Groundwater of Mount Etna (Italy), the largest volcano in Europe and the biggest hydrogeological reservoir of Sicily, widely used by the local population for potable purposes, contains high levels of Vanadium with an average concentration of 54.9 mu g/l and peak values over 200 mu g/l. This peak concentration has been found in Ciapparazzo drainage gallery, that supplies 400 lis of water for potable purpose. The USEPA lists vanadium in the "3rd Drinking Water Contaminant Candidate List", while the Italian Regulation on drinking water sets a Maximum Contaminant Level (MCL) of 50 mu g/l of V. Due to the rare occurrence in natural water and unproved toxicity, few data are available on vanadium removal from drinking water. Most studies have investigated vanadium removal form waters not intended for human consumption or from synthetic waters. The overall objective of this study was to assess, by pilot-scale testing, the ability of ferric chloride addition and hydroxide precipitation to remove vanadium. Specifically, the influence of coagulation, flocculation and filtration was investigated. An inductively coupled plasma optical emission spectroscopy, ICP-OES (Perkin Elmer Optima 4300 DVTM) was used for the analysis of metals. Concentrations of relevant ions were determined by ion chromatography (Dionex, DX-600). A portable digital pH-meter was used (mod. 340/SET-1, WTW). For the calibration of analytical instruments standard solutions were used. Sludge samples were dried at 105 degrees C and digested with nitric acid at 65% in a microwave digester. All test were conducted using a continuous flow pilot plant employing coagulation followed by flocculation and two sand filters in series. During experimental runs, two samples were collected every hour of the effluent from each of the filters: one was acidified, in order to evaluate total residuals, whereas the other was filtered by 0,45 mu m cellulose membranes in order to remove vanadium adsorbed to particulate iron (these will be referred as "microfiltered" effluent). pH and pressure drops were monitored during the runs. Vanadium was effectively removed below the MCL by adsorption onto iron hydroxides produced by dosing ferric-chloride as coagulant. However, the breakthrough of iron precipitates with adsorbed vanadium above MCLs limited the duration of the process cycle, as proved by observing data obtained from microfiltered effluents from the granular media filters. When a cationic polymer was used, removal of iron oxide particles in the granular media filters improved and no substantial differences were observed with the microfiltered samples. As expected sludge production increases increasing either FeCl3 dose or cationic polymer dose, therefore the coagulation process was optimized at pilot scale to minimize the sludge production.
|Titolo:||COPRECIPITATION OF VANADIUM IN NATURAL WATER WITH IRON (HYDR)OXIDES|
|Data di pubblicazione:||2013|
|Appare nelle tipologie:||1.1 Articolo in rivista|