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Dredging operations produce considerable quantities of materials, to be managed and this opens an opportunity for valorization in civil engineering. However, the contamination of the dredged sediments has become a major problem to solve. The major contaminants are heavy metals and organic compounds. This study focuses on the use of phosphoric acid (H 3 PO 4) to stabilize heavy metals from sediments and destroy organic matter by calcination at 650 °C with a goal of using sediments in roadworks. Several studies have been conducted in this field. The stabilized materials obtained have been used in civil engineering. The main purpose of this work is to discuss the environmental behavior of marine sediment treated by phosphatation and calcination. Two types of phosphoric acids were used. The pH dependence leaching test has been used as the basic characterization to evaluate the effect of the type of phosphoric acid on the metals behavior in a valorization scenario. The standard leaching test and the Toxicity Characteristic Leaching Procedure (TCLP) were conducted as compliance tests. In regards of the obtained results, the environmental assessment has also shown a reduction in the availability of targeted heavy metals in alkaline environment whatever the type of acid used for treatment. This opens opportunities for co-valorization. [ABSTRACT FROM AUTHOR]

Turtle shells comprising of cortical and trabecular bones exhibit intriguing mechanical properties. In this work, compression tests were performed using specimens made from the carapace of Kinixys erosa turtle. A combination of imaging techniques and mechanical testing were employed to examine the responses of hierarchical microstructures of turtle shell under compression. Finite element models produced from microCT-scanned microstructures and analytical foam structure models were then used to elucidate local responses of trabecular bones deformed under compression. The results reveal the contributions from micro-strut bending and stress concentrations to the fractural mechanisms of trabecular bone structures. The porous structures of turtle shells could be an excellent prototype for the bioinspired design of deformation-resistant structures. In this study, a combination of analytical, computational models and experiments is used to study the underlying mechanisms that contribute to the compressive deformation of a Kinixys erosa turtle shell between the nano-, micro- and macro-scales. The proposed work shows that the turtle shell structures can be analyzed as sandwich structures that have the capacity to concentrate deformation and stresses within the trabecular bones, which enables significant energy absorption during compressive deformation. Then, the trends in the deformation characteristics and the strengths of the trabecular bone segments are well predicted by the four-strut model, which captures the effects of variations in strut length, thickness and orientation that are related to microstructural uncertainties of the turtle shells. The above results also suggest that the model may be used to guide the bioinspired design of sandwich porous structures that mimic the properties of the cortical and trabecular bone segments of turtle shells under a range of loading conditions. [ABSTRACT FROM AUTHOR]

An apatitic calcium phosphate gel (HaG) was elaborated and used to treat municipal wastewater in a physicochemical cycle prior to the standard biological degradation process. Preliminary laboratory batch experiments outlined the kinetics of heavy metal sorption by monitoring the concentrations found in filtered fractions as a function of treatment time. On site experiments were performed in a municipal wastewater treatment plant by derivation of real wastewater into an experimental tank. In this case, the sorption of organic and metal pollution was studied on the whole effluent. The solid and liquid phases were both characterized using elemental analysis, total and organic carbon, and thermal analysis of the solids collected. Results showed significant reductions in heavy metal contents of about 50 to 60% for main metals such as lead, aluminum and iron in the liquid phase. The concentrations went respectively from initial values of 0.07, 0.15 and 1.80 ppm to 0.04, 0.11 and 0.03 ppm in the treated waters for these elements. Organic matter also reacted with the HaG by adsorbing to the solid particles, with the contents of organic carbon increasing from zero to 80 g/Kg on the solids and decreasing from 130 ppm to 24 ppm in the liquid phase. This allows foreseeing improvements in the biological treatment process following this physicochemical purification step. The elemental analysis showed that up to 50 and 90 percent of the heavy metals could be removed from the effluent. The presence of the organic matter adsorbed on calcium phosphate was confirmed by thermal methods. [ABSTRACT FROM AUTHOR]

Biogas is a valuable renewable energy that can be used as a fuel or as raw material for the production of hydrogen, synthesis gas and chemicals. Apart from its main constituent of CH 4 and CO 2 , it also contained various undesirable contaminants. The removal of these contaminants such as H 2 S will significantly improve the quality of the biogas for further use. This work involved the valorization of calcium carbonate (CaCO 3 )-based solid wastes for the removal of H 2 S from the biogas stream. The solid wastes were analyzed by different physicochemical methods CaCO 3 was found as the main component of both solid wastes, while trace amounts of other elements such as Mg, Al, etc. were also present. The solid wastes were dispersed in water and the resulted suspensions were tested for the removal of H 2 S from the gas phase, using a triphasic gas/liquid/solid glass reactor at room temperature and pressure. A commercial activated carbon (AC) and a pure commercial calcite were also used for comparison purpose. In addition, mixtures of AC with CaCO 3 waste in different ratios were also tested. The influence of the matrix of gas (air or biogas) on the removal of H 2 S was evaluated. Both solid wastes showed higher performance compared to the pure commercial calcite for H 2 S removal. The coupling of a CaCO 3 waste and AC allowed improving the sorption performance compared to pure commercial CaCO 3 and AC used alone. The results obtained open a new promising way for the valorization of CaCO 3 -based wastes for H 2 S removal from biogas. [ABSTRACT FROM AUTHOR]

The valorization of gypsum (by-product of phosphoric acid production) into useful product seems to be of important interest. In this study, the adsorption of lead (II) and cadmium (II) in an aqueous solution using both commercial gypsum (CG) and industrial gypsum by-product (IG) as adsorbents, has been investigated. The use of highly-purity CG allows the understanding of the adsorption phenomenon. The use of an IG as received from an industrial site allows the evaluation of its reactivity compared to pure CG. The adsorption experiments were carried out at ambient conditions for 24 h and the pH was recorded along the reaction. FTIR analyses were performed in order to examine the modification in the sulfate bound arrangement in the case of use of lead and/or cadmium. The obtained results have shown that the retention capacity of lead (II) and cadmium (II) by IG was similar that those obtained in the case of CG. However, gypsum by-product may be used as an alternative material to remove heavy metals in wastewaters. [ABSTRACT FROM AUTHOR]

Huge amounts of dyes-containing wastewaters are discharged into the environment sometimes without any remediation or land filled as sludges which are difficult to handle and eliminate whatever the method of treatment used. Due to the lack of reliable data on the structural diversity of these harmful compounds, further information is needed about the retention mechanisms especially on synthetic or natural mineral adsorbents like hydroxyapatite HA, a friendly ecological compound commonly found in soils as phosphate rock. We already showed the potential use of hydroxyapatite HA to remove textile dyes from various industrial waste water by coprecipitation with HA which could be thereafter regenerated and reused following repeated dye removal by thermal treatment. As the dihydroxyanthraquinone Alirarin or its salt (ARS) is regarded as a model compound for more complex dyes, this led us to investigate the way calcium ions interact simultaneously with phosphate and ARS. The interaction of ARS with hydroxyapatite (HA) was shown to proceed by formation of whether catecholate salt formation or akin to chelate formation with a phenolic hydroxyl group and adjacent quinone oxygen as already mentioned in the literature. However important details point to a situation more complex than simple adsorption. To clarify the mode of action of HA on the removal of dyes or organic matter in general, we investigated the interactions of alizarinsulfonate ARS with calcium and phosphate ions in solution as a function of pH and dye/adsorbent ratio. The possibility of the formation of mixed complexes of the type phosphate-calcium-dye which reveals the competition for calcium ions between phosphate and organic ligands is emphasized and reported herein. [ABSTRACT FROM AUTHOR]

Dredging of sediments is necessary in order to maintain maritime activities and for flood prevention. However the increased industrial activities are causing accumulation of pollutants in the sediments. The main contaminants are heavy metals and organic compounds. Because of the cost of storage, treatment and valorization can be economically sound. This study focuses on the technology to treat heavy metals from dredged sediments using phosphoric acid (H 3 PO 4 ) (the Novosol ® process developed by Solvay company) with a goal to stabilize heavy metals by capturing them in calcium phosphate matrix and to destroy organic matter by calcination at 650 o C. Several studies have been conducted in this field. The stabilized materials obtained have been used in civil engineering. However these studies have never assessed the effect of the composition of the phosphoric acid on the treatment. In this paper the effect of two types of phosphoric acids with various composition and origins were compared. The investigation focuses on the effect of the phosphoric acids on the environmental behavior of metals and on the geotechnical properties of the dredged sediment. [ABSTRACT FROM AUTHOR]

The control of emission gas from incinerators appears as a key issue for the improvement of the incineration technology. In this paper, we developed new sorbent materials based on calcium hydroxyapatite (Ca–HA) matrix. Using gelatine and bio–glass as porous and structural agents, which are largely available and have reasonable costs, powder of Ca–HA could be easily formulated into desired morphologies. As an example, a Ca–HA based accumulator having good porosity and mechanical stability was obtained by mixing Ca–HA powder with gelatine, bio–glass and water, followed by molding, then calcination steps. This accumulator showed an interesting capacity for the collection and tracing of Cd used as single model heavy metal in gas phase. [ABSTRACT FROM AUTHOR]

Porous composite materials containing calcium phosphate and calcium sulphate were elaborated by mixing various hydroxyapatites with calcium sulphate hemihydrate, adding water and moulding the paste into shape. The composite material was broken into small granules of 5 mm size to test for heavy metal retention in a column configuration. It was found that the amount of zinc ions retained depended on the contents in apatites present in the composite, and that results were similar to the results obtained for equivalent amounts of pure apatite put in the same column. These results are interesting because previous work on pure apatites showed release of small sub-micrometer sized metal phosphates when the apatite particles were contacted with heavy metals in a flow-through experiment. Thus, the plaster matrix does not prevent metal uptake from aqueous solutions and helps minimize release of fines from the used apatite. The breakthrough curves and zinc retention capacities will be presented for various composite compositions, flow rates and zinc concentrations. [ABSTRACT FROM AUTHOR]

Heavy metal pollution in soils, wastewater or fly ashes is a persistent environmental problem. This pollution in water or wastewater is an ongoing environmental problem and the rules to control and decrease this pollution are increasingly strict. The extreme toxicity of heavy metals even at low concentration and their bio-accumulation cause a lot of environmental problems. Minerals such as the calcium phosphate of general formula M 10 (XO 4 ) 6 Y 2 with M a divalent cation, (XO 4 ) 3- a trivalent anion and Y - a monovalent anion are well know for trapping metal ions. The retention of heavy metals by calcium phosphate has been already widely studied in aqueous solutions. In this study, a low cost calcium phosphate gel (Ca-HA) synthesized from a calcium carbonate industrial waste was used as a sorbent for wastewater treatment. We have characterized this sorbent before and after use. The physical characterization showed a decrease of the specific surface area and density. The granulometry measurements showed an increase of the particles diameter explained by the sorption of pollutants (organic molecules). The presence of these molecules was confirmed by total and organic carbon measurement and thermal analysis. The elemental measurements confirmed also the heavy metal sorption by the Ca-HA. A calcination of the contaminated Ca-HA was carried out at different temperatures. After calcination the solid contained less organic molecules and heavy metals were concentrated in the matrix. [ABSTRACT FROM AUTHOR]

Heavy metal pollution in soils, wastewater or fly ashes is a persistent environmental problem. This pollution in water or wastewater is an ongoing environmental problem and the rules to control and decrease this pollution are increasingly strict. The extreme toxicity of heavy metals even at low concentration and their bio-accumulation cause a lot of environmental problems. Minerals such as the calcium phosphate of general formula M 10 (XO 4 ) 6 Y 2 with M a divalent cation, (XO 4 ) 3- a trivalent anion and Y - a monovalent anion are well know for trapping metal ions. The retention of heavy metals by calcium phosphate has been already widely studied in aqueous solutions. In this study, a low cost calcium phosphate gel (Ca-HA) synthesized from a calcium carbonate industrial waste was used as a sorbent for wastewater treatment. We have characterized this sorbent before and after use. The physical characterization showed a decrease of the specific surface area and density. The granulometry measurements showed an increase of the particles diameter explained by the sorption of pollutants (organic molecules). The presence of these molecules was confirmed by total and organic carbon measurement and thermal analysis. The elemental measurements confirmed also the heavy metal sorption by the Ca-HA. A calcination of the contaminated Ca-HA was carried out at different temperatures. After calcination the solid contained less organic molecules and heavy metals were concentrated in the matrix. [ABSTRACT FROM AUTHOR]

The valorization of gypsum (by-product of phosphoric acid production) into useful product seems to be of important interest. In this study, the adsorption of lead (II) and cadmium (II) in an aqueous solution using both commercial gypsum (CG) and industrial gypsum by-product (IG) as adsorbents, has been investigated. The use of highly-purity CG allows the understanding of the adsorption phenomenon. The use of an IG as received from an industrial site allows the evaluation of its reactivity compared to pure CG. The adsorption experiments were carried out at ambient conditions for 24 h and the pH was recorded along the reaction. FTIR analyses were performed in order to examine the modification in the sulfate bound arrangement in the case of use of lead and/or cadmium. The obtained results have shown that the retention capacity of lead (II) and cadmium (II) by IG was similar that those obtained in the case of CG. However, gypsum by-product may be used as an alternative material to remove heavy metals in wastewaters. [ABSTRACT FROM AUTHOR]

Huge amounts of dyes-containing wastewaters are discharged into the environment sometimes without any remediation or land filled as sludges which are difficult to handle and eliminate whatever the method of treatment used. Due to the lack of reliable data on the structural diversity of these harmful compounds, further information is needed about the retention mechanisms especially on synthetic or natural mineral adsorbents like hydroxyapatite HA, a friendly ecological compound commonly found in soils as phosphate rock. We already showed the potential use of hydroxyapatite HA to remove textile dyes from various industrial waste water by coprecipitation with HA which could be thereafter regenerated and reused following repeated dye removal by thermal treatment. As the dihydroxyanthraquinone Alirarin or its salt (ARS) is regarded as a model compound for more complex dyes, this led us to investigate the way calcium ions interact simultaneously with phosphate and ARS. The interaction of ARS with hydroxyapatite (HA) was shown to proceed by formation of whether catecholate salt formation or akin to chelate formation with a phenolic hydroxyl group and adjacent quinone oxygen as already mentioned in the literature. However important details point to a situation more complex than simple adsorption. To clarify the mode of action of HA on the removal of dyes or organic matter in general, we investigated the interactions of alizarinsulfonate ARS with calcium and phosphate ions in solution as a function of pH and dye/adsorbent ratio. The possibility of the formation of mixed complexes of the type phosphate-calcium-dye which reveals the competition for calcium ions between phosphate and organic ligands is emphasized and reported herein. [ABSTRACT FROM AUTHOR]

Dredging of sediments is necessary in order to maintain maritime activities and for flood prevention. However the increased industrial activities are causing accumulation of pollutants in the sediments. The main contaminants are heavy metals and organic compounds. Because of the cost of storage, treatment and valorization can be economically sound. This study focuses on the technology to treat heavy metals from dredged sediments using phosphoric acid (H 3 PO 4 ) (the Novosol ® process developed by Solvay company) with a goal to stabilize heavy metals by capturing them in calcium phosphate matrix and to destroy organic matter by calcination at 650 o C. Several studies have been conducted in this field. The stabilized materials obtained have been used in civil engineering. However these studies have never assessed the effect of the composition of the phosphoric acid on the treatment. In this paper the effect of two types of phosphoric acids with various composition and origins were compared. The investigation focuses on the effect of the phosphoric acids on the environmental behavior of metals and on the geotechnical properties of the dredged sediment. [ABSTRACT FROM AUTHOR]

Porous composite materials containing calcium phosphate and calcium sulphate were elaborated by mixing various hydroxyapatites with calcium sulphate hemihydrate, adding water and moulding the paste into shape. The composite material was broken into small granules of 5 mm size to test for heavy metal retention in a column configuration. It was found that the amount of zinc ions retained depended on the contents in apatites present in the composite, and that results were similar to the results obtained for equivalent amounts of pure apatite put in the same column. These results are interesting because previous work on pure apatites showed release of small sub-micrometer sized metal phosphates when the apatite particles were contacted with heavy metals in a flow-through experiment. Thus, the plaster matrix does not prevent metal uptake from aqueous solutions and helps minimize release of fines from the used apatite. The breakthrough curves and zinc retention capacities will be presented for various composite compositions, flow rates and zinc concentrations. [ABSTRACT FROM AUTHOR]

The control of emission gas from incinerators appears as a key issue for the improvement of the incineration technology. In this paper, we developed new sorbent materials based on calcium hydroxyapatite (Ca–HA) matrix. Using gelatine and bio–glass as porous and structural agents, which are largely available and have reasonable costs, powder of Ca–HA could be easily formulated into desired morphologies. As an example, a Ca–HA based accumulator having good porosity and mechanical stability was obtained by mixing Ca–HA powder with gelatine, bio–glass and water, followed by molding, then calcination steps. This accumulator showed an interesting capacity for the collection and tracing of Cd used as single model heavy metal in gas phase. [ABSTRACT FROM AUTHOR]

Abstract: Dredged sediments are being chemically treated with phosphoric acid on an industrial scale. The effectiveness of the treatment was evaluated by performing the chemical reaction in a tubular reactor, followed by convective drying and maturation of the treated sediment at ambient temperature and finally thermal destruction of the organic matter by calcinations (500°C–900°C). The influence of acid concentration and calcination temperature on the specific surface area of the sediment was investigated. The stabilization of the heavy metals was evaluated by leaching tests and sequential extraction procedures. The phosphoric acid treatment is effective in reducing heavy metal mobility, a prerequisite for recycling the sediments in various construction materials. [Copyright &y& Elsevier]