HEXAVALENT CHROMIUM LEACHING FROM CEMENTS AND CEMENT COMPOSITES
Chromium is one of the 25 most widespread elements in the Earth’s crust and occurs as an indelible non-volatile trace element in raw materials used in cement clinker production (clay, limestone and iron additives in particular). Chromium in raw materials mentioned above is mainly in form of trivalent chromium. Naturally occurring chromium (III) is not initially harmful, since it is chemically stable. Only at high temperatures found in cement rotary kilns, inert trivalent chromium oxidizes to form more dangerous hexavalent chromium. The paper presents the results of the experimental investigation of the hexavalant chromium releasing from cement samples and cement composites to the water environment under various conditions. The samples of Portland cement as well as the cement composites with different composition were used for the experiments. The chemical composition of cement samples and cement composites were determined by using X-ray fluorescence analysis (XRF); the soluble hexavalent chromium concentrations in cement leachates and cement composites leachates were analysed by colorimetric analysis. The determination of chromium (VI) by spectrometry was based on the reaction of hexavalent chromium with diphenylcarbazide by forming the purple coloured compound. The content of water soluble chromium was measured to be lower in cement composites leachates than in cement leachates. The soluble hexavalent chromium concentrations in cement composites were measured from 0.13 to 0.22 mg/kg and 0.07 to 0.15 mg/kg, when studied powdered and compact cement composites leachates, respectively. The concentration of Cr (VI) in cement leachates reached the average value of 2.85 mg/kg.
A method for the determination of total Cr(VI) in cement
Abstract Portland cement is often used to solidify wastes in order to prevent heavy metals from eluting, despite the fact that most cements contain traces of soluble Cr(VI). It was found that the leachability of Cr(VI) for the soil stabilized by cement was high in some cases, and the amount of Cr(VI) leached was larger than could be accounted for by the “soluble Cr(VI)” in the cement as determined by the standard method. Since the existing analytical standards only deal with “soluble Cr(VI)” in cement, we had to develop a new procedure to measure the total Cr(VI) in cement, making use of a complete dissolution in acid. Application of this method to several different ordinary Portland cements showed that 50–80% of their total Cr is typically extracted as Cr(VI). We also observed that the interstitial (calcium aluminate/ferrite) phase in Portland cement clinker usually contains higher concentrations of both Cr and Cr(VI) than the calcium silicate phases.
Beings of nature and reason: mythological masculinities in early 18th-century French art and visual culture
Statement of Originality Acknowledgments List of Illustrations Introduction 11 Chapter One Of Myth and Men 27 Chapter Two In the Likeness of Bacchus 62 Chapter Three Venus and a Satyr 97 Chapter Four Pan and Syrinx 141 Chapter Five Marsyas Flayed by the Order of Apollo 175 Conclusion 212 Catalogue of Images 227 Bibliography 300