Dominique Pareau

Solvent extraction of titanium by tributylphosphate, trioctylphosphine oxide and decanol from chloride media

Abstract Solvent extraction of titanium from both hydrochloric acid and calcium chloride solutions has been investigated. Polarographic analysis showed that the dissolved titanium is present as Ti(IV) in chloride solutions. Two extractants, tributylphosphate (TBP) and decanol, were used separately and mixed. The effects of the reaction time, the concentration of HCl and CaCl 2 in the aqueous phase, and the extractant concentration in the organic phase were studied. It is shown that the kinetics of the extraction process are very fast, since equilibrium is reached after 3 min. In addition, the extraction of Ti(IV) increases with the total chloride concentration in the aqueous phase, as well as with the extractant concentration in the organic phase. Extraction of about 95% of titanium by 1 mol/1 TBP from hydrochloric acid media was possible, as well as the extraction of 99% of titanium by 0.5 mol/l TOPO from a 6 mol/l solution of total chloride.

Nitrogen and phosphate removal from wastewater with a mixed microalgae and bacteria culture

Graphical abstract

Nonlinear predictive control for maximization of CO2 bio-fixation by microalgae in a photobioreactor

In the framework of environment preservation, microalgae biotechnology appears as a promising alternative for CO2 mitigation. Advanced control strategies can be further developed to maximize biomass productivity, by maintaining these microorganisms in bioreactors at optimal operating conditions. This article proposes the implementation of Nonlinear Predictive Control combined with an on-line estimation of the biomass concentration, using dissolved carbon dioxide concentration measurements. First, optimal culture conditions are determined so that biomass productivity is maximized. To cope with the lack of on-line biomass concentration measurements, an interval observer for biomass concentration estimation is built and described. This estimator provides a stable accurate interval for the state trajectory and is further included in a nonlinear model predictive control framework that regulates the biomass concentration at its optimal value. The proposed methodology is applied to cultures of the microalgae Chlorella vulgaris in a laboratory-scale continuous photobioreactor. Performance and robustness of the proposed control strategy are assessed through experimental results.

Thermodynamic and kinetic studies of palladium (II) extraction by extractant mixtures containing LIX 63: Part I. Thermodynamic study

Abstract Extraction of palladium (II) by LIX 63, TOPO, TIBPS, Aliquat 336 and HDEHP individually or in mixture with LIX 63, was studied in HCl (1 mol l−1). It was found that the association of LIX 63 with TOPO or Aliquat 336 enhances the extraction rate of Pd(II). Aliquat 336 is the most powerful additive, the extraction thermodynamics were carefully investigated for this case. The comparison of the distribution curves, for individual extractants and their mixtures, indicated a significant synergism that was explained by the formation of a mixed species of Pd(II), LIX 63 (H2Ox) and Aliquat 336 (Ali): [PdCl 3 (H 2 Ox)](Ali) , in addition to those formed with the individual extractants: [PdCl 4 ](Ali) 2 and [PdCl 2 (H 2 Ox) 2 ] ; the formation constants of these three compounds were determined.

SOLVENT EXTRACTION OF NICKEL(II) BY MIXTURE OF 2-ETHYLHEXANAL OXIME AND BIS(2-ETHYLHEXYL) PHOSPHORIC ACID

The extraction of nickel(II) from acidic aqueous solutions using a mixture of 2-ethylhexanal oxime (EHO) and bis(2-ethylhexyl) phosphoric acid (D2EHPA) in dodecane has been investigated as a function of total concentrations of each extractant, metal and protons. The aqueous salt concentration is proved to have no significant effect for both ammonium nitrate and chloride. The extracted organic complex is then Ni(Ox)2(HOx)2(HA)2 or Ni(HOx)4A2, where HA denotes the organo-phosphoric acid and HOx the oxime. A complementary isomolecular study has been achieved to confirm this stoichiometry. As aggregation plays a crucial role in extraction phenomenon, Vapor Pressure Osmometry (VPO) measurements have been carried out in order to determine the aggregation numbers for either the separate extractants or their mixtures. The bis(2-ethylhexyl) phosphoric acid is mainly under dimer and trimer forms, while no mixed aggregation is observed.

Study of the multicomponent system wet process phosphoric acid-methyl isobutyl ketone at 40 ◦ C phase equilibria and extraction performances

This work concerns the purification of wet process phosphoric acid (WPA) by solvent extraction with methyl isobutyl ketone (MIBK) at 40 ◦ C. For this purpose, an exhaustive study of the multicomponent extraction system WPA–MIBK was carried out. In a first step, the distribution of the main components (H3PO4 ,H 2O, MIBK) and the major impurities of WPA (Ca 2+ ,M g 2+ ,A l 3+ ,F e 3+ ,S O 4 2− ,F − ) between the conjugated phases was systematically studied. Then, expression of phase compositions in terms of H3PO4 ,H 2O and MIBK on an impurity-free basis enabled us to compute the characteristics of the H 3PO4 countercurrent multistage extraction using the Mac Cabe–Thiele method. Both as-received and water-saturated MIBK were considered as solvent. From graphical results, optimum conditions to conduct the extraction of H3PO4 from concentrated WPAs (53.5–58% P2O5) were determined. To validate experimentally the obtained results, continuous countercurrent extractions were performed on a laboratory-scale mixer-settler unit. A good agreement was observed.

Paraquat detoxication with multiple emulsions

In this study, we show that detoxifying W/O/W multiple emulsions, prepared with an appropriate extractant/trapping couple, represent a promising technology for quick and safe poisoning treatments, with application to the highly toxic herbicide Paraquat, responsible of poisonings from low-dose exposure leading to several deaths every year. In vitro tests led to the choice of an appropriate extractant/trapping couple system with significant detoxication performance. In vivo tests showed (i) that rats receiving high doses of Paraquat, then a detoxifying emulsion, presented an increase from 50% to 100% of the MST (median survival time) and (ii) that no mortality was observed during 30 days with rats dosed with emulsions initially loaded with Paraquat at a concentration much higher than the lethal dose, proving the stability and the inocuity of the detoxifying multiple emulsion in the gastrointestinal tract.

Growth modeling of the green microalga Chlorella vulgaris in an air-lift photobioreactor

Abstract Considering the increasing impact of the environmental concerns in the current worldwide policy, the application of biological processes, namely the bio-fixation of CO 2 by microalgae, represents a promising solution and an increasingly attractive strategy. Indeed, these photosynthetic microorganisms have the great capacity to fix and tolerate high CO 2 concentrations converting it to biomass and highly valuable molecules. Thus, modeling of microalgae growth represents an essential tool for the optimization of the carbon dioxide consumption in engineered systems such as photobioreactors. In this context, the main goal of this work is the identification of the growth model parameters of Chlorella vulgaris , the model organism used in this study. The growth model developed in this study takes into account the combined influence of light intensity and the total inorganic carbon available per cell. First, an experimental campaign of batch culture was carried out in a well-stirred lab-scale photobioreactor under optimal conditions. Finally, model results of biomass dynamics and total inorganic carbon evolution over time are compared with data of batch and continuous cultures, confirming the accuracy of the identified model parameters.

Thiosubstituted Organophosphorus Acids as Selective Extractants for Ag(I) from Acidic Thiourea Solutions

Abstract This paper deals with the solvent extraction of silver from thiourea leaching Ag ore liquors as an alternative to the traditional process involving cyanide. The investigation of the extraction mechanism of silver from acidic thiourea solution had not been clearly established to date. The extraction behavior of silver using di(2‐ethylhexyl)dithiophosphoric acid (D2EHDTPA) and di(2,4,4‐trimethylpentyl) thiophosphinic acid (CYANEX 302) was studied. The effect of various parameters such as concentrations of metal, mineral acid, thiourea, and extractant has been investigated. The extracted complexes have been identified through a slope method analysis as AgX(HX)5 for CYANEX 302 and AgX for D2EHDTPA, where HX denotes the extractant. Moreover, complete stripping was ensured with a mixture of NH4SCN and H2SO4. In addition we showed that a first step of extraction with D2EHPA or CYANEX 272 results in the preferential separation of Fe(III) from the Ag(I) leach solution.

Managing the Complexity of Environmental Assessments of Complex Industrial Systems with a Lean 6 Sigma Approach

The integration of environmental concerns into the product design process has highlighted a new problem that arises when confronted with complex systems. Indeed environmental assessment methodologies like Life Cycle Assessment (LCA) become in this case particularly heavy to implement. Considering aluminium electrolysis substations as a complex industrial system, we propose a new eco-design methodology based on a Lean Six Sigma approach. Including the environmental parameter as the fourth dimension of the Quality, Costs, Time triangle this methodology has the advantage to cover and systematize the entire eco-design process. It answers to most of the limits raised in our study and allows managing a part of the complexity that appears in particular during the goal and scope definition and the inventory phases of LCA. An application of aluminium electrolysis substations is mentioned.