Ahmed Hannachi

Removal of fluoride from aluminum fluoride manufacturing wastewater by precipitation and adsorption processes

In this study, the treatment of aluminum fluoride manufacturing Wastewaters (AFMW) by precipitation‐neutralization using calcium hydroxide (lime) or calcium carbonate (limestone) and adsorption using activated clay has been investigated. Effects of experimental conditions such as lime or limestone dose, clay mass, initial fluoride concentration and initial pH on the fluoride removal efficiency and the final pH have been evaluated. Results of this study indicated that precipitation‐neutralization processes can be successfully used to remove more than 90% of fluoride from AFMW. The treatment of AFMW containing different fluoride concentrations ranging from 167 to 5295 mg/L by precipitation with lime using [Ca 2+ ]/[F − ] molar ratio of 0.8 led to fluoride removal higher than 95% with a final pH within the range 6.5 ± 0.1 to 8.5 ± 0.1. Precipitation with CaCO3 needed higher [Ca 2+ ]/[F ‐ ] molar ratio of 2 to reach 90% of fluoride removal and obtain a final pH in the range from 6.5 ± 0.1 to 8.5 ± 0.1. The results of the treatment of AFMW by adsorption on activated bentonite clay indicated that using [clay]/[F ‐ ] mass ratio of 60 under different pH varying from pH 2 ± 0.1 to pH 12 ± 0.1 can lead to 80% fluoride removal. Synthetic calcium fluoride (SCFL) generated by precipitation‐neutralization with lime SCFL contains 77.9% of CaF2; however, only 48.3% of CaF2 are contained in solids generated from precipitation‐neutralization with limestone SCFLS.

Bipolar membrane electrodialysis and ion exchange hybridizing for dilute organic acid solutions treatment

In this work, treatment of very dilute effluents of organic acids by means of an electro-membrane hybrid process is studied. Dilute organic acids effluents are generated by numerous processes. Converting such effluents into pure more concentrated fluxes is a key step in the valorization process. An experimental study has been performed to recover acetic acid by bipolar membrane electrodialysis (BMED). The experiments performed when coupling BMED and ion exchange have clearly demonstrated that hybridization reduces energy consumption. This improvement is due to the decrease of the electrical resistance of the diluted compartment thanks to the ionic conductivity provided by the resins. The effect of back diffusion on the current efficiency was also studied. In the case of acetic acid effluent treatment, investigation of the influence of the resin initial form showed that hydroxyl and acetate initial forms result in very close performances. It is therefore useless regenerating the resin bed.

Scaling tendency assessment in reverse osmosis modules

ABSTRACT A mathematical model was developed to predict super saturation along reverse osmosis modules (RO) for water desalination. This model is based on conservation principles and chemical equilibrium equations for concentrated solutions. Pitzer’s model was used for the activity coefficient calculations. An average rejection rate for each ionic species was also considered. Supersaturations with respect to all calcium carbonate forms and to calcium sulfate are calculated. The model allows assessing when scale is likely to occur along the RO modules. The results for two brackish water qualities and seawater are shown.

Experimental and thermodynamic comparison of the separation of CO 2 /toluene and CO 2 /tetralin mixtures in the process of organogel supercritical drying for aerogels production

An organogel is firstly prepared by synthesizing an aminoacid-type organogelator which is able to immobilize aromatic solvents, such as tetralin or toluene. Aerogels are obtained from organogels by extracting the solvent with a stream of supercritical CO2 in an autoclave. The CO2/solvent mixture leaving the autoclave is separated in a cascade of three cyclone separators. The experimental results showed a good solvent recovery rate in the case of tetralin, exceeding 90%, but an unsatisfactory separation for toluene with a yield below 65%. A thermodynamic study was carried out to model the separation for both solvents. The Peng–Robinson equation of state with van der Waals mixing rules and temperature-dependent binary interaction coefficients was selected to predict the CO2/solvent thermodynamic behavior. Measurements of isothermal bubble points of the CO2/tetralin system were conducted using a high-pressure variable-volume visual cell confirming the relevancy of this model. Then, the first separator was simulated as a simple theoretical equilibrium stage. Simulations using PRO/II software were in good agreement with experimental solvent recovery rate for both toluene and tetralin. The best operating pressure and temperature for the separation were computed by a numerical parametric study.Graphical abstractThermodynamic study to explain theoretical recovery in organogel supercritical drying: comparison between two solvents (T=20 °C, P=50 bar).

Simulation of air lift packed column

In this work we have developed steady state mode for simulating an airlift packed column used for heat and mass transfer. These equations are based on energy and momentum balances. For a given air mass flow rate and a submersion ratio, the model allows to determine water mass flow rate and void fraction along the column. The conducted simulations allowed evaluating pumps efficiency along with gas flow rate and void fraction effect on pumping performances. The obtained results demonstrate that simulations based on the adopted model could be an interesting tool air-lift pumps sizing and optimization.

Mass Transfer During Combined Processes of Osmotic Dehydration and Blanching

Pomegranate, especially the Punica granatum L. variety, is widely grown in Tunisia. This fruit is a rich source of phenolic compounds including ellagitannins, phenolic acids and flavonoids.