title: Synthesis of ettringite: a way to deal with the acid wastewaters of aluminium anodising industry.
abstract: Synthesis of ettringite from acid wastewaters of the aluminium anodising industry has been studied as a possible route of reducing the emissions to the environment, recovering at the same time resource materials as a useful marketable mineral. Wastewaters of different concentrations have been subjected to the process of synthesis suspending calcium oxide and calcium aluminate powders at different time and pH conditions. High caustic alkalinity (pH approximately 12) and low sulphate concentrations (<0.1 M) are the most suitable conditions to synthesise ettringite. The mineral characterisation has been performed using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and differential thermal analysis (DTA), proving the high purity of the pursued solid product when hydrated in the appropriate sodium hydroxide concentrations. In such conditions, around 90% of the aluminium initially present in the wastewater solutions is recovered in the form of ettringite.
authors.affiliation: Faculty of Applied Sciences, Department of Chemical Technology, Delft University of Technology, Julianalaan 136, 2638 BL Delft, The Netherlands. e.alvarez@tnw.tudelft.nl
authors.forename: E
authors.initials: E
authors.lastname: Alvarez-Ayuso
authors.forename: H W
authors.initials: HW
authors.lastname: Nugteren
mesh_terms: D000535:Aluminum / Q000737:chemistry / Q000302:isolation & purification*; D017607:Aluminum Compounds / Q000737:chemistry*; D017610:Calcium Compounds / Q000737:chemistry*; D011232:Chemical Precipitation; D004055:Differential Thermal Analysis; D004563:Electrochemistry; D006863:Hydrogen-Ion Concentration; D007220:Industrial Waste; D008669:Metallurgy; D008903:Minerals / Q000138:chemical synthesis / Q000737:chemistry*; D010087:Oxides / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared; D013818:Thermogravimetry; D014874:Water Pollutants, Chemical / Q000302:isolation & purification*; D018508:Water Purification / Q000379:methods*; D014961:X-Ray Diffraction
chemical_list: D017607:Aluminum Compounds; D017610:Calcium Compounds; D007220:Industrial Waste; D008903:Minerals; D010087:Oxides; D014874:Water Pollutants, Chemical; C501337:ettringite; C035219:calcium aluminate; C016538:lime; D000535:Aluminum