Etude expérimentale de la dissolution de l'apatite (impact sur le cycle biogéochimique dans le milieu naturel)

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

Surface characterization of natural apatites used to remove phosphates from wastewater in constructed wetlands: which techniques to use?

Phosphorus is an essential element for all life forms. However, an excessive concentration of phosphates is the most common cause of water bodies eutrophication as phosphorous is usually the limiting nutrient involved in plant growth. In constructed wetlands (CWs) treating domestic wastewaters, good treatment performances are obtained on main pollutants except with phosphates. In order to improve phosphate removal by CWs, different experiments were performed considering a series of reactive substrates. Among those, natural apatitic materials showed a high sorption capacity for phosphates. This paper presents the various analytical techniques that were used to characterize five natural apatitic materials which were tested in experiments performed at different scales (laboratory, pilot plant and full-scale experiments). These apatitic materials have been studied using X-ray powder diffraction, Raman spectroscopy and scanning electron microscopy. In addition, chemical compositions were obtained from X-ray fluorescence and ICP-MS analyses. The results suggest that the studied apatitic materials present a wide spectrum of physical, mineralogical and chemical characteristics. This variety is related to the presence of impurities in the natural materials (5–60% w/w). Therefore, the characterization of the natural apatitic materials available is necessary in order to select the ones that would lead to the best performances in terms of phosphate removal. Moreover, the observation of the surface of the grains before and after the percolation of phosphate containing solutions showed that the primary apatitic peloids were progressively covered with a carbonate hydroxyapatite precipitate layer formed with the phosphates removed from the treated solution

Rétention du phosphore par apatite en filtres plantés de roseaux : recommandations de dimensionnement

International audiencePhosphorus (P) removal in constructed wetlands (CWs) has received particular attention during the last decades by using specific materials which promote P adsorption/precipitation phenomena. Recent studies have shown an interest in using apatite materials to promote P precipitation onto their surface. About ten years of experiments at different scales (laboratory, pilot, full scale) have passed. The process is now open in France. This paper presents the first design recommendations according to the apatite mineral quality and treatment outlet requirements. Kinetics and their evolution with the material saturation degree are presented based on the k-C* model. The process can achieve 1 mgP.l-1 for long term while using surface P removal filter area of 0.5 m².p.e.-1. With a low land footprint and high P removal efficiency, the interest of the process also result in the orthophosphates accumulation on a phosphate mineral which makes easier to reuse phosphorus from wastewater once saturated

Rétention du phosphore par apatite en filtres plantés de roseaux : recommandations de dimensionnement

International audiencePhosphorus (P) removal in constructed wetlands (CWs) has received particular attention during the last decades by using specific materials which promote P adsorption/precipitation phenomena. Recent studies have shown an interest in using apatite materials to promote P precipitation onto their surface. About ten years of experiments at different scales (laboratory, pilot, full scale) have passed. The process is now open in France. This paper presents the first design recommendations according to the apatite mineral quality and treatment outlet requirements. Kinetics and their evolution with the material saturation degree are presented based on the k-C* model. The process can achieve 1 mgP.l-1 for long term while using surface P removal filter area of 0.5 m².p.e.-1. With a low land footprint and high P removal efficiency, the interest of the process also result in the orthophosphates accumulation on a phosphate mineral which makes easier to reuse phosphorus from wastewater once saturated

The dissolution kinetics and apparent solubility of natural apatite in closed reactors at temperatures from 5 to 50 degrees C and pH from 1 to 6

International audienc

Kinetics and mechanism of natural fluorapatite dissolution at 25 °C and pH from 3 to 12

International audienceThe dissolution rates of natural fluorapatite (FAP), Ca10(PO4)6F2, were measured at 25 °C in mixed-flow reactors as a function of pH from 3.0 to 11.7, and aqueous calcium, phosphorus, and fluoride concentration. After an initial preferential Ca and/or F release, stoichiometric Ca, P, and F release was observed. Measured FAP dissolution rates decrease with increasing pH at 3 ? pH ? 7, FAP dissolution rates are pH independent at 7 ? pH ? 10, and FAP dissolution rates again decrease with increasing pH at pH ? 10. Measured FAP dissolution rates are independent of aqueous Ca, P, and F concentration at pH ? 3 and pH ? 10. Apatite dissolution appears to be initiated by the relatively rapid removal from the near surface of F and the Ca located in the M1 sites, via proton for Ca exchange reactions. Dissolution rates are controlled by the destruction of this F and Ca depleted surface layer. The destruction of this layer is facilitated by the adsorption/penetration of protons into the surface at acidic conditions, and by surface hydration at neutral and basic conditions. Taking into account these two parallel mechanisms, measured fluorapatite forward dissolution rates can be accurately described using r(molms)=6.61×10aK1+aK+aCa4aF1.4aOH0.6aH6K+3.69×10[CaOH2+] where ai refers to the activity of the ith aqueous species, [CaOH2+] denotes the concentration of hydrated calcium sites at the surface of the leached layer (mol m?2), and Kex and Kads stand for the apparent stability constants of the Ca2+/H+ exchange and adsorption/penetration reactions, respectively

Kinetics and mechanism of natural fluorapatite dissolution at 25DC and pH from 3 to 12

International audienc