The aim of this work is to investigate the ability of an adsorbent of a clay mineral composite to remove and recover gold and silver ions from wastewater. The composite was prepared by mixing phosphogypsum (PG), obtained from an industrial waste, and a natural clay mineral. The materials were characterized before and after use in adsorption by several techniques. Batch adsorption experiments were carried out, and the effects of the contact time and the pH and temperature of solution on the removal processes were investigated. The optimum pH for the adsorption was found to be 4. The adsorption of these metal ions reached equilibrium after 2 h of contact. The pseudo-first-and the pseudo-second-order kinetic models, as well as the Freundlich and the Langmuir isotherm equations, were considered to describe the adsorption results. The maximum adsorbed amount of 85 mg/g Ag(I) and 108 mg/g Au (III) was found. The recovery of the adsorbed gold and silver ions from the adsorbent was also analyzed. Strong acids appeared to be the best desorption agents to recover gold and silver ions. The use 2 of aqua regia gave regeneration rates close to 95.9% and 94.3% for Ag(I) and Au(III), respectively. Finally, the removal of gold and silver ions from an industrial wastewater was tested in batch experiments, and percentage recoveries of 76.5% and 79.9% for Ag(I) and Au(III), respectively, were obtained. To carry out the industrial application of the proposed methodology, an economic viability study is required.

Phosphogypsum (PG) generated from the phosphate beneficiation plant was investigated to be valued as raw material for ceramic materials (bricks). X-ray diffraction (XRD), X-ray fluorescence (XRF), Fourier Transformer Infra-Red spectroscopy (FTIR) and laser granulometer were used for the mineralogical, morphological, chemical and granulometric characterizations of raw materials. Firstly, the raw materials were ground, dried and mixed with various level phosphogypsum addition (from 0 to 50 percent by weight of clay). Secondly, the mixtures were spread out in a stainless steel mold while they were pressed using a hydraulic press to obtain compacted discs. Finally, the obtained materials were sintered in a programmable furnace. The study involved physical properties (density, porosity, and water absorption), chemical, thermal, structural and mechanical tests performed on ceramic materials. The obtained results showed that the ceramic with 40% of PG incorporation successfully satisfied the standard requirements. The increase in the percentage of PG contributing to decreasing the mechanical strength of the samples, but it is still higher than the standard limit. In addition, the thermal conductivity was decreased with the increase in the percentage of PG, which gives the prepared material the insulating property.

In this study, a new composite ceramic material using a red clay matrix with different amount of clinker from the cement industry has been developed. The aim is to valorize some natural resources such as red clay and sub-products from the cement industry as clinker in order to develop new materials for industrial and/or catalytic uses. Raw materials were grounded in order to reduce the particle size and obtain a homogeneous slip. The samples were mixed and compressed into pellets and undergo a heat treatment up to 1100˚C. Geotechnical characterization has been carried out. Firing proprieties (shrinkage, water absorption, and mechanical resistance to the inflection) were measured. The composition of the ceramic material was investigated by X-ray diffraction, XRF, SEM and EDS methods. The incorporation of clinker in the ceramic composite material up to 50 wt% exhibits good behaviors (physical and mechanical proprieties) and can be used as a ceramic product.

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Silicon-rich SixC1-x layers have been deposited by OMCVD at low pressure in the temperature range 800-1000°C using the organometallic compound SiEt4 for both Si and C source. A Si enrichment of these amorphous SixC1-x coatings was obtained by addition of SiH4 to the gas-phase. The influence of this silane partial pressure increase on the growth rate, the composition and optical properties of the films has been investigated. In spite of the silicon excess, evidence for free carbon was found both in the variation of the optical band gap and the IR spectra. The XPS (X-ray Photoelectron Spectroscopy) analysis argues also for a heterogeneous microstructure for these amorphous ceramic thin films