCB),perchloroethylene, hexachlorobenzene and chlordane. The results showed that a eutectic mixture of caustic sodium and potassium hydroxides(41 wt.% NaOH and 59 wt.% KOH) led to a low melting point below 300°C and a relatively high chlorine retention efficiency(CRE) with TCB as a representative COWs. The amounts of hydroxides, reaction time, and temperature all had notable influence on CRE. When the mass ratio of hydroxides to TCB reached 30:1,approximately 98.1% of the TCB was destroyed within 2.5 hr at 300°C with CRE of 71.6%.According to the residue analysis, the shapes of reaction residues were irregular with particles becoming swollen and porous. The benzene ring and C–Cl bonds disappeared, while carboxyl groups formed in the residues. The stripped chlorine was retained and condensed to form chloride salts, and the relative abundance of the chloride ions associated with the mass of TCB in residues increased from 0 to 75.0% within the 2.5 hr reaction time. The observed concentration of dioxins in residues was 5.6 ngTEQ/kg. A reaction pathway and possible additional reactions that occur in this dechlorination system were proposed. Oxidizing agents may attack TCB and facilitate hydrogenation/dechlorination reactions, making this process a promising and environmentally friendly approach for chlorine-containing organic waste treatment.
