Waste electrical and electronic equipments as urban mines in Burkina Faso: Characterization and release of metal particles.

Like other developing countries, Burkina Faso is one of the preferential destinations for second-hand electrical and electronic equipments (EEE). At the end of their life, these EEEs are classified as waste electrical and electronic equipment (WEEE) including Printed Circuit Boards (PCB). A particle size reduction is realized for the release of metals by shredding and grinding to obtain particles smaller 1.5 mm. A granulometric sorting was realized and nine granulometric portions were obtained. Particles were characterized by optical microscopy and Scanning Electron Microscopy coupled with Energy Dispersive X-ray Spectroscopy (EDS). The experiments confirmed that the fractions contained polymers, glass fibers and metals under the form of single metals or alloys. The release of metal was efficient for particles with a size smaller than 0.71 mm. Three digestion procedures were experimented on four components to assess the impact on metals leaching. Microwave-assisted digestion method was the best procedure, compared to the analysis methods ISO 11466: 1995, and method 3050B, adapted. The characterization by Inductively coupled plasma atomic emission spectroscopy (ICP-AES) of these PCBs exhibited important amounts of precious metals (Ag, Au, Pd) and other metals in greater quantities (Cu, Pb, Ni, Co, etc.), leading to their qualification as "Urban Mines" calling for their recovery. The characterization of metals in each granulometric portion is realized. Precious and others metals were distributed in all granulometric size portions. So granulometric size reduction was not efficient for metal separation and recovery from PCBs and alternative methods should be investigated for selective precious metal recovery.

Adsorptive removal of α-endosulfan from water by hydrophobic zeolites. An isothermal study.

This paper deals with the removal of α-endosulfan from water over HY and steamed HBEA zeolites. Experiments were performed to understand the adsorption mechanisms of α-endosulfan on zeolites and to determine the most efficient adsorbent for the purification of water contaminated by this pesticide. The experiments exhibit that α-endosulfan was adsorbed in the micropores. In the case of HY zeolites an adsorption of α-endosulfan molecules on BrØnsted sites was pointed out, due to a preferential water adsorption in mesopores. Moreover a physisorption of α-endosulfan occurred in micropores. For steamed HBEA zeolites physisorption in micropores was pointed out as the adsorption mode. For both types of zeolites a decrease of the adsorption capacities was noticed when the acidity of zeolites increased. There was also a linear relation between the adsorption capacities of α-endosulfan and the hydrophobicity (HI) of the samples and by determining the values of HI for a type of zeolite it was possible to deduce the uptake of α-endosulfan. The HY(40) sample was the most efficient for the removal of α-endosulfan from water because of preferential adsorption of water molecules in mesopores and lower acidity. For this sample the adsorption capacity for α-endosulfan was about 833.33 mg/g where for the most effective HBEA sample (St700(3)) the adsorption capacity was about 793.65 mg/g.

Separation of monobranched and dibranched Isomers of n-hexane on zeolitic molecular sieves: a thermodynamic study.

A thermodynamic study was realized by competitive adsorption over zeolitic adsorbents to determine the efficiency of these solids for the separation of monobranched and dibranched isomers of n-hexane. The effect of the zeolite structure was studied. The medium-pores ZSM-5-type zeolites were better than the large-pores BEA and MOR zeolites. The size and number of the extraframework cations had an important influence on the efficiency of the separation over ZSM-5 zeolites. The sodic Na(6)ZSM-5 sample was found to be the better adsorbent for the separation of the studied mixture because of steric hindrance induced by the presence of Na(+) cations in the zeolite structure. The initial composition of the mixture also had an important influence on the separation. In fact, when the initial mixture was equimolar the monobranched isomer was preferentially adsorbed, whereas when the molar percentages of the isomers were different in the initial mixture the adsorption of the majority isomer was favored. The temperature of the adsorption was another important parameter influencing the separation. Indeed, when the temperature of adsorption was low the separation was more effective. At an adsorption temperature of 333 K the Na(6)ZSM-5 sample was the most efficient by adsorbing 65% of the monobranched isomer and only 35% of the dibranched isomer.