Electrokinetic remediation, variably named as electromigration, electrokinetic decontamination or electroreclamation, uses a low-level direct current (DC) as the cleaning agent to extract radionuclides, heavy metals and mixed inorganic species from soils. So far, only a number of experiments have been carried out for the remediation of bottom-ash from municipal solid waste incinerator (MSWI). The electrokinetic extraction of heavy metals from ashes is limited by the high buffer capacity of the latter, especially when in alkaline condition; on the other hand, a great extent of chloride migration was proven. Reducing soluble salts content in ash improves the environmental characteristics in view of recycling. Limitation of contaminant leaching requires the application of extra safety measures when bottom ash from MSWI is used in (road) construction. Aim of this study was to test the electrochemical stabilization for the improvement of the quality of bottom ash – with respect to the leaching of copper, lead, barium and chlorides in particular – to the extent that this waste material could be used in (road) construction with lower risks of adverse effects on the surrounding environment. In order to buffer the OH- generated at the cathode during the electroreclamation, which cause precipitation of metals as hydroxides, phosphoric acid has been used: such a choice was done also to provide the system with phosphate anions, which are particularly suitable in immobilizing heavy metals. Seven different tests were carried out, varying the following experimental conditions: cell voltages, phosphoric acid amount (at least 5-10 ml per kg of ash), and time of treatment (at least 2-3 days). The UNI EN 12457/2 method was followed to compare the leaching of pollutants from untreated and treated specimens. The treated ash presented a low water content (10-12%), which significantly affected chloride migration: a 85% of extraction was found at the end of the best test. The action of phosphates on the stabilization of lead and barium was confirmed, the leaching being reduced by a 95%. The release of copper still exceeded the law limits, and the use of other stabilizers such as sulphides or soluble silicates could allow a better stabilization.
Electrokinetic stabilization of wastes in view of recycling: the case of the bottom-ash from the MSWI of Milan
DE BATTISTI, Achille;FERRO, Sergio;
2006
Abstract
Electrokinetic remediation, variably named as electromigration, electrokinetic decontamination or electroreclamation, uses a low-level direct current (DC) as the cleaning agent to extract radionuclides, heavy metals and mixed inorganic species from soils. So far, only a number of experiments have been carried out for the remediation of bottom-ash from municipal solid waste incinerator (MSWI). The electrokinetic extraction of heavy metals from ashes is limited by the high buffer capacity of the latter, especially when in alkaline condition; on the other hand, a great extent of chloride migration was proven. Reducing soluble salts content in ash improves the environmental characteristics in view of recycling. Limitation of contaminant leaching requires the application of extra safety measures when bottom ash from MSWI is used in (road) construction. Aim of this study was to test the electrochemical stabilization for the improvement of the quality of bottom ash – with respect to the leaching of copper, lead, barium and chlorides in particular – to the extent that this waste material could be used in (road) construction with lower risks of adverse effects on the surrounding environment. In order to buffer the OH- generated at the cathode during the electroreclamation, which cause precipitation of metals as hydroxides, phosphoric acid has been used: such a choice was done also to provide the system with phosphate anions, which are particularly suitable in immobilizing heavy metals. Seven different tests were carried out, varying the following experimental conditions: cell voltages, phosphoric acid amount (at least 5-10 ml per kg of ash), and time of treatment (at least 2-3 days). The UNI EN 12457/2 method was followed to compare the leaching of pollutants from untreated and treated specimens. The treated ash presented a low water content (10-12%), which significantly affected chloride migration: a 85% of extraction was found at the end of the best test. The action of phosphates on the stabilization of lead and barium was confirmed, the leaching being reduced by a 95%. The release of copper still exceeded the law limits, and the use of other stabilizers such as sulphides or soluble silicates could allow a better stabilization.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
