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.
Total and soluble chromium, nickel and cobalt content in the main materials used in the manufacturing of Spanish commercial cements
One of the problems that some industries, and more specifically cement industries, still have to deal with is the requirement to determine and control the content of some chromium, nickel and cobalt compounds due to their allergenic effects on human health (mainly cement dermatitis). This paper focuses on the quantification of total and soluble chromium, nickel and cobalt content in different materials used normally in the manufacturing of Spanish commercial cements (limestone, clay minerals, raws and clinkers). These materials belong to three different cement factories, which could be representative of Spanish Portland cements. This study is a follow-up of a previous research carried out by the same authors, which provides a valuable contribution to establish possible limitations of these allergenic compounds in future national as well as international standards.
Determination of chromium by electrothermal atomic absorption spectrometry after rapid microwave-assisted digestion of sediment and botanical samples
Determination of chromium by electrothermal atomization atomic absorption spectrometry with normal electrographite tube has been investigated after microwave-assisted digestion of sediment and botanical samples. Microwave oven-assisted procedures involve digestion with aqua regia, HF (for sediments) and H2O2 in a poly (tetrafluoroethylene)(PTFE) reactor followed by treatment with saturated H3BO3(where HF is used in the earlier step). Comparative studies on the determination of chromium using three previously reported chemical modifiers, Mg(NO3)2, Pd(NO3)2 and Triton X-100, and a new modifier NaVO3, have been made. Sodium vanadate was identified as an effective chemical modifier for chromium in botanical samples such as tomato leaves and citrus leaves. Whereas, for river sediment and sewage sludge, chromium has been determined accurately without the need of any chemical modifier. The advantages of the present method are its simplicity, low cost, high speed of sample attack and rapid calibration.