[Show abstract][Hide abstract] ABSTRACT: This study used batch-equilibrium techniques to evaluate the soil sorption and desorption of target steroids, representative of the estrogen, androgen, progestogen and corticosteroid families. The sorption kinetics exhibited an immediate rapid sorption followed by a slow process with a duration dependent on soil particle size. Adsorption and desorption isotherms could be described by the Freundlich equation, in a non-linear form (1/n < 1). High organic carbon-water partitioning coefficient (K(OC)) values indicate that a large mass fraction of the hormones will be associated with the sorbed phase. As a result of the poor linear correlation between log K(OC) and log K(OW) (octanol-water partition coefficient), it could be assumed that both hydrophobic and hydrogen bonding interactions contribute to the sorption mechanisms of the selected steroids. A hysteresis phenomenon was observed, varying with particle size, indicating strong irreversible interactions between some steroids and soil.
Full-text · Article · Nov 2012 · Journal of Environmental Science and Health Part A Toxic/Hazardous Substances & Environmental Engineering
[Show abstract][Hide abstract] ABSTRACT: The threshold limit corresponds to the maximum amount of trace element that could be incorporated into clinker whilst reaching the limit of solid solution of its four major phases (C3S, C2S, C3A and C4AF). For Cu, Zn or Sn, these threshold limits in a standard clinker (65% C3S, 18% C2S, 8% C3A and 8% C4AF) were equal to 0.35, 0.7 and 1 wt.% respectively (Gineys et al., in press). This paper presents the effect of the clinker composition on these threshold limits. Laboratory made clinkers having different mineralogical compositions was characterised by XRD and SEM. Results showed that the threshold limits for Cu, Zn or Sn were consistent. The threshold limit for Sn was affected by the Bogue content in interstitial phases. On the other hand, the threshold limit for Zn was affected by the Bogue content in C3S of clinker while that of Cu was unaffected by any modifications of clinker composition.
No preview · Article · Aug 2012 · Cement and Concrete Research
[Show abstract][Hide abstract] ABSTRACT: The maintenance of waterways generates large amounts of dredged sediments that are an environmental issue. This paper focuses on the use of fluvial sediment to replace a portion of the raw materials of Portland cement clinker, which would otherwise come from natural resources. The mineralogy of the synthetic cement was characterised using X-ray diffraction and scanning electron microscopy and its reactivity was followed by isothermal calorimetry. Comparisons were made to a commercial ordinary Portland cement (CEM I 52.5). Compressive strength measurements were conducted on cement pastes at 1, 2, 4, 7, 14, 28 and 56 days to study strength development. The results showed that Portland cement clinker can be successfully synthesised by using up to 39% sediment. The compressive strengths developed by the cement made from sediment were equivalent to those obtained with the reference at early ages and 20% higher at long term.
No preview · Article · Jul 2012 · Cement and Concrete Composites
[Show abstract][Hide abstract] ABSTRACT: This paper aims at defining precisely, the threshold limits for several trace elements (Cu, Ni, Sn or Zn) which correspond to the maximum amount that could be incorporated into a standard clinker whilst reaching the limit of solid solution of its four major phases (C3S, C2S, C3A and C4AF). These threshold limits were investigated through laboratory synthesised clinkers that were mainly studied by X-ray Diffraction and Scanning Electron Microscopy. The reference clinker was close to a typical Portland clinker (65% C3S, 18% C2S, 8% C3A and 8% C4AF). The threshold limits for Cu, Ni, Zn and Sn are quite high with respect to the current contents in clinker and were respectively equal to 0.35, 0.5, 0.7 and 1wt.%. It appeared that beyond the defined threshold limits, trace elements had different behaviours. Ni was associated with Mg as a magnesium nickel oxide (MgNiO2) and Sn reacted with lime to form a calcium stannate (Ca2SnO4). Cu changed the crystallisation process and affected therefore the formation of C3S. Indeed a high content of Cu in clinker led to the decomposition of C3S into C2S and of free lime. Zn, in turn, affected the formation of C3A. Ca6Zn3Al4O15 was formed whilst a tremendous reduction of C3A content was identified. The reactivity of cements made with the clinkers at the threshold limits was followed by calorimetry and compressive strength measurements on cement paste. The results revealed that the doped cements were at least as reactive as the reference cement.
No preview · Article · Nov 2011 · Cement and Concrete Research
[Show abstract][Hide abstract] ABSTRACT: This study compares two methods to immobilise the same amount of Zn in cement paste. In the first method, Zn is introduced into the raw material before clinkerisation, whereas in the second process, Zn is introduced in the liquid phase used to make the cement paste, which is often referred to as solidification/stabilisation. In laboratory-made clinker, Zn was mainly fixed within a new compound (Ca6Zn3Al4O15). Also, Zn was observed in tricalcium silicate (C3S) and in the interstitial phase (C3A and C4AF) with the exception of dicalcium silicate (C2S). In the present study, the threshold limit value corresponds to the maximum amount of Zn that could be incorporated without the stability of the clinker phases being modified. This threshold was reached when a decrease in C3A content and/or the presence of Ca6Zn3Al4O15 were observed by X-ray diffraction. The threshold limit of Zn in the studied clinker was established at 0.7% by weight. The reactivity of synthesised cement doped with Zn was studied by isothermal calorimetry measurements. These tests revealed that the incorporation of Zn had no effect on calcium silicate hydration (C3S and C2S), even if the Zn content exceeded the threshold limit value, i.e., 1%. These results were compared with those obtained through the solidification/stabilisation treatment of Zn in a cement paste. In these experiments, a Zn content of 0.7% induced a significant delay in the cement hydration. This difference in behaviour is due to the slower flow of zinc ions released in solution when it is incorporated in the clinker phases. Thus, the immobilisation during clinkerisation is a good alternative to treat waste with a high Zn content in Ordinary Portland Cement (OPC) without causing the well-known, deleterious effect on cement setting time.
No preview · Article · Jul 2011 · Cement and Concrete Composites
[Show abstract][Hide abstract] ABSTRACT: The aim of this work is to investigate the effect of the addition of Cu, Cd, Ni, Pb and Zn nitrate salts on the compressive strength of a CEM I Portland cement. Concentrations of 0.018 or 0.18mol/kg of cement of each trace element were tested. After 2days age, the compressive strength was reduced by various extents by addition of heavy metals, with the exception of Ni. This difference is due to a delay in tricalcium silicate hydration (C3S) as shown by an isothermal calorimetry test. Trace elements also influence the 28-days compressive strength, whereas the measured degree of hydration of these cement pastes is the same. As shown by scanning electron microscopy and X-ray diffraction, Cu and Pb are predominantly absorbed in the calcium silicate hydrate gel (C–S–H) while Cd, Ni and Zn are mainly precipitated as hydroxides within the intergranular porosity. Thus, trace elements precipitated as hydroxides have only a slight effect on the compressive strength. In contrast, Cu and Pb cause an increase in mechanical resistance by changing the C–S–H nanometric assembly and its density.
No preview · Article · Sep 2010 · Cement and Concrete Composites