title: Chromium liquid waste inertization in an inorganic alkali activated matrix: leaching and NMR multinuclear approach.
abstract: A class of inorganic binders, also known as geopolymers, can be obtained by alkali activation of aluminosilicate powders at room temperature. The process is affected by many parameters (curing time, curing temperature, relative humidity etc.) and leads to a resistant matrix usable for inertization of hazardous waste. In this study an industrial liquid waste containing a high amount of chromium (≈ 2.3 wt%) in the form of metalorganic salts is inertized into a metakaolin based geopolymer matrix. One of the innovative aspects is the exploitation of the water contained in the waste for the geopolymerization process. This avoided any drying treatment, a common step in the management of liquid hazardous waste. The evolution of the process--from the precursor dissolution to the final geopolymer matrix hardening--of different geopolymers containing a waste amount ranging from 3 to 20%wt and their capability to inertize chromium cations were studied by: i) the leaching tests, according to the EN 12,457 regulation, at different curing times (15, 28, 90 and 540 days) monitoring releases of chromium ions (Cr(III) and Cr(VI)) and the cations constituting the aluminosilicate matrix (Na, Si, Al); ii) the humidity variation for different curing times (15 and 540 days); iii) SEM characterization at different curing times (28 and 540 days); iv) the trend of the solution conductivity and pH during the leaching test; v) the characterization of the short-range ordering in terms of TOT bonds (where T is Al or Si) by (29)Si and (27)Al solid state magic-angle spinning nuclear magnetic resonance (ss MAS NMR) for geopolymers containing high amounts of waste (10-20%wt). The results show the formation of a stable matrix after only 15 days independently on the waste amount introduced; the longer curing times increase the matrices stabilities and their ability to immobilize chromium cations. The maximum amount of waste that can be inertized is around 10 wt% after a curing time of 28 days.
authors.affiliation: University of Modena and Reggio Emilia, Department of Engineering "Enzo Ferrari", Modena, Italy. Electronic address: chiara.ponzoni@unimore.it.
authors.forename: Chiara
authors.initials: C
authors.lastname: Ponzoni
authors.affiliation: University of Modena and Reggio Emilia, Department of Engineering "Enzo Ferrari", Modena, Italy.
authors.forename: Isabella
authors.initials: I
authors.lastname: Lancellotti
authors.affiliation: University of Modena and Reggio Emilia, Department of Engineering "Enzo Ferrari", Modena, Italy.
authors.forename: Luisa
authors.initials: L
authors.lastname: Barbieri
authors.affiliation: University of Palermo CGA-UniNetLab, Palermo, Italy.
authors.forename: Alberto
authors.initials: A
authors.lastname: Spinella
authors.affiliation: University of Palermo CGA-UniNetLab, Palermo, Italy.
authors.forename: Maria Luisa
authors.initials: ML
authors.lastname: Saladino
authors.affiliation: University of Palermo, Department STEBICEF, Palermo, Italy.
authors.forename: Delia Chillura
authors.initials: DC
authors.lastname: Martino
authors.affiliation: University of Palermo CGA-UniNetLab, Palermo, Italy; University of Palermo, Department STEBICEF, Palermo, Italy.
authors.forename: Eugenio
authors.initials: E
authors.lastname: Caponetti
authors.affiliation: University of Palermo, Department STEBICEF, Palermo, Italy.
authors.forename: Francesco
authors.initials: F
authors.lastname: Armetta
authors.affiliation: University of Modena and Reggio Emilia, Department of Engineering "Enzo Ferrari", Modena, Italy.
authors.forename: Cristina
authors.initials: C
authors.lastname: Leonelli
mesh_terms: D000538:Aluminum Silicates / Q000737:chemistry*; D002857:Chromium / Q000737:chemistry*; D007220:Industrial Waste; D009682:Magnetic Resonance Spectroscopy; D014865:Waste Disposal, Fluid / Q000379:methods*
chemical_list: D000538:Aluminum Silicates; D007220:Industrial Waste; D002857:Chromium
keywords: Chromium liquid waste; Inertization; Leaching test; ss MAS NMR geopolymers