The synthesis of a Mg2+-Al3+-SO2−4-hydrotalcite-type compound from the acid wastewaters of the aluminum-anodizing industry has been studied as a possible means of recovering the unused Al resource materials as a useful mineral. The synthesis has been carried out from wastewaters of different concentrations (from 6.7 g Al/L to 134 mg Al/L) using the method of precipitation at constant pH, proving that all of them are suitable for such a process. The mineral was characterized using X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, differential thermal analysis and chemical analysis, all of which indicated characteristics typical of the desired compound. Almost 100% of the Al initially present in the wastewater solutions is recovered in the form of the Mg2+-Al3+-SO42−-hydrotalcite-type compound.

Iron is the fourth most common element by mass in the Earth's crust and forms compounds in several oxidation states. Iron (hydr)oxides, some of which form inherently and exclusively in the nanometre-size range, are ubiquitous in nature and readily synthesized. These facts add up to render many Fe (hydr)oxides suitable as catalysts, and it is hardly surprising that numerous studies on the applications of Fe (hydr)oxides in catalysis have been published. Moreover, the abundant availability of a natural Fe source from rocks and soils at minimal cost makes the potential use of these as heterogeneous catalyst attractive.

Besides those Fe (hydr)oxides that are inherently nanocrystalline (ferrihydrite, Fe5HO8.4H2O, and feroxyhyte, δ’-FeOOH), magnetite (Fe3O4) is often used as a catalyst because it has a permanent magnetization and contains Fe in both the divalent and trivalent states. Hematite, goethite and lepidocrocite have also been used as catalysts in their pure forms, doped with other cations, and as composites with carbon, alumina and zeolites among others.

In this review we report on the use of synthetic and natural Fe (hydr)oxides as catalysts in environmental remediation procedures using an advanced oxidation process, more specifically the Fenton-like system, which is highly efficient in generating reactive species such as hydroxyl radicals, even at room temperature and under atmospheric pressure. The catalytic efficiency of Fe (hydr)oxides is strongly affected by factors such as the Fe oxidation state, surface area, isomorphic substitution of Fe by other cations, pH and temperature.

Après une brève revue des projets de traitement d'effluents polluants par culture de micro-algues, les résultats d'un travail de laboratoire, réalisé avec un effluent urbain, sont présentés. Le pouvoir épurateur et la croissance des cultures de Scenedesmus sur milieux modifiés ont été comparés dans le but de connaître les facteurs contrôlables pouvant en influencer la performance. Un épuisement supérieur à 90 % est obtenu en 48 h pour l'azote et le phosphore. A partir d'un inoculum de faible importante (2 mg/L), l'accroissement de biomasse se poursuit jusqu'au 7e jour alors que celle-ci atteint environ 350 mg (matière sèche)/L, sans différence notable entre les trois milieux de culture (effluent brut, effluent filtré et effluent filtré enrichi de CO2). L'ajout de vitamines à l'effluent brut ou à un effluent synthétique est sans effet significatif sur la croissance de Scenedesmus sp. Parmi les neuf milieux étudiés, il ressort que l'effluent brut assure une croissance supérieure au milieu synthétique et comparable à l'effluenl filtré, même enrichi en CO2. Les résultats obtenus font ressortir le potentiel de Scenedesmus comme agent de traitement tertiaire.