Every year, millions of tonnes of hazardous waste are generated in the world. Because of the hazardous waste leakage in the past and of the inefficiencies in waste handling techniques, thousand of sites throughout the world are contaminated by heavy metals (HMs). Accumulation of HMs in the soil constitute a health risk to both animals and human beings. In this chapter mainly membrane (hybrid) techniques, to be applied in water treatment from soil remediation will be reviewed and discussed with the aim to remove/recovery metals and recycling water. In some cases a comparison with the results obtained with other techniques will be performed. Cleanup of soils contaminated with toxic metal ions represents one of the most difficult tasks, owing to their toxicity and the long-lasting adsorption of ions by soils. The developed technologies are based on two principles: (1) immobilization, (2) mobilization. Wide used mobilization techniques to remove metals from soil are the chelant assisted soil washing and the Electrodialytic Remediation (EDR) of polluted soils. The EDR technique employs an ion-exchange membrane in conjunction with the electrokinetic transport, and represents a very time-consuming and energy-consuming method for soil remediation. Besides, the HMs are recovered in concentrated aqueous solutions, thus requiring additional treatment. The washing solutions obtained applying the chelant assisted soil washing and/or the concentrated solution from EDR are collected and processed to remove heavy metals by: precipitation as insoluble species, electrolytic recovery, degradation of metal chelates and separation of released HMs by absorption. Other than the recovery of dissolved metals, it is also important the recycle of water owing to the well known problem of water scarcity. Some studies used membrane processes, such as reverse osmosis or nanofiltration, to concentrate the washing solution followed by an electrochemical deposition for metal disposal. An high reduction of toxic ions is achieved, but these processes fail in selectivity (no metal recovery). Furthermore, the final fate of some aqueous streams and then water recycle were not considered. Besides, the operating costs of reverse osmosis or nanofiltration are moderately high. A possible alternative to overcome these limitations is the use of Complexation/Ultrafiltration (CP-UF) technique, which combines the bonding of metal and its chelates to a water-soluble polymers with the use of UF membranes. Main advantages of this method are: process selectivity, low energy requirements, optimal quality of treated water thus realizing polymer recycle, metal recovery and water recycling.
Hybrid Membrane Operations in the Removal and/or Recovery of Metal Ions and Water Recycling from Washing Solutions of Contaminated Soil, Chap. 5
MOLINARI, Raffaele;
2009-01-01
Abstract
Every year, millions of tonnes of hazardous waste are generated in the world. Because of the hazardous waste leakage in the past and of the inefficiencies in waste handling techniques, thousand of sites throughout the world are contaminated by heavy metals (HMs). Accumulation of HMs in the soil constitute a health risk to both animals and human beings. In this chapter mainly membrane (hybrid) techniques, to be applied in water treatment from soil remediation will be reviewed and discussed with the aim to remove/recovery metals and recycling water. In some cases a comparison with the results obtained with other techniques will be performed. Cleanup of soils contaminated with toxic metal ions represents one of the most difficult tasks, owing to their toxicity and the long-lasting adsorption of ions by soils. The developed technologies are based on two principles: (1) immobilization, (2) mobilization. Wide used mobilization techniques to remove metals from soil are the chelant assisted soil washing and the Electrodialytic Remediation (EDR) of polluted soils. The EDR technique employs an ion-exchange membrane in conjunction with the electrokinetic transport, and represents a very time-consuming and energy-consuming method for soil remediation. Besides, the HMs are recovered in concentrated aqueous solutions, thus requiring additional treatment. The washing solutions obtained applying the chelant assisted soil washing and/or the concentrated solution from EDR are collected and processed to remove heavy metals by: precipitation as insoluble species, electrolytic recovery, degradation of metal chelates and separation of released HMs by absorption. Other than the recovery of dissolved metals, it is also important the recycle of water owing to the well known problem of water scarcity. Some studies used membrane processes, such as reverse osmosis or nanofiltration, to concentrate the washing solution followed by an electrochemical deposition for metal disposal. An high reduction of toxic ions is achieved, but these processes fail in selectivity (no metal recovery). Furthermore, the final fate of some aqueous streams and then water recycle were not considered. Besides, the operating costs of reverse osmosis or nanofiltration are moderately high. A possible alternative to overcome these limitations is the use of Complexation/Ultrafiltration (CP-UF) technique, which combines the bonding of metal and its chelates to a water-soluble polymers with the use of UF membranes. Main advantages of this method are: process selectivity, low energy requirements, optimal quality of treated water thus realizing polymer recycle, metal recovery and water recycling.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
