Immobilization of molybdenum by alternative cementitious binders and synthetic C-S-H: An experimental and numerical study.

Excavation operations during construction produce millions of tons of soil sometimes with high leachable molybdenum (Mo) contents, that can lead to risks for both human health and the environment. It is therefore necessary to immobilize the Mo in excavated soils to reduce pollution and lower the costs of soil disposal. This paper studies the immobilization of Mo by three cementitious binders. To this end, one Ordinary Portland cement (OPC), one binder composed of 90% ground granulated blast furnace slag (GGBS) and 10% OPC, and one supersulfated GGBS binder were spiked with sodium molybdate at six different Mo concentrations from 0.005 wt% to 10 wt% before curing. In addition, to gain mechanistic insights, the capacity of synthetic calcium silicate hydrates (C-S-H) to immobilize Mo was studied. This study was completed by thermodynamic modeling to predict the immobilization of Mo at low Mo concentrations (<0.005 wt%). Paste leaching tests results showed that more than 74% of the initial Mo spike was immobilized by the three binders. The supersulfated GGBS binder consistently showed the highest retention levels (92.0 to 99.7%). The precipitation of powellite (CaMoO4) was the dominant mechanism of Mo retention in all binders and most leaching solutions were oversaturated with respect to powellite. Also, in C-S-H syntheses, Mo was largely immobilized (>95%) by the coprecipitation of powellite. Thermodynamic modeling was in good agreement with measured values when the equilibrium constant of powellite was modified to LogK = -7.2. This suggested that powellite is less stable in cementitious environments than would be expected from thermodynamic databases. Moreover, modeling showed that, for a solution at equilibrium with portlandite or C-S-H, the Mo concentration is limited to 1.7 mg/L by powellite precipitation. In contrast, for a solution saturated with respect to ettringite, the threshold concentration for powellite precipitation is 6.5 mg/L.

The implementation of a synchronous telemedicine platform linking off-site pediatric intensivists and on-site fellows in a pediatric intensive care unit: A feasibility study.

OBJECTIVE: The aim of this study was to assess the feasibility of implementing a synchronous telemedicine platform in a pediatric intensive care unit (STEP-PICU). METHOD: A prospective mixed study was conducted. Two sources of data were mobilised: a survey with structured questionnaires and direct non-intrusive observation. The study site was the PICU of a university hospital. Users' perceptions of six aspects of the STEP-PICU were studied: telemedicine system quality, data quality, quality of technical support, use of the new system, overall satisfaction and system benefits. RESULTS: During the 6-month experimentation period, use of the telemedicine platform was rather limited and fell short of the promoter's expectations.The mean scores for the six user perception dimensions were low, with no differences between the two groups of users. A Mann-Whitney test showed that being an off-site pediatric intensivist or on-site fellow did not make a statistically significant difference in responses on system quality (p = .518), data quality (p = 1.00), quality of technical support (p = 1.00), system use (p = .556), overall satisfaction (p = .482), or benefits (p = .365). The low use of the STEP-PICU was attributed to three root causes: human factors, the platform's functionalities, and technical problems. DISCUSSION: The synchronous telemedicine service for PICU was feasible but would need good pre-implementation preparation to be truly helpful. Its usefulness during the night shift and holiday on-call periods was scored as low by the off-site pediatric intensivists and the on-site fellows. It would appear that such a service could be more beneficial for communications with other remote healthcare facilities, where there is a greater need for the expertise of a pediatric critical care intensivist.

Synthesis of alpha'L-C2S cement from fly-ash using the hydrothermal method at low temperature and atmospheric pressure.

The objective of this study was the synthesis of alpha'(L)-C(2)S (Ca(2)SiO(4)) belite cement, starting from fly-ash of system CaO-SiO(2)-Al(2)O(3)-SO(3), and using the hydrothermal method in alkaline solution. The lime deficit in these ashes was compensated by the addition of slaked lime from lime bagging workshops. The hydrothermal treatment of the mixture was carried out in demineralized water, NaOH or KOH solution, continually stirred at a temperature below 100 degrees C and atmospheric pressure. The dehydration and calcination of the mixtures at temperatures between 800 and 1100 degrees C allowed alpha'(L)-C(2)S-rich cement to be obtained. The optimization of the synthesis parameters (temperature and time of stirring, pH of solution, temperature and duration of mixture burning) was also studied. The phase formation during various synthesis stages was studied by X-ray diffraction (XRD). Other techniques, such as SEM and EDX, were used to characterize the cement minerals. The results obtained showed that these ashes could form belite cement composed of only one dicalcium silicate phase (alpha'(L)-C(2)S).

Characteristics of industrial and laboratory meat and bone meal ashes and their potential applications.

This paper reports the characterization of four meat and bone meal (MBM) ashes obtained from specific incineration (laboratory) and from co-incineration (industrial process). Three out of the four MBM ashes were mainly composed of calcium phosphates (hydroxyapatite and whitlockite). Their compositions (major and trace) were in the range for natural phosphate rocks. Trace element contents, including heavy metals, were below 0.6% and industrial ashes contained much more heavy metals than laboratory ash. The amounts of leached elements were low, especially for laboratory ash. According to the European classification of waste to be landfilled, the laboratory ash can be classified as an inert waste. Two industrial ashes are mostly inert. Only one ash is highly leachable and needs a stabilization treatment to be classified at least in the category of hazardous waste. It seems, from these results, that possibilities other than landfilling could be considered to give economic value to these ashes.

Optimization of a high-pressure pore water extraction device.

High-pressure squeezing is a technique used for the extraction of the pore water of porous materials such as sediments, soils, rocks, and concrete. The efficiency of extraction depends on the maximum pressures on the materials. This article presents the design of a high-pressure device reaching an axial pressure of 1000 MPa which has been developed to improve the efficiency of extraction. The increase in squeezing pressure implies high stresses inside the chamber, so specialized expertise was required to design a safe, functional device that could withstand pressures significantly higher than common laboratory equipment. The design includes finite element calculations, selection of appropriate materials, and descriptive construction details for the apparatus. It also includes an experimental study of the performance of the apparatus in terms of extraction efficiency.